Abstract
Raster-scan optoacoustic mesoscopy (RSOM), also termed photoacoustic mesoscopy, offers novel insights into vascular morphology and pathophysiological biomarkers of skin inflammation in vivo at depths unattainable by other optical imaging methods. Using ultra-wideband detection and focused ultrasound transducers, RSOM can achieve axial resolution of 4 micron and lateral resolution of 20 micron to depths of several millimeters. However, motion effects may deteriorate performance and reduce the effective resolution. To provide high-quality optoacoustic images in clinical measurements, we developed a motion correction algorithm for RSOM. The algorithm is based on observing disruptions of the ultrasound wave front generated by the vertical movement of the melanin layer at the skin surface. From the disrupted skin surface, a smooth synthetic surface is generated, and the offset between the two surfaces is used to correct for the relative position of the ultrasound detector. We test the algorithm in measurements of healthy and psoriatic human skin and achieve effective resolution up to 5-fold higher than before correction. We discuss the performance of the correction algorithm and its implications in the context of multispectral mesoscopy.
Highlights
Raster-scan optoacoustic mesoscopy (RSOM) is a biomedical optical imaging technique[1, 2], capable of visualizing tissue morphology[3, 4] and pathophysiological biomarkers of inflammatory diseases[5] through several millimeters of depth while preserving high resolution
RSOM image formation is achieved by raster-scanning a focused ultrasound detector over the region of interest (ROI) to collect optoacoustic waves generated in the tissue in response to pulsed laser illumination
The increase in effective resolution was apparent at the epidermal-dermal junction (Fig. 2d): the uncorrected maximum amplitude projections (MAPs) showed an unstructured pattern, while the motion-corrected MAP showed a structured pattern of capillary loops
Summary
Raster-scan optoacoustic (photoacoustic) mesoscopy (RSOM) is a biomedical optical imaging technique[1, 2], capable of visualizing tissue morphology[3, 4] and pathophysiological biomarkers of inflammatory diseases[5] through several millimeters of depth while preserving high resolution. Generating a two-dimensional skin scan based on a grid of 250 × 250 points may require ~60 seconds when the laser has a pulse repetition rate (PRR) of 1 kHz; this scan time is longer when larger grids, multi-wavelength illumination, lower laser safety limits or data averaging are used[1, 3,4,5,6, 8, 10,11,12,13,14] During this time, the subject’s movement, e.g. breathing motion at a respiratory rate of up to 30 times per minute[15, 16], can alter the position of the ultrasound detector relative to the sample, affecting RSOM image quality[8, 17]. We examined the performance of the algorithm by tracing the level of blood oxygenation along single vessels, and show that motion correction is necessary for correcting corrupted readings of blood oxygenation
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