Automatic exposure control and estimation of effective system noise in diffuse fluorescence tomography.

A diffuse fluorescence tomography system, based upon time-correlated single photon counting, is presented with an automated algorithm to allow dynamic range variation through exposure control. This automated exposure control allows the upper and lower detection levels of fluorophore to be extended by an order of magnitude beyond the previously published performance and benefits in a slight decrease in system effective noise. The effective noise level is used as a metric to characterize the system performance, integrating both model-mismatch and calibration bias errors into a single parameter. This effective error is near 7% of the reconstructed fluorescent yield value, when imaging in just few minutes. Quantifying protoporphyrin IX concentrations down to 50 ng/ml is possible, for tumor-sized regions. This fluorophore has very low fluorescence yield, but high biological relevance for tumor imaging, given that it is produced in the mitochondria, and upregulated in many tumor types.