Tomorrow's Test

Tomorrow I have a PET scan. I can already predict the results.

"Dear sir:

Most of your pets are spoiled, fat and ill-behaved. The exception is Max, who is merely spoiled and ill-behaved. Your dog smells like Beef-a-roni and the cats have fish-breath from eating canned salmon. Oh, and while you weren't looking, the other dog ate all your fig newtons."

That's the sort of PET scan I expect.

PET scans are actually fascinating. I don't know if anyone's all that interested in the mechanics of the thing, but suffice it to say that it involves anti-matter. Yes, anti-matter, that great hokum from Star Trek. The way it works is that imitation glucose molecules are tagged with radioactive isotopes of carbon, nitrogen, oxygen or fluorine (usually the latter because if its slightly longer half-life). Inside the body, the radioactive isotopes undergo what is called beta decay, and in the process emit positrons. A positron is the anti-particle of the electron - yes, Virginia, it's real anti-matter.

These positrons fly out into your tissues, where they quite by accident encounter normal electrons. The two particles completely destroy one another and produce a pair of gamma rays that are in the ballpark of 511 keV, moving in almost exactly opposite directions (the conservation of momentum isn't just a good idea, it's the dad-gummed law). The gamma rays are then received by the scanner, which exploits the paired nature of the gamma rays to selectively reject gamma rays that come from elsewhere.

The result is a three-dimensional model of the metabolic activity taking place in your body. The brain and heart are pretty active, but so are cancers, and by noting the prevalance of metabolically "hot" lymph nodes in one's scan, one can determine the extent of one's cancer.

And my dog really does smell like Beef-a-roni, by the way. I don't know why.