Abstract
Over the last two and a half decades, photoacoustic (PA) imaging has become an important area of research in biomedical optics. Combining the high contrast of optical imaging with the high spatial resolution of ultrasound (US) imaging, PA imaging can simultaneously visualize anatomical structures while interrogating their functionality through multiwavelength optical spectroscopy. Alongside technological developments and imaging applications in optical and acoustic resolution PA imaging, a family of PA signal analysis techniques can extract additional information about the sample being imaged. This Tutorial focuses on techniques that rely on the analysis of PA signals in a manner similar to that in the complimentary field of quantitative ultrasound (QUS) imaging of soft tissues. In QUS, signal analysis techniques have been developed to analyze the US signals resulting from the scattering of many unresolved scatterers within the resolution volume of the imaging device. The implementation of these US techniques in PA can enable new applications in biomedicine beyond traditional anatomical PA imaging, further increasing the utilization and impact of this promising modality.
Highlights
We will divide our description of PA imaging into following two broad categories: (1) Photoacoustic microscopy (PAM), where a focused laser beam is used to achieve high spatial resolution imaging at shallow depths; and
Unlike optical resolution photoacoustic microscopy (OR-PAM), where individual vessels can be resolved, the broad illumination and acoustic detection schemes employed in this setup cannot typically resolve the smaller vessels of the vasculature; the lower acoustic frequency and broader illumination greatly increase the depths from which PA signals can be acquired
PAM and Photoacoustic tomography (PAT) have traditionally been used for imaging, resolving structures with length scales from micrometers to centimeters
Summary
We discuss the role that a PA signal plays in the reconstruction of images, the structural and functional information encoded within it, and highlight several applications in microscopy and tomography. We provide our perspective on how one can perform PA tissue characterization across multiple biological length scales
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