What Is PET and PET/CT?

What is PET?
Positron Emission Tomography (PET) is a non-invasive form of medical imaging. While other medical imaging technologies, such as Computerized Axial Tomography (CT) or Magnetic Resonance Imaging (MRI), provide data primarily on anatomy and structure, PET provides critical information on the biochemical and metabolic function of internal organs leading to accurate diagnostic information on the cellular metabolism of disease and the disease process.

As disease proceeds, there are changes in the biochemistry of cells and tissues. PET has the ability to detect changes caused by disease at the cellular level before the occurrence of anatomic or structural changes that may be detected by CT or MRI.

What is PET/CT?
PET/CT combines two scanning techniques – the PET (Positron Emission Tomography), which shows different functions of the body, and the CT (Computed Tomography), which shows detailed structural anatomy- into one clinical study. This PET/CT information will enable your physician to pinpoint the exact location of interest and helps in making an accurate diagnosis.

Because of its unique capabilities, PET/CT can play a significant and unique role in providing information about diagnosis and staging of disease as well as the planning and monitoring of treatment.

The PET/CT examination combines two scanning techniques—the PET (positron emission tomography), which shows different functions of the body, and the CT (computed tomography), which shows detailed structural anatomy—into one clinical study.

How Do PET and PET/CT Work?
PET is a nuclear medicine imaging test in which a “radiopharmaceutical” is injected into patients to obtain images that show metabolic process within the body. We generally use the radiopharmaceutical FDG (Fluordeoxyglucose), which is a radioactive form of glucose, or sugar, with a half-life of about 110 minutes. The FDG travels throughout the patient’s body, emitting positively charged electrons, known as “positrons”, as it decays. These positrons move through tissue for several millimeters before colliding with electrons. This collision produces “photons” which are sent out at a direction of 180 degrees.

The PET scanner’s ring contains thousands of detectors that surround the patient’s body. These detectors identify the photons as they travel from the body. Computers within the PET machine take this information and create an image showing the distribution of radioisotope within the patient’s body and organ systems. Cancerous cells generally have much higher rates of growth and glucose metabolism than surrounding, healthy tissue. Because of this, cancerous cells will absorb more FDG than healthy tissue, emitting more positrons that are then detected by the PET camera. With the use of the glucose-based FDG as a radioisotope, PET can identify cancers as “hot” areas on a whole body image.

What are the clinical areas in which PET and PET/CT are useful?
PET and PET/CT are now used as a clinical tool in the following areas:

• Cancer, for detection and determination of benign versus malignant tumor, as well as for “staging” and detection of cancer recurrence;
• Neurology, for examination of seizure disorders and assessment of dementias such as Alzheimer’s Disease;
• Cardiology, for examination of the heart tissue to determine if tissue is alive and can benefit from bypass surgery.