QuickScan Reviews in Radiology, March 31 2009

Objective: To determine if diffusion-weighted imaging (DWI) combined with conventional dynamic contrast-enhanced MRI examination is more sensitive than dynamic contrast-enhanced MRI alone in the detection of small hepatocellular carcinomas (HCCs). Design: Prospective analysis. Participants/Methods: This study was comprised of 37 patients with chronic liver disease suspected of having small HCCs measuring 2 cm detected on basis of clinical findings, CT, or MRI. Thirty patients had surgical confirmation, 6 via percutaneous biopsy and 1 via characteristic angiographic findings and iodized oil CT. Four of the 30 surgically confirmed cases were via liver transplantation. Follow-up dynamic contrast-enhanced MRI examinations were preformed for a minimum of 6 months. MRI examinations were preformed on 1.5T systems. Sequences included T2-weighted turbo spin-echo and T1-weighted fast low-angle shot. DWI consisted of a single shot spin-echo planar sequence with a b-value of 500 seconds/mm2. Dynamic images were obtained prior to and following IV gadolinium administration during late arterial, portal, and equilibrium phases at 20 to 25, 70 to 90, and 180 seconds, respectively. Criteria for HCC on dynamic contrast-enhanced MRI included arterial phase enhancing nodule with washout on portal venous and equilibrium phases or nonenhancing nodule with mosaic pattern, peritumoral capsule, or fatty metamorphosis. Lesions that were only seen on the arterial phase and not on any other unenhanced or enhanced images were referred to as hepatic artery phase enhancement-only lesions. Criteria for HCC on combined diffusion-weighted and dynamic contrast-enhanced MRI included a hyperintense nodule on DWI, which did not have characteristics of a cyst, hemangioma, metastasis, or other specific appearance on the dynamic contrast-enhanced portion of the examination. The images were reviewed by 2 gastrointestinal radiologists. Two separate image sets were reviewed: the unenhanced and dynamic contrast-enhanced images and the unenhanced and dynamic contrast-enhanced images combined with DWIs. A receiver operating characteristic (ROC) curve analysis was performed for each imaging set. Results: 47 small lesions were detected. There was an increased sensitivity in detection of small HCC for the combined DWI and dynamic contrast-enhanced images compared to dynamic contrast-enhanced images alone. The area under the ROC curve was also higher for all small lesions. Seven of the 47 lesions were only detected on the DWI. The positive predictive values were slightly higher for both observers when DWI was added to the dynamic contrast-enhanced protocol. Reviewer's Comments: The results of this study are useful in that they illustrate the potential added benefit of including DWI in the standard abdominal MRI protocol. This can increase the sensitivity for the detection of small HCC lesions in those with chronic liver disease as shown in this study. A limitation reported in this study was that not all of the lesions were confirmed with liver transplantation specimens.