Ex vivo hemoglobin status study using photoacoustic computed tomography small animal scanner

Purpose: The purpose of this study is to calibrate the PCT scanner to quantify the hemoglobin status utilizing a blood flow phantom. Materials and Methods: A blood circulation system was designed and constructed to control the oxygen saturation and hemoglobin concentration of blood. As a part of the circulation system, a 1.1mm FEP tube was placed in the center of imaging tank of PCT scanner as the imaging object. Photoacoustic spectra (690-950 nm) was acquired for different hemoglobin concentrations (CtHb) and oxygen saturation levels (SaO2), where the formers was formed by diluting blood samples with PBS and the latter by mixing blood with gases at different oxygen content. Monte Carlo simulations were performed to calculate the photon energy depositions in the phantom tube, which took into account photon losses in water and blood. A Kappa value which represents the energy transfer efficiency of hemoglobin molecule was calculated based on the PCT measurement and simulation result. The final SaO2 value of each blood sample was calculated based on the PCT spectrum and Kappa value. These oxygen saturation results were compared with co-oximeter measurements to obtain systematic errors. Results and Conclusion: The statistic error of calculating Kappa value from hemoglobin concentration experiment was less than 5%. The systematic error between PCT spectra analysis and co-oximeter analysis for hemoglobin oxygen saturation was -4.5%. These calibration techniques used to calculate Kappa and hemoglobin absorption spectra would be used in hypoxia measurements in tumors as well as for endogenous biomarkers studies.