I imagine there are lots of different types of "myocardial imaging" out there, but I will tell you of the ones I know a little bit about...
1)Probably the most common & most invasive = Cardiac Cath.
A catheter is passed up into coronary arteries, usually introduced in the femoral artery, and radioactive material is injected to see if there has been an infarction (a blockage in blood flow to the coronary arteries, causing death of myocardium). This has to be done with a team of nurses/techs as well as in interventional cardiologist present, so it usually doesn't happen extremely quickly. Most commonly in hospitals a patient is diagnosed as having had an MI through some other means (i.e. sestamibi, as below, 80-lead ECG, MRI even, but usually just serial blood draws for cardiac enzyme levels - if these spike in a characteristic pattern it means muscle is dying) and then admitted and sent to the Cath Lab the next day, where they look for the location of the MI and possibly even do baloon angioplasty or place a stint to open up the circulation again, or find out that the patient needs to have bypass surgery.
2) Sestamibi - this may be called other things at other institutions, but at my school (I only know because I worked there for 2 years before starting classes) it is used on almost anyone with chest pain. It only misses less than 5% of MIs (that was what I last heard...), and is quick and pretty non-invasive. To perform it you only need a patient who can lay still and flat on their backs for 20 minutes and a is less than 300lbs and a RadTech. The radiologist reads it later, possibly even remotely if you've got a good computer setup. Basically its heart-specific perfusion imaging, involving the injection of a radioactive "dye" and a series of images taken from all angles to see if the heart has a blockage in blood flow. Leveling systems are usually used in conjunction with this so that more acute patients get them first, but the most acute - people with MIs that you can see on a 12-lead, either get clot-busters or go to the Cath Lab (they are usually on-call) depending on the hospital's protocol and the patient's history. The idea of this is to over-cover and do it on anyone so that nothing is missed, and it also gives quick diagnosis of something that with drawing serial enzymes may have taken hours. I don't, however, think this is widely used outside of educational hospitals.
Hope this helps.
