Diffusion weighted MRI of osteoid osteomas: Higher ADC values after radiofrequency ablation

• After RFA of osteoid osteomas, significantly increased ADC values and decreased DCE MRI signal intensities were demonstrated.
• Low spatial resolution of diffusion weighted imaging limited delineation of ablation areas.

PurposeFeasibility of diffusion weighted MRI (DWI) pre- and post-radiofrequency ablation (RFA) in patients with osteoid osteoma (OO).Material and methodsTen patients (1 female, 24 ± 9 years) received RFA of OO (mean size 8.7 ± 3.2 mm). Two OO recurred, in one of these a second RFA was performed. A 1.5 T DWI (b = 50, 400, and 800 s/mm2) and a fat saturated DCE MRI were obtained the day before and after RFA. In DWI, the mean apparent diffusion coefficient (ADC) was recorded. With DCE MRI, signal-to-noise ratio, contrast-to-noise ratio, absolute signal intensity (SI), relative SI, and SI ratio were documented. All parameters were compared pre- and post-RFA using paired Wilcoxon rank test.ResultsADC values were significantly higher post-ablation, 1.6 ± 0.5 μm2/ms versus 1.3 ± 0.6 μm2/ms (p < 0.05). Perfusion was significantly reduced after ablation [SNR, CNR, SI, %SI, and SI OO/SI muscle]; post-RFA: 55 ± 13, 27 ± 20, 757 ± 534, 102 ± 16, and 1.6 ± 0.2; pre-RFA: 88 ± 37, 65 ± 22, 1038 ± 755, 226 ± 51, and 2.0 ± 0.5 (p < 0.05).DiscussionDWI is feasible in OO. ADC values increased and contrast enhancement decreased after RFA of OO. This may be explained by RFA-induced necrosis and devascularization.