PRINCIPLES & PRINCIPLES & APPLICATIONS OF PET - APPLICATIONS OF PET -

CT and PET - MRCT and PET - MRPRESENTATION BY-

CHARUSMITA CHAUDHARY

Moderator: Prof. (HOD) R .K. GOGOI

INTRODUCTIONINTRODUCTIONCancer is one of leading causes of morbidity and mortality in

developed countries.

Most radiologic procedures map the anatomy and morphology of

tumors with little or no information about their metabolism

Positron emission tomography (PET) is a coalition of physics,

chemistry, physiology, and medicine united in an effort to measure

physiologic parameters noninvasively.

Positron Emission Tomography and Computed Tomography / MRI

is the combination of functional imaging as well as anatomical

imaging.

HistoryHistory

1978 the first commercial PET scanner was introduced

70s and 80s PET was mainly used for research

1990s being used in clinics regularly

First approval in 1998.

PRINCIPLE OF PETPRINCIPLE OF PET The concept of PET is to radiolabel a bio-compound, inject it into the patient, and

then measure its bio-distribution as a function of time to determine physiologic

quantities associated with the biocompound.

All PET compounds are radiolabeled with positron-emitting radionuclides.

These radionuclides have decay characteristics that enable localization in the

body.

A positron is emitted from the nucleus, travels a short distance, and annihilates

with its antiparticle (an electron), which results in two 5 I l-keV photons traveling

in opposite directions.

After both photons are detected, the activity is localized somewhere along the line

defined by the two detectors.

2-[F-18]Fluoro-2-Deoxy-D-Glucose (FDG)

OH

O

OH

HO

F

H

H

H

HH

CH2OH

511 keV photon

511 keV photon

E = mc2

180o

+ -

UCLA

producing radiotracers

Synthesizing radiopharmaceuticals from the tracers

administering the radiopharmaceutical to a patient

measuring the resulting radioactivity distribution in an organ of interest

interpreting activity distribution as a function of physiologic parameters.

A PET study consists of

PRODUCTION OF RADIONUCLIDEPRODUCTION OF RADIONUCLIDE

PET radionuclides are positron emitters.

There are 5 convenient nuclides-

HALF LIFE (min)

Rubidium- 82 1.23

Fluorine – 18 109

Oxygen- 15 2

Nitrogen- 13 10

Carbon- 11 20

Commonly produced isotopes : “F O N C”

SYNTHESIS OF F-18 &FDGSYNTHESIS OF F-18 &FDG

Over 500 PET compounds have been

synthesized since 1970.

Natural substrates such as amino acids,

analogues ,fluorinated glucose &drugs.

MC used is a glucose analogue, 2-[F18]fluoro-

2-deoxy-D-glucose (FDG).

Why is 18 F the most used positron emitter?

18F is a small atom.

its addition to a molecule does not deform it to the point

where it is not recognized by the body anymor

has a half-life of 109 minutes.

This is long enough to perform a complicated chemistry

(labelling) , and to allow transport over some distance.

It is also long enough to keep the radiation burden to patient

low

USES

Fluorodeoxyglucose

[18F]-labeled 2-deoxyglucose (FDG) is used in neurology,

cardiology and oncology to study glucose metabolism. FDG is

potentially useful in differentiating benign from malignant forms of

lesions because of the high metabolic activity of many types of

aggressive tumors.

Oxygen

[15O]-labeled water is used to evaluate myocardial oxygen

consumption and oxygen extraction fraction. It can also be used to

measure tumor necrosis.

Ammonia[13N]-labeled ammonia can be used to measure blood flow.

Leucine[11C]-labeled methionine and leucine can be used to evaluate amino acid uptake and protein synthesis, providing an indicator of tumor viability.

Fluorine IonRadiolabeled fluorine ion [18F-] was once a standard agent for clinical bone scanning.

A typical production schedule for FDG is 3hours in duration,

starting from the time the chemist walks into the laboratory

until the radiochemical is produced.

The synthesis is 50%-60% efficient, so accounting for this and

the radioactive decay, about 200 mCi (7.4 GBq) of FDG is

available at the end of the synthesis.

A patient usually receives A patient usually receives 10 mCi (370 MBq).

If two scanners are available so that a patient can receive an injection If two scanners are available so that a patient can receive an injection

every half hour, every half hour, one production run will allow scanning about run will allow scanning about six

patients per day. .

  

Principle of metabolic imaging with FDG

Glucose 18 FDG Blood vessel

Cell

Glucose 6 Phosphate 18FDG 6 Phosphate

Fructose 6 Phosphate

Pyruvate

Anaerobic resp Citric acid cycle

G LUT

SCANNER DESIGNSCANNER DESIGN

A positron emission tomography (PET) scanner is a large machine with a round, doughnut shaped hole in the middle

Within this machine are multiple rings of detectors that record the emission of energy from the radiotracer in your body.

A nearby computer aids in creating the images from the data obtained by the camera or scanner.

SCANNER DESIGN….SCANNER DESIGN….

Detectors are 18-40 rings of crystals forming a cylindrical field of view about 15cm long that can acquire many slices of coincidence data

PET scanners use crystals with higher density & higher Z numbers due to sensitivity

Group of crystals is put together into a block Four PMT’s to each block of crystalUse “electronic collimation” to detect location of

annihilation event

SCANNER DESIGN….SCANNER DESIGN….

Localizing the site of impact is achieved by measuring the light detected in each PMT

Signal is then amplified System must be able to determine which signals

come from paired 511keV photons and record the time of detection (timing discriminator)

Coincidence circuit then examines signals to confirm it if it occurred with in the time window

CRYSTALS USED IN PETCRYSTALS USED IN PET

BaFBaF22 – Barium

Flouride(0.8ns)BGO BGO – Bismuth Germinate

Oxide(300ns)LSOLSO – Lutetium

Orthosilicate(40ns)GSOGSO – Gadolineum

Orthosilicate(60ns) YLSO YLSO – Yttrium Lutetium

Orthosilicate(40ns)

COINCIDENCE DETECTIONCOINCIDENCE DETECTION

Photons should arrive with in a certain time of one another

A coincidence timing window allows detection of the PMT electrical signal from photon pair (4-12ns)

If it falls within timing window it is registered as a true event

When two different annihilation events are detected with in the timing window is known as “random event”

DATA ACQUSITIONDATA ACQUSITIONThe detection of photon pairs by opposing crystals

create one event (LOR)Millions of these event will be stored with in

sinograms and used to reconstruct the image Spatial resolution is determined by the size of

crystal and their separation and is typically 3-5mmPET is 50-100 times more sensitive and produces

higher quality than a SPECTReconstruction is similar to SPECT

RECONSTRUCTIONRECONSTRUCTIONPET reconstruction can be performed with a

variety of algorithms

o Filtered back projection

o Iterative reconstruction(ordered subset reconstruction )

ATTENUATION CORRECTIONATTENUATION CORRECTION

Mathematical attenuation correction techniques may be used if tissue attenuation is the same at all areas within a transaxial slice .

Measured attenuation may be performed by two methods:– Transmission scan using a radioactive source rotating it

around the patient – CT scan to measure tissue density

The ability to correct for attenuation improves quality and permits absolute quantification of radioactivity in the body

Resolution in PET is determined by three factors:

distance the positron travels before it annihilates with an electron,

variation in angle between the two annihilation photons, and

physical size of the detectors.

A positron will travel between 0.5 and 2 mm in tissue before annihilation, depending on its energy.

Typical detector sizes are 1 -3 mm.

The best possible resolution of a PET scanner is 1-2mm. Typical clinical scanners have a resolution of approximately 4-7 mm.

PET vs. CT & MRIPET vs. CT & MRIPET CT and MRI

Shows extent of diseaseDetects changes in body structure

Can help in monitoring treatment and shows it’s effectiveness

Simply confirms the presence of a mass

Reveals disease earlier, can diagnose faster

Can detect whether a mass is benign of malignant

Can detect abnomalities before there is an anatomical change

SAFETY ASPECTS OF PETSAFETY ASPECTS OF PET PET has 511Kev gamma rays energy, that is 3 times of

140Kev gamma ray energy of Technitium99m Due to their high energy 16 times more lead is required to

obtain the same stopping effect for 511Kev photons as compared to 140Kev photons

SAFETY ASPECTS OF PETSAFETY ASPECTS OF PET

So Tungsten shielding is used for Positron emitting radionuclide. It provides 1.4 times the shielding capability for the same thickness of Lead

CONTRA INDICATIONSCONTRA INDICATIONS

Pregnancy Use of caffeine, tobacco, or alcohol in past 24hours before scanUsing sedativesUsing medicines that change metabolism ex: INSULIN.

PRINCIPLE OF PET-CTPRINCIPLE OF PET-CT

PET-CT FUSIONPET-CT FUSION

FDG PET is a strictly functional modality and lacks anatomic landmarks.

Unless anatomic correlation is available to delineate normal structures,

pathologic sites of FDG accumulation can easily be confused with normal

physiologic uptake, leading to false-positive or false-negative findings.

Coregistration of PET scans with CT using a combined PET-CT scanner

improves the overall sensitivity and specificity of information provided by

PET or CT alone .

advantage is ability to correlate findings at two complementary imaging

modalities in a comprehensive examination. Hence, PET-CT provides more

precise anatomic definition for both the physiologic and pathologic

uptake seen at FDG PET

Max coverage during combined study

Distance betwn pet and ct scanner

SCANNING TECHNIQUESCANNING TECHNIQUE

Nil orally for approximately 4–6 hours avoid caffeinated or alcoholic beverages but can have water during this period.blood glucose level of less than 150 mg/dL is desirable. Avoid strenuous activity to avoid physiologic muscle uptake of FDG water-soluble iodinated contrast media orally for bowel opacification except for head and neck study. 10 mCi injected intravenously Patient activity and speech are limited for 20 minutes immediately following injection Pet study is started 60 mins after injection.

CT TECHNIQUE

Contrast material–enhanced helical CT is performed following injection of

125 mL of a contrast medium at a rate of 4 mL/sec by using a power

injector .

Whole-body PET-CT study scanning begins at the level of the skull base

and extends caudally to the level of the symphysis pubis.

PET TECHNIQUE

The PET scanner is located behind the CT scanner and housed in the same

extended-length gantry. PET is performed following the CT study without

moving the patient in the caudocranial direction, starting at the thighs to

limit artifacts from the FDG metabolite excretion into the urinary system

Typical scout image obtained during an FDG PET-CT study. The blue-purple rectangle

represents CT coverage during the study, and each overlapping green rectangle

represents PET coverage.

INTERPRETATION OF IMAGESINTERPRETATION OF IMAGES

PET provides images of quantitative uptake of the

radionuclide injected that can give the concentration of

radiotracer activity in kilobecquerels per milliliter .

Methods for assessment of radiotracer uptake –

• visual inspection

• standardized uptake value (SUV)

• glucose metabolic rate

LIMITATIONS AND ARTIFACTS OF PET-CTLIMITATIONS AND ARTIFACTS OF PET-CT 1.Patient motion may cause confusion as to the correct position of the

origin of the detected photon.

Patient motion is minimized by – carefully instructing patients not to move during the study; placing them in a comfortable position before the start of the

study; ensuring that they are not taking diuretics, which may otherwise

require them to evacuate the bladder during the study; having patients empty their bladder before the start of the study

or catheterizing the bladder.

2.Attenuation (transmission) correction artifacts highly attenuating objects in the path of the CT beam, such as hip prostheses, pacemakers, dental devices, and contrast-enhanced vessels

ADVANTAGES OF PET-CTADVANTAGES OF PET-CT1. helpful in accurate localization of small areas of increased radiotracer

activity that would have been difficult or not possible to localize on

PET images alone .

2. helps in distinguishing structures that normally show high metabolic

activity from those with abnormally increased activity.

3. PET-CT combines the advantages of the excellent functional

information provided by PET and the superb spatial and contrast

resolution of CT

4. Finally, attenuation correction for quantitative or semi quantitative

assessment of data is possible by using the CT data,

Whole-body PET/MRIWhole-body PET/MRI::The Future in Oncological The Future in Oncological

ImagingImaging

PET/MRIPET/MRI: TECHNICAL EVOLUTION: TECHNICAL EVOLUTION

The idea to combine PET and MRI arose as early as the mid 1990s, even before PET/CT was introduced.

The PET/MRI combination requires 3 risky technologic steps that modify state-of-the-art PET and MRI. 1. First, the photomultiplier technology must be replaced with magnetic

field–insensitive photodiodes .

2. Second, compact PET detectors must be constructed so that it shouldn't interfere with the field gradients or MR radiofrequency.

3. Finally, the MRI scanner must be adapted to accommodate the PET detectors and to allow simultaneous data acquisition without mutual interference.

Based on the technologic challenges to combine PET and MRI into a single gantry, Philips and Siemens proposed 2 fundamentally different prototype PET/MRI designs.

In the Siemens prototypes include 4 dedicated brain PET scanners that fit into a standard 3-T clinical MRI scanner.

The PET/MRI system, together with a dedicated radiofrequency head coil, allows simultaneous PET/MRI data acquisition of the human

brain or body extremities. Philips developed a PET/MRI design in which the gantries are

approximately 2.5 m apart but share a common patient handling system. This implementation does not allow for simultaneous data acquisition and, therefore, results in longer examination times.

Scanner DesignScanner Design

CLINICAL POTENTIAL OF PET/MRICLINICAL POTENTIAL OF PET/MRI It is reasonable to expect that brain PET/MRI will provide new

insights in the field of neuroscience and neurologic disorders, such as neuro degeneration, brain ischemia, neuro oncologyor seizures .

It is feasible with current prototypes and future-generation systems to simultaneously study brain function, metabolism, oxygen consumption, and perfusion.

In oncology, an accurate spatial match between PET and MRI data is mandatory for both radiation therapy planning and biopsy guidance.

Combining PET with cardiac MRI may enable detection and differentiation of vulnerable plaques and diseased myocardium.

Advantage of PET/MRI over PET/CT

1. is not associated with significant radiation exposure

2. has a much higher soft tissue contrast.

3. MRI allows for additional techniques - such as angiography, functional MRI ,diffusion ,spectroscopy and perfusion techniques within one single examination.

PHYSIOLOGIC VERSES PATHOLOGIC FDG UPTAKE PHYSIOLOGIC VERSES PATHOLOGIC FDG UPTAKE of FDGof FDG

There are several sites of normal physiologic accumulation of FDG. FDG

accumulation is most intense in the cerebral cortex, basal ganglia,

thalamus, and cerebellum. The myocardium expresses insulin-sensitive

glucose transporters, which facilitate the transport of glucose into muscle. A

recent meal often causes intense myocardial FDG uptake because of the

associated elevated serum insulin levels

Because FDG appears in the glomerular filtrate and, unlike glucose, is not

reabsorbed in the tubules, intense FDG activity is seen in the intrarenal

collecting systems, ureters, and bladder

The most common areas of normal distribution of FDG

include the brain, myocardium, and genitourinary tract.

SEMI QUANTITATIVE VALUE- CALCULATION OF INTENSITY OF FDG UPTAKE IN REGION OF INTERST.

SUV-5 Indicates five times the average uptake.

RISUV - new index, Retention Index SUV after 3 hours.

STANDARDISED UPTAKE VALUE

Physiologic FDG uptake

The distribution of FDGwithin a normal individual (MIP).

Chest

•Moderate to high FDG uptake is noted in patients with thymic

rebound and should not be confused with asymmetric uptake due

to lymphoma in this location .

•In pediatric patients, anatomic correlation is necessary following

chemotherapy to differentiate the enlarged thymus from residual or

recurrent disease at this location, especially with focal thymic

uptake .

Physiologic thymic uptake in a 23-year-old woman with a

history of Hodgkin disease of the chest who was referred for

posttherapy evaluation.

Low to moderate FDG uptake is noted in the distal esophagus,

particularly in patients with gastroesophageal reflux secondary to

inflammatory changes.

However, high-grade uptake in the same location may be caused

by malignant processes (ie, carcinoma of the distal esophagus,

usually associated with morphologic esophageal changes)

Nonneoplastic esophageal uptake in a 21-year-old woman with a

history of non-Hodgkin lymphoma

Esophageal adenocarcinoma in a 52-year-old man who was

referred for presurgical evaluation.

THE ROLE OF PET/CT IN LUNG CANCER

Assessment of the solitary pulmonary nodule (SPN)

Staging of non-small cell lung cancer (NSCLC)

Assessment of mediastinal lymphadenopathy

Identification of distant metastatic disease

Detection of recurrent disease

Solitary pulmonary noduleSolitary pulmonary nodule

? Benign or malignant

No activity. Diagnosis: benign bronchocoele

Top TipApproximately 85% of metabolically active pulmonarynodules are malignant. If an FDG positive pulmonarynodule is found, it should be assumed to be malignant untilproved otherwise.

Bilateral pulmonary nodules. Diagnosis: metabolicallyactive pulmonary sarcoidosis.

False positive SPN False negative SPN

1.Granulomas BAC

2.Sarcoidosis Scar adenoca

3.Infection carcinoids

4.Adenomas

5.Hamartomas

6.Neurofibromas

Top TipWithout the aid of PET/CT it can be difficult to distinguishactive tumor from collapsed lung or necrotic tissue.

Identification of distant metastatic disease

Top TipEvidence suggests that the removal of a solitary adrenaldeposit at the time of resection of the lung primary results in an increased life expectancy.Liver, adrenal, brain and bony deposits are common withlung cancer but many of the lesions are undetected inthe course of conventional staging

PET/CT IN RADIOTHERAPY PLANNING

Patient for radiotherapy. Where does the tumor end and thecollapsed lung begin ?

The Role of PET/CT in Lymphoma Assess response to therapy/residual disease Identify recurrent disease Initial diagnosis and staging Identify suitable sites for biopsy Disease surveillance Radiotherapy planning

An example of stage 4disease. NHL with disease in the mediastinum,neck, and abdomen

ASSESSMENT OF TREATMENT RESPONSE

Pretherapy and post therapystudies showing a complete metabolicresponse to therapy.

Top Tip

Brown fat activation can cause confusion and care mustbe taken to ensure that each area of uptake corresponds to fat. Activated brown fat is seen more commonly in thin individuals during the winter months, but there is also an increased incidence in women and in patients suffering from lymphoma

Intense marrow activationfollowing granulocyte stimulating factor.

Head and Neck

Moderate to high FDG uptake is noticeable in the muscles,

including the ocular muscles.

may be a potential source of false-positive findings in patients

with malignant head and neck tumors.

Contraction-induced FDG uptake in cervical muscles in tense

patients can be confused with lymph node metastasis which

constitutes a serious problem in patients with

asymmetric muscle uptake due to prior neck

dissection.

FDG accumulates in the striated laryngeal muscles in

proportion to contractile activity during speech.

This phenomenon is a major concern and may lead to false

readings in patients with head and neck cancers .

Rigorous approach to preventing physiologic FDG uptake in

the laryngeal muscles should be adopted to avoid false-positive

findings.

 Physiologic laryngeal uptake in a 52-year-old woman

with squamous cell carcinoma of the floor of the mouth.

 

 Primary tumor of the larynx in a 45-year-old man with epiglottic

carcinoma who was referred for presurgical evaluation.

NEUROLOGY INDICATIONSNEUROLOGY INDICATIONS

NEURO-ONCOLOGYTumor recurrence versus radiation necrosisDiagnosisGrading

Monitoring response to therapy Radiotherapy planning Biopsy planningSEIZURE FOCUS IDENTIFICATIONSTROKEDEMENTIAS OTHER APPLICATIONS

Brain injury- vascular, traumaPsychiatry- depression, schizophrenia,anxietyMovement disorders with 18F-dopaMiscellaneous- infection, substance abuse,eating disorders

rerelymphoma

Residual glioma

rt parietal gbm

LOSS OF VISION BOWEL & BLADDER INCONTINENCESINCE I MONTH

BUTTERFLY GLIOMA

High precision Radiation therapy Planning

PETPET

CTCT

PET/CTPET/CT

Biopsy Planning

Localizing

the most

viable tissue

in the lesion

Comparison of MRI time-to-peak (TTP) and PET O2 extraction fraction (OEF) images

Extensive hypo metabolism of entire brain parenchyma, except thalami & basal ganglia

METABOLIC ENCEPHALOPATHY

PET in NeurologyPET in Neurology

The Active Human BrainThe Active Human Brain

PET in Brain DisordersPET in Brain Disorders

Simultaneous PET/MRI study in Alzheimer disease

Hypo metabolism in left temporal lobe secondary to epilepsy

Abdomen and Pelvis

Moderate to high FDG uptake is visible in the muscles that contribute to breathing in patients with chronic obstructive pulmonary disease.

due to difficulty in breathing and use of accessory muscles to facilitate

breathing. In addition, due to an imbalance between oxygen supply and increased demand,

the decrease in oxygen delivery causes a switch to anaerobic metabolism. Hence, the increased uptake seen in the diaphragmatic cruces may be the result

of accentuated abdominal breathing effort and the anaerobic metabolism that leads to increased FDG uptake similar to the physiologic alterations in cancer cells.

Any disease process involving the celiac or perigastric lymph nodes (eg, lymphoma, nodal metastatic disease) can be difficult to interpret in patients with diaphragmatic uptake, especially in the posttherapy setting.

 

Physiologic diaphragmatic uptake in a 49-year-old woman with a

history of abdominal lymphoma and severe COPD who was

referred for posttherapy follow-up.

Low to moderate uptake is usually observed in

the stomach.

Focal and irregular uptake in the stomach is

usually due to a malignant process;

nevertheless, local gastritis cannot be excluded

with certainty without the help of CT.

Physiologic gastric uptake in a 52-year-old man with colorectal

cancer who had undergone surgical tumor resection.

Gastric cancer in a 59-year-old woman

The importance of FDG PET in the evaluation of colorectal cancer is well

established.

Both small and large bowel may demonstrate varying degrees of FDG

uptake, usually with a diffuse and linear pattern.

However, focal physiologic uptake is not an uncommon finding in short

segments of the bowel.

Unless CT correlation is available, the configuration of uptake in these cases

may be indistinguishable from malignant processes .

Adenocarcinoma of the cecum in a 77-year-old man.

Gallbladder uptake of FDG is not a common finding.

When activity is observed in this anatomic location,

choleductal cancer, adenocarcinoma of the gallbladder,

and primary or metastatic disease of the liver should be

considered in the differential diagnosis.

CT correlation is most helpful in delineating anatomic

landmarks and distinguishing a benign gallbladder

variant from malignant lesions.

Chronic cholecystitis in a patient with papillary thyroid

cancer who underwent thyroidectomy

Liver metastasis in a 55-year-old man with rectal adenocarcinoma.

Unlike glucose, FDG is not reabsorbed by the renal tubules

after filtration.

Thus, significant FDG accumulation is seen in the intrarenal

collecting system and renal pelvis.

This accumulation may interfere with the identification of

renal parenchymal or pelvic urothelial tumors.

However, anatomic information provided by CT allows proper

assessment and characterization of renal masses

 Renal cell carcinoma in a 60-year-old woman

Focal FDG accumulation in the ureters is a

common finding due to the pooling of radiotracer

in the recumbent patient.

although the intensity and location of uptake

usually allow accurate identification of the ureters

in patients with abdominal malignancies, this

finding can be misdiagnosed as pelvic lymph

node metastasis or nodal lymphoma.

Physiologic uptake in the renal pelvis in a 66-year-old man

with a history of colorectal cancer .

There is usually no FDG accumulation in the uterus, although focal

FDG uptake in the uterus during menstruation has been described.

can be attributed to heavy bleeding or to necrotic endometrial

epithelium due to sudden reduction of estrogen and progesterone

levels at the end of the secretory phase of the menstrual cycle.

It may not be possible to differentiate this uptake pattern from uterine

carcinoma, even with the help of PET-CT .

However, FDG uptake is usually more irregular, diffuse, and

extensive in uterine cancer . 

Physiologic uterine uptake in a 40-year-old woman with a

history of lymphoma who was referred for posttherapy

evaluation.

Endometrial cancer in a 66-year-old woman.

Cardiac PET and Cardiac PET and Myocardial perfusion ImagingMyocardial perfusion Imaging

Rb Distributed in the myocardium depending on the regional blood flow

Rb delivery limited to ischemic or underperfused areas

These areas will appear as defect on initial images

On delayed images(2-4hrs) post inj

Defects resolves due to redistribution which reflects not only eventual accumulation of Rb in viable ischemic zones but release & washout from

normally perfused area

(Areas of myocardial infarction or fibrosis present as permanent defects due to lack of perfusion)

CARDIAC PET and PET CT IMAGING

The stress images show a severe perfusion defectthroughout the anterolateral wall that is completely reversible at rest

The first heart has a mycardial infarction. The arrows point to damaged areas (‘dead’ tissue).Therefore it is assumed that the patient will not benefit from heart surgery.

The second heart is normal

Example: Myocardial Viability

                                                                    

PET IN INFLAMMATORY CONDITIONS

Hepatic and splenic uptake of FDG are generally low grade and diffuse

In the setting of infection, splenic uptake can be intense.

Acquired Immuno-deficiency Syndrome.

Till now, gallium imaging radionuclide imaging - study of choice in evaluating opportunistic infections in AIDS patients.

FDG – PET – helpful in many CNS conditions in AIDS patients.

Lymphoma and toxoplasmosis are frequent CNS complications – not always distinguishable at CT and MRI.

CNS LYMPHOMA- Highly metabolically active.

TOXOPLASMOSIS- metabolically inactive.

FDG PET of Infection and Inflammation1

Toxoplasmosis in an AIDS patient

Acquired Immuno-deficiency Syndrome

CNS lymphoma in a different AIDS patientCNS lymphoma in a different AIDS patient

Acquired Immuno-deficiency Syndrome

2. Fever of unknown origin.

FDG PET- LT PL EFF: HYPERMETABOLIC FOCUS SUB PLEURAL AREA.

CTPA- LEFT LOWER LOBE PULMONARY EMBOLI, WEDGE SHAPED PULMONARY INFARCT.

FINAL DIAGNOSIS- PULMONARY EMBOLISM C INFARCTION.

3.OSTEOMYELITIS

Increased metabolic activity in inflammation results in increased FDG uptake.

Also occur ina. inflammatory arthritisb. acute fractures,c. normally healing bone after surgery.

Differentiation between inflammatory and malignant lesions.

Traditionally, a single time point SUV of 2.0–3.0 has been proposed as the optimal threshold for separating malignant from benign lesions.

With the exception of granulomatous lesions- malignant lesions shows increased SUV values on delayed images i.e., increased RI SUV ( RETENTION INDEX SUV ).

DUAL TIME FDG PET imaging at two intervals appears promising now. Lesions with decreased SUV s over time are likely to have a benign etiology. Malignant lesions tend to have increase in SUV over time.

PET vs. SPECTPET vs. SPECT

PET have superior sensitivity and resolution

Greater flexibility of incorporating positron labels into biomolecules

PET is more expensive and requires the presence of an onsite cyclotron

PEM PEM Positron Emission Mammography PEM is a specialized & improved

form of PET for imaging breasts and other small body parts.

Camera and detectors are closer to the area affected with cancer which produces a very sharp detailed image of tumors and cancerous tissue.

Can see cancers as small as 1.5 – 2mm about the width of a grain of rice.

Also allows for the earlier detection of elusive cancers such as DCIS (ductal carcinoma in situ).

PEMPEM

Breast PET MRI Breast PET MRI

Schematic diag of pet insert and mri coil

Understand the differences between whole-body PET and PEM

Spatial Resolution

better spatial resolution (1-2 mm vs. 5-10 mm). This comes at the cost of field-of-view

Photon-Detection Sensitivity •Closer proximity of PEM detectors increases geometric

sensitivity Allows lower dose/faster imaging/longer uptake time

differences between mammography and PEM Transmission vs. Emission Imaging Anatomical vs. Functional Imaging Planar vs. Tomosynthesis (or Tomographic) •Planar is single projection view with considerable tissue

overlap •Tomosynth./tomographic is 3-dimensional volumetric image Utilities, cost, dose

CONCLUSIONCONCLUSIONDetection of coincidence photons emitted during positron annihilation is the key to

PET imaging, whereas accurate coregistration of this quantitative/functional

information with the CT data is the key to successful PET-CT imaging.

Specific attention to patient preparation, data acquisition, data reconstruction, and

image interpretation is crucial to obtaining high-quality PET-CT images.

Fusion of the anatomic and functional images by using a dedicated PET-CT /Pet

mri scanner is exploited for optimal results required in the management of complex

clinical scenarios faced by our clinical colleagues. Having witnessed an impressive

technologic development of PET detector technology, first PET/MRI prototype

systems, and MRI-based PET attenuation correction, as well as encouraging clinical

and specifically preclinical PET/MRI results, we now seek opportunities to translate

these technologic advances into clinical benefits

CT/PET/MRI-Anatomical + Functional imaging.

18F-FDG-Increase glucose utilisation in malignancies.

Oncology,Neurology ,CardiologyDiagnosis.Staging.Restaging.Monitoring response to therapy.Guided biopsy.Radiotherapy planning

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