RadteraVentilation/Perfusion (V/Q) Lung Scan
NM+ ContrastChest
Indications
- Suspected pulmonary embolism (especially when CTPA contraindicated: renal failure, contrast allergy, pregnancy)
- Preoperative quantitative lung function (lobectomy/pneumonectomy)
- Pulmonary hypertension / chronic thromboembolic disease
Patient prep
- Recent chest radiograph (within 24 h) required for correlation
- No fasting required
- Assess for pregnancy; V/Q often preferred over CT in pregnancy (lower fetal/breast dose); perfusion-only with reduced dose may be used
Contrast
AgentVentilation: Tc-99m DTPA aerosol, Technegas, or Xe-133 gas. Perfusion: Tc-99m MAA (macroaggregated albumin)
RouteVentilation: inhalation. Perfusion: IV
DoseTc-99m MAA 4-5 mCi (~200,000-500,000 particles); Tc-99m DTPA aerosol ~25-35 mCi to deliver ~1 mCi to lungs; Xe-133 10-20 mCi
TimingImaging immediately after each phase
Technique
- LEHR collimator, 140 keV (Xe-133 81 keV)
- Ventilation performed first (or per dual-isotope/dose ratio); perfusion follows
- Multiple planar views: anterior, posterior, both posterior obliques, both anterior obliques, both laterals (8 views)
- MAA injected with patient supine to ensure even distribution
Series / Sequences
| # | Series / Sequence | Plane | Notes |
|---|---|---|---|
| 1 | Ventilation | Multiple planar (8 views) | Aerosol/gas distribution; wash-in/equilibrium/wash-out for Xe |
| 2 | Perfusion | Multiple planar (8 views) | Same projections as ventilation for matching |
| 3 | SPECT (optional) | Axial | Increasingly used for improved sensitivity/specificity |
Key points
- PE: segmental perfusion defect with normal ventilation (mismatch)
- Interpret with modified PIOPED / PISA-PED criteria
- Inject MAA supine; do not draw blood back into syringe (forms hot clots/artifact)
- Reduce MAA particle number in right-to-left shunt, pregnancy, pulmonary hypertension
- Always correlate with current chest x-ray
References
• SNMMI/EANM Practice Guideline for Lung Scintigraphy 4.0
• ACR-SPR Practice Parameter for the Performance of Pulmonary Scintigraphy
• Radiopaedia: V/Q scan link
• ACR-SPR Practice Parameter for the Performance of Pulmonary Scintigraphy
• Radiopaedia: V/Q scan link
Source: Researched — verify against your institution
Reference template — verify and adapt to your scanner, vendor and institution before clinical use. Not a substitute for clinical judgment.