Is patient preparation required for a coronary PET‑CT angiogram?

Patient Preparation for Coronary PET-CT Angiogram

Yes, specific patient preparation is absolutely required for a coronary PET-CT angiogram, particularly when using FDG as the radiotracer, with the primary goal of suppressing physiologic myocardial glucose uptake to enable accurate detection of cardiac pathology.

Critical Preparation Requirements

Fasting Protocol

• Patients must fast for at least 4-6 hours prior to FDG injection, consuming only plain, unflavored water during this period 1, 2
• For morning studies, patients should not eat after midnight and should have only a light meal the evening before 1
• Avoid all simple carbohydrates, caffeinated beverages (even "sugar-free"), and any liquids other than plain water 1, 2

Enhanced Cardiac Preparation (For Cardiac Sarcoidosis Evaluation)

The evidence strongly suggests that standard fasting alone is often insufficient for cardiac imaging. Research demonstrates that:

• A prolonged 72-hour high-fat, high-protein, very-low-carbohydrate (HFHPVLC) diet significantly reduces indeterminate scans from 41.7% to 3.6% compared to 24-hour preparation 3
• Fasting duration and heparin administration significantly affect diagnostic accuracy (P = 0.01 and 0.02 respectively) 4
• Inadequate dietary preparation causes diffuse or focal-on-diffuse FDG uptake that mimics pathology in the absence of true inflammation 5

Blood Glucose Management

• Check blood glucose upon arrival at the imaging center 1, 2
• For clinical studies: proceed if plasma glucose <11 mmol/L (200 mg/dL); reschedule if ≥11 mmol/L 1
• Discontinue parenteral nutrition and glucose-containing IV fluids at least 4 hours before FDG injection 1, 2

Hydration Requirements

• Patients should consume approximately 1 liter of water during the 2 hours prior to injection to reduce urinary FDG concentration and improve radiation safety 1, 2
• An additional 500 mL may be consumed during the uptake period to reduce bladder activity 2

Pre-Scan Activity Restrictions

• Avoid strenuous exercise for at least 6 hours, preferably 24 hours, before the scan 1, 2
• Patients must remain seated or recumbent and silent during the 60-minute uptake phase after FDG injection 1, 2
• Keep patients warm starting 30-60 minutes before injection and throughout the uptake period to minimize brown fat FDG accumulation 1, 2

Contrast-Specific Considerations

When the PET-CT includes diagnostic CT with intravenous contrast:

• Assess renal function (creatinine/GFR) according to national guidelines 1
• Screen for contrast allergy and arrange premedication if necessary 1
• Avoid other contrast studies within 24-48 hours of the PET-CT 1
• If renal function is suboptimal, initiate nephrotoxicity prevention protocols (hydration, medication) 1

Medication Review

Document all current medications, with particular attention to:

• Antidiabetic medications 1
• Corticosteroids and growth factors 1
• Sedatives (may be needed for claustrophobic patients) 1

Special Populations

Pregnancy

• Weigh benefits against potential harm before proceeding 1
• Standard FDG dose (259 MBq/7 mCi) delivers 4.7 mGy to the non-gravid uterus 1
• Consider pregnancy testing; apply the 10-day rule in non-emergency situations 1

Breastfeeding

• Breastfeeding does not need to be interrupted 1
• Limit close contact between mother and infant for 12 hours post-injection to reduce external radiation exposure 1, 2
• Breastfeed immediately before injection and express milk for bottle feeding during the 12-hour period 1

Day-of-Scan Protocol

• Measure body weight directly prior to examination (essential for SUV calculations) 1
• Patient must void immediately before scanning to reduce bladder activity 1, 2
• Position with arms above head using proper support devices 1
• Ensure patient can lie still for 20-45 minutes; address claustrophobia concerns in advance 1

Common Pitfalls to Avoid

• Insufficient fasting duration is the most common cause of failed cardiac studies, leading to diffuse physiologic myocardial uptake that obscures pathology 4, 3
• Failure to implement specialized cardiac preparation (prolonged low-carbohydrate diet) results in high indeterminate scan rates 3
• Scheduling other contrast studies too close to PET-CT can interfere with image quality 1
• Not checking glucose levels early enough to allow time for correction if elevated 1