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4.10.10

Positron Emission Tomography (PET) is a dirty business

Prior to starting my PhD at Berkeley I worked at the UCLA Brain Mapping Center (which really needs a new website!) as the PET scanner operator. That was awesome! But wow were there some items that were not in the job description... good and bad.

Bradley Voytek Bill Nye


Good: yeah, that's me "scanning" Bill Nye the Science Guy for the "adult" version of his kid's TV show, which was named The Eyes of Nye. He was doing an episode on drugs and drug abuse. Since that's what my boss (and by extension, I) was studying at the time, he came and did part of his show in our lab.

I started working at UCLA a few months after finishing up my undergraduate work at USC. As I've talked about a bit, I was a downright awful student as an undergraduate. Terrible. Like, kicked-out-of-school bad. So when I decided I wanted to pursue a career in academia, I knew I needed some research experience to overcome my crap GPA.

When I got the job at UCLA, I was pretty excited about being able to work on my own side-projects! Ultimately I got one first-authored manuscript (Differences in regional brain metabolism associated with marijuana abuse in methamphetamine abusers) and two others (here and here) out of my two years in the lab.

All of these papers used PET and involved former methamphetamine abusers, but those weren't the only people we scanned. Because I was the primary PET scanner, I worked with many collaborators including Sanajaya Saxena (who was Jack Nicholson's psychiatric consultant for OCD in As Good As It Gets).

That's what happens when you're a scientist in LA: you work with TV and movie stars all the time. It's not just all the waiters and baristas that are actors; all the scientists are, too!

Now, here's how PET works: a radioactive substance is put into the body—either through ingestion, inhalation, or injection—where the specific radioligand determines the pattern of uptake. To study brain function, the radiotracer we used was F18 fluorodeoxyglucose (FDG). This is effectively a radioactive version of glucose, which is a very important "fuel" for the brain. Regions of the brain that are "working harder" require more fuel, and thus more radioactive glucose is more concentrated in them. The PET scanner detects the relative density of the radioactive glucose in the brain, and thus can be used to build a 3D statistical representation of neural activity distributions.

Bradley Voytek Synapse 2005 Differences in regional brain metabolism associated with marijuana abuse in methamphetamine abusers


Here is an example from my only first-author PET paper showing that long-term marijuana users who are also methamphetamine abusers show lower glucose metabolism in temporal lobe and basal ganglia regions compared to methamphetamine-only abusers.

Now those of you paying attention may think, "but gee, you're injecting radioactive substances into the body, isn't that dangerous?!" "Noooooo, not at the doses used in our experiments", I would say! 75% of the radioactivity has decayed within 2 hours of production, which gave us narrow time-windows for research. I would pick up the FDG at the cyclotron, walk it back over to the PET scanner (shielded in a very heavy lead container), and start the experiments.

However, FDG is cleared through the body largely via the bladder. Thus, if we had subjects pee after our study, we could lower the radioactive dose further. Even though the doses are low, getting them lower is always better.

Now, did you catch that?

We can lower the radioactive dose by having subjects pee.

Pee. RADIOACTIVE PEE.

Here's the part that wasn't in the job description:

Part of my job was to grab my Geiger counter, put on my gloves, grab my radioactive spill cleaner, and head into the bathroom after our subjects peed. Then I got to scan the entire bathroom and scrub up any "hot spots" (spilled radioactive pee).

Guys suck at peeing. We splash everywhere. I know this as a verifiable scientific fact now.

And now you all know my futuristic, radioactive neuro-janitorial story.