Type of Examination

Abdominal Doppler of the Hepatic Portal Circulation

Definition

Acute or chronic hepatocellular disease can block the flow of blood throughout the liver, causing it to back up into the hepatic portal circulation. This causes the blood pressure in the hepatic circulation to increase (portal hypertension). In an effort to relieve the pressure, collateral veins are formed that connect to the systemic veins. This is known as varicose veins and occurs most frequently in the area of the esophagus, stomach, and rectum. Rupture of these veins may cause massive bleeding that may result in death.

Objective

To identify the direction and patency of flow in the portal venous system, hepatic veins, and hepatic artery

Indication(s)

• Suspected portal hypertension secondary to liver disease

• Portal vein compression or thrombosis

• Acute onset of hepatic vein occlusion (Budd-Chiari syndrome), constrictive pericarditis, or congestive heart failure with tricuspid regurgitation

• Congenital/ traumatic/ or neoplastic arterioportal fistula

Limitations/Contraindications

• bandages, surgical sutures

• patient unable to suspend respiration

• patient size

• excessive bowel gas

Equipment & Supplies

• Duplex imaging system: LOGIQ 700, LOGIQ 500

• Transducers: 2-5MHz curved array (may be necessary to use lower frequency or multifrequency to penetrate the liver; the patient may be scanned with one frequency to image hepatic structures and then use a lower frequency Doppler to improve sensitivity and color fill-in. Harmonics may also improve the greyscale image.)

• System setups for abdominal ultrasound evaluation

• Ultrasound gel

• Towels

• Materials for documentation of the study [video, prints, film]

Patient Preparation & Positioning

• The abdominal Doppler examination is explained to the patient and any questions are answered.

• A history is obtained from the patient focusing on risk factors, signs, and symptoms of hepatocellular disease. Previous medical history relating to hepatocellular disease should be noted.

• Any recent surgical intervention of shunt placement within the portal venous system is documented in the patient history work sheet.

• The patient is placed initially in the supine position; the patient may be rolled into a slight left lateral decubitus position to obtain a better intercostal window. The images and Doppler evaluation may be obtained in the longitudinal, coronal, oblique, or transverse planes.

• Breath holding is very important in obtaining good Doppler color and spectral waveforms. Initially scan the patient in shallow respiration to set up your controls and depth. Then instruct the patient to stop breathing when you obtain the Doppler images.

General Technical Points

• Place ultrasound gel on the abdomen to ensure good transducer-to-skin contact during the abdominal Doppler imaging examination.

• The transducer's orientation marker should be pointing toward the patient's right side during the examination when a transverse scan is performed; the orientation marker is directed toward the patient's head when a longitudinal scan is performed.

• The examination is performed with both gray scale and Doppler evaluation of the portal venous system, the hepatic veins, and hepatic arteries.

• Remember, the transducer must be PARALLEL to the vessel; the Doppler angle should be less than sixty degrees to obtain the maximum peak systolic velocity.

• At the end of the examination, the ultrasound gel should be removed from the patient and any excess gel should be removed from the transducer. The transducer should be cleaned using a disinfectant.

Doppler

• The evaluation of the portal venous system, hepatic veins, and hepatic artery is performed during the Doppler imaging examination.

• Doppler signals or color Doppler imaging should be obtained from the imaging plane that allows the beam to be as parallel to the vessel as possible.

• A liver Doppler should also evaluate flow in the extra-hepatic portal venous system, and IVC. These images should be obtained prior to the PW evaluation.

• Also document the size of the CBD, liver, kidneys, and spleen.

• Look in the pelvic cavity and lower quadrants for the presence of free fluid.

Doppler Technique

• The pulse repetition frequency (PRF) allows one to record lower velocities as the PRF is lowered; as the PRF is increased, the lower velocities are filtered out to record only the higher velocity signal.

• The PRF may be changed with the scale control on the Doppler panel (look at the color bar on the left side of the monitor, the PRF will change as the "scale" on the Doppler control is changed.

• The PRF increases as imaging depth increases and decreases as depth decreases. Flow within the normal hepatic venous system is low; therefore a lower PRF is necessary to record the flow pattern. As the flow increases beyond 40 cm/sec, the PRF should be increased to prevent aliasing. (Aliasing may also be reduced by scanning at a lower frequency).

• The Doppler sample volume should be smaller than the diameter of the lumen. If you have difficulty finding the vessel, increase the width of the sample volume to locate the flow, and then reduce the volume width to clean up the spectral waveform.

• The Doppler angle correction should be less than 60 degrees to display the peak spectral velocity.

• Wall filters help to eliminate "noise" or low level Doppler shifts seen within the vessel.

Types of Doppler:

• Pulse wave provides quantitative information from a selected location

• Color Doppler Velocity

• Dependent on direction of flow, velocity, and angle to flow

• Important to angle color box as parallel to vessel as possible

• Positive Doppler shift shows flow towards the transducer; negative shows flow away from transducer on color bar

• Laminar flow distinguished from turbulent flow by varying shades of color

• Color Doppler Energy

• Relies on echo amplitude

• Each energy signal is assigned a hue that is related to number of blood cells in the sample volume (displayed on color bar)

• Different hues represent number of blood cells in sample volume, not the velocity

• CDE not dependent on velocity, direction or angle of flow

Color Doppler Technique

• Color Doppler gain

• Color Doppler scale

• Angle the color box (sample volume)

• Decrease the size of the color box

Doppler Measurement

• Peak systolic velocity (calculate highest velocity in cm/sec)

• Resistive Index (RI): subtract the end diastolic velocity from the peak systolic velocity and divide by the peak systolic velocity. Normal or low resistive RI measures <.7.

Hepatic Artery

• Low resistance waveform; forward flow in diastole above baseline

• Vessel is tortuous; flow may appear to move toward and away from the transducer.

• Systolic window with narrow bandwidth with parabolic flow profile

• Spectral fill-in of systolic window due to small vessel diameter

• High resistance waveforms may indicate veno-occlusive disease

Portal Venous System

• Continuous low velocity phasic signal; phasic means that the velocity increases and decreases with respirations giving the signal a smooth wavelike appearance

• Normal flow is termed hepatopedal (toward the liver)

• Reversed flow is hepatofugal.

• Portal venous thrombosis or post op anastomosis from a liver transplant can cause an abnormal portal vein signal: results from decreased vessel lumen size which reduces the pressure, and consequently increases the velocity of flow through the narrowed region - "choppy" appearance as result of increased velocities.

• NOTE: The hepatic artery and portal vein flow should be in the same direction as the hepatic artery runs parallel with the portal vein.

Hepatic Venous System

• Multi-phasic pulsatile flow pattern secondary to proximity of the right atrium with flow above and below the baseline due to close proximity to the right atrium which results in hemodynamic changes

• Right sided heart failure may cause the hepatic veins to become pulsatile and dilated.

• Increased intrahepatic pressure or venous obstruction demonstrates a more continuous or monophasic signal

Inferior Vena Cava

• Continuous waveform with respiratory variations; become more pulsatile as it empties into the right atrium.

• Best imaged with a slight cranial-caudal sweep in the longitudinal plane with the patient in deep inspiration

• Anastomosis from surgical transplantation may alter the normal flow into the IVC

• Thrombosis can cause the IVC waveform to appear monophasic with high velocities ("choppy" appearance). Evaluate for thrombus in the renal veins as well.

• If a surgical shunt is present, be sure to check the patient's history to find out the specific type of shunt (portal/cava or mesenteric/cava) is in place.

Terminology:

• Left hepatic vein - LHV

• Left hepatic artery - LHA

• Left portal vein - LPV

• Right hepatic vein - RHV

• Right hepatic artery - RHA

• Right portal vein - RPV

• Common (main) hepatic artery - CHA

• Main portal vein - MPV

• Middle hepatic vein - MHV

The hepatic vessels should be imaged at four anatomical locations:

• Midline, beneath the xyphoid for the LHV, LHA, and LPV;

• Mid-clavicular and intercostal at the portal hepatis for the MHA and MPV;

• Lateral and intercostal at the right lobe for the RHA and RPV;

• Subcostal and midclavicular for the RHV and MHV.

Click on image for larger view

Interpretation	Gray scale Compression	Doppler Signal	Color Doppler
Portal Veins:
A. Normal
B. Thrombosis
C. Portal Hypertension
D. Cavernous Transformation
Hepatic Artery:
A. Normal
B. Thrombosis
Inferior Vena Cava:
A. Normal
B. Thrombosis
C. Right sided heart failure
Hepatic Veins:
A. Normal
B. Thrombosis/ Budd Chiari

Dahnert, Wolfgang, Radiology Review Manual, 3rd Edition, Williams & Wilkins, 1995.

DeJong, Robert, The Use of Doppler in the Abdomen, The Johns Hopkins Hospital, 1998.

Hagen-Ansert SL, Textbook of Diagnostic Ultrasonography, 5th Ed. Mosby, 2001.

Kurtz, AB and Middleton WD, Ultrasound: The Requisites, Mosby, 1996.

Rumack CM, Wilson SR and Charboneau JW, Diagnostic Ultrasound, 2nd Ed, Mosby, 1998.

Thibodeau, GA and Patton, KT. The Human Body in Health & Disease, 2nd Edition, Mosby, 1997.