A V/Q scan evaluates ventilation and perfusion of the lungs to diagnose pulmonary embolism (PE). It involves inhaling a radioactive gas to assess ventilation and receiving an IV injection of radioactive albumin to assess perfusion. Mismatched defects indicate PE while matched defects can indicate lung disease. The PIOPED study established criteria for classifying scans as high, intermediate, or low probability of PE. A normal scan makes PE unlikely while a high probability scan makes PE very likely. Other tests for PE include CT pulmonary angiogram, pulmonary angiogram, and chest x-ray.

2. V/Q SCAN
A type of medical imaging using scintigraphy to
evaluate the circulation of air and blood within a
patient's lungs .
 The ventilation part of the test looks at the ability of
air to reach all parts of the lungs
The perfusion part evaluates how well blood
circulates within the lungs.

3. INDICATIONS
 Most commonly done to check the presence of a
blood clot or abnormal blood flow inside the lungs.
PE
COPD
Pneumonia
Post lobectomy

4. Pulmonary embolism
Pathophysiology
Rudolph Virchow, 1858
Triad:
 Hypercoagulability
 Stasis to flow
 Vessel injury

5. Risk Factors
Hypercoagulability
Malignancy
Pregnancy
Postpartum status (<4wk)
Estrogen/ OCP’s
Venous Stasis
Bed rest > 24 hr
Recent cast or external fixator
Long-distance travel or prolong automobile travel
Venous Injury
surgery
trauma (especially the lower extremities and pelvis)

6. Presentation
Dyspnea
Pleuritic chest pain
Low-grade fever
Tachycardia

7. RADIOGRAPHIC EVALUATION
• CXR
• V/Q Scan
• Spiral CT with contrast
• Angiogram

8. CXR
Initial CXR usually normal.
May progress to show
 atelactasis
 pleural effusion
 elevated hemi diaphragm.

9. CXR
Chest X-Ray Myth:
“You have to do a chest x-ray so you can find
Hampton’s hump or a Westermarck sign.”
Reality:
Most chest x-rays in patients with PE are
nonspecific and insensitive
9

10. Chest X-ray Eponyms of PE
Westermarck's sign
A dilation of the pulmonary vessels proximal to the
embolism along with collapse of distal vessels,
sometimes with a sharp cutoff.
Hampton’s Hump
A triangular or rounded pleural-based infiltrate or
consolidation with the apex toward the hilum.

11. Westermark’s
Sign
Hampton’s Hump

12. 

13. CXR

14. Ventilation/Perfusion Scan
- “V/Q Scan”
A common modality to image the lung and its use
still stems from the PIOPED study.
Relatively noninvasive
In many centers remains the initial test of choice
Preferred test in pregnant patients
 50 mrem vs 800mrem (with spiral CT)

15. Procedure
• Ventilation phase
a gaseous radionuclide such Krypton ,Xenon or
technetium DTPA in an aerosol form is inhaled by the
patient through a mask.
• The perfusion phase involves the I/V inj of radioactive
technetium macro aggregated albumin (Tc99m-
MAA).
• A gamma camera acquires the images for both phases
of the study.

16. The ventilation and perfusion phases of a V/Q lung
scan are performed together along with a chest x-ray
for comparison or to look for other causes of lung
disease

17. NORMAL PERFUSION IMAGES

18. NORMAL VENTILATION
IMAGES

19. PIOPED STUDY
PIOPED STUDY The Prospective Investigation of
Pulmonary Embolism Diagnosis (PIOPED) was a
multicenter, collaborative effort designed to
determine the sensitivity and specificity of the V/Q
scan in patients with suspected acute PE

20. Defect Descriptors, as Used in
PIOPED
 Small defect (small subsegmental): Less than 25% of
a segment.
 Moderate defect (moderate subsegmental): > 25%,
but < 75% of a segment.
 Large defect (segmental): Greater than 75% of a
segment.

21. PERFUSION DEFECTS
Mismatched Perfusion defects:
-Ventilation is normal in that segment
-Indicative of PE.
Matched Perfusion defects:
-Ventilation defect in that segment.
-It is usually seen in parenchymal lung disease.

22. Normal
 No perfusion defects or perfusion exactly outlines the
shape of the lungs seen on the chest radiograph.

24. High probability criteria
• 2 or more large (>75% of a segment) mismatched
perfusion defects with no corresponding CXR
abnormalities
• 1 large and >2 moderate sized (25-75% of a segment)
mismatched
• perfusion defects with no corresponding CXR
abnormalities
• or 4 or more moderate-sized mismatches with no
corresponding CXR

25. Intermediate probability
A mixture of matched and unmatched defects
or single moderate-sized mismatch with normal CXR
or triple match in lower zone
or matched VQ defect with small effusion
or doesn't fit into normal, low or high probability
categories

26. Low probability Criteria
• multiple matched VQ defects, regardless of size,
with normal CXR
• triple matched (i.e. matched VQ defect plus CXR
lesion in same area) in upper or mid zone
• or perfusion defects surrounded by normally
perfused lung (stripe sign)
• or matched VQ defect with large effusion
• or any perfusion defect with a substantially larger
CXR abnormality

29. RESULTS
Normal perfusion scan:
means that the patient is very unlikely to have acute
PE.
Low probability V/Q scan:
means that the patient has less than 20% probability
of having acute PE.

30. High probability V/Q scan:
means that the patient has greater than 80%
probability of having acute PE.
Intermediate probability V/Q scan:
means that the patient has between 20 – 80%
probabilities of having acute PE.

31. Visible renal uptake indicates a right to left shunt
 faulty radiopharmaceutical preparation
 Thyroid activity usually indicates the presence of
unbound per technetate in injected dose.

33. Artefacts may result from clumping of inhaled
particles with severe airways disease
OR
where errors occurred in the preparation or
administration of the particles

35. CONTRAINDICATIONS
No absolute CI
RELATIVE CI
Pulmonary Hypertension
Right to Left shunts e.g. VSD.

36. Spiral (Helical) Chest CT
Advantages
Rapid
Alternative Diagnosis
Disadvantages
Costly
Risk to patients with borderline renal function
Hard to detect subsegmental pulmonary emboli

37. CT Angiogram

38. Pulmonary angiogram
Gold Standard.
Positive angiogram provides 100% certainty that an
obstruction exists in the pulmonary artery.
Negative angiogram provides > 90% certainty in the
exclusion of PE.

39. PULMONARY ANGIOGRAPHY

40. Summary
Plain chest radiograph – Usually normal and non-specific
signs.
Radionuclide ventilation-perfusion lung scan.
CT Angiography of the pulmonary arteries – Quickly
becoming method of choice.
Pulmonary angiography – Gold standard but invasive.

41. QUESTION
A 52 yr old male presented with SOB and his V/Q
scan showed multiple matched V/Q defects and his
CXR was normal.
 Where will you place the pt in terms of probability.
 Describe the scheme for interpretation of V/Q scan.
Describe the different investigation for diagnosis of
PE and its plain CXR findings.

42. THANK YOU