Dual isotope carotid scintigraphy in patients with amaurosis fugax attacks

A method of simultaneous dual-radionuclide cardiac imaging with technetium 99m and thallium 201. I: Analysis of interradionuclide crossover and validation in phantoms

BACKGROUND

Simultaneous dual-radionuclide technetium 99m/thallium 201 scintigraphy can potentially produce perfectly aligned stress and rest images in less time than conventional protocols. However, interradionuclide crossover limits diagnostic accuracy. Accordingly, we evaluated 99mTc and 201Tl crossover in line and heart phantoms.

METHODS AND RESULTS

99mTc crossover in the 201Tl imaging window constituted as much as one half of the counts in the 99mTc window, varied significantly with attenuation, and was spatially incoherent. 201Tl crossover was relatively small, less variable, and spatially similar to the primary image. Based on these findings, the following simultaneous dual-radionuclide 99mTc/201Tl method was developed, and validated in line and heart phantoms. The 99mTc source is imaged first into dual 201Tl/99mTc windows, followed by 201Tl administration and dual-radionuclide imaging. The single-radionuclide 99mTc image in the 201Tl window is count-normalized for acquisition time and then subtracted from the dual-radionuclide 201Tl image to specifically correct for 99mTc crossover. Image quality of the corrected dual-radionuclide 201Tl images approached their single-radionuclide counterparts. Correction for 201Tl crossover was relatively unimportant.

CONCLUSION

Simultaneous dual-radionuclide 99mTc/201Tl myocardial scintigraphy is feasible with 99mTc crossover correction specific to each acquisition. The proposed dual-radionuclide 99mTc/201Tl method and the principles on which it is based can be applied to a broad range of dual-radionuclide pairs.