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Scale Adjustments to Facilitate Two-Dimensional Measurements in OCT Images.

Garcia Garrido M, Mühlfriedel RL, Beck SC, Wallrapp C, Seeliger MW - PLoS ONE (2015)

Bottom Line: The problems encountered with two-dimensional measurements in cases of unequal scales are demonstrated and an estimation of the resulting errors is provided.In this work, we highlight the distortion-related problems in OCT image analysis induced by unequal X and Y scales.Our results demonstrate the need for a proper two-dimensional calibration of OCT data, and we believe that equal scaling will certainly improve the efficiency of OCT image analysis.

View Article: PubMed Central - PubMed

Affiliation: Division of Ocular Neurodegeneration, Institute for Ophthalmic Research, Centre for Ophthalmology, Tuebingen, Germany.

ABSTRACT

Purpose: To address the problem of unequal scales for the measurement of two-dimensional structures in OCT images, and demonstrate the use of intra¬ocular objects of known dimensions in the murine eye for the equal calibration of axes.

Methods: The first part of this work describes the mathematical foundation of major distortion effects introduced by X-Y scaling differences. Illustrations were generated with CorelGraph X3 software. The second part bases on image data obtained with a HRA2 Spectralis (Heidelberg Engineering) in SV129 wild-type mice. Subretinally and intravitreally implanted microbeads, alginate capsules with a diameter of 154±5 μm containing GFP-marked mesenchymal stem cells (CellBeads), were used as intraocular objects for calibration.

Results: The problems encountered with two-dimensional measurements in cases of unequal scales are demonstrated and an estimation of the resulting errors is provided. Commonly, the Y axis is reliably calibrated using outside standards like histology or manufacturer data. We show here that intraocular objects like dimensionally stable spherical alginate capsules allow for a two-dimensional calibration of the acquired OCT raw images by establishing a relation between X and Y axis data. For our setup, a correction factor of about 3.3 was determined using both epiretinally and subretinally positioned beads (3.350 ± 0.104 and 3.324 ± 0.083, respectively).

Conclusions: In this work, we highlight the distortion-related problems in OCT image analysis induced by unequal X and Y scales. As an exemplary case, we provide data for a two-dimensional in vivo OCT image calibration in mice using intraocular alginate capsules. Our results demonstrate the need for a proper two-dimensional calibration of OCT data, and we believe that equal scaling will certainly improve the efficiency of OCT image analysis.

No MeSH data available.


Related in: MedlinePlus

Bead visualization after OCT image correction.Localization of GFP-expressing beads in autofluorescence mode (A, D) and position of horizontal and vertical OCT scans. Using the predetermined correction factor, both subretinal (B, C) and epiretinal beads (E, F) show the correct spherical shape. Scale bars: 200 μm.
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pone.0131154.g004: Bead visualization after OCT image correction.Localization of GFP-expressing beads in autofluorescence mode (A, D) and position of horizontal and vertical OCT scans. Using the predetermined correction factor, both subretinal (B, C) and epiretinal beads (E, F) show the correct spherical shape. Scale bars: 200 μm.

Mentions: The imaging data were obtained as part of a neuroprotection study that included a comparison between subretinal and epiretinal placement of the beads (Figs 3 and 4). Typically, unprocessed raw data (Fig 3C and 3D) show a highly elliptical appearance of both subretinal (Fig 3C) and epiretinal beads (Fig 3D). The original images (.bmp format) acquired with the Heidelberg Eye Explorer software on the Spectralis system were then scaled manually to obtain a spherical shape of the beads (Fig 3G and 3H) with the help of a circular template. We found that, despite a dissimilar appearance of the beads in OCT due to the differences in the environment, there was no perceivable difference in their physical extensions. A correction factor of 3.350 ± 0.104 was found for subretinal beads and of 3.324 ± 0.083 for epiretinally located beads (Fig 3E and 3F), which were not significantly different (p = 0,57). Once the scaling factor has been reliably determined for a certain population, it may be applied to all similar recordings with the respective setup and species. In case a sample to be tested differs greatly from the one in which the correction factor was determined, it would be good to reassure that the factor is valid also for this population. In the specific equipment used here, X and Z scales were found to be largely identical, as can be estimated from X-Z plane sections generated from a 3D ‘volume scan’ dataset. We therefore suggest to scale the Y axis of an OCT scan with the correction factor so that X, Y, and Z have identical scales. An example of images with applied correction (i.e. using the predetermined factor not derived from that specific image) is shown in Fig 4. The known size of the objects further allows to check the absolute calibration and possibly adapt the scales accordingly.


Scale Adjustments to Facilitate Two-Dimensional Measurements in OCT Images.

Garcia Garrido M, Mühlfriedel RL, Beck SC, Wallrapp C, Seeliger MW - PLoS ONE (2015)

Bead visualization after OCT image correction.Localization of GFP-expressing beads in autofluorescence mode (A, D) and position of horizontal and vertical OCT scans. Using the predetermined correction factor, both subretinal (B, C) and epiretinal beads (E, F) show the correct spherical shape. Scale bars: 200 μm.
© Copyright Policy
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC4482384&req=5

pone.0131154.g004: Bead visualization after OCT image correction.Localization of GFP-expressing beads in autofluorescence mode (A, D) and position of horizontal and vertical OCT scans. Using the predetermined correction factor, both subretinal (B, C) and epiretinal beads (E, F) show the correct spherical shape. Scale bars: 200 μm.
Mentions: The imaging data were obtained as part of a neuroprotection study that included a comparison between subretinal and epiretinal placement of the beads (Figs 3 and 4). Typically, unprocessed raw data (Fig 3C and 3D) show a highly elliptical appearance of both subretinal (Fig 3C) and epiretinal beads (Fig 3D). The original images (.bmp format) acquired with the Heidelberg Eye Explorer software on the Spectralis system were then scaled manually to obtain a spherical shape of the beads (Fig 3G and 3H) with the help of a circular template. We found that, despite a dissimilar appearance of the beads in OCT due to the differences in the environment, there was no perceivable difference in their physical extensions. A correction factor of 3.350 ± 0.104 was found for subretinal beads and of 3.324 ± 0.083 for epiretinally located beads (Fig 3E and 3F), which were not significantly different (p = 0,57). Once the scaling factor has been reliably determined for a certain population, it may be applied to all similar recordings with the respective setup and species. In case a sample to be tested differs greatly from the one in which the correction factor was determined, it would be good to reassure that the factor is valid also for this population. In the specific equipment used here, X and Z scales were found to be largely identical, as can be estimated from X-Z plane sections generated from a 3D ‘volume scan’ dataset. We therefore suggest to scale the Y axis of an OCT scan with the correction factor so that X, Y, and Z have identical scales. An example of images with applied correction (i.e. using the predetermined factor not derived from that specific image) is shown in Fig 4. The known size of the objects further allows to check the absolute calibration and possibly adapt the scales accordingly.

Bottom Line: The problems encountered with two-dimensional measurements in cases of unequal scales are demonstrated and an estimation of the resulting errors is provided.In this work, we highlight the distortion-related problems in OCT image analysis induced by unequal X and Y scales.Our results demonstrate the need for a proper two-dimensional calibration of OCT data, and we believe that equal scaling will certainly improve the efficiency of OCT image analysis.

View Article: PubMed Central - PubMed

Affiliation: Division of Ocular Neurodegeneration, Institute for Ophthalmic Research, Centre for Ophthalmology, Tuebingen, Germany.

ABSTRACT

Purpose: To address the problem of unequal scales for the measurement of two-dimensional structures in OCT images, and demonstrate the use of intra¬ocular objects of known dimensions in the murine eye for the equal calibration of axes.

Methods: The first part of this work describes the mathematical foundation of major distortion effects introduced by X-Y scaling differences. Illustrations were generated with CorelGraph X3 software. The second part bases on image data obtained with a HRA2 Spectralis (Heidelberg Engineering) in SV129 wild-type mice. Subretinally and intravitreally implanted microbeads, alginate capsules with a diameter of 154±5 μm containing GFP-marked mesenchymal stem cells (CellBeads), were used as intraocular objects for calibration.

Results: The problems encountered with two-dimensional measurements in cases of unequal scales are demonstrated and an estimation of the resulting errors is provided. Commonly, the Y axis is reliably calibrated using outside standards like histology or manufacturer data. We show here that intraocular objects like dimensionally stable spherical alginate capsules allow for a two-dimensional calibration of the acquired OCT raw images by establishing a relation between X and Y axis data. For our setup, a correction factor of about 3.3 was determined using both epiretinally and subretinally positioned beads (3.350 ± 0.104 and 3.324 ± 0.083, respectively).

Conclusions: In this work, we highlight the distortion-related problems in OCT image analysis induced by unequal X and Y scales. As an exemplary case, we provide data for a two-dimensional in vivo OCT image calibration in mice using intraocular alginate capsules. Our results demonstrate the need for a proper two-dimensional calibration of OCT data, and we believe that equal scaling will certainly improve the efficiency of OCT image analysis.

No MeSH data available.


Related in: MedlinePlus