Relevance of b-values in evaluating liver fibrosis: A study in healthy and cirrhotic subjects using two single-shot spin-echo echo-planar diffusion-weighted sequences

Purpose To investigate the relevance of increasing b‐values in evaluating liver fibrosis through the agreement of two diffusion‐weighted (DW) sequences. Materials and Methods A total of 29 cirrhotic patients and 29 healthy volunteers were studied on a 1.5T system. Two single‐shot spin‐echo echo‐planar sequences were acquired using sets of increasing b‐values: 0, 150, 250, and 400 seconds/mm2 (first sequence: DW1a) and 0, 150, 250, 400, 600, and 800 seconds/mm2 (second sequence: DW2a). Apparent diffusion coefficients (ADCs) of the hepatic parenchyma were calculated on ADC maps. Noise‐scaled single‐point ADCs were calculated for each sequence from b = 400 seconds/mm2. Results ADCs resulted significantly lower in cirrhotic patients compared to controls using both DW1a (mean 1.14 ± 0.20 × 10−3mm2/second vs. 1.54 ± 0.12 × 10−3mm2/second; P < 0.0001) and DW2a (mean 0.91 ± 0.18 × 10−3mm2/second vs. 1.04 ± 0.18 × 10−3mm2/second; P = 0.0089). DW1 and DW2, respectively significantly differed in diagnostic performance at receiver operating characteristic (ROC) curve analysis (P = 0.003), showing AUCs of 0.93 (sensitivity 89.7%, specificity 100%) and 0.73 (sensitivity 62.1%, specificity 79.3%), respectively. Noise‐scaled single‐point ADCs showed a progressive convergence to similar values in cirrhotic and healthy livers at b = 800 seconds/mm2 (1.12 ± 0.27 × 10−3mm2/second vs. 1.13 ± 0.17 × 10−3mm2/second). Conclusion A DW sequence is accurate in assessing liver fibrosis using intermediate (400 seconds/mm2) rather than high (800 seconds/mm2) maximum b‐values, but after proper recalculation of ADCs the effects of perfusion rather than diffusion should be considered responsible for the higher accuracy at lower b‐values. J. Magn. Reson. Imaging 2008;28:411–419. © 2008 Wiley‐Liss, Inc.