radiology,nuclear medicine

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