Reference selection of NIR breast imaging using perturbation approach

A typical perturbation-based image reconstruction technique requires a homogeneous reference for accurate estimation of target-caused perturbation and accurate reconstruction of target optical properties. Therefore reference selection is critical. In this report, we analyze the influence of different references on reconstructed optical images when a typical perturbation approach, such as Born method, is used for imaging reconstruction. A new photon tracking method using Monte Carlo simulation is developed and used to analyze the contributions of a target and a chest-wall layer underneath the breast tissue to the NIR measurements. We have found that a chest-wall layer has much larger contribution than the target when the breast-tissue layer thickness is less than 1.5 to 2.0 cm deep depending on bulk optical properties. Different references, such as optical property-matched and depth-unmatched reference, depth-matched and property-unmatched reference, property-unmatched and depth-unmatched reference, and property-matched and depth-matched reference, are compared and evaluated using the total perturbation and the reconstructed image quality as quantitative criteria. We have found that the property-matched and depth-matched reference provides the best result with error less than 5%, and the depth-matched and property-unmatched reference provides the worst results with error larger than 60%. Phantom experiments confirm with the simulation results. As results, we suggest using the measurements from a normal contralateral site of the same quadrant as the breast lesion with matched propagation depth as best property-matched and depth-matched reference with the help of coregistered ultrasound in clinical trials.