title: Clinical evaluation of 'local contrast enhancement' for oral fluorescein angiograms.
abstract: OBJECTIVE
  To describe and assess the clinical impact of 'local contrast enhancement' on oral fluorescein angiograms.
  
  
  METHODS
  Oral fluorescein angiograms (OFA) were performed on 12 patients with a range of diabetic retinopathy. The digital images were processed using two enhancement techniques: histogram equalization, a widely available method; and 'local contrast enhancement'. Twelve control images and 24 enhanced images were randomised and subjectively graded for clarity between 1 and 100 on a visual analogue scale by two masked observers. A score of 50% was chosen as the cut-off for clinically useful images.
  
  
  RESULTS
  The mean score for the unenhanced images was 38.8% (SD 19.4); the histogram equalization performed better at 54.7% (SD 10.0) (p = 0.016) and 'local contrast enhancement' at 69.4% (SD 13.6) (p < 0.001). These results equate to a 14.7% improvement in comparison with histogram equalization and a 30.3% improvement with the 'local contrast enhancement' technique. All the 'local contrast enhancement' images were clinically useful, compared with 58.3% of the histogram equalization images (chi 2 2.08, p = 0.2), and 33.3% of the control images (chi 2 = 6.75, p = 0.01).
  
  
  CONCLUSIONS
  This pilot study has demonstrated the power of 'local contrast enhancement' techniques for low-contrast fluorescein angiograms. Using 'local contrast enhancement' oral fluorescein angiograms can give high-quality images and may allow safer patient investigation.
authors.affiliation: Department of Physics, Kings College London, UK. rbnewsom@dircon.co.uk
authors.forename: R S
authors.initials: RS
authors.lastname: Newsom
authors.forename: C
authors.initials: C
authors.lastname: Sinthanayothin
authors.forename: J
authors.initials: J
authors.lastname: Boyce
authors.forename: A G
authors.initials: AG
authors.lastname: Casswell
authors.forename: T H
authors.initials: TH
authors.lastname: Williamson
mesh_terms: D000284:Administration, Oral; D003287:Contrast Media / Q000008:administration & dosage; D003930:Diabetic Retinopathy / Q000175:diagnosis*; D005069:Evaluation Studies as Topic; D019793:Fluorescein / Q000008:administration & dosage; D005451:Fluorescein Angiography / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D010865:Pilot Projects
chemical_list: D003287:Contrast Media; D019793:Fluorescein