title: Signal normalization reduces systematic measurement differences between spectral-domain optical coherence tomography devices.
abstract: OBJECTIVE
  To test the effect of a novel signal normalization method for reducing systematic optical coherence tomography (OCT) measurement differences among multiple spectral-domain (SD) OCT devices.
  
  
  METHODS
  A total of 109 eyes from 59 subjects were scanned with two SD-OCT devices (Cirrus and RTVue) at the same visit. Optical coherence tomography image data were normalized to match their signal characteristics between the devices. To compensate signal strength differences, custom high dynamic range (HDR) processing was also applied only to images with substantially lower signal strength. Global mean peripapillary retinal nerve fiber layer (RNFL) thicknesses were then measured automatically from all images using custom segmentation software and were compared to the original device outputs. Structural equation models were used to analyze the absolute RNFL thickness difference between original device outputs and our software outputs after signal normalization.
  
  
  RESULTS
  The device-measured RNFL thickness showed a statistically significant difference between the two devices (mean absolute difference 10.58 μm, P < 0.05), while there was no significant difference after normalization on eyes with 62.4-μm or thicker RNFL (mean absolute difference 2.95 μm, P < 0.05).
  
  
  CONCLUSIONS
  The signal normalization method successfully reduces the systematic difference in RNFL thickness measurements between two SD-OCT devices. Enabling direct comparison of RNFL thickness obtained from multiple devices would broaden the use of OCT technology in both clinical and research applications.
authors.affiliation: UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania.
authors.forename: Chieh-Li
authors.initials: CL
authors.lastname: Chen
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ishikawa
authors.forename: Yun
authors.initials: Y
authors.lastname: Ling
authors.forename: Gadi
authors.initials: G
authors.lastname: Wollstein
authors.forename: Richard A
authors.initials: RA
authors.lastname: Bilonick
authors.forename: Juan
authors.initials: J
authors.lastname: Xu
authors.forename: James G
authors.initials: JG
authors.lastname: Fujimoto
authors.forename: Ian A
authors.initials: IA
authors.lastname: Sigal
authors.forename: Larry
authors.initials: L
authors.lastname: Kagemann
authors.forename: Joel S
authors.initials: JS
authors.lastname: Schuman
mesh_terms: D000368:Aged; D003430:Cross-Sectional Studies; D005260:Female; D005901:Glaucoma / Q000175:diagnosis*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D009412:Nerve Fibers / Q000473:pathology; D041623:Tomography, Optical Coherence / Q000295:instrumentation* / Q000379:methods
keywords: image analysis; optical coherence tomography; retina