A method for the assessment of blood flow in the Coronary arteries and diagnosing flow disturbances caused by stenosis (narrowing) of these arteries.

The examination is performed by injecting the radio-isotope Thallium 201 and following its absorption in various areas of the Myocardium.

Perfusion (blood flow) defects show as areas emitting less or no radioactive radiation and are visible as "cold spots" on computerized imaging making use of a gamma scanner.