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: DWla) and 0, 150, 250, 400, 600, and 800 seconds/mm2 (second sequence: 9W2a). Apparent diffusion- coefficients (ADCs) of the hepatic parenchyma were calculated on ADC maps. Noisescaled single-point ADCs were calculated for each sequence from b = 400 seconds/mm'. Results: ADCs resulted significantly lower in cirrhotic patients compared to controls using both OW 1 a (mean 1.14 0.20 x 10 3mm2/second vs. 1.54 _ 0.12 x 10-3mm2/ second; P < 0.0001) and DW2a (mean 0.91 0.18 x 10 3mm2/second vs. 1.04 0.18 x 10-3mm2/second; P= 0.0089). DW 1 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 x 10 3mm2/second vs. 1.13 *_ 0.17 x 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.