PET scans (positron emission tomography scans) are often done in conjunction with CT scans (computerized tomography scans) or MRI scans (magnetic resonance imaging scans).

While CT and MRI scans show images of your body’s internal organs and tissues, PET scans can give your healthcare provider a view of complex systemic diseases by showing problems at the cellular level.

Unlike MRIs, PET scans use positrons. A tracer is injected into your body that allows the radiologist to see the area scanned.

An MRI scan can be used when your organ shape or blood vessels are in question, whereas PET scans will be used to see your body’s function.

MRI exams use magnetic fields and radio waves to take images of organs or other structures inside of your body.

These images can be used to determine if you have injured or unhealthy tissue within your body.

A PET scan is an imaging exam that’s used to diagnose diseases or issues by looking at how the body is functioning.

It uses a special dye with radioactive tracers to help the machine capture changes in how the body’s working, such as how it absorbs sugar or how the brain’s functioning.

A PET scan is usually performed to:

  • identify lapses in cognitive function
  • show how the heart is working
  • find cancer
  • examine how the body is reacting to cancer
  • find an infection

PET scans are often performed on CT/PET or MRI/PET combination machines.

This makes the process quite similar to an MRI procedure.

If your PET scan is performed on a combination machine:

  1. You’ll first receive the radioactive tracer. The tracer may take up to an hour to be absorbed.
  2. You may be offered ear plugs or headphones to help protect your ears from the noise of the machine.
  3. You’ll be asked to lie down on the table. The table will slide into the MRI/PET machine.
  4. The MRI/PET machine will begin imaging your body. This process can take up to an hour and a half. You must remain still during the imaging process.
  5. The table slides out of the machine.

CT/PET machines have been in operation longer than MRI/PET machines, which are typically more costly.

Although the first consideration is whether or not you need an MRI, your healthcare provider might have other reasons for choosing a CT/PET over an MRI/PET.

Why your doctor might recommend a CT/PET?

  • established procedures
  • familiarity
  • been in use for a long time
  • exams can be done quickly
  • accuracy is established
  • less expensive
  • better soft tissue visibility
  • convenience if you also need an MRI
  • no radiation
  • better time capture
  • better anatomic resolution

Why your doctor might recommend a PET/MRI?

  • increased sensitivity for certain organs
  • less exposure to radiation

Your healthcare provider might suggest a PET scan if there’s a need to see how the body’s functioning in regard to:

  • blood flow
  • oxygen use
  • metabolism of organs and tissue

Most PET Scans are done in a CT/PET combination machine. If you need both an MRI and a PET scan, they can be done at the same time in newer MRI/PET machines.

If you have metal, medical implants, tattoos, experience claustrophobia, or may be pregnant, you should notify your healthcare provider before getting an MRI, PET, or CT scan.