Diffusion-Weighted MR Superior to T2-Weighted MR Imaging for Detection of Focal Liver Lesions; Equal for Characterization

The objective of a recent study was to compare DW and standard breath-hold T2-weighted MR imaging in the detection and characterization of focal liver lesions (FLL).

The study has concluded that more liver lesions were detected using diffusion-weighted (DW) MR imaging when compared to standard breath-hold T2-weighted images, while both sequences were comparable for lesion characterization in this study.

Methodology
This retrospective analysis was comprised of 53 patients. MR imaging was performed using a 1.5-Tesla system. DW MR images were obtained utilizing fat-suppressed, single shot echoplanar sequence using b values of 0, 50, and 500 sec/mm2. Unenhanced T1- and T2-weighted, and dynamic-enhanced T1-weighted images were also obtained and reviewed by two radiologists.

DW images with b values of 0 and 50 sec/mm2 were used for lesion detection. DW images with b values of 0 and 500 sec/mm2 were used to characterize the lesions. Lesions considered benign were hyperintense on T2-weighted images and on DW images with a b value of 0 sec/mm2, which subsequently showed decreased signal at a b value of 500 sec/mm2.

A lesion was felt to be malignant if it demonstrated mild to moderately hyperintense signal on T2-weighted images and DW images with a b value of 0 sec/mm2, which subsequently remained hyperintense at a b value of 500 sec/mm2, with a lower apparent diffusion coefficient (ADC).

Results of the Study
There was a significantly higher detection rate of both benign and malignant lesions using DW imaging. More malignant liver lesions were detected with DW imaging than with T2-weighted imaging. When accounting for lesion size, DW imaging performed better than T2-weighted imaging in detecting malignant lesions measuring between 1 and 3 cm in size. There was no significant difference in the detection of lesions measuring >=3 cm.

DW imaging was equally effective at detecting lesions located in the right lobe or in the left lobe, whereas T2-weighted imaging was not as effective in detecting lesions in the left lobe. Regarding lesion characterization, both DW images and T2-weighted images were more accurate in characterizing malignant as opposed to benign lesions. The mean ADC values of benign lesions were found to be significantly higher than those of malignant lesions.

Conclusions
DW MR imaging was superior to T2-weighted imaging for FLL detection and was equal to T2-weighted imaging for FLL characterization.

Reviewer’s Comments
The results of this study are useful in demonstrating a promising role of DW imaging in the evaluation of FLL. As demonstrated in this study, more malignant lesions were detected with DW imaging than with T2-weighted imaging, especially those measuring between 1 and 3 cm in size.

However, these two sequences were comparable in the characterization of malignant as opposed to benign lesions. A limitation noted in this study was that pathologic confirmation was not available for most of the patients and/or lesions.

Author: John C. Sabatino, MD, MSD

Reference
Parikh T, Drew SJ, et al. Focal Liver Lesion Detection and Characterization With Diffusion-Weighted MR Imaging: Comparison With Standard Breath Hold T2-Weighted Imaging. Radiology; 2008; 246 (March): 812-822: