Sci-Fri AM(1): Imaging-08: Improved Diffusion Weighted MR Imaging of Liver in Normal Subjects

Abstract

The aim of this study was to perform reliable measurements of the diffusion (D) and perfusion ( D * ) coefficients and perfusion fraction (f) for normal liver using IVIM model. Six volunteers considered to have normal liver underwent DW imaging at 1.5 Tesla. A respiratory triggered diffusion‐weighted single‐shot echo‐planar MRI sequence was performed. The diffusion gradients were applied in the slice select direction and the b values used in the protocol were: 0, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 650 and 800 s / mm 2 . Diffusion decays for all regions of interest (ROIs) were analyzed using a Levenberg‐Marquardt nonlinear least‐squares fit to the IVIM model equation and the parameters D, f, and D * were obtained. Diffusion coefficients and perfusion fraction maps were calculated on a pixel‐by‐pixel basis as well and color overlaid onto the corresponding anatomical images ( b =0 s / mm 2 ). No significant difference in results was observed between the whole‐liver ROIs and the peripherally located 100 pixel ROIs. To within experimental error, all patients had the same values of D ( 1.041±0.105 mm 2 / s ), D * ( 54.97±14.92 mm 2 / s ), and f (43.11±4.06 %). This shows that there are no gradual variations across the liver, as long as areas that contain large blood vessels are excluded. By increasing both the number and the range of b‐values used in the protocol we were able to get more consistent results than previously reported in the literature. Correct values for D, D * and f for normal liver are critically necessary when evaluating any distribution of patients, normal or abnormal.