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S. Low, E. L. Ong, P. S. Lee, M. Richardson, P. J. Foster, P. T. Khaw, F. W. Fitzke; Improvement of Anterior Segment Optical Coherence Tomography Scan Resolution Using a Novel Image Averaging Technique. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5078.
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© ARVO (1962-2015); The Authors (2016-present)
To assess if resolution of anterior segment optical coherencetomography (ASOCT) scans could be improved by applying an imageaveraging technique.
Sixty-four images of one eye of the same subject (normal angleanatomy) were acquired with Visante ASOCT and the Slit-lampOCT (SL-OCT). Fifteen subjects (15 eyes) with primary angle-closure(PAC) were assessed with a minimum of 6 images on SL-OCT. Finalimages were calculated by aligning the single frames accordingto the scleral spur and averaging them with GRABBER 5 (version1.0, UCL Institute of Ophthalmology, London, UK). Custom software(MATLAB 7.0, MathWorks, CA) was used to calculate the mean squareerror (MSE) and peak signal-to-noise ratio (PSNR). MSE and PSNRreflect image quality, the latter takes into account noise inthe signal. Both are scaled to account for differences in contrast.Averaged images of 4, 16, 32 and 64 frames were compared topre-processed images (eg. Figure 1).
For the eye with normal anatomy, averaged images demonstratedan improvement in image quality (eg. Figure 2, 64 frames). Thescaled MSE was better on Visante than SL-OCT at 0.42 pixelsand 0.16 pixels respectively. By averaging 64 frames, scaledPSNR was 7.47 dB on Visante and 16.04 dB on SL-OCT. However,image averaging was not possible for 4 of 15 PAC subjects examinedon the SL-OCT due to rotational movements. Mean scaled MSE was0.16 pixels and scaled PSNR 16.3 dB for the remaining 11 subjects.
Averaging of multiple ASOCT images usually improves resolutionthat may assist identification of key clinical landmarks.
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