Deeply penetrating photoacoustic tomography in biological tissues enhanced with an optical contrast agent

TLDR

The study developed a circular‑scanning photoacoustic tomography system to image deeply embedded optical heterogeneity in tissues and examined how detection bandwidth across four ultrasonic transducers affects image quality. The system uses 800‑nm near‑infrared laser pulses and Indocyanine Green dye, whose absorption peak matches the laser wavelength, to maximize optical penetration and contrast while evaluating bandwidth effects. Optimized PAT imaged objects up to 5.2 cm deep—over six times the 1/e optical penetration depth—in chicken breast muscle with <780 µm resolution and <7 pmol ICG sensitivity, though resolution slowly deteriorates with depth.

Abstract

Photoacoustic tomography (PAT) in a circular scanning configuration was developed to image deeply embedded optical heterogeneity in biological tissues. While the optical penetration was maximized with near-infrared laser pulses of 800-nm wavelength, the optical contrast was enhanced by Indocyanine Green (ICG) dye whose absorption peak matched the laser wavelength. This optimized PAT was able to image objects embedded at depths of as much as 5.2 cm, 6.2 times the 1/e optical penetration depth, in chicken breast muscle at a resolution of <780 µm and a sensitivity of <7 pmol of ICG in blood. The resolution was found to deteriorate slowly with increasing imaging depth. The effects of detection bandwidth on the quality of images acquired simultaneously by four different ultrasonic transducers are described.