Radionuclide Pulmonary imaging (LUNG V/Q SCAN)

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Radionuclide Pulmonary imaging(LUNG V/Q SCAN)

• Dr Hussein Farghaly
• Nuclear Medicine Consultant
• RMH

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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

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Evaluation

• ABG Respiratory alkalosis, hypoxia
• ECG Sinus tachycardia S1Q3T3
• D-Dimer
• CXR
• Spiral CT with contrast
• V/Q Scan
• Angiogram

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Question 1

• Pulmonary angiography as gold standard
• Sensitivity for PE is
• 97
• 93
• 87

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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

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Question 3

• Accuracy of multiple slice CTA incorrect
  answer?
• Variable sensitivities from 53 to 87 in
  different studies
• Readers experience is important
• Specificity gt 90
• Sensitivity is higher than specificity

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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

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Diagnostic Pathways in Acute Pulmonary
EmbolismRecommendations of The PIOPED II
Investigators
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Diagnostic Pathways in Acute Pulmonary Embolism
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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)

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The diagnostic yield of D-Dimer is lower in
cancer patient, the elderly, inpatient, recent
trauma or surgery and during pregnancy
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CHEST X- Ray

• Initial CXR usually normal.
• May progress to show atelectasis, plueral
  effusion and elevated hemidiaphram.
• Hamptons hump and Westermark signs are classic
  findings but are not usually present.

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• Hamptons 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.

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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.
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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

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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
• 2632753-9 

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PIOPED Probability of PE
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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.

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Likelihood of PE PIOPED
Predictive values gt 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.
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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
  gt90
• Negative Q scan and low clinical suspicion NPV
  of 97.

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Pisa Ped perfusion scan categories and
interpretation criteria
Normal No perfusion defects of any kind
Near normal 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 with pulmonary embolism (PE) Single or multiple wedge-shaped perfusion defects with or without matching chest-roentgenographic adnormalities. Wedge-shaped areas of overperfusion usually coexist.
Abnormal not compatible with pulmonary embolism (PE-) Single or multiple perfusion defects other than wedge-shaped with or without matching chest-roentgenographic abnormalities. Wedge-shaped areas of overperfusion are 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 199615413871393.
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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

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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

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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
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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
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Focal Hot Spots on Perfusion Scan