Doppler US of helical flow in the portal vein

Reference values for 4D flow magnetic resonance imaging of the portal venous system

PURPOSE

The purpose of this work was to establish normal reference values for 4D flow MRI-derived flow, velocity, and vessel diameters, and to define characteristic flow patterns in the portal venous system of healthy adult subjects.

METHODS

For this retrospective study, we screened all available 4D flow MRI exams of the upper abdomen in healthy adults acquired at our institution between 2012 and 2022 at either 1.5 T or 3.0 T MRI after ≥ 5 h fasting. Flow, velocity, and effective diameter were quantified in the 8 planes in the portal venous system (splenic vein, superior mesenteric vein, main, right, and left portal veins). Vessel delineation was manually adjusted over time. Reference ranges for were defined as the mean ± 2 standard deviations. Three readers noted helical and vortical flow on time-resolved pathline visualizations. Conservation of mass flow analysis was performed for quality assurance.

RESULTS

We included 44 healthy subjects (26 female, 18-74 years) in the analysis. We report reference values for mean and peak flow, mean velocity, and vessel diameter in the healthy portal vein using 4D flow MRI. Normal flow patterns in the portal vein included faint helical (66%) or linear flow (34%). Conservation of mass analysis demonstrated a relative error of 1.1 ± 4.6% standard deviation (SD) at the splenomesenteric confluence and - 1.4 ± 4.1% SD at the portal bifurcation.

CONCLUSION

We have reported normal hemodynamic values that are necessary baseline data for emerging clinical applications of 4D flow MRI in the portal venous system. Results are consistent with previously published values from smaller cohorts.

Liver cirrhosis: relationship between fibrosis-associated hepatic morphological changes and portal hemodynamics using four-dimensional flow magnetic resonance imaging

PURPOSE

The mechanisms underlying the morphological changes in liver cirrhosis remain unknown. This study aimed to clarify the relationship between fibrotic hepatic morphology and portal hemodynamic changes using four-dimensional flow magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Overall, 100 patients with suspected liver disease who underwent 3-T MRI were evaluated in this retrospective study. Liver fibrosis was assessed using a combination of visual assessment of the hepatic morphology and quantitative measures, including the fibrosis-4 index and aspartate transaminase-to-platelet ratio. It was classified into three groups according to the severity of fibrosis as follows: A (normal), B (mild-to-moderate), and C (severe). Quantitative indices, including area (mm²), net flow (mL/s), and average velocity (cm/s), were measured in the right portal vein (RPV) and left portal vein (LPV), and were compared across the groups using the Kruskal-Wallis and Mann-Whitney U tests.

RESULTS

Among the 100 patients (69.1 ± 12.1 years; 59 men), 45, 35, and 20 were categorized into groups A, B, and C, respectively. The RPV area significantly differed among the groups (from p < 0.001 to p = 0.001), showing a gradual decrease with fibrosis progression. Moreover, the net flow significantly differed between groups A and B and between groups A and C (p < 0.001 and p < 0.001, respectively), showing a decrease during the early stage of fibrosis. In the LPV, the net flow significantly differed among the groups (from p = 0.001 to p = 0.030), revealing a gradual increase with fibrosis progression.

CONCLUSION

The atrophy-hypertrophy complex, which is a characteristic imaging finding in advanced cirrhosis, was closely associated with decreased RPV flow in the early stage of fibrosis and a gradual increase in LPV flow across all stages of fibrosis progression.

Morphometric changes and imaging findings of diffuse liver disease in relation to intrahepatic hemodynamics

Diffuse hepatic diseases have a variety of etiologies, with each showing characteristic morphometric changes. These changes are closely related to micro- and macro-level intrahepatic hemodynamics, in addition to the specific underlying pathophysiology. Short-term disorders in intrahepatic hemodynamics caused by each pathophysiological condition are compensated for by the balance of blood perfusion systems using potential trans-sinusoidal, transversal, and transplexal routes of communication (micro-hemodynamics), while long-term alterations to the intrahepatic hemodynamics result in an increase in total hepatic vascular resistance. Blood flow disorders induced by this increased vascular resistance elicit hepatic cellular necrosis and fibrosis. These changes should be uniformly widespread throughout the whole liver. However, morphometric changes do not occur uniformly, with shrinkage or enlargement not occurring homogeneously. Against this background, several macro-intrahepatic hemodynamic effects arise, such as asymmetrical and complicating morphometric structures of the liver, intricate anatomy of portal venous flow and hepatic venous drainage, and zonal differentiation between central and peripheral zones. These hemodynamic factors and pathophysiological changes are related to characteristic morphometric changes in a complicated manner, based on the combination of selective atrophy and compensatory hypertrophy (atrophy-hypertrophy complex). These changes can be clearly depicted on CT and MR imaging.

The "streamline phenomenon" of the portal vein flow and its influence on liver involvement by gastrointestinal diseases: current concepts and imaging-based review

The streamline flow in the portal system is a phenomenon by which blood from superior mesenteric vein goes preferentially to the right hepatic lobe, while splenic and inferior mesenteric veins divert preferentially to the left lobe. Such a phenomenon results in different patterns of distribution of several liver diseases. The purpose of this article is to discuss the concepts behind the theory of streamline flow and to perform an imaging-based review of representative cases, demonstrating how it may influence the patterns of liver involvement in different gastrointestinal diseases.

MRI-based modeling of spleno-mesenteric confluence flow

Characterization of hepatic blood flow magnitude and distribution can lead to a better understanding of the pathophysiology of liver disease. However, the underlying patterns and dynamics of hepatic flow, such as the helical flow structure that often develops following the spleno-mesenteric confluence (SMC) of the hepatic portal vein, have not yet been comprehensively studied. In this study, we used magnetic resonance image (MRI)-based computational models to study the effects of the helical flow structure and SMC geometry on portal blood flow distribution. Additionally, we examined these flow dynamics with four-dimensional (4D) flow MRI in a group of 12 cirrhotic patients and healthy subjects. A validation model was also created to compare computational data to particle image velocimetry (PIV) data. We found significant correlations between flow structure development, vessel geometry, and blood flow distribution in both virtually modified models and in healthy and cirrhotic subjects. However, the direction of these correlations varied among vessel configuration types. Nonetheless, validation model results displayed good qualitative agreement with computational model data.

Sonographic Evaluation of the Portal and Hepatic Systems

Color and spectral Doppler are used to evaluate flow characteristics in the portal and hepatic vessels. On occasion, suprahepatic pathologies are reflected in the flow characteristics of the hepatic veins and transmitted to the portal venous system across the hepatic sinusoids. Few definitive duplex findings are pathognomic for portal hypertension. Evaluation of the portal venous system is analogous to a puzzle. A picture of the processes can only be attained after many of the pieces are assembled.

Altered Doppler flow patterns in cirrhosis patients: an overview

Doppler ultrasonography of the hepatic vasculature is an integral part of evaluating precirrhotic and cirrhotic patients. While the reversal of the portal venous flow is a well-recognized phenomenon, other flow patterns, although not as easily understood, may play an important role in assessing the disease status. This article discusses the different characteristic flow patterns observed from the portal vein, hepatic artery, and hepatic vein in patients with liver cirrhosis or related complications and procedures. Knowledge of these different flow patterns provides additional information that may reinforce the diagnosis of cirrhosis, help in staging, and offer prognostic information for determining the direction of therapy. Doppler ultrasonography is invaluable when liver transplantation is being considered and aids in the diagnosis of cirrhosis and portal hypertension.

Comparison of vortical structures induced by arteriovenous grafts using vector Doppler ultrasound

Arteriovenous prosthetic grafts are used in hemodialysis. Stenosis in the venous anastomosis is the main cause of occlusion and the role of local hemodynamics in this is considered significant. A new spiral graft design has been proposed to stabilize the flow phenomena in the host vein. Cross-flow vortical structures in the outflow of this graft were compared with those from a control device. Both grafts were integrated in identical in-house ultrasound-compatible flow phantoms with realistic surgical configurations. Constant flow rates were applied. In-plane 2-D velocity and vorticity mapping was developed using a vector Doppler technique. One or two vortices were detected for the spiral graft and two to four for the control, along with reduced stagnation points for the former. The in-plane peak velocity and circulation were calculated and found to be greater for the spiral device, implying increased in-plane mixing, which is believed to inhibit thrombosis and neo-intimal hyperplasia.

Post-operative imaging in liver transplantation: State-of-the-art and future perspectives

Orthotopic liver transplantation (OLT) represents a major treatment for end-stage chronic liver disease, as well as selected cases of hepatocellular carcinoma and acute liver failure. The ever-increasing development of imaging modalities significantly contributed, over the last decades, to the management of recipients both in the pre-operative and post-operative period, thus impacting on graft and patients survival. When properly used, imaging modalities such as ultrasound, multidetector computed tomography, magnetic resonance imaging (MRI) and procedures of direct cholangiography are capable to provide rapid and reliable recognition and treatment of vascular and biliary complications occurring after OLT. Less defined is the role for imaging in assessing primary graft dysfunction (including rejection) or chronic allograft disease after OLT, e.g., hepatitis C virus (HCV) recurrence. This paper: (1) describes specific characteristic of the above imaging modalities and the rationale for their use in clinical practice; (2) illustrates main imaging findings related to post-OLT complications in adult patients; and (3) reviews future perspectives emerging in the surveillance of recipients with HCV recurrence, with special emphasis on MRI.

Secondary flow in peripheral vascular prosthetic grafts using vector Doppler imaging

Prosthetic grafts are used for the treatment of peripheral arterial disease. Re-stenosis in the distal anastomosis of these grafts is a common reason for graft occlusion. The role of local hemodynamics in development of neo-intimal hyperplasia is well known. A new graft design has been proposed for the induction of optimized spiral flow in the host vessel. The secondary flow motions induced by this graft were compared with those of a control device. Both types of grafts were connected with vessel mimic and positioned in ultrasound flow phantoms with identical geometry. Constant flow rates were applied. Data collected in the cross-sectional view distal from the graft outflow and dual-beam vector Doppler was applied to create 2-D velocity maps. A single-spiral flow pattern was found for the flow-modified graft, and double or triple spirals for the control graft. In-plane maximum velocity was greater for the flow-modified graft than for the control device.

Cirrhotic right and left portal veins: how slow do they go? Identification of threshold velocities associated with subsequent development of hepatofugal flow

OBJECTIVE

The purpose of this study was to identify threshold right and left portal vein sonographic velocities that are correlated with subsequent development of hepatofugal flow in the main portal vein (MPV), a marker of portal hypertension.

METHODS

A database containing 6019 Doppler liver ultrasound reports from an academic hospital was parsed using a Visual Basic computer algorithm. Right and left portal vein velocities were identified from 65 patients who developed hepatofugal MPV flow. Patients with a liver transplant or transjugular intrahepatic portosystemic shunt were excluded. Similarly, right and left portal vein velocities were identified from 195 patients free of chronic hepatic disease. The right and left portal vein velocities of these 2 groups were analyzed using a receiver operating characteristic curve to identify threshold velocities with the optimal sensitivity and specificity for patients who will develop hepatofugal flow in the MPV.

RESULTS

A threshold velocity of 11 cm/s in the right portal vein is associated with 81.8% sensitivity and 93.5% specificity in distinguishing patients who develop hepatofugal flow from otherwise healthy control subjects. Likewise, a threshold velocity of 8 cm/s in the left portal vein is associated with a 62.3% sensitivity and a 94.5% specificity.

CONCLUSIONS

A threshold right portal vein velocity of 11 cm/s can be used with high sensitivity and specificity to identify patients who may develop hepatofugal flow in the MPV. A left portal vein velocity less than 8 cm/s is 94.5% specific for the development of hepatofugal flow.

Portal glucose delivery stimulates muscle but not liver protein metabolism

Portal vein glucose delivery (the portal glucose signal) stimulates glucose uptake and glycogen storage by the liver, whereas portal amino acid (AA) delivery (the portal AA signal) induces an increase in protein synthesis by the liver. During a meal, both signals coexist and may interact. In this study, we compared the protein synthesis rates in the liver and muscle in response to portal or peripheral glucose infusion during intraportal infusion of a complete AA mixture. Dogs were surgically prepared with hepatic sampling catheters and flow probes. After a 42-h fast, they underwent a 3-h hyperinsulinemic (4× basal) hyperglucagonemic (3× basal) hyperglycemic (≈160 mg/dl) hyperaminoacidemic (hepatic load 1.5× basal; delivered intraportally) clamp (postprandial conditions). Glucose was infused either via a peripheral (PeG; n = 7) or the portal vein (PoG; n = 8). Protein synthesis was assessed with a primed, continuous [(14)C]leucine infusion. Net hepatic glucose uptake was stimulated by portal glucose infusion (+1 mg·kg(-1)·min(-1), P < 0.05) as expected, but hepatic fractional AA extraction and hepatic protein synthesis did not differ between groups. There was a lower arterial AA concentration in the PoG group (-19%, P < 0.05) and a significant stimulation (+30%) of muscle protein synthesis associated with increased expression of LAT1 and ASCT2 AA transporters and p70S6 phosphorylation. Concomitant portal glucose and AA delivery enhances skeletal muscle protein synthesis compared with peripheral glucose and portal AA delivery. These data suggest that enteral nutrition support may have an advantage over parenteral nutrition in stimulating muscle protein synthesis.

Segmental difference of the hepatic fibrosis from chronic viral hepatitis due to hepatitis B versus C virus infection: comparison using dual contrast material-enhanced MRI

OBJECTIVE

We wanted to identify the geographic differences in hepatic fibrosis and their associations with the atrophy-hypertrophy complex in patients with chronic viral hepatitis using the dual-contrast material-enhanced MRI (DC-MRI) with gadopentetate dimeglumine and ferucarbotran.

MATERIALS AND METHODS

Patients with chronic C (n = 22) and B-viral hepatitis (n = 35) were enrolled for determining the subjective grade of fibrosis (the extent and thickness of fibrotic reticulations) in the right lobe (RL), the caudate lobe (CL), the medial segment (MS) and the lateral segment (LS) of the liver, with using a 5-grade scale, on the gradient echo T2(*)-weighted images of DC-MRI. The fibrosis grades of different segments were compared using the Kruskal-Wallis test followed by post-hoc analysis to establish the segment-by-segment differences. The incidences of two pre-established morphologic signs of cirrhosis were also compared with each other between the two groups of patients.

RESULTS

There were significant intersegmental differences in fibrosis grades of the C-viral group (p = 0.005), and the CL showed lower fibrosis grades as compared with the grades of the RL and MS, whereas all lobes were similarly affected in the B-viral group (p = 0.221). The presence of a right posterior hepatic notch was significantly higher in the patients with intersegmental differences of fibrosis between the RL and the CL (19 out of 25, 76%) than those without such differences (6 out of 32, 19%) (p < 0.001). An expanded gallbladder fossa showed no significant relationship (p = 0.327) with the segmental difference of the fibrosis grades between the LS and the MS.

CONCLUSION

The relative lack of fibrosis in the CL with more advanced fibrosis in the RL can be a distinguishing feature to differentiate chronic C-viral hepatitis from chronic B-viral hepatitis and this is closely related to the presence of a right posterior hepatic notch.

Double contrast-enhanced MRI of viral hepatitis-induced cirrhosis: correlation of gross morphological signs with hepatic fibrosis

The purpose of this study was to evaluate the diagnostic ability of the expanded gallbladder fossa and right posterior hepatic notch signs for hepatic fibrosis determined by double contrast-enhanced MRI. For patients with chronic viral hepatitis B (n = 96) or hepatitis C (n = 13) who underwent gadopentate dimeglumine-enhanced dynamic MRI followed by ferucarbotran-enhanced gradient-echo imaging, the degree of parenchymal fibrosis was categorised into three groups based on the extent of reticulation and nodularity: (1) pre-cirrhotic or minimal fibrosis; (2) mild to moderate fibrosis; (3) advanced cirrhosis. Each group was evaluated for the presence of a sharp notch in the posterior-medial surface of the right lobe of the liver and expanded gallbladder fossa. The expanded gallbladder fossa sign gradually increased with an increasing degree of fibrosis (Group 1, 50%; Group 2, 61%; Group 3, 78%), and there was no significant difference (p>0.5) between hepatitis B (67%) and C (73%). In the case of the right posterior hepatic notch sign, only 6% of Group 1 and Group 2 patients were positive; 27% of hepatitis B patients and 90% of hepatitis C patients in Group 3 exhibited the sign (p<0.05). Owing to its low prevalence, even in advanced cirrhosis, the right posterior hepatic notch sign is of little value in the diagnosis of cirrhosis due to chronic hepatitis B virus infection, whereas an expanded gallbladder fossa could be used as a non-specific indicator of early fibrosis before the gross appearance of advanced hepatic fibrosis.

Doppler sonography of portal hypertension

Doppler sonography is frequently obtained in patients with chronic liver disease, patients with suspected portal hypertension, and patients with known portal hypertension. In this clinical setting, it is important to understand both the normal hemodynamics of the liver and the morphological and hemodynamic changes that occur with portal hypertension. Among the many findings of portal hypertension are enlargement of the portal vein, decreased portal vein velocity, increased congestion index, development of portosystemic collaterals, and reversal of portal vein flow. The most important portal systemic collaterals to focus on with Doppler are the coronary vein and the umbilical vein. Using all of these clues, it is possible to diagnose portal hypertension with a high degree of sensitivity and specificity in most patients.

Spectrum of normal or near-normal sonographic findings after orthotopic liver transplantation

The initial imaging immediately after orthotopic liver transplantation is generally performed with ultrasound. Although significant posttransplant complications do occur, many abnormal findings including minor vascular waveform abnormalities, anastomotic mismatches, and fluid collections can be seen in asymptomatic patients. It is important to differentiate these benign findings from more serious complications to avoid unnecessary intervention.

Optimizing Doppler and color flow US: application to hepatic sonography

In the imaging of patients with chronic liver disease or portal hypertension or who have undergone liver transplantation or surgery, accurate evaluation of the hepatic vasculature is usually necessary. Because Doppler ultrasonography (US) is capable of accurately characterizing the nature of flow within the major hepatic arteries and the portal and hepatic veins, it is widely used for imaging the liver vasculature. An informed choice of transducer and scanning techniques is important in the evaluation of the liver vasculature. In addition, there are a variety of operator-dependent technical parameters (eg, baseline, frame rate, wall filters, gain, velocity range, angle correction, gate size and position) that must be optimized when performing Doppler US of the liver. Changes in these parameters independently influence both the color and spectral components of the Doppler US examination; therefore, the parameters should be optimized separately for each patient. Failure to appropriately adjust these parameters may result in artifacts or misinterpretation of the study, which will frequently affect patient treatment. In contrast, knowledge of these operator-dependent parameters will permit optimization of the study and improve the overall utility of liver Doppler US.

Direct assessment and distribution of regional portal blood flow in the pig by means of fluorescent microspheres

Measurement of regional organ blood flow by means of fluorescent microspheres (FM) is an accepted method. However, determination of regional portal blood flow (RPBF) cannot be performed by microspheres owing to the entrapment of the spheres in the upstream capillary bed of the splanchnic organs. We hypothesized that an adequate experimental setting would enable us to measure RPBF by means of FM and to analyze its distribution within the pig liver. A mixing chamber for the injection of FM was developed, and its capability to distribute FM homogeneously in the blood was evaluated in vitro. The chamber was implanted into the portal vein of six anesthetized pigs (23.5 +/- 2.9 kg body wt). Three consecutive, simultaneous injections of FM of two different colors into the chamber were performed. Reference portal blood samples were collected by means of a Harvard pump. At the end of the experiment, the liver was explanted and fixed in formalin before dissection. FM were isolated from the tissue samples by an automated process, and fluorescence intensity was determined. Comparison of 5,458 single RPBF values, determined by simultaneously injected FM, revealed good agreement (bias 2.5%, precision 12.7%) and high correlation (r = 0.97, r2 = 0,95, slope = 1.04, intercept = 0.05). Median RPBF was 1.07 +/- 0.78 ml x min(-1) x g(-1). Allocation of the blood flow values to the anatomic regions of the liver revealed a significantly higher RPBF (P = 0.01) in the liver tissue located close to the diaphragm compared with the rest of the organ and a significantly lower RPBF (P = 0.01) in the left liver lobe compared with the median and right lobes. The results show that the model presented makes it possible to measure RPBF by means of FM reliably and that RPBF is distributed heterogeneously in the porcine liver.

Doppler Ultrasound Evaluation of Transjugular Intrahepatic Portosystemic Shunt Function

The current literature reflects controversy regarding the accuracy of Doppler ultrasound for the detection of transjugular intrahepatic portosystemic shunt (TIPS) malfunction. Experience has revealed many pitfalls and artifacts that can potentially interfere with the proper performance and interpretation of Doppler studies in patients with TIPS. In this article the author discusses and illustrates the spectrum of pitfalls that may be encountered during Doppler evaluation of TIPS function.

Radiology in liver transplantation

Imaging studies are becoming essential in the management of orthotopic liver transplantation (LT). They have a very important role in the preoperative evaluation and selection of suitable candidates. At the same time, they are essential in the early detection of postoperative complications, the recognition of which allows the prompt institution of appropriate therapeutic measures. Timely recognition of complications improves the success of LT; furthermore, some complications can be treated with interventional radiologic procedures, avoiding additional surgery. This article reviews the current application of diagnostic and interventional imaging in liver transplantation, both for cadaveric and living donor transplants.

Hepatofugal flow in the portal venous system: pathophysiology, imaging findings, and diagnostic pitfalls

Hepatofugal flow (ie, flow directed away from the liver) is abnormal in any segment of the portal venous system and is more common than previously believed. Hepatofugal flow can be demonstrated at angiography, Doppler ultrasonography (US), magnetic resonance imaging, and computed tomography (CT). The current understanding of hepatofugal flow recognizes the role of the hepatic artery and the complementary phenomena of arterioportal and portosystemic venovenous shunting. Detection of hepatofugal flow is clinically important for diagnosis of portal hypertension, for determination of portosystemic shunt patency and overall prognosis in patients with cirrhosis, as a potential pitfall at invasive arteriography performed to evaluate the patency of the portal vein, and as a contraindication to specialized imaging procedures (ie, transarterial hepatic chemoembolization and CT during arterial portography). Hepatofugal flow is generally diagnosed at Doppler US without much difficulty, but radiologists should beware of pitfalls that can impede correct determination of flow direction in the portal venous system.

Enlargement of hilar periportal space: a sign of early cirrhosis at MR imaging

The purpose of this study was to determine whether the finding of an enlarged hilar periportal space is a sign for early cirrhosis at magnetic resonance (MR) imaging. Forty-one pathologically proved cirrhotic patients in the early stage of disease who did not show conventional imaging findings of cirrhosis (early cirrhosis group) and 47 patients without history of chronic liver diseases (control group) were included in this study. MR images were qualitatively and quantitatively evaluated for the presence of enlargement of the periportal space. Enlargement of the periportal space was seen in 98% of patients in the early cirrhosis group, while this finding was seen in 11% of patients in the control group (P < 0.0001). The mean value of the hilar periportal fat thickness was significantly greater (P < 0.0001) in the early cirrhosis group (15.5 +/- 6.2 mm) than in the control group (5.3 +/- 3.1 mm). The sensitivity, specificity, accuracy, and positive predictive value of this finding for the MR diagnosis of cirrhosis with a cutoff value of 10 mm were 93%, 92%, 92%, and 91%, respectively. Enlargement of the hilar periportal space is a helpful sign at MR imaging in the discrimination between normal and early cirrhotic livers.

Color Doppler applications in hepatic imaging

Color Doppler sonography is an important modality in the non-invasive evaluation of the liver. It is commonly used to evaluate vascular changes which accompany cirrhosis. Doppler techniques are also used to evaluate patients who have undergone liver transplantation or transjugular intrahepatic portosystemic shunt (TIPS) placement. This review describes the various applications of color Doppler in hepatic imaging.