• Tomohiro Ohira, Tomohisa Okuma, Toshiyuki Matsuoka, Yasuhiro Wada, Kenji Nakamura, Yasuyoshi Watanabe, and Yuichi Inoue.
• Department of Radiology, Osaka City University Graduate School of Medicine, Osaka, Japan.
• Cardiovasc Intervent Radiol. 2009 Jan 1; 32 (1): 114-20.

AbstractThe objective of this study was to evaluate the early changes after radiofrequency ablation (RFA) in VX2 rabbit tumors implanted into the back muscles by diffusion-weighted magnetic resonance (MR) imaging and (18)F-2-fluoro-2-deoxy-D-glucose positron emission tomography ((18)F-FDG PET). Percutaneous CT-guided RFA was conducted in seven rabbits with implanted VX2 tumors. VX2 tumors on the other side were untreated and served as the control. MR imaging was performed with a clinical 1.5-T instrument 2 days after RFA, and FDG-PET, using a high-resolution PET scanner for small animals, was obtained 3 days after the procedure. The mean apparent diffusion coefficient (ADC) values and radioactivity count of untreated and ablated tumors were calculated. Untreated VX2 tumors showed hyperintensity on T1-, T2-, and diffusion-weighted MR images, ring-enhanced on contrast-enhanced T1-weighted imaging, and ring-shaped FDG accumulation on FDG-PET. Ablated VX2 tumors showed slight hyperintensity on T1-, T2-, and diffusion-weighed images, slight enhancement on contrast-enhanced T1-weighted images, and low accumulation on FDG-PET. The ADC value of ablated VX2 tumors (1.52 +/- 0.24 x 10(-3) mm(2)/s) was significantly higher than that of untreated tumors (1.09 +/- 0.12 x 10(-3); p < 0.05). The tumor/muscle ratio of ablated tumors (0.5 +/- 0.3) was significantly lower than that of untreated tumors (11.6 +/- 3.2; p < 0.05). Histopathological examination confirmed the lack of viable tumor cells in the ablated lesions. The results indicate that both ADC value and FDG-PET are potentially useful markers for monitoring the early effects of RFA.

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