SIMULTANEOUS DUAL ENERGY ACQUISITION FOR TL-201 TC-99M PARATHYROID SUBTRACTION SCINTIGRAPHY - PHYSICAL AND PHYSIOLOGICAL CONSIDERATIONS

Time/activity curves over thyroid, abnormal parathyroid, and background regions were analysed in ten patients (nine females, one male, age 45±9 years) with primary hyperparathyroidism and scintigraphically positive single parathyroid adenomas after intravenous injection of 74 MBq99Tcmas pertechnetate and 74 MBq201T1 chloride. In the 70 keV ±10% thallium window, peak activity occurred over all three regions within 2 min after injection, then decreased linearly 1.2+0.4% min-1and 0.87+0.3% min-1for thyroid and parathyroid, respectively, during the next 28 min. The slopes of the curves did not differ significantly (p = 0.15). Thyroid and parathyroid phantoms were also studied to determine201Tl/99TCmcrossover: 201T1 scatter contributed 5.4% of the overall counts to the99Tcmimage, and99Tcmscatter contributed 7.4% to a 201T1 image. To minimize the acquisition time, avoid patient movement between99Tcmand201T1 acquisition, equalize as near as possible the net-count rates, and retain data for background and motion correction, an optimized dynamic acquisition protocol using a simultaneous dual-energy-window technique (seven double frames of 4 min each) is presented. © 1990 Chapman and Hall Ltd.