Positron Emission Tomography (PET) scanning is an imaging technique that provides a detailed view of the functional and metabolic activity within the body’s tissues and organs. Unlike X-rays or CT scans, which primarily show structure, a PET scan reveals how well cells are working, making it a valuable tool for diagnosing diseases like cancer, as well as certain neurological and cardiovascular conditions. Successful imaging relies heavily on the patient’s precise adherence to pre-scan instructions, as preparation directly influences the accuracy of the metabolic data collected.
Hygiene Guidelines Before the Scan
Patients can and should shower before a PET scan to ensure good personal hygiene, but there are strict limitations on the products that can be used. The general rule is to avoid applying any external products to the skin after showering on the day of the procedure. This includes all lotions, creams, oils, and moisturizers, as they can sometimes contain ingredients that interfere with the scan.
One of the most commonly restricted items is deodorant, particularly antiperspirants containing aluminum. Metallic compounds, even in trace amounts, can cause artifacts on the accompanying CT portion of a PET/CT scan, creating bright spots that might be mistaken for abnormal metabolic activity. Patients should also refrain from using heavy perfumes, colognes, hairsprays, and makeup, especially if the scan is focused on the head and neck area. The primary concern with these products is the potential for image distortion or the body’s metabolism of certain ingredients, which could locally alter the tracer’s distribution and lead to misinterpretation.
Understanding the Role of the Radiotracer
The scientific rationale behind the preparation rules centers on the specific radiotracer used, which is most often Fluorodeoxyglucose (FDG). FDG is a glucose analog, meaning it chemically mimics the sugar glucose that the body’s cells use for energy. Once injected, FDG is transported into metabolically active cells, where it is trapped because the final step of sugar metabolism cannot occur, effectively highlighting areas of high glucose consumption.
Cells that are rapidly dividing, such as cancer cells, exhibit an increased rate of glycolysis and therefore take up significantly more FDG than healthy cells, creating the “hot spots” seen on the scan. However, FDG is not cancer-specific; any cell that is highly active will also absorb the tracer, including activated immune cells at sites of inflammation or infection, and muscle tissue that has been recently used. This physiological uptake outside of the targeted area is known as “false uptake” and can obscure a potential finding or create a false-positive result.
Critical Systemic Preparation Steps
Preparation extends well beyond external hygiene, focusing on modifying the body’s internal metabolism to ensure the FDG tracer goes to the intended areas.
Fasting and Diet
Fasting is a primary requirement, typically involving no food or caloric drinks for four to six hours before the scan, though plain water is usually permitted and encouraged. This fast lowers the body’s circulating blood glucose levels, reducing competition with the injected FDG tracer and maximizing its uptake into the target tissues. Patients are often instructed to follow a low-carbohydrate, low-sugar, high-protein diet for 24 hours beforehand to further deplete the body’s glucose stores.
Activity and Medication Restrictions
Restrictions on physical activity are strictly enforced, usually requiring the patient to avoid strenuous exercise for 24 to 48 hours prior to the procedure. Any recent muscle activity, such as running, heavy lifting, or even chewing gum, will cause the muscle cells to utilize glucose, leading to high FDG uptake in those muscles and potentially masking a true area of concern. Specific medication adjustments are also necessary, especially for diabetic patients; insulin and oral diabetes medications must be carefully managed or withheld for a set period, as high blood sugar levels can compromise the scan’s accuracy.
What to Expect During the Procedure
The actual procedure begins once the patient arrives at the facility and all preparation steps are confirmed. After checking in and changing into a gown, the process follows several steps:
- An intravenous (IV) line is placed, and a blood glucose level is checked to ensure it is within the acceptable range for accurate imaging.
- The small, safe dose of the FDG radiotracer is then injected through the IV line.
- The patient undergoes an “uptake” period (30 to 90 minutes), resting quietly and remaining as still as possible in a reclined position to allow the tracer to accumulate in the target tissues.
- The final scan takes place, lasting 20 to 45 minutes, during which the patient must remain absolutely still on a narrow table inside the PET scanner.
Excessive movement, talking, or even reading during the uptake period can activate muscles, diverting the tracer and degrading image quality.