MPS. I believe you are referring to a myocardial perfusion scan, where technitium sestamibi 99 is the radioactive isotope that is injected intravenously so that images can can be taken of the heart at rest and 'stressed' or exercrsing -which brings us to the adenosine: a pharmacological agent used to 'stress' the heart instead of walking on a treadmill. Lexiscan is the stress agent of choice now.
Previously answered. This has been answered multiple times now. For example, please see dr. Charles jost's reply: https://www.Healthtap.Com/#user_questions/42020-what-is-the-sestamibi-stress-test-with-adenosine.