What is the protocol to be followed for assessing coronary stent infection with FDG (fluorodeoxyglucose) PET-CT (positron emission tomography–computed tomography)?

Protocol for Assessing Coronary Stent Infection with FDG PET-CT

For suspected coronary stent infection, perform FDG PET-CT with dedicated myocardial suppression preparation using at least one high-fat/low-carbohydrate meal the evening before with overnight fasting, followed by whole-body imaging from skull to toes 60 minutes post-injection, and confirm any abnormal uptake on non-attenuation-corrected images to avoid metal artifact. 1

Patient Preparation Protocol

Myocardial Suppression Regimen (Critical for Cardiac Imaging)

The success of detecting stent infection depends entirely on suppressing physiologic myocardial glucose uptake to visualize pathologic uptake around the stent 1:

For morning scans:

• Consume at least one high-fat/low-carbohydrate meal (>35g fat, <5g carbohydrate) for dinner the evening before
• Fast overnight (minimum 12 hours, preferably 18 hours if tolerated)
• No breakfast on scan day 1

For late morning/afternoon scans:

• High-fat/low-carbohydrate dinner the night before
• High-fat/low-carbohydrate breakfast as a "boost"
• Fast at least 4 hours after breakfast before FDG injection 1

For vegan/vegetarian patients unable to consume high-fat meals:

• Single prolonged fast >18 hours before the study 1

Do NOT use adjunctive heparin - despite theoretical benefits, its effect on myocardial glucose suppression is unclear and inconsistent 1

Special Considerations for Diabetic Patients

Type 1 Diabetes:

• Continue prescribed daily insulin doses when consuming preparation meals
• Avoid short-acting insulin 4-6 hours before the study
• Sliding-scale insulin may be used during meal preparation but avoid on scan day 1

Type 2 Diabetes:

• Stop oral hypoglycemic medications during fasting period and morning dose
• Long-acting insulin (e.g., insulin glargine) the evening before is acceptable if needed
• No insulin 4-6 hours before the study 1

Pre-Injection Requirements

• Blood glucose level must be <220 mg/dL before FDG injection 1
• Document and record any antibiotic therapy (duration and timing) - studies can still be performed during treatment but interpret with caution 2
• Record glucocorticoid use - consider 2-week discontinuation if clinically safe 2
• Document fever, inflammatory markers (ESR, CRP), recent procedures, and time since stent placement 2

Image Acquisition Protocol

Radiopharmaceutical Administration

• Dose: 10-15 mCi (370-555 MBq) FDG intravenously 1
• Administer in quiet patient preparation room
• Uptake time: Minimum 60 minutes, preferably 90 minutes before imaging 2, 1

Scanning Parameters

Perform whole-body PET/CT from skull vertex to toes - this is critical even though the stent is in the chest, as you must assess for:

• Extracardiac infection sources
• Bacterial emboli (particularly brain and spleen from left-sided infections)
• Septic emboli in lungs (from right-sided infections) 1

CT acquisition:

• Low-dose CT without contrast for attenuation correction and anatomical localization
• Alternatively, diagnostic CT with contrast if clinically indicated 1

Consider ECG-gated acquisition for coronary stent evaluation to improve spatial resolution and reduce cardiac motion artifact 3

Image Interpretation

Systematic Evaluation Approach

1. Evaluate the stent itself on cross-sectional PET and CT images:

   • Look for abnormal FDG uptake higher than adjacent tissue
   • Describe distribution pattern: focal, diffuse, or focal-on-diffuse background 1

2. Critical step - Confirm on non-attenuation-corrected images:

   • Any abnormal uptake seen on attenuation-corrected PET must be verified on non-attenuation-corrected images
   • This avoids false positives from CT attenuation correction artifacts from metal stent 1

3. Assess CT findings:

   • Soft tissue mass around stent
   • Pericardial fluid collections
   • Abscess formation
   • Fistulae 3

4. Evaluate for complications:

   • Adjacent lymph node reaction
   • Pericardial involvement
   • Mycotic aneurysm formation 1

5. Whole-body assessment:

   • Brain and spleen for emboli (left-sided infections)
   • Lungs for septic emboli (right-sided infections)
   • Bone marrow/spleen hypermetabolism (suggests septic shock)
   • Alternative infection sources 1

Interpretation Pitfalls

Do NOT use SUV values - standardized uptake values have not been shown useful for differentiating infection from inflammation 1

Do NOT use target-to-blood pool ratios - significance and reliability not established for cardiac device evaluation 1

Beware of inadequate myocardial suppression - physiologic myocardial uptake occurs in up to 20% of patients despite optimal preparation, which can obscure stent infection 1

Standardized Reporting Elements

Your report must include 1:

1. Clinical history: Type of stent, implantation date, recent clinical course, laboratory results (WBC, CRP, blood cultures), antibiotic therapy and duration
2. Procedure details: FDG dose, injection route, uptake time, blood glucose level, scan range, contrast use
3. Comparison studies: Prior PET/CT, echocardiography, or cardiac CT
4. Findings: Start with stent area on PET and CT, then adjacent structures, then distant sites
5. Impression: Concise answer to clinical question - presence/absence of findings compatible with stent infection

Clinical Context

Coronary stent infection is extremely rare but life-threatening with nonspecific symptoms 3. FDG PET-CT can detect infection earlier than conventional imaging by identifying metabolic changes before anatomical damage occurs 1. The combination of metabolic (PET) and anatomic (CT) information, particularly with ECG-gating, provides superior assessment of subtle peri-stent pathology that conventional imaging may miss 3.

Timing considerations: Preferentially perform before antibiotic initiation, but do not delay treatment - studies remain interpretable during therapy though sensitivity may be affected 2.