Image Quality in Positron Emission Tomography (PET)

In this article, we explain some of the performance parameters that directly impact the image quality in positron emission tomography (PET) imaging. PET, when combined with computed tomography (CT), is a proven tool in oncology for staging diseases and tracking the effectiveness of treatment. PET/CT enables physiological processes, as seen on PET, to be mapped on the patient's anatomy, as seen by CT. PET/CT systems also have cardiology and neurology applications.

While the technologies used by each manufacturer for the CT portion are similar, there are different technologies available for PET. One reason for the differences is that each technology represents a compromise between the different factors affecting image quality.

A great deal of research has been done to establish the factors that lead to acceptable PET image quality and to develop objective measures of it (as found, for example, in the National Electrical Manufacturers Association's NU 2-2012, Performance Measurements of Positron Emission Tomographs PETs). Buyers should use these objective measures—such as noise equivalent count rate (NECR), which we will explain. However, to understand these measures, it is necessary to first discuss how a PET image is acquired and what parameters affect the PET detection efficiency and characterize the detection system.

For most PET studies, a radiopharmaceutical tracer is administered to the patient, composed of carrier molecules tagged with a positron-emitting radionuclide. Specific carrier molecules and radionuclides are used in different PET studies. The radiopharmaceutical interacts with specific molecules in the body; that is why PET/CT imaging is also called molecular imaging.

The whole process is as follows:

2. The patient is placed in the bore of the PET/CT scanner.

3. The radionuclide in the radiopharmaceutical decays and emits positrons. This positron emitter usually...