Thank you for your question,
We do thallium scan in such situation to see the blockage at the micro level arteries. Angiography
does not show these small arteries and person after having stents implanted and still having symptoms might be suffering from blockage to the micro arteries so we do this test to see those arteries.
If blockage is found then we proceed with high dose of statins, aspirin
, nitrates, beta blockers and ACEi.
I hope this helps you to understand why the doctors are doing this test.