MR angiography of the portal venous system: techniques, interpretation, and clinical applications

ACG Clinical Guideline: Disorders of the Hepatic and Mesenteric Circulation

Disorders of the mesenteric, portal, and hepatic veins and mesenteric and hepatic arteries have important clinical consequences and may lead to acute liver failure, chronic liver disease, noncirrhotic portal hypertension, cirrhosis, and hepatocellular carcinoma. Although literature in the field of vascular liver disorders is scant, these disorders are common in clinical practice, and general practitioners, gastroenterologists, and hepatologists may benefit from expert guidance and recommendations for management of these conditions. These guidelines represent the official practice recommendations of the American College of Gastroenterology. Key concept statements based on author expert opinion and review of literature and specific recommendations based on PICO/GRADE analysis have been developed to aid in the management of vascular liver disorders. These recommendations and guidelines should be tailored to individual patients and circumstances in routine clinical practice.

Usefulness of three-dimensional magnetic resonance cholangiopancreatography with partial maximum intensity projection for diagnosing autoimmune pancreatitis

PURPOSE

To compare three-dimensional magnetic resonance cholangiopancreatography (MRCP) with/without partial maximum intensity projection (MIP) and endoscopic retrograde cholangiopancreatography (ERCP) in patients with autoimmune pancreatitis (AIP).

MATERIALS AND METHODS

Three-dimensional MRCP and ERCP images were retrospectively analyzed in 24 patients with AIP. We evaluated the narrowing length of the main pancreatic duct (NR-MPD), multiple skipped MPD narrowing (SK-MPD), and side branches arising from the narrowed portion of the MPD (SB-MPD) using four MRCP datasets: 5 original images (MIP₅), 10 original images (MIP₁₀), all original images (full-MIP), and a combination of these three datasets (a-MIP). The images were scored using a 3- or 5-point scale. The scores of the four MRCP datasets were statistically analyzed, and the positive rate of each finding was compared between MRCP and ERCP.

RESULTS

The median scores for SB-MPD on MIP₅ and a-MIP were significantly higher than those on MIP₁₀ and full-MIP. In other words, partial MIP is superior to full-MIP for visualization of detailed structures. The positive rate for SB-MPD on full-MIP was significantly lower than that on ERCP, whereas the positive rate on MIP₅, MIP₁₀, and a-MIP was not significantly different from that on ERCP. Moreover, the positive rate for NR-MPD and SK-MPD on the MRCP images was significantly higher than that on the ERCP images.

CONCLUSION

Partial MIP is useful for evaluating the MPD and is comparable with ERCP for diagnosing AIP.

Extrahepatic Portal Vein Obstruction in Children: Role of Preoperative Imaging

Aim:

Extrahepatic portal vein obstruction (EHPVO) is characterized by features of recent thrombosis or portal hypertension with portal cavernoma as a sequel of portal vein obstruction. Imaging of spleno-portal axis is the mainstay for the diagnosis of EHPVO. The aim of this study is to analyze the role of imaging in the preoperative assessment of the portal venous system in children with EHPVO.

Materials and Methods:

A hospital-based cross-sectional study was conducted on twenty children with EHPVO aged between 1 and 18 years over a period of 1 year. The children were evaluated clinically, followed by upper gastrointestinal endoscopy. Radiological assessment included imaging of the main portal vein, its right and left branches, splenic vein, and superior mesenteric vein using color Doppler ultrasonography (CDUSG) and magnetic resonance portovenogram (MRP). Evidence of portal biliopathy, status of collaterals, and possible sites for portosystemic shunt surgery were also examined.

Results:

All the patients presented in chronic stage with portal cavernoma and only one patient (5%) had bland thrombus associated with cavernoma. The CDUSG and MRPs had a sensitivity of 66.6-90% and 96.7% and specificity of 91.5% and 98.3% respectively with regard to the assessment of the extent of thrombus formation and flow in the portal venous system. Both the modalities were found to be complementary to each other in preoperative assessment of EHPVO. However, the sensitivity of MRP was slightly superior to CDUSG in detecting occlusion and identifying portosystemic collaterals and dilated intrahepatic biliary radicals.

Conclusion:

Results of the present study indicate that MRP is well suited and superior to CDUSG in the preoperative imaging of patients with EHPVO.

Assessment of Liver Perfusion by IntraVoxel Incoherent Motion (IVIM) Magnetic Resonance-Diffusion-Weighted Imaging: Correlation With Phase-Contrast Portal Venous Flow Measurements

OBJECTIVES

To prospectively verify, in vivo, Le Bihan's model of signal decay in magnetic resonance/diffusion-weighted imaging (intravoxel incoherent motion) in healthy liver parenchyma.

METHODS

Informed consent and institutional board approval were obtained. To measure both underfasting and postprandial conditions, apparent, slow, and fast diffusion (D*) coefficients and perfusion fraction of liver parenchyma, 40 healthy volunteers (19 women and 21 men) underwent a 3.0-T magnetic resonance imaging examination, including portal venous flow measurements by a 2-dimensional phase-contrast sequence, and multi-b diffusion-weighted imaging acquired before and 30 minutes after a 600-Kcal meal. Parameters were measured by fitting procedure with regions of interest drawn on the right liver lobe. Paired-sample t test was performed to search for any statistically significant difference between preprandial and postprandial values of each parameter and of portal flow. Pearson correlation coefficients were calculated to evaluate the relationship between portal flow increase and diffusion-weighted imaging parameter changes in postprandial conditions. Interobserver agreement for measurement of the intravoxel incoherent motion parameters was determined, both for preprandial and postprandial values.

RESULTS

Mean increase in postprandial portal flow was 98% (P < 0.0009). The t test did not show any statistically significant difference between the preprandial and postprandial values for apparent, slow diffusion coefficients and perfusion fraction (P ≥ 0.05), whereas a statistically significant postprandial increase (P < 0.01) of D* was detected. Correlation with portal venous flow increase at Pearson test was statistically significant for D* (P = 0.04) and nonsignificant for the other parameters. All the parameters showed wide variability, with a higher percent coefficient of variation for D*. Interobserver agreement was always greater than 0.70.

CONCLUSIONS

This study verifies Le Bihan's theory, confirming that in the liver, D* is influenced by perfusional changes related to portal venous flow.

Splanchnic venous thrombosis and pancreatitis

Pancreatitis is an inflammatory process with local and systemic manifestations. One such local manifestation is thrombosis in splanchnic venous circulation, predominantly of the splenic vein. The literature on this important complication is very sparse. This review offers an overview of mechanism of thrombosis, its pathophysiology, diagnosis, and management in the setting of acute as well as chronic pancreatitis.

Spontaneous portoazygos shunt in a patient with portal hypertension

We present a case of spontaneous portoazygos shunt in a patient with liver cirrhosis and portal hypertension. The shunt was incidentally detected by abdominal magnetic resonance imaging for routine evaluation of liver cirrhosis. Multiplanar reconstruction images demonstrated the portal vein communicating with the azygos vein that was dilated and tortuous along its course to the mediastinum. Although there has been a case of congenital portoazygos shunt reported in a neonate with multiple congenital anomalies, to the best of our knowledge, this is the first case of spontaneous portoazygos shunt developed in an adult with portal hypertension.

Portosystemic collateral vessels in liver cirrhosis: a three-dimensional MDCT pictorial review

PURPOSE

Portosystemic collateral vessels (PSCV) are a consequence of the portal hypertension that occurs in chronic liver diseases. Their prognosis is strongly marked by the risk of digestive hemorrhage and hepatic encephalopathy.

MATERIALS AND METHODS

CT was performed with a 16-MDCT scanner. Maximum intensity projection and volume rendering were systematically performed on a workstation to analyze PSCV.

RESULTS

We describe the PSCV according to their drainage into either the superior or the inferior vena cava. In the superior vena cave group, we found gastric veins, gastric varices, esophageal, and para-esophageal varices. In the inferior vena cava group, the possible PSCV are numerous, with different sub groups: gastro and spleno renal shunts, paraumbilical and abdominal wall veins, retroperitoneal shunts, mesenteric varices, gallbladder varices, and omental collateral vessels. Regarding clinical consequences esophageal and gastric varices are most frequently involved in digestive bleeding; splenorenal shunts often lead to hepatic encephalopathy; the paraumbilical vein is an acceptable derivation pathway for natural decompression of the portal system.

CONCLUSION

Knowledge of precise cartography of PSCV is essential to therapeutic decisions. MDCT is the best way to understand and describe the different types of PSCV.

Role of contrast-enhanced 3D magnetic resonance portography in evaluating portal venous system compared with color Doppler ultrasonography

AIM

The purpose of this study was to evaluate the capability of contrast-enhanced three-dimensional (3D) MR portography in detecting abnormal findings associated with the portal venous system compared with the results of color Doppler ultrasonography (CDUS).

MATERIALS AND METHODS

MR portography findings were retrospectively compared with the results of CDUS examinations in 161 patients, who were suspected of having portal venous system abnormalities. Portal venous vessels were divided into main 5 groups including the main portal vein, its left and right intrahepatic branches, splenic vein and superior mesenteric vein. Imaging findings were classified as normal, occluded, or partially thrombosed. Results of clinical and imaging follow-up examinations including CDUS, MR portography or angiography, if available, were used as a proof of final diagnosis. The potential sites of varicose veins and collateral vessels were also examined by both imaging methods.

RESULTS

Vascular abnormalities were identified in 79 of 161 patients. There was a statistically significant agreement between the results of MR portography and CDUS in evaluating portal venous system (kappa = 0.871, P < 0.05). The sensitivity of MR portography was slightly superior to CDUS in detecting partially thrombosis and occlusion in the main portal venous vessels. In addition, MR portograms were superior to CDUS in the management of patients with portal hypertension by identifying portosystemic collaterals more adequately, and clearly demonstrated portal venous vessels that cannot be visualized at CDUS.

CONCLUSION

Results of present study indicates that contrast-enhanced 3D MR portography is well suited and superior to CDUS in the management of patients with portal hypertension.

Prospective intraindividual comparison between respiratory-triggered balanced steady-state free precession and breath-hold gradient-echo and time-of-flight magnetic resonance imaging for assessment of portal and hepatic veins

The purpose of this study was to compare respiratory-triggered balanced steady-state free precession (bSSFP) with breath-hold contrast-enhanced dynamic two-dimensional (2D) gradient-echo (GRE) and time-of-flight (TOF) magnetic resonance imaging (MRI) for portal and hepatic vein visualization and assessment of portal and hepatic venous variants. Sixty patients with liver disease underwent nonenhanced bSSFP and contrast-enhanced GRE, bSSFP, and TOF imaging. Contrast-to-noise ratios (CNRs) for portal and hepatic veins were measured. Two readers rated the quality of portal and hepatic vein visualization on a 5-point Likert scale. The diagnostic performance of each MRI series in the detection of portal and hepatic venous variants was assessed in 40/60 patients who also underwent contrast-enhanced multidetector-row computed tomography (MDCT). CNRs for portal and hepatic veins were highest on contrast-enhanced bSSFP images. Image quality of portal and hepatic veins was rated higher for nonenhanced bSSFP than for contrast-enhanced GRE (p<0.03) and TOF (p<0.003) and higher for contrast-enhanced than for nonenhanced bSSFP (p<0.003). Compared with MDCT, portal and hepatic venous variants were identified with an accuracy of 99% on bSSFP images, with an excellent interobserver agreement (kappa=0.97). Compared with MDCT, presence of surgically important portal and hepatic venous anatomical variants can be predicted with high accuracy on bSSFP images.

CT-maximum intensity projection is a clinically useful modality for the detection of gastric varices

AIM

To evaluate the efficacy of CT-maximum intensity projection (CT-MIP) in the detection of gastric varices and their inflowing and outflowing vessels in patients with gastric varices scheduled to undergo balloon-occluded retrograde transvenous obliteration (B-RTO).

METHODS

Sixteen patients with endoscopically confirmed gastric varices were included in this study. All patients were evaluated with CT-MIP using three-dimensional reconstructions, before and after B-RTO.

RESULTS

CT-MIP clearly depicted gastric varices in 16 patients (100%), the left gastric vein in 6 (32.5%), the posterior gastric vein in 12 (75.0%), the short gastric veins in 13 (81.3%), gastrorenal shunts in 16 (100%), the hemiazygos vein (HAZV) in 4 (25.0%), the pericardiophrenic vein (PCPV) in 9 (56.3%), and the left inferior phrenic vein in 9 patients (56.3%). Although flow direction itself cannot be determined from CT-MIP, this modality provided clear images of the inflowing and the outflowing vessels. Moreover, in one patient, short gastric veins were not seen on conventional angiographic portography images of the spleen, but were clearly revealed on CT-MIP.

CONCLUSION

We suggest that CT-MIP should be considered as a routine method for detecting and diagnosing collateral veins in patients with gastric varices scheduled for B-RTO. Furthermore, CT-MIP is more useful than endoscopy in verifying the early therapeutic effects of B-RTO.

Types and frequencies of biliary tract variations associated with a major portal venous anomaly: analysis with multi-detector row CT cholangiography

PURPOSE

To retrospectively determine whether major portal venous variation was more frequently associated with biliary variants, with consideration of the types and frequencies of biliary tract variations in the right and left liver lobes.

MATERIALS AND METHODS

Before undergoing computed tomographic (CT) cholangiography, patients gave informed consent. The retrospective research protocol was approved, and informed consent was waived by the ethics committee. Forty-four patients aged 29-80 years who underwent multi-detector row CT cholangiography had a major portal vein variation in which the main portal vein diverged into the common trunk of the left portal vein and right anterior sectorial portal vein. One hundred fifty-eight consecutive patients aged 26-89 years who did not have this variation served as the control group. Three radiologists retrospectively evaluated the confluence pattern of the bile duct, the relationship between this pattern and the portal vein, and the major branching pattern of the portal vein. Pearson chi2 and Fisher exact tests were performed to identify significant differences between the two patient groups.

RESULTS

The classic hilar confluence pattern, where the right posterior sectorial duct connects supraportally with the right anterior sectorial duct, was less frequent in the patients with the portal vein variation than in the control subjects (32% vs 73%, P < .05). The following biliary tract variations were identified more frequently in the variation group than in the control group (P < .05): right posterior sectorial duct joining left hepatic duct with a supraportal course (34% vs 12%), right posterior sectorial duct joining right anterior sectorial duct with an infraportal course (13% vs 4%), right posterior sectorial duct following an infraportal course (23% vs 8%), and left lateral segmental ducts caudal to the umbilical portion of the portal vein (14% vs 3%). The right hepatic duct, which receives all biliary ducts from the right lobe, was significantly less frequently developed in the variation group (46% vs 79%, P < .05). In addition, retroportal bile ducts were seen in four patients with the portal vein variation (P < .05).

CONCLUSION

Bile duct configurations in patients with portal vein variation were significantly different from those in control subjects.

Gadolinium-Enhanced Phase-Contrast Magnetic Resonance Portography

PURPOSE

The purpose of this study was to investigate the effect and usefulness of gadolinium-chelated contrast medium in phase-contrast magnetic resonance (MR) portography.

METHODS

Twenty-six patients (21 men, 5 women; aged 34 to 79 years, mean 62 years) underwent respiratory-triggered 3-dimensional phase-contrast portography before and after administration of gadolinium in a 1.5T MR unit. Coronal maximum intensity projection (MIP) images of the portal vein were reconstructed and compared to conventional arterial portograms regarding visualization. Signal-to-noise ratio (SNR) and portal vein-to-liver contrast-to-noise ratios (CNR) of main, right, right anterior, right posterior, left portal veins, and umbilical portion were measured on both non-enhanced and gadolinium-enhanced images and compared.

RESULTS

Portal veins and branches were more clearly visualized on the gadolinium-enhanced than on the non-enhanced images. Compared to arterial portography, gadolinium-enhanced portography showed similar performances in visualization, except in the right posterior branch and left portal vein. No severe image degradation from respiration was experienced. SNR was significantly higher on the gadolinium-enhanced than on non-enhanced images except in the right anterior branch. CNR was significantly higher on the gadolinium-enhanced than on the non-enhanced images at all measured locations.

CONCLUSIONS

Administration of gadolinium improves the SNR and CNR of phase-contrast portography and visualization of the portal vein. The phase-contrast technique with gadolinium enhancement can be used to evaluate the portal vein as a supplemental technique.

Three-dimensional multi-detector row CT portal venography in the evaluation of portosystemic collateral vessels in liver cirrhosis

Multi-detector row computed tomography (CT) offers distinct advantages over traditional spiral CT. Multi-detector row CT scanners are faster and allow thinner collimation than single-detector row spiral CT scanners. The use of multi-detector row CT combined with postprocessing of the imaging data with a variety of three-dimensional reformatting techniques (eg, maximum intensity projection, shaded surface display, volume rendering) allows creation of vascular maps whose quality equals or exceeds that of maps created at classic angiography for many applications. Three-dimensional multi-detector row CT portal venography can help determine the extent and location of portosystemic collateral vessels (eg, left gastric vein, short gastric vein, esophageal and paraesophageal varices, splenorenal and gastrorenal shunts, paraumbilical and abdominal wall veins) in patients with liver cirrhosis and is probably the optimal imaging technique in this setting.

Noninvasive assessment of portomesenteric venous thrombosis: current concepts and imaging strategies

Rapid, noninvasive imaging strategies, especially multidetector spiral CT and CT angiography (CTA) as well as gadolinium-enhanced MR angiography (MRA), have facilitated early diagnosis of splanchnic venous thrombosis, a potentially lethal cause of intestinal ischemia. Single breath-hold volumetric acquisitions permit superior temporal and contrast resolution while eliminating motion artifact and suppressing respiratory misregistration. Increased spatial resolution is aided by thinner slice collimation. These cross-sectional imaging techniques are becoming a preferred noninvasive alternative to conventional selective mesenteric angiography with delayed imaging for venous evaluation and should be considered the primary diagnostic modalities for evaluating patients with high clinical suspicion of nonsurgical mesenteric ischemia.

Magnetic resonance angiography of the pediatric abdomen and pelvis

Although abdominal and pelvic vascular disease is much less common in children than in adults, MR angiographic techniques widely used in adults can also be readily applied in the pediatric population with suspected vascular disease. MR techniques, equipment, and image analysis software are in a continual state of development and refinement. Given the advantages of MR angiography (i.e., its absence of ionizing radiation, capability to obtain images without iodinated contrast material, and limited invasiveness), the applications of MR angiography in the pediatric abdomen and pelvis are likely to continue to increase.

Assessment of portal venous system patency in the liver transplant candidate: a prospective study comparing ultrasound, microbubble-enhanced colour Doppler ultrasound, with arteriography and surgery

AIM

To determine the role of microbubble-enhanced colour Doppler ultrasound (CDUS) in assessing portal venous patency prior to liver transplantation.

MATERIALS AND METHODS

Over a 2-year period, all patients with chronic liver disease undergoing routine pre-transplant CDUS examination in whom the portal venous system was inadequately demonstrated were recruited to the study. CDUS was performed in 368 patients and 33 patients (9%) were recruited. A repeat CDUS examination following an intravenous bolus injection of the microbubble contrast agent Levovist (Schering Healthcare AG, Berlin, Germany) was performed. Diagnostic confidence was recorded on a free linear analogue scale for both examinations. Findings were compared with indirect portography and surgery.

RESULTS

Of the 33 patients with sub-optimal baseline examinations, improvement in portal vein visualization was achieved in 31 patients (94%). Median diagnostic confidence increased from 50% (interquartile range 30-60) to 90% (interquartile range 75-98) (P < 0.001) following administration of Levovist. Overall accuracy of portal vein assessment using microbubble-enhanced CDUS in 15 patients in whom a definitive diagnosis was made within 2 months was 87%.

CONCLUSION

Microbubble-enhanced CDUS is a simple, inexpensive adjunct to standard pre liver transplant screening of the portal vein. It is particularly helpful in patients with end-stage cirrhosis who are at high risk of portal vein thrombosis and in whom the conventional examination is sub-optimal.

Mesenteric venous thrombosis: diagnosis and noninvasive imaging

Mesenteric venous thrombosis is an uncommon but potentially lethal cause of bowel ischemia. Several imaging methods are available for diagnosis, each of which has advantages and disadvantages. Doppler ultrasonography allows direct evaluation of the mesenteric and portal veins, provides semiquantitative flow information, and allows Doppler waveform analysis of the visceral vessels; however, it is operator dependent and is often limited by overlying bowel gas. Conventional contrast material-enhanced computed tomography (CT) allows sensitive detection of venous thrombosis within the central large vessels of the portomesenteric circulation and any associated secondary findings; however, it is limited by respiratory misregistration, motion artifact, and substantially decreased longitudinal spatial resolution. Helical CT and CT angiography, especially when performed with multi-detector row scanners, and magnetic resonance (MR) imaging, particularly gadolinium-enhanced MR angiography, enable volumetric acquisitions in a single breath hold, eliminating motion artifact and suppressing respiratory misregistration. Helical CT angiography and three-dimensional gadolinium-enhanced MR angiography should be considered the primary diagnostic modalities for patients with a high clinical suspicion of mesenteric ischemia. Conventional angiography is reserved for equivocal cases at noninvasive imaging and is also used in conjunction with transcatheter therapeutic techniques in management of symptomatic portal and mesenteric venous thrombosis.

Congenital and acquired anomalies of the portal venous system

Knowledge of the normal anatomy, most frequent variants, and congenital and acquired anomalies of the portal venous system is of great importance for liver surgery and interventional procedures such as creation of transjugular intrahepatic portosystemic shunts. Radiologic studies of the portal venous system include color Doppler ultrasonography (US), computed tomography (CT), magnetic resonance imaging, and arterial or direct portography. Among the most common branching variants of the portal vein are trifurcation, right anterior portal branch arising from the left portal vein, and right posterior portal branch arising from the main portal vein. Agenesis of the right or left portal vein is the most frequently reported congenital anomaly. Venous collateral vessels due to portal hypertension and cavernous transformation of the portal vein are best evaluated with cross-sectional imaging. Intrahepatic portosystemic, arterioportal, and arteriosystemic fistulas and associated perfusion anomalies have characteristic features at dual-phase helical CT. Color Doppler US is the single most useful tool for demonstration of aneurysms of the portal venous system and bland or neoplastic portal vein thrombosis. CT is also the best means of evaluating gas in the portal venous system, which is no longer an ominous sign and must be differentiated from aerobilia.

Assessment of portal hypertension in humans

Patients suspected of having portal hypertension (either by clinical history, physical examination, or previous diagnosis) should undergo ultrasonography and upper gastrointestinal endoscopy. Ultrasonography, preferably using the duplex technique, can disclose the patency of the portal venous system, the presence of signs of portal hypertension (splenomegaly, portocollateral vessels, repermeabilization of the umbilical vein, and so forth) and provide additional information about liver, biliary, or pancreatic diseases that may be the cause of portal hypertension. Endoscopy can assess the presence and size of gastroesophageal varices, the appearance of the variceal wall, and the presence and severity of portal hypertensive gastropathy. Patients showing a patent portal vein should have hepatic vein catheterization to evaluate the presence of presinusoidal, sinusoidal, or postsinusoidal portal hypertension. Patients in whom presinusoidal portal hypertension is suspected (those having esophageal varices with an HVPG below 10 mm Hg) should have liver biopsy and percutaneous transhepatic measurement of portal pressure. In sinusoidal portal hypertension, the results of endoscopy and HVPG measurement are decisive for the therapeutic management of the patients. The authors' results indicate that, before starting prophylactic therapy with beta-blockers, all patients should undergo at least an hepatic vein catheterization to assess HVPG; it would be preferable to have a variceal pressure measurement also. These measurements must be repeated 3 to 4 weeks after the final dose of therapy has been reached to assess the risk of variceal bleeding or rebleeding.

Superior diagnostic strength of combined contrast enhanced MR-angiography and MR-imaging compared to intra-arterial DSA in liver transplantation candidates

To evaluate the diagnostic value of combined contrast enhanced MRA (ce-MRA) and MRI compared to that of intra-arterial DSA (i.a.DSA) in liver transplantation, transjugular porto-systemic (TIPSS) and spleno-renal shunt candidates. 50 patients in the workup for liver transplantation underwent ce-MRA/MRI and i.a.DSA within a three days interval. Both examinations were assessed with respect to vessel anatomy and patency of the arterial, portal venous, porto-systemic collateral and systemic venous system. The results were compared with the intra-operative findings when available. Malignancy detection in ce-MRA/MRI and i.a.DSA were compared. There are no significant differences for the arterial part of the vascular supply to the liver that is important for transplantation. Although the differences for the portal system are not significant, the difference between the two techniques is of clinical importance because i.a.DSA failed to detect portal vein occlusion in 4 patients. Ce-MRA is significantly better for the detection of collaterals (p < 0.001) and the assessment of the inferior vena cava, the hepatic and the renal veins (p < 0.001). Although the detection of liver malignancy is poor in both techniques, ce-MRA/MRI is superior to i.a.DSA. This study shows that a one step diagnostic approach with a combination of ce-MRA and MRI is a valuable radiological tool with a superior diagnostic strength compared to i.a.DSA in the liver transplantation and shunt candidate. Therefore, ce-MRA/MRI should replace i.a.DSA in these patients groups.

Gadolinium enhanced three-dimensional magnetic resonance portography with subtraction

The aim was to evaluate a subtraction technique for breath-hold gadolinium enhanced three-dimensional magnetic resonance portography (3D-MRP). 26 patients with gastric and/or duodenal varices related to portal hypertension were investigated by 3D-MRP with two phase acquisitions. A partial volume maximum intensity projection (MIP) image after subtracting selective arterial phase images from subsequent portal venous phase images (subtraction 3D-MRP) was compared with the partial volume MIP without subtraction (non-subtraction 3D-MRP) to assess visualization of the portal vein and its collaterals. Subtraction 3D-MRP depicted excellent visualization of the portal vein, although this was not significantly better than non-subtraction 3D-MRP. However, subtraction 3D-MRP gave superior visualization of portal collaterals, with effective suppression of arterial and renal signal intensities, compared with non-subtraction 3D-MRP (p<0.001).

Contrast-enhanced three-dimensional MR portography

Three-dimensional (3D) magnetic resonance (MR) portography with contrast material enhancement is a fast means of evaluating the portal venous system that has some advantages over currently used modalities, such as digital subtraction angiography, helical computed tomography, ultrasonography, and nonenhanced MR angiography with time-of-flight and phase-contrast techniques. With contrast-enhanced 3D MR portography, a first-pass study of the mesenteric vasculature is performed after rapid bolus injection of gadopentetate dimeglumine; a 3D fast field echo sequence is used, which can demonstrate the intrahepatic and extrahepatic portal venous system clearly. Repeated sequences after administration of gadopentetate dimeglumine allow separate demonstration of the splanchnic arteries and portomesenteric veins. The images are reconstructed by means of maximum-intensity projection postprocessing, and a subtraction technique can be used to eliminate arterial enhancement and demonstrate portosystemic shunts. The coronal source images simultaneously demonstrate parenchymal lesions of the liver, pancreas, biliary tract, and spleen. This technique is clinically indicated in portosystemic shunt, portal vein thrombosis, hepatocellular carcinoma, pancreatobiliary tumor, hepatic vein obstruction, differentiation of splanchnic arterial from portal venous disease, and gastrointestinal hemorrhage. Its limitations include allergic reactions to contrast media, inappropriate positioning of the 3D acquisition slab, respiratory motion artifacts, and pseudodissection.