Near infrared imaging of tissue heterogeneity: probe design and sensitivity analysis.

A CW type handheld near infrared tissue oximeter called P-Scan tissue imager was developed for real time imaging of tissue oxygen saturation ([StO2]) and hemoglobin concentration ([Hbt]). The probe consists of eight dual-wavelength light sources (690nm and 830nm) and eight photon detectors forming a 2.5cm X 2.5cm matrix. The local tissue oxygen saturation and hemoglobin concentration was calculated based on optical measurement of absorption coefficients for oxy and deoxy hemoglobin. A superimposition algorithm was developed for direct imaging of local tissue [StO2]/[Hbt] without complex inverse reconstruction. The measurement sensitivity of such a P-Scan device with respect to tumor size, tumor depth, tumor lateral location and tumor optical contrast was studied. First order Born approximation was used to simulate the photon migration in a 2D turbid model with an embedded absorber. The simulation results implied that the P-Scan imager is able to detect the tissue heterogeneity up to 1.5 cm deep with reasonably high sensitivity. Simulation also indicated that among multiple factors that may influence the P-Scan sensitivity, tumor size and tumor depth are dominant factors.