title: Histogram Matching Extends Acceptable Signal Strength Range on Optical Coherence Tomography Images.
abstract: OBJECTIVE
  We minimized the influence of image quality variability, as measured by signal strength (SS), on optical coherence tomography (OCT) thickness measurements using the histogram matching (HM) method.
  
  
  METHODS
  We scanned 12 eyes from 12 healthy subjects with the Cirrus HD-OCT device to obtain a series of OCT images with a wide range of SS (maximal range, 1-10) at the same visit. For each eye, the histogram of an image with the highest SS (best image quality) was set as the reference. We applied HM to the images with lower SS by shaping the input histogram into the reference histogram. Retinal nerve fiber layer (RNFL) thickness was automatically measured before and after HM processing (defined as original and HM measurements), and compared to the device output (device measurements). Nonlinear mixed effects models were used to analyze the relationship between RNFL thickness and SS. In addition, the lowest tolerable SSs, which gave the RNFL thickness within the variability margin of manufacturer recommended SS range (6-10), were determined for device, original, and HM measurements.
  
  
  RESULTS
  The HM measurements showed less variability across a wide range of image quality than the original and device measurements (slope = 1.17 vs. 4.89 and 1.72 μm/SS, respectively). The lowest tolerable SS was successfully reduced to 4.5 after HM processing.
  
  
  CONCLUSIONS
  The HM method successfully extended the acceptable SS range on OCT images. This would qualify more OCT images with low SS for clinical assessment, broadening the OCT application to a wider range of subjects.
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, United States 2Department of Bioengineering, Swanson School of En.
authors.forename: Chieh-Li
authors.initials: CL
authors.lastname: Chen
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, United States 2Department of Bioengineering, Swanson School of En.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ishikawa
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, United States 2Department of Bioengineering, Swanson School of En.
authors.forename: Gadi
authors.initials: G
authors.lastname: Wollstein
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, United States 3Department of Biostatistics, Graduate School of Pu.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Bilonick
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, United States 2Department of Bioengineering, Swanson School of En.
authors.forename: Ian A
authors.initials: IA
authors.lastname: Sigal
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, United States 2Department of Bioengineering, Swanson School of En.
authors.forename: Larry
authors.initials: L
authors.lastname: Kagemann
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, United States 2Department of Bioengineering, Swanson School of En.
authors.forename: Joel S
authors.initials: JS
authors.lastname: Schuman
mesh_terms: D000328:Adult; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007089:Image Enhancement; D008297:Male; D012160:Retina / Q000033:anatomy & histology*; D041623:Tomography, Optical Coherence / Q000379:methods*