Photoacoustic tomography reconstructing absorption coefficient and effect of regularization minimizing p-norm

Photoacoustic (PA) tomography can be useful to measure the hemoglobin concentration in blood vessels and tissues, and provide important information to determine the course of treatment for hypoxic malignant cancer which possesses the resistance to treatment. To image the hemoglobin concentration and oxygen saturation, the reconstruction of absorption coefficients at multiple wavelengths is required to correct the penetration depths of the multiple wavelengths of light. In this study, the authors tried the image reconstruction of the absorption coefficient for various concentration of photon absorber. Additionally, the effects of the regularizations minimizing 1-norm and p-norm (0<p<1) were compared to examine the improvement of the spatial resolution limited by the characteristics and configurations of the ultrasound transducer and illumination. The PA pressure waves were measured by the probe consisted of the optical fiber and the focused ultrasound transducer. The absorption coefficients of the tubes containing black ink in the phantom made of aqueous solution of Intralipid were from 0.2 to 1.0 mm(-1) at a wavelength of 755 nm, corresponding to the range from normoxic to hypoxic condition of the whole blood. Although the tubes with various absorption coefficients were reconstructed with 1-norm regularization, the tube was reconstructed broadly. On the other hand, the regularization technique minimizing p-norm (0<p<1) localized the tube better than 1-norm regularization. The regularization minimizing p-norm (0<p<1) will improve the spatial resolution of the PA tomography.