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

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.

Fifteen rats with liver implantation of 30 rhabdomyosarcomas were treated with combretastatin 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 (ADClow), 500, 750, and 1000 seconds/mm2 (ADChigh), 0, 500, and 1000 seconds/mm2 (ADC3b), and 0-1000 seconds/mm2 (ADC10b) for tumor, liver, therapeutic necrosis, and phantoms were compared and validated with ex vivo microangiographic and histopathologic findings.

Except ADClow between 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.

Advantageous over postmortem DWI, in vivo DWI provides a noninvasive easy-performing tool for distinguishing between liver, viable tumor, and necrosis. ADClow and ADChigh better reflect tissue perfusion and water diffusion, respectively.