Speckle-free phase-contrast ultrasound imaging

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ABSTRACT Ultrasound (US) imaging is one of the most common methods of medical imaging, and has had tremendous impact in the practice and delivery of healthcare. Advantages of ultrasound imaging are that it is non-invasive, cost-effective, and provides images with penetration depths commensurate with human organ imaging. In this last regard, US imaging has a considerable advantage over optical imaging techniques, which are hampered by very poor depth penetration in comparison. This proposal rests on the fact that there is a close analogy between optical imaging and US imaging. We have recently developed a new optical microscopy technique called Oblique Back-illumination Microscopy (OBM) that provides DIC-like phase contrast in arbitrarily thick tissue. While OBM is a remarkably simple method to obtain fast, high resolution, label-free imaging of tissue structure, it is limited in depth penetration to about 100µm. Such limited depth penetration restricts the applicability of OBM to superficial imaging of epithelial tissue only. Motivated by the close analogy between optical and US imaging, we propose to extend the concept of OBM directly to acoustics, enabling the possibility of what we believe to be an entirely new modality of US imaging, called Oblique Backscattering Ultrasound (OBUS) imaging. Specifically, OBUS imaging is unusual in that it is based on the detection of transmitted rather than reflected sound, even though it is configured in a reflection geometry. As such, it can operate in arbitrarily thick tissue, thus differing from previous transmission US imaging techniques. Because it is based on phase contrast, OBUS imaging reveals fundamentally different sample features than standard echography. Moreover, OBUS imaging is speckle-free, which has been a long- standing challenge in US imaging. We propose to improve OBUS by combining it with a technique called Differential Aberration Imaging, enabling it to work with the same samples and with the same hardware as a conventional echographic US imaging. Information from both contrast modalities will be obtained simultaneously, and combined to enable augmented sample reconstruction. Our goal will be to lay the necessary groundwork for the future development of this new technology, which we believe represents a paradigm shift in US imaging that may have significant clinical impact.