A spectral unfolding method to determine source depth distribution

The depth distribution in tissue of a gamma-emitting isotope can be estimated by observing the energy spectrum of photons emerging from the body. Monte Carlo methods were used to compute surface energy spectra for 99Tcm point sources at various depths. From these noise-free results a discrete response matrix was constructed to relate the input source depth to the corresponding output spectrum. Observed spectra with noise were then simulated independently by Monte Carlo calculations assuming various measurement times and source strengths. The source distribution was determined by solving the discrete inverse unfolding problem by the Method of Regularisation. The effective depth resolution is seen to depend strongly upon measurement time. The results show that limited depth resolution can be obtained from a single view of the object region.