Diffusion-weighted magnetic resonance imaging using different b -value combinations for the evaluation of treatment results after volumetric MR-guided high-intensity focused ultrasound ablation of uterine fibroids

Objectives To assess the value of diffusion-weighted magnetic resonance imaging (DWI) and apparent diffusion coefficient (ADC) mapping using different b- value combinations for treatment evaluation after magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU) of uterine fibroids. Methods Fifty-six patients with 67 uterine fibroids were treated with volumetric MR-HIFU. Pre-treatment and post-treatment images were obtained using contrast-enhanced T1-weighted MRI (CE-T1WI) and DWI using b = 0, 200, 400, 600, 800 s/mm 2 . ADC maps were generated using subsets of b- values to investigate the effects of tissue ablation on water diffusion and perfusion in fibroids treated with MR-HIFU. Four combinations of b- values were used: (1) all b- values; (2) b = 0, 200 s/mm 2 ; (3) b = 400, 600, 800 s/mm 2 ; and (4) b = 0, 800 s/mm 2 . Results Using the lowest b- values (0 and 200 s/mm 2 ), the mean ADC value in the ablated tissue reduced significantly ( p < 0.001) compared with baseline. Calculating the ADC value with the highest b- values (400, 600, 800 s/mm 2 ), the ADC increased significantly ( p < 0.001) post-treatment. ADC maps calculated with the lowest b- values resulted in the best visual agreement of non-perfused fibroid tissue detected on CE images. Other b- value combinations and normal myometrium showed no difference in ADC after MR-HIFU treatment. Conclusions A decrease in contrast agent uptake within the ablated region on CE-T1WI was correlated to a significantly decreased ADC when b = 0 and 200 s/mm 2 were used. Key Points • DWI could be useful for treatment evaluation after MR-HIFU of uterine fibroids • The ADC in fibroid tissue is influenced by the choice of b- values • Low b-values seem the best choice to emphasise perfusion effects after MR-HIFU