HIFU transducer focal pressure levels for the transducers with F-numbers of 0.77, 1.02, and 1.52 operating at 1.5 MHz (a) and the transducer with F-number 1.52 operating at 1 MHz, 1.5 MHz, and 1.9 MHz (c). Dashed vertical lines indicate transducer output levels corresponding to fully developed shock front in the focal waveform. (b),(d) Focal pressure waveforms with fully developed shock front for the three transducers in (a) and the transducer with F-number of 1.52 at three different frequencies in (c), respectively.