How and when should PET scans be used? What do they show?

What is an FDG PET CT scan and when should it be used? PET CT, as I mentioned, combination of PET and CT. It's only mentioning PET, but usually we do it with a CT. The PET part, positron emission tomography, is you infuse radioactive tracer, which is very short half-life, so it's not dangerous for you. You give a tracer in the vein and then it distributes in the body. This tracer is a nucleotide that is emitting radiation and it's attached to a sugar. The cells in our body that use a lot of sugar are, for example, the brain cells. Actually it's not shown here, but usually the brain lights up very well. The brain cells, cancer cells, inflammatory cells. There is where you see the tracer. We know where the inflammation usually is, like in the teeth. Oftentimes there's something lighting up, or in the lymph nodes if you have a cold. We also know that the brain has a lot of sugar uptake, but other than that, if something appears on the PET, then we know there might be malignant cells. This is pretty sensitive and pretty well established. It shows us the metabolism. High metabolism is a very strong signal for cancer cells. It is of prognostic significance. If you have a lot of those cancer cells in your body, it's worse, of course. It shows disease activity together, this combination of tumor mass and proliferative metabolism activity. The negative, the disadvantages are that you can have false positive results. As I mentioned, you can have an inflammation somewhere and you don't know if this is inflammation or is it tumor. As I mentioned, since we know where the inflammation usually is, most of the time we can differentiate. In the worst case, we have to stick a needle in there to see if it's really myeloma or if it's just an inflammation. The radiation dose is of course a bit higher because you add the nuclear tracer, which still has a low radiation dose, but it's not zero, to the actual CT that also has some radiation exposure. This combination has a bit higher radiation. But again, the information we gain from that is so valuable that I think it's really worth taking this very, very, very tiny risk of getting a cancer from radiation exposure. PET stands for Polytron Emission Tomography. It's a very sensitive technique. It's a functional imaging technique and it is different from an anatomical imaging technique such as CT scan or MRI in that it tells us about functional changes before anatomical changes happen, such as changes in the bone marrow or in the soft tissues, which can sometimes be missed by a more traditional, less sensitive imaging technique. So PET uses radioactive imaging agents, which are positron emitters and a positron travels a certain millimeters in the body. It collides with an electron and it makes two almost 180 degrees apart gamma photons and we detect those gamma photons. Very little amount of the contrast agent is given in a PET scan and so it's very sensitive and powerful and now we are getting better and better at the PET technology to give you less dose and get more qualitative and quantitatively accurate data. If you use the regular PET CT, yes, it's different because the CT part, PET is showing you where there's activity, where it's metabolism, where sugar is taken up and cancer cells do that, myeloma cells do that. So that's the PET part, but the CT part shows you the actually, if you only do a PET, you have kind of clouds of tracer uptake and you can kind of estimate where the body is, but the CT gives you kind of the background. It shows you, okay, there's the skeleton, there's the brain, there's the organs, there's the limbs. So the CT is in the PET CT is mostly just to allocate where the uptake is. What we recommend also in the new guidelines that we say we want to, and a CT, we can do a CT has a much higher sensitivity. It's not just showing the background of the body. It really shows the bones. It really shows the areas where the myeloma is taking place. So we recommend that if you do a PET CT in myeloma that you use this good quality CT and use it as the allocation part of the PET CT. So it's not only that you kind of can guess where things are, but you really have the full information from the CT plus the full information from the PET. So a standard PET usually has a very low resolution CT, a little bit higher resolution CT gives us both, best of both worlds basically. So PET CT should have a good CT in it if it's used for multiple myeloma. How does a PET CT detect cancer cells and how long is the procedure? This, it depends on the tracer with FDG. It's rather short. You give an infusion with this tracer, which is a radioactive sugar, only for you hours is radioactive. So you give this as an infusion and then it distributes through the blood in the body. And then the cells that have a high metabolism need a lot of sugar, are very active like cancer cells, but also like inflammatory cells, also like brain cells and heart cells. So the brain and the heart, they always light up because they need a lot of sugar. But we know that, so we ignore that more or less. And then you give this infusion, the sugar goes into those cells and then you take a picture a few hours later and then combine that with the CT. So you see where those sugar accumulations are basically and that's what we do. So it takes a few hours, but you're not a few hours in the machine, you're just getting the infusion, then you wait until it's distributed and taken up and then you get the CT. When should PET CT be used? At the moment, the FDG PET CT gives us the most information in symptomatic disease because a major thing in symptomatic disease is what is left after our treatment, for example, high dose chemotherapy. We want to know what is left after that and their PET CT is at the moment the best choice. So in symptomatic patients, PET CT before and after treatment is our recommendation.