Figure 4

Evolution of the ionoacoustic signals with the pulsing period of the spread-out Bragg peak. Ionoacoustic signals measured for the spread-out proton beam and 25-cycle proton pulse of 400 ns period in water (gray) compared to (a) SonoVue microbubbles / India ink mixture in water (orange), (b) simulated signal in water (black dashed line), (c) SonoVue microbubbles in water (blue), (d) India ink in water (red). All the experimental measurements have been averaged over 3000 acquisitions. (e) Evolution of the signal amplitude for irradiation with the ripple filter depending on the pulse period. The amplitude was extracted from the Fourier transformed signals at the temporal excitation frequency to disentangle the high and low frequency components of the signal. All the experimental measurements have been averaged over 3000 acquisitions and filtered using PyWavelets Python package. All error bars correspond to measurement uncertainties obtained from 30 consecutive measurements and given with a confidence level of 99%.