Ultrasound assisted NIR imaging for breast cancer detection

We have constructed a nearly real-time combined imager suitable for simultaneous ultrasound and near infrared (NIR) diffusive light imaging and co-registration. The imager consists of a combined probe and associated electronics for data acquisition. A two-dimensional ultrasound array occupies the center of the combined probe, while 12 dual wavelength laser source fibers (780 nm and 830 nm) and 8 optical detector fibers are deployed in the periphery. We have experimentally evaluated the effects of missing optical sensors in the middle of the combined probe upon the accuracy of the reconstructed optical absorption coefficient, and assessed the improvements of reconstructed absorption coefficient with the guidance of the co-registered ultrasound. The results have shown that when the central ultrasound array area is in the neighborhood of 2 × 2 cm², which corresponds to the size of most commercial ultrasound transducers, the quality of optical images will not be degenerated. In addition to the acoustic information for cancer discrimination, NIR image reconstruction becomes much easier and more reliable. According to our results, the iterative inversion algorithm converges very fast with the guidance of a priori target temporal and spatial distributions. Only one iteration is needed to reconstruct accurate optical absorption coefficient.