Diffusion-weighted MRI of hepatic tumor in rats: Comparison between in vivo and postmortem imaging acquisitions

Abstract

Purpose: To determine the feasibility of in vivo diffusion-weighted imaging (DWI) to distinguish between normal liver, viable tumor and necrosis compared to postmortem DWI in a rat model with vascular-targeting treatment. Materials and Methods: Fifteen rats with liver implantation of 30 rhabdomyosarcomas were treated with combret-astatin A-4-phosphate (CA4P) at 10 mg/kg. Two days after treatment, T2-weighted imaging, precontrast T1-weighted imaging, postcontrast T1-weighted imaging, and DWI were performed in vivo and postmortem with a 1.5T scanner. Apparent diffusion coefficients (ADCs) calculated from DWIs with b values of 0, 50, and 100 seconds/mm2(ADClob), 500, 750, and 1000 seconds/mm2 (ADChigh), 0,500, and 1000 seconds/mm2 (ADC 3b), and 0-1000 sec-onds/mm2 (ADC10b) for tumor, liver, therapeutic necrosis,and phantoms were compared and validated with ex vivo microangiographic and histopathologic findings. Results: Except ADClowbetween tumor and necrosis, in vivo ADCs successfully differentiated liver, viable tumor, and necrosis (P < 0.05). Compared to in vivo outcomes, postmortem ADCs significantly dropped in tumor and liver (P < 0.05) except ADChigh of tumor, but not in necrosis and phantoms. Compared to ADClow, ADChigh was less affected by vital status. Conclusion: Advantageous over postmortem DWI, in vivo DWI provides a noninvasive easy-performing tool for distinguishing between liver, viable tumor, and necrosis. ADClowand ADChigh better reflect tissue perfusion and water diffusion, respectively. © 2009 Wiley-Liss, Inc.