Can a Positron Emission Tomography (PET) scan be performed without Intravenous (IV) contrast?

Can a PET Scan Be Done Without IV Contrast?

Yes, PET scans can be performed without IV contrast, and in most clinical scenarios, IV contrast is not required for the PET component of the examination. 1

Understanding PET vs. PET/CT Imaging

The question requires clarification between standalone PET imaging and combined PET/CT imaging:

• Standalone PET imaging never requires IV contrast - the radiotracer (typically FDG) is administered intravenously, but this is not "contrast" in the traditional CT sense 1
• PET/CT combines metabolic (PET) and anatomic (CT) imaging - the decision about IV contrast relates only to the CT portion of the study 1

When IV Contrast Is NOT Required for PET/CT

For most oncologic indications, PET/CT without IV contrast provides adequate diagnostic information. 1

Lymphoma Response Assessment

• IV contrast is not required if there is no liver or splenic involvement at initial staging 1
• PET/CT without IV contrast provides similar information to PET plus separately performed contrast-enhanced CT for nodal and most extralymphatic organ assessment 1
• Non-contrast PET/CT adequately detects small pulmonary lesions that may not be visible on PET alone 1

General Oncologic Staging

• Low-dose, non-contrast CT serves the purpose of anatomic correlation and attenuation correction of PET images 2
• For plasma cell disorders, whole-body low-dose CT without contrast is considered sufficient for anatomic evaluation in most cases 1

When IV Contrast IS Recommended for PET/CT

IV contrast should be added to PET/CT in specific clinical scenarios where detailed anatomic assessment is critical:

Hepatic or Splenic Involvement

• If liver or splenic involvement was demonstrated at initial staging, IV contrast-enhanced PET/CT is required for response assessment 1
• Non-enhanced CT has significant limitations in detecting small hepatic or splenic lesions 1

Vascular or Structural Invasion Assessment

• When knowledge regarding vascular structures or tumor invasion into adjacent structures is needed, contrast-enhanced CT as part of PET/CT should be implemented 3
• For extramedullary disease requiring accurate anatomical delineation and relationship to important structures 1

Colorectal Cancer Staging

• For distant metastasis staging, CT with IV contrast is rated as "usually appropriate" (rating 9) 1

Technical Considerations

Attenuation Correction with IV Contrast

• CT with IV contrast can be safely used for PET attenuation correction without reducing clinical diagnostic value 4, 5
• IV contrast causes a measurable increase in standardized uptake values (SUV), particularly in the subclavian vein (27% increase), heart (17% increase), and tumor sites (8% increase) 5
• Despite these SUV increases, the changes are clinically insignificant and do not alter diagnostic interpretation 4, 5
• No contrast-introduced artifacts affect clinical evaluation 4

Radiation Exposure Considerations

• Dual-phase CT (without and with contrast) is not recommended for PET/CT due to unnecessary radiation exposure 6
• Single-phase contrast-enhanced CT is preferred when contrast is indicated 6

Special Patient Populations

Renal Impairment

• In plasma cell disorder patients with high rates of myeloma-related kidney disease, whole-body low-dose CT without contrast is preferred 1
• If IV contrast is required, serum creatinine and estimated glomerular filtration rate should be measured, and volume repletion prior to the study is protective 1

Contrast Allergy

• For patients with history of severe contrast reactions, unenhanced CT examination is strongly preferred 1

Clinical Algorithm for Decision-Making

1. Determine the clinical indication:

   • Lymphoma without liver/splenic involvement → No IV contrast needed 1
   • Lymphoma with liver/splenic involvement → IV contrast required 1
   • Plasma cell disorders → Usually no IV contrast needed 1
   • Colorectal cancer metastasis staging → IV contrast recommended 1

2. Assess patient factors:

   • Renal function impairment → Avoid IV contrast when possible 1
   • Contrast allergy history → Use non-contrast CT 1

3. Consider anatomic requirements:

   • Need for vascular assessment or invasion evaluation → Add IV contrast 3
   • Standard nodal or pulmonary assessment → No IV contrast needed 1

Common Pitfalls to Avoid

• Do not assume IV contrast is always needed for PET/CT - most oncologic indications do not require it 1
• Do not perform dual-phase CT (with and without contrast) as part of PET/CT due to excessive radiation exposure 6
• Do not withhold PET/CT in patients who cannot receive IV contrast - non-contrast PET/CT provides excellent diagnostic information for most indications 1
• Do not forget that the interpreting physician must report lesion size, not just metabolic activity, regardless of whether IV contrast is used 1