Abstract
Energy spectra from a thyroid fluorescence scanner demonstrate inherent background radiation (excitation beam scatter), which interferes with the detection of characteristic iodine x-rays and influences imaging and iodine quantitation. The amount of scattering material within the beam field is one factor that varies the counting rate detected in the iodine peak region. The technique of constant background subtraction, which is found in conventional radionuclide scanners, is sub-optimal because a variable correction is required. A fluorescence scanning system that continuously monitors and subtracts background from the iodine peak region (dynamic background subtractor) was evaluated and found to make appropriate background corrections while scanning. Radionuclides administered before a fluorescence scan produce image artifacts and erroneous quantitation of iodine results, using either background subtraction technique.