MRI of skull bone marrow after MRI-guided focused ultrasound

The following pages show axial T2-weighted MRI obtained at 24 hours and at 3-15 months after MRgFUS. The images shown here were registered to the same reference frame that was used in the thermal simulations; every third image is shown. To segment the bone marrow lesions, the registered images were toggled back and forth between the two time points to detect obvious changes. The lesion segmentations were completed before the acoustic and thermal simulations were performed. They were originally done on the native T2-weighted images acquired at 3-15 months after FUS. Relevant MRI parameters are indicated for each patient (TR: repetition time; TE: echo time; ETL: echo train length). The MRI parameters varied in the MRI at 3-15 months because the patients were sometimes imaged at other institutions. When thick slices were used at 3-15 months, dorsal regions of the skull were often challenging to interpret. These MRI were obtained to image the lesion in the thalamus and were not optimized for detecting skull lesions. Thus, in some cases the imaging did not cover the entire skull. In such cases, the missed areas were not included in our estimates of the lesion thresholds or in other comparisons of the isotherms and lesion segmentations. The patient number and the parameters used for MRgFUS are noted. The images on the top show simulated maximum temperature projections onto the surface of the skull (see Fig. 5-6 in the main manuscript for details).