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Optical Coherence Tomography Angiography, a new revolution toward visualization of retinal and choroidal vasculatures.

This technology is a better multimodal imaging approach compared to Fluorescein Angiography (FA) and Indocyanine Green Angiograhy (ICGA because:

·         It is a non-invasive approach

·         Require no contrast agent

·         It allows 3-Dimensional visualization and analysis of the area being observed

·         Improved scanning speed where it make up to 80,000 scans/second

Referances:
Dalton, M. (2015, July). Technology Advances in Optical Coherence Tomography. Retrieved from https://www.eyeworld.org/article-technology-advances-in-optical-coherence-tomography

Landry, D. A. (2019, June 08). What OCTA Shows Us. Retrieved from https://www.optometrytimes.com/itech/what-octa-shows-us

Waheed, N. K., & Arya, M. (2018, July 01). Upcoming Advance in Optical Coherence Tomography Angiography. Retrieved from https://www.retinalphysician.com/issues/2018/january-2018/upcoming-advances-in-optical-coherence-tomography

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Here is a YouTube link to a short video about OCT Angiography specifically by OPTOVue.
https://www.youtube.com/watch?v=auSNvLRKJN0

Reference:
Optovue. (2017, September 18).

OCT Angiography (OCTA) by Optovue [Transform your view of retinal vasculature with OCT Angiography (OCTA)]. YouTube. https://www.youtube.com/watch?v=auSNvLRKJN0

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Examples of OCT Angiography Visualization

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Examples of OCT Angiography Visualization

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3-D imaging are acquired via combining the mutiple B-scans.

Below are the examples of imaging using OCT Angiography.

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What's the latest improved OCTA?

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Spectral Domain (SD-OCTA) or also known as Fourier Domain

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Spectral Domain (SD-OCTA) or also known as Fourier Domain

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Ø  Apply Fourier domain detection techniques

Ø  Light source: Broadband near-infrared superluminescent diodes

Ø  Detector: Spectrometer.

Ø  Image acquisition speed = 80, 000 A scans per second

Ø  Image resolution= 5-8micron

Ø  Wavelength used= 840nm-850nm

An example of image by SD-OCTA can be seen on the below attachment.

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Ø  Apply Fourier domain detection techniques

Ø  Light source: Tunable swept laser

Ø  Detector: single photodiode

Ø  Image acquisition speed: 100,000-400,000 A scans per second.

Ø  Wavelength used: 1,050nm

Ø  Higher image resolution

Below is an example of scanned image (12 mm x 12 mm scans) of a normal eye. The SS OCTA used was the swept-source Zeiss Plex Elite 9000.

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It's easier to understand with the help of the link below, ;)

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It's easier to understand with the help of the link below, ;)

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SS OCT Angio - OCT Angiography for Topcon Swept Source OCT

https://www.youtube.com/watch?v=gY_qHnJLLwI

Reference:
Topcon Europe Medical. (2016, May 11). SS OCT Angio - OCT Angiography for Topcon Swept Source OCT [Topcon  SS OCT Angio, is an OCT Angiography modularity specially for the Topcon Swept OCT, DRI OCT Triton. It is the only system that combines high-quality OCT Angiography with a Swept Source OCT]. YouTube. https://www.youtube.com/watch?v=gY_qHnJLLwI

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Why this technology is favourable:

1.       Able to acquire a 3-Dimensional datas for both retinal structure and blood flow

2.       Faster scanning speed

3.       Denser scan patterns

4.       Wider field of view

5.       Increase A-scans and B-scans densities

6.       Provide greater number of B-scans repeat at the location  being observed

7.       Able to penetrate deeper into eye’s layer due to the longer wavelength.
8.       Higher resolution

Reference:
Miller, A. R., Roisman, L., Zhang, Q., Zheng, F., De Oleiveira Dias, J. F.,Yehoshua, Z., . . . Rosenfeld, P. J. (2017, April). Investigative Opthalmology & Visual Science. Comparison Between Spectral-Domain and Swept-Source Optical Coherence Tomography Angiograhy Imaging of Choroidal,58(3), 1499-1505. https://doi.org/10.1167/iovs.16-20969

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Main Application of Optical Coherence Tomography Angiography

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Main Application of Optical Coherence Tomography Angiography

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1.    Assess diabetic retinopathy and identify the abnormal anatomical finding

2.    Assess the choroidal Neovascularization due to age-related macular degeneration (AMD)

3.    Retinal telangiectasia (vascular anomaly) and retinal vein occlusions diagnosis

Reference:
Cury, Jr. C. D. (2017, December 06). OCT Angiography: Applications and Limitations. Retrieved from https://www.longdom.org/proceedings/oct-angiography-applications-and-limitations-56805.html

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Technical Principles and Image Processing of OCTA.

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Technical Principles and Image Processing of OCTA.

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- Optical Coherence Tomography Angiography (OCTA) is an renewal intsruments of OCT that provides the data on retinal and choroidal circulations and it does nor necessary for dye injections.

- It requires many trial of scnanning at the same specific location in order to detect the motion.

- The development itself was not nor succeed during the time where the slower speed time domain systems.

- It is improved in the term of scanning speed of OCT by a factor 50 during the initial introduction of Fourier-domain OCT systems.

- This instrument also described in various form in 2006 by Makita et, she is using 18.7 kHz spectral-domain OCT (SD-OCT) system.

- The higher quality of OCT angiogrmas could be generated with the less image artifacts duw to improvement of OCT hardware and advancement in data processing techniques.

REFERENCES :
Hagag, A.M., Goa,S.S., Jia, Y., & Huang, D. (2017).Optical coherence tomography angiography: Technical principles and clinical applications in ophthalmology. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5617355/#:~:text=Optical%20coherence%20tomography%20angiography%20(OCTA,OCTA%20has%20become%20clinically%20feasible.

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1.   The 3-D aspect of volumetric OCT (Scans X,Y and Z axes).
Function :
- This Z axis gives the ability to determine depth of vascular structure.
- To create an image.

2.  Split-spectrum amplitude-decorrelation angiography (SSADA)
Function :
- Splits the spectrum into multiple smaller bands, resulting in improved signal-to-noise ratio.

3.  feature space-based optical microangiography method (fsOMAG)
Function :
-  Suppression of angiographic signals from the static background.

4.  OCT angiography ratio algorithm (OCTARA)
Function :
-  Keeps the full spectrum intact which may preserve axial resolution.

5.   Eye tracking systems
Function :
-  Detecting eye movement for real-time correction of motion artifacts.
-  Reduce motion artifacts and improve the reliability of OCTA scans.

6. “projection-resolved” OCTA (PR-OCTA)
Function :
- To suppress the projected flow signal while preserving the natural continuity of ocular microvasculature.
- Improved visualization and quantification of different retinal vascular layers in normal and diseased eyes.

REFERENCES : -
1)   Darrin A. Landry, C. (2019, June 08). What OCTA shows us. Retrieved from
https://www.optometrytimes.com/itech/what-octa-shows-us/page/0/1

2)  Themes, U. (2019, March 08). The Future of Optical Coherence Tomography Angiography. Retrieved from https://entokey.com/the-future-of-optical-coherence-tomography-angiography/

3)  Hagag, A. M., Gao, S. S., Jia, Y., & Huang, D. (2017). Optical coherence tomography angiography: Technical principles and clinical applications in ophthalmology. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5617355/#:~:text=Optical-coherence-tomography-angiography

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Limitations of SS-OCTA

·         Higher cost of light source

·         Lower axial resolutions

·         Worse signal-to-noise ratio than SD-OCTA

·         Worse motion artefact compared to SD-OCTA

·         Normative databases are absent

Reference:

Krader, C. G. (2018, October 29). Understanding Advantages, Limitations of SS-OCT. Retrieved from https://www.ophthalmologytimes.com/view/understanding-advantages-limitations-ss-oct

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- Ocular perfusion using OCT was first introduced in the mid 1990 and suffered from drawbacks include the abality to detect blood flow perpendicular to the OCT beam as well.

- It is turned out to be OCT software algorithms for angiographic imaging was developed. Other than that, the development also include the split-spectrum amplitude-decorrelation angiographic (SSADA) and optical microangigraphic (OMAG).

-  SSADA is utilized in the OCTA device RTYue XR A vanti manufactured by Optovue, Inc, (Fremont, CA, USA). The function of this device is, it detecs the contrast in OCTsignal intensityto represetn flow.

- Other OCTA techniques, SSADA relies on the comparison of sequential OCT B-scans.

- Suprisingly, SSADA divide the spectrum of light into multiple spectral bands, calculates each band and averages the outcomes.

REFERENCES
Alessandro.I. Mariano.C. Giovsnni.S. (2019). Optical Coherence Tomography and Optical Coherence Tomography Angiography in Uveitis: A Review. Retrieved from https://pubmed.ncbi.nlm.nih.gov/30719788/

MEASURED SSADA  DECORRELATION

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1. BAHIJAH BINTI AHMAD TARMIZI
(2019230732)
2. ANNERA LEA BANUS
(2019619328)
3. NUR FATIN HAKIMAH BINTI MOHAMAD SABRIN
(2019257274)

Latest Technology in Instruments Used in Optometry Practices:

Optical Coherence Tomography Angiography (OCTA).