Artifacts Associated with Spectral-Domain Optical Coherence Tomography

Hyung Jun Kim; Hyewon Chung; Hyung Chan Kim

doi:10.3341/jkos.2011.52.8.943

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Kim, Chung, and Kim: Artifacts Associated with Spectral-Domain Optical Coherence Tomography

Original Article

J Korean Ophthalmol Soc 2011;52(8):943-951.

Published online: 7 September 2011

DOI: https://doi.org/10.3341/jkos.2011.52.8.943

Artifacts Associated with Spectral-Domain Optical Coherence Tomography

Hyung Jun Kim, MD, Hyewon Chung, MD, PhD, Hyung Chan Kim, MD, PhD

Department of Ophthalmology, Konkuk University Medical Center, Konkuk University School of Medicine, Seoul, Korea

Address reprint requests to Hyung Chan Kim, MD, PhD Department of Ophthalmology, Konkuk University Medical Center #4-12 Hwayang-dong, Gwangjin-gu, Seoul 143-729, Korea Tel: 82-2-2030-8180, Fax: 82-2-2030-5273, E-mail: eyekim@kuh.ac.kr

Received 16 December 2010 Revised 11 February 2011 Accepted 17 May 2011

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose

To report frequencies of image artifacts associated with spectral-domain optical coherence tomography (SD-OCT) and to evaluate the impact of artifacts on foveal thickness measurements.

Methods

This retrospective study included 267 eyes of 267 patients who underwent OCT volume scanning using Spectralis HRA+OCT (Heidelberg Engineering, Heidelberg, Germany). Macular volume scans of normal and diseased eyes were systematically evaluated for image artifacts within each scan overall and within the center 1-mm area. The frequency of each artifact type was compared for scans stratified by diagnosis category.

Results

Among the volume scans, 79.4% had at least 1 artifact overall, and 26.6% had at least 1 artifact in the center 1-mm area. The highest percentage of inner retina misidentification occurred in the epiretinal membrane (36.1%), whereas the highest percentage of outer retina misidentification occurred in neovascular age-related macular degeneration (wet AMD, 40.0%). Clinically significant artifacts involving the center 1-mm area were observed in 6.4% of volume scans and were most common in wet AMD (43.3%).

Conclusions

Image artifacts in SD-OCT volume scanning are common, but relatively less common in the center 1-mm area of scans. Clinicians should carefully review scans for artifacts when using SD-OCT images and retinal thickness measurements because clinically significant artifacts may affect retinal thickness measurements.

Keywords: Artifact, Spectral domain optical coherence tomography

References

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Figure 1.

Example of Spectralis volume scan output display. (A) Fundus image showing scan area and individual horizontal line scans. (B) Cross-sectional image and segmentation line of a normal eye with inner retina layer segmentation at the internal limiting membrane and outer retina layer segmentation at the Bruch's membrane. (C) False-color thickness map with overlying 1, 3, 6 mm concentric circles, corresponding thickness measurements and thickness map.

Figure 2.

Types of artifacts. (A) Inner retina misidentification. (B) Outer retina misidentification. (C) Incomplete segmentation line. (D) No segmentation line. (E) Off-center. (F) Out of register. (G) Cut edge. (H) Degraded.

Figure 3.

Segmentation error correction and retinal thickness maps. (A) Line scan from a patient with age-related macular degeneration. White arrows indicate places where automated segmentation algorithm fail to follow the retinal pigment epithelium (RPE) pattern created by drusen. Automated macular center thickness (red rectangle) and foveal thickness (red circle) measurements are shown. (B) Same cross-sectional image with segmentation manually adjusted to follow the RPE contour of the outer retina boundary. Note the changes in macular center thickness (red rectangle) and foveal thickness (red circle) measurements. Red arrows point to thinner retinal areas associated with drusen not seen on the uncorrected thickness map.

Table 1.

Frequency and percentage of volume scans and percentage of individual line scans with any artifacts for all diagnoses

Artifact	All			Center 1 mm
Artifact	No. of scans^*	% scans^†	% lines^‡	No. of scans^*	% scans^†	% lines^‡
IRM	56	21.0	6.9	24	9.0	3.4
ORM	119	44.6	10.5	46	17.2	9.6
ISL	144	53.9	12.5	0	0	0
NSL	0	0	0	0	0	0
Degraded	3	1.1	0.1	1	0.4	0.1
Out of register	14	5.2	0.8	0	0	0
Cut edge	56	21.0	8.4	0	0	0

All = artifacts within entire volume scan; Center 1 mm = artifacts within center 1mm fovea; IRM = inner retina misidentification; ORM = outer retina misidentification; ISL = incomplete segmentation line; NSL = no segmentation line.

^* Number of volume scans with given artifact type seen in at least 1 B-scan

^† Percentage of volume scans with specific type of image artifacts

^‡ Percentage of total individual line scans with specific type of image artifacts.

Table 2.

Frequency of off-center artifacts by diagnosis categories

Disease category	No. of scans	Foveal depression^*	Off center^†	%^‡
Normal	38	38	0	0
ERM	40	16	1	6.3
DME	40	12	0	0
CSC	42	15	1	6.7
Intermediate uveitis	22	16	2	12.5
MH	23	23	0	0
Dry AMD	32	23	0	0
Wet AMD	30	7	0	0
Total	267	149	4	2.7

ERM = epiretinal membrane; DME = diabetic macular edema; CSC = central serous chorioretinopathy; MH = macular hole; AMD = age-related macular degeneration.

^* Number of volume scans with identifiable foveal depression on color retinal thickness map

^† Number of scans with foveal depression located outside of center 1-mm area

^‡ Percentage of scans with identifiable foveal depressions that were off center.

Table 3.

Percentage of line scans with artifacts, stratified by artifact type and diagnosis categories

Artifact	Normal	ERM	DME	CSC	Intermediate uveitis	MH	Dry AMD	Wet AMD
IRM	0.8	36.1	2.9	0.4	2.4	8.2	0.1	0.3
ORM	2.6	5.7	6.1	8.4	8.7	8.2	9.0	40.0
ISL	1.6	13.2	16.2	14.2	10.7	4.4	11.4	8.3
NSL	0	0	0	0	0	0	0	0
Degraded	0.1	0.1	0	0.2	0	0	0	0
Out of register	0.7	0.7	1.5	0.4	0	0	2.0	0.3
Cut edge	4.9	5.6	12.2	6.0	5.1	5.4	13.6	14.4

ERM = epiretinal membrane; DME = diabetic macular edema; CSC = central serous chorioretinopathy; MH = macular hole; AMD = age-related macular degeneration; IRM = inner retina misidentification; ORM = outer retina misidentification; ISL = incomplete segmentation line; NSL = no segmentation line.

Table 4.

Percentage of line scans in center 1mm with artifacts, stratified by artifact type and diagnosis categories

Artifact	Normal	ERM	DME	CSC	MH	Dry AMD	Wet AMD
IRM	0	13.0	0	0	18.3	0	0
ORM	1.6	1.0	1.0	8.6	0	12.5	55.3
ISL	0	0	0	0	0	0	0
NSL	0	0	0	0	0	0	0
Degraded	0.1	0	0	0	0	0	0
Out of register	0	0	0	0	0	0	0
Cut edge	0	0	0	0	0	0	0

Table 5.

Comparison of artifact frequency by disease category versus normal eyes

Artifact	ERM	DME	CSC	Intermediate uveitis	MH	Dry AMD	Wet AMD
IRM	<0.001	0.001	0.182	0.016	<0.001	0.037	0.123
ORM	0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001
ISL	0.039	0.895	0.166	0.002	<0.001	0.003	<0.001
NSL	−	−	−	−	−	−	−
Degraded	0.971	0.305	0.623	0.447	0.436	0.359	0.374
Out of register	0.923	0.111	0.283	0.044	0.039	0.021	0.185
Cut edge	0.584	<0.001	0.302	0.902	0.703	<0.001	<0.001

The proportion of line scans with artifacts was compared for disease category compared with normal eyes. All values shown are p-values from chi-square analysis. p<0.05 was considered significant and is shown in boldface. Dashes (−) indicate that the artifact was not observed and frequencies were not compared.

ERM = epiretinal membrane; DME = diabetic macular edema; CSC = Central serous chorioretinopathy; MH = macular hole; AMD = age-related macular degeneration; IRM = inner retina misidentification; ORM = outer retina misidentification; ISL = incomplete segmentation line; NSL = no segmentation line.

Table 6.

Comparison of artifact frequency in center 1-mm area by disease category versus normal eyes

Artifact	ERM	DME	CSC	Intermediate uveitis	MH	Dry AMD	Wet AMD
IRM	<0.001	−	−	−	<0.001	−	−
ORM	0.613	0.680	0.001	0.282	0.271	<0.001	<0.001
ISL	−	−	−	−	−	−	−
NSL	−	−	−	−	−	−	−
Degraded	0.305	0.305	0.293	0.447	0.436	0.359	0.374
Out of register	−	−	−	−	−	−	−
Cut edge	−	−	−	−	−	−	−

Table 7.

Percentage of volume scans, stratified by artifact severity and diagnosis categories

Artifact severity	Normal	ERM	DME	CSC	MH	Dry AMD	Wet AMD
Mild	5.3	20.0	2.5	11.9	8.7	12.5	23.3
Moderate	0	10.0	0	4.8	8.7	6.3	23.3
Severe	0	2.5	0	2.4	34.8	6.3	36.7
Clinically significant error	0	0	0	0	8.7	6.3	43.3

ERM = epiretinal membrane; DME = diabetic macular edema; CSC = Central serous chorioretinopathy; MH = macular hole; AMD = age-related macular degeneration.

Table 8.

Impact of artifacts on center 1-mm thickness measurements

Artifact severity	No. of scans^*	Average \|△ MCT\|^†	Average \|△ FT\|^‡
Mild	29	5.7	4.3
Moderate	17	25.1	18.1
Severe	23	36.4	39.7
Clinically significant error	17	49.5	54.0

Thickness measurement changes after segmentation error corrections.

^* No. of scans = number of volume scans per artifact severity grade

^† Average of the absolute value of differences between automated and corrected manual macular center thickness measurements (micrometers)

^‡ Average of the absolute value of differences between automated and corrected foveal thickness (micrometers).

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