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, Lowgrade 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 Embolism
Recommendations of The PIOPED II Investigators
Diagnostic Pathways in Acute Pulmonary Embolism
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 Respir Crit 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 wedgeshaped 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
PIOPED: Probability of PE
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
Normal
Near normal
No perfusion defects of any kind
Perfusion defects smaller or equal in size and shape to the
following roentgenographic abnormalities: cardiomegaly,
enlarged aorta, hila and mediastinum, elevated diaphragm,
blunting of the costophrenic angle, pleural thickening,
intrafissural collection of liquid.
Abnormal compatible Single or multiple wedge-shaped perfusion defects with or
with pulmonary
without matching chest-roentgenographic adnormalities.
embolism (PE+)
Wedge-shaped areas of overperfusion usually coexist.
Abnormal not
Single or multiple perfusion defects other than wedge-shaped
compatible with
with
or
without
matching
chest-roentgenographic
pulmonary embolism abnormalities. Wedge-shaped areas of overperfusion are
(PE-)
usually not seen.
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
Causes of perfusion
defects
Primary vascular lesions: Mismatch Q/V
Pulmonary thrombpembolism
Septic, fat and air emboli
PA hypoplesia or atresia
Vasculitis
Primary ventilation Abnormality
Pneumonia Atelectasis pulmonary
edema
Asthma
COPD, Emphysema, Chronic bronchitis
Bullae
Mass Effect:
Tumor
Adenopathy Mismatch Q/V
Pleural effusion
Iatrogenic
Surgery: pneumonectomy, lobectomy
Radiation fibrosis: Mismatch Q/V
Causes of Nonsegmental
perfusion defects
Pacemaker artifact
Tumors
Pleural effusion
Trauma
Hemorrhage
Bullae
Cardiomegaly
Hilar adenopathy
Atelectasis
Pneumonia
Aortic ectasia or aneurysm
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
Focal Hot Spots on Perfusion Scan