Validation study of a quantitative photoacoustic image reconstruction using Monte Carlo method and linearization

Abstract

By reconstructing the optical properties such as the absorption coefficient, quantitative photoacoustic tomography (QPAT) images the micro blood vessels and the hemoglobin concentration quantitatively. QPAT is accomplished by solving the inverse problem of the photoacoustic (PA) measurement based on the phenomena of the light and PA pressure wave propagation. The light propagation is described by the radiative transfer equation, which is approximately calculated with the Monte Carlo (MC) simulation. The propagation of the PA pressure wave is described by the PA wave equation. The authors have been studying the QPAT image reconstruction algorithm using MC simulation and linearization. Near-infrared light with a wavelength of 755 nm that penetrates deep inside the biological medium was used. The absorption coefficient was reconstructed from the PA signals measured by the probe, which was the combination of the optical fiber and the focused ultrasound transducer consisting of P(VDF-TrFE) piezo electric film. The QPAT image with 10-mm depth was reconstructed in the numerical and phantom experiments. Pursuing more realistic situation of the micro vessel imaging, we conducted animal experiment to validate the QPAT image reconstruction. In the animal experiments, we tried to image the blood vessels of rabbit’s ear. The rabbit ear was placed under the tissue-mimicking scattering layer. Through the numerical, phantom, and animal experiments, the instrumental and computational conditions for QPAT for pathological imaging will be investigated by comparing the QPAT images of the phantom and animal.