Gadolinium-enhanced magnetic resonance venography of the portal venous system prior to transjugular intrahepatic portosystemic shunts and liver transplantation. Original investigation

The role of noninvasive vascular imaging in splanchnic and mesenteric pathology

Traditionally, catheter angiography (CA) has been the mainstay of diagnosis for mesenteric arterial diseases. However, CA is invasive and is associated with complications that result from the procedure itself, depending on the experience of the operators, site of vascular access, ionized radiation that could be significant when combined with interventional procedures, and administered contrast material. During the past 2 decades, technical improvements in computed tomography (CT) and magnetic resonance hardware and methods have contributed new, noninvasive tools, specifically CT angiography (CTA) and 3-dimensional gadolinium-enhanced magnetic resonance angiography (3D Gd-MRA). This article outlines the current applications, strengths, and weaknesses of CTA and 3D Gd-MRA in imaging of the mesenteric vessels.

Magnetic resonance angiography versus endoscopy for the assessment of gastroesophageal varices in biliary atresia

This study was undertaken to compare magnetic resonance angiography (MRA) and gastrointestinal tract endoscopy (ENDO) for detecting varices in postoperative biliary atresia (BA) patients. Thirty-four BA patients were divided into groups according to age and liver function; group 1: 1-4 years old; group 2: 5-9 years old; group 3: over 10 years old; group A: normal liver function; and group B: moderate liver dysfunction. All subjects had MRA and ENDO. ENDO showed esophageal or gastric varices in 16 of 34 subjects. MRA depicted gastroesophageal vessels in 12 of 16 cases with varices on ENDO (sensitivity: 75%). Two subjects appeared to have varices on MRA that could not be confirmed on ENDO. Sixteen subjects had no varices on ENDO and normal MRA (specificity: 88.9%). Sensitivities and specificities of MRA for detecting varices were 20 (1/5) and 100% (6/6) in group 1 (n = 11), 100 (6/6) and 66.7% (4/6) in group 2 (n = 12), 100 (5/5) and 100% (6/6) in group 3 (n = 11), 100 (8/8) and 100% (9/9) in group A (n = 17), 50 (4/8) and 77.8% (7/9) in group B (n = 17), respectively. From these findings, MRA was not accurate in BA patients less than 10 years old or with moderate liver dysfunction. Therefore, periodic endoscopic examination is recommended for the accurate assessment and follow-up of varices in postoperative BA patients.

Evaluation of Living Liver Transplant Donors: Method for Precise Anatomic Definition by Using a Dedicated Contrast-enhanced MR Imaging Protocol

Liver transplantation from a living donor involves removal of part of the donor liver in a fashion that does not endanger its vascular supply or metabolic function. The radiologist plays an important role in evaluation of the living donor to define the conditions under which graft donation is contraindicated and to identify anatomic variations that may alter the surgical approach. In the past, diagnostic work-up of the donor involved costly and invasive tests. Currently, dynamic contrast material-enhanced computed tomography and magnetic resonance (MR) imaging are the imaging tests performed, each of which has advantages and limitations. MR imaging performed with liver-specific and extravascular contrast agents may be used as a single imaging test for comprehensive noninvasive evaluation of living liver transplant donors. MR imaging provides valuable information about variations in the vascular and biliary anatomy and allows evaluation of the hepatic parenchyma for diffuse or focal abnormalities.

MR portal venography: preliminary results of fast acquisition without contrast material or breath holding

RATIONALE AND OBJECTIVES

The authors performed this study to evaluate the feasibility of using the steady-state free precession (SSFP) sequence to perform magnetic resonance (MR) venography of the portal venous system without the use of contrast material or breath holding.

MATERIALS AND METHODS

Eleven patients underwent MR venography with the SSFP technique. Coronal three-dimensional images were obtained with respiratory triggering. Contrast material and respiratory suspension were not used. All patients had recently undergone at least one other imaging study (conventional angiography, transhepatic portal venography, ultrasound, or contrast-enhanced computed tomography), and these findings were correlated with those from MR venography. The structures evaluated were the main portal vein, right portal vein, left portal vein, superior mesenteric vein, and splenic vein.

RESULTS

MR venography with SSFP accurately depicted the status of these veins in all cases except one. In this patient, MR venography depicted portal vein thrombus but could not indicate that it was tumor thrombus.

CONCLUSION

MR venography with SSFP accurately depicted the portal venous system in 10 of 11 patients without the use of respiratory suspension or contrast material.

Diagnostic techniques in assessing vessels of the gastrointestinal tract

Vascular disorders of the gastrointestinal tract include a variety of different underlying diseases, thus requiring different and, in many cases, more than one imaging procedure. Only a knowledge of the newest developments in vascular imaging techniques with all the possibilities and limits will ensure a time- and cost-effective, accurate and reliable diagnosis. In many acute cases and also as a screening procedure, ultrasound in combination with colour Doppler and duplex sonography, plays an important role in setting the right course for further imaging techniques, and can provide the correct diagnosis in many cases.Depending on the most prominent symptoms and the expected disease, the right choice of technique saves valuable time. Computed tomography (CT) and magnetic resonance imaging (MRI) are cross-sectional imaging techniques that not only demonstrate lesion vascularization, but also provide information about neighbouring structures and complications in an understandable and demonstrable way. The use of angiography as an invasive tool should be limited to cases where a high temporal and spatial resolution is necessary to make the diagnosis or where therapeutic interventions are also likely to be performed within the same setting. For the diagnosis of gastrointestinal vascular diseases, often no generally valid recommendation can be given, since the impact of all imaging techniques will depend on the examiner's experience, the technical equipment and on their 24-h availability in a hospital. This chapter tries to give some information about the inherent limits and indications of the different imaging techniques, as well as the newest study results concerning the most frequent vascular diseases of the gastrointestinal tract.

Optimization of scantiming in abdominal breathhold contrast-enhanced MRA: an empirical guideline

The objective of this study to determine a suitable scan timing scheme in contrast enhanced MRA for the depiction of the arterial, the portal and the systemic venous system in the abdomen with maximum signal intensity in healthy subjects and in patients with cirrhosis. The signal intensity in the aorta, hepatic artery, portal vein, left renal vein and the supra- and infrarenal IVC were measured in 40 consecutive orthotopic liver transplantation candidates with cirrhosis and 20 healthy renal donors in a bolus triggered arterial scan and after 30, 60, 90 and 150 s respectively. The aorta and hepatic artery showed the highest signal intensity on the arterial scan. The portal and left renal vein showed the highest signal intensity after 30 s, the suprarenal IVC after 60 s and the infrarenal IVC after 90 s. No significant differences were found between healthy subjects and patients with cirrhosis. The arterial, portal and systemic venous system in the abdomen can be visualized selectively with maximum signal intensity by proper timing of the scans, hereby reducing redundant scans. Scanning at just the right time to achieve optimal vessel opacification can be promoted by using data from this study. The proposed scan scheme is suitable for subjects with and without cirrhosis.

Magnetic resonance imaging and diseases of the liver and biliary tract. Part 2. Magnetic resonance cholangiography and angiography and conclusions

Magnetic resonance cholangiography (MRC) relies on the strong T2 signal from stationary liquids, in this case bile, to generate images. No contrast agents are required, and the failure rate and risk of serious complications is lower than with endoscopic retrograde cholangiopancreatography (ERCP). Data from MRC can be summated to produce an image much like the cholangiogram obtained by using ERCP. In addition, MRC and conventional MRI can provide information about the biliary and other anatomy above and below a biliary obstruction. This provides information for therapeutic intervention that is probably most useful for hilar and intrahepatic biliary obstruction. Magnetic resonance cholangiography appears to be similar to ERCP with respect to sensitivity and specificity in detecting lesions causing biliary obstruction, and in the diagnosis of choledocholithiasis. It is also suited to the assessment of biliary anatomy (including the assessment of surgical bile-duct injuries) and intrahepatic biliary pathology. However, ERCP can be therapeutic as well as diagnostic, and MRC should be limited to situations where intervention is unlikely, where intrahepatic or hilar pathology is suspected, to delineate the biliary anatomy prior to other interventions, or after failed or inadequate ERCP. Magnetic resonance angiography (MRA) relies on the properties of flowing liquids to generate images. It is particularly suited to assessment of the hepatic vasculature and appears as good as conventional angiography. It has been shown to be useful in delineating vascular anatomy prior to liver transplantation or insertion of a transjugular intrahepatic portasystemic shunt. Magnetic resonance angiography may also be useful in predicting subsequent variceal haemorrhage in patients with oesophageal varices.

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.

Magnitude subtraction vs. complex subtraction in dynamic contrast-enhanced 3D-MR angiography: basic experiments and clinical evaluation

Magnitude subtraction and complex subtraction in dynamic contrast-enhanced three-dimensional magnetic resonance (3D-MR) angiography were compared using a phantom and 23 human subjects. In phantom studies, complex subtraction showed far better performance than magnitude subtraction, especially for longer echo times, with thicker slices, and without fat suppression. With complex subtraction, non-fat-suppressed studies showed contrast-to-noise ratios comparable to those in fat-suppressed studies. In human subjects, complex subtraction was superior to magnitude subtraction in 9 subjects, but comparable to magnitude subtraction in 14 subjects. There were no cases in which magnitude subtraction was superior to complex subtraction. Although the differences observed in human studies when complex subtraction was applied with thinner slices, shorter echo times, and the fat-suppression technique were not as pronounced as those seen in phantom studies, complex subtraction should be performed in dynamic contrast-enhanced 3D-MR angiography because there are no drawbacks in complex subtraction. Further research is necessary to assess the feasibility of dynamic contrast-enhanced 3D-MR angiography without fat suppression in human subjects using complex subtraction, as suggested by the results of phantom studies. If it is found to be feasible, dynamic contrast-enhanced 3D-MR angiography without fat suppression using complex subtraction may prove to be a robust technique that eliminates the need for shimming and can reduce the acquisition time. J. Magn. Reson. Imaging 1999;10:813-820.