How is PET/CT different from traditional PET imaging?

Today, most of the Positron Emission Tomography (PET) scanners you find in hospitals, or delivered via mobile imaging, are actually PET/CT cameras. Modern PET/CT scanners combine both PET and Computed Tomography (CT) scans almost simultaneously to provide a greater amount of clinical data to assist in the diagnosis process.

Combining the benefits of PET and CT

A PET/CT scan includes two parts: a PET scan and a CT scan. The CT portion of the scan produces a 3-D image that shows a patient’s anatomy. The PET scan demonstrates function and what’s occurring on a cellular level. The PET scan is unique because it images the radiation emitted from the patient while the CT records anatomical x-rays, showing the same area from another perspective.

The role of attenuation correction

PET/CT scans not only pinpoint localization; they also offer significant help with attenuation correction, a huge advantage. During a CT scan, the system records numbers, called Hounsfield units, which measure the density of the tissue that it travels through. Not only does the CT produce images, but they also have numbers assigned to each individual pixel.

The PET scan measures the level of radiation coming from the patient and compiles information that the system needs to decipher. It uses algorithms and corrections, including the Hounsfield units from the CT scan, and adjusts the images in accordance with the corrected densities for each region.

In the 1990’s or early 2000’s, a PET-only scan would have used a transmission scan for attenuation correction or forgone it completely. Today, however, there is better technology available. Using both CT and PET to cross-check data and corroborate each other is a way to increase confidence and reduce guesswork. It gives significantly more data points to reference in order to determine a diagnosis and treatment plan.

PET/CT is more than just oncology

One of the biggest misconceptions about PET/CT is that its benefits are limited to diagnosing cancer. There are many new uses that are benefiting from PET/CT technology that fall outside of oncology. For example, in neurology, a brain CT or MRI only looks at the structure. The benefit of looking at function through an FDG-PET scan is that a functional change on the cellular level will be seen before a possible structural change. The same can be said for cardiac imaging, epilepsy, Alzheimer’s disease, dementia, infection and inflammation and a host of others. These are areas that could benefit from taking advantage of the advancements in the PET/CT world.


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