Optical coherence tomography angiography explained

Optical coherence tomography angiography (OCTA)[1] [2] is a non-invasive imaging technique based on optical coherence tomography (OCT) developed to visualize vascular networks in the human retina,[3] [4] [5] [6] [7] choroid,[8] [9] [10] [11] skin[12] and various animal models.[13] [14] [15] OCTA may make use of speckle variance optical coherence tomography.

OCTA uses motion contrast between cross-sectional OCT scans (B-frames) to differentiate blood flow from static tissue, enabling imaging of vascular anatomy.[16] To correct for patient movement during scanning, bulk tissue changes in the axial direction are eliminated, ensuring that all detected changes are due to red blood cell movement. This form of OCT requires a very high sampling density in order to achieve the resolution needed to detect the tiny capillaries found in the retina.[17] This has allowed OCTA to obtain detailed images of retinal vasculature in the human retina[18] and become widely used clinically to diagnose a variety of eye diseases, such as age related macular degeneration (AMD),[19] diabetic retinopathy (DR),[20] [21] artery and vein occlusions, and glaucoma.[22]

Medical uses

While conventional dye-based angiography is still the common gold standard, OCTA has been evaluated and used across many diseases.[23] OCTA was first introduced in clinical eyecare in 2014.[24]

OCTA has applications in several diseases, including leading causes of blindness such as glaucoma and age-related macular degeneration.[25] In diabetic retinopathy (DR), OCTA was shown to resolve previously established markers of severe disease (i.e., vitreous proliferation). Moreover, OCTA was shown to provide a plethora of additional biomarkers including subclinical loss of vessel density.[26] [27] [28] [29] Thus, OCTA may offer in future the potential to monitor the progression of DR at an earlier, pre-clinical state. Similarly, OCTA was shown to provide more refined information compared to dye-based angiography in other vascular occlusive diseases such as central (or branch) retinal vein occlusion.[30] [31]

How it works

OCTA detects moving particles (red blood cells) by comparing sequential B-scans at the same cross-sectional location. To simply put it, the backscattered light reflected back from static samples would remain the same over multiple B-scans while the backscattered light reflected back from moving samples would fluctuate. Multiple algorithms have been proposed and utilized to contrast such motion signals from static signals in various biological tissues.[32] [33] [34] [35] [36] [37]

Calculating blood flow

An algorithm developed by Jia et al. is used to determine blood flow in the retina. The split-spectrum amplitude decorrelation angiography (SSADA) algorithm calculates the decorrelation in the reflected light that is detected by the OCT device.

The blood vessels are where the most decorrelation occurs allowing them to be visualized, while static tissue has low decorrelation values.[38] The equation takes into account fluctuations of the received signal amplitude or intensity over time. Greater fluctuations receive a greater decorrelation value and indicate more movement.

A significant challenge when trying to image the eye is patient movement and saccadic movement of the eye. Movement introduces a lot of noise into the signal making tiny vessels impossible to distinguish. One approach to decreasing the influence of movement on signal detection is to shorten the scanning time. A short scan time prevents too much patient movement during signal acquisition. With the development of Fourier-domain OCT, spectral-domain OCT, and swept source signal acquisition time was greatly improved making OCTA possible. OCTA scan time is now around three seconds, however, saccadic eye movement still causes a low signal-to-noise ratio. This is where SSADA proves to be very advantageous as it is able to greatly improve SNR by averaging the decorrelation across the number of B-scans, making the microvasculature of the retina visible.[38]

History

Initial efforts to measure blood flow using OCT utilized the Doppler effect.[39] [40] By comparing the phase of successive A-mode scans, the velocity of blood flow can be determined via the Doppler equation. This was deemed Optical Doppler Tomography; the development of spectral domain OCT (SD-OCT) and swept-source OCT (SS-OCT) greatly improved scan times since this phase information was readily accessible. Still, Doppler techniques were fundamentally limited by bulk eye motion artefacts, especially as longer scan times became important for increasing sensitivity.[41] In the mid-2000s systems began compensating for bulk eye motion, which significantly reduced motion artefacts. Systems also began to measure the variance and power of the Doppler phase between successive A-mode and B-mode scans; later it was shown that successive B-mode scans must be corrected for motion and the phase variance data must be thresholded to remove bulk eye motion distortion.[41] [42] [43] [44]

By 2012, split spectrum amplitude decorrelation was shown to be effective at increasing SNR and decreasing motion artefacts.[36] Commercial OCT-A devices also emerged around this time, beginning with the OptoVue AngioVue in 2014 (SD-OCT) and the Topcon Atlantis/Triton soon after (SS-OCT).[41]

Other angiography techniques

The most common angiographic techniques were fluorescein (FA) or indocyanine green angiography (ICGA), which both involve the use of an injectable dye. Intravenous dye injection is time-consuming and can have adverse side effects. Furthermore, the edges of the capillaries can become blurred due to dye leakage and imaging of the retina can only be 2D when using this method.[45] With OCTA, dye injection is not needed making the imaging process faster and more comfortable while at the same time improving the quality of the image.

The current gold standards of angiography, fluorescein angiography (FA) and indocyanine green angiography (ICGA), both require dye to be injected.[46] [47]

OCTA does not need dye but is susceptible to motion artefacts. The dyes used in FA and ICGA can cause nausea, vomiting, and general discomfort, and only have an effective lifetime on the order of a few minutes.[48]

From a physics perspective, both dye-based methods utilize the phenomenon of fluorescence. For FA, this corresponds to an excitation wavelength of blue (around 470 nm) and an emission wavelength near yellow (520 nm).[49] For IGCA, the newer method, the excitation wavelength is between 750 and 800 nm while emission occurs above 800 nm.[50]

Notes and References

  1. Jia Y, Tan O, Tokayer J, Potsaid B, Wang Y, Liu JJ, Kraus MF, Subhash H, Fujimoto JG, Hornegger J, Huang D . 6 . Split-spectrum amplitude-decorrelation angiography with optical coherence tomography . Optics Express . 20 . 4 . 4710–4725 . February 2012 . 22418228 . 3381646 . 10.1364/OE.20.004710 . 2012OExpr..20.4710J .
  2. Jia Y, Bailey ST, Hwang TS, McClintic SM, Gao SS, Pennesi ME, Flaxel CJ, Lauer AK, Wilson DJ, Hornegger J, Fujimoto JG, Huang D . 6 . Quantitative optical coherence tomography angiography of vascular abnormalities in the living human eye . Proceedings of the National Academy of Sciences of the United States of America . 112 . 18 . E2395–E2402 . May 2015 . 25897021 . 4426471 . 10.1073/pnas.1500185112 . 2015PNAS..112E2395J . free .
  3. Gao SS, Jia Y, Zhang M, Su JP, Liu G, Hwang TS, Bailey ST, Huang D . 6 . Optical Coherence Tomography Angiography . Investigative Ophthalmology & Visual Science . 57 . 9 . OCT27–OCT36 . July 2016 . 27409483 . 4968919 . 10.1167/iovs.15-19043 .
  4. Hormel TT, Jia Y, Jian Y, Hwang TS, Bailey ST, Pennesi ME, Wilson DJ, Morrison JC, Huang D . 6 . Plexus-specific retinal vascular anatomy and pathologies as seen by projection-resolved optical coherence tomographic angiography . Progress in Retinal and Eye Research . 80 . 100878 . January 2021 . 32712135 . 7855241 . 10.1016/j.preteyeres.2020.100878 .
  5. Kashani AH, Lee SY, Moshfeghi A, Durbin MK, Puliafito CA . Optical Coherence Tomography Angiography of Retinal Venous Occlusion . Retina . 35 . 11 . 2323–2331 . November 2015 . 26457395 . 10.1097/iae.0000000000000811 . 26880837 .
  6. Spaide RF, Klancnik JM, Cooney MJ . Retinal vascular layers imaged by fluorescein angiography and optical coherence tomography angiography . JAMA Ophthalmology . 133 . 1 . 45–50 . January 2015 . 25317632 . 10.1001/jamaophthalmol.2014.3616 . free .
  7. Gildea D . The diagnostic value of optical coherence tomography angiography in diabetic retinopathy: a systematic review . International Ophthalmology . 39 . 10 . 2413–2433 . October 2019 . 30382465 . 10.1007/s10792-018-1034-8 . free .
  8. Camino A, Guo Y, You Q, Wang J, Huang D, Bailey ST, Jia Y . Detecting and measuring areas of choriocapillaris low perfusion in intermediate, non-neovascular age-related macular degeneration . Neurophotonics . 6 . 4 . 041108 . October 2019 . 31528658 . 6739623 . 10.1117/1.NPh.6.4.041108 .
  9. You QS, Chan JC, Ng AL, Choy BK, Shih KC, Cheung JJ, Wong JK, Shum JW, Ni MY, Lai JS, Leung GM, Cheung CM, Wong TY, Wong IY . 6 . Macular Vessel Density Measured With Optical Coherence Tomography Angiography and Its Associations in a Large Population-Based Study . Investigative Ophthalmology & Visual Science . 60 . 14 . 4830–4837 . November 2019 . 31747685 . 10.1167/iovs.19-28137 . 208215569 . free .
  10. Levison AL, Baynes KM, Lowder CY, Kaiser PK, Srivastava SK . Choroidal neovascularisation on optical coherence tomography angiography in punctate inner choroidopathy and multifocal choroiditis . The British Journal of Ophthalmology . 101 . 5 . 616–622 . May 2017 . 27539089 . 10.1136/bjophthalmol-2016-308806 . 29133966 .
  11. Chu Z, Weinstein JE, Wang RK, Pepple KL . Quantitative Analysis of the Choriocapillaris in Uveitis Using En Face Swept-Source Optical Coherence Tomography Angiography . American Journal of Ophthalmology . 218 . 17–27 . October 2020 . 32413411 . 7529782 . 10.1016/j.ajo.2020.05.006 .
  12. Xu J, Song S, Men S, Wang RK . Long ranging swept-source optical coherence tomography-based angiography outperforms its spectral-domain counterpart in imaging human skin microcirculations . Journal of Biomedical Optics . 22 . 11 . 1–11 . November 2017 . 29185292 . 5712670 . 10.1117/1.jbo.22.11.116007 . 2017JBO....22k6007X . free .
  13. Fischer MD, Huber G, Beck SC, Tanimoto N, Muehlfriedel R, Fahl E, Grimm C, Wenzel A, Remé CE, van de Pavert SA, Wijnholds J, Pacal M, Bremner R, Seeliger MW . 6 . Noninvasive, in vivo assessment of mouse retinal structure using optical coherence tomography . PLOS ONE . 4 . 10 . e7507 . October 2009 . 19838301 . 2759518 . 10.1371/journal.pone.0007507 . free . 2009PLoSO...4.7507F .
  14. Merkle CW, Zhu J, Bernucci MT, Srinivasan VJ . Dynamic Contrast Optical Coherence Tomography reveals laminar microvascular hemodynamics in the mouse neocortex in vivo . NeuroImage . 202 . 116067 . November 2019 . 31394180 . 6819266 . 10.1016/j.neuroimage.2019.116067 . free .
  15. Chen S, Liu Q, Shu X, Soetikno B, Tong S, Zhang HF . Imaging hemodynamic response after ischemic stroke in mouse cortex using visible-light optical coherence tomography . Biomedical Optics Express . 7 . 9 . 3377–3389 . September 2016 . 27699105 . 5030017 . 10.1364/boe.7.003377 .
  16. de Carlo TE, Romano A, Waheed NK, Duker JS . A review of optical coherence tomography angiography (OCTA) . International Journal of Retina and Vitreous . 1 . 1 . 5 . April 2015 . 27847598 . 5066513 . 10.1186/s40942-015-0005-8 . free .
  17. Drexler W, Liu M, Kumar A, Kamali T, Unterhuber A, Leitgeb RA . Optical coherence tomography today: speed, contrast, and multimodality . Journal of Biomedical Optics . 19 . 7 . 071412 . 2014 . 25079820 . 10.1117/1.jbo.19.7.071412 . free . 2014JBO....19g1412D .
  18. Campbell JP, Zhang M, Hwang TS, Bailey ST, Wilson DJ, Jia Y, Huang D . Detailed Vascular Anatomy of the Human Retina by Projection-Resolved Optical Coherence Tomography Angiography . Scientific Reports . 7 . 1 . 42201 . February 2017 . 28186181 . 5301488 . 10.1038/srep42201 . 2017NatSR...742201C .
  19. Jia Y, Bailey ST, Wilson DJ, Tan O, Klein ML, Flaxel CJ, Potsaid B, Liu JJ, Lu CD, Kraus MF, Fujimoto JG, Huang D . 6 . Quantitative optical coherence tomography angiography of choroidal neovascularization in age-related macular degeneration . Ophthalmology . 121 . 7 . 1435–1444 . July 2014 . 24679442 . 4082740 . 10.1016/j.ophtha.2014.01.034 .
  20. Hwang TS, Jia Y, Gao SS, Bailey ST, Lauer AK, Flaxel CJ, Wilson DJ, Huang D . Optical Coherence Tomography Angiography Features of Diabetic Retinopathy . 6 . Retina . 35 . 11 . 2371–2376 . November 2015 . 26308529 . 4623938 . 10.1097/IAE.0000000000000716 .
  21. Hwang TS, Gao SS, Liu L, Lauer AK, Bailey ST, Flaxel CJ, Wilson DJ, Huang D, Jia Y . 6 . Automated Quantification of Capillary Nonperfusion Using Optical Coherence Tomography Angiography in Diabetic Retinopathy . JAMA Ophthalmology . 134 . 4 . 367–373 . April 2016 . 26795548 . 4978127 . 10.1001/jamaophthalmol.2015.5658 .
  22. Jia Y, Wei E, Wang X, Zhang X, Morrison JC, Parikh M, Lombardi LH, Gattey DM, Armour RL, Edmunds B, Kraus MF, Fujimoto JG, Huang D . 6 . Optical coherence tomography angiography of optic disc perfusion in glaucoma . Ophthalmology . 121 . 7 . 1322–1332 . July 2014 . 24629312 . 4082728 . 10.1016/j.ophtha.2014.01.021 .
  23. Kashani AH, Chen CL, Gahm JK, Zheng F, Richter GM, Rosenfeld PJ, Shi Y, Wang RK . 6 . Optical coherence tomography angiography: A comprehensive review of current methods and clinical applications . Progress in Retinal and Eye Research . 60 . 66–100 . September 2017 . 28760677 . 5600872 . 10.1016/j.preteyeres.2017.07.002 .
  24. Spaide RF, Fujimoto JG, Waheed NK, Sadda SR, Staurenghi G . Optical coherence tomography angiography . Progress in Retinal and Eye Research . 64 . 1–55 . May 2018 . 29229445 . 6404988 . 10.1016/j.preteyeres.2017.11.003 .
  25. Jia, Yali; Bailey, Steven T.; Wilson, David J.; Tan, Ou; Klein, Michael L.; Flaxel, Christina J.; Potsaid, Benjamin; Liu, Jonathan J.; Lu, Chen D.; Kraus, Martin F.; Fujimoto, James G.; Huang, David (2014-07). "Quantitative Optical Coherence Tomography Angiography of Choroidal Neovascularization in Age-Related Macular Degeneration". Ophthalmology. 121 (7): 1435–1444. doi:10.1016/j.ophtha.2014.01.034. PMC 4082740. PMID 24679442.
  26. Papakostas TD, Kiss S . Optical Coherence Tomography Angiography to Evaluate Ischemia in Diabetic Eyes . JAMA Ophthalmology . 136 . 8 . 936–937 . August 2018 . 29902300 . 10.1001/jamaophthalmol.2018.2256 . 49213827 .
  27. Wang B, Camino A, Pi S, Guo Y, Wang J, Huang D, Hwang TS, Jia Y . 6 . Three-dimensional structural and angiographic evaluation of foveal ischemia in diabetic retinopathy: method and validation . Biomedical Optics Express . 10 . 7 . 3522–3532 . July 2019 . 31360604 . 6640826 . 10.1364/BOE.10.003522 .
  28. Al-Sheikh M, Akil H, Pfau M, Sadda SR . Swept-Source OCT Angiography Imaging of the Foveal Avascular Zone and Macular Capillary Network Density in Diabetic Retinopathy . Investigative Ophthalmology & Visual Science . 57 . 8 . 3907–3913 . July 2016 . 27472076 . 10.1167/iovs.16-19570 . free .
  29. Freiberg FJ, Pfau M, Wons J, Wirth MA, Becker MD, Michels S . Optical coherence tomography angiography of the foveal avascular zone in diabetic retinopathy . Graefe's Archive for Clinical and Experimental Ophthalmology . 254 . 6 . 1051–1058 . June 2016 . 26338819 . 4884570 . 10.1007/s00417-015-3148-2 .
  30. Wons J, Pfau M, Wirth MA, Freiberg FJ, Becker MD, Michels S . Optical Coherence Tomography Angiography of the Foveal Avascular Zone in Retinal Vein Occlusion . Ophthalmologica. Journal International d'Ophtalmologie. International Journal of Ophthalmology. Zeitschrift Fur Augenheilkunde . 235 . 4 . 195–202 . 2016 . 27160007 . 10.1159/000445482 . 22808467 .
  31. Tang W, Guo J, Zhuang X, Zhang T, Wang L, Wang K, Chang Q, Liu W, Xu G . 6 . Wide-Field Swept-Source Optical Coherence Tomography Angiography Analysis of the Periarterial Capillary-Free Zone in Branch Retinal Vein Occlusion . Translational Vision Science & Technology . 10 . 2 . 9 . February 2021 . 34003897 . 7881276 . 10.1167/tvst.10.2.9 .
  32. Enfield J, Jonathan E, Leahy M . In vivo imaging of the microcirculation of the volar forearm using correlation mapping optical coherence tomography (cmOCT) . Biomedical Optics Express . 2 . 5 . 1184–1193 . April 2011 . 21559130 . 3087575 . 10.1364/boe.2.001184 .
  33. Barton J, Stromski S . Flow measurement without phase information in optical coherence tomography images . EN . Optics Express . 13 . 14 . 5234–5239 . July 2005 . 19498514 . 10.1364/OPEX.13.005234 . Jennifer Barton . free . 2005OExpr..13.5234B .
  34. Fingler J, Zawadzki RJ, Werner JS, Schwartz D, Fraser SE . Volumetric microvascular imaging of human retina using optical coherence tomography with a novel motion contrast technique . EN . Optics Express . 17 . 24 . 22190–22200 . November 2009 . 19997465 . 2791341 . 10.1364/OE.17.022190 . 2009OExpr..1722190F .
  35. Wang RK, Jacques SL, Ma Z, Hurst S, Hanson SR, Gruber A . Three dimensional optical angiography . EN . Optics Express . 15 . 7 . 4083–4097 . April 2007 . 19532651 . 10.1364/OE.15.004083 . free . 2007OExpr..15.4083W .
  36. Jia Y, Tan O, Tokayer J, Potsaid B, Wang Y, Liu JJ, Kraus MF, Subhash H, Fujimoto JG, Hornegger J, Huang D . 6 . Split-spectrum amplitude-decorrelation angiography with optical coherence tomography . Optics Express . 20 . 4 . 4710–4725 . February 2012 . 22418228 . 3381646 . 10.1364/oe.20.004710 . free . 13838091 . 2012OExpr..20.4710J . 1721.1/73109 .
  37. Ryu G, Park D, Lim J, van Hemert J, Sagong M . Macular Microvascular Changes and Their Correlation With Peripheral Nonperfusion in Branch Retinal Vein Occlusion . American Journal of Ophthalmology . 225 . 57–68 . May 2021 . 33412121 . 10.1016/j.ajo.2020.12.026 . 231192745 .
  38. Koustenis A, Harris A, Gross J, Januleviciene I, Shah A, Siesky B . Optical coherence tomography angiography: an overview of the technology and an assessment of applications for clinical research . The British Journal of Ophthalmology . 101 . 1 . 16–20 . January 2017 . 27707691 . 10.1136/bjophthalmol-2016-309389 . 11456379 .
  39. Izatt JA, Kulkarni MD, Yazdanfar S, Barton JK, Welch AJ . In vivo bidirectional color Doppler flow imaging of picoliter blood volumes using optical coherence tomography . Optics Letters . 22 . 18 . 1439–1441 . September 1997 . 18188263 . 10.1364/ol.22.001439 . 1997OptL...22.1439I .
  40. Chen Z, Milner TE, Srinivas S, Wang X, Malekafzali A, van Gemert MJ, Nelson JS . Noninvasive imaging of in vivo blood flow velocity using optical Doppler tomography . Optics Letters . 22 . 14 . 1119–1121 . July 1997 . 18185770 . 10.1364/ol.22.001119 . 30205866 . 1997OptL...22.1119C .
  41. Spaide RF, Fujimoto JG, Waheed NK, Sadda SR, Staurenghi G . Optical coherence tomography angiography . Progress in Retinal and Eye Research . 64 . 1–55 . May 2018 . 29229445 . 6404988 . 10.1016/j.preteyeres.2017.11.003 . free .
  42. Makita S, Hong Y, Yamanari M, Yatagai T, Yasuno Y . Optical coherence angiography . Optics Express . 14 . 17 . 7821–7840 . August 2006 . 19529151 . 10.1364/oe.14.007821 . free . 2006OExpr..14.7821M . 2241/108149 .
  43. Fingler J, Zawadzki RJ, Werner JS, Schwartz D, Fraser SE . Volumetric microvascular imaging of human retina using optical coherence tomography with a novel motion contrast technique . Optics Express . 17 . 24 . 22190–22200 . November 2009 . 19997465 . 2791341 . 10.1364/oe.17.022190 . 2009OExpr..1722190F .
  44. Wang RK, Jacques SL, Ma Z, Hurst S, Hanson SR, Gruber A . Three dimensional optical angiography . Optics Express . 15 . 7 . 4083–4097 . April 2007 . 19532651 . 10.1364/OE.15.004083 . 2007OExpr..15.4083W . free .
  45. Gao SS, Jia Y, Zhang M, Su JP, Liu G, Hwang TS, Bailey ST, Huang D . 6 . Optical Coherence Tomography Angiography . Investigative Ophthalmology & Visual Science . 57 . 9 . OCT27–OCT36 . July 2016 . 27409483 . 4968919 . 10.1167/iovs.15-19043 .
  46. Gass JD, Sever RJ, Sparks D, Goren J . A combined technique of fluorescein funduscopy and angiography of the eye . Archives of Ophthalmology . 78 . 4 . 455–461 . October 1967 . 6046840 . 10.1001/archopht.1967.00980030457009 .
  47. Slakter JS, Yannuzzi LA, Guyer DR, Sorenson JA, Orlock DA . Indocyanine-green angiography . Current Opinion in Ophthalmology . 6 . 3 . 25–32 . June 1995 . 10151085 . 10.1097/00055735-199506000-00005 . 43888613 .
  48. Yannuzzi LA, Rohrer KT, Tindel LJ, Sobel RS, Costanza MA, Shields W, Zang E . Fluorescein angiography complication survey . Ophthalmology . 93 . 5 . 611–617 . May 1986 . 3523356 . 10.1016/s0161-6420(86)33697-2 .
  49. Web site: Fluorescein Angiography . https://web.archive.org/web/20160527214507/https://www.aao.org/bcscsnippetdetail.aspx?id=429f2356-bb01-42a0-a845-6a535e98d9cf . 27 May 2016 . American Academy of Ophthalmolog .
  50. Alander JT, Kaartinen I, Laakso A, Pätilä T, Spillmann T, Tuchin VV, Venermo M, Välisuo P . 6 . A review of indocyanine green fluorescent imaging in surgery . International Journal of Biomedical Imaging . 2012 . 940585 . 2012 . 22577366 . 3346977 . 10.1155/2012/940585 . free .

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