title: Low yield of ventilation and perfusion imaging for the evaluation of pulmonary embolism after indeterminate CT pulmonary angiography.
abstract: OBJECTIVE
  Ventilation and perfusion (VQ) imaging is common following suboptimal CT pulmonary angiogram (CTPA) for pulmonary embolism (PE) evaluation; however, the results of this diagnostic pathway are unclear. The purpose of our study is to determine the incidence of PE diagnosed on VQ scans performed in patients with suboptimal CTPAs.
  
  
  METHODS
  One hundred twenty-two suboptimal CTPAs with subsequent VQ scans within 1 week were retrospectively identified. VQ reports utilizing modified ​prospective investigation of pulmonary embolism diagnosis (PIOPED) and prospective investigative study of acute pulmonary embolism diagnosis (PISAPED) criteria were evaluated for presence of PE; intermediate probability, high probability, and PE present were considered PE positive. Three hundred consecutive reports of each diagnostic CTPA and diagnostic VQ studies were reviewed to estimate baseline PE positive rates at our institution. These were compared to the positive VQ scan rate after suboptimal CTPA by Fisher's exact test. Reported reason for suboptimal CTPA was noted. When contrast bolus timing was suboptimal, we measured main pulmonary artery (mPA) Hounsfield units (HU). Potential alternative diagnoses in CTPA reports were noted.
  
  
  RESULTS
  97.5% (119/122) of VQ scans following suboptimal CTPA were negative for PE, and 2.5% (3/122) were positive for PE. This was significantly lower than baseline PE positive rate of 10.7% (32/300, p < 0.01) for VQ imaging, and 10.3% (31/300, p < 0.01) for CTPA at our institution. Most (79.5%) CTPAs were suboptimal due to contrast timing. Average mPA density in these cases was 164 ± 61 HU. Most of these studies ruled out central PE. Potential alternative diagnosis was reported in 34/122 (28%) of suboptimal CTPAs, for which pneumonia accounted 59%.
  
  
  CONCLUSIONS
  There is very low incidence of PE diagnosed on VQ imaging performed after suboptimal CTPA. This may be attributed to the ability of most suboptimal CTPAs to rule out central PE.
authors.affiliation: Department of Radiology, Thomas Jefferson University Hospital, 132 South 10th Street, Philadelphia, PA, 19107, USA. brian.curtis@jefferson.edu.
authors.forename: Brian R
authors.initials: BR
authors.lastname: Curtis
authors.affiliation: Department of Radiology, Thomas Jefferson University Hospital, 132 South 10th Street, Philadelphia, PA, 19107, USA.
authors.forename: Mougnyan
authors.initials: M
authors.lastname: Cox
authors.affiliation: Department of Radiology, Thomas Jefferson University Hospital, 132 South 10th Street, Philadelphia, PA, 19107, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Poplawski
authors.affiliation: Department of Radiology, Thomas Jefferson University Hospital, 132 South 10th Street, Philadelphia, PA, 19107, USA.
authors.forename: Andrej
authors.initials: A
authors.lastname: Lyshchik
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000072226:Computed Tomography Angiography / Q000379:methods*; D003287:Contrast Media; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D055420:Perfusion Imaging; D011446:Prospective Studies; D011655:Pulmonary Embolism / Q000000981:diagnostic imaging*; D019275:Radiopharmaceuticals; D012189:Retrospective Studies; D013668:Technetium Tc 99m Aggregated Albumin; D014692:Ventilation-Perfusion Ratio
chemical_list: D003287:Contrast Media; D019275:Radiopharmaceuticals; D013668:Technetium Tc 99m Aggregated Albumin
keywords: CT; PE; Pulmonary angiography; Suboptimal; VQ scan