Magnetic resonance-guided focused ultrasound for the treatment of painful bone metastases: role of apparent diffusion coefficient (ADC) and dynamic contrast enhanced (DCE) MRI in the assessment of clinical outcome.

PURPOSE: To assess the correlation between functional MRI, including ADC values obtained from DWI and DCE, and clinical outcome in patients with bone metastases treated with MRgFUS.

METHODS AND MATERIALS: Twenty-three patients with symptomatic bone metastases underwent MRgFUS treatment (ExAblate 2100 system InSightec) for pain palliation. All patients underwent clinical and imaging follow-up examinations at 1, 3 and 6 months after treatment. Visual Analog Scale (VAS) score was used to evaluate treatment efficacy in terms of pain palliation while ADC maps obtained by DWI sequences, and DCE data were used for quantitative assessment of treatment response at imaging. Spearman Correlation Coefficient Test was calculated to assess the correlation between VAS, ADC and DCE data.

RESULTS: All treatments were performed successfully without adverse events. On the basis of VAS score, 16 (69.6 %) patients were classified as complete clinical responders, 6 (26.1 %) as partial responders and only one (4.3 %) was classified as a non-responder. The mean VAS score decreased from 7.09 ± 1.8 at baseline to 2.65 ± 1.36 at 1 month, 1.04 ± 1.91 at 3 months and 1.09 ± 1.99 at 6 months (p < 0.001). Baseline mean ADC value of treated lesions was 1.05 ± 0.15 mm(2)/s, increasing along follow-up period (1.57 ± 0.27 mm(2)/s 1st month; 1.49 ± 0.3 mm(2)/s 3rd month; 1.45 ± 0.32 mm(2)/s 6th month, p < 0.001). Non perfused volume (NPV) was 46.4 at 1 month, 45.2 at 3 months and 43.8 at 6 months. Spearman Coefficient demonstrated a statistically significant negative correlation between VAS and ADC values (ρ = -0.684; p = 0.03), but no significant correlation between VAS and NPV (ρ = 0.02216, p = 0.9305). Among other DCE data, Ktrans significantly changed in complete responders (3 months Ktrans = 2.14/min; -ΔKt = 52.65 % p < 0.01) and was not significantly different in partial responders (3 months Ktrans 0.042/min; ΔKt = 11.39 % p > 0.01).

CONCLUSION: In patients with painful bone metastases treated with MRgFUS, ADC and Ktrans variation observed in the ablated lesions correlate with VAS values and may play a role as objective imaging marker of treatment response.