PET/CT is a combination of two imaging techniques.

Hear Dr. Peterson talk about PET/CT technology. (QuickTime required)

PET
The PET portion of PET/CT stands for positron emission technology. Physicians use PET scans to assess the body's biochemical activity. In a full-color image, PET shows us the rate at which the body's cells are metabolizing (breaking down and using) glucose. Glucose is a type of sugar and one of the body's main energy sources. Every cell in the body uses glucose to function, and cancer cells metabolize glucose at a faster rate than normal cells. PET scans display the metabolic activity of cells throughout the body, which helps us locate cancer cells that may otherwise go undetected by other diagnostic methods, such as x-rays or MRI (magnetic resonance imaging).

How a PET image is achieved is a complex process. In brief, a sugar solution is tagged with a small amount of radioactive material (called a radioisotope) and injected into the bloodstream. After the radioisotope has had an opportunity to circulate throughout the body, it begins to break down. As it decays, the radioisotope gives off particles called positrons (the "p" part of PET). When a positron collides with its opposite particle, called an electron, both particles are completely destroyed in a process called electron-positron annihilation, and as a result, light in the form of gamma rays is produced. The PET machine is able to use these gamma rays to construct a color-coded picture of the metabolic activity inside the body. In places where the radioactive sugar solution is being metabolized the most—such as organs and cancerous tumors—more gamma rays will be produced, allowing us to see where tumors are occurring in the body.

Because PET can pick up on the slightest abnormalities in cellular activity, we are able to detect malignant tumors much earlier, even before the patient experiences any symptoms. And as most people know, earlier detection increases our chances of finding a treatment that works. PET is also an important tool in staging tumors (determining how far the cancer has developed) and discovering if and how far the cancer may have spread. This information also helps us determine more effective treatment options.

CT
The CT in PET/CT stands for computer tomography. Originally referred to as CAT Scan (computed axial tomography), CT creates three-dimensional (3-D) images of the body's internal structures by taking multiple x-rays from many different angles. The computer then combines these two-dimensional x-rays (called slices) to form a 3-D graphical representation that serves as a kind of digital map of the body. CT scans can provide us with clear, 3-D images of bone tissue, soft tissue, organs, muscles and any existing tumors. CT scanning is an extremely fast and efficient process; up to four slices of data can be obtained in less than 350 microseconds. The whole body can be scanned from head to toe in the span of just a few seconds. When CT first began to be used in the 1970s, images were 100 times clearer than traditional x-rays, and the technology has only advanced since then. Because of the clarity of the anatomical images provided by CT, physicians are able to locate and analyze the exact size and shape of tumors with greater precision and accuracy.

PET/CT
When you combine the anatomical imaging of CT with the biochemical imaging of PET, the result is a powerful diagnostic tool. PET and CT alone have their limitations, but by obtaining simultaneous CT and PET scans, physicians can pinpoint exactly where in the body abnormal cell activity is taking place. We can also determine how far along any cancer has progressed, if cancerous cells have migrated, and an optimal surgical route if cancer removal is necessary. Because PET and CT scans are performed at the same time using just one machine, the risk that the images won't align due to shifts in the patient's position is eliminated. In fact, studies have shown that PET/CT is 33% more likely to accurately detect a tumor than if PET and CT scans are performed separately. Ultimately, the most important benefit of the combined PET/CT scanner is an increased potential to catch and locate cancer and other life-threatening conditions earlier and with more accuracy to save and prolong the lives of our patients.