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Myocardial perfusion imaging is a very useful test when looking for coronary artery disease. Bone scans, a number of indications there. A very common test. H. pylori breath test is a new test study that’s being used to diagnose H. pylori because as everybody realizes, that needs to be completely eradicated. Hepatobiliary imaging. There’s a new variation on this theme. It’s called cholecystokinin and we actually look at a gall bladder ejection fraction, sort of like a left ventricular ejection fraction. If the gallbladder does not contract sufficiently, that’s an indication of disease. Thyroid imaging and VQ scans will be discussed.
Myocardial perfusion imaging. The diagnosis of coronary artery disease is critical. Cardiolyte is the best agent for this. There are three different agents that we can use. What everyone thinks of when they think of myocardial perfusion imaging is thallium scans. There’s also a newer agent called Myoview and on the top, the whole category of agents, the most common of which is cardiolyte imaging. They all pretty much do the same thing. I would leave it up to your nuclear medicine
Another time that myocardial perfusion imaging can really help you out is when you have discrepancies between your stress test results and your clinical impression. Again, if you have a positive exercise treadmill study which is very common in, say, younger females where there’s a low incidence of coronary disease, that’s where you’d want to add our test and we will improve the specificity.
One of the other things it can do for you is tell you if there are other vessels involved. In other words, did this gentleman have single vessel disease? He’s infarcted what he’s going to infarct. End of story. Now we know he has coronary disease. Let’s work on his risk factors but we don’t have to be incredibly aggressive about looking for another stenosis to angioplasty or perhaps bypass. Versus does this man have three vessel disease and he’s only infarcted one of his territories and we need to be very aggressive.
It can also tell you the size of the infarct. Obviously the larger the infarct, the more at risk the patient is. The more proximal the stenosis is in the vessel, the larger the infarct will be and, again, if ischemia is present, you may want intervention.
Consider in this patient population also doing a thallium scan. The times you do a thallium scan is when you’re looking for something called viable myocardium. Basically, viable myocardium are cells that have been damaged by the hypoxia but have retained their cell wall integrity and enough of the myocardial cell functions that if you resupply or reestablish the oxygen supply they will completely recover and start to contract normally again.
Bone scans. Detection and followup of skeletal metastases is probably the number one indication that I see bone scans for. The cancers that are the most relevant, unfortunately, which are also very common are breast, lung and prostate cancer. Now, typically with breast cancer, anybody that’s Stage III or above on their initial diagnosis needs a bone scan, anybody at any stage who has bone pain and for the followup of anyone who develops bone pain.
MRI is very good for looking at the bone marrow. Therefore it’s very good at looking at bone metastases because they generally spread through the bone marrow. Thin cut CT is better for looking at the bone cortex so you might want to use that if there is a suspicion of a fracture. You may even need a biopsy. Let’s say you have somebody who’s just been diagnosed with cancer, has a single lesion on the bone scan, the plain films are normal .
Some other nononcologic indications for bone scans include stress fractures. Again, what you’re looking at is stress fractures versus shin splints. This is that young athlete, that fanatical person that exercises for hours and hours every day, they’re training for something, they’re on the high school track team or whatever it is and these people do not want to stop. They want you to tell them that their pain is due to something that is reversible and they can continue to exercise.
HIDA scans. I’m going to just briefly tell you a little bit about gall bladder ejection fraction. Again, think of the gall bladder as basically a muscular sac. It needs to relax, dilate, contain the bile, store the bile, and then upon stimulation by CCK, it needs to then contract and eject the bile into the small intestine. So if it cannot do that, that evidence of dysfunction has been associated with chronic cholecystitis. Patients that have right upper quadrant pain and a low ejection fraction who do have a cholecystectomy, 90% of them have complete and permanent resolution of their right upper quadrant pain. I personally know a number of patients whose only abnormal study was the ejection fraction on the HIDA scan.
Thyroid imaging is about as far as I’m probably going to get and I just want to skim over it and reiterate the indications. Evaluation of the etiology of hyperthyroidism and planning therapy for hyperthyroidism. Basically what we want to before we give anybody radioactive iodine is we want to be sure that they don’t have subacute thyroiditis. A completely reversible process and the only test that you can do for that is a radioactive iodine uptake.
Toxic nodules can cause hyperthyroidism. Usually you see complete suppression of the rest of the thyroid gland. Usually you have already performed thyroid function tests and you already have an idea if they are hyperthyroid. Function nodules are autonomous if they continue to produce hormone despite TSH suppression. They are very easily treated with radioactive iodine because all of the radiation goes right to that overfunctioning nodule and wipes it out. The rest of the gland is protected because there is such a low TSH, it’s not taking up any radiation. Very easy to treat with radioactive iodine.
Multinodular goiters are very common in middle aged females. They are usually benign. They are usually not toxic. They’re usually euthyroid but if they are toxic and they do need treatment, you could go with radioactive iodine or PTU, again for the hyperthyroidism of multinodular goiters. A scan is a good idea in a multinodular goiter, mostly because you want to rule out a dominant cold nodule, again, which might indicate malignancy.
Graves’ disease, everybody knows about. Subacute thyroiditis, remember, is an inflammatory process. It’s transient. They’re just releasing all this preformed