title: Noninvasive pulmonary nodule elastometry by CT and deformable image registration.
abstract: OBJECTIVE
  To develop a noninvasive method for determining malignant pulmonary nodule (MPN) elasticity, and compare it against expert dual-observer manual contouring.
  
  
  METHODS
  We analyzed breath-hold images at extreme tidal volumes of 23 patients with 30 MPN treated with stereotactic ablative radiotherapy. Deformable image registration (DIR) was applied to the breath-hold images to determine the volumes of the MPNs and a ring of surrounding lung tissue (ring) in each state. MPNs were also manually delineated on deep inhale and exhale images by two observers. Volumes were compared between observers and DIR by Dice similarity. Elasticity was defined as the absolute value of the volume ratio of the MPN minus one normalized to that of the ring.
  
  
  RESULTS
  For all 30 tumors the Dice coefficient was 0.79±0.07 and 0.79±0.06 between DIR with observers 1 and 2, respectively, close to the inter-observer Dice value, 0.81±0.1. The elasticity of MPNs was 1.24±0.26, demonstrating that volume change of the MPN was less than that of the surrounding lung.
  
  
  CONCLUSIONS
  We developed a noninvasive CT elastometry method based on DIR that measures the elasticity of biopsy-proven MPN. Our future direction would be to develop this method to distinguish malignant from benign nodules.
authors.affiliation: Department of Radiation Oncology, Stanford University, United States.
authors.forename: Mohammadreza
authors.initials: M
authors.lastname: Negahdar
authors.affiliation: Department of Radiation Oncology, Stanford University, United States.
authors.forename: Carolina E
authors.initials: CE
authors.lastname: Fasola
authors.affiliation: Department of Radiation Oncology, Stanford University, United States.
authors.forename: Amy S
authors.initials: AS
authors.lastname: Yu
authors.affiliation: Department of Radiation Oncology, Stanford University, United States.
authors.forename: Rie
authors.initials: R
authors.lastname: von Eyben
authors.affiliation: Department of Radiation Oncology, University of California, Davis, United States.
authors.forename: Tokihiro
authors.initials: T
authors.lastname: Yamamoto
authors.affiliation: Department of Radiation Oncology, Stanford University, United States.
authors.forename: Maximilian
authors.initials: M
authors.lastname: Diehn
authors.affiliation: Department of Radiology, Stanford University, United States.
authors.forename: Dominik
authors.initials: D
authors.lastname: Fleischmann
authors.affiliation: Department of Health Research and Policy, Stanford University, United States.
authors.forename: Lu
authors.initials: L
authors.lastname: Tian
authors.affiliation: Department of Radiation Oncology, Stanford University, United States. Electronic address: bwloo@stanford.edu.
authors.forename: Billy W
authors.initials: BW
authors.lastname: Loo
authors.affiliation: Department of Radiation Oncology, Stanford University, United States. Electronic address: pmaxim@stanford.edu.
authors.forename: Peter G
authors.initials: PG
authors.lastname: Maxim
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004548:Elasticity; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D014057:Tomography, X-Ray Computed / Q000379:methods
keywords: Deformable image registration (DIR); Elasticity; Lung cancer; Malignant pulmonary nodule (MPN); X-ray CT