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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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Standard deviations (SDs) after averaging in normal human eyes.The SD of the gray value of the OCT images decreases as the number of images averaged increases. ROI, region of interest; vit, vitreous body; IPL, inner plexiform layer; INL, inner nuclear layer; ONL, outer nuclear layer; ELM, external limiting membrane; IS/OS, photoreceptor inner segment/outer segment junction; COST, cone outer segment tip; RPE, retinal pigment epithelium. ART indicates automatic real time (ART) averaging. **; P<0.01, *:P<0.05, post hoc Tukey's HSD tests.
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pone-0110550-g004: Standard deviations (SDs) after averaging in normal human eyes.The SD of the gray value of the OCT images decreases as the number of images averaged increases. ROI, region of interest; vit, vitreous body; IPL, inner plexiform layer; INL, inner nuclear layer; ONL, outer nuclear layer; ELM, external limiting membrane; IS/OS, photoreceptor inner segment/outer segment junction; COST, cone outer segment tip; RPE, retinal pigment epithelium. ART indicates automatic real time (ART) averaging. **; P<0.01, *:P<0.05, post hoc Tukey's HSD tests.

Mentions: A high SD indicates higher speckle noise [5]. The SD decreased after each increase in the number of images averaged (P<0.01 for all: repeated measures ANOVA). The SD value for an image averaged 100 times (ART = 100) was significantly lower than that for either ART = 1 or ART = 5 (P<0.05; post hoc Tukey's HSD tests), but the difference in the SDs between ART = 20 and ART = 100 was not significant. Thus, ART = 20 is the optimal number of OCT images to average (Figure 4 and Table S1 in File S1).


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)

Standard deviations (SDs) after averaging in normal human eyes.The SD of the gray value of the OCT images decreases as the number of images averaged increases. ROI, region of interest; vit, vitreous body; IPL, inner plexiform layer; INL, inner nuclear layer; ONL, outer nuclear layer; ELM, external limiting membrane; IS/OS, photoreceptor inner segment/outer segment junction; COST, cone outer segment tip; RPE, retinal pigment epithelium. ART indicates automatic real time (ART) averaging. **; P<0.01, *:P<0.05, post hoc Tukey's HSD tests.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4206300&req=5

pone-0110550-g004: Standard deviations (SDs) after averaging in normal human eyes.The SD of the gray value of the OCT images decreases as the number of images averaged increases. ROI, region of interest; vit, vitreous body; IPL, inner plexiform layer; INL, inner nuclear layer; ONL, outer nuclear layer; ELM, external limiting membrane; IS/OS, photoreceptor inner segment/outer segment junction; COST, cone outer segment tip; RPE, retinal pigment epithelium. ART indicates automatic real time (ART) averaging. **; P<0.01, *:P<0.05, post hoc Tukey's HSD tests.
Mentions: A high SD indicates higher speckle noise [5]. The SD decreased after each increase in the number of images averaged (P<0.01 for all: repeated measures ANOVA). The SD value for an image averaged 100 times (ART = 100) was significantly lower than that for either ART = 1 or ART = 5 (P<0.05; post hoc Tukey's HSD tests), but the difference in the SDs between ART = 20 and ART = 100 was not significant. Thus, ART = 20 is the optimal number of OCT images to average (Figure 4 and Table S1 in File S1).

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