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PET SCAN question


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Hi -

The PET scan shows changes in cellular metabolism...basically blood flow to areas..... which means you see things before structiral anatomy changes...as you know they will inject some radioactive dye into your veins so that they can see everything in perfect detail. I think the no food, etc is simply done to ensure that your body is in a pristine state to be viewed and to erase the small chance that you may get sick to your tummy from the dye (my mom never did.) Caffeine makes sense as it constricts blood vessels (which you don't want.) --- Hope this helps, it is my layman's opinion...I do know that most doctors want you drinking water as it keeps you hydrated.

Someone may have a better answer...but don't be concerend about the no eating, etc.

Please let us know how it goes,


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The radioactive dye given for PET or PET/CT is not the same as is given for standard CT. It is actually a glucose solutuion with a radioactive tracer. This does not pose the same potential allergenic reactions as the dye used for CT. There would be no reason at all this should upset one's stomach. Some facilities have you drink a contrast medium and some don't. I believe the latest research suggests that large volumes of water work better then the contrast medium in this application.

The goal of the PET scan is to determine whether something is metabolically active or not. On CT alone a spot could be scar tissue, an inflammatory process or a benign cyst, one can't be sure. With PET if these areas are cancerous they will take up a LOT of the glucose solution, if they're not they will take little or none at all.

Inflamed areas of the body will "light" up as well but usually at lower levels.

You are asked to refrain from eating primarily to keep blood sugar levels low and to keep digestive activity to a minimum. Certain parts of the body naturally take in more sugar then others (brain, heart, kidneys, bowels). Typically you will be asked to have a low carb or Atkin's type meal for dinner the night before if you're having a morning exam. I've also been told to refrain from exercise for at least 24 hours (some places say 48 ).

The goal is to minimize all activity so false positives will not be an issue.

All of that being said, on my last scan I prepped for it like I have in the past, only to have to be called back to do the scan again 2 hours later after having eaten high carb foods, drunk a whole bunch of coffee and running around. :) They assured me the test would be fine despite the food and coffee. Go figure. :)

Hope this helped.


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Both answers are correct.

The need to keep Blood Sugars low is also due to the fact that the radioactive isotopes are in a glucose solution. Glucose is sugar. If your Blood sugar is too high before the test the tests cannot be given since the glucose will only drive it higher.

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