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.

A fast and accurate ultrasound pressure field measurement is necessary for the progress of ultrasound application in medicine. In general, a hydrophone is used to measure the ultrasound field, which takes a long measurement time and might disturb the ultrasound field. Hence, we proposed a new method categorized in an optical method called Phase Contrast method to overcome the drawback in the hydrophone method. The proposed method makes use of the spatial DC spectrum formed in the focal plane to measure the modulated optical phase induced by ultrasound propagation in water. In this study, we take into account the decreased intensity of the DC spectrum at high ultrasound intensity to increase the measurement accuracy of the modulated optical phase. Then, we apply a non-continuous phase unwrapping algorithm to unwrap the modulated optical phase at high ultrasound intensity. From, the unwrapped result, we evaluate the quantitativeness of the proposed method.

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