Sunday, March 22, 2009

Thoughts about the PET scan

This is Ian writing. Calin's PET scan scheduled for Tuesday inspired me to ask her permission to be a guest blogger for a day and share a few thoughts about PET scans.

When Calin first had some PET scans in 2001, I became fascinated by the idea because I had a vague memory from high school physics that the positrons which form the basis for the PET (a.k.a.Positron Emission Tomography) are a form of antimatter. Indeed, positrons are the antimatter counterpart of the electron. Electrons are negatively charged and positrons are positively charged. When an electron and a positron bump into each other they are both annihilated and gamma rays are given off.

The idea of the PET scan, as I understand it now, is that you are injected with a bunch of positrons, which are magically attached to something like glucose or estrogen. Any cancer cells in your body will be growing faster than normal cells, and therefore taking up lots of glucose or estrogen (depending on what type of cancer you have). The positrons will therefore concentrate in cancer cells. They will keep bumping into electrons and getting annihilated, and the gamma rays given off by these annihilations (having been detected by a giant donut around your body) can be used to draw a picture of where the glucose, or whatever, was being taken up. Abnormal concentrations are likely indicative of cancer, as opposed to scar tissue left behind by dead cancer cells. The differences between cancer and scar tissue are hard to detect on other types of scans, so the PET scan will likely provide insight into how Calin's treatments are progressing.

So that's everything I know, or think I know, about the science of the PET scan. However, there's more too it than that. Reading about the science still doesn't get me past the fundamental question of “What the heck? Antimatter?!?”

To explore a slightly less scientific aspect of antimatter, I did some research in the form of viewing a 1967 episode of Lost in Space, called “The Antimatter Man” (you can view it here). This episode presents antimatter the way that I think seems more natural: as the stuff of which a parallel universe is made, a parallel universe filled with people who look identical to us, but are actually our nemeses, and who are bent on trapping us in their world and taking our position in ours. At first you may recognize them by their symbolically black and white patterned outfits (see picture below), but after they steal our clothes, only a telltale scar can reveal the difference (that and the fact that they act like evil jerks).

Of course the climax of the episode must surely be when the matter and antimatter versions of the same man battle each other to see who will live on. This was also the case in the Star Trek episode “The Alternative Factor” (available here) of similar vintage, where the nature of the epic struggle between a man and his antimatter nemesis caused Kirk to wonder, “How would it be?...Trapped forever with a raging madman at your throat...until time itself came to a stop...for eternity...how would it be?”

OK, back to “reality.” It seems to me that the reality of the PET scan, which includes the creation and collection of antimatter positrons by smashing particles in a cyclotron (either somewhere underground in the UW Medical Center, or perhaps at a new facility in Kent, which has come a long way since the tractor pull reputation of yore), the attachment of the antimatter to familiar substances to trick the cancer cells into building up concentrations of positrons, the continuous annihilation of the positron and electron alter-ego pairs, the detection of the highly energetic gamma rays as they flee the annihilation events, and the creation of detailed images to aid cancer diagnosis and treatment, are far more far fetched than anything that the Lost in Space and Star Trek writers could have thought up.

1 comment:

Robert said...

Hey Ian, you should be a science teacher if fish population predicting doesn't work out.