Biphasic spiral computed tomography versus digital subtraction angiography for evaluation of arterial thrombosis after orthotopic liver transplantation

Imaging panorama in postoperative complications after liver transplantation

The liver is the second most-often transplanted solid organ after the kidney, so it is clear that liver disease is a common and serious problem around the globe. With the advancements in surgical, oncological and imaging techniques, orthotopic liver transplantation has become the first-line treatment for many patients with end-stage liver disease. Ultrasound, and Doppler are the most economical and cost-effective imaging modalities for evaluating postoperative fluid collections and vascular complications. Computed tomography (CT) is used to confirm the findings of ultrasound and look for pulmonary complications. Magnetic resonance imaging (MRI) is used for the diagnosis of biliary complications, bile leaks and neurological complications. This article illustrates the imaging options for diagnosing the various complications that can be encountered in the postoperative period after liver transplantation.

The importance of portal venous blood flow in ischemic-type biliary lesions after liver transplantation

Ischemic-type biliary lesions (ITBL) are the most frequent cause of nonanastomotic biliary strictures after liver transplantation. This complication develops in up to 25% of patients, with a 50% retransplantation rate in affected patients. Traditionally, ischemia-reperfusion injury to the biliary system is considered to be the major risk factor for ITBL. Several other risk factors for ITBL have been identified, including the use of liver grafts donated after cardiac death, prolonged cold and warm ischemic times and use of University of Wisconsin preservation solution. In recent years however, impaired microcirculation of the peribiliary plexus (PBP) has been implicated as a possible risk factor. It is widely accepted that the PBP is exclusively provided by blood from the hepatic artery, and therefore, the role of the portal venous blood supply has not been considered as a possible cause for the development of ITBL. In this short report, we present three patients with segmental portal vein thrombosis and subsequent development of ITBL in the affected segments in the presence of normal arterial blood flow. This suggests that portal blood flow may have an important contribution to the biliary microcirculation and that a compromised portal venous blood supply can predispose to the development of ITBL.

Multi-detector computed tomography angiography of the hepatic artery in liver transplant recipients

PURPOSE

To evaluate the ability of multi-detector row computed tomography angiography (CTA) in detecting hepatic artery complications in the follow-up of liver transplant patients, performing volume-rendering as reconstruction technique.

MATERIAL AND METHODS

The anatomy of hepatic artery was studied in 27 liver transplant recipients with a four-row CT scanner using the following parameters: collimation, 1 mm; slice width, 1 mm; table feed, 6-8 mm/s; spiral reconstruction time, 0.5 s; reconstruction interval, 0.5 mm; mAs, 160; kVp, 120. Before the study, the patients received 1000 ml of water as oral contrast agent to produce negative contrast in the stomach and the small bowel. A non-ionic contrast medium was infused intravenously at a rate of 5 ml/s with a bolus tracking system. Volume-rendering of hepatic artery was performed with the 3D Virtuoso software.

RESULTS

The celiac trunk, the hepatic artery, and the right and left hepatic arteries were successfully displayed in high detail in all patients. Side branches, including small collaterals, and hepatic artery anastomosis could also be readily visualized. Volume-rendered CTA detected six hepatic artery stenoses, two hepatic artery thromboses, and two intrahepatic pseudoaneurysms. In two cases, CT detected hepatic artery stenosis with a diameter reduction of less than 50%, while digital subtraction angiography showed a normal artery.

CONCLUSION

Volume-rendered multi-detector CTA is a promising non-invasive technique, since it allows images of high quality to be generated with excellent anatomical visualization of the hepatic artery and its complications in liver transplant recipients.

Three-dimensional multislice helical computed tomography with the volume rendering technique in the detection of vascular complications after liver transplantation

BACKGROUND

Hepatic artery stenosis and thrombosis are common complications in liver transplant patients. Digital subtraction angiography (DSA) has served as the gold standard to make this diagnosis. More recently, three-dimensional helical computed tomographic arteriography (3D CTA) with maximum intensity projection and shaded surface display techniques has been compared with DSA. The purpose of this study was to determine whether 3D CTA with the volume rendering technique is a useful and accurate tool in the detection of vascular complications after liver transplantation.

METHODS

Thirty-five consecutive liver transplant patients underwent 3D CTA with volume rendering technique. The standard of reference was DSA for 20 patients and imaging and clinical follow-up for 15 patients. Two blinded reviewers evaluated the axial and 3D CTA images in consensus.

RESULTS

3D CTA with volume rendering technique detected 10 hepatic artery stenoses, six hepatic artery thromboses, two hepatic artery pseudoaneurysms, two splenic artery aneurysms, two portal vein stenoses, and four redundant hepatic arteries. In one case computed tomography (CT) detected a moderate hepatic artery stenosis, while conventional angiography showed a normal artery. The sensitivity of CT for detecting vascular lesions was 100%, specificity was 89% (8 of 9), accuracy was 95% (19 of 20), positive predictive value was 92% (11 of 12), and negative predictive value was 100% (8 of 8).

CONCLUSIONS

3D CTA is a useful and accurate noninvasive technique for detection of vascular complications in liver transplant patients.

Vascular and extravascular complications of liver transplantation: comprehensive evaluation with three-dimensional contrast-enhanced volumetric MR imaging and MR cholangiopancreatography

OBJECTIVE

Our purpose was to evaluate a comprehensive MR imaging strategy for recipients of liver transplants that relies on dynamic interpolated three-dimensional (3D) MR imaging for simultaneous vascular, parenchymal, and extrahepatic imaging.

MATERIALS AND METHODS

Twenty-three consecutive adult patients underwent 30 MR imaging examinations between 2 days and 99 months (mean, 15 months) after transplantation using a breath-hold 3D gradient-echo sequence (TR range/TE range, 3.7-4.7/1.8-1.9; flip angle, 12-30 degrees ) with an intermittent fat-saturation pulse and interpolation in the section-select direction to enable pixel size 3 mm or less in all dimensions. Unenhanced and triphasic contrast-enhanced 3D imaging (average dose, 0.13 mmol/kg of gadopentetate dimeglumine) was performed. A subset of patients (n = 13) also underwent MR cholangiopancreatography using half-Fourier single-shot turbo spin-echo imaging. MR imaging examinations were correlated with digital subtraction angiography (n = 8), contrast-enhanced cholangiography (n = 9), sonography (n = 13), and histopathology (n = 14).

RESULTS

MR imaging revealed abnormal findings in 27 (90%) of 30 examinations, including vascular disease in nine, biliary complications in four, and evidence of intra- or extra-hepatic hepatocellular carcinoma recurrence in six. Digital subtraction angiography confirmed seven MR angiography examinations but suggested disease overestimation in one. Contrast-enhanced cholangiography confirmed findings of MR cholangiopancreatography in seven cases but suggested disease underestimation in two.

CONCLUSION

Dynamic interpolated 3D MR imaging combined with dedicated MR cholangiopancreatography can provide a comprehensive assessment of vascular, biliary, parenchymal, and extrahepatic complications in most recipients of liver transplants.

Contrast media research

This selective review highlights research in contrast media development and application in the field of diagnostic radiology in 1998 and 1999. The focus is on research published in Investigative Radiology, supplemented with work from other publications in the few areas not extensively covered by the journal. Studies continue to be performed, although at a low level, examining safety issues. Most preclinical investigations have focused on MR and ultrasound agents. In MR, the research effort is concentrated on the development of targeted agents; in ultrasound, work is focused on the characterization of basic contrast mechanisms. The demonstration of clinical applications is still dominated by work with MR, both in disease models and human investigations. The use of extracellular gadolinium chelates to enhance visualization of blood vessels (the field of contrast-enhanced MR angiography) is the largest single new clinical application of contrast media to emerge in several years. New clinical applications continue to be pursued with contrast media in CT, ultrasound, and x-ray angiography. As intravenously injected ultrasound contrast agents come to market, trials demonstrating clinical applications and subsequent scientific publications will increase in number.

Gadolinium-enhanced 3D MRA prior to isolated hepatic perfusion for metastases

PURPOSE

Isolated hepatic perfusion (IHP) is a new treatment for patients with isolated unresectable liver metastases, which can result in a partial or complete response in approximately 75% of patients. Preoperative knowledge of hepatic arterial anatomy is important to adequately perfuse the liver. Digital subtraction angiography (DSA) is currently used to identify the hepatic arterial anatomy. The purpose of this study was to determine if MR angiography (MRA) could replace DSA prior to IHP.

METHOD

Twenty-seven patients scheduled to undergo IHP underwent MRA with a contrast-enhanced 3D time-of-flight gradient echo sequence. Both maximal intensity projections (MIPs) and source coronal images were used to evaluate the images. The results of the MRA were interpreted by two readers who were blinded to the surgical results. The first 17 patients also underwent DSA, and a separate comparison was made with those results. Anatomy was characterized as either normal hepatic arteries (NHAs), normal vasculature with an accessory left hepatic artery (aLHA), or a replaced right hepatic artery (rRHA).

RESULTS

MRA correctly detected all 22 patients with NHAs but also identified 6 aLHAs, of which only 2 were confirmed surgically. MRA correctly detected all five rRHAs. MIP images alone accurately depicted the hepatic arterial anatomy in only 9 of 27 (33%), usually because significant vessels were not visualized or their origin could not be determined. Source coronal images were required to accurately determine the anatomy in all patients. Among the 17 patients who underwent DSA, MRA detected 14 of 14 with NHA and 3 of 3 with rRHA. Six aLHAs were identified by MRA and five were confirmed by DSA.

CONCLUSION

Enhanced 3D MRA is an accurate method of depicting the hepatic arterial supply. In comparison to surgery, MRA overestimates the number of aLHAs, but this may be because these small vessels are not detected at surgery. Based on the results of this study, DSA has been replaced by MRA in the planning of IHP at our institution. A better display of MRA images is needed as MIP images were usually insensitive for the small caliber arteries supplying the liver.