Considerations for Cardiac Imaging with lndium-111- labeled Radiopharmaceuticals

lndium-111-labeled radiopharmaceuticals are now being used clinically for cardiac imaging. Their use means that some of the imaging strategies employed for Tl and mTc must be reassessed to determine if there are alternatives that may provide improved image quality. The need for this reassessment results from the higher energy photons emitted by 111 In. The theoretical implications of this difference in energies from Tl and mTc in terms of attenuation in the tissues of the patient's body, the camera collimator, the side shielding of the camera, and the thickness of the crystal are presented as well as the results of an experimental investigation using four different collimators and four different energy windows. Finally, conclusions are drawn regarding collimator and energy window selection.