A Positron Emission Tomography (PET) scan is a diagnostic imaging procedure that provides a functional map of the body’s metabolic activity. The test relies on injecting a small amount of a radioactive tracer, typically fluorodeoxyglucose (FDG), a glucose analog. Since this tracer visualizes how cells utilize sugar, accurate results depend on careful patient preparation to ensure the tracer is distributed correctly.
Required Abstinence Time for Smoking and Nicotine Use
It is mandatory to abstain from smoking and nicotine products before undergoing a PET scan. This rule is in place because nicotine is a potent stimulant that directly interferes with the body’s baseline metabolism. Most facilities require a minimum abstinence period of 12 hours before the scheduled appointment.
Some medical centers or specialized scans may require up to 24 hours of abstinence, and for heavy smokers, a 48-hour period is sometimes recommended to fully minimize nicotine’s effects. This restriction applies universally to traditional cigarettes, cigars, chewing tobacco, and nicotine replacement therapies. Nicotine patches, gums, lozenges, and vaping devices must also be avoided, as the active ingredient still impacts the body’s systems. Failure to adhere to this guideline often results in the scan being rescheduled because the resulting image quality would be compromised.
How Smoking Alters Metabolic Activity
The primary function of the PET scan is to track the injected FDG tracer, which accumulates in tissues with high glucose metabolism, such as tumors or brain tissue. Nicotine interferes with this process by activating the sympathetic nervous system, essentially putting the body into a state of heightened alert. This stimulation leads to an artificial increase in glucose uptake in non-target areas, which is the mechanism that compromises the scan.
Nicotine can cause skeletal muscle tension, particularly in the neck, shoulders, and chest, leading to increased localized glucose consumption in those areas. The FDG tracer is then diverted to these active muscles instead of the intended target, an effect known as tracer “mislocalization.” This diversion can create “false positive” results in otherwise healthy tissue or, conversely, cause the intended target area, like a tumor, to appear less active than it truly is, leading to a “false negative” or an underestimation of disease severity.
Nicotine is known to increase the metabolic activity of Brown Adipose Tissue (BAT), a type of fat tissue that burns energy to generate heat. When BAT is stimulated by nicotine, it rapidly consumes FDG, appearing as bright spots on the scan that can be mistaken for cancer or inflammation. The overall effect of smoking is a chaotic distribution of the tracer, making it extremely difficult for the radiologist to accurately interpret the metabolic map of the body.
Other Essential Pre-Scan Patient Guidelines
Proper preparation for a PET scan extends beyond avoiding smoking and nicotine. Patients must adhere to specific dietary and activity restrictions to ensure the body’s metabolism is stable before the tracer injection. A minimum fasting period of four to six hours is required before the scan, with some facilities preferring six hours.
During the fasting window, nothing should be consumed except plain water; chewing gum, breath mints, or hard candies are prohibited. These items contain sugars or stimulate muscle activity in the mouth, causing FDG uptake in the facial muscles. Many facilities instruct patients to follow a low-carbohydrate, high-protein diet for 24 hours leading up to the appointment.
Physical activity must be managed, as strenuous exercise causes localized muscle repair that consumes glucose. Patients are instructed to avoid heavy lifting or intense physical activity for 24 hours before the scan, with some guidelines suggesting 48 hours. Even mild activities like prolonged walking or climbing stairs should be minimized on the day of the exam.
Special consideration is given to patients with diabetes, as blood glucose levels must be within a specific range (often below 200 mg/dL) for the scan to be accurate. They receive individualized instructions regarding the timing of their insulin or oral diabetic medications to ensure blood sugar is controlled. Patients are also advised to stay warm before and during the scan, as shivering activates muscle metabolism and can divert the FDG tracer from the target areas.