What is the main purpose of administering 1-1.5 mCi of 201 Tl thallous chloride before rest myocardial imaging?

The main purpose of administering 1-1.5 mCi of 201 Tl thallous chloride before rest myocardial imaging is to demonstrate reversible ischemia more readily. Thallium-201 is a radionuclide that behaves like potassium and is taken up by viable myocardial cells. In cases of myocardial ischemia, where there is a restricted blood flow to certain areas of the heart, the use of thallium-201 allows for the visualization of these affected regions.

When the heart is under stress or during exercise, areas that are ischemic but still viable will take up the thallium, which will appear on imaging. This helps differentiate between tissue that is irreversibly damaged (infarcted) and tissue that is still viable but may be temporarily ischemic, allowing clinicians to assess the presence of reversible ischemia.

This imaging technique allows for improved diagnostic accuracy in evaluating coronary artery disease and planning for appropriate interventions. By providing a functional assessment of myocardial perfusion, clinicians can make informed decisions about patient management. This is why the correct choice focuses on demonstrating reversible ischemia specifically.