Question about Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET) - does one technology supercede the other, or are they used in entirely different applications?
-FK
MRI is an all-purpose passive scan and can identify different types of tissue. It can replace conventional X-rays and CAT scans.
PET scan uses a radioactive tracer coupled to sugar molecules. After you are injected with this tracer, a scanner is used to find where the sugar molecules are migrating to. Fast growing tumors have high metabolism so those areas show up brightly on PET scans. You can also use it to find which areas of your heart and brain are active (alive). So it’s a very specific purpose test and complements MRI scans.
Well…
Standard x-rays are more useful when, say, you’re looking for a broken arm or if someone got some metal shavings in their eye…something like that. You can’t get into an MRI tube with ferrous metal in you (bad, bad juju), and metal makes weird, starlike artifacts in CT scans.
In a PET scan, you have to be looking for something that is metabolizing fast and furiously…like a neoplasm (tumor). They can tag different agents with the positron emitter to look at different areas (potassium for bone, for example). You get a whole body scan, and rapidly metabolizing areas show up as hot spots. That’s one of the way they can see if a tumor has metastasized.
MRI scans typically take longer to perform, so they’re not generally the thing you’d use for, say, someone that got into a car wreck. They’re great for soft tissue like brains, cartilage, and muscle, though.
CT is real good at looking at bony structure, and injectable contrast can be used to look at things like kidneys, arteries, etc.
They all serve a purpose.
In short then: CT (and other X-rays) & MRI look at structure. PET scanning looks at function.