A Positron Emission Tomography (PET) scan is a medical imaging test that provides a functional view of the body’s tissues and organs. Unlike traditional imaging that shows anatomy, a PET scan uses a small amount of radioactive material, called a radiotracer, to visualize metabolic activity. Because the test relies on measuring specific biological function, careful preparation is required to ensure the resulting images are accurate and interpretable.
Showering and External Hygiene Instructions
Patients are generally allowed to shower before a PET scan; cleansing the skin is helpful for removing contaminants. However, patients must avoid using most external products afterward, as they can interfere with the scanner’s ability to capture clear images. This includes lotions, creams, powders, and perfumes, which leave residue on the skin. Antiperspirant deodorants often contain metallic compounds that can cause artifacts, or bright spots, on the final images, potentially leading to misinterpretation.
Patients must also wear clothing without metallic components to the appointment. Metal zippers, snaps, belts, or underwire bras can distort the scan results, particularly when combined with a CT scan. All jewelry, especially around the neck or chest, should be removed before arriving at the facility.
Why Preparation is Essential for Accurate Results
Preparatory instructions are designed to control the body’s metabolism so the radiotracer collects only in the intended target areas. The most common tracer is Fluorodeoxyglucose (FDG), a molecule similar to glucose but containing a radioactive tag. Cells with high metabolic rates, such as cancer cells, rapidly absorb FDG, causing them to “light up” on the scan.
If preparations are skipped, the FDG tracer may be absorbed by normal, high-activity tissues instead of the target area. For instance, cold exposure activates brown fat, a metabolically active tissue that absorbs the tracer and can obscure areas of interest. Similarly, recent strenuous muscle activity causes skeletal muscles to take up excessive FDG, creating misleading results. Minimizing tracer uptake in these normal tissues allows for clearer visualization of the disease process.
Dietary and Activity Restrictions
Preparation involves strict rules concerning diet and physical exertion to manage the body’s glucose levels and muscle activity. Patients are typically required to fast, consuming nothing but plain water for four to six hours before the scan. This fasting period lowers the body’s circulating glucose and insulin levels, ensuring the injected FDG tracer is not inhibited by high blood sugar.
Patients are often advised to follow a high-protein, low-carbohydrate diet for 24 hours leading up to the scan to further manage glucose levels. Additionally, strenuous exercise, such as running or heavy lifting, must be avoided for at least 24 hours prior to the appointment. Patients with diabetes receive specific instructions regarding the timing of insulin and oral medication, as blood sugar levels over a certain threshold (often 150 mg/dL) may require the scan to be rescheduled.