title: Incidence of a single subsegmental mismatched perfusion defect in single-photon emission computed tomography and planar ventilation/perfusion scans.
abstract: OBJECTIVE
  This study aims to compare the incidence of ventilation/perfusion (V/Q) scans interpreted as indeterminate for the diagnosis of pulmonary embolism (PE) using single-photon emission computed tomography (SPECT) versus planar scintigraphy and to consider the effect of variable interpretation of single subsegmental V/Q mismatch (SSM).
  
  
  METHODS
  A total of 1300 consecutive V/Q scans were retrospectively reviewed. After exclusion and matching for age and sex, 542 SPECT and 589 planar scans were included in the analysis. European Association of Nuclear Medicine guidelines were used to interpret the V/Q scans, initially interpreting SSM as negative scans. Patients with SSM were followed up for 3 months and further imaging for PE was collected.
  
  
  RESULTS
  Indeterminate scans were significantly fewer in the SPECT than the planar group on the basis of the initial report (7.7 vs. 12.2%, P<0.05). This is irrespective of classification of SSM as a negative scan (4.6 vs. 12.1%, P<0.0001) or an indeterminate scan (8.3 vs. 12.2%, P<0.05). Of the 21 patients who had SSM, 19 underwent computer tomography pulmonary angiogram and embolism was found in one patient. None of these patients died at the 3-month follow-up.
  
  
  CONCLUSIONS
  V/Q SPECT has greater diagnostic certainty of PE, with a 41% reduction in an indeterminate scan compared with planar scintigraphy. This is irrespective of the clinician's interpretation of SSM as negative or intermediate probability. Patients with SSM would not require further computer tomography pulmonary angiogram imaging.
authors.affiliation: aDepartment of Nuclear Medicine, Royal Free NHS Foundation Trust, London bRadcliffe Department of Medicine, Division of Cardiovascular Medicine, University of Oxford, Oxford, UK.
authors.forename: Matthew
authors.initials: M
authors.lastname: Stubbs
authors.forename: Kenneth
authors.initials: K
authors.lastname: Chan
authors.forename: Helena
authors.initials: H
authors.lastname: McMeekin
authors.forename: Shaunak
authors.initials: S
authors.lastname: Navalkissoor
authors.forename: Thomas
authors.initials: T
authors.lastname: Wagner
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D055420:Perfusion Imaging / Q000379:methods* / Q000706:statistics & numerical data; D011237:Predictive Value of Tests; D011655:Pulmonary Embolism / Q000000981:diagnostic imaging*; D012189:Retrospective Studies; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods* / Q000706:statistics & numerical data; D014692:Ventilation-Perfusion Ratio; D055815:Young Adult