PET stands for positron emission tomography. The machine detects gamma rays which are emitted indirectly by a tracer (positron-emitting radionuclide) which is placed in the body on a biologically active molecule. The images are reconstructed by computer analysis. Modern machines often use a CT X-ray scan which is performed on the patient at the same time in the same machine.

PET scans can be used to diagnose cancer activity and recurrence. PET scans are often used to see how effective an ongoing treatment is.

 

A CT or MRI scan can assess the appearance of body organs and but cannot assess function. A PET scan looks at function. Often, information obtained on a PET scan is evaluated in conjunction with the findings on a CT or MRI examination.