PET Scan Preparation: Exercise and Lorazepam Guidelines
You should avoid brisk walking the day before your PET scan, and taking lorazepam 12 hours before the scan is generally acceptable for anxiety or claustrophobia but should be discussed with your imaging center.
Brisk Walking Before PET Scan
Patients must avoid strenuous exercise for at least 6 hours before the FDG PET/CT study, and preferably for 24 hours 1. This recommendation is critical because:
- Physical activity causes increased FDG uptake in skeletal muscles, which can interfere with accurate tumor detection and create false-positive findings 1.
- The 24-hour avoidance period is the preferred standard to ensure minimal muscle uptake that could compromise image quality 2.
- Even moderate exercise like brisk walking can activate muscle glucose metabolism, leading to unwanted tracer accumulation in exercised muscle groups 1.
Common pitfall: Many patients underestimate what constitutes "strenuous" activity. Brisk walking, while seemingly mild, can activate leg muscles sufficiently to affect scan quality, particularly if done the day before when you're within the 24-hour window 1.
Lorazepam Before PET Scan
Lorazepam taken 12 hours before your scan is generally safe and should not interfere with the imaging procedure, based on the following considerations:
- Medications can be taken as prescribed according to EANM guidelines 1.
- The guidelines specifically mention that premedication planning for claustrophobia is appropriate, and inquiring about this when scheduling can help reduce non-diagnostic studies and cancellations 1.
- For plasma cell disorders, guidelines note that regular use of sedatives such as short-acting benzodiazepines in adult patients is not recommended, but this refers to routine use rather than occasional pre-scan anxiety management 1.
Pharmacokinetic Considerations
- Lorazepam has an elimination half-life of approximately 12 hours 3, meaning that a dose taken 12 hours before your scan will be substantially metabolized by scan time.
- The drug reaches peak blood concentrations about 2 hours after oral administration and is completely eliminated within 1 week 3.
- Lorazepam is metabolized to inactive glucuronide conjugates with no active metabolites, making it relatively safe for use before imaging 4.
Important Caveats
- You must inform your imaging center that you plan to take lorazepam, as they need to ensure you can lie still for 20-45 minutes during the scan 1.
- If you require sedation for claustrophobia, the imaging center may prefer to administer it themselves with specific timing relative to the FDG injection 1.
- Some centers use diazepam (5mg IV) 10 minutes before FDG injection specifically to reduce brown fat uptake, so they have protocols for benzodiazepine use 1.
Additional Critical Preparation Requirements
To ensure optimal scan quality, you must also:
- Fast for at least 4 hours before the scan (no food, simple carbohydrates, or liquids except plain water) 1, 2.
- Avoid caffeinated beverages even if sugar-free, as they may contain trace carbohydrates and cause excitant effects 1, 2.
- Drink adequate water (approximately 1 liter during the 2 hours before injection) for hydration and to reduce urinary artifacts 1, 2.
- Remain seated or recumbent and silent after FDG injection during the uptake phase to minimize muscle uptake 1, 2.
- Stay warm starting 30-60 minutes before injection to minimize brown fat activation 1, 2.