Читать книгу Overcome the Challenges of Cancer Care - M. D. Rosenberg - Страница 21

Preparing for PET/CT scans involves injecting a labeled sugar that’s taken up by the body; we can then see that sugar on a scanner. Cancer cells use up lots of sugar quickly and inefficiently (remember the Warburg effect), so we can see cancer cells “light up” on PET/CT scans.

The lighting up of a region in PET is called activity. The activity indicates how much sugar a part of the body has taken up, which gives the region a glow. The greater the glow, the faster the cells are using sugar, and the more of them there are. Sounds like cancer, right?

The PET image we get is grainy. This makes it hard to determine exactly where the activity is. To help pinpoint the area, we get a CT scan the same day. That’s why we get a PET and CT together—to see the activity and help localize it.

So why wouldn’t we just use PET/CT for everything? A PET depends on cells taking up labeled sugar. The cancer cells want to use sugar because they’re trying to overtake the rest of the body, like weeds in a garden. They need the energy to keep things moving. But there are also normal fast-growing cells that take up sugar—say, cells of the immune system. Immune system cells take up a lot of sugar to fight off invaders or even cancer! It’s often hard to tell inflammation from cancer on a scan.

Furthermore, not all cancer cells reliably take up the labeled sugar. A PET/CT scan is good for seeing some cancers but bad for others.

PET/CT scans are also of limited use in parts of the body that use lots of sugar normally, like the brain. The brain is always working hard and taking in lots of sugar. This makes it hard to see any cancer that might have gone to the brain.

Finally, you may remember the magical one-centimeter size in scans. PET/CT scans are no different! These scans have limited resolution; they can’t see a single cancer cell. Masses that aren’t big enough don’t show up in the scans.