Influence of Collimator Design, Photon Energy and Radiation Dose on Detection Effectiveness in Liver Scanning

Abstract

An experimental test was made of four different focused lead collimators with a phantom to represent the liver containing a solid non-radioactive ` tumour ' void positioned at different depths. Six different radionuclides were used with photon energies ranging from 30 kev to 412 kev. To explore the influence of collimator design and photon energy, a figure of merit Q/ρ was used as an index of detection effectiveness. The best Q/ρ was found using 158 kev photons and the lower energy collimator with a 3 in. focal length. A second figure of merit, Q/D, which was normalized to unit absorbed liver dose, was used as an index of detection effectiveness when radiation dose to the patient was considered as the significant parameter. Of four compounds used in liver scanning, the most effective agent was found to be ^99mTc colloid. The analysis showed that a marked improvement in liver scanning data should result from the use of large millicurie amounts of radionuclides with physical characteristics that keep the liver dose low. A smaller, but still substantial, improvement should result if the photon energy is chosen to be in the 150 kev range and a collimator is used that is appropriately designed for lower energy radiation.