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Pete Soule asked:
In an eleven month period recently I had 3 CAT scans and one PET scan. For the last two CAT scans they said “no contrast”, which was, apparently something to drink 15 minutes before the scan. I thought it might be something with a large scattering cross section for X-radiation but I don’t know – 15 minutes seemed like a short time to get to the blood. What is it and what does it bring out??
Contrast is a substance you inject (or administer) into people, which is usually something like Barium or Iodine (hopefully you wouldn’t inject Barium – it’s not very nice) these have big nuclei which scatter x-rays. They circulate in the blood stream and if you have a cancer or something, the blood vessels which supply cancer are leakier than blood vessels supplying healthy tissue, so you tend to get a build up of contrast agent in the abnormal area.