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Radionuclide Pulmonary imaging (LUNG V/Q SCAN). Dr Hussein Farghaly Nuclear Medicine Consultant RMH. ACUTE PULMONARY EMBOLISM. CLINICAL PRESENTATION: (Non-specific) Haemoptysis , Dyspnea and Pleuritic Chest pain ( Virchows triad)
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Radionuclide Pulmonary imaging(LUNG V/Q SCAN) Dr Hussein Farghaly Nuclear Medicine Consultant RMH
ACUTE PULMONARY EMBOLISM CLINICAL PRESENTATION: (Non-specific) • Haemoptysis, Dyspnea and Pleuritic Chest pain (Virchows triad) • Back or Abdominal pain, cough, SOB, Low-grade fever,---------- • May be asympotmatic
Evaluation • ABG – Respiratory alkalosis, hypoxia • ECG – Sinus tachycardia & S1Q3T3 • D-Dimer • CXR • Spiral CT with contrast • V/Q Scan • Angiogram
Question 1 Pulmonary angiography as “gold standard” Sensitivity for PE is: • 97% • 93% • 87%
Question 2 Accuracy of V/Q scan in PIOPED – incorrect answer? • 98% sensitivity • 10% specificity • High-probability V/Q scans as PE criteria: Failed to detect PE in 59% of patients • 70% specificity
Question 3 Accuracy of multiple slice CTA – incorrect answer? • Variable sensitivities from 53% to 87% in different studies • Reader’s experience is important • Specificity > 90% • Sensitivity is higher than specificity
Question 4 Diagnostic accuracy of CTA – incorrect answer? • Dependent on clinical probability for PE • CTA has high NPV similar to that at V/Q scan • Independent from clinical probability for PE
Diagnostic Pathways in Acute Pulmonary EmbolismRecommendations of The PIOPED II Investigators
Pre Imaging Objective clinical probability • Three clinical scoring system have been tested prospectively and validated in large scale clinical trials: Wells’ score (Ann Intern Med 1998) Geneva Score (Arch Intern Med 2001, Ann Intern Med 2006) Pisa Score (Ann RespirCrit Care Med 1999, Ann j Med 2003)
The diagnostic yield of D-Dimer is lower in cancer patient, the elderly, inpatient, recent trauma or surgery and during pregnancy
CHEST X- Ray • Initial CXR usually normal. • May progress to show atelectasis, plueral effusion and elevated hemidiaphram. • Hampton’s hump and Westermark signs are classic findings but are not usually present.
Hampton’s Hump – consists of a pleura based shallow wedge-shaped consolidation in the lung periphery with the base against the pleural surface. • Westermark sign – Dilatation of pulmonary vessels proximal to embolism along with collapse of distal vessels, often with a sharp cut off.
Lung V/Q scan • Should lung scan be omitted for pulmonary embolism diagnosis in the age of multislice spiral CT? A) YES B) NO NO, Lung scan has a role in PE diagnosis When there are: Contraindications to CT Scan: Allergy to iodinated contrast agent Renal failure Pregnancy? High diagnostic yield and avoidance of unnecessary radiation exposure. Pregnancy Young patient with normal X-ray.
Interpretation Criteria of V/Q scan - Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED), 1990 • Revised PIOPED, 1995 • PISA-PED, 1996: Perfusion scan only • PIOPED II , 2006 • Modified PIOPED II : perfusion and CXR
PIOPED • 933/1,493 patients analyzed • 755 of these patients with pulmonary angiography within 12– 24 h of V/Q scan • Posterior xenon-133 ventilation scan, followed by an 8-view Tc-99m MAA perfusion lung scan • One-year follow-up: New PE, major bleeding complications, or death 1Value of the ventilation/perfusion scan in acute pulmonary embolism. Results of the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED). The PIOPED Investigators. JAMA 1990; 263:2753-9
V/Q scan accuracy: PIOPED • Based on PA: 98% sensitivity and 10% specificity for V/Q scan • High-probability V/Q scans (V/Q mismatch) as criteria for PE: Failed to detect PE in 59% of patients, based on PA.
Likelihood of PE: PIOPED Predictive values > 90%: Only 22% of patients. Combined V/Q scan and clinical probability: Highest diagnostic accuracy. High clinical probability & high-probability V/Q scan: 95% likelihood of PE. Low clinical probability & low-probability V/Q scan: 4% likelihood of PE.
PISA-PED, 1996: Perfusion scan only • 890 patients with Q scan, compared with PA • 413/670 (62%) patients with abnormal Q scans had PA; no PA if normal/near normal Q scan • 92% sensitivity and 87% specificity • Positive Q scan and high clinical suspicion: PPV >90% • Negative Q scan and low clinical suspicion: NPV of 97%.
Pisa Ped perfusion scan categories and interpretation criteria Miniati M, et al: Value of perfusion lung scan in the diagnosis of pulmonary embolism: Results of the Prospective Investigative Study of Acute Pulmonary Embolism Diagnosis (PISA-PED). Am J Respir Crit Care Med 1996;154:1387–1393.
PISA-PED: Conclusion • Q scanning alone: Much closer to angiography than V/Q scanning • Q scanning rather than V/Q scanning: Imaging technique of first choice for diagnosis of PE
PIOPED II: V/Q scan results • PE present or PE absent: 74% (PISA-PED: 75%) • Sensitivity for PE present: 77% (CTA: 83%) • Specificity of PE absent: 98% (CTA: 98%) Conclusions: V/Q scan provides definitive diagnosis in a majority of patients (74%) Sostman HD, et al. Acute pulmonary embolism: sensitivity and specificity of ventilation perfusion scintigraphy in PIOPED II study. Radiology 2008; 246: 941-946
Stripe Sign: A thin line (stripe) of activity between a Q defect and adjacent pleural surface: sometime in emphysema. Only 6% prevalence of PE.Triple match: Matching Q and V defect, and CXR abnormality, regardless of size: Atelectasis, consolidation. Prevalence of PE: 26% (upper - 11%; middle - 12%; lower - 33%)1
