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What Is a PET/CT Scan?
A PET/CT scan combines positron emission tomography (PET) — which images cellular metabolic activity — with computed tomography (CT), which provides detailed anatomical images. Together, they allow correlation between metabolic activity and body anatomy in a single imaging session.
Educational content only. PET/CT is a specialized imaging study ordered in specific clinical contexts determined by a licensed provider. DOD does not perform or interpret PET/CT scans.
Quick Answer
A PET/CT scan uses a radioactive tracer (typically FDG, a glucose analog) administered intravenously to show areas of high metabolic activity in the body, combined with CT to provide anatomical detail. The study takes approximately 2–4 hours including preparation, radiotracer uptake time, and scanning. It involves radiation from both the radiotracer and the CT component. Provider orders are required. DOD can review PET/CT order requests for eligible patients in supported states.
How PET/CT Works
PET imaging works by detecting gamma rays emitted by a radiotracer injected into the patient. The most commonly used radiotracer is F-18 fluorodeoxyglucose (FDG) — a form of glucose labeled with a radioactive fluorine isotope. Cells with higher metabolic activity absorb more FDG. After approximately 60 minutes of uptake time (the patient rests quietly), the patient is placed in the PET/CT scanner.
The PET component detects gamma rays and generates a functional map of metabolic activity. The CT component simultaneously acquires anatomical images. A computer fuses the PET and CT images, allowing radiologists and clinicians to see both metabolic activity and anatomy in context. According to RadiologyInfo.org, total appointment time is typically 2–4 hours, with most of that time being the uptake period.
Important preparation note: patients typically fast for 4–6 hours before PET/CT to reduce background glucose levels. Diabetic patients should discuss blood glucose management with the facility. Vigorous exercise should be avoided for 24 hours before the scan. Patients should follow preparation instructions from their specific facility.
Frequently Asked Questions — PET/CT
Sources and Further Reading
- PET/CT Scan — Patient Information — RadiologyInfo.org (ACR / RSNA)
- PET Scan — MedlinePlus (NIH)
- Nuclear Medicine — U.S. Food and Drug Administration (FDA)
Related Education and Order Pages
Need a Provider Review Before Scheduling PET/CT?
$40 virtual provider review. Orders issued only when medically appropriate. Facility acceptance varies.
Start Virtual Consult — $40Not for emergencies. Orders not guaranteed.
Educational content only. DOD does not perform or interpret PET/CT scans. All clinical decisions should be made by qualified licensed healthcare providers.