PET scan: in nuclear medicine, an advanced technique of positron emission tomography (PET) for visualizing or scanning details of soft internal organs, for example, the brain, that do not show up on an X-ray film.

Dictionary of Sexology Project: Main Index

A positron emission tomograph is a medical imaging device that allows for a functional rather than an anatomical analysis of the human body. The technique employs a glucose molecule that has been radioactively labeled by chemically binding a fluorine molecule to it. This fluorine molecule was first placed in a particle accelerator (a cyclotron) to bring it in an unstable state. Fluorine, when hit by an ion beam in such a cyclotron, becomes an unstable positron emitter with a half life of 2 hours. The chemical bond of fluorine and glucose is known as FDG (fluorodeoxyglucose).

After injection of FDG in the study object (e.g. a patient), the body starts to metabolise the FDG as if it were glucose. Cells with high metabolism have higher energy needs and thus take up more glucose, or FDG, from the bloodstream. Typically, cancer cells have high energetic needs and thus take up most of the FDG presented. At these sites of high FDG concentration, the concentration of positron particles emitted is consecutively high.

When such a positron collides with an electron, they annihilate (after briefly forming a positronium) into pure energy. Because of the law of conservation of energy, two photons (basically energy quanta) are formed, each having half of the original energy and they are emitted in exactly opposite directions. When a scanning device detects two such photons striking a detector ring at 180° simultaneously, their origin had to be a positron emitted from the FDG.

This way, a PET scanner is able to visualise high FDG concentrations in the body, such as those occuring in cancer cells.

"PET scan? What, are they looking for,
little cats and dogs inside you?
What fresh hell is this?"
- wertperch

I had a PET scan on Wednesday morning, Oct. 8. The technical explanation, above, covers the imaging process - this is the more personal version.

The PET scan started out about 24 hours before the scan itself - I was not supposed to exercise. That meant I missed my Tuesday morning dance class - major bummer. But even 24 hours after exercising hard, muscles are still uptaking glucose, so it can obscure the scan.

It also requires fasting for 6 hours beforehand, which I don't really mind, since I often skip breakfast. What it did mean, though, is that I couldn't have my usual Yorkshire tea, and arrived at the doctor's offices with a raging caffeine headache. I seriously considered cheating, and told the nurse with all the pokey pokey. She laughed, and said that actually, they've tested it, and that caffeine increases the glucose uptake, and it can, indeed, obscure the test. Glad I didn't cheat.

Injection of the radioactive glucose, and a command that I was not even allowed to READ for the next hour - so the muscles holding up the book wouldn't steal the glucose. Who knew? But along with a fairly hefty dose of Valium, I did what any stressed-out, worried, former cancer patient would do - I fell asleep in the chair for an hour.

Then they helped me stagger in to the PET machine, where I lay for 45 minutes while the machine buzzed and whirred. The only uncomfortable part is that I had to hold my arms up over my head the whole time - I didn't know it was possible to get muscle cramps in your shoulders.

Then, thank the Powers That Be, they let me go, and wertperch walked me down the street to the local coffee and tea shop. Food! Strong. Black. Assam. It had to be one of the top three cups of tea I've had in my entire life.


My doctor called me in the early afternoon.

Although I don't know a lot of the details, apparently there are seven locations that showed up as "hot spots" on the scan - two behind my right collarbone (the ones I was nagging the docs about in the first place), two in my right chest wall, and three along my mediastinum - adjacent to the trachea, apparently. Given the pattern, it's very unlikely that it's not a recurrence of the previous breast cancer.

I will know much more when I speak with my oncologist, this afternoon. From what I read, this is a regional recurrence - the next layer of lymph nodes out from the original cancer site.

Good things - if it is contained within the lymph nodes, it's a better prognosis than if they are new tumors. The fact that it's within the lymph nodes means my immune system is still fighting the cancer, and in addition that the cancer has not invaded any other organs. Breast cancer is most likely to go next to the brain, bones, liver and other abdominal soft tissue, and lungs. The fact that there is no evidence of any additional metabolic activity in any of those is a good sign.

Also, the fact that the CA-15-3 numbers are not up means that it's not invaded my bloodstream, so thus another indicator that it's contained within the lymph nodes.

Down side - wertperch and the imp are distraught.

I'm fairly philosophical about the whole thing. I'm VERY glad I bullied my docs into taking a second look at that beastly lymph node above my collarbone - proves my intuition is more accurate than their biopsies. (So there!)

The upside of having done the treatment before is that I know what to expect - although the treatment is brutal, I survived, I recovered, and was back to pretty much full health, barring the odd shoulder stiffness and reflux. I've also been getting more exercise, and the tougher I am going into it, the better the results usually are. Can you say, "durable"? And I even still have my own axe and teeth!

So I will add an update to this sometime over the weekend. Sometimes it takes me a few days to process all the medical gobbledygook, and then we'll all know what we are in store for. (For what we are in store?) - We'll all know what to expect.

Love to all,


INCONCLUSIVE. Apparently PET scans have a fairly high rate of false positives - around 20%, so we won't really know the verdict and the treatment (if any) until after I have the supraclavicular nodes removed. (And now aren't you impressed that I know such big words?)

But from my perspective, this is positive. Yes, we have to wait more, which is sort of hellish, but it's possible that it's not a recurrence at ALL - just weird, overactive lymph nodes. So light a candle for us, and hope it all turns out to be a false alarm. Hugs!

(r) (8.4 min) @wertperch says re PET scan: Now you have to say that they produces falls paw-sittives
(r) (8.4 min) @wertperch says re PET scan: Arf, arf, arf...

Log in or register to write something here or to contact authors.