Acousto-optic interaction strengths in optically scattering media using high pressure acoustic pulses

Ultrasound optical tomography (UOT) is a developing medical imaging technique with the potential to noninvasively image tissue oxygenation at depths of several centimeters in human tissue. To accurately model the UOT imaging, it is necessary the calculate the signal produced by the interaction between ultrasound and light in the scattering medium. In this paper we present a rigorous description for modeling this process for ultrasound pulses in the non-linear regime with peak pressures ranging up to the medical safety limit. Simulation results based on the presented model agree well with measurements performed with fully characterized ultrasound pulses. Our results also indicate that the UOT modeling process can be accurately simplified by disregarding the acoustically induced movement of scatterers. Our results suggest that the explored model and its software implementation can be used as a virtual lab to aid future development of pulses and UOT imaging algorithms. Ultrasound optical tomography (UOT) is a nonintrusive medical imaging modality which since its emergence in the 1990s has seen steady development [1,2]. In this imaging scheme, tissue is illuminated by light while simultaneously being illuminated by ultrasound (US). In the interaction region between the acoustic and optical fields, part of the light is shifted in frequency and "tagged" due to the acousto-optic effect. As it is the overlap of the two fields which produces the signal, the high scattering of light allows for the much less scattered US to create a source of tagged light from the untagged light, which due to scattering reaches a large tissue volume. By steering the direction of the US pulses within this volume and timing optical pulses to probe different depths, it is possible to create images of the optical properties of the medium by recording the tagged signal strength for the varying US pulse positions. This tagged light must, however, first be differentiated from the much stronger background of untagged light which has not interacted with the ultrasound. This separation is possible using