Time-of-flight non-contact fluorescence diffuse optical tomography with numerical constant fraction discrimination

We introduce a novel non-contact fluorescence diffuse optical tomography (FDOT) approach for localizing a fluorescent inclusion embedded in a scattering medium. It uses the time of flight of early photons arriving at several detector positions around the medium. It is a true and direct time-of-flight approach in that arrival times are converted to distance. The arrival time of early photons is found via, a recently introduced numerical constant fraction discriminator applied to fluoresced photons time-of-flight distributions (fluorescence time point-spread functions (FTPSFs)). Time-correlated single photon counting and an ultrafast photon counting avalanche photodiode are used for measuring FTPSFs that form tomographic data sets. The FDOT localization algorithm proceeds in two steps. The first determines the angular position of the inclusion as the average, over projections, of angular detector positions with smallest arrival time. The second determines the inclusion's radial position based oil relative arrival times obtained at several detector positions within each tomographic projection relatively to a reference detector position, the latter being that of shortest arrival time in the projection. The radial position found minimizes the discrepancy between relative arrival times computed for several possible inclusion positions and relative arrival times deduced from experimental data. Two methods are presented for this.