NeuroLove

PET and cancer?

FLT PET is a relatively newer way to look at cancer. This shows the image of a woman with leukemia (blood cell/bone marrow cancer) before and after chemotherapy. FLT is similar to FDG (which is the glucose usage monitoring PET ligand I discussed before). FLT also shows glucose usage but it seems to be better at showing cancer-related cell division activity than FDG is. It won’t of course only show cancer activity, but it might help to visualize cancer during treatments and thus, treatment success. This is an interesting usage of PET and I’ll be curious to see if as time goes on it will become more mainstream. I think it’s really interesting that you can see the affected bone marrow here. This is not a structural scan at all- you do not get to see bones with PET- it’s not like x-rays or CT scans. PET is functional imaging, which means you just see where that radioligand is active, and in this case, you can see it in bone marrow, and it almost looks like a colored x-ray! Of course, PET imaging itself has some downsides, which I will try to talk about in the future that might prevent something like this from becoming more commonplace.

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This is another PET image, but this time comparing the brain of a non-smoker to a smoker and with a different radioligand.  This time, it is not measuring glucose metabolism but instead MAO-B (monoamine oxidase type B) levels. MAO-B breaks down dopamine in the brain.  There is something about smoking that hinders the breakdown of dopamine, the feel-good neurotransmitter that is the culprit in addiction (pretty much all drugs of addiction skyrocket dopamine levels in the brain- which is not to say that dopamine itself is bad, it’s actually very important, but such high levels due to a foreign compound cause that compound to be addicting).  This is probably the way that smoking is addictive, because it will increase the levels of dopamine in the brain by hindering dopaminergic breakdown.  You can see that smoking has a huge effect on MAO-B levels.

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In my last post, I introduced a bit about PET (positron emission tomography).  These are more glucose-metabolism based PET images of a person doing different activities.  It is pretty awesome that you can see which areas of the brain are active based on where it is using energy (glucose).  These match up with the fMR (functional magnetic resonance) images that you would get from a person doing these same tasks in an MRI machine.

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PET images of Alzheimer’s brain

PET (positron emission tomography; said like “pet”- the animals you have at home) is a type of imaging that relies on a radioactive ligand (injected into the patient) to give off a signal for a particular type of chemical.  For instance, if you want to look at a specific receptor or neurotransmitter, you could put in a competitive radioactive ligand that would bind to that receptor and it would tell you where that receptor is and how much of the neurotransmitter is binding.  It’s not completely straightforward (for instance, if the signal decreases, it could mean more neurotransmitter is taking up the receptors OR it could mean there are fewer receptors there in general).

This is a PET image of a healthy control and an early/late-stage AD patient’s brain.  This type of PET is glucose-based, so it’s just tracking overall brain metabolism.  You can see the early AD brain is already decreased in overall glucose metabolism (how much energy the brain is using), and by the late stage, it is severely decreased.  This is likely due to the severe, progressive neurodegeneration that occurs in AD.

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