PET/CT
How does PET/CT work?
PET/CT is a combination of a PET scan and a CT scan
obtained at one time and by a single piece of equipment.
Positron emission tomography, or PET, is a painless diagnostic
test that allows radiologists a unique view of the body’s
biological functions. The PET scan differs from an x-ray
or CT image in that it looks at the body’s metabolic activity
and provides important information about the body’s internal
physiology. Almost all diseases alter the body’s biological
processes. PET is able to discover these changes in their
earliest stages, often before any symptoms appear. With this
information on early developing cancers, effective treatment
plans can be initiated sooner. PET can sometimes eliminate
the need for other invasive procedures and, by correctly staging
cancers, may prevent unnecessary surgical procedures.
Cancer cells have higher metabolic rates than normal cells,
and show up as denser areas on a PET scan.
Unlike the PET, the CT scan very accurately evaluates anatomy. By combining these studies,
physicians can take advantage of the strengths of both modalities. Before the scan
begins, a radiopharmaceutical (tracer), which is comprised of a radiolabeled form of
glucose, is injected into the patient. The patient then waits about an hour for the tracer to
distribute within the body.
The patient is then placed on a table that moves into the scanner and first undergoes a very
fast CT scan. This takes less than a minute in most circumstances. The table then moves the
patient into the PET scanning portion of the camera. The PET scanner consists of
hundreds of radiation detectors that surround the patient. Using the emissions given off by
the injected radionuclide, the PET scanner measures the amount of metabolic activity at a
site in the body and a computer reassembles the signals into three-dimensional images
of tissue function. The PET scan portion of the exam takes a little more than 15 minutes.
The entire exam lasts about 20 minutes for most patients.
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