Quantitative measurement of focused ultrasound pressure field by background-subtracted shadowgraph using holographic diffuser as screen

Abstract

In the development of medical ultrasound techniques, fast and accurate pressure field measurement is important. The most common method of measuring an ultrasound pressure field is by using a mechanically scanned hydrophone, which might disturb the acoustic field, and it takes a long time. In this study, we used an optical shadowgraph method. For quantitative measurement using the shadowgraph, it is important to define precisely the optical propagation length between the phase object and the imaging plane. We used a holographic diffuser as the imaging screen for this purpose. A computed tomography (CT) algorithm was used to reconstruct a pressure field, and the result was compared with that of hydrophone measurement. By combining two shadowgraph results from smaller and larger propagation lengths, the result was very close to that of the hydrophone and was successfully reconstructed in the pressure range where nonlinear deformation was clear.