title: Objective analysis of whole lung and lobar ventilation/perfusion relationships in pulmonary embolism.
abstract: OBJECTIVE
  Lung scintigraphy using single photon emission computed tomography (SPECT) allows accurate regional measurement of the ventilation/perfusion (V/Q) relationship. Objective V/Q analysis has been shown to be useful in the diagnosis of pulmonary embolism (PE). By using anatomical information provided by co-registered computed tomography, we describe methodology for determining the extent of V/Q heterogeneity at a lobar level. We investigate this methodology using simulated data, and demonstrate its potential application in the clinical setting of PE.
  
  
  METHODS
  Data representing an incremental perfusion defect involving the right lung, together with an unaffected ventilation dataset, were modelled using Monte Carlo simulation. For each increase in the size of the perfusion defect, the whole lung V/Q relationship was objectively determined. In addition, using an image mask of the pulmonary lobes, lobar V/Q relationships were also determined. V/Q heterogeneity was characterized using the log(10) standard deviation of the V/Q ratio (log SDVQR), ventilation (log SDV) and perfusion (log SDQ) distributions. Finally, this methodology was explored in clinical cases.
  
  
  RESULTS
  As an increasing number of segments were involved by perfusion defects, there was a progressive increase in all objective parameters of V/Q heterogeneity. The relative change was greatest for log SDV. Analysis of both the simulated and clinical studies demonstrated sensitive changes in the lobar V/Q profiles to the presence of PE.
  
  
  CONCLUSIONS
  Segmentation and analysis of SPECT ventilation-perfusion scintigraphy at a lobar level can be used to quantify regional V/Q relationships. This objective methodology is sensitive to the presence of PE, and may be useful in a clinical setting.
authors.affiliation: Department of Respiratory Medicine, Royal North Shore Hospital, St Leonards, Sydney, Australia. bharris@med.usyd.edu.au
authors.forename: Benjamin
authors.initials: B
authors.lastname: Harris
authors.forename: Dale L
authors.initials: DL
authors.lastname: Bailey
authors.forename: Peter
authors.initials: P
authors.lastname: Chicco
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Bailey
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Roach
authors.forename: Gregory G
authors.initials: GG
authors.lastname: King
mesh_terms: D000368:Aged; D003198:Computer Simulation; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009010:Monte Carlo Method; D011237:Predictive Value of Tests; D011651:Pulmonary Artery / Q000000981:diagnostic imaging / Q000503:physiopathology; D011652:Pulmonary Circulation; D011655:Pulmonary Embolism / Q000000981:diagnostic imaging* / Q000503:physiopathology; D012123:Pulmonary Ventilation; D015899:Tomography, Emission-Computed, Single-Photon; D014057:Tomography, X-Ray Computed; D014692:Ventilation-Perfusion Ratio