title: Reproducibility of four-dimensional computed tomography-based lung ventilation imaging.
abstract: OBJECTIVE
  A novel ventilation imaging method based on four-dimensional (4D) computed tomography (CT) has been applied to the field of radiation oncology. Understanding its reproducibility is a prerequisite for clinical applications. The purpose of this study was to quantify the reproducibility of 4D CT ventilation imaging over different days and the same session.
  
  
  METHODS
  Two ventilation images were created from repeat 4D CT scans acquired over the average time frames of 15 days for 6 lung cancer patients and 5 minutes for another 6 patients. The reproducibility was quantified using the voxel-based Spearman rank correlation coefficients for all lung voxels and Dice similarity coefficients (DSC) for the spatial overlap of segmented high-, moderate-, and low-functional lung volumes. Furthermore, the relationship between the variation in abdominal motion range as a measure of the depth of breathing and variation in ventilation was evaluated using linear regression.
  
  
  RESULTS
  The voxel-based correlation between the two ventilation images was moderate on average (0.50 ± 0.15). The DSCs were also moderate for the high- (0.60 ± 0.08), moderate- (0.46 ± 0.06), and low-functional lung (0.58 ± 0.09). No patients demonstrated strong correlations. The relationship between the motion range variation and ventilation variation was found to be moderate and significant.
  
  
  CONCLUSIONS
  We investigated the reproducibility of 4D CT ventilation imaging over the time frames of 15 days and 5 minutes and found that it was only moderately reproducible. Respiratory variation during 4D CT scans was found to deteriorate the reproducibility. Improvement of 4D CT imaging is necessary to increase the reproducibility of 4D CT ventilation imaging.
authors.affiliation: Department of Radiation Oncology, Stanford University School of Medicine, 875 Blake Wilbur Dr., Stanford, CA 94305-5847, USA.
authors.forename: Tokihiro
authors.initials: T
authors.lastname: Yamamoto
authors.forename: Sven
authors.initials: S
authors.lastname: Kabus
authors.forename: Jens
authors.initials: J
authors.lastname: von Berg
authors.forename: Cristian
authors.initials: C
authors.lastname: Lorenz
authors.forename: Melody P
authors.initials: MP
authors.lastname: Chung
authors.forename: Julian C
authors.initials: JC
authors.lastname: Hong
authors.forename: Billy W
authors.initials: BW
authors.lastname: Loo
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Keall
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000503:physiopathology*; D005260:Female; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D012123:Pulmonary Ventilation; D015203:Reproducibility of Results; D013990:Tidal Volume