Figure 8.

Canine prostate HIFU ablation. (a) Magnitude image during heating, with the masked ℓ₂ method’s mask indicated by the highlighted region. (b) The unwrapped phase image used for thermometry. As indicated by the arrow, large phase discontinuities exist at the boundary of the aqueous prostate and the fatty tissue surrounding it. (c) Water and fat masks, derived from multiecho image data. The fat mask was included as an additional basis function in the masked ℓ₂ and reweighted ℓ₁ method, to permit an additional global phase shift in this region, relative to the water regions. (d) Temperature estimates overlaid on the GRE image. Both referenceless methods estimate temperature maps that are similar to the baseline subtraction estimate, but the reweighted ℓ₁ method does not require careful placement of a frame around the prostate.