Image: An example of an MRI in a potential living liver donor demonstrating hepatic steatosis (yellow) of the whole liver (Photo courtesy of the University of Toronto).
New magnetic resonance imaging (MRI) contrast agents and pulse sequence techniques can be used to noninvasively evaluate the livers of potential live donors, according to a new review.
Researchers at the University of Toronto (Canada) conducted a review of studies that focusing on the role of state-of-the-art MRI-based techniques in the comprehensive evaluation of living donors in a single-visit. The techniques reviewed include assessment of the liver vasculature via MRI angiography; assessment of the biliary tract via conventional T2-weighted MRI cholangiography and T1-weighted gadoxetate disodium–enhanced MR cholangiography; and evaluation of hepatic steatosis via T2-corrected multiecho chemical shift–based water-fat separation MRI and high-speed T2-corrected multiecho MR spectroscopy (MRS).
Contrast-enhanced MR angiography (MRA), for example, permits hepatic arterial system visualization to the segmental level using gadopentetate dimeglumine as the contrast agent, providing a high signal-to-noise ratio due to its high T1 relaxation rate. Contrast-enhanced MRA has been shown to be as accurate as computerized tomography angiography (CTA) at detecting surgically important anatomic variants of the hepatic vasculature in donor candidates, with accuracy of 86%, 93%, and 68% for the hepatic artery, portal vein, and hepatic vein, respectively.
The increasing use of hepatocyte-specific contrast agent in liver MRI, such as gadobenate dimeglumine and gadoxetic disodium, can accurately display intrahepatic and extrahepatic biliary anatomy. A recent study classified normal and variant biliary systems correctly using a single-dose of gadoxetic disodium enhanced T1-weighted MRC, which could prove an alternative to CT cholangiogram for preoperative evaluation of donor candidates. Other studies show the quality of hepatobiliary phase images obtained using the CAIPIRINHA technique are significantly improved, which could enable gadoxetic disodium–enhanced T1-weighted MRC to provide a better visualization of biliary variants.
MRI techniques can also be used for noninvasive evaluation of hepatic steatosis by separating liver signal into its fat and water signal components first, and then calculating the hepatic fat fraction. MRI-measured hepatic fat fraction, which includes signal fat fraction and proton-density fat fraction, has a strong correlation with histologic grade. The researchers also reviewed MRI and MRS methods used for signal fat fraction and proton-density fat fraction measurement for the evaluation of hepatic steatosis. The review was published in the July 2017 issue of the American Journal of Roentgenology.
“Since the first adult-to-adult transplantation of a right liver lobe reported in 1994, the number of living-donor liver transplants has increased dramatically with good results, similar to those of cadaver liver transplantation,” said lead author Kartik Jhaveri, MD, of the Joint Department of Medical Imaging. “To guide safe harvesting of the graft from donors, an accurate preoperative evaluation of potential living liver donors for conditions that increase the donor's surgical risk is crucial.”
University of Toronto