What is the definition or description of: thallium stress test?

Stress with Thallium: A radioactive isotope of thallium, often 201, is injected iv. Heart muscle cells pump some of the radioactive thallium inside; less if blood flow past the cells is limited. Thus cells (or scar tissue) with low blood flow intake less thallium & emit less radiation. A gamma camera detects some of the radiation which exits the body. Only severe, not mild, artery disease complications can be detected.