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2017: V/Q in PE What’s up?

This article reviews the current status of ventilation-perfusion (V/Q) scintigraphy in suspected pulmonary embolism, discussing imaging techniques, probabilistic vs. definitive reporting, and the rationale for planar vs. SPECT vs. SPECT-CT formats. It covers the history of V/Q scans, interpretation in the US, the small clot controversy, and the diagnosis and management of venous thromboembolism. The importance of diagnosing PE, treatment implications, recurrence rates, and various interpretation schemes are explored, shedding light on the challenges and advancements in this field.

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2017: V/Q in PE What’s up?

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  1. 2017: V/Q in PE What’s up? Darlene Metter, MD, FACR

  2. Disclosure • None

  3. Thank you • Mark Tulchinsky, MD* • Leonard M Freeman, MD* * Co-authors for “Current Status of Ventilation-Perfusion Scintigraphy in Suspected Pulmonary Embolism” Mar 2017 AJR

  4. Learning Objectives • Describe current V/Q imaging techniques • Explain probabilistic vs definitive reporting • Compare the rationale for planar vs SPECT vs SPECT-CT

  5. Format 1. VQ scans: then and now 2. VQ interpretation in the US 3. The small clot controversy

  6. Venous Thromboembolism • PE or DVT = venous thrombosis • PE: Life threatening DVT PE

  7. PE • PE: > 90% have DVT • DVT: 30-50% will have PE • unRx: up to 30% die

  8. PE • US annual estimates: - 900,000 DVT or PE - 60,000-100,000 deaths • Symptoms: nonspecific; need high clinical suspicion • Diagnosis: usually imaging (VQ, CT)

  9. VQ Scans: Then and Now

  10. The Scan • Ventilation: - gas (133Xe) - liquid droplets (99mTc agents) - particles (non-US: Technegas) • Perfusion: 99mTc MAA

  11. Ventilation • Gas: 133Xe: dynamic imaging, 1 view; need co-operative pt; most sensitive for airway disease • Liquid droplets: 99mTc DTPA, PYP, MDP, SC: concordant V to Q views; central airway deposition; swallowed RP; most often used in US

  12. Ventilation • Gas: 133Xe: dynamic imaging, 1 view; need co-operative pt; most sensitive for airway disease • Liquid droplets: 99mTc DTPA, PYP, MDP, SC: concordant V to Q views; central airway deposition; swallowed RP; most often used in US

  13. Ventilation • Particles: Technegas (non-US); subµ carbon particles, ideal SPECT agent A B Which is Technegas?

  14. Perfusion Sensitive test Maps blood flow at the time of injection Defects are nonspecific R L Anterior Posterior LPO RPO

  15. PE Diagnosis • Ventilation perfusion mismatch • Normal CXR and ventilation with a segmental perfusion defect

  16. 1968: LUL and RLL PE (I-131 MAA) Courtesy LM Freeman

  17. 1968: LUL and RLL PE (I-131 MAA) Courtesy LM Freeman

  18. Perfusion Imaging • Planar: 6-8 static views; - PRO: easy to see entire lung; easy to see extra-pulmonary activity; miss small clot - CON: assessing seg/non-seg defect due to summation effect

  19. Perfusion Imaging • SPECT: - PRO: Increase contrast resolution, increase sensitivity, no additional pt radiation - CON: added imaging time; seg vs non-seg defects; over diagnosis Image courtesy of Dr Niraj Patel.

  20. Perfusion Imaging • SPECT-CT: - PRO: anatomic CT correlate, increase sensitivity & specificity - CON: added pt dose from CT; over diagnosis of small PE Image courtesy of Dr Niraj Patel.

  21. Imaging • SPECT-CT: - QUESTION: Are all segmental defects w/o anatomic CT correlate PEs? Significance? - Differential Dx: vasculitis, spasm, “normal clot?” But are there other DDX? Image courtesy of Dr Niraj Patel.

  22. Segmental Q defects • PE • Hypoplastic/dysplastic pulmonary artery • Vasculitis • XRT • Mediastinitis • Granulomatous disease • Tumor

  23. Segmental Q defects* • Spontaneous vasospasm – extremely rare • Plexogenic arteriopathy (severe PAH) • Iatrogenic non-thrombosis: vertebroplasty, glue from AVM, silicone emboli • Pulmonary parasites (Schistosomiasis, Echinococcus) * UT Chest radiologist: Dr CS Restrepo .

  24. SPECT-CT • Gutte (Denmark) - 81 consec pt ; clinical, +D-dimer or Wells >2 - VQ SPECT/CT and CTPA; 6 month FU - 38% PE consensus dx: clinical, CTA, V/Q SPECT (incorporation bias) Sens Specif - VQ SPECT 97% 88% - VQ SPECT/CT 97% 100% - Q SPECT/CT 93% 51% - CTA 68% 100% * Gutte et al. J Nucl Med 2009;50:1987-1992.

  25. SPECT-CT • Gutte (Denmark) - 81 consec pt ; clinical, +D-dimer or Wells >2 - VQ SPECT/CT and CTPA; 6 month FU - 38% PE consensus dx: clinical, CTA, V/Q SPECT (incorporation bias) Sens Specif - VQ SPECT 97% 88% - VQ SPECT/CT 97% 100% - Q SPECT/CT 93% 51% - CTA 68% 100% * Gutte et al. J Nucl Med 2009;50:1987-1992.

  26. Format 1. VQ scans: then and now 2. VQ interpretation in the US 3. The small clot controversy

  27. Basic Principle • Importance of diagnosing PE • Pt has survived the insult (PE) • Treat to prevent the potentially fatal PE • PE recurrence • Untreated: 25% • Treated: 7%

  28. Interpretation Schemes • US: PIOPED I & II, mod PIOPED I (probabilities) • Europe/Canada/Australia: modified PIOPED II with Q scan/CXR & PISAPED (outcomes) • survey 15/18 acad sites*; 1 hybrid * 2015: PE present, PE absent & few non-dx; 2/18 sites

  29. PIOPED I* (1990) Multi-site prospective (> 900) S/S of V/Q scan V/Q & pulm angio c/w clinical outcomes Dev categ & criteria for prob of acute PE, later modified (1993)** Prevalence: 33% (68% inpt) * Prospective Investigation of Pulmonary Embolism Diagnosis * * One segmental MM (low → intermediate)

  30. PIOPED I: Major Problems 1) Only 28% definitive diagnosis • 72% inconclusive, 44% intermediate 2) Low probability had unacceptable high frequency of PE* 3) High probability had a low sensitivity (41%) * Up to 20% probability of PE

  31. PIOPED II (2002) Multi-site prospective (> 800) Assess efficacy of CTA-CTV in acute PE & evaluate the “very low probability” V/Q scan (PPV<10%) V/Q, CTA, CTV, USN, DSA Prevalence: 23% (11% inpt)

  32. CTA vs V/Q • 1990’s to 2000’s dec VQ scans • High # of “non-diagnostic” VQ • ↑ use of CTA in PE • ↓ use of V/Q • 2012: CTA procedure of choice in PE; reported PE +/PE -;6% tech • Propose VQ as “outcomes” (like CT)

  33. The V/Q Response: Modified PIOPED II * Sostman HD et al Radiol Mar 2008:246(3): 941-946 • 2008 Sostman* • Retrosp analysis of PIOPED II pt using V/Q • 74% classified as PE+/PE- • PIOPED I: 28% conclusive/72% inconclusive

  34. The V/Q Response: Modified PIOPED II * Sostman HD et al Radiol Mar 2008:246(3): 941-946 • 2008 Sostman* • Retrosp analysis of PIOPED II pt using V/Q • 74% classified as PE+/PE- • PIOPED I: 28% conclusive/72% inconclusive

  35. Modified PIOPED II • 2 versions: • V/Q & CXR • Q scan & CXR* • Reporting: • V/Q: High, nondx, very low, normal • Q: PE present, PE absent, nondx *1994 Stein (Gottschalk): perfusion only

  36. Modified PIOPED II • 2 versions: • V/Q & CXR • Q scan & CXR* • Reporting: • V/Q: High, nondx, very low, normal • Q: PE present, PE absent, nondx *1994 Stein (Gottschalk): perfusion only

  37. Modified PIOPED II • 2 versions: • V/Q & CXR • Q scan & CXR* • Reporting: • V/Q: High, nondx, very low, normal • Q: PE present, PE absent, nondx *1994 Stein (Gottschalk): perfusion only

  38. V/Q High: 2 or > V/Q MM V Low: nonseg, Q<CXR, triple </= seg M mid/upper, 1-3 sm, 2 or >/= M w/o CXR, stripe sign, lg effusion Normal: no defects NonDx: All others (low, intermediate) Q scan PE(+): 2 or >/= Q/CXR MM PE(-): nonseg, Q<CXR, 1 match mid/upper, 1-3 small, “stripe sign”, one large effusion NonDx: All other findings Modified PIOPED II

  39. PISA-PED* (1995) Clinical prob + CXR + Q scan 176 pt; prevalence 35%; 1° inpt PE present, PE absent, non-Dx - 37 PE; 69/176 abn (21% PE) - S/S: 89%/92%; PPV 95%;NPV 81%; accuracy 90% * Prospective Investigative Study of Acute Pulmonary Embolism Diagnosis

  40. PISA-PED • PE present: >/= 1 wedged shaped Q defect (SHAPE is important) • PE absent: non-wedged shaped Q defect, near normal or normal Q • Non-diagnostic: Cannot classify as PE+ or PE- * 2011 SNM Practice Guideline For Lung Scintigraphy

  41. PISA-PED Critique • ¼ abn but PE(-): no angio or F/U • ½ abn: no angio (contraindications) • PE(+): not all had angio • No angios on normal/near normal • Same reviewer for clinical assessment & scan interpretation (clinical bias)

  42. Question Raised • PISA-PED and Mod PIOPED II (Q only): Is a ventilation study needed? • Re-looked at Q only studies using PIOPED II database (prevalence 19%)

  43. 2008 Comparative Trial: Q* Q + CXR: Mod PD II vs PISA-PED Nondx: mod PD II 21%; PISA-PED 0 If exclude nondx, S/S mod PD II: 85%/93% PISA-PED: 80%/97% PISA-PED = Mod PD II (Q only) but less non-Dx studies * Sostman HD et al J Nucl Med 2008 Vol 49, No 11. p1741-1748

  44. Imaging Acute PE* *Mettler FA , Guiberteau MJ Essentials of Nuclear Medicine Imaging 6th ed. 2012: p 212.

  45. Imaging Acute PE* *Mettler FA , Guiberteau MJ Essentials of Nuclear Medicine Imaging 6th ed. 2012: p 212.

  46. 2 Major Benefits for Q Only • Lower radiation dose* • Whole body CT ED > 5 times V/Q • 4-16/64: 5.4 mSv/19.9 mSv • VQSPECT/CT: 2.8 mSv • Female breast**: ● CT: 10-70 mSv: V/Q: 1.5 mSv ● CT 60% females; 27% < 40 yrs 2. Lower cost * Stein PD. Pulmonary Embolism 3rd ed. 2016 p 416 ** Metter DF et al. AJR 2017;208:489-494.

  47. 2 Major Benefits for Q Only • Lower radiation dose* • Whole body CT ED > 5 times V/Q • 4-16/64: 5.4 mSv/19.9 mSv • VQSPECT/CT: 2.8 mSv • Female breast**: ● CT: 10-70 mSv: V/Q: 1.5 mSv ● CT 60% females; 27% < 40 yrs 2. Lower cost 15% ED of CTA * Stein PD. Pulmonary Embolism 3rd ed. 2016 p 416 ** Metter DF et al. AJR 2017;208:489-494.

  48. Change 2 Categories • The low probability scan 2. The single moderate or large segmental mismatch defect

  49. Low Probability • Sostman (2008)*: • PIOPED II database: 6.7% incidence of PE • Stein (2016)**: Reviewed 4 outcome studies in low probability scans w/o Rx • Incidence of nonfatal PE: 0.13% • Incidence of fatal PE: 0% • Low probability = “No evidence of PE” * Radiology 2008. 245:941-946. ** Stein PD Pulmonary Embolism, 3rd ed. Chickester, W Sussex, Hoboken, NJ. Wiley Blackwell. 206:408-409.

  50. Single MM Vascular Defect • Stein* • Vascular defect: • PPV of one moderate or large perfusion defect is similar • “Vascular defect” equates a moderate to a large perfusion • Simplifies V/Q interpretation for PE * Chest 1993. 104:1468-1471.

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