Should intravenous iodinated contrast be administered for a PET/CT evaluation of suspected coronary stent infection with FDG uptake adjacent to the stent?

IV Contrast for PET/CT in Suspected Coronary Stent Infection

IV contrast is not necessary for the primary diagnostic evaluation of suspected coronary stent infection with FDG-PET/CT, but may be added if clinically indicated for better anatomical delineation of vascular structures, pseudoaneurysm, or abscess formation.

Standard Protocol for Cardiac Device Infection Imaging

According to the most recent expert consensus, a low-dose CT without contrast is the standard acquisition method for FDG-PET/CT when evaluating cardiac device infections 1. This non-contrast CT serves two essential purposes:

• Attenuation correction for the PET images
• Anatomical colocalization of FDG uptake

The guideline explicitly states: "A low-dose CT without contrast is acquired for attenuation correction and anatomical colocalization. Alternatively, a diagnostic CT with contrast may be performed if clinically indicated" 1.

When to Consider Adding IV Contrast

Add IV contrast when you need to:

• Define vascular anatomy and assess for pseudoaneurysm formation (a common finding in coronary stent infections) 2, 3, 4
• Evaluate for abscess formation or fluid collections around the stent 1
• Assess tumor invasion into adjacent structures or vascular involvement in oncologic cases 5
• Obtain a comprehensive diagnostic-quality CT as part of a single examination 6

In the specific scenario of coronary stent infection, contrast-enhanced CT has proven valuable for identifying pseudoaneurysms and defining the anatomical extent of infection 2, 4. Multiple recent case reports demonstrate that CT angiography successfully delineated peri-stent pathology including pseudoaneurysms and soft tissue collections 2, 3, 4.

Safety and Artifact Considerations

The concern about IV contrast causing PET quantification artifacts is largely unfounded in clinical practice:

• Multiple studies confirm no statistically or clinically significant elevation in SUV values with IV contrast 7, 8, 9
• High-concentration contrast media (400 mg iodine/mL) does not increase PET artifacts compared to lower concentrations 8
• Any theoretical interference with uptake quantification is negligible compared to the inherent variability of SUV measurements 6
• Contrast-enhanced PET/CT does not negatively affect diagnostic quality or workflow 9

Critical Pitfalls to Avoid

1. Metal artifact awareness: Any abnormal FDG uptake seen on attenuation-corrected PET images must be confirmed on non-attenuation-corrected images to exclude CT attenuation correction artifacts from the metal stent 1

2. Contrast precautions: If using IV contrast, follow all standard precautions for iodinated contrast administration, particularly in patients with kidney failure 10

3. Don't rely solely on SUV: SUV measurements have not proven useful for differentiating infection from inflammation in cardiac device infections 1

Practical Algorithm

For suspected coronary stent infection:

1. Start with standard FDG-PET/CT using low-dose non-contrast CT
2. Add IV contrast if:
   • Coronary angiography shows pseudoaneurysm
   • You need to define extent of peri-stent soft tissue involvement
   • Surgical planning requires detailed vascular anatomy
   • Initial imaging is equivocal and better anatomical detail would change management

The FDG uptake pattern itself (focal uptake adjacent to the stent with SUVmax >18 in recent cases) provides the primary diagnostic information 2, 4, while contrast-enhanced CT adds anatomical context that guides surgical intervention 3, 4.