Comparison of Transmissions from Er, Mo and Tm vs Pb for use in Reduction of Cross-Talk Photons in Nuclear Cardiology Collimators

Abstract

Technetium-99m (99mTc) and Thallium-201 (201Tl) are radionuclides that are used to analyze the health of myocardial tissue. The amount of each radionuclide present in the myocardium is imaged using a gamma camera which allows medical professionals to determine the health of a patient’s heart. Collimators are large metal gratings that are constructed to allow only geometrically orthogonal photons to be captured by the gamma camera in order to obtain the highest resolution possible to aid in accurate diagnosis. Lead (Pb) is commonly used as a collimator material, but has an 88 keV K-shell photon, which interferes with the lower energy photons from the 70-80 keV energy 201Tl peaks. This phenomenon is known as “down-scatter” or “cross-talk”. This project is designed to test the feasibility of using dense metal attenuators (Erbium, Er; Molybdenum, Mo; and Thulium, Tm) rather than lead (Pb) to reduce the significant 99mTc cross-talk photons in the 201Tl photopeak range. Use of other dense metals with low k-shell absorption peaks should reduce the down-scatter component and eliminate the Pb x-ray cross-talk interference in the 201Tl energy window. Acquisitions of energy spectra for the dual isotopes will be obtained for the non-Pb metals Er, Mo, and Tm. Spectra and transmission and attenuation acquisitions were analyzed using comparative statistics to ascertain the extent of scatter component and interference reduction gained through the use of a non-Pb collimator. T-tests confirmed that all three metals performed better than Pb in the 201Tl range but not the 99mTc range.