Intravoxel incoherent motion diffusion-weighted MRI for characterizing regional variability and monitoring serial changes of parameters in rabbit VX2 liver tumors.

ABSTRACT

PURPOSE: To characterize intravoxel incoherent motion (IVIM) parameters in different regions of interest (ROIs) of rabbit VX2 liver tumors during a follow-up of 4 weeks. MATERIALS AND METHODS: This study was approved by the Institutional Animal Care and Use Committee. In 18 VX2 liver tumor-bearing rabbits, IVIM DW imaging was serially performed at the 2nd, 3rd, and 4th week separately after tumor implantation at 1.5T by using 12 b values. Three ROIs were drawn on the apparent diffusion coefficient (ADC) maps, including the whole lesion, the visibly most restricted diffusion area (MRDA), and peripheral area of tumor. For each ROI of tumors, serial changes in ADC and D, D*, and f at three timepoints were calculated. The differences of IVIM parameters in different ROIs of tumors at each timepoint were compared. RESULTS: Serial measurements of f in all three ROIs (P = 0.000, P = 0.002, and P = 0.000), ADC for the whole lesion, MRDA (P = 0.000 and P = 0.024), and D for MRDA (P = 0.001) from the 2nd to 4th week illustrated a statistical difference. The overall comparison of ADC (P = 0.000, P = 0.014, and P = 0.000), D (P = 0.000, P = 0.001, and P = 0.000), and f (P = 0.001, P = 0.001, and P = 0.000) for three tumor regions at weeks 2, 3, and 4 showed significant differences. D* in all three ROIs at each timepoint showed no significant differences (P = 0.612, P = 0.723, and P = 0.699; 95% confidence interval 0.184-0.950). CONCLUSION: The peripheral area of tumor could be used as an alternative to the whole lesion as ROIs to assess the VX2 liver tumor with IVIM DW imaging, and in the period between weeks 2 and 3.