Diffusion-weighted MR: Therapeutic evaluation after chemoembolization of VX-2 carcinoma implanted in rabbit liver

Rationale and Objectives. The study goal was to evaluate the ability of diffusion-weighted imaging (DWI) in assessing the viability of rabbit liver VX-2 tumor after transcatheter arterial chemoembolization (TACE). Materials and Methods. VX-2 tumors were grown in the livers of 19 rabbits, and chemoembolization was performed. MR imaging was acquired 1 week after TACE. The rabbits were killed for histologic investigation immediately after MR imaging, and the proportion of viable tumor was calculated based on histopathologic examination. Apparent diffusion coefficient (ADC) values were measured in viable and necrotic tumor portion, and were compared using the paired Student's t test. Results. Viable tumors were absent (n = 3), less than 5% (n = 6), and 5% or more (n = 10) at pathology examination. On DWI, three tumors with no viable portion were interpreted as having no viable portion, but three of six tumors with a viable portion of less than 5% were considered as having no viable portion. The mean ADC values of necrotic and viable tumor were 1.653 +/- 0.126 mm(2)/sec and 0.883 +/- 0.407 mm(2)/sec (b = 1000 sec/mm(2)), respectively, and the ADC values of necrotic tumors were significantly greater than those in viable tumors (p <.01). Conclusion. Although DWI is a useful tool for assessing tumor viability, viable tumor may not be detected on DWI when it is too small.