PET, PET/CT – these are the technologies available today. It really can be quite confusing.
Here is an analogy that can help you sort everything out. Imagine flying over the United States at night. As you look out your window, you see the lights from all the cities and towns. It is not too difficult to identify the big cities, but it can be challenging to identify the small towns. A PET scan alone is a lot like that. The PET scan shows a bunch of hot spots floating in 3D space. It is not always easy for the radiologist to know what structures in the body correspond to those hotspots.
Now imagine that you have a device which allows you to see the state lines as you look out the window. This would make it much easier to identify the small towns. This is what CT adds to PET.
Before PET/CT was invented, some imaging centers tried to create PET/CT by doing a PET scan, then moving the patient to the CT scanner and getting a CT scan. Back to our analogy, this would be like flying across the country twice. Once to get a picture of all the lights. Another time get a picture of the state boundaries. Not only does that take twice as long, but it depends on the plane following the exact same path each time so that the picture of the lights lines up with the picture of the state boundaries.
PET/CT is like a plane that can take both pictures at the same time. This means that you only have to fly across the country once and that the pictures will be exactly aligned.
In fact, PET/CT is twice as fast as PET for complicated physics reasons. This means that you will have to lie still in the scanner for about 20 minutes instead of 40 minutes. And the PET/CT scan will also be the most accurate. It’s not often that you get both faster and better!