title: Scan length optimization for pulmonary embolism at CT angiography: analysis based on the three-dimensional spatial distribution of 370 emboli in 100 patients.
abstract: OBJECTIVE
  To determine the size and three-dimensional spatial distribution of pulmonary emboli (PE) at computed tomography angiography (CTA) to optimize the scan length.
  
  
  METHODS
  Two experienced radiologists jointly reviewed 100 consecutive, positive PE CTA studies performed in the Emergency Department (53 women; age 61±17 years). All studies were conducted on a 16-detector row CT machine. In each case, the number of emboli was counted and the proximal and distal spatial coordinates of each embolus documented. Coordinates of the main pulmonary artery bifurcation (MPAb) and carina were recorded. For normalization, the thoracic cavity height (H)-from inlet to lowest hemidiaphragm-was measured. The minimal scan lengths for (a) capturing all emboli and (b) rendering a positive diagnosis were determined.
  
  
  RESULTS
  Three hundred and seventy (370) emboli were detected. The average number of PE per patient was 3.7 (maximum 12, minimum 1). Their average length was 2.7 cm. Nine patients had saddle emboli (9%), and 71% of emboli were at or below the MPAb. An 18 cm (0.90×H) scan length, centred 4 cm (0.18×H) below the carina, captures all PE in this dataset while reducing z-axis coverage by 29% (34% for normalized data). Moreover, a 14.2 cm (0.78×H) scan length appropriately centred captures at least one embolus in all patients while reducing coverage by 44% (43%). Decreasing scan length to the lesser of 14.2 cm and 0.78×H per patient reduces coverage by 47%.
  
  
  CONCLUSIONS
  Scan length at CTA for PE can be reduced by up to 47% while preserving diagnostic accuracy for PE detection.
authors.affiliation: Department of Diagnostic Imaging, Rhode Island Hospital, Warren Alpert School of Medicine of Brown University, 593 Eddy Street, Providence, RI 02903, USA. atalay_99@yahoo.com
authors.forename: M K
authors.initials: MK
authors.lastname: Atalay
authors.forename: N L
authors.initials: NL
authors.lastname: Walle
authors.forename: D J
authors.initials: DJ
authors.lastname: Grand
authors.forename: W W
authors.initials: WW
authors.lastname: Mayo-Smith
authors.forename: J J
authors.initials: JJ
authors.lastname: Cronan
authors.forename: T K
authors.initials: TK
authors.lastname: Egglin
mesh_terms: D000368:Aged; D042241:Early Diagnosis; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008875:Middle Aged; D011651:Pulmonary Artery / Q000000981:diagnostic imaging*; D011655:Pulmonary Embolism / Q000000981:diagnostic imaging*; D011857:Radiographic Image Interpretation, Computer-Assisted; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*