Hepatic Doppler

• Doppler principles The shift in sound frequency is

proportional to the speed of flowing blood: f = 2fi

v cos Practical implications of the principle:

faster flow (v) results in bigger Doppler shift higher incident frequency (fi) results in bigger

Doppler shift smaller angle of insonation (cos) results in

bigger Doppler shift

Hepatic Doppler• Align the ultrasound

beam in the direction of flow (small angle) Shallow angle

results in bigger Doppler shift

Shallow angle minimizes errors introduced by inaccurate angle correction

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Hepatic Doppler

• Technologist controlled variables Machine settings:

power output transducer frequency system gain sample volume (gate size) angle assignment pulse repetition frequency (velocity scale) display size sweep speed wall filter

Hepatic Doppler

• Technologist controlled variables Transducer frequency

Select for best gray scale image 3.5 curved is the workhorse for the liver When imaging superficial structures (left portal

vein, recanalized umbilical vein, hepatic capsule) use higher frequency and linear transducers

2.5 sector may provide best fit in small window Use a lower frequency transducer for high

velocity flow in a deep vessel (avoids aliasing)

Hepatic Doppler

• Technologist controlled variables System gain

Gray scale and Doppler gain are set independently

Gain used to amplify weak signal (don’t use gain to compensate for inappropriate transducer selection, wall filter, or PRF)

When performing Doppler, narrow the imaging window to permit identification of the vessel, but eliminate extraneous noise

Hepatic Doppler

• Technologist controlled variables Sample volume

Enlarge sample volume when searching for flow in small or obstructed vessels and in main portal vein

Sample volume should be kept as small as reasonably possible when recording Doppler signal to minimize extraneous signals from adjacent tissue and vessels

Use color Doppler to assist sample volume position in flow stream (center of the vessel in most cases)

Listen to the Doppler signal to assist in sample volume placement

Hepatic Doppler

• Technologist controlled variables Angle assignment

May be performed during acquisition or on frozen/stored image

Angle correction aligned parallel to vessel walls in most cases

Angle correction oriented to the direction of flow (color may assist in demonstrating flow direction in a curving or stenotic vessel)

Hepatic Doppler

• Technologist controlled variables Pulse repetition frequency (PRF)

“velocity scale” PRF controls how frequently the machine sends a

Doppler pulse Aliasing occurs if the Doppler frequency shift is

more than twice of the sampling rate (PRF) The PRF and baseline should both be adjusted so

the spectral signal (unidirectional or bidirectional) occupies 2/3 of the window

Adjust color baseline to avoid (or exaggerate) aliasing

Hepatic Doppler

• Technologist controlled variables Display size

Gray scale images should be enlarged or magnified (zoomed) so the region (vessel) of interest occupies half the image

Gray scale and spectral Doppler windows should each occupy half of the monitor display

Hepatic Doppler

• Technologist controlled variables Sweep speed

Use slow sweep speed to demonstrate pulsatility of flow (e.g. cardiac or respiratory pulsatility)

Use fast sweep speed for measurements (acceleration time, peak systolic, diastolic, RI, PI, etc.)

Hepatic Doppler

• Technologist controlled variables Wall filter

Used to eliminate low frequency vibrations of the vessel wall and solid tissue around vessels

Typical preset 25 kHz (optional 25-150 kHz) Set as low as possible to permit identification of

low velocity flow

Hepatic Doppler

• Doppler Options Continuous wave Pulsed (spectral) Duplex Color Triplex imaging Power (amplitude)

Hepatic Doppler

• Pulsed Doppler Machine sends pulses of sound energy at

intervals to allow sound to travel to the sample gate and return to the transducer before sending the next signal

Returning signal is analyzed (FFT) to separate the different frequencies (velocities) of flowing blood

The sample is displayed on the monitor to demonstrate the range of velocities and their change over time

Hepatic Doppler

• Doppler spectrum Time is displayed on the X

axis; Doppler frequency on Y

Blood flow towards the transducer is conventionally displayed as an upwards deflection

At any moment in time, the entire range of RBC velocities within the sample volume is displayed in the spectrum

Pulsatility Index = S-D/mean

Resistive Index = S-D/S

Hepatic Doppler

• Duplex Doppler Combines grey scale image with

pulsed Doppler in “real time” (time sharing)

Machine acquires a grey scale image, stores it, then acquires a pulsed Doppler signal and displays it

Machine can prioritize grey scale or Doppler acquisitions

Hepatic Doppler

• Optimize the duplex exam Narrow the grey scale image to only include

structures necessary to identify the anatomy For deep vessels with high velocity, decrease

transducer frequency to minimize aliasing Decrease frame averaging (persistence) to

minimize aliasing; increase frame averaging for slow flow

Lower wall filter for low flow states (veins) Listen to the Doppler signal for optimal gate

placement

Hepatic Doppler

• Color Doppler A “duplex” examination of flow in a large area Because multiple vessels imaged simultaneously,

Doppler shifts are displayed in color, not spectra Displays flow direction by color (e.g. red and blue)

and flow velocity by color saturation Doppler sampling of large area slows the frame

rate and maximal pulse repetition frequency (velocity)

Gray scale image is frozen (or periodic refresh) during color/spectral Doppler acquisition

Hepatic Doppler

• Optimize the color exam Attempt to image from a position that aligns the

ultrasound beam in the direction of flow of the vessel of interest

Adjust focal zone to the level of primary interest Adjust color sample volume so that vessel(s) of

interest occupies 1/2 of box Adjust PRF and baseline to fill vessel lumen (slow

flow along walls) without aliasing

Hepatic Doppler

• Hepatic Blood Supply

Portal vein 75% of blood flow to the

liver Deoxygenated but

nutrient rich Hepatic artery

25% of blood flow to the liver

Oxygenated Sole source of flow to

bile ducts

Hepatic Doppler

• Hepatic Sinusoids Functional unit of liver

Parallel columns of hepatocytes surrounded by portal triads

Portal triads include branches of the portal vein, hepatic artery, bile ducts

Portal venous and hepatic arterial blood mixes in sinusoids and drains into central vein

Hepatic Doppler

• Hepatic venous drainage Central veins empty

into hepatic veins Right, middle, left No valves in hepatic

veins therefore reflect cardiac pressures and pulsatility

Hepatic Doppler

• Hepatic Physiology Processes dietary amino acids, carbohydrates, lipids,

to synthesize fats (cholesterol) and proteins Metabolizes toxins Glycogen storage Produces clotting factors Blood markers of liver function:

AST/AST (aspartate transaminase/alanine transaminase) Alkaline phosphatase GGT(glutamyl-transferase) Albumin Bilirubin (direct, indirect, total) PT (prothrombin time) CBC (platelets)

Hepatic Doppler

• Hepatic pathology Acute injury (hepatitis) results in influx of

inflammatory cells, cytokine release and cell death

Chronic injury leads to parenchymal fibrosis (cirrhosis) with focal areas of hepatic repair called regenerating nodules

Fatty liver (steatosis) may be related to excess triglycerides (diet, diabetes) or response to injury

Hepatic Doppler

• Cirrhosis – common causes Alcohol (60%) Viral hepatitis B, C, and D (10%) Non-alcoholic fatty liver disease (10%) Biliary obstruction (5%) Others

Hemochromatosis Drugs/toxins Genetic metabolic Chronic heart failure

Hepatic Doppler

• Child-Pugh Cirrhosis Classification Class A: score 5-6 Class B: score 7-9 Class C: score >9

Score Bilirubin Albumin INREnceph-

alopathy

Ascites

1 <2 mg/dl>3.5 gm/dl

<1.7 None None

2 2-3 mg/dl 2.8-3.5 1.7-2.2 1-2 Mild

3 >3 mg/dl<2.8 gm/dl

>2.2 3-4 severe

Hepatic Doppler• Gray scale

diagnosis of diffuse liver disease Acute hepatitis

Hepatomegaly (normal 15 -17 cm)

Starry night - not useful

Mottled or normal texture (without nodules)

Hepatic Doppler

• Gray scale diagnosis of diffuse liver disease Fatty liver (two or more findings)

Liver echogenicity exceeds that of renal cortex and > spleen

Attenuation of the ultrasound wave (difficult to image the diaphragm)

Poor definition of the intrahepatic architecture Often focal or areas of fatty sparring Intra- and interobserver reproducibility 76% and

72%

Hepatic Doppler

Hepatic Doppler

Hepatic Doppler

• Gray scale diagnosis of diffuse liver disease Cirrhosis

Surface nodularity (linear transducer right and left lobes)

Mottled texture Loss of fine architectural detail Normal size or hepatomegaly Caudate lobe hypertrophy

Hepatic Doppler

Hepatic Doppler• Portal vein dynamics

Normal PV pressure 5-10 mm Hg

Normal flow direction is towards the liver (hepatopetal)

Portal volume 20-1500 cc/min

Flow influenced by: Eating/fasting Abdominal pressure

(inspiration/expiration, Valsalva, ascites, obesity)

Patient position (supine, LPO, sitting)

Hepatic Doppler

• PV Doppler - Normal Hepatopetal Peak velocity 20-30

cm/sec (Haktanir)

Mild cardiac pulsatility (Pulsatility Index 0.2 to 0.5) (Barakat)

Moderate spectral broadening (preservation of 30% window) (Barakat)

Hepatic Doppler

• Portal Venous hypertension (wedged hepatic vein pressure 5mm Hg greater than IVC pressure) Obstruction to PV flow

Prehepatic (PV thrombosis, pancreatitis) Intrahepatic (cirrhosis) Posthepatic (right heart failure, Budd-

Chiari) Increased PV flow

Arterioportal shunt (hepatic artery-PV fistula following trauma, surgery, AVM)

Hepatic Doppler

• PV hypertension – “soft” findings

Decreased PV velocity (<20 cm/sec) (Haktanir)

Spectral broadening Decreased pulsatility PV diameter >15mm Diminished response

to inspiration (<20% change in diameter)

Hepatic Doppler

• PV hypertension – “hard” findings Reversed flow

(hepatofugal) Portosystemic

collaterals Splenomegaly Ascites

Hepatic Doppler

• PV hypertension PV flow reverses

(hepatofugal) when extra-hepatic collateral pathways develop between PV branches and systemic veins

Requires examination of splenic and superior mesenteric veins

Hepatic Doppler

• Portosystemic collaterals

Gastric-esophageal most important – from coronary and gastrosplenic veins

10-20% spontaneous splenorenal shunt

Paraumbilical Inferior mesenteric-

hemorrhoid Look for common

collateral pathways

Hepatic Doppler

• Portal venous hypertension Intrahepatic shunts complicate detection of flow reversal Examination of intrahepatic left and right PV branches

required

Hepatic Doppler• Hepatic Artery

Doppler - Normal Hepatopetal Peak systolic

velocities 30 – 60 cm/sec

Low impedance (RI = 0.60 – 0.68) (Haktanir)

Rapid acceleration time (<0.08 sec)

Intrahepatic branches more sensitive to disease states

Hepatic Doppler

• Hepatic Artery - Abnormalities

Hepatitis (inflammation) and cirrhosis

Increased flow Increased impedance

(RI >0.72) (Haktanir)

PV thrombosis Increased flow Decreased

impedance (RI <0.68) (Platt)

Hepatic Doppler

• Hepatic Artery - Abnormalities Hepatic artery

stenosis Decreased flow Tardus/parvus

downstream from stenosis

High velocity jet at stenosis

Hepatic Doppler

• Hepatic Vein Doppler – Normal

Triphasic Antegrade (hepatofugal)

peaks during atrial diastole and ventricular diastole

Retrograde (hepatopetal) flow during atrial systole

Affected by respiration

Hepatic Doppler

• Hepatic Vein Doppler – Altered flow

Hepatic “stiffness” prevents hepatic veins from distending during atrial systole

Hepatofugal flow maintained

Biphasic or monophasic

Nonspecific response to steatosis, acute or chronic injury

Hepatic Doppler

• Hepatic Vein Doppler – Occlusion Budd-Chiari syndrome (abdominal pain, ascites,

hepatomegaly) 75% associated with hypercoagulable conditions

(polycythemia, antiphospholipid disease, protein S or factor V Liden deficiency, postpartum)

25% secondary to extrinsic compression of IVC (tumors) or vascular webs

Complications include cirrhosis, hepatic necrosis, encephalopathy,

Treated with paracentesis, anticoagulants, transplant for liver failure

Hepatic Doppler

• Hepatic Vein Doppler – Thrombosis

Color Doppler demonstrates absent flow in one or more hepatic veins (+/- IVC)

Intrahepatic shunts and subcapsular collaterals

Secondary findings: Failure to visualize

hepatic veins High velocity venous jets Hepatofugal portal flow Hepatomegaly and ascites

Hepatic Doppler

• Transjugular Intrahepatic Portosystemic Shunt (TIPS) High rate of

obstruction (25-75% within 12 months)

Thrombosis or pseudointimal hyperplasia

Hepatic Doppler

• TIPS obstruction Absent color flow

(good angle, low flow settings)

Decreased peak velocity (<50 cm/sec) mid stent

Focal jet (>250 cm/sec)

Hepatic Doppler

• Liver Transplant Mechanical

complications at sites of anastomosis

Bile duct obstruction, stenosis, leak (25%)

Hepatic artery thrombosis, stenosis, pseudoaneurysm (4-12%)

Portal and hepatic vein thrombosis or stenosis (1%)

Hepatic Doppler

• Hepatic Doppler Protocol Limited Abdominal US (76705)

Prep Technique Documentation

Abdomen Doppler Complete (93975) Technique Documentation

Hepatic Doppler

• Hepatic Doppler Protocol• Fasting 6 hours• Supine or LPO, suspended inspiration Abdominal imaging

liver (13 images) biliary system (3 images) spleen (2 images)

Color and spectral Doppler portal venous system (8 images) hepatic artery (3 images) hepatic veins (4 images) inferior vena cava (1 image)