What are the pre-scan instructions for a PSMA PET scan?

PSMA PET Scan Preparation Guidelines

For optimal PSMA PET scan results, patients should fast for at least 4-6 hours before the procedure, empty their bladder immediately before the scan, and remove all metallic items prior to imaging. 1

General Pre-Scan Instructions

Patient Information Requirements

• Provide complete clinical history including:
  • Previous treatments (surgery, radiotherapy, systemic therapy)
  • Recent biopsies or resections
  • Recent MRI results if available
  • History of seizures
  • Current medications 2
• Document body weight for SUV measurements 2
• Inform patients about the procedure to ensure compliance 2

Timing Considerations

• Wait at least 1 month after radiotherapy or surgery before scheduling a PSMA PET scan to reduce false positive results from inflammation 2
• For optimal image quality, patients should be able to lie still for 5-20 minutes during static acquisitions (30-50 minutes for dynamic scans) 2

Specific Preparation Instructions

Day Before the Scan

• Follow a low carbohydrate diet for 24 hours prior to the scan 1
• Avoid strenuous exercise for at least 6 hours before the scan, preferably 24 hours 1

Day of the Scan

• Fast for at least 4-6 hours before the scan 1
• Stay hydrated by drinking approximately 1 liter of plain water during the 2 hours before radiotracer injection 1
• Only plain (unflavored) water is permitted; avoid coffee, caffeinated beverages, and "sugar-free" drinks 1
• Empty bladder immediately before the scan to:
  • Maximize patient comfort
  • Reduce radiation exposure to the bladder
  • Minimize scatter and halo artifacts 2
• Remove all metallic items including:
  • Dental prostheses
  • Jewelry
  • Clothing with zippers or buttons 2
• Wear cotton clothing provided by the facility 2

Blood Glucose Monitoring

• Blood glucose must be measured prior to the scan
• For FDG PET scans, glucose should be below 160 mg/dl (8.9 mmol/L) 2, 1
• For diabetic patients, glucose should be checked upon arrival to allow time for correction if needed 1

Special Considerations

MRI Compatibility (for PET/MRI)

• Complete MRI safety screening using standardized checklist for:
  • Previous contrast agent reactions
  • Implants (ports, catheters, metallic implants)
  • Vascular stents, coils
  • Active implants (cardiac pacemakers)
  • Claustrophobia 2
• Implants are categorized as:
  • "MRI unsafe" (absolute contraindication)
  • "MRI conditional" (relative contraindication with specific conditions)
  • "MRI safe" (no contraindication) 2

During the Uptake Phase

• Remain seated or lying down and quiet to minimize muscle uptake of the radiotracer 2, 1
• Keep warm starting 30-60 minutes before injection and throughout the procedure to minimize brown fat activation 2, 1
• For PSMA-specific scans, optimal imaging is typically performed 60 minutes after injection, though some protocols may use different timing 3, 4

Common Pitfalls to Avoid

• Inadequate hydration can lead to concentrated radiotracer in the urinary tract, causing artifacts 1
• Recent exercise can alter radiotracer distribution 1
• Acute correction of hyperglycemia with insulin does not improve image quality 2
• Implants can lead to artifacts and geometric distortions in MRI images 2
• For PSMA-specific imaging, increasing liver uptake over time may limit detection of liver metastases 4

By following these preparation guidelines, patients can help ensure optimal PSMA PET scan quality, leading to more accurate diagnosis and staging of prostate cancer.