Hepatic Doppler Ultrasonography

Anatomy and Physiology

The liver plays a vital role in the body's metabolic functions and is composed of a relatively complex vascular architecture.[1] One-quarter of the cardiac output goes to the liver.[2] The liver is divided into various hepatic segments, and each hepatic lobule receives a branch of the portal vein, hepatic artery, and biliary tract, collectively called the portal triad.[3] These branches involve the following anatomic structures:

1. Portal vein: The portal vein constitutes 75% of the hepatic blood supply. The blood from the portal vein is deoxygenated and carries mainly nutrients. The portal vein is formed by the confluence of the superior mesenteric and the splenic veins. The portal vein drains all the upper and middle parts of the gastrointestinal tract, pancreas, gallbladder, and spleen.[4] Within the liver, the portal is divided into 2 branches: the left and the right portal veins. The left supplies segments II, III, and IV, while the right portal vein supplies segments V, VIII, VI, and VII. Variants of the portal venous system are not uncommon.[5]
2. Hepatic veins: The hepatic veins are 3 branches (right, left, and middle) that drain blood into the inferior vena cava (IVC).[6] The most common hepatic venous morphology includes a right hepatic vein and a common trunk for the middle and left hepatic veins.[7]
3. Hepatic artery: The hepatic artery supplies 25% of the hepatic blood flow and constitutes the main bulk of oxygenated blood to the liver.[2] Frequent variations of the origin of the hepatic artery exist, with the most common type constituting the common hepatic artery arising from the celiac artery in 70% of patients.[8] 
4. Inferior vena cava: The IVC represents the confluence of the right and left common iliac veins and is the retroperitoneal draining vessel to the hepatic veins. The IVC subsequently empties deoxygenated blood to the right heart.[9]

Hepatopetal and Hepatofugal Flow

Hepatopetal flow refers to blood flow towards the liver (from the portal hepatis to the liver periphery). Hepatopetal flow is typically used to describe the normal blood flow direction in the portal vein.[10] This occurs in a normal liver and allows it to detoxify the blood entering it after it absorbs nutrients from the intestine via the portal vein.

Hepatofugal flow refers to blood flow away from the liver in the portal vein and is sometimes referred to as "retrograde" flow. In other words, the portal venous blood flow pattern is from the periphery of the liver towards the porta hepatis.[10] This occurs when the portal venous pressure is high in the case of portal hypertension (see Image. Portal Hypertension). Thus, portosystemic shunts are reopened, with additional findings including a more narrowed portal vein and prominence of the hepatic artery.[11] Occasionally, a to-and-fro bidirectional blood flow pattern alternating between hepatopetal and hepatofugal flow can be seen in the portal vein before the onset of frank hepatofugal flow.[12]

While HVPG (hepatic venous pressure gradient) is the gold standard for measuring portal and hepatic venous pressures, it requires catheterization of the hepatic vessels.[13] On the other hand, Doppler ultrasound is a noninvasive procedure and can evaluate for abnormal physiology of the hepatic vasculature.

Indications

Liver Posttransplantation Assessment

Hepatic Doppler is used for the early detection of vascular occlusion or graft rejection and is the preferred follow-up method due to its low cost and noninvasiveness.[14] Sonographic assessment of a posttransplant liver includes a gray-scale evaluation of the hepatic parenchyma and the hepatic biliary tree. Doppler evaluation of the hepatic vasculature involves both gray-scale and Doppler assessment. Evaluation of strictures can reveal varying degrees of vessel narrowing.[15] 

Thrombus formation in the portal vein and IVC can be evaluated with both gray-scale and Doppler imaging (see Image. Portal Vein Thrombosis). A normal hepatic artery will demonstrate a rapid systolic upstroke lasting up to 80 milliseconds. The resistive index of the hepatic artery, calculated as the ratio of peak systemic velocity minus peak diastolic velocity divided by peak systolic velocity, should be between 0.5 and 0.7.[15] In the setting of posttransplant evaluation, the portal vein should demonstrate a continuous hepatopetal flow pattern with only mild velocity variations on inspiration and expiration. Hepatic veins and the IVC should demonstrate a phasic flow pattern corresponding to the cardiac cycle.[15]

Diagnosis of Portal Hypertension and Patency of Collaterals

Cirrhosis and alterations in portal hemodynamics ultimately increase the portal venous pressure gradient, leading to abnormal portal venous blood flow away from the liver.[16] Doppler ultrasonography can assess blood flow direction and evaluate the presence of collateral vessels. Doppler indices include portal and splenic venous velocities, flow directions, and resistive/pulsatility indices of the arterial vasculature.[17] 

Additional strengths of Doppler assessment include real-time observation, while limitations include a poor detection of slow blood flow and a reduced frame rate.[18] Other useful parameters in the diagnosis of cirrhosis include liver and spleen size, evaluation of liver echotexture, and evaluation of the bluntness of the liver edge.[19] The normal portal vein pressure is less than 6 mm Hg. Portal hypertension is clinically manifested when this pressure exceeds 12 mm Hg. 

Diagnosis of Budd Chiari Syndrome

Budd-Chiari syndrome is an outflow obstruction of the hepatic veins, most commonly secondary to a prothrombotic disorder.[20] Doppler in Budd-Chiari syndrome is diagnosed by occlusion of hepatic venous outflow, either by stenosis or thrombosis of the hepatic veins or the higher-draining inferior vena cava. Doppler in Budd-Chiari syndrome is performed by measuring the flow direction and velocity, as well as the vessel diameter.[21] 

Nonvisualization of the hepatic venous vasculature is often noted on Doppler color ultrasound. A fibrous cord, a luminal thrombus, and stenosis are present.[22] Collaterals can also be seen in a spiderweb morphology, often extending to the inferior vena cava or other hepatic veins. 

Diagnosis and Follow-Up of Thrombosis

Chronic thrombus formation can occur in the portal veins, hepatic veins, or the inferior vena cava. Thrombosis appears as an absent signal on color Doppler evaluation. The gold standard for diagnosing vessel thrombosis is angiography of the suspected vessel, but angiography is an invasive procedure.[23] In chronic thrombosis, collaterals begin to form alongside recanalization of the obstructed vessel. Portal vein thrombosis could be due to benign obstruction of the portal vein (caused by the over-coagulable state, slow blood flow, or vascular injury) or malignant obstruction (caused by infiltration of the endovascular lining of the vessel).[24]

Evaluation of a Transjugular Intrahepatic Portosystemic Shunt Stent

The transjugular intrahepatic portosystemic shunt (TIPS) procedure is a treatment option for patients with cirrhosis or noncirrhotic total hypertension. TIPS shunts function to treat those who suffer from refractory ascites and variceal bleeding.[25] TIPS dysfunction has a high incidence and can be secondary to malpositioning, thrombosis, and pseudointimal hyperplasia.[26] Ultrasound can assess TIPS velocities (typically 90 to 190 cm/s), portal venous blood velocity before entering the shunt (normal is around 30 cm/s), waveforms, and the presence of stenosis.[27]

Assessment of Hemodynamics of Hepatic Focal Lesions

Doppler evaluation can be used in the assessment of benign hemangiomas and telangiectasia.[28] Hypoechoic hepatic focal lesions may be detected during screening of high-risk populations for hepatocellular carcinoma. The lesions may be associated with enlarged portal hepatic lymph nodes or para-aortic lymph nodes in metastasis. The vascular flow on color Doppler around the focal lesion can be evaluated for neovascularization.[29][30]

Hemodynamics in Heart Failure

Doppler ultrasound can also be utilized to assess heart failure. Heart failure can result in hepatic venous congestion and retrograde flow, inferior vena cava congestion with dilated diameters of the vessels, and increased portal vein pulsatility.[31]

Contraindications

Doppler ultrasound of the liver is a noninvasive procedure that has no contraindications.

Equipment

Doppler ultrasound for abdominal examination includes 2 modalities: pulsed Doppler and color Doppler. Continuous Doppler, commonly used to evaluate high-frequency flow in cardiac valves and vascular structures, is not well suited for assessing the portal veins, hepatic veins, or inferior vena cava.

Personnel

Usually, Doppler ultrasound is performed by an experienced sonographer, either a radiologist or a gastroenterologist.

Preparation

Fasting is preferred (4 to 6 hours before the examination) to reduce gaseous distension and abdominal fluid, thereby increasing the visibility of the vessels.[32] Before starting the examination, adjusting the device's gain, frequency, and depth is crucial.[33][34]

Technique or Treatment

General Doppler Ultrasound Technique

Incorporating hepatic Doppler ultrasound into a standard abdominal ultrasound enhances operator proficiency by improving probe manipulation and facilitating clearer visualization of hepatic vasculature. The combined use of abdominal ultrasound and hepatic Doppler does not substantially increase examination time.

Patient breath-holding may improve image quality during vascular assessment.[35] On most ultrasound systems, red color coding indicates blood flow toward the probe, while blue indicates flow away from the probe. The portal vein demonstrates a thick fibrous wall, appearing as an echogenic line surrounding the vessel, whereas hepatic vein walls remain thin and often not visualized. Portal vein diameter typically ranges from 7 to 15 mm, hepatic vein diameter from 5 to 7 mm, and inferior vena cava diameter from 13 to 22 mm, with normal collapsibility under pressure.[36][37]

Optimal patient positioning includes supine or left lateral decubitus positioning. Initial scanning in the right subcostal region enables visualization of the portal vein, with the confluence of the splenic and superior mesenteric veins identified as the probe is moved left toward the midline. Substernal scanning allows visualization of the inferior vena cava, which should appear compressible, along with the aorta in the midline using a posteriorly directed probe in longitudinal or transverse orientation. Hepatic veins are best assessed from the right intercostal approach with medial probe orientation to evaluate drainage of all 3 hepatic veins into the inferior vena cava. Additional visualization of the hepatic veins may be achieved via the subcostal approach with a posterior probe orientation, while the left and middle hepatic veins are optimally assessed from the substernal window.

Limitations

Obesity may limit visualization of vessel flow and velocity during Doppler assessment. Postprandial states may increase portal pressure and widen the vessel diameter, while ingested contents and associated gaseous distension can further impede clear visualization of hepatic vessels. Fasting for at least 4 to 6 hours before Doppler examination improves imaging quality and diagnostic accuracy.

Incorrect device settings, including improper adjustment of gain and frequency, may lead to inaccurate interpretation of hepatic hemodynamics. Low-frequency settings may lead to false-positive identification of portal vein thrombosis. Inadequate breath-holding capacity may also hinder vessel visualization; however, synchronization of probe movement with patient inhalation can help mitigate this limitation and improve image acquisition.

Clinical Significance

Hepatic Doppler ultrasound is a noninvasive investigative tool that can help clinicians, especially when added to an abdominal ultrasound exam. The procedure is cost-effective and has no complications. Doppler ultrasound is the preferred imaging modality for assessing the vascular condition in the following diseases: 

• Portal hypertension associated with cirrhosis 
• Portal or hepatic vein thrombosis (see Image. Ultrasound of Portal Vein Thrombosis) [38]
• Vascularity of the hepatic focal lesions [39]
• Follow-up after TIPS or liver transplantation [40]
• Measuring the hepatic vein and artery patency, blood velocity, and direction

Referral to other invasive investigative or treatment procedures, eg, hepatic venous pressure gradient HVPG, angiography, transjugular intrahepatic portosystemic shunt TIPS, and other procedures, depends on initial assessment on Doppler ultrasound. In a study comparing rats with fatty liver disease to normal rats, no significant difference was observed between the 2 groups in portal vein diameter and flow, and a normal increase in diameter in both groups with meals was observed.[41]

Furthermore, a study on 120 patients found that portal vein diameter and splenic area were inversely correlated to the platelet count, where the platelet count is a strong indicator of liver fibrosis as shown by histopathological score (Ishak score) [42] A recent meta-analysis and a systematic review found that on comparing hepatic vein resistive index versus hepatic artery resistive index, that the former had a higher diagnostic accuracy in detecting liver fibrosis of F2 or greater (indicating liver fibrosis stage of moderate scarring in the liver, with bands of scar tissue forming but no cirrhosis) as diagnosed by liver biopsy.[43]

A study on 94 patients with hepatitis B virus infection showed that as the liver inflammation increased, the diameter of the portal vein increased while its velocity decreased; moreover, as the degree of liver fibrosis increased, the diameter of the portal vein increased, while its velocity decreased, associated with decreased velocity of the superior mesenteric and splenic veins. A flat or unidirectional flow of the hepatic veins accompanies this. Thus, Doppler ultrasound of the liver may be more useful than conventional abdominal ultrasound for noninvasive assessment of the degree of liver fibrosis.[44]

Enhancing Healthcare Team Outcomes

Doppler liver ultrasonography serves as a noninvasive, cost-effective modality for evaluating hepatic vascular anatomy, blood flow direction, and hemodynamic abnormalities associated with liver disease. Assessment of portal venous, hepatic venous, hepatic arterial, and inferior vena cava waveforms assists in diagnosing portal hypertension, portal or hepatic vein thrombosis, Budd-Chiari syndrome, hepatic congestion from heart failure, and complications following liver transplantation or TIPS placement. Recognition of hepatopetal and hepatofugal flow patterns, vessel patency, resistive indices, and abnormal waveform morphology improves diagnostic accuracy and supports timely intervention. Doppler ultrasonography also aids in evaluating focal hepatic lesions, monitoring progression of fibrosis, and guiding referral for invasive procedures such as angiography, hepatic venous pressure gradient measurement, or TIPS revision. Technical factors, including patient positioning, fasting status, respiratory motion, obesity, and equipment settings, significantly influence image quality and interpretation.

Interprofessional collaboration strengthens diagnostic precision, patient safety, and longitudinal management of hepatic vascular disorders. Radiologists, hepatologists, gastroenterologists, transplant surgeons, primary care clinicians, and advanced practitioners coordinate evaluation, interpretation of Doppler findings, and selection of appropriate follow-up testing or intervention. Nurses reinforce patient preparation instructions, monitor procedural tolerance, and facilitate communication across care teams. Pharmacists assist with anticoagulation management, medication reconciliation, and prevention of drug-related hepatic complications. Sonographers optimize image acquisition and recognize abnormal flow patterns requiring urgent escalation. Shared decision-making promotes patient understanding of diagnostic findings, surveillance strategies, transplant follow-up, and risk reduction measures, while timely referral and coordinated monitoring reduce complications such as graft failure, progressive portal hypertension, and thrombotic events.