Treatment envelopes based on 3D MRTI. Three orthogonal views of treatment envelopes based on the relative near-field heating, calculated as the ratio between the hottest focal spot voxel and the mean of the ten hottest near-field voxels for the 29 and 32 heatings in the phantom (a) and lamb (b) studies. This type of envelope can only be derived from 3D MRTI data. In the phantom study, ratios of up to 3 can be observed for the most central regions. For the lamb study, the highest ratio observed is about 1, meaning that for the majority of the intracranial volume, the near-field region will be heated more than the focal spot. For both (a) and (b), the temperature maps are overlayed on corresponding magnitude images. In (a) and (b), the three views are color coded, with the colored frame and arrows indicating each view’s position in the other two views.