A review of low-cost and portable optical coherence tomography

Abstract

Optical coherence tomography (OCT) is a powerful optical imaging technique capable of visualizing the internal structure of biological tissues at near cellular resolution. For years, OCT has been regarded as the standard of care in ophthalmology, acting as an invaluable tool for the assessment of retinal pathology. However, the costly nature of most current commercial OCT systems has limited its general accessibility, especially in low-resource environments. It is therefore timely to review the development of low-cost OCT systems as a route for applying this technology to population-scale disease screening. Low-cost, portable and easy to use OCT systems will be essential to facilitate widespread use at point of care settings while ensuring that they offer the necessary imaging performances needed for clinical detection of retinal pathology. The development of low-cost OCT also offers the potential to enable application in fields outside ophthalmology by lowering the barrier to entry. In this paper, we review the current development and applications of low-cost, portable and handheld OCT in both translational and research settings. Design and cost-reduction techniques are described for general low-cost OCT systems, including considerations regarding spectrometer-based detection, scanning optics, system control, signal processing, and the role of 3D printing technology. Lastly, a review of clinical applications enabled by low-cost OCT is presented, along with a detailed discussion of current limitations and outlook.

Keywords: low cost; ophthalmology; optical coherence tomography; portable imaging modality.

Figure 1.

Custom low-cost spectrometer design for SD-OCT. (a) Loop configuration of the spectrometer. Matrix of spot diagrams generated with Zemax at (b) 815 nm, (c) 840 nm, (d) 860 nm. Adapted with permission from [58] © The Optical Society. (e) 3D schematic of components in the spectrometer. (f) Fully enclosed spectrometer in a 3D-printed housing. Reprinted with permission from [58] © 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.

Figure 2.

(a) MEMS-based scanning in a handheld SS-OCT probe. Reprinted with permission from [51] © 2013 Optical Society of America. (b) Anatomy of portable SD-OCT scanner with a MEMS mirror for primary care imaging. [56] John Wiley & Sons. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. 2014, Journal of Biophotonics, Wiley-VCH. (c) Low-cost retinal OCT scanner design, using a MEMS mirror and a liquid lens for dynamic focusing. Reproduced from [74]. CC BY-NC-ND. With permission. (d) OCT borescope scanning mechanism, which includes a MEMS mirror. Reprinted with permission from [85] © 2019 Optical Society of America.

Figure 3.

Proximal vs distal scanning approaches. In proximal scanning, a rotary junction is used to allow the probe fiber to rotate while scanning, and a torque coil transmit the rotational force to the distal optics. In distal scanning, static fiber connections can be used to connect to the probe, but a motor is needed in the probe itself to rotate a mirror and scan the beam.

Figure 4.

Fully enclosed, portable OCT devices. (a) First low-cost OCT engine. Reprinted with permission from [58] © 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement. (b) Low-cost OCT system for retinal imaging. Reproduced from [74]. CC BY-NC-ND. With permission. (c) Compact briefcase OCT system. Reproduced from [66] © 2018 Society of Photo-Optical Instrumentation Engineers (SPIE) 1083–3668/2018/$25.00 © 2018 SPIE. (d) Visotec Home care OCT concept rendering. 2021 Reproduced with permission from Visotec Home Diagnostics. (e) Notal Vision Home OCT concept rendering. 2021, reproduced with permission from Notal Vision.

Figure 5.

(a) Retinal low-cost OCT system mounted on a chin rest to facilitate clinical imaging. (b) Schematic of scanner, which allows it to be both handheld and mounted on a chin rest. Reproduced from [74]. CC BY-NC-ND. With permission.

Figure 6.

Images acquired on the low-cost OCT system from pathological retinas compared to those captured on the Heidelberg Spectralis system. Reproduced from [74]. CC BY-NC-ND. With permission.

Figure 7.

Images acquired using OCT on a chip. (a) Single-frame and (b) five times averaged B-scan acquired near the fovea with AWG 1 at 67 kHz. (c) Single-frame and (d) five times averaged B-scan with AWG 1 at 34 kHz. (e) Single-frame and (f) five times averaged B-scan with AWG 2. (g) Volumetric rendering of the foveal region with AWG 1 at 67 kHz. (h) Corresponding angiogram calculated. Reproduced from [72]. CC By 4.0. Copyright © 2021, The Author(s).

Figure 8.

Left: 3D printed OCT paddle probe. Right: OCT image acquired in vivo from human esophagus on a 3D printed 1310 nm spectrometer. E: epithelium. LP: lamina propria. MM: muscularis mucosa. SM: submucosa.

Figure 9.

Left: low-cost OCT system with handle adapted for borescope scanning. Right: OCT B-scan images of articular cartilage of varying thicknesses, overlaid with a false-color map. (scale bars = 250 μm). Reprinted with permission from [85] © 2019 Optical Society of America.

Figure 10.

OCT images of tympanic membranes for (a) normal, (b) acute OM, (c) chronic OM and their corresponding (d)–(f) en face images from an otoscope. Scale bars = 150 μm. Yellow lines indicate location of the TM and blue lines indicate biofilm. [128] John Wiley & Sons. © 2015 The American Laryngological, Rhinological and Otological Society, Inc.