Arterial Blood-Mediated Deep-Tissue Photoacoustic Oximetry

Photoacoustic tomography is uniquely capable of high-resolution deep-tissue blood-oxygenation (sO₂) imaging (oximetry) due to its optical absorption contrast. However, wavelength-dependent optical fluence changes within tissue, i.e., spectral coloring, have impeded the development of photoacoustic oximetry. We present the arterial prior method (APM+; + denotes intravascular fluence correction), which leverages the high arterial sO₂ to locally calibrate the optical fluence within tissue to circumvent spectral coloring and reliably estimate the sO₂ near the artery. In phantom experiments with ex vivo animal tissue, APM+ resulted in a median estimation error of 2.9% compared to 9.8% from the traditional linear unmixing method (LUM). In human imaging experiments of the radial artery-vein pair in eight healthy adult volunteers, the estimated venous sO₂s from APM+ (median: 72.3%, interquartile range/IQR: 8.9%) were concentrated around the typical 60%-80% range in healthy individuals, whereas those from LUM (median: 75.2%, IQR: 34.4%) varied widely. When imaging the wrists of the eight subjects through ex vivo animal tissue of thicknesses up to 1.5 cm, APM+ provided more consistent estimates than LUM, indicating its robustness with depth.