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/mm 2 (first sequence: DW1a) and 0, 150, 250, 400, 600, and 800 seconds/mm 2 (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/mm 2 . Results ADCs resulted significantly lower in cirrhotic patients compared to controls using both DW1a (mean 1.14 ± 0.20 × 10 −3 mm 2 /second vs. 1.54 ± 0.12 × 10 −3 mm 2 /second; P < 0.0001) and DW2a (mean 0.91 ± 0.18 × 10 −3 mm 2 /second vs. 1.04 ± 0.18 × 10 −3 mm 2 /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/mm 2 (1.12 ± 0.27 × 10 −3 mm 2 /second vs. 1.13 ± 0.17 × 10 −3 mm 2 /second). Conclusion A DW sequence is accurate in assessing liver fibrosis using intermediate (400 seconds/mm 2 ) rather than high (800 seconds/mm 2 ) 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.