Time-correlated single-photon counting based method for submillimeter transillumination imaging of objects embedded in tissue-phantoms

We test the performances of an imaging system in revealing either opaque, light diffusing, or transparent objects embedded in tissue phantoms. The method relies on measuring the time-of-flight distributions of near-infrared photons emerging from the phantom within a collection angle of 0.6 mrad about the direction of the incident light by means of a time-correlated single-photon counting apparatus. The apparatus is based on new generation single photon avalanche photodiodes, which are endowed with 35 ps resolution, low dark-count rate, short dead time and relatively high quantum efficiency in the near-infrared. The weakly-scattered (ballistic/snake) photons, bringing the relevant image information, are efficiently discriminated from the multiply scattered ones. Thus, the profiles of the embedded objects can be reconstructed and their nature can be assessed. Opaque objects are localized with 220 m spatial resolution. The potential of the new detectors in medical imaging applications is discussed.