THE UNIVERSITY OF NEW MEXICOCOLLEGE OF PHARMACY

ALBUQUERQUE, NEW MEXICO

The University of New Mexico

Correspondence Continuing Educationfor

Nuclear Pharmacists and Nuclear Medicine

VOLUME 111, NUMBER 3

●Radiopharmaceuticals for the

ofHepatobiliary

by:

Scintigraphic

Function

Courses

Professionals

Assessment

Anne-Line Anderson, M.S,

Co-sponsored by: mpipharmacy services incan ~mersham company

●M

The University of New Mexico College of Pharmacy is approved by the American Council on Pharrnaceulical

Education as a provider of continuing pharmaceutical education. Program No. 180-039-93-006. 2.5 ContactHours or .25 CEU’S

UI

Editor

Director of Ptimcy Continuing Education

William B. Hladik III, M.S., R. Ph.College of Pharmacy

University of New Mexico

Production Spectiist

Sharon I. Ramirez, Staff AssistantCollege of Pharmacy

University of New Mexico

While the advice and information in this publication are believed to bc true and accurate at press time, neither the author(s) northe editor nor the publisher can accept any legal responsibility for tiny errors or omissions that may bc made. The publishermakes no warranty, express or implid, with respect to the mtiterial contained herein.

Copyright 1994University of New Mexico

Phamcy Continuing EducationAlbuquerque, New Mexico

RADIOPHARMA CEUTICALS FOR THE SCINTIGR.APHIC ASSESSMENT

OFHEPATOBILL4RY FUNCTION

STATEMENT OF OBJECTIVES

The goal of this correspondence lesson is to increase the reader’s knowledge and understanding of currenthepatobiliary radiopharmaceuticals. To that end, this course discusses hepatobiliary anatomy and finction,hepatocyte uptake, metabolism, and excretion of endogenous and exogenous compounds, and the pathway ofbile excretion. In addition, gallstone formation, composition, and treatment is reviewed. The coursepresents information related to the development of current hepatobiliary radiopharmaceuticals, optimalcharacteristics of such agents, and the in vivo and in vitro properties of agents available for routine use inthe U.S. This is followed by a discussion of the clinical use of hepatobiliary radiopharmaceuticals, includingaugmented cholescintigraphy, and a review of quantitative methods for the assessment of hepatocyte function.

Upon successful completion of this mate~l, the retier shouti be able to:

1.2.3.4.

●5.6.

7.

8.

9.

10.

11.12.

13.14.15.16.

17.

18.19,20.21.22.

●23.24.

Describe hepatobiliary anatomy and function.Explain the major functions of the hepatocyte.Describe the biliary uptake and excretion pathways for bile acids and organic anions.List three major components of bile.Explain the origin, conjugation, enterohepatic circulation and function of bile acids.Describe the origin and excretion pathway of bilirubin and how it affects hepatocyte excretion of otherorganic anions.Discuss the factors that affect gallbladder filling and emptying.Explain the current understanding of the underlying causes for gallstone formation.Explain methods used in the treatment of gallstone disease.List the required chemical and pharmacologic characteristics of an ideal hepatobiliaryradiopharmaceutical.Discuss the development of current hepatobiliary radiopharmaceuticals.Explain the role that analysis of structure-activity relationships has played in the development of improvedcholescintigraphic agents.List hepatobiliary radiopharmaceuticals currently available for routine use in the U.S.Describe the preparation and radiochemical quality control of Tc-99m iminodiacetic acid (IDA) analogs.Compare the in vivo characteristics in humans of routinely used Tc-99m IDA radiopharmaceuticals.List the four organs that receive the highest absorbed radiation doses from Tc-99m iminodiacetic acid(IDA) radiopharmaceuticals.Understand how drug therapy can interfere with the movement of cholescintigraphic agents through thehepatobiliary system.List the principal applications for cholescintigraphy.Describe how hepatobiliary imaging studies are performed.Explain the three types of pharmacologic interventions used in augmented cholescintigraphy.Discuss the various causes of cholecystitis.Explain the two most common causes of neonatal jaundice and the role of cholescintigraphy in thedifferential diagnosis.Discuss the current status of methods for quantitation of hepatocellular function.Describe the hepatocyte uptake and handling of Tc-99m galactosyl-neogly coalbumin.

1

COURSE

I. INTRODUCTION

II. HEPATOBILIARYFUNCTION

111. HEPATOBILIARY

A. Bile AcidsB. Lipids

OUTLINE

ANATOMY AND

PHYSIOLOGY

c. Organic Anions

D. Organic Cations

E. Pathway of Bile Excretion

F. Gallstones

IV. CHAR4CTERlSTICS OF O~IMAL

~PATOBILIARY RADIOPHAR-

MACEUTICALS

v. DEVELOPMENT OF CURRENT

~PATOBILIARY RADIOPHAR-

MACEUTICALS

A. Historical Perspective

B. Technetium-99m Pyridoxylidene

Amino Acid Complexesc. Technetium-99m Acetanilido-

iminodtacetatesD. Relationship BetweerIBiodistribution

and Chemical Structure

VI. COMMERCIALLY AVAILABLEHEPATOBILIARYRADIOPHARMACEUTICALS

A. Agents Available in the U. S.B. Radiochemical Quality Control

Methodsc. In Vitro StabilityD. Pharmacoklnetics in Humans

VII. RADIATION DOSIMETRY

VIII. PRECAUTIONS

A. Drug Interference1. Narcotic Analgesics2. Nicotinic Acid3. Total Parenteral Nutrition

(TPN) Therapy4. Miscellaneous Drugs

B. Adverse Reactionsc. Use During Pregnancy and in Nursing

Mothers

Ix. HEPATOBILIARY IMAGING

A. Imaging Methods and Analysis1. Patient Preparation2. Imaging Technique and ●

Analysis

B. Augmented Cholescintigraphy1. Cholecystokinetic Agents2. Morphine3. Phenobarbital

c. CholecystitisD. Sphincter of Oddi DysfunctionE. Biliary ObstructionF. Bile ~kage and RefluxG. Nanatal Jaundice

X. QUANTITATION OF HEPATIC FUNCTION

A. Measurement of Hepatic ExtractionFraction (HEF) Using Tc-99m IDAAnalogs

B. Quantitation of Hepatic BindingProtein Rweptors

RADIOPHARMACEUTICALSFOR THE SCJNTIGRAPHIC ASSESSMENT

OFHEPATOBILIARY FUNCTION

By:

Anne-Line Anderson, M.S.Clinical Professor of Radiological Sciences

Department of Radiological Sciences‘Division of Nucledr Medicine

University of California, Irvine, MedicalOrange, California

INTRODUCTION

He~atohiliary radiopharmaceuti cals

Center

are an.important adjunct in the differential diagnosis of acuteand chronic abdominal pain. Due to the excellentphysical and biological properties of current Tc-99mlabeled radiopharmaceuticals, cholescintigraph y isconsidered to be both a noninvasive and very sensitivetest for evaluation of the functional Sbdtusof the cysticduct and the gallbladder. Hepatobiliary imaging canalso be helpful in the differentiation between surgical

2

and medical jaundice, and it is an excellent method forvisualizing the pathway of bile following surgery ortrauma. The greatwt impact has been on the

●diagnostic evaluation of suspected acute. cholecystitis(l). More than 90% of cases of acute cholecystitisresult from cystic duct obstruction by gallstones,which cause stasis in the gallbladder followed bychemically-induced inflammation and mucosal injury(2). Biliary tract disease caused by gallstones(cholelithiasis) is a major mdical and surgicalproblem in many parts of the world. It is estimatedthat 20 million individuals in the United States havegallstones. Although gallstones do not causesymptoms in the majority of individuals, gallstone-related disease afflicts up to two million Americansannual]y, leading to direct health care costs exceeding$2 billion per year. Cholelithimis is the mostcommon single indication for abdominal surgery in theUnited States, with around 500,000 cholecystectomiesperformed annually (2). The epidemiology, symptoms,diagnostic workup, and available treatment forcholecystitis and some other abnormalities of thehepatohiliary system will he reviewed in the followingsections.

HEPATOBILIARY ANATOMY AND FUNCTION

● The 1iver is tie largest organ in the body, weighing1200-1600 g in normal adults. The hepaticparenchyma contains a complex network of bloodvessels and excretory ducts. The liver has dual bloodsupply with about 80% coming from the G.I. tract viathe portal vein, and the rest being supplied by thehepatic artery (2,3). The blood is mixed in a vastnetwork of hepatic sinusoids lined by endothelial andKupffer cells. These cells are part of thereticuloendothel ial system and remove foreignparticles from blood by phagocytosis. Pores orfenestrae between the endothelial cells allow plasma toflow into the space of Disse, where it comes incontact with the hepatic parench ymal cells. Theparenchymal cells (hepatocytes) account for 60% ofliver cells and 80% of organ volume. Thehepatocytes are polygonal cells, 30 pm in diameter,and are organized in pIates to form a continuous three-dimensional lattice. A network of exchange vesselsnourishes each parenchymal cell on several sides. Thehepatocyte is charged with the ~dskof detoxi~ing andexcreting harmful compounds and of regulatingplasma levels of beneficial nutrients (3,4). The

●various transport pathways for hepatocyte uptake andexcretion are discussed in the next section. Thehepatocyte also performs the important function of bileformation. “Biliaryexcretion is an essential pathwayfor the elimination of many substanc~s removal from

blood by the hepatocytes, including bile acids andbilirubin. The alternate pathway of excretion issecretion back into plasma and subsequent clearanceby the kidneys. The biliary excretory system beginswith the bile canalicular network, which drains into aseries of progressively larger ducts that eventuallycombine to form the common hepatic duct. This isjoined by the cystic duct from the gallbladder to formthe common bile duct, which empties into theduodenum through the sphincter of Oddi. Just priorto entering the duodenum, the common biIe duct isusually joined by the pancreatic duct. During fasting,bile is diverted into the gallbladder where it isconcentrated and stored. In response to a meal, thesphincter of Oddi relaxes, the gallbladder contracts,and concentrated bile empties into the duodenum.

HEPATOBILIARY PHYSIOLOGY

The first step in hepatobiliary excretion is up~dkeacross the hepatocyte membrane. Receptor bindingsites on the sinusoidal plasma membrane ofhepatocytes are responsible for selective uptake of avariety of endogenous and exogenous compounds.Specific carrier-mediated active transport systemsappear to exist for various classes of compounds suchas organic anions, bile acids, organic cations, andneutral organic compounds (3,5), Distinct transpofimechanisms exist for inorganic ions as well; thetransport of these ions in and out of hepatocytes isregulated by various “pumps” that maintain conditionsrequired for optimal cellular function (2). Researchwithin the last 10-15 years has providd a great dealof new knowledge regarding the mechanism by whichhepatocytes handle electrolytes and other solutes (5),However, only a few of the carrier-mediated transportsystems of the liver have been systematically studied(3). The liver is important for the elimination ofweakly polar and non-polar compounds that are poorlyexcreted via the kidneys because of protein bindingand tubular reabsorption. The chemical propertiesthat determine if a compound is primarily excreted viathe hepatobiliary pathway are discussed in the nextsection. When protein-ligand complexes enter theproximity of hepatocyte carriers with high ligandaffinity, the ligand is removed from the protein andtaken up by the hepatocyte. A primary function of thehepatocfie is to convert nonpolar drugs and toxinsinto more water-soluble compounds that can beeffective y excreted. However, compounds that arerelatively polar and are ionized at physiologic pH maybe excreted unchanged into the biliary tract (3,5).

The hepatobiliary system produces approximately600 ml of bile daily. Bile acids, water andelectrolytes constitute the major components of bile.

3

Compared to other bodily swretiom, bile is relativelyrich in lipids, principally cholesterol and thephospholipid lecithin. Bile also contains a variety ofother lipophilic substances, including vitamins andsteroids. Bilirubin, which giva bile its yellow color,normally reprwenta IWS than 1% of total biliarysolids. Physiologic control of bile secretion is complexand incompletely understood. Hepatic bile flow isclosely related w the size of the bile acid pool,determined by the rate at which bile acids areprocessed through the liver. Changes in the rate ofbile acid delivery to the liver correspond to thefeeding cycle. This is usually referred to as the bileacid dependent portion of canalicular bile formation.Other, bile-acid independent, factors are also believedto take part in the regulation of canalicular bilesecretion, but these factors and their significance arenot well understood (2,3 ,5,6).

B~le AcidsBile acids (also referred to as bile salts) are the

end-products of cholesterol degradation and the majororganic constituents of human bile. Thti primary bileacids, cholic acid and chenodeoxycholic acid aresynthesized in the liver. They are virtually completelyconjugated, usually with glycine or taurin, beforebeing excretd into bile. Bile acids are natural ionicdetergents and play an important role in theabsorption, transport and secretion of lipids, such asfat-soluble vitamins and cholesterol (2,5). Bile acidsare effective y (95%) absorbed from the intestinal tractand returned to the liver in portal blood, bound toalbumin. The removal of bile acids from sinusoidalblood is very efficient, allowing bile acids to circulatethrough the liver and intestines eight to 10 times perday (2,5). This enterohepatic circulation effectivelypreserves the bile acid pool.

The mechanisms responsible for hepatocyte uptakeand secretion of bile acids are not completelyunderstood, but are clearly different from themechanisms responsible for handling other organicanions such as bi~irubin. Different bile acids are nothandled identically, and it is generally accepted thateach bile acid undergoes its own enterohepaticcirculation (6). Certain bile acids, for exampletaurocholate, enter the hepatocytes via a sodium-dependent, carrier-mediated active transportmechanism (3). More hydrophilic bile acidspresumably enter hepatocytes by non-ionic diffusion(2,5). Following hepatocyte uptake, bile acids aretransported across the cell toward the canalicular pole.There is evidence that cytosolic binding proteins andvarious hepatocyte organelles play a role in theintracellular storage and transport of bile acids.Glutathione S-transferases (ligandin) have been

4

demonstrated to bind bile acids (5,6). The secretionof conjugated primary bile acids into the canalicularlumen haa been shown to take place via a carrier-mediated transport mechanism distinct from that ofother organic anions (2,3). Different primary biloacids compete for biliary secretion, but sulfated bileacids appear to use the general organic anion transportmechanism for canalicular secretion (5,6). Evidenceindicates that canalicular membrane transport is therate-limiting step in overall hepatocyte bile acidtrmsport (5), and that the excretion step is easilyimpaired by liver disease (3).

LipidsSecretion of the two major lipids in bile, lecithin

and cholesterol, is coupled with the secretion of bilesalts. In humans, the liver is normally the most activesite of cholesterol synthesis. Elimination ofcholesterol from the body takes place by thecatabolism of cholesterol to form bile salts, and alsoby direct secretion into bile. Bile salts, along withlecithin, solubilize cholesterol in bile in the form ofmixed micelles and mixed lipid vesicles. The exactmechanism for transport of lipids through thehepatocyte is not well understood (3,5).

Organic ArdonsAlthough organic anions make up a minor

component of bile, biliary clearance is an importantroute of excretion for this group of compounds.Bilirubin, the principal end-product of hemedegradation, belongs to this class of compounds. It isoften used as a model compound for the transport ofother organic anions such as certain dyes, drugs, andhormones (5). Examples of compounds that share theorganic anion pathway for hepatobiliary excretion withbilirubin include the dyes sodium sulfobromophthalein(BSP) and indocyanine green (ICG), the radiographiccontrast agent iopanoic acid, and severalcholescintigraphic radiopharmaceuticals such as theiminodiacetic acid (IDA) derivatives (7). Thetranshepatic transport of these organic anions is rapidand may occur by several cellular pathways (3,5).Some compounds are metabolized in the liver prior tobiliary secretion, wherein others are excretedunchanged. The normal liver has a very largecapacity for excretion of organic anions and canprocess up to ten times the normal daily production ofbilirubin (2).

As much as 80% of bilirubin is derived fromhemoglobin following its release due to the destructionof senescent red blood cells in the reticuloendothelialsystem, primarily in the spleen (3,7). Bilirubin ispoorly water-soluble and is a neurotoxic substance ifallowed to accumulate in the body (2). Unconjugated

●

●

●

(indirect) bilirubin passes into plasma where it bindsnoncovalently to albumin, Because of the largebinding capacity of albumin, large amounti ofunbound, unconjugated bilirubinrarely occur clinicallyexcept in the nwnate, in whom the capacity andaffinity of albumin to bind bilirubin are less than inadults (7). From the spleen, bilirubin is transported tothe liver sinusoids via portal venous blood. Afterdissociation from albumin, bilirubin is taken up by thehepatocytes. Special domains of the sinusoidalhepatocyte membrane have high affinity for organicanions such as bilirubin. Good evidence exists thathepatocyte uptake of bilirubin and related compoundsinvolves a carrier-mediated, saturable process.Compounds in this class exhibit mutually competitiveinhibition of uptake, but there is no competitionbetween these anions and bile acids. Several transportproteins in the sinusoidal membrane appear to mdiatethe uptake process (3,5,7). IrI the hepatocyte,bilirubin is conjugated to form water-solublederivatives suitable for excretion in bile. The processof conjugation and transport across the hepatocyte tothe canalicular membrane involves a complexinteraction with multiple intracellular hepatocytecomponents. The hepatocyte has a mechanism fortemporary storage of bilirubin; this may bepredominantly associatd with the cytosolic proteinligandin (2,3,7). Ligandin may also act aa a carrierprotein to facilitate diffusion of bilirubin to theendoplasmic reticulum where esterification takes place(2,3). More than 85% of bilirubin is normallyconjugated with glucuronic acid; the majority is in theform of diconjugates (2,3,7). Although it is notpossible to sample bile at the point of canalicularexcretion, evidence indicates that the transport ofconjugated bilirubin and related organic anions acrossthe canalicular membrane involves a saturable, carrier-mediated process. Different organic anions competefor excretion, but organic cation and unsulfated bileacid transport is not affected. More than one carriersystem may be involved in the secretion step, whichappears to he the rate-limiting step of overalltranshepatic bilirubin transport (2,3,5). From the bilecanaliculus, biliruhin conjugates pass with the bile intothe small intestine. Very 1ittle reabsorption takesplace; normally more than 90% of bilirubin is ex-cretd in feces either unchanged or as intestinalmetabolic products (7). Elevatiom in serum direct(conjugated) bilirubin above the normal range of ().3-1.0 mg/dl may be of prehepatic (e.g., hdemolysis),hepatic (hepatitis, cirrhosis), or cholestatic (obstructionof bile flow) origin (8). Because conjugated bilirubinis water-soluble, urinary excretion is observed inpatitinta with direct hyperbilirubinemia (2).

Organic CationsDmpite the fact that most dregs are positively

charged at physiologic ph, relatively little is knownabout the hepatic hmdling of organic cations. Whatis known is the rwult of work with model compoundssuch as procainamide ethobromide andchlorpromazine. The overall process appears to besimilar to organic anion handling in many respects.For example, competition between different cationshas been demonstrated. Organic anions do notcompete for the uptake and secretion of cations, andbiliary excretion of cations is not altered by bile acidinfusion (5). No successful cholescintigraphicradiopharmaceutical belongs to the organic cationclass.

Pathway of Bile ExcretionHepatic bile, which is normally produced at the

rate of about 600 ml per day, may enter theduodenum directly, or it may flow into the gallbladderwhere it is concentrated and stored (2,3,5).Gallbladder filling and emptying is affected by anumber of factors, including the rate of hepatic bilesecretion, sphincter of Oddi contraction, cystic ductpressure, serum levels of the hormone cholecystokinin(which stimulates gallbladder contraction), andpossibly by cholinergic mechanisms. The gallbladdercan store only 30-50 ml of bile, but due to itsremarkable ability to concentrate bile by absorption offluid through the gallbladder mucosa, it canaccommodate the total volume of hepatic bile (2). Inaddition, it has been demonstrated that periods ofgallbladder filling are punctuated by brief periods ofpartial emptying of concentrate bile, and that muchof the bile secreted at night may bypass thegallbladder altogether (5), During gallbladder storagehepatic bile is concentrated by removal of an isotonicsolution containing primarily Na’, HCO~– and Cl ‘.The resulting bile has a very high concentration ofbile salts and Na’ m well as K+ and Ca2’ (5).

GallstonesThe formation of gallstones represents a Fdilure to

maintain certain biliary solutes, principally cholesteroland calcium salts, in a solubilized srdte (5).Gallstones have traditionally been divided into twomajor types: cholesterol stones and pigment stones(2). In the United Srdtes, more than 75% of stonware considered to be chol~terol stones. Th~e stonware formed in the gallbladder and contain more than50% cholesterol by weight. Since cholesterol is notradiopaque, most of these stones are not visible onplain abdominal radiographs (2). Their formation isclearly related to supersaturation of bile withcholesterol, but this ~one does not explain the

5

pathogenwis, since supersaturation is common innormal fasting subjects without stone formation (2,8).It is not well understood how other promoting factorsare involved but this is an active area of research.Pigment stones can be subdivided into black andbrown stones. Both typw contain sufficient amountsof calcium salta to be radiopaque. Brown pigmentstones are seen mainly in the Orient and are almostalways associated with biliary bacterial infection. Theprimary calcium salt in brown stones is bilirubinate.Brown stonw contain more cholwterol than blackstones, and are usually formed in the bile ducts ratherthan in the gallbladder. Black pigment stonw arecomposed of a mixture of calcium salts includingbilirubinate, carbonate and phosphate salts, and areusually formed in the gallbladder. Black stones havebeen linked with chronic hemolytic disorders andcirrhosis (2,6).

Although this classification of gallstones may beuseful for the purpose of selecting an appropriatecourse of therapy, in reality gallstones have beenfound to cover the full spectrum from “pure”cholesterol stones to stones of variable calcium andbile pigment content, leading to the classification ofmany stones as “mixed.” Even so-called “pure”cholesterol stones contain calcium salts in the center,and current rwearch suggesw that the precipitation ofcalcium in the biliary tree is a critical event in theinitial nucleation of both cholesterol and pigmentstones (5,6).

Over the years, numerous epidemiological studieshave been undertaken to try to uncover the causes forgallstone formation. This, in turn, would presumablylead to ways of preventing the formation of gallstones.Diet, sex, obesity, and hormonal status are some ofthe factors that have been implicated (6). Much workremains to be done to understand the factors thateither promote or prevent cholelithiasis. A betterundersbdnding of the pathogenwis of gallstoneformation is expected to lead to better methods to treatpatienfi with gallstone diseme, At the present timecholecystectomy is the only therapy proven to curecholesterol gallstone disease (2,9). This type ofsurgery has recent]y become less traumatic due torefinement in technique. Laparoscopiccholecystectomy is now widely used in many parts ofthe world and has been found to reduce bothpostoperative pain ad the recovery period, as well kscost (2).

Pharmacologic dissolution of cholwterol gallston~using orally administered bile acids has beenextensively investigated. Two compounds have beenfound to be effective in clinical studiw:chenodwxycholic acid (CDCA) and ursodaxycholicacid (UDCA). UDCA has been reported to have less

side eff~ts than CDCA, and combined therapy usingboth drugs is more effective than either drug done.The optimal oral dose is 10 to 15 mg/kg/day (2,6,8).Not all patients with gallstone disease are suitablecandidatw for this type of therapy, however. The ●drugs are not effective for highly calcified stones, andwork best for buoyant stones lms than 15 mm indiameter (6). Presence of a functioning gallbladder isdso required. Complete treatment rndy take as muchas two years, and the drugs are relatively expensive.Even with a carefully selected patient population, thesuccess rate for complete gallstone dissolution is on]y40-60% (8), and recurrence rates of up to 50 % in fiveye~s have been reported (6). The true success rate ofstone dissolution is actually unknown, since currentdiagnostic methods have limited resolution. Tinyresidual stones may be missed, and when bile revertsto its supersaturated state afier the drug isdiscontinued these residual stones may start growing.

Extracorporeal shock wave lithotripsy (ESWL) isanother non-surgical method for removal of gallstones(2,8). By sending focused shock waves from outsidethe body, stones can be reduced to 2-3 mm particlesthat can easily pass into the intestinal tract. Thetechnique works best in patienw with single smallstones, and can be combined with dissolution therapy.Because these non-surgical treatments of cholesterolcholelithiasis have no lasting effect on the underlyingcause of gallstone formation, and does not preventrecurrence, the overall therapeutic results have so farbeen disappointing.

CHARACTERIS~CS OF O~IMAL HEPATO-BILIARY RADIOPHARMACE~CALS

Hepatobiliary radiopharmaceuticals are usd toobtain scintigraphic images and functional data thatcan be used to evaluate hepatocyte function, thepatency of intrahepatic ducts, the functional sratus ofthe cystic duct and the gallbladder, and also thepatency of downstream portions of the biliary tract(10). The optimal or ideal radiopharmaceutical forevaluating the functional status of an excretorypathway such as the hepatobiliary system would be anagent that passes through rapidly in bolus form. Theagent should not be partially cleared by otherpathways or localized in arem outside the pathway ofinterest. In other words, the extraction efficiencyshould be 100%, and excretion steps such asmembrane transport and metabolism should be rapid.There should be no reabsorption of the originalcompound or of any radiolabeled metabolizes. Inaddition, the radiopharmaceutical must be labeled witha radionuclide with suitable half-life and radiationemissions. The labeling must be stable, and the

oI

16

combination of half-life and clearance rate should besuch that the radiation doso to the patient is not toohigh at dose levels required to obtain satisfactoryimages. If quantitation of function is- desired, theclearance rate should only be affected by thefunctional status of the excretion pathway, and not byconcentration changes of other substances that arehandled by the same pathway.

Hepatobiliary imaging goes back to theintroduction of I-131 rose bengal by Taplin andcoworkers in 1955 (11). As will be explained furtherin the next section, I-131 Rose Bengal is not an idealradiopharmaceutical for hepatobiliary imaging. It wasreplaced in the 1970s by Tc-99m-labeled compoundswith more optimal characteristics. Investigations havecontinued to the present time with the aim ofdeveloping even better agents to study specific aspectsof hepatocyte function.

A number of chemical properties have been foundto be of impowance for a substance to be excretedefticicntly by the hepatobiliary pathway. Althoughinterrelated, these properties can be convenientlydivided into three groups: molecular weight, polarity,and rnolecular structure. Compounds with molecularweight below 300 are preferentially eliminated in theurine, whereas bile is the dominant pathway above500 Da (12). Animal studies have shown a markedspecies difference in the extent of biliary versusurinary excretion for organic anions in the 300 to 500Da range (13), It has long been recognized that lipidvolubility of a molecule is an important determinant ofits biliary excretion (12). Lipophilic groups bindstrongly to albumin, which prevents filtration by thekidneys and increases ligand volubility in circulation.Although molecules preferentially eliminated in bilehave an overall hydrophobic structure, the presence ofone or more polar groups (e.g., ionizable groups) isan essential requirement for quantitative biliaryexcretion to occur (3). That is why highly lipid-soluble molecules must be conjugated prior toexcretion into bile canaliculi. In a review article,Firnau (14) compared the molecular structure of anumber of compounds proposed as hepatobil iaryradiopharmaceuticals. He concluded that for extensivebiliary excretion to occur, a molecule may need toexhibit a certain balance between the polar andnonpolar aspects of its structure. Another feature ofthese compounds was that they all contained at ledst

two cyclic structures arranged in two different planes.Although it is not fully understood how changes inmolecular structure influences biliary excretion, it hasbeen shown that introduction of certain groups afiectsbiliary excretion rate without significantly alteringlipid volubility or molecular weight (3, 12).

Due to its optimal radiation properties, low cost,

and convenient availability, Tc-99m is widelyregarded as the radionuclide of choice for diagnosticimaging (15). Technetium-99m is the decay productof Mo-99 (tl,q = 2.75 days), and can be obtained asan isotonic, sterile and pyrogen-free solution ofsodium pertechnetate from commercially availableMo-99/Tc-99m generator systems. The physical half-life of Tc-99m is 6.02 hours; this is generally well--suitedto hepatobiliary excretion kinetics. It decays toTc-99 by isomeric transition, emitting abundant (89%)140 keV photons and minimal amounts of non-penetrating radiations. Labeling of suitablecompounds with Tc-99m using well-establishedmethods results in radiopharmaceuticals of high purityand stability. The photons from Tc-99m are optimalfor detection by standard nuclear medicine imagingequipment and r~sults in a low patient radiation doseper usable photon.

DEVELOPMENT OF CURRENT HEPATOBIL-IARY RADIOPHARMACEUTICALS

Historical PerspectiveDespite its many shortcomings, 1-131 rose bengal

(11) was the principal radiopharmaceutical for studiesof hepatobiliary finction for many years. Rose bengalis a halogenated fluorescein dye, principallytetrachlorotetraiodo-fluorescein. It can be effective yradioiodinated by exchange labeling methods to yielda preparation of high specific activity. Iodine-131 isa beta emitter with a relatively long physical half-life(8 days). Its photon emission of 364 keV is notoptimal for standard imaging equipment, and theadministered dose was limited to about 300 pCi (111MEtq), resulting in poor quality images. Due to therelatively slow transit of 1-131 rose bengal through theliver, it becomes difficult to visualize the gallbladderagainst the high background activity in the liver.Rose bengal is cleared through the same hepatocyteexcretion pathway as bilirubin, but does not competewell for excretion at elevated bilirubin levels, addinganother complication to its clinical usefulness. Thephysical disadvantages of 1-131 could be overcome byreplacing it with I-123, a cyclotron product with aprincipal gamma emission of 159 keV. Iodine-123,however, has a physical half-life of only 13 hours.Although 1-123 rose bengal was successfullydeveloped (16), its high cost and problematic supplylogistics resulted in very limited clinical use.

Because of the excellent physical characteristics ofTc-99m, a large number of Tc-99m complexes havebeen investigated as potential hepatobiliaryradiopharmaceuticals. The first agent to showpromise, Tc-99m-D-penicillamine was introduced in1972 (17). A discussion of all the agents that were

7

subsequently proposed is beyond the scope of thiscontinuing education lwson. Several well-referencedreview articles have been published (10, 18). The twogroups of cholescintigraphic agents that haveundergone extensive clinical investigations arediscussed below.

Technetium-99m Pyridoxylidene Hlno AcidComplexm

Starting with Tc-99m Pyridoxylidene glutamate(Tc-PG) (19), a large number of similar complexeswere investigated as hepatobiliary imaging agents. Thecondensation of pyridoxal and an amino acid such asglutamate results in formation of a complex known asa Schiffs base ligand (Figure 1), which is stabilkedby binding to metallic cations (20,21). In the originalpreparation, Tc-99m pertechnetate ww added to anequimolar mixture of pyridoxal and glutamate of ph 8-9 and autoclave for 30 minutes at 12@C. In thismethod technetium is probably reduced by thealdehyde group on pyridoxal to a lower oxidation statethat can readily form coordination complexes withSchiffs base ligands. This method resulted in apreparation containing multiple Tc-99m complexes asshown by electrophoresis and HPLC (19,22,23).However, Tc-PG showed significant promise as acholescintigraphic radiopharmaceutical in severalanimal species (19,22,23 ,24). Blood clearance wasrapid, and the biliary tract and gallbladder could beclearly visualized as early as 10-15 minutes afterinjection. There was no evidence of reabsorption orhepatocyte metabolism (23), and acute and chronictoxicity studies in animals showed a wide margin ofsafety for diagnostic purposes (19). The majordisadvantage of Tc-PG was the high degree of urinaryexcretion, which was reported to be in the range of 20to 50% of injected dose, depending on animal species.This may be partly due to a low degree of proteinbinding, which was estimated to be only 20%immediate y following injection in rabbits (23).

HOOC–CH~CH~fH-COONa

NHC4

aH0CH2 / OH

\I

N CH3

Figure1. Structure of Pyridoxylideneglutawte.

Several clinical studies subsequently established theadvantage of Tc-PG over 1-131 rose bengal forhepatobiliary imaging (25,26). In normals, thecommon bile duct, gallbladder, and duodenum wasseen 15-30 minutes post-injection, and renal retentiondid not interfere with scan interpretation. However,urinary excretion increased in jaundiced patienti, andthe biliary tract was not well-visualized with serumbilirubin levels above 4 mg/dl. The presence ofactivity in the gastrointestinal tract on late (18-24hours) imagw still allowed differentiation betweenpartial and complete obstruction.

Effofi to reduce the amount of urinary excretioninitially centered on replacing glutamate with otheramino acids (22,23 ,27), but this did not producesignificant improvements. Some of the problemsassociated with the variable mixtures of complexes inthe autoclave products were solved by Kato andH-e (28). They developed a new labeling methodusing stannous ion as the reducing agent in an alkalinemdium with wcorbic acid as a stabiltier. Two-component kits using several different amino acidswere prepard; in the final labeling step Tc-99mpertechnetate was incubated with aliquots of the twokit components for one hour at room temperature.Biliary excretion of this new series of compounds wasfound to correlate well with lipophilicity as determinedby thin-layer and paper chromatography. Furtherimprovements were realized when kits containing N-pyridoxylamino acids were introduced (29). Thissignificantly increased the stability of the Iigmds, and(Sn)-N-pyridoxalaminate kits were prepared that couldbe efficiently labeled with Tc-99m in a brief boilingstep. Of the amino acid complexes tested, Tc-99m(Sn)-N-pyridoxyl-5-methyltryptophan was the mostpromising. In rats, over 90% of the activity passedthrough the liver in the first 30 minutes after injection,and only 2% was excreted in urine. Continuousinfusion of sulfobromophthalein (BSP), designed tosimulate elevated bilirubin levels, had minimal effecton the rate of biliary clearance as well as the extent ofurinary excretion. No hepatobiliary radiopharma-ceutical based on pyridoxal and amino acids has beencommercially available in the United States, but thisgroup of agents has been used extensively in Asia andthe Far East.

Technetium-99m AcetanilideiminodiacetatmThe development of Tc-99m-N-(2,6-

dimethylphenylcarbamoylmethyl) iminodiacetic acid~cdimethyl-IDA) was first reported by Loberg andcoworkers in 1976 (30). The ligand was synthesizedin a two-step procedure Starting with 2,6-dimethylailine and chloroacetic acid. The rmultingintermediate was then reacted with iminodiacetic acid

3

to form the dimethyl-IDA complex Figure 2). Theiminodiacetic group has excellent chelating propertiesand forms a complex with stannous-reduced Tc-99m

●at room temperature. Analysis by paper and gelchromatography showed insignificant amounts of Tc-99m in the form of pertechnetate or colloids. Initialanimal distribution studies in mice showed that Tc-dimethyl IDA was cleared rapidly from the blood bythe 1iver, with more than 80% of the injected dose inbile after 50 minutes. Urinary excretion in dogs was17% at 5 hours afier injection (30). This agentclear]y showed great promise, and extensiveinvestigations of Tc-dimethyl-IDA and similar IDAcomplexes as potential cholescintigraphicradiopharmaceuticals followed. Studies of thechemical structure (31) indicated that the molar ratioof dimethyl-IDA to technetium is 2:1, suggesting a bisstructural complex. Tin ions are not part of the finalcomplex. Technetium is present in the + 3 oxidationstate, giving the complex an overall charge of -1,Mass spectroscopy studies (32) have subsequentlyconfirmed a his-structural anionic ligand complex ofTc +3, presumably octahedral in structure. A massvalue of 685 was observed.

m d

‘3 ‘2

Figure 2. Structure of acetanilidoiminodticetic acid.

Animal distribution and imaging studies using Tc-dimethyl IDA in a variety of animal species confirmdthat this complex is primarily excreted in bile, withonly moderate amounts of urinary excretion(27,33,34,35). Tc-dimethyl IDA is not extensivelyprotein bound (36) or metabolically altered in vivo(30,31). Safety studies in mice (37) indicated that theLDWfor dimethyl-IDA exceded the proposed humandose by a factor of 1,000 on a per-weight basis. Todetermine the mechanism of hepatobiliary clearance ofTc-dimethyl-IDA, Harvey and coworkers (38)performed competitive clearance studies in dogs withBSP, an anion, and oxyphenonium, a cation. Theadministration of saturating levels of BSP resulted inu decrease in the one-hour cumulative biliary excretionfrom 55 to 1.5% of the injectd Tc-dimethyl-IDA.The one-hour urinary excretion increased from 13%to 44% as a result of BSP infusion. No effect wasobserved with oxyphenonium, demonstrating tiat Tc-dimethyl-IDA is clearti through hepatocytes via the

particularly well-suited for use in jaundiced patients(33). The low degree of urinary clearance of TMB-IDA was later contirrnd in normal humans; this was

9

Iorganic anion pathway. This suggested that in thejaundiced patient, bilirubin maybe able to prevent Tc-dimethyl-IDA and related radiopharmaceuticals frombeing eticiently excreted by the hepatobiliary system.

Initial human studies with Tcdimethyl-IDA (37) innormal subjects and non-jaundiced patients showedrapid concentration of tracer by the liver, with 14% ofthe injected dose excretd in urine by 90 minutes.Activity was present in the biliary tract afier 10 to 20minutes. In jaundiced patients as much as 53% of theinjected dose was in the urine at 18-24 hours. Bloodclearance was delayed and the biliary system was notvisualized in patients with severe jaundice. However,intestinal activity, indicating biliary tract patency, wasobserved on late images in patients with incompletecommon duct obstruction. Safety studies in the samegroup of patients did not detect any alterations invarious hematological and biochemical tests afteradministration of Tc-dimethyl-IDA. Following theinitial successful clinical use of Tc-dimethyl-IDA,many researchers attempted to prepare an even betterradiopharmaceutical by manipulating various parts ofthe basic IDA molecule. The goal was to produce anagent with increased hepatobiliary specificity,decreased renal excretion, and improved competitionfor excretion in the presence of elevated serumbilirubin levels.

Over the next few years some 60 different Tc-99mlabeled IDA analogs were tested in animals(27,34,35,39,40,41). Most of the new analogs haddifferent Chemiudl substitutions only on the aromaticring of the basic IDA structure, and in general it wasobserved that hepatobiliary specificity improvd withincreased Iipophilicity. Changes introduced in the sidechain were less successful, sometimes resulting inunstable complexes or increased urinary excretion(39,42). The in vivo kinetics of only the moreextensively investigated analogs will be reviewed here.When the methyl groups on the phenyl ring werereplaced by ethyl, increased hepatobiliary specificityand decreased urinary excretion was observed in ababoon model (27). However, these two amdogs(dimethyl and diethyl) performed essentially identicalin normal humans (43). Increasing the substituentgroup in the ortho positions further, as in di-isopropylIDA, did not reduce renal excretion significantly, butthe hepatic excretion rate increased (33,43). Urinaryexcretion of less than 2 % of the dose 30 minutw afterinjection was observed in animals with p-butyl-IDA(35) and 2,4,6-trimethyl-3-brumo-IDA (TMB-lDA)(41). The p-butyl analog cleared very slowly throughthe liver, a characteristic thought to make it

combined with increasd hepatocyte extractionefficiency compared @ the di-isopropyl-IDA analog(43,44). During thae investigations, severalimportant observations were made, leading to animproved understanding of how chemical structureaffects hepatobiliary vs. renal excretion of Tc-99m-IDA analogs.

Relationship Betw&n Biodlstribution and ChemicalStructure

The development of new and improv~radiopharmaceuticals has generally followed pathwayssimilar to those used for other groups of drugs. Theprocess must begin with the identification of acompound with inter~ting biological activity (45). Ahypothesis must be arrived at regarding whichchemical features are relatd to bioactivity. Newcompounds must be synthwized and tested in anappropriate biological assay to evaluate the hypothesis.Based on this analysis, several modifications to theoriginal hypothesis may have to be developed andtested. This process is intended to disclose howchanges in the molecular structure affect biologicalactivity, i.e., a structure-activity relationship (sAR) iSidentified.

A number of methods for quantitative SAR(QSAR) analysis using computers have been developdduring the last 30 years. QSAR methods utilizemathematical models which describe the structuraldependence on biological activities either byphysiochemical parameters (Hansch analysis), byindicator variables encoding different structuralfeatures (Free-Wilson analysis), or by three-dimensional molecular property profiles of thecompounds (comparative molecular field analysis,COMFA) (46). Hansch (47) examined QSAR betweenbiological activity and the underlying chemicalproperties such as atomic chargw, oil-water partitioncoefficients, and molecular volumes. The mostfrequently used approach involves the determination ofthe change (T) in the Iipophilicity of a parentcompound caused by the introduction of a substituentgroup. The value of r is defined as the difference inthe log of the partition coefficient (log P) betweenoctanol and water of the parent compound and that ofthe substituted analog. A basic assumption of thismethod is that the effect of an analog of the parentcompound equals the effect of the parent compoundplus the effect of one or more substituent groups, inother words, pdditivity is assumed. At least in thesimplest model it is also assumed that activity of asubstituent group is independent of other substituents.The Free-Wilson analysis (48), sometimes referral toas the de novo approach, was one of the earliestQSAR methods. It represents a statistical approach

for rtilng substituent group contributions tobiological behavior without specifying anyphysiochemical propertia. One of the limitations ofthis method is that activity predictions cannot be madefor a compound containing a substituent which was ●not included m an observation in the original analysis.It is, however, a useful twhnique in casw whereadditivity is a reasonable assumption and where onlya limited number of substituents are involved (45). Itshould be pointed out that prdiction of the mostdwirable compound is not the primary goal of QSARanalysis. Rather, it should be considered as a tool torationalize and shorten the path from a lead structureto an analog with the dmired biological activity.

Structure-activity analysis has been applied in thedevelopment of radiopharmaceuticals ordy recently(15). One of the first examples of the use of SAR inradiopharmaceutical development was for the Tc-99mlabeled cholescintigraphic agents. Since radiophmma-ceuticals generally have no pharmacologic action, andwe are primarily interested in in vivo distribution, theterminology “structure-distribution relationship”(SDR) is frequently used instead of SAR.

In 1977, Burns and coworkers (49) reported on thepreparation and twting of five different Tc-IDAanalogs. Biodistribution studies in mice revealed alinear relationship between biliary excretion and thenatural log of the molecular weight divided by thecharge. A few years later Nurm, et al. (41) reported ●on correlations between physiochemical parameters,structural effects, and in-vivo characteristics of a totalof 33 Tc-IDA derivatives with different combinationsof substituent groups on the phenyl ring, Lipophilicitywas measured using a reverse-phme HPLC system,and compared to tharetical u values from publishedreference tablw. A linear relationship was apparentwhen the compounds were divided into groups basedon the location of the substituents. The extent ofprotein binding was determined in vitro using a HSA-aff’’nity column. Hepatic and renal excretion at 30minutes were determind in rats, and imaging studiesin rabbits were used to measure intrahepatic kinetics.This body of data was correlatd to gain a betterunderstanding of the relative importance of the size,type, and location of substituent groups. No attemptwas made to do a QSAR analysis. Increasedlipophilicity generally resulted in increased hepaticspecificity and reduced renal excretion. Increasedprotein binding of the para substituted analogscorrelated with increasing theoretical Iipophilicity.This was not observed for substituents in the orthopositions; no correlation was observ~ with either ●protein binding or thmretical lipophilicity. When asingle lipophilic group was pr~ent in para position,hepatocyte transit time increased significant y, whereds

diortho substitution resulted in decreased hepatocytetransit time. Initial studies led the investigators to testadditional compounds based on what they had learned.When a group of IDA analogs with variousarrangements of methyl and bromo substituents wastested, TMB-IDA was found to have the best overallin vivo characteristics in rats and rabbits.

The structure-activity relationship for Tc-PGanalogs has also been investigated (50) using deriv-atives of Tc-99m(Sn) pyridox ylidenephenyl alanine.Fluoro-, chloro-, and six different alkyl substituentswere introduced in various positions on the phenylgroup of the phenylalanine moiety. The lipophilicityof the analogs was determined by measuring theoctanol/buffer partition coefficient. In vivodistribution studies in rats showed that increasdlipophilicity correlated well with a decrease in renalexcretion. Generally, many of the observed effects ofsubstituent groups on the phenyl ring corresponded towhat had been observed with the Tc-99m IDAanalogs. Preliminary SDR work with a differentgroup of potential hepatobiliary radiopharmaceuticalsrelatd to indocyanine green has also been reported(51). Indotricarbocyanine, a symmetrical compoundwith two phenyl rings, was synthesized andmonoiodinated with I-131. Dihalogenated compoundswere also prepared by introducing F, Cl, Br or I onthe second phenyl ring. The in vivo characteristicswere studied in several animal models. All theanalogs had rapid blood clwdranceand hepatic uptake,and minimal urinary clearance. Liver clearance ratewas significantly affected by the second halogengroup, and a correlation was observed between liverclearance rate and the polarity of the halogensubstituent.

The QSAR method of Free and Wilson (48) hasbeen used to investigate the effect of various alkylsubstituents on the phenyl ring of Tc-99m IDAcomplexes (52). Seven analogs, includingunsubstituted Tc-99m IDA, were initially usd. Theanalogs wero substituted in either the para or bothortho positions. The following in vivo parameterswere determined in rabbits: activity in urine at 30minutes, time to reach maximum liver uptake, andliver clearance half-time. The response measures usdin this QSAR model were the log of theexperimen~dlly measured values. A computer modelallowed calculation of the contribution to biologicalactivity for each of the substituent groups @ara or di-ortho), as well as the activity of the unsubstituted Tc-IDA. It then combined this data to give predictednumbers for a total of 16 related Tc-IDA analogs(including those tested). An additional analog wassubsequently tested and added to the data set. Withinthe range of experimen~dl errors associated with

animal studies, good agreement was seen betweenpredicted and experimental values.

COMMERCIALLY AVAILABLE -ATO-BILIARY RADIOPHARMACEUTICALS

Agents Available in the U.S.At the present time, three radiopharmaceutical kits

for the preparation of Tc-99m cholescintigraphicagents are available in the United States. They are allderivatives of Tc-IDA, and are available as lyophilizedmixtures of the IDA analog and stannous ions sealedunder nitrogen to prevent oxidation. The Tc-99mcomplex is formal by simply adding Tc-99mpertechnetate solution followed by a brief incubationperiod at room temperature. During theirdevelopment, these IDA analogs have been referral toin the literature by a variety of names and acronyms.The generic names of commercially available IDAderivatives are as follows:

dimethyl-IDA: Iidofenindiisopropyl-IDA: disofenintrimethyl-bromo-IDA: mebrofenin

These are the names adopted by the United StatesAdopted Names (USAN) Council. In addition, thevarious kit manufacturers have given their product atrade name flable 1). The formulation, as given incurrent package inserts (53,54,55), of commercial kitsfor the preparation of these Tc-99m labeled IDAanalogs are given in Table 1.

Table 1 Formulation of mmmerdally available Te9m h?palnbiliary radlOph*~,reutical,

Trade Name Manufatlurcr K!t r“ntenls ‘“- Preparation and Storasc(Qneric Name) . . . . .?whn~an HIDA Merck rto$$t I,dofenin 10 mg Add 2.10 ml .rc.Wm t;rlwhnetale.

(Lidofcnin) Canada for SnCl, * ?H,O up to lINJ mm (3 7 CBq)

Mallinchdt, 1.. O.*11lng It,ctd>atlonlime 15minut<%.HC1, “r N,(IH !. ad)ust Use wilh,n 6 hours,

pt[103.q-i 1. Store at 2-W

1Ivpatc>lil,, hPon t I>hanna Uwfrtlln Zfl !mg Add 4-5 ml Tc-Wm FrlLYIII!*laIe,

(~wlenin) snc~ . 211,0 12-lM mC, (444-7700 MBq)

u24 U6 !,1s Incubation ttt>le 5 minuteI lCL andlur NaOH 10 Use with,n b hours.aqwt pll to 4-5 store at 15.WC.

Ch”l,tec ~“ibb Dlagno$!im M.hr”(en,n 45 mg Add 1.5 ml 1 c.WIn pcrt?chnelate,

(Mebrof,nin) snF, .211,0 UP 10 1~ mci (37~ MBq).0%tolu3n2g, Incubat,<,n l,mC, 15 nllllu(m.

Use with,. 18 hoursSbre at 15K.

Methylptrabcnup105 2 mgn“pylparabn up to 058 tllgHCI“rNaU11 to ad)wt [,[1to giveap!1of42.57 in thet=onstitutti pr~uct

Radiochemical Quality Control MethodsThe most common radiochemical impurities in

Tc-99m radiopharmaceuticals prepared withstannous ion rductant are Tc-99m pertechnetate(TcO,”-) and rduced, hydrolyzed Tc-99m (R-Tc)species. A number of rapid thin-layer

11

chromatographic methods have been dmcribed for theseparation of Tc-99m complexes from these twoimpurities (56). In order to separate the Tc-99m IDAcomplex (Tc-IDA) from TcOq–and R-Tc, two instantthin-layer chromatographic (ITLC) systems must beused. Silicic acid (SA) ITLC strips in 20% methanolcan be used to separate TcOQ–~ = 1.0) from theother components (R~= O) (57). The amount of R-Tccan be determined using silica gel (SG) ITLC stripsand either water or acetonitrile:water (3: I) ~ thesolvent (41,57). In these systems both TcOd-and Tc-IDA move with the solvent front, and only R-Tcremains at the origin. More time-consuming, butreliable, gel chromatographic and paperelectrophoretic methods can also be used (42,57).

Several repoti have been published regarding thepresence of an intermediate reaction product duringthe formation of Tc-99m IDA complexes (41,58).This can be observed during HPLC analysis, butseparation is insufficient using ITLC methods. Thisdoes not appear to be a problem as long as suff~cientincubation time is allowed following Tc-99mpertechnetate addition.

In Vitro StibilityMajewski, et al. (59) studied the in vitro stability

of several Tc-99m IDA analogs. The amounts of Tc-99m in the form of TcO,’ and R-Tc were determinedby ITLC methods (57) up to 24 hours followingpreparation. All Tc-99m Iidofenin preparationscontained <4% TcOd”-and < 1% R-Tc up to 8 hoursafter preparation. The corresponding numbers for Tc-99m disofenin were < 2% and < 1%. There was nosignificant change in percent R-Tc for either agent upto 24 hours. Some increase was observed for TcOd-,but it did not significantly exceed 10% in anypreparation. Technetium-99m mebrofenin was notincluded in this analysis. It should be noted that Tc-99m rnebrofenin can be used up to 18 hours afterpreparation, whereas the other producm should not beused past six hours (Table 1). The difference is dueto the presence of bacteriostatic additives in themebrofenin kit, but it also indicates that themanufacturer has been able to show that the agentretains high radiochemical purity.

Pharmacokinetics in HumansThe in vivo behavior of current hepatobiliary

imaging agents in humms generally reflects what wasobserved in animal studiw, although some speciesdifferences have been observed. The scintigraphicdelineation of hepatobiliary anatomy is primarilydetermined by the degree of hepatic uptake as well asthe rate of elimination from the liver into bile. Allcurrent agents are rapidly cleared from the blood and

12

taken up by the hepatocytw, with relatively little renalexcretion in normals (Table 2). Of the three agents,Tc-99m mebrofenin reachw maximum liver uptakesooner than the others, and also has the fastest livertransit time as expressed by hepatic excretion half-time ●(time from maximum liver uptake to 50% ofmaximum), All the agen~ reach maximum liveruptake within 10-15 minutw after injection, andactivity in the common bile duct is usually seen within10 minutes. The gallbladder is usually visualizedwithin 30 minutes, and intestinal activity is apparentby 60 minutw in 80% of patients (43).

Table z fi-ecukfntim of hepat~lllary raflophmmtlck h nm,ls (w)

Agent % bin Bld. . . ..—

% h m Urine 1lepatic E.xcreli(mat w mum M W“, 24 Hr t ,,1 Min.)

.,.,. -..,.-T..% Iido[eni. 3,0*05 7.6.t.1,0 15.5? 2.7 42*5

T* dti(e.i. 2,0t06 6.1 t 1,0 II,]*1 5 19+3

T- mebrolenir, 08.+ 0,1 06A0.I 1,5?03 17+1——”.

In patients with increased serum bilirubin levels,blood clearance and hepatic transit of Tc-99m IDAanalogs is usually delayed, and a larger proportion ofthe dose is excreted in urine. However, extensiveclinical use has shown that both Tc-99m mebrofeninand Tc-99m disofenin can be used successfully injaundiced patients (10,43,44,62@), wherein lidofeninis more severely affected and should not be used. Theeffect of BSP and bilirubin on the hepatocyte uptake ●of Tc-99m mebrofenin was studied in vitro usingisolated rat hepatocytes (41). Uptake decreasedsomewhat with increasing concentrations of both BSPand bilirubin, but the decrease was only about 25% ata bilirubin level of 20 mg/dl. Similarly, bilirubinemiainduced by bilirubin infusion in rabbits with normalliver finction did not significantly alter pharmacokine-tics of four different Tc-IDA analogs (35). It has beensuggested by POWSCU(60) ti~t it is not high serumbilirubin levels per se, but rather altered hepatocellularfunction due to liver cell damage, that limits the biliaryexcretion of Tc-IDA amlogs. This view is supportedby Sarkar (61), who reported normal hepatic uptakeand excretion of Tc-lDA in a p~tient with a plasmabilirubin level of 36 mg/dl. This patient suffered froma hereditary biliary conjugation disorder, but did nothave parenchymal hepatic disease.

RADIATION DOSIMETRY

The recommend injected dose for hepatobiliaryscintigraphy in non-jaundiced patients is 5 mCi (185MBq) or less; in jaundiced patients a higher dose, up ●to 10 mCi (370 MBq) can be used. The estimatedabsorbd radiation doses according to themanufacturer’s package insert (53,54,55) are given in

II

●

●

●

Table 3 for normal and jaundiced individuals. TheMIRD scheme for dose calculations using publishd“S” valuw for an average 70 kg man was used forthese calculations. Different assumptions may resultin different dose &stimates, and large individualdifferences in weight, organ size, and clearancekinetics may result in actual doses that deviate bymore than an order of magnitude from publishedestimates. The effect of a fatty med given at the endof hepatobiliary scintigraph y on the absorbed radiationdose has been reported by Wu and coworkers (65).A scheme for estimating absorbed radiation dose tonewborns from Tc-99m diethyl-IDA has also beenreportd (66).

T.IIIIc 3. Fslit>>alti abrkd radiation doies [r”., 113mCi (370 MHq)

1.!”?, 029 1291 045 (4 5) Ow (?8) o 6? (h?) 047(471 OM1 (H])

Cq,llt,lJddcr I ,33 (13.3) OT9 (79) 1.2 (120) 140 (14 o) 137 (1?.7) 125 [12 5)wall

small 2.08 (21J8) 018 (1 8) 22 (22(1) 163 (163) 2,W (299) I ho (160)lnt-tine

UPPI Large 3 m l?7.~) n 22 (2.21 38 (38 O) 3.25 (32.5) 474 (47 4) 2,48 (24,8)I“i*line

Lower Ldrge 1.58 (15.8) 024 (24) 2.8 (28 0) 2 M (225) 3M (364) 197 (1Y 7)IT,t<%d”v

Udney 020 [2.0) 026 (2 (,) n 22 (2.2) 019 (19)

Urln.ry 0 % (S.6) 3.05 (30 5) 092 (9.21 003 (88) 0.29 (29) 242 (24.2)Bladder Wall

Ovariw 039 (3 q) 021 (2,1) 082 (n 2) 075 (751 101 (101) O,u (64)

Tstm 0.06 (0.6) 0.13 (13) 0.06 (0.6) 0.06 (O6) 003 (0.5) 011 (1 1)

Red Mamw o Za (2.8) 0.15 (! 5) 034 (34) 0.25 (25)

PRECAUTIONS

Drug InterferenceA variety of drugs have been reported to interfere

with the movement of radiopharmaceuticals throughthe hepatobiliary system (67,68).

Narcotic Atigesics. Morphine in particular andopiates in general cause impaired emptying of bile intothe small intestine because they induce spasm in thesphincter of Oddi (69). Cholescintigraphy in thepresence of narcotic analgesics will show prolongedvisualization of the gallbladder and the common bileduct and no movement of activity into the bowel.This could result in the erronmus diagnosis of biliaryduct obstruction. This is significant, since narcoticanalgesics are often the treatment of choice forpatients presenting with severe abdominal pain.Ideally, hepatobiliary imaging should not beundertaken until the effect of the drug dissipates,which may require 6-12 hours (70).

Nicotinic Acti. Large doses of nicotinic acid havebeen known to cause significant hepatic dysfunction,resulting in poor hepatocyte uptake of

cholescintigraphic radiopharmaceuticals (71), Thisappears to be a dosedependent toxic effect, and liverfinction returns to normal after nicotinic acid intakeis stopped or reducd.

Total Paretieml Nuttion (TP~ ~empy.Absent or delayd visualization of the gallbladder hasbeen reported in patients who are receiving TPNtherapy (72). This may result in false-positive imagesin patients without grdlbladder disease. During TPNtherapy, the gallbladder is relatively inactive, which isthought to result in bile stasis and the formation ofhighly viscous gallbladder bile that impties the flowof additional bile into the gallbladder.

Mkcellaneous Dregs. The effect on gallbladdercontractility of a number of drugs including atropine,calcium channel blockers, and progesterone has b~nreviewed by Kloiber, et al (73). This is of particularconcern in gallbladder ejection fraction studies, a topicthat will be discussed later.

Adverse RactinnsExceedingly few incidents of adverse reactions

attributed to current hepatobiliary radiopharma-ceuticals have been reportd. Single cases of chillsand nausea have been observed following injection ofTc-99m lidofenin (54). A few cases of itching at theinjection site and development of hypersensitivityreactions such as skin eruptions have also beenreportd (53,55).

Use During Pregnancy and in Nursing MothersAccording to the manufacturers, it is not known if

hepatobiliary radiopharmaceuticals could cause fetalharm (53,54,55). These radiopharmaceuticals shouldnot be given to pregnant or possibly pregnant womenurdess a nuclear medicine study is clearly needed.Package insefi also state that it is not known if thesehepatobiliary agents are excreted in human milk.However, Tc-99m pertechnetate, which may bepresent in small amounts, is known to be excreted inbrewt milk during lactation and the manufacturerstherefore recommend that formula feedings shouldtemporarily be substituted for breast feeding. Actualmeasurements of Tc-99m disofenin excretion haverecently been performed in a group of six lactatingwomen (74). Up to at least 24 hours following Tc-99m disofenin administration, less than 0.3% of theinjected dose ‘was found in breast milk, and theauthors conclude that interruption of breast feeding isnot essential. If intermption is preferred, and it ispossible to plan in advance, patients should beencouraged to express and save extra milk prior toadministration of radiotracer; this can then be usedduring the interruption period.

13

HEPATOBILIARY

Biliary disease is

IMAGING

highly prevalent in our society,and is seen in a variety of settings ranging frombiliary colic in otherwise healthy young women tolife-threatening biliary sepsis in elderly patients withsevere intercurrent disease. The initial assessment ofpatients with symptoms suggwtive of biliary diseasemust include a full clinical examination and history.In patients with gallstones, the symptoms may besufflciently typical to diagnose gallbladder diseasefrom historic information only. Other patients maypresent with vague and ill-defined symptoms thatcould be caused by a variety of pathological conditions(5,9). Various laboratory tests and imaging modalitiesother than cholescintigraphy add valuable diagnosticinformation to the workup of these patients, but willnot be reviewed here. Hepatobiliary imaging is animportant diagnostic modality in the differentialdiagnosis of many hepatobiliary abnormalities, whichwill be discussed in the following sections.

Imaging Methods and AnalysisPatient Preparation. Patients are fasted for at least

two hours before the study, preferably overnight, butnot for longer than 24 hours (1,2,70,75). In thepresence of food in the upper ga.strointestinal tract thegallbladder may be contracting, which interferes withinflow of radioactive bile and may lead to a false-positive study. Prolonged fasting should be avoidedas it may also cause non-visualization of a normalgallbladder. Narcotics or sedatives that act on thesphincter of Oddi should be stopped six to 12 hoursbefore the examination (70).

Imuging Technique and Adysis. The usual doserange for Tc-99m cholescintigraphic agents is 3-10mCi (100-370 MBq) for adult patients. In childrenthe dose is adjusted according to age and weight.Cholescintigraphy is best performd with a large field-of-view scintillation camera equipped with a low-energy, high-resolution collimator. The patient isplaced under the camera in the supine position suchthat the liver, gallbladder, and duodenum is within thefield of view. Sequential images are obtained using a20% energy window centered at 140 keV. Imagingprotocols vary between institutions and depend onwhat information is to be obtained. Typically, serialanterior images are obtained at five- to 15-minuteintervals up to 60 minutes after injection. The firstimage is acquired for 750,000 to one million countsand subsequent images are acquired for the same timeas the first image (1,70,75). Simultaneous y, adynamic study can be obtained at a rate of one frameper minute and stored in a computer. Time-activitycurves may be generated from this data by placing

regions of interwt over 1iver parenchyma, commonbile duct, or gallbladder. Functional parameters suchas hepatic extraction fraction or gallbladder ejectionfraction can then be evaluated (70). Additionalimagw in the lateral or oblique projections may help ●define the anatomic location of “collections of radio-activity. For example, a lateral view may help distin-guish activity in the gallbladder (anterior) from renalexcretion @osterior). Delayed images are obtained ifall the desired information is not obtained during thefirst hour. The normal appearance rate of cholescint-igraphic tracers in the various parts of the hepato-biliary system has already been discussed. In theevaluation of hepatobiliary images, the physician con-siders the various functional steps leading from radio-tracer delivery to the liver to the appearance of activityin the gut as well as hepatobiliary morphology (75).

Augmented Chol@cintigraphyCholecystokinetic Agetis. In humans, gallbladder

emptying in response to a fatty meal is primarily dueto the release of endogenous cholecystokinin (CCK).This hormone, as well as its synthetic C-terminaloctapeptide analog, sincalide, have been used asadjuncts in the evaluation of hepatobiliary disease.Their effects include gallbladder contraction,relaxation of the sphincter of Oddi, and increased bilesecretion (73,76). A fatty meal or a standardizedpreparation such as Nw-Cholex, a 50% emulsion ofcorn oil in water, will have the same effect. Xynos,et al (77) reported on the reproducibility ofgallbladder emptying studies with Tc-99m diethyl-IDAfollowing ingestion of 250 ml milk. Thirtyindividuals were studied twice, two to five weeksapart. The milk was given 30 minutes after theradioactive tracer dose. Good reproducibility wasobserved for both gallbladder ejection fraction and forthe lag time between milk ingestion and start ofemptying. However, use of CCK or sincalide doesprovide control of both dose and infusion rate, whichmay make it easier to compare studies from differentinstitutions. Sincalide for intravenous administrationis available in 5 pg vials from Squibb Diagnosticsunder the trade name Kinevac. Reported side effectsinclude nausea, abdominal pain, and the urge todefecate. Transient dizziness and flushing have alsobeen reported. The ordy contraindication to its use issensitivity to sincalide. The usual intravenous dose ofsincalide is 0.02 pg/kg to be infused at a uniform rateover a three- to five-minute period (70,76,78,79).The dose must not be injected as a bolus, and somereports advocate a slower infusion rate of up to 15minutes (73,75) in order to reduce the incidence ofabdominal pain.

Gallbladder emptying can be utilized in two

14

different ways in cholwcintigraphy: (a) to empty thegallbladder prior to radiopharmaceutical injection inorder to optimize subsequent filling, and (b) to study

●the contractile function of the gallbladder. The firstapproach may be useful in patients who have beenfasting for a prolonged (> 24 hours) period of time,or who are on total parenteral nutrition (70,76). Aspreviously mentioned, the prwence of very viscousgallbladder bile in these patients rndy preventradiotracer flow through the cystic duct. Sincalideshould be given 30 minutes prior to radiotracerinjection (76). It has been suggwted that rather thanroutinely pretreating this group of patients, it is betterto use this technique only when the gallbladder is notvisualized within one to two hours of tracer injection(80). At this point, sincalide can be injectd, followedby a second radiotracer dose 30 minutes later.

IrIgallbladder ejection fraction studies, sincalide isnot infused until after the gallbladder is visualized. Adynamic study of gallbladder emptying is obtained andused to determine the ejection fraction. Assumingcomplete mixing of radiotracer with gallbladdercontents, the percent decrease in activity corrwpondsto the volume being evacuated (73). Although thereis no universal agreement regarding what a normalejection fraction should be, most investigators feel thatan ejection fraction below 35-40% is clearly abnormal

,( 75,78,79). It should, however, be noted that ejectionfraction can vary significantly depending on both doseand duration of sincalide infusion (64). Variousmedications may either inhibit or stimulate gallbladderemptying, and should be discontinued prior to anejection fraction study, Care is also required inpatients with systemic diseases that may have an effecton gallbladder contraction (73). The inability of thegallbladder to contract and eject bile normally is ahelpful piece of information in the evaluation ofpatients with suspectd chronic acalculous biliarydisease, which will be discussed later.

Morphine. Cholescintigraphy is considereddiagnostic for acute cholecystitis if the gallbladder isnot visualized within four hours ofradiopharmaceutical injection. Markedly delayedvisualization may be observed in patients with chroniccholecystitis, bile stasis secondary to prolongedfasting, and alcoholic liver disedse (81). Morphineaugmented cholescintigraphy can be utilized to speedup the differentiation of patients with complete cysticduct obstruction from those who for other reasonshave impaired flow of tracer into the gallbladder (82).

●Morphine acts by constricting the sphincter of Oddi,resulting in a prompt elevation of biliary tract pressurethat may cause radionuclide to flow into thegallbladder (76,8 1). The usual protocol is toadminister morphine if, after 40 to 60 minutes the

15

radiotracer is visualizd in the common bile duct andsmall bowel, but not in the gallbladder. There mustbe sufficient activity left in the hepatobiliary trw topermit gallbladder visualization. Imaging is continualfor another 30 minutes; persistent non-visualization isconsidered to indicate acute cholecystitis (76,82).

The usual dose is 0.04 mg/kg (up to 4 mg) ofmorphine sulfate diluted to 10 ml with saline forinjection. Administration is by slow I.V, push overtwo to three minutes (76), The increasd intraductalprasure causal by morphine can result in symptomsranging from epigastric distress to typical biliarycolic. In Choy’s initial study (81) about 40% ofpatien~ reportd transient cramps. If very severe painshould occur, the effect of morphine can be reversedwith naloxene. Morphine may produce a widespectrum of unwanted effects such as respiratorydeprwsion, nausea, and vomiting. Administration ofa single dose as in these augmentation studies appearsto be well tolerated, however (81). There are fewcontraindications to the use of morphine. Allergicreactions may occur, and it may not be advisable touse this approach in patien~ with a history ofmorphine addiction. False-positive studies can occursecondary to many causes, the most common beingchronic cholecystitis (76,82,83). False-negativestudies are less common. Studies comparing delayedirndging to morphine augmentation have shown thatthe false-positive rate can be decreased usingmorphine (84,85),

PhenobarbU. Phenobarbital has been used in thepediatric population in conjunction withcholwcintigraphy to improve the accuracy ofdifferentiating neonatal hepatitis from biliary atrwia(76,86). The general stimulating effect ofphenobarbital on the liver is well known.Phenobarbital incrwdses bilirubin conjugation andexcretion, enhances bile flow, and increas= thehepatic uptake of other organic anions such m thecommon hepatobiliary imaging agents (76,86).Increased uptake and visualization of the liver leads toa more reliable determination of the underlyingetiology of neonatal jaundice (to be discussed later). Inphenobarbital-augmented cholescintigraphy, thepatientis premeditated orally with 5 mg/kg per day ofphenobarbital for three to sevm consecutive days.The radiotracer, usually around 1 mCi (37 MBq) Tc-99m disofenin, is then injected (76,86), Serial imagesare obtained and computer-generated time-activitycurves can also be generated. Lateral images can helpto separate activity in the bowel from renal excretion.Delayed images are obtained up to 24 hours afierinjection if the bowel is not seen on earlier imagw.If any radiotracer passes into the bowel, the diagnosisof biliary atresia is excluded. Phenobarbiti is

available in a variety of dosage forms, includingliquids. The safety of phenobarbital therapy inchildren and neonates has been established (86).Allergic reactions such as swelling have been observedin individuals who are hypersensitive to barbiturates.

CholecystitisCholecystitis, or inflammation of the gallbladder,

may be acute or chronic in its presentation. In acutecholecystitis the cystic duct is completely obstructed,which incites an inflammatory response in thegallbladder. The acute attack is most often anexacerbation of underl ying chronic cholecystitis, andalthough it may be convenient to view the two asseparate entities, cholecystitis frequently represents acontinuum of dise~e (1,8). Acute cholecystitis isnearly always associated with gallstone disease. Inacute acalculous cholecystitis the cystic ductobstruction is caused by edema from the inflamedgallbladder. The factors that induce gallbladderinflammation are not well understood, but a numberof factors have been implicated, such as lithogenicbile, trappd bile acids, regurgitated pancreatic juice,prostaglandins, and others (8,9).

Cholecystitis is one of the most common abdominalemergencies and must be distinguish from otherabdominal conditions with similar symptoms. Promptdiagnosis and treatment is of the essence, particularlyin patients who are both very ill and elderly. Patientsmay present with a wide variety of complaints andphysical findings. Symptoms vary from vague,poorly-defined abdominal discomfort to short spasmsof biliary colic or severe right upper quadrant painthat may last for several days (9). The rapid andintense pain of biliary colic is typically caused by astone passing through the cystic duct, but if the stonebecomes lodged in the cystic duct the pain willcontinue until the stone passes through (2,9). Acutecalculous cholecystitis is self-limiting in 85% ofpatients, but recurrence may eventually follow unlessthe gallbladder is removed (8). If a stone remainsIodgti in the cystic duct the patient will developserious complications such as complete necrosis of thegallbladder wall and perforation (5,8,9). Aspreviously discussed, cholecystectomy remains theonly definitive cure for gallstone disease, and maytake place as soon as the diagnosis has beenestablished, or after several weeks, when the patientis stabilized and the inflammatory process has resolved(2,8,9). The epidemiology of acalculous cholecystitisdiffers from cholecystitis associated with stones (2).Acute acalculous cholecystitis has been linked toprevious surgery, mwsive trauma, extensive burns,cardiovascular disorders, and malignancy (5,8).Removal of the gallbladder is warranted in patients

diagnosd with acute acalculous cholecystitis (5,9).Cholescintigraphy is a non-inv~sive and highly

sensitive diagnostic test for evaluation of cystic ductobstruction. Failure to visualize the gallbladder within4 hours of radiotracer injection has been 98 % accurate ●in the diagnosis of acute cholecystitis (63). Calculousand acalculous acute cholecystitis present withidentical imaging patterns, As discussed earlier, anumber of conditions are associated with delayd aswell as non-visualization of the gallbladder in theabsence of complete cystic duct obstruction. The useof sincalide or morphine augmentation as well asdelayd imaging up to 24 hours results in increasedsensitivity in thwe patients. Depending on the patientpopulation and the imaging protocol, the diagnosis ofacute cholecystitis by Tc-99m IDA scintigraphy has anoverall sensitivity of 92-100% and specificity of 95-100% (63,64,70,76,81).

Chronic cholecystitis is the most common biliarydisorder but also the most di~cult to evaluate (2,8),It is most frequently associated with gallstone disease(8,87) and patients may have experienced episodes ofbiliary colic. Most patients have functional cysticducts, and although many patients may have delayedgallbladder visualization, cholescintigrams aregenerally normal. Since biliary calculi can bedetected using ultrasound, the usefulness ofcholescintigraphy in this group of patients is limited(1,87). A subset of patients with chronic cholecystitis ●will not have calculi. These patients present withrecurrent right upper quadrant pain, but bloodchemistries, oral cholecystograms, and ultrasoundstudies are normal (8, 87). Three major categories ofabdominal disease can produce typical “biliary” painin the absence of gallstones: (a) chronic acalculouscholecystitis or gallbladder dyskinesia, (b) cystic ductsyndrome or sphincter of Oddi dysfunction, and (c)irritable bowel syndrome. If the symptoms are due toimpaired gallbladder evacuation (as in cystic ductsyndrome) and/or impaired gallbladder contraction (asin chronic acalculous cholecystitis and gallbladderdysfunction), the patient could benefit fromcholecystectomy. A number of recent studies(73,76,79) support the use of gallbladder emptyingstudies using sincalide to predict which patients willbecome symptom-free following gallbladder removal.

Sphincter of Oddi DysfunctionSphincter of Oddi dysfunction is characterized by

a physiologic obstruction to bile drainage from thecommon bile duct into the bowel. It is seen inpatients with recurrent pain afier cholecystectomy ●(70,75). Sincalide augmented cholescintigraphy hasbeen proposed as a method to detect sphincter of Oddidysfunction. The disorder can be identified if there is

16

.—

a delay in biliary-to-bowel transit of radiotracer and afidilure of the sphincter of Oddi to relax followingsincalide administration (76,83). A scoring system

●that combines visual and quantitative criteria haashown improved sensitivity and specificity for thediagnosis of sphincter of Oddi dysfunction (88).

Biliary ObstructionIn the presence of good hepatocyte function, acute

total bile duct obstruction by gallstones can be readil yidentified using cholescintigraph y. Hepatic uptake oftracer will be prompt, with no evidence of hiliaryexcretion by four hours. In the later stages of totalobstruction, hepatic uptake will decrease anddifferentiation of obstruction from hepatocellulardisease becomes progressively more difficult. Inpartial bile duct obstruction, the biliary tree isvisualized to the level of obstruction, filling defec~ ornarrowing may he observed, and some radiotracer willbe seen downstream from the area of obstruction(70,75). Patients with partial common bile ductobstruction also show reduction in the sincalideinduced gallbladder ejection fraction and ejection rate(43).

Bilti bkage and RefluxHepatobiliary scintigraph y has proven to be a very

sensitive method of disclosing and monitoring intra-and extrahepatic bile leaks. These are seen mostcommon]y following biliary tract surgery, but can alsobe a result of abdominal trauma or inflammatoryerosion of the gallbladder wall (75,87,89), Thelocation of bile accumulation depends on the site ofinjury, and images in several different projections willbe helpful in distin~ishing free bile from normalareds of radiotracer localization. Delayed imagesshould also be obtained. Cholescintigraphy is also anexcellent technique for demonstrating patency andfunction of biliary-enteric anastomoses (75,89). Thenon-invasive detection and quantitation ofenterogastric bile reflux can only be performed usingcholescintigraphy (83). The technique is of value forthe confirmation and follow-up of bile reflux aftersurgical interventions.

Neonattil JaundiceIn the pediatric population, cholescintigraphy is a

valuable noninvasive technique for the evaluation ofprolongti jaundice. Jaundice in the nwnate can havenumerous causes, but conjugated hyperbilirubinemiathat persists beyond the first month of life is usuallydue to either neonatal hepatitis or biliary atresia (5).It is important to identify the cause as early aspossible, because the treatment and prognosis of thesetwo conditions are quite different. Extrahepatic bile

duct atresia is defined as the lack of lumen in part orall of the extrahepatic biliary tract, causing completeobstruction to bile flow. It is considered to be therwult of a progrmsive, d~tructive inflammatoryprocess of unknown etiology that eventually destroysthe whole bile duct system and results in death fromcirrhotic liver disease. Biliary atresia can be treatdsuccessfully by surgery only if performed at a veryearly age (5,86,87). Nwnatal hepatitis is a clinicalsyndrome that is not associated with a specific viralinfection in the majority of cases. There are manycausw for prolonged conjugated hyperbilirubinemia innmnat~, including me~~bolic disorders, infectiousdiseases, and intoxicants (78,87). In many casescholestasis attributable to these causes is mdicallytreatable and reversible (5). The clinical, biochemicaland histologic features of these two disorders are oftensimilar, making the differential diagnosis extremelydifficult.

In biliary atresia, the radiotracer does not enter thebowel. In the absence of significant cirrhosis,hepatocyte function is preserved, and there is rapidblood clearance and hepatic uptake, resulting in earlydefinition of liver boundaries, which persiststhroughout the study (76,86). Patients with nwnatalhepatitis in the presence of a patent extrahepaticbiliary tree may present with a more variable imagingpattern (86). Depending on the severity of cholestasisand hepatocellular disease, initial liver uptake may benormal or markedly decredsed. The gallbladder is notalways visualized. Hepatic clearance is delayd,resulting in delayed visualkation of bowel activity.However, detection of even the slightwt amount ofradioactivity in the bowel in these patients identifiesbiliary patency and argues against surgical intervention(75). If hepatic uptake is extremely poor due to veryhigh serum bilirubin levels, it may not be possible toidentifi bowel activity on images. The liver uptakepattern still makes it feasible to make a differentialdiagnosis. If hepatocyte function is severelycompromise, the activity initially seen in the liver isprimarily due to blood pool activity, and it can beobserved that it will decreme over time at the samerate as cardiac activity, a pattern not seen in biliaryatresia (86). As previously mentioned, pretreatmentwith phenobarbital significantly improves the accuracyof cholescintigraphy in differentiating extrahepaticbiliary atresia from nwnatal hepatitis, at least whenthe agent Tc-99m paraisopropyl-IDA was used (86).In a seriu of 27 patien~ with nwnatal jaundice thatdid not receive phenobarbiti pretreatment, Gerholdand his msociatw (90) reportd that the most usefuldiagnostic criterion for biliary atresia was absence ofintestinal radioactivity up to 24 hours after radiotracerinjection. All nine patients who demonstrated

17

intestinal activity did so by three hours, Thesepatients were studied with either Tc-99m disofenin orTc-99m diethyl-IDA. The sensitivity and specificityfor biliary atresia in their study were 97% and 82%,respectively.

QUANTITATION OF HEPATIC FUNCTION

In the early stagw of liver disease, serialquantitative assessment of liver function would behelpful in monitoring therapy and in determiningprognosis. However, current noninvasive methods areneither simple nor reliable (8,9 1). Due to themultitude of metabolic tasks performed by the liver,none of the liver function parameters that can beeasily measured will reflect overall hepatic capacity.Another major use of such a method would be to helpdifferentiate between biliary obstruction andhepatocellular disease in the jaundiced patient. Up tovery recently, techniques using radiopharmaceuti calshave met with limited success. The idealradiopharmaceutical for quantitation of hepatocytefunction should be highly specific for liver uptake,and should remain in the hepatocyte long enough toallow sufficient data acquisition. The in-vivodistribution should be solely a function ofhepatocellular function, and should not be affected byfactors such as elevated bilirubin levels (38).Attempts at quantitation of liver filnction have beenmade using Tc-99m sulfur colloid, however, colloidsare taken up by reticuloendothelial cells and are notspecific for the liver. Liver uptake often correlatespoorly with hepatocellular function (5). Hepatobiliaryradiopharmaceuticals have been studied extensive y,going back to 1-131 rose bengal. More recently, theTc-99m IDA analogs have been used. Quantitativemeasurement of liver uptake of Tc-99m IDA analogsis complicated in the jaundiced patient by delaydblood clearance and simultaneous renal excretion.Recirculation of tracer and active hepatocyte uptake isprolonged, and this is further complicated by excretioninto bile of tracer that was taken up by the liver earlyon, Multicompartmental analysis of blood pool andhepatic uptake using pharmacokinetic models ofvarying complexity have been attempted, but resultshave been discouraging (91).

Measurement of Heptitic Extraction Fraction (HEF)Using Tc-99m IDA Analogs

Estimation of the fraction of radiotracer that can beremoved by the liver during a single pass, orextraction fraction, has been proposed as a quantitativemeasure of liver function (91,92). If the tracer couldbe presented as a bolus directly into the blood supplyof the liver, hepatic extraction fraction (HEF) could

be measured directly. However, because of the liver’sdual blood supply and the complication ofsimultaneous hepatocellular uptake and excretion, thisis not possible using Tc-99m IDA analogs. Juni andcoworkers have calculated HEF by an indirect method●using deconvolution analysis (9 1,92,93).Deconvolution analysis is a computer-assistedmathematical technique which can correct an organ’stime-activity curve for the dynamical y changingpattern of blood activity (obtained from the heart’stime-activity curve) being presentd to that organ (92).Care must be taken so that no biliary, renal, or majorvascular activity or scatter is included in the region(s)of interest used to generate the hepatic time-activitycurve (93). In a group of 53 patients with acutejaundice, Juni et al. (91) found that this measure ofHEF was most specific during the first few days afteronset of j aundice, with fairly good separation betweenpatients with normal livers (80-100%) or acute biliaryobstruction (65- 100%) versus those with acutehepatocellular dysfunction (14-77 %). Another study(93) showed markedly decredsed HEF in patients withalcoholic cirrhosis compared to patients with diseasesconfined primarily to the biliary tract. It appears thatHEF is an improved quantitative measure of hepaticfunction compared to other parameters assessd usinghepatobiliary radiopharmaceuticals. The deconvolu-tion analysis is rapid and entirely automatd and canbe performed using standard commercial nuclear ●mdicine computers (91). Its clinical utility will betested further as more institutions add this analysis totheir hepatobiliary imaging procedures.

Quantitation of Hepatic Binding Protein RweptorsIn addition to the transport pathways for hepatocyte

uptake discussed earlier, the liver also has the abilityto selectively extract macromolecular ligands fromblood by receptor-mediated endocytosis (2,5). Of thereceptors on the hepatocyte surface, theasialoglycoprotein receptor is the best characterized.This receptor is found only on mammalian hepato-cytes, and is often referred to as hepatic bindingprotein (HBP) receptor (94). The hepaticasialoglycoprotein receptor promotes the clearance ofserum glycoproteins that have exposed galactosylresidues made terminal by removal of sialic acid.After binding at the hepatocyte membrane, the ligand-receptor complex is internalized and transported tohepatic lysosomes where the complex dissociates andthe ligand is catabolized. The receptors recycle backto the hepatocyte membrane where the entire processis repedted. It has been postulated, but not proven,that the HBP receptor participates in the regulation ofturnover of serum glycoproteins. Alterations inasialoglycoprotein receptor binding has been

demonstrated in specific physiologic and pathologicalstates (5). Since the HBP receptor is highly specificfor ligands containing exposed galactose rwidues, thistype of ligand has been investigated as a potentialradiopharmaceutical for quantitation of hepatocytefunction. There is currently a great deal of interest inreceptor-specific radiopharmaceuticals (15). Thepotential exists for the utilization of mathematicalmodels to obtain in vivo measurements of receptornumber and affinity from imaging observations usingreceptor-specific radiopharmaceuticals. It is antici-pated that such data may provide a quantitative indexfor patient diagnosis and management (15,95).

Technetium-99m galactosyl-nwglycoalbumin (Tc-NGA) is a synthetic ligand that exhibits highspecificity for HBP receptor binding (95,96,97,98).The NGA ligand is prepard by covalently attachingthe galactosyl unit to human serum albumin (99). Thenumber of galactose units per albumin molecule canbe controlled, and since it is known that the ability ofglycoproteins to bind to the HBP receptor increasesdramatically as more galactose units are added (5),this gives control of both affinity and binding rate.NGA has commonly been radiolabeled with Tc-99musing an electrolytic method (99) for the reduction ofpertechnetate. In Japan, Tc-99m-DTPA-galactosylhuman serum albumin (Tc-GSA) is available as astannous ion containing kit (100). Both methodsresult in stable preparations of high radiochemicalpurity. Animal studies have confirmd that Tc-NGAis highly specific for liver with a rapid uptake phaseand a low rate of metabolism and liver exit (97,99).Both renal and gastrointestinal excretion does occur,but the excretion rate is too low to affect liver tirne-activity curves during the first 30 minutes afterinjection. Since Tc-NGA is not taken up by thegeneral anion extraction mechanism, it is not affectedby high serum bilirubin levels. Its rate of hepatocyteaccumulation is dependent on the amount of Iigandinjected and is proportioned to the number ofgalactose units on the albumin (97). Thisradiopharmaceutical can be designed to have moderatereceptor affinity so that the rate at which it binds isnot governed solely by blood flow, but depends on theconcentrations of both ligand and receptor (e.g., asecond order process) (97). Since Tc-NGA has beenshown to have relatively low toxicity (99), it can beused in a dose large enough to produce a second orderresponse. Changes in liver and blood time-activitycurves obtained with Tc-NGA in pigs were observdwhen either hepatic blood flow, Iigand-receptoraffinity, or molar dose of ligand were altered (101).

Tc-NGA appears to exhibit the unique properties ofreceptor-specific ligands: high ligand affinity,specificityy, saturability, and distribution in relation to

physiologic rwponse (15). The parameters thatgovern the rate of a receptor-binding process are thereceptor and Iigand concentrations, and the forwardand reverse binding constats (102). Since thebinding of Tc-NGA is highly irreversible (96), thereverse binding constant can be ignored (102). Amathematical model has been developed that permitsestimation of kinetic parameters that represent receptorconcentration and forward binding rate from imagingstudies using 4+ mCi (148-222 MB@ Tc-99m NGA.The kinetic model requires liver and heart time-activity data for the first 30 minutes after injectionplus activity determination in a blood sample taken atthree minutes (98, 102). The kinetic model has beenvalidated by independent in vitro assay of tissueobtaind by liver biopsy (95), Multiple clinicalstudies using Tc-NGA and Tc-GSA have beenreported from investigators in the United States,Europe, and Japan. A recent review article (98)providw an overview of the various liver disordersthat have been studied, which include chronic liverdisease, primary and secondary liver carcinoma, livertransplantation, and acute viral hepatitis. Thistechnique for fictional hepatic imaging showspromise as a sensitive measure of functioninghepatocyte mass, of particular interest whenhepatectomy for hepatocellul~ carcinoma or livertransplantation is contemplated. Serial studies mayhelp document changes in hepatocyte function inpatients being trwdted for active viral hepatitis. Thistechnique, while still undergoing validation, holdssignificant potential for obtaining information that isnot readily available using other imaging techniques orconventio-nal liver function tests.

CONCLUSIONS

Currently available Tc-99m labeled hepatobiliarvradiopharmaceuticals have been developed based o;what is known about the liver’s organic anionclearance pathway. This group of radiophar-maceuticals serves as an example of the utilization ofstructure-activity relationship analysis during thedevelopment phase. Technetium-99m IDA analogs inuse today satisfy most of the criteria for an idealradiopharmaceutical to study the hepatobiliaryexcretion pathway. Although the clearance of theseagents by the liver is reduced in the presence of highserum bilirubin levels, clinically useful imagw can beobtained in most situations. Chol~cintigraphy withTc-99m IDA analogs is a noninvasive, highly sensitivetest for the evaluation of the functional status ofhepatic and cystic and the gallbladder. It is also usdto localize bile leaks and alterations in the bilepathway rwulting from surgery or trauma, and to

19

differentiate between surgical and medical jaundice inthe nmnate. Improved diagnostic information maybeobtained by utilizing drug-augmentedcholescintigraphic methods. Technetium-99m IDAanalogs do not possess ideal characteristics forquantitative assessment of liver function. However,hepatic extraction fraction estimates may be ob~~inedusing a computer-assistd technique that allowscontinuous correction for blood pool activity,Receptor-specific agenw, Tc-99m labeled NGA andGSA, are currently being evaluated for quantitationof fictional hepatocyte mass. These agents are notaffected by elevated serum bilirubin levels, and arehighly specific for the asialogylcoprotein receptorwhich is found ordy on mammalian hepatocytes.

ACKNOWLEDGEMENT

me author would like to thank Betty Trent Jor her

skillfil assistance in the preparation of thti wnuscript.

References

1.

2.

3.

4,

5.

6.

7.

8.

9.

10.

Freitas JE. Cholescintigraphy in acute and chronic

chol=ystitis. Semin Nucl Med 1982; 12:18-26.

Gholson CF, Bacon BR. Essentiak of ClinicalHematology. St, buis: Mosby-Year Book, 1993.

Tavoloni N, Berk, PD, editors. Hepatic Tramponand Bile Secretion. New York: Raven Press, 1993.

LeBouton AV, editor. Molecular and Cell Biologyof the Liver, Boca Raton: CRC Press, 1993.

Zakim D, Boyer TD, ditors. Hepaiology. A

Textbook of Liver Diseme. 2nd 4. Philadelphia:Saunders, 1990.

Barbara L, Dowling RH, Hofmann AF, Roda E.

Recent Advances in Bile Acid Research. NewYork: Raven Press, 1985.

Stein JH, editor-in-chief. Internal Medicine. St.Louis: Mosby, 1994.

Sherlock S, Dooley J. Disewes of the Liver andBiliary System. 9th ed. Oxford: BlackWell Sci.

Publications, 1993.

Greenfield LJ, Mulholland MW, Oldham KT,Belenoch GB. Surge~: Scientl~c Principles and

Prac~ice. Philadelphia: J.B. Lippincott Co., 1993.

Fritzberg AR. Advances in the development ofhepatobiliary radiopharmaceuticals. In: FritzbergAR, editor. Radiophamaceuticals: Progress and

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

20

Clinical Perspectives. Vol I. Boca Raton: CRCPress, 1986:89-116.

Taplin GV, Meredith OM, Kade H. Theradioactive (I-1 31 tagged) rose bengal uptake- ●excretion test for liver fimction using external

gamma-ray scintillation counting twhniques. JLub Clin Med 1955; 45:665-678.

smith RL. me ficreto~ Function of Bile.

hndon: Chapman& Hall, 1973.

Hirom PC, Millburn P, Smith RL, Williams RT.Species variations in the threshold rnolectiar-weight factor for the biliary excretion of organic

anions. Biochem J 1972;129: 1071-1077.

Firnau G. Why do Tc-99m chelates work for

cholescintigraphy? Eur J Nucl Md 1976; 1:137-139.

Eckelman WC. The development of single-photonemitting receptor-binding radiotracers. In: Nunu

AD, editor. Radiophamaceuticals: Chemistiy andPharmacology. New York: MarMl Dekker, Inc.,1992:167-219.

Serafti AN, Smoak WM, Hupf HB, Beaver JE,Holder J, GilSon AJ. Iodine-123 rose bengal: animproved hepatobiliary imaging agent. J NUC1Med 1975; 16:629-632. ●Tubis M, Krishnatnurthy GT, Endow JS, BIahdWH. ~c-penicillamine, a new cholescinti-

graphic agent. J Nucl Med 1972; 13:652-654.

Chervu LR, Nunn AD, Loberg MD. Radiophar-

maceuticals for hepatobiliary imaging. Semin NuclMed 1982; 12:5-17.

Baker RJ, Bellen JC, Ronai PM. Technetium-

99m-pyridoxylideneglutamate: a new hepatobiliary

radiopharrnaceutical. I. Experimental aspects. J

Nucl Med 1975; 16:720-727.

Eichhorn GL, Dawes JW. Ihe metal complexesof vitamin BAand Schiffs base derivatives. J Am

Chem Soc 1954; 76:5663-5667.

Davis L, Roddy F, Metz,ler DE. Metal chelatw ofimina derived from pyridoxal and amino acids.J Am Chem Soc 1961; 83: 127-134.

Chiotellis E, Subramartian G, McAfee JG.Preparation of Tc-99m labeled pyridoxal-amino

acid complexes and their evaluation. Znt J NUC1 ●Med Biol 1977 ;4:29-41.

23.

●24.

25.

26.

27.

28.

0 29.

30.

31.

32.

33.

●

Jansholt A-L, Krohn KA, S~ RC, Matolo

NM, DeNardo GL. Catabolism and proteinbinding of Tc-99m pyridoxylideneglutamate. JNUCl Med 1978; 19:1036-1044.

Kubota H, Eckelman WC, Poulose KP, Reba RC.Technetium-99m-pyridoxylidene-glutarnate, a newagent for gallbladder imaging: comparison with1311-rose bengal. J Nucl Med 1976; 17:36-39.

Ronai PM, Baker RJ, Bellen JC, Collins PJ,

Anderson PJ, Lander H. Technetium-99 m-

pyricloxylideneglutamate: a new hepatohiliaryradiophamceutical. II. Clinical aspects. J Nucl

Med 1975; 16:728-737.

Stadalnik RC, Matolo NM, Jansholt A-L, KrohnKA, DeNardo CL, Wolfman EF. Technetium-99m pyridoxylideneglutamate (P. G.)cholescintigraphy. Radiology 1976; 121:657-661.

Wistow BW, Subrarnanian G, Van H&rtum RL,Henderson RW, Gagne GM, Hall RC, McAf~JG. h evaluation of We-labeled hepatobiliary

agents. J Nucl Med 1977; 8:455-461.

Kato M, Hazue M. Tc-99m (Sri)pyridoxyliden-minates: preparation and biologicevaluation. J Nucl Med 1978; 19:397-406.

Kato-Azuma M. Tc-99m (Sn)-N-pyridoxyl-

arninates: a new series of hepatobiliary imagingagents. J Nucl Med 1982; 23:517-524.

Loberg MD, Cooper M, Harvey E, Callery P,Faith W. Development of new radiophar-maceuticals based on N-substitution ofirninodiacetic acid. J Nucl Med 1976; 17:633-638.

Loberg MD, Fields AT. Chemical structure ofteclmetium-99m-labeled N-(2,6 -dimethylphenyl-carbamoylmethyl)- iminodiacetic acid (Tc-HIDA).

IntJ Appl Radiut Lvotopes 1978; 29: 167-173.

Costello CE, Brodack JW, Jones AG, Davison A,Johnson DL, Kasina S, tit al. The investigation ofradiopharmaceutical components by fast atombombardment mass spwtrometry: the identificationof Tc-HIDA and the epimers of Tc-C02-DADS.

J Nucl h4ed 1983;24:353-355.

Wistow BW, Subramanian G, Gagne GM,Henderson RW, McAf& JG, Hall RC, et al.Experimenhl and clinical trials of new ‘Tc-

Iabeld hepatobiliary agents, Radiology 1978;128:793-794.

34.

35.

36.

37.

38.

39.

40.

41.

42.

43.

va Wyk AJ, Fourie PJ, van Zyl WH, titter MG,

mnaar PC. Synthesis of five new wc-HIDAM.

isomers and comparison with yc-HIDA. Eur JNucl Med1979;4:445-448.

Jansholt A-L, Vera DR, Krohn KA, S~ RC.In vivo kinetics of hepatobiliary agents in

jaundiced animals. h: Radiophannaceuticak ILProc. Second Internat. Symposium onRadiopharmaceuticals. New York: Sot. Nucl.

Med. 1979, 555-564.

Nicholson RW, Herman KJ, Shields RA, TestsHJ. The plasma protein binding of HIDA. Eur J

Nucl Med 1980; 5:311-312.

Ryan J, Cooper M, bberg M, Harvey E,Sikorski S. T&hnetium-99m-labeld N-(2,6-

dimethylphenylcarbamoylmethyl) iminodiaceticacid (Tc-99m HID A): a new radiopharmaceuticalfor hepatobiliary imaging studies. J NUCl Med1977; 18:997-1004.

Harvey E, Loberg M, Ryan J, Sikorski S, Faith

W, Cooper M. Hepatic clearance mmhanism ofTc-99m-HIDA and its effect on quantitation of

hepatobiliary function: concise communication. JNucl Med 1979; 20:310-313.

Chiotellis E, Varvarigou A. ~c-labeled N-substituted carbamoyl iminodiacetates: relationship

betw=n structure and biodistribution. Int J NuclMed Biol 1980;7: 1-7.

Chiotellis E, Varvarigou A, Koutoulidis C.Comparative in vivo kinetics of some new ‘Tc-

labeled acetanilido irninodiacetates. Eur J NuclMed 1981; 6:241-244.

Nunn AD, Loberg MD, Conley RA. A structure-distribution-relationship approach leading to thedevelopment of Tc-99m mebrofenin: m improved

chol=intigraphic agent. J NUC1 Med 1983;24:423-430.

Fields AT, Porter DW, Callery PS, Harvey EB,bberg MD. Synthesis and radiolabeling oftwhnetium radiopharmaceuticals based on N-

substituted iminodiacetic acid: effect ofradiolabeling conditions on radiochemicalpurity.J Label Compd Radiopham 1978; 15:387-399.

Krishnamurthy S, Krishnamurthy GT.Technetium-99m-iminodiacetic acid organicanions: review of biokinetics and clinical

application in hematology. Hematology 1989;9: 139.153.

21

44.

45.

46.

47.

48.

49.

50.

51.

52.

53.

54.

55.

56.

Klingensmith WC, Fritzberg AR, Spitmr VM,Kuni CC, WilliamsonMR, Gerhold JP. Work inprogrws: clinical evaluation of Tc-99m-trimethylbromo-IDAmd Tc-99m-diisopropyl-IDAfor hepatobiliary imaging. Radiology1983; 146:181-184.

Maliski EG, BradshawJ. QSAR and the role ofcomputers in drug design. In: Ganellin CR,

Robetis SM, editors. Medicinal Chemistry, 2nd4. San Diego: AcademicPress, 1993.

Kubinyi H. QSAR:Hansch Analysis and RelatedApproaches. New York: VCH, 1993.

Hansch C. A quantitative approach to biochemical

structure-activity relationships. Acc Chem Res1969; 2:232-239.

Frw SM, Wilson JW. A mathematical

contribution to structure-activity studies. J Med

Chem 1964; 7:395-399.

Burns HD, Marzilli L, Sowa D, Baum D, WaWerHN Jr. Relationship betw=n molecular structureand biliary excretion of tihnetium-99m HIDA andHIDA analogs [abstract]. J Nucl Med1977; 18:624.

Kato-AzumaM. Lipopbilic derivativesof *Tc-(Sn)pyridoxylidenephenylalanine: a structuredistribution relationship (SDR) study of’technetium-99mcomplexes.Int J Appl Radiat Isot1982; 33:937-944.

Reiffers S, bbrwht RM, Wolf AP, ChistmanDR, Ansari AN, Atkins HL. Cyclotron isotopes

and radiopharrnaceuticals XXXIII. Synthesis andstructure effwk of selective biliary secretion ofhalogenati indotricarbocyanines. Int J Appl Rad

]SO~ 1983; 34:1383-1393.

lansholt A-L, Scheibe PO, Vera DR, Krohn KA,Stadalnik RC. Correlation analysis of substituenteffects on the pharmacokinetics of hepatobiliaryagents, J Label Compd Radiopharm 198 1; 18:198-

200.

DuPont Pharma. Hepatolite package insert.Billerica, MA, 1991.

Mallinckrodt, ~C. TechneScan HIDA packageinsert. St. Louis, MO, 1989.

Squibb Diagnostics. Choletw package insert.

Princeton, N. J., 1990.

Robbins PJ. Chromatography of Technetium-99m

Radiophamaceuticals -A Prac~ical Guide. New

57.

58.

59.

60.

61.

62.

63.

64,

65.

66.

67.

York The Society of Nuclear Medicine, Inc.,

1984.

Zimmer AM, Majewski W, Spies SM. Rapidminiaturiti chrowtography for Tc-99m IDA ●agents: comparison with gel chromatography. EurJ Nuci Med 1982; 7:88-91.

Fritzberg AR, bwis D, HPLC analysis ofTc-99m iminodiacetate hepatobiliary agents and aquestion of multiple peaks: concise

communication. J Nucl Med 1980;21: 1180-1184.

Majewski W, Zimmer AM, Spies SM, HingeveldJ. RadioChemical evaluation of commercial

iminodiacetatehepatobiliaryradiopharroamuticals.J Nucl Med Tech 1981;9: 185-187.

Popescu HI. Hepatic clearance mwhanism of Tc-99m-N- (acetanilido)-iminodiaceticacid derivatives

[letter]. J Nucl Med 1980;21:1 110-1111.

Sarkar SD. Hepatic clearance of technetium-99m-iminodiacetic acid derivatives in hyperbili-

rubinemic states [editorial]. J Nucl Med1992; 33:1551-1552.

Hernandez M, Rosenthal L. A cross-over studycomparing the kinetics of Tc-99m-labeled

diisopropyl and p-butyl IDA analogs in patients.

Clin Nucl Med 1980;5: 159-165. ●Weissman HS, Sugarrnan LA, Fr&man LM. Theclinical role of tihnetium-99m iminodiacetic acidcholescintigraphy. In: Fr&man LM, Weissman

HS, editors. Nuclear Medicine Annual 1981.New York: Raven Press, 1981, 35-80.

Krisnamurthy GT, Turner FE. Pharmacokinetics

and clinical application of technetium-99m-labeledhepatobiliary agents. Semin Nucl Med1990; 20: 130-149.

Wu RK, Siegel JA, Rattner Z, Malmud LS. Tc-99m HIDA dosimetry in patients with vdrioushepatic disorders. J Nucl Med 1984;25:905-912.

Hahn K, Lingenfelder B, Wolf R, Eissner D.Radiation absorbed dose to newborns after

application of Wc-diethyl IDA. In: Raynaud C.editor. Nuclear Medicine and Biology. Vol IV.Paris. Pergamon Press 1982:2955-2957.

Hladik WB IIf, Ponto JA, Lentle BC, Laven DL.Iatrogenic alterations in the biodistribution ofradiotracers as a result of drug therapy: reported ●instances. In: Hladik WM W, Saba GB, Study KT,editors. Essentik of Nuchar Medicine Science.Baltimore: WiUiams and Wilkins, 1987; 189-219.

22

68.

●69.

70.

71.

72.

73.

74.

75.

76.

77.

78.

79.

●80.

Hesslewood S, hungradiophamceuticals.1994;21:348-356.

E. Drug interactionswithEur J Nucl Med

Joehl RJ, Koch KL, Nahrwold DL. Opiod drugscause bile duct obstruction during hepatobiliaryscans. Am J Surg1984;147: 134-138.

Kim EE, Moon T-Y, Delpas-d ES, PodoloffDA, Haynie TP. Nuclar hepatobiliary imaging.

Rd Clin North Am 1993; 31:923-933.

Richards AG, Brighouse R. Nicotinic acid - acause of failed HIDA scanning. J Nucl Med1981; 22:746-747.

Shuman WP, Gibbs P, Rudd TG, Mack LA.PIPIDA scintigraphy for cholecystitis: falsepositives in alcoholism and total parenteral

nutrition. AJR 1982;138:1-5.

Kloiber R, Molnar CP, Shaffer EA. Chronicbiliary-typepain in the absence of gallstones: thevalue of cholecystokinin cholescintigraphy.AJR1992; 159:509-513.

Rubow S, Klopper J, Wasserman H, Baard B, van

Niekirk M. The excretion of radiopharmaceuticalsin human breast milk: additional data and

dosimetry. Eur J Nucl Med1994;21: 144-153.

GottschalkA, Hoffer PB, PotchenEJ. DiagnosticNuclear Medicine, Vol. 2. Baltimore: Williamsand Wilkins, 1988.

Fink-BennettD. Augmentedcholescintigraphy:itsrole in det=ting acuteand chronicdisordersof thehepatobiliarytree. Semin Nucl A4ed 1991 ;21: 128-

139.

Xynos E, Pwhlivanides G, Znras OJ, Chrysos E,

Tzovaras G, Fountos A, et al. Reproducibility ofgallbladder emptying scintigraphic studies. J NuclMed 1994; 35:835-839.

Fink-Bennett D, DeRidder P, Kolo~si W, GordonR, Rapp J. Cholecystokinin cholescintigraphic

findings in the cystic duct syndrome. J Nucl Med1985;26:1 123-1128.

Reed DN Jr, Fernandez M, Hicks RD. Kinevac-assisted cholescintigraphy as m accurate predictorof chronic acalculous gallbladder disease and thelikelihood of symptom relief with cholwystectomy.Amer Surg 1993; 59:273-277.

Freeman LM, Sugarman LA, Weissman HS. Roleof cholmystokinetic agents in WC-IDA chole-

scintigraphy. Semin Nucl Med 1981; 11:186-193.

81.

82.

83.

84.

85.

86.

87.

88.

89.

90.

91.

92.

Choy D, Shi EC, McLeanRG, Hoschl R, MurrayIPC, Ham JM. Cholescintigraphy in acutecholecystitis: w of intravenous morphine.Radiology 1984; 151:203-207.

Fink-BennettD, BalonHR. The role of morphine-augmented cholescintigraphy in the detection ofacute cholwystitis. Clin Nucl Med 1993; 18:891-

897.

Drane WE. Nucl~r medicine techniquw for theliver and biliary syskm. Update for the 1990s.

Radiol C/in NAer 1991; 29: 1129-1150.

Kim CK, Tse KKM, Juweid M, Moz.ley PD,Woda A, Alavi A. Cholescintigraphy in the

diagnosis of acute cholwystitis: morphineaugmentation is superior to delayed imaging. J

Nucl Med 1993; 34: 1866-1870.

Flancbaum L, Wilson GA, Choban PS. Thesignificance of a positive test of morphinecholescintigraphy in hospitalized patien~~. Surg

Gynecol Obstet 1993; 177:227-230.

Majd M, Reba RC, Altman RP. Effect ofphenobarbital on -c-IDA scintigraphy in theevaluation of nmnatal jaundice. Semin Nucl Med

1981 ;11:194-204.

Grainger RG, Allison DJ, editors. DiagnosticRadiology. 2nd ed. Edinburgh: ChurchillLivingstone, 1992.

Sostre S, Kalloo AN, Spiegler EJ, Camargo EE,Wagner HN Jr. A noninvasive test of sphincter ofOddi dysfunction in postcholecystitomy patienh:

the scintigraphic score. J Nucl Med1992; 33:1216-1222.

Weissman HS, Gliedman ML, Wik PJ, Sugarman

LA, Badia J, Guglielmo K, et al. Evaluation ofthe postoperative patient with -c-IDA chole-scintigraphy. Semin Nucl Med 1982; 12:27-52.

Gerhold JP, Klingensmith WC, Kuni CC, Lilly

JR, Silverman A, Fritzberg AR, et al. Diagnosisof bilia~ atresia with radionuclide imaging.

Radiology 1983; 146:499-504.

Juni JE, Reichle R. Measurement ofhepatocellular function with d=onvolutionanalysis: application in the differential diagnosis ofacute jaundice. Radiology 1990; 177:171-175.

Juni JE, Thrall JH, Froelich JW, Wiggins RC,Campbell DA, Tusca M. The appndd curvetechnique for deconvolution analysis - method and

validation. Eur J Nucl Med 1988; 14:403-407.

23

93.

94.

95.

96.

97.

98,

99.

100.

101.

102.

Brown PH, Juni JE, Lieberman DA,Krishnamurthy GT. Hepatocyte versus biliarydisease: a distinction by deconvolution aalysis of

twhnetium-99m IDA time-activity curv~. J NuclMed 1988; 29:623-630.

Stockert RJ, Morell AG. Hepatic binding protein:the galactose-specific r-ptor of mammalim

hepatocytes. Hematology 1983 ;3:750-757.

Kudo M, Vera DR, Trudwu WL, Stadalnik RC.Validation of in vivo receptor measurements via invitro radioassay: technetium-99m-galactosyl-nmgl ycoalbumin as prototype model. J Nucl Med1991 ;32:1177-1182.

Vera DR, Krohn KA, Stadalnik RC, Scheibe PO.

Tc-99m galactosyl-nmglycoalbumin: in vitro

characterization of receptor-mdiated binding. JNucl Med 1984; 25:779-787.

Vera DR, Krohn KA, Stadalnik RC, Scheibe PO.Tc-99m- galactosyl-nmglycoalburnin: in vivocharacterimtion of r~eptor-mediated binding to

hepatocyks. Radiology 1984; 151:191-196.

$tadalnik RC, Kudo M, EckelmanWC, Vera DR.In vivo functionalimaging using receptor-bindingradiophamaceuticals. Technetium 99m-galactosyl-

neoglycoalbumin as a model. Invest Radiol

1993; 28:64-70.

Vera DR, Stadalnik RC, Krohn KA. T=hnetium-99m galactosyl-nmglycoalbumin: preparation and

preclinical studies. J Nucl Med 1985; 26: 1157-1167.

Torizuka K, Ha-Kawa SK, Ikekubo K, Suoa Y,

Tanaka Y, Hino M, et al. Phase I clinical studyon WC-GSA, a new agent for functional imagingof the liver. Jpn J Nucl Med 1991; 28: 1321-1331.

Vera DR, Woodle ES, Stadalnik RC. Kineticsensitivity of a receptor-binding radiopharma-ceutical: technetium-99m galactosyl-neoglyco-

albumin, J iVucl Med 1989; 30: 1519-1530.

Vera DR, Stadalnik RC, Trudeau WL, Scheibe

Po, Krohn KA. Measurement of rweptor

concentration and forward-binding rate constant viaradiopharmacokineticmodeling of technetium-99 m-galactosyl-nmgl ycoalbumin. J Nucl Med1991; 32:1169-1176.

1. A main

A.

B.c.D.

QUESTIONS

function of the hepatocyte is:

oremoval of foreign particles fromcirculationbreakdown of senescent blood cellsdetoxification of harmful compoundscomplexation to make polar compounds

less water-soluble

2. The main function of the gallbladder is:

A. degradation of cholesterolB. storage and concentration of bilec. absorption of unconjugated bile acidsD. m~lation of canalicularbile swretion

3. The overall excretionrate of organic anions intobile dependsprimarily on:

A. the carrier-mdiatti canaliculartransport process

B. the number of availablehepatocytestorage sites

c. the rate of bile formation and excretionD. the number of available receptor sites on

the sinusoidal membrane

4. There is no competition for biliary excretion @between Tc-99m disofenin and

A. bilirubinB. chlorpromazinec. indocyanine g=nD. sulfobromophthalein

5. Compounds that are primarily excretd in urinerather than in bile are characterized by being

A. of molecular weight above 600B. highly protein boundc. labeled with radioiodineD. strongly polar

6. Which of the following statements pertainkg to

hepatic bile is &e?

A. secreted at an average rate of 25 ml per

hourB. bilirubin usually represents 10% of total

bile solidsc. cholesterol is a major lipid componentD. flow is related to the bile acid pool

●

24

7. Which of the following statements pertaining tobile acids is @e?

o A. primary bile acids are synthesiti inreticuloendothel ial cells

B. circulating bile acids are less than 5 %protein bound

c. less than 10% of conjugated bile acidsare reabsorbed in the gastrointestinaltract

D. bile acids are conjugati with glycin andtaulin

8. The most importantcharacteristicof bilirubin isthat it:

A. promotes G.I. tract absorptionof lipidsB. is a degradationproduct of hemec. kwps lipids in bile in solutionD. promotes bile formation and flow

9. The organic anion pathway for hepatocyteexcretion is not followd by:

A. asialoglycoproteinB. indocyanine gr=n

c. rose bengalD. iopanoicacid

9 10. Acute cholecystitis is a result of cystic ductobstruction by gallstones in:

A. more than 90% of cases

B. less thm 50% of cases

c. most patientswith supersaturatedbileD. patients trtited long-term with opioid

pain killers

1.1. The presence of calculi in the gallbladder causesymptoms in:

A. patients with short cystic ducts

B. more than SO% of individualsc. patients with bilirubin levels above

3 mgldlD. a rninorit y of individuals

12. Gallstones classified as cholesterol stontis:

A. are common in patients with biliary tractinfection

B. contains calcium in the center

c. are poorly suited for dissolution therapywith bile salts

D. are not usually visualized using

ultrasound imaging

13.

14.

15.

16.

17.

25

The best therapy to prevent recurrence ofgallstones is:

A. laparoscopic cholecyst=tomyB. dissolution therapy with

chenodwxycholic acid

c. shock-wavelithotripsyD. gallbladderejection treatment

The major disadvantageof Tc-99mpyridoxylideneglutamateprepared by theautoclavemethod was:

A. gastrointestinalabsorptionofradiochernicalimpurities

B. very slow blood cl~rancec. high degree of urinary excretion

D. in vitro instability

Which of the following statements best describesstructure-activity relationship (SAR) analysis?

A. SAR analysis is a method to reduce thenumber of related analogs that must besynthesized and testd

B. SAR analysis makes it possibl~ to

identify new chemical compoundsdesird biological activity

c. All SAR methods rquire bothphysiochemical md biologicalmeasurements

with

D. Lipophiiicity measurements usd in SARanalysis are usually perfomed in anacetronitrile: water system

In the preparation of Tc-99m dimethyl-IDA,

A.

B.c.D.

For the

the final complex is a Tc-Sn-bis-complex with dimethyl-IDAthe oxidation state of technetium is +4the overall charge of the complex is -1the molecular weight of the complex isless than 600

preparation of Tc-99m IDAradiopharmaceuticals,

A. kits are availabIe that utili= eitherstannous ion or electrolysis for reductionof pertechnetate

B. the shelf-life following addition of Tc-99m pertechnetate is 18 hours

c. the agent is ready to use as soon as allsolids are completely dissolved

D. the usual amount of Tc-99m to add is

100 mCi or less

18. Clinical studiw with commercial Tc-99m IDAradiopharrnaceuticals available in the U.S. haveshown that

A. increased serum bilirubin levels result inincrti renal excretion for all agents

B. there is no significant change in bloodclearance rak with increasd bilirubinlevels

c. of the firm agents, Tc-99m disofeninhas the fastest liver transit kinetics

D. in normals, the gallbladder cm usuallynot be visuali~ until 45-60 minutesafter injection

19. Which of the following statements related todrug effats on hepatobiliary kinetics is me?

A. Nicotinic acid in large doses prolongsgallbladder contraction

B. Phenobarbital is used to spd up livertrmsit of hepatobiliary agents in patientswith poor liver function

c. After administration of morphine,emptying of bile into the gastrointestinaltract is delayed

D. Morphine administration reduces thepressure within the gallbladder

20. In augmented hepatobiliary imaging studies withcholecystokinetic agents,

A. a normal gallbladder should eject atleast 75% of its content following an

iv. dose of 0.02 mg/kg of sincalideB. viscous bile can be ejected from the

gallbladder prior to scintigraphy tofacilitate gallbladder filling withradiotracer

c. gallbladder emptying initiated by a fattymeal is not a reproducible technique

D. a gallbladder ejation fraction study isperformed by injwtion of radiotracer

15-30 minutes following sincalideinfusion

21. Which of the following statements pertaining togallbladder filling and emptying is we?

A. Partial gallbladder emptying takes placeperiodically during the tilling phase

B. Delayd gallbladder filling may beassociated with alcohol ic liver disease

c. Gallbladder emptying cannot be inducedby a fatty mal unless the gallbladdercontains at least 50 ml of bile

D. The cystic duct syndrome is associatedwith impaired gallbladder emptying

22. Nonvisualization of a normal gallbladder withcholescintigraphy is ~t a result ofi

A. pain management using morphineB. fasting in excess of 24 hoursc, fatty meal taken one hour prior to

study

D. total parenteral nutrition therapy

●the

23. Which of the following statements related to

bilia~ tract dim is we?

A. Cholescintigraphy is a highly sensitivetest for evaluation of cystic ductobstruction

B. Prolonged cystic duct obstruction leadsto biliary duct inflammation andnecrosis

c. Cholecystectomy is never indicati inpatients with non-calculous gallbladderdisease

D. Non-visualization of the gallbladder isnot highly spwific for acute chnlecystitis

24. In n~natal jaundice,

A. the gallbladder is usually visurdi~ byfour hours on cholescintigraphy

B. a dose of phenobarbital should be given30-60 minutes prior to cholescintigraphy

c. evidence of Tc-99m disofenin in the o

bowel at four hours excludes biliary

atresia

D. cauti by hepatitis, the underlying

disease process is usually a vimsinfection

25. Which of the following statements related tohepatic extraction fraction (HEF) studies is ~e?

A. Deconvolution analysis is used tocorrect liver uptake for bloodbackground activity

B. The blood time-activity curve is

obtained from a region of interest overthe hepatic artery

c. HEF provides a quantihtive measure ofhepatic binding prohin receptor affinity

D. Corr~tion for kidney activity is done byobtaining images in the lateral pro] mtion

26