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.