How is a 201 Tl resting redistribution scan performed, and how are the results of a resting redistribution scan used clinically?
In a resting-redistribution scan, the patient receives an injection of 201 Tl at rest and undergoes scanning approximately 15 minutes later. The patient is scanned again approximately 4 hours later and sometimes 24 hours after injection. Images are reconstructed in the typical tomographic projections. The images are evaluated for perfusion and for reversibility of defects observed on the initial scan. The general idea is that a patient with known CAD has several segments of the myocardium that have undergone ischemic injury. The question is whether these segments are viable, which can be determined because they either have some perfusion on initial images or show some degree of reversibility. Areas of the myocardium that show this type of viability typically respond well after revascularization by regaining some degree of function. Areas that are not viable typically do not respond to revascularization. 201 Tl resting-redistribution studies can help to determine what parts of the heart, and what vessels, might be the best targets for revascularization.