1991 Volume 40 Issue 6 Pages 234-239
Comparison of myocardial imaging with simultaneous administration of 201TlCl and 123I-MIBG are examined. However, as there are both cross talks on to 201Tl-photopeak window from 123I and to 123I-photopeak window from 201Tl, it is important that we understand these quantitative cross talks, previously. The purpose of this study is to estimate the relative cross talk on to each photopeak window from another nuclide. These cross talks determined from gamma rays spectra, which were measured by inputting signals from a gamma camera into a multi-channel (2048 ch.) pulse height analyser.
Three types of collimators, which are HR (high resolution), AP (all purpose) for low energy, and ME (medium energy), and cuboid phantoms (size of the base: 10×10 cm2) were used in this experiment. As a result of the cross talk measurement, uses of the HR- and the AP-collimator were not suitable for myocardial imaging with 123I-MIBG, because 123I emits mostly gamma rays with energy of 159 keV and some gamma rays of higher energies, moreover, the lead characteristic X-rays contribute considerably on to 201Tl-photopeak window. When the phantom containing both nuclides of 201Tl and 123I with equal activities was imaged with the gamma camera, the cross talk fractions to the 201Tl-photopeak window were 45-50% for the HR-, 34-40% for the AR-, and 9-10% for ME-collimator. Also, those to the 123I-photopeak window were 9-12%, 9-12%, and 7-11% for the HR-, the AP-, and the ME-collimator, respectively.
From the above results, we recommend the use of the ME-collimator for myocardial imaging with simultaneous administration of 201Tl and 123I.