Rapid dynamic contrast-enhanced magnetic resonance imaging of the liver and portal vein

Left-sided portal hypertension

Left-sided portal hypertension is a rare clinical syndrome which may lead to bleeding from isolated gastric varices. Pancreatic disease is the most common etiology. Left-sided portal hypertension should be considered in the presence of gastrointestinal bleeding with normal liver function and unexplained splenomegaly. It may be difficult to diagnose this entity both endoscopically and radiologically. While splenectomy is the treatment of choice for cases complicated by variceal bleeding, there is no consensus on the treatment of asymptomatic patients. The prognosis of left-sided portal hypertension mainly depends on the underlying etiology.

Magnetic resonance angiography of portal collateral pathways after hepatic portoenterostomy in biliary atresia: comparisons with endoscopic findings

BACKGROUND/PURPOSE

This study was undertaken to assess the usefulness of magnetic resonance angiography (MRA) in detecting varices and to investigate the possibility of avoiding routine endoscopy after surgery for biliary atresia (BA).

METHODS

The subjects are 21 patients who have undergone periodical MRA since 1996. The esophageal and gastric vessels were investigated as the sites of potential development of collateral vessels. The collateral vessels on MRA were compared with endoscopic findings.

RESULTS

(1) Detection of collateral vessels: of 21 patients examined, 9 patients had 12 varices. MRA depicted collateral vessels in all of the 12 varices (sensitivity, 100%). However, all MRA findings, but one was compatible with endoscopic findings (specificity, 92.9%). Outside of a series of these 21 patients, there were 3 additional patients who had undergone endoscopic treatments previously with success, and in whom esophageal vessels were not depicted on MRA, but endoscopy showed remnant varices. (2) Time-dependent relationship between the appearance of collateral vessels and varices: of 4 varices that appeared after the start of MRA, 3 esophageal varices were found endoscopically simultaneously with or after delineation of collateral vessels on MRA. In the remaining patient, varices were found enodscopically 6 months before the MRA delineation, because a simultaneous MRA was not performed in this case. All these varices were in the early stage.

CONCLUSIONS

MRA was highly sensitive and specific in detecting esophagogastric collateral vessels of the portal venous system. An endoscopic examination is unnecessary until collateral vessels are seen on MRA after surgery for BA.

Detection of thrombosis in the portal venous system: comparison of contrast-enhanced MR angiography with intraarterial digital subtraction angiography

PURPOSE

To determine whether intraarterial digital subtraction angiography (DSA) can be replaced by contrast material-enhanced magnetic resonance (MR) angiography in the assessment of patency or thrombosis of the portal venous system in patients with portal hypertension.

MATERIALS AND METHODS

Thirty-six patients with portal hypertension underwent contrast-enhanced MR angiography and intraarterial DSA for assessment of the portal venous system. The images were evaluated for vessel patency or thrombosis of the portal, splenic, or superior mesenteric vein.

RESULTS

Of the 101 vessels evaluated, 42 were thrombosed. Overall sensitivity, specificity, and accuracy for the detection of thrombosis were 100%, 98%, and 99%, respectively, for MR angiography and 91%, 100%, and 96%, respectively, for DSA; differences between the imaging methods were not statistically significant. Only in four patients with six vessels (6%) were there discordant findings between MR angiography and DSA.

CONCLUSION

Noninvasive contrast-enhanced MR angiography has the potential to replace intraarterial DSA as the standard method to assess the whole portal venous system.

Hepatic blood supply: comparison of optimized dual phase contrast-enhanced three-dimensional MR angiography and digital subtraction angiography

PURPOSE

To optimize and determine the value of dual-phase contrast material-enhanced three-dimensional (3D) magnetic resonance (MR) angiography for preoperative evaluation of the blood supply to the liver.

MATERIALS AND METHODS

Dual phase 3D MR angiography of the hepatic arteries and portal vein was performed in 140 patients. In 80 patients, the value of fat saturation, digital image subtraction, an anticholinergic agent, and a high-caloric meal were evaluated. In the next 60 patients, MR angiographic and digital subtraction angiographic (DSA) image quality and diagnostic value were compared.

RESULTS

Fat-saturated images were of significantly better quality (P < .01) than non-fat-saturated images. Digital image subtraction was useful in only 23 of 40 patients. The injection of an anticholinergic agent was superfluous, whereas administration of a high-caloric meal helped in demonstration of the superior mesenteric artery and portal vein. Classification on MR angiograms of the arterial blood supply was correct in 57 of 60 patients. All arterial and portal venous lesions were seen on MR angiograms, and MR angiograms had a significantly higher subjective image-quality ranking than did DSA images in the evaluation of the portal vein (P < .05).

CONCLUSION

Fat saturation and use of a high-caloric meal improve the results of MR angiography of hepatic vessels. MR angiography was comparable to DSA for evaluation of the arterial system and was superior for demonstration of the portal vein; therefore, MR angiography could replace intraarterial DSA.

T2-weighted and dynamic enhanced MRI in acute pancreatitis: comparison with contrast enhanced CT

The purpose of this study was to compare T2-weighted and dynamic contrast enhanced MRI with contrast enhanced CT in patients with severe acute pancreatitis. Thirty-two patients were examined using axial T2-weighted spin-echo imaging (TR 1801, TE 15/90) and a multi-slice rapid gradient-echo sequence (TR 135, TE 4, FA 80 degrees) (FLASH) in axial and coronal planes. Fifteen 5 mm axial slices at 10 mm intervals were acquired during a single breath-hold of 19 s before, and at 10 and 40 s after a bolus injection of Gd-DTPA. Additional FLASH images in the coronal plane were obtained 2 min after injection of contrast medium. MR was compared with contemporary enhanced CT by two blinded observers who scored pancreatic viability and the content of intra and extra-pancreatic fluid collections. The presence of gas, calcification and haemorrhage was noted. Abnormalities in adjacent organs, evidence of vascular occlusion and indicators of aetiology were also recorded. MR and CT were concordant in distinguishing viable pancreatic tissue from areas of necrosis. MR appeared to be more effective than CT in characterizing the content of fluid collections and in demonstrating gall stones, although CT remains superior in detecting flecks of gas and calcification. MR carries some advantages over CT and can be regarded as an alternative primary technique in patients with severe pancreatitis.

Comparison of dynamic contrast enhanced MRI and Doppler ultrasound in the pre-operative assessment of the portal venous system

The purpose of this study was to compare dynamic contrast enhanced MRI (DCEMR) with Doppler ultrasound (US) in the assessment of portal venous anatomy and to analyse the causes of discrepancy. Over a 1 year period, 97 patients undergoing assessment prior to hepatic surgery underwent imaging of the liver and portal venous system using US with colour and spectral Doppler and MRI with axial T2 weighted spin echo (SE) and coronal oblique T1 weighted rapid gradient echo (GRE) imaging before and immediately after bolus injection of Gd-DTPA (0.1 mmol kg-1). When the US and MRI findings were discrepant, the images were reviewed by two observers and compared with surgical findings. US and DCEMR were concordant in 90 patients (portal vein patent in 80, occluded in 10). In three patients with cirrhosis and gross ascites the portal vein was reported as occluded on US and patent on MRI; surgery confirmed the MRI findings. In one patient the portal vein was patient on US but not on MRI, but there was a 3 week interval between the examinations. In three patients the portal vein was patent on US, but MRI detected occlusion of intrahepatic portal vein branches in two, and encasement of an intrahepatic branch in the third case. Spontaneous splenorenal shunts were seen in 15 patients only on MRI; varices were seen in 39 patients on MRI and in 22 patients on US. Both US and DCEMR contribute to the pre-operative assessment of the portal venous system. MRI provides additional information over US in assessing intrahepatic portal branches and detecting varices and splenorenal shunts, and is recommended for all surgical candidates and in patients with abnormal portal venous anatomy and equivocal US findings.

Evaluation of portal MR angiography using superparamagnetic iron oxide

The purpose of our research was to determine the effects of superparamagnetic iron oxide on MR imaging of the portal venous system. Eight piglets were examined in deep anaesthesia and respiratory arrest using a time-of-flight magnetic resonance fast low angle shot, two-dimensional angiography sequence at 1.5T, MR angiograms were acquired precontrast and after intravenous administration of a cumulative dose of 10, 20 and 40 mumol/kg SHU 555A, a superparamagnetic iron oxide contrast agent for MR imaging with a particle size of 60 nm. For each dose, two subsequent sets of scans were obtained and reconstructed by a maximum-intensity-projection algorithm. Hepatic parenchymal and portal venous signal intensities were measured, and portal vein contrast calculated for each set of scans. All examinations were visually rated as to portal vein contrast and homogeneity by two blinded observers. Receiver operating characteristics of both observers were analyzed. The contrast agent reduced hepatic parenchymal signal in a dose-dependent way. After a cumulative dose of 10 mumol iron oxide, hepatic parenchymal signal intensity decreased to 63 +/- 6% (average of measurements at 4 and 14 minutes, mean +/- standard error of the mean), after 20 mumol to 24 +/- 3%, and after 40 mumol to 12 +/- 1% of control. Intravascular signal in the left main portal vein branch increased to 117 +/- 6%, 127 +/- 10%, and 133 +/- 9% of control, respectively. The contrast-to-noise ratio of the portal vein improved (521 +/- 90%, 891 +/- 178%, and 995 +/- 201% of control in the left portal vein main branch). Intravascular signal intensities increased slightly. The combined effect improved contrast of the portal vein stem and its branches. Receiver operating characteristics analysis documented dose-dependency of contrast medium effects on portal venous contrast and intravascular homogeneity. Visual rating also indicated a positive effect on portal venous contrast. The superparamagnetic iron oxide agent improved portal venous contrast with surrounding hepatic parenchyma in this normal animal model, and could potentially result in more accurate diagnosis of portal venous pathology.

Transient increased segmental hepatic enhancement distal to portal vein obstruction on dynamic gadolinium-enhanced gradient echo MR images

The purpose of the present study was to demonstrate the frequency of occurrence of transient increased segmental hepatic enhancement distal to portal vein obstruction in patients with a lobar (main branch) portal vein obstruction. MR images of all patients with main and lobar branch portal vein obstruction examined by dynamic gadolinium enhanced gradient echo MR images between December 1990 and July 1994 were reviewed retrospectively. All studies included T2-weighted imaging, T1-weighted spoiled gradient echo 'fast low angle shot ([FLASH])', and postgadolinium enhanced FLASH imaging at 1, 45, and 90 sec and 10 min. Fourteen patients were identified with portal vein obstruction which included: six with main portal and right and left branch occlusion, six with right lobar, and two with left lobar. In the six patients with main portal vein obstruction, enhancement on 1-sec postgadolinium FLASH images was homogenous (three patients), diffusely heterogeneous (two patients), or peripherally hyperintense (one patient). In eight of eight patients with isolated obstruction of the right or left lobar portal vein, transient-increased segmental enhancement distal to portal vein occlusion was observed on immediate postcontrast images. Relatively high signal intensity of the involved segments was present on 1-sec images and liver parenchymal enhancement became more homogeneous by 45 to 90 sec in all cases. In conclusion, transient-increased segmental enhancement occurred in eight of eight patients with isolated right or left portal vein occlusion. We postulate that this effect occurs due to increased hepatic arterial blood flow in the presence of portal vein obstruction.

Magnetic resonance imaging in the detection of focal liver lesions: comparison of dynamic contrast-enhanced TurboFLASH and T2 weighted spin echo images

In a previous study using dynamic contrast-enhanced TurboFLASH (DCETF) for demonstration of the portal venous system we found that this technique showed more liver lesions than T2 weighted spin echo (T2WSE) imaging in the same patients. In this study we have formally compared axial T2WSE images (TR 2000, TE 45/90) with TurboFLASH images (TR 135, TE 4, FA 80 degrees) acquired immediately after bolus injection of Gd-DTPA (0.1 mmol kg-1) in 41 patients referred for hepatic magnetic resonance imaging (MRI) prior to surgery for liver lesions. The images of each sequence were independently reviewed by two observers. The lesions were counted and each sequence was scored for conspicuity, level of artefact and subjective image quality. Contrast-to-noise ratios using user defined regions of interest were calculated. Significantly more lesions were seen on DCETF (n = 186) images than on T2WSE (n = 123) images (p < 0.001). Lesion conspicuity was equal in 53% of cases, better on DCETF in 36% and better on T2WSE in 11%. Contrast-to-noise ratios were significantly higher on DCETF images (p < 0.05). DCETF imaging provided a substantial improvement in lesion detection compared with T2WSE imaging.

Dynamic MRI of the pancreas--gadolinium enhancement in normal tissue

The purpose of this study was to measure signal enhancement over time in the normal pancreas after intravenous bolus infection of gadolinium-DTPA (Schering Health Care Ltd) (Gd-DTPA). Data was obtained from 25 patients with no evidence of pancreatic disease before, immediately after and over a 2 min period following injection of Gd-DTPA (Magnevist 0.2 ml per kg). Scans were obtained using a turboFLASH sequence which allows 11 slices to be acquired during a single breathhold period of 19 s. Five mm thick slices were acquired in the coronal/oblique plane at 0.5 mm intervals. A pre-contrast block of slices was obtained followed by dynamic post-contrast scanning with the first of four acquisitions beginning 12-15 s after bolus injection. A 10 s interval between each acquisition was selected to allow the patients to breathe. Signal intensity for each acquisition was measured for the pancreatic head and tail and also for the liver. All values were normalized to fat. Marked enhancement of the pancreas was seen in all cases with peak enhancement occurring in the first and second post-contrast acquisition. The pancreatic duct was more easily seen after contrast injection.

Comparison of MR and CT scanning in severe acute pancreatitis: initial experiences

Magnetic resonance imaging was performed at 1.0 T in seven patients with severe acute pancreatitis. A T2-weighted spin echo sequence and a breath-hold multislice rapid gradient echo sequence (TurboFLASH) were used in each patient. TurboFLASH imaging was performed before and after intravenous gadopentetate-dimeglumine (Gd-DTPA). All MRI images were compared with a recent contrast-enhanced CT scan. Postgadolinium MRI was equivalent to contrast-enhanced CT in differentiating viable pancreatic parenchyma from areas of pancreatic necrosis. MRI identified the presence of gas in a case of pancreatic abscess but failed to identify small foci of pancreatic calcification demonstrated in one case by CT. MRI was also equivalent to CT in assessing the location and extent of peripancreatic inflammatory changes and fluid collections. However, MRI, particularly the T2-weighted spin echo, was superior to CT in characterizing the complex nature of such inflammatory changes in one case. Initial experience suggests that MRI is a valuable technique in assessing patients with severe acute pancreatitis.