Fig. 3

Treatment profile heterogeneity. a The measured acoustic profile of a 10.5 × 10.5 mm plane perpendicular to the beam path for one of the transducers where Δx = Δy = 0.7 mm < 0.5 λ. b The mask used to select a circular region for calculating homogeneity in a, where black represents the selected area. c The measured “heterogeneity” of each slice at different points along the acoustic axis from 13 to 17 mm for one of the transducers, showing a local minimum at z = 16 mm. This point was chosen as the optimal near field treatment distance for this transducer