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Objective determination of optimal number of spectral-domain optical coherence tomographic images of retina to average.

Shirasawa M, Sakamoto T, Terasaki H, Yamashita T, Uchino E, Sonoda S - PLoS ONE (2014)

Bottom Line: The SDs decreased significantly when the number of images averaged increased from 1 to 5 and also from 5 to 20 (P<0.05, post hoc Tukey's honestly significant difference tests).Similar results were obtained with the phantom eye model.Although the image quality of the SD-OCT images of the retina improved with an increase in the number of images averaged, it does not improve significantly by averaging more than 20 images.

View Article: PubMed Central - PubMed

Affiliation: Department of Ophthalmology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.

ABSTRACT

Purpose: To determine by objective methods the minimum number of spectral-domain optical coherence tomographic (SD-OCT) images to average to obtain the clearest retinal image.

Methods: SD-OCT Images were obtained from 9 healthy eyes and also from a phantom eye model. The SD-OCT images were obtained by averaging 1, 5, 20, 60, and 100 B-scan images. The reflectivity (mean gray value) of the different retinal layers was evaluated in these images. The image quality was evaluated by the size of the standard deviations (SDs) and the contrast-to-noise ratios (CNRs). A phantom eye model made by TiO2 silicone plates was also examined.

Results: The SDs decreased significantly when the number of images averaged increased from 1 to 5 and also from 5 to 20 (P<0.05, post hoc Tukey's honestly significant difference tests). The SD of the automatic real time averaging of 1 (ART = 1) and ART = 5 were significantly larger than the SD of ART = 100 (P<0.05). The SDs of all other averaged numbers were not significantly larger than that of ART = 100. The CNR increased with an increase in the number of images averaged, and there was a significant increase between ART = 1 to 5 and between ART = 5 to 20 (P<0.05). No significant differences in the CNR was observed between ART = 5, ART = 20 and ART = 60. Similar results were obtained with the phantom eye model.

Conclusions: Although the image quality of the SD-OCT images of the retina improved with an increase in the number of images averaged, it does not improve significantly by averaging more than 20 images.

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Results of phantom eye model.Representative SD-OCT images of phantom eye model (A–C). A, ART = 1; B, ART = 20; C, ART = 100. ART =  number of frames averaged. The phantom eye model is composed of four layers with different concentrations of titanium dioxide (TiO2) powder: 0%, 0.125%, 0.5%, and 2% (from the top to the bottom, black arrows). The upper surface appears as a hyperreflective line because of surface reflection (white arrowheads). The region of interest (ROI) in each layer of phantom eye model (D). D, TiO2 0.5% layer was selected as ROI (white box). SD after averaging in phantom eye model (E). SD of gray reflectivity on OCT decreased according as increase of averaging number. **; P<0.01, *:P<0.05, post hoc Tukey's HSD tests. CNR of phantom eye model (F). CNR of each layer was significantly higher than in that of ART = 20 than that of ART = 1 or ART = 5 (*; P<0.05, **; P<0.01; post hoc Tukey's HSD tests.
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pone-0110550-g006: Results of phantom eye model.Representative SD-OCT images of phantom eye model (A–C). A, ART = 1; B, ART = 20; C, ART = 100. ART =  number of frames averaged. The phantom eye model is composed of four layers with different concentrations of titanium dioxide (TiO2) powder: 0%, 0.125%, 0.5%, and 2% (from the top to the bottom, black arrows). The upper surface appears as a hyperreflective line because of surface reflection (white arrowheads). The region of interest (ROI) in each layer of phantom eye model (D). D, TiO2 0.5% layer was selected as ROI (white box). SD after averaging in phantom eye model (E). SD of gray reflectivity on OCT decreased according as increase of averaging number. **; P<0.01, *:P<0.05, post hoc Tukey's HSD tests. CNR of phantom eye model (F). CNR of each layer was significantly higher than in that of ART = 20 than that of ART = 1 or ART = 5 (*; P<0.05, **; P<0.01; post hoc Tukey's HSD tests.

Mentions: The “Phantom eye model” was used to simulate the OCT images of human retina, and the four layers of the phantom eye were imaged by SD–OCT as in human eyes (Figure 6, A-D). The SD was significantly decreased after averaging from ART = 1 to ART = 5 (P<0.01: repeated measures ANOVA, Figure 6, E). The SD of images with 100 averages was significantly lower than either ART = 1 (P<0.05; post hoc Tukey's HSD tests, Table S3 in File S1), but not than that of ART = 20 or ART = 60.


Objective determination of optimal number of spectral-domain optical coherence tomographic images of retina to average.

Shirasawa M, Sakamoto T, Terasaki H, Yamashita T, Uchino E, Sonoda S - PLoS ONE (2014)

Results of phantom eye model.Representative SD-OCT images of phantom eye model (A–C). A, ART = 1; B, ART = 20; C, ART = 100. ART =  number of frames averaged. The phantom eye model is composed of four layers with different concentrations of titanium dioxide (TiO2) powder: 0%, 0.125%, 0.5%, and 2% (from the top to the bottom, black arrows). The upper surface appears as a hyperreflective line because of surface reflection (white arrowheads). The region of interest (ROI) in each layer of phantom eye model (D). D, TiO2 0.5% layer was selected as ROI (white box). SD after averaging in phantom eye model (E). SD of gray reflectivity on OCT decreased according as increase of averaging number. **; P<0.01, *:P<0.05, post hoc Tukey's HSD tests. CNR of phantom eye model (F). CNR of each layer was significantly higher than in that of ART = 20 than that of ART = 1 or ART = 5 (*; P<0.05, **; P<0.01; post hoc Tukey's HSD tests.
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pone-0110550-g006: Results of phantom eye model.Representative SD-OCT images of phantom eye model (A–C). A, ART = 1; B, ART = 20; C, ART = 100. ART =  number of frames averaged. The phantom eye model is composed of four layers with different concentrations of titanium dioxide (TiO2) powder: 0%, 0.125%, 0.5%, and 2% (from the top to the bottom, black arrows). The upper surface appears as a hyperreflective line because of surface reflection (white arrowheads). The region of interest (ROI) in each layer of phantom eye model (D). D, TiO2 0.5% layer was selected as ROI (white box). SD after averaging in phantom eye model (E). SD of gray reflectivity on OCT decreased according as increase of averaging number. **; P<0.01, *:P<0.05, post hoc Tukey's HSD tests. CNR of phantom eye model (F). CNR of each layer was significantly higher than in that of ART = 20 than that of ART = 1 or ART = 5 (*; P<0.05, **; P<0.01; post hoc Tukey's HSD tests.
Mentions: The “Phantom eye model” was used to simulate the OCT images of human retina, and the four layers of the phantom eye were imaged by SD–OCT as in human eyes (Figure 6, A-D). The SD was significantly decreased after averaging from ART = 1 to ART = 5 (P<0.01: repeated measures ANOVA, Figure 6, E). The SD of images with 100 averages was significantly lower than either ART = 1 (P<0.05; post hoc Tukey's HSD tests, Table S3 in File S1), but not than that of ART = 20 or ART = 60.

Bottom Line: The SDs decreased significantly when the number of images averaged increased from 1 to 5 and also from 5 to 20 (P<0.05, post hoc Tukey's honestly significant difference tests).Similar results were obtained with the phantom eye model.Although the image quality of the SD-OCT images of the retina improved with an increase in the number of images averaged, it does not improve significantly by averaging more than 20 images.

View Article: PubMed Central - PubMed

Affiliation: Department of Ophthalmology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.

ABSTRACT

Purpose: To determine by objective methods the minimum number of spectral-domain optical coherence tomographic (SD-OCT) images to average to obtain the clearest retinal image.

Methods: SD-OCT Images were obtained from 9 healthy eyes and also from a phantom eye model. The SD-OCT images were obtained by averaging 1, 5, 20, 60, and 100 B-scan images. The reflectivity (mean gray value) of the different retinal layers was evaluated in these images. The image quality was evaluated by the size of the standard deviations (SDs) and the contrast-to-noise ratios (CNRs). A phantom eye model made by TiO2 silicone plates was also examined.

Results: The SDs decreased significantly when the number of images averaged increased from 1 to 5 and also from 5 to 20 (P<0.05, post hoc Tukey's honestly significant difference tests). The SD of the automatic real time averaging of 1 (ART = 1) and ART = 5 were significantly larger than the SD of ART = 100 (P<0.05). The SDs of all other averaged numbers were not significantly larger than that of ART = 100. The CNR increased with an increase in the number of images averaged, and there was a significant increase between ART = 1 to 5 and between ART = 5 to 20 (P<0.05). No significant differences in the CNR was observed between ART = 5, ART = 20 and ART = 60. Similar results were obtained with the phantom eye model.

Conclusions: Although the image quality of the SD-OCT images of the retina improved with an increase in the number of images averaged, it does not improve significantly by averaging more than 20 images.

Show MeSH
Related in: MedlinePlus