title: High dynamic range imaging concept-based signal enhancement method reduced the optical coherence tomography measurement variability.
abstract: OBJECTIVE
  To develop and test a novel signal enhancement method for optical coherence tomography (OCT) images based on the high dynamic range (HDR) imaging concept.
  
  
  METHODS
  Three virtual channels, which represent low, medium, and high signal components, were produced for each OCT signal dataset. The dynamic range of each signal component was normalized to the full gray scale range. Finally, the three components were recombined into one image using various weights. Fourteen eyes of 14 healthy volunteers were scanned multiple times using time-domain (TD)-OCT before and while preventing blinking in order to produce a wide variety of signal strength (SS) images on the same eye scanned on the same day. For each eye, a pair of scans with the highest and lowest SS with successful retinal nerve fiber layer (RNFL) segmentation was selected to test the signal enhancement effect. In addition, spectral-domain (SD)-OCT images with poor signal qualities were also processed.
  
  
  RESULTS
  Mean SS of good and poor quality scans were 9.0 ± 1.1 and 4.4 ± 0.9, respectively. TD-OCT RNFL thickness showed significant differences between good and poor quality scans on the same eye (mean difference 11.9 ± 6.0 μm, P < 0.0001, paired t-test), while there was no significant difference after signal enhancement (1.7 ± 6.2 μm, P = 0.33). However, HDR had weaker RNFL compensation effect on images with SS less than or equal to 4, while it maintained good compensation effect on images with SS greater than 4. Successful signal enhancement was also confirmed subjectively on SD-OCT images.
  
  
  CONCLUSIONS
  The HDR imaging successfully restored OCT signal and image quality and reduced RNFL thickness differences due to variable signal level to the level within the expected measurement variability. This technique can be applied to both TD- and SD-OCT images.
authors.affiliation: University of Pittsburgh Medical Center Eye Center, Eye and Ear Institute, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ishikawa
authors.forename: Chieh-Li
authors.initials: CL
authors.lastname: Chen
authors.forename: Gadi
authors.initials: G
authors.lastname: Wollstein
authors.forename: Jonathan L
authors.initials: JL
authors.lastname: Grimm
authors.forename: Yun
authors.initials: Y
authors.lastname: Ling
authors.forename: Richard A
authors.initials: RA
authors.lastname: Bilonick
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: D000465:Algorithms; D016477:Artifacts; D016208:Databases, Factual; D005901:Glaucoma / Q000473:pathology*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation / Q000379:methods* / Q000592:standards; D008962:Models, Theoretical; D012016:Reference Values; D012160:Retina / Q000473:pathology; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D059629:Signal-To-Noise Ratio; D041623:Tomography, Optical Coherence / Q000295:instrumentation / Q000379:methods* / Q000592:standards