OCT Technology and Market
Optical Coherence Tomography, or OCT, is a non-invasive imaging technique with broad uses in ophthalmology, cardiology, and gastroenterology. OCT instrumentation is divided into three categories- time-domain OCT (TDOCT), spectral-domain OCT (SDOCT), and swept-source OCT (SSOCT). Key performance metrics of OCT technology span across resolution, imaging depth, intrusiveness, acquisition time, and complexity. The use of incandescent sources to realize axial resolutions, polarization-sensitive imaging, as well as the use of OCT technology in additive manufacturing and 3D printing of medical devices are some of the recent developments in OCT.
Overview of OCT Technology
- OCT technology has been likened to the ultrasound, only that OCT uses light waves instead of sound waves used in ultrasounds. OCT can reconstruct an axial profile of a sample structure by using time-delayed information captured by light waves from different depths. 3D images of the sample structure are created when light waves are scanned across a sample's surface.
- According to Fraunhofer IPT, OCT technology is based on short-coherent interferometry and through the use of infrared light, realizes penetration depths of several millimeters. The resolution achieved spans a few micrometers.
- OBEL posits that it is the optical bandwidth of light sources available in OCT technology that enables the applications of OCT systems in in-vivo imaging through "thick sections of the human body". It further notes that OCT technology is considered an established standard imaging modality in ophthalmology.
- In cardiology, OCT is used during angiograms to take detailed images of blood vessels walls. UptoDate, a website dedicated to contemporary advances in best care decisions, postulates that endoscopists can use OCT technology to enhance endoscopic imaging of the gastrointestinal tract, which may potentially help them identify mucosal abnormalities like Barrett's esophagus.
Properties of OCT Technology
- OCT technology is categorized into 3 groups; time-domain OCT (TDOCT), spectral-domain OCT (SDOCT), and swept-source OCT (SSOCT).
- According to OBEL, TDOCT is the earliest research and instrumentation based on OCT technology. It is considered more intuitive to understand.
- SDOCT is rapidly replacing TDOCT as it offers more significant advantages in sensitivity and imaging.
- Both SDOCT and SSOCT are considered to offer faster scan speeds, improved sensitivity, better resolution, and fewer artifacts compared to TDOCT. However, Review Education Group notes that SSOCT provides a longer wavelength, less disparity in sensitivity depth, and higher acquisition speed in comparison to SDOCT.
- The schematic components of the TDOCT, SDOCT, and SSOCT systems are shown in the images below respectively.
Key Performance Metrics
1. Resolution and Imaging Depth
- Compared to ultrasounds, x-rays, and MRI, OCT technology has limited imaging depths of between 2 and 10 millimeters, but OBEL asserts that it offers a greater resolution.
- In ophthalmology, SSOCT is considered to aid further imaging into the anterior tissue of the eye, as well as deeper imaging into the ocular tissue of the eye.
2. Acquisition Time
- OBEL further asserts that OCT's acquisition time, much like ultrasounds, is short enough to support imaging at video rates. This makes OCT technology more forbearing to subject motion, unlike computer tomography (CT) scans or MRI.
- OCT technology requires no physical contact with the sample, and OBEL posits that because of this feature, OCT may be used for tomography imaging of air-filled hollow organs; a feat that cannot be completed by ultrasounds.
- OCT technology also employs the use of biologically-safe levels of non-ionizing radiation, which OBEL notes, allows for longer exposure times.
- OBEL notes that OCT's complexity is closer to ultrasounds, which may allow for low-cost and portable OCT scanners.
- The point-scanning properties of OCT technology may be executed in fiber optics, which OBEL states, makes endoscopic and catheter-based imaging a reality.
Recent Development in OCT Technology
- OBEL asserts that the use of incandescent sources will realize axial resolutions of 1 micrometer, an improvement from the 10 millimeters realized by the current semiconductor sources. This, OBEL posits, may be achieved through the use of "extremely broad" bandwidth in multiple forms of optic fiber.
- OBEL also notes that the advantages of polarization-sensitive imaging are being realized as birefringence and dichroism are being explored as potential contrast mechanisms. OBEL defines birefringence and dichroism as factors of polarization based on phase velocity and amplitude respectively.
- Axsun Technologies, a US-based photonics products manufacturer of medical devices, began to look into incorporating OCT technology in 3D printing and additive manufacturing in 2017, with Axsun reporting that it was a novel concept in the market. Research uncovered that the only other use of OCT technology in 3D printing was noted in 2019, as Inkbit, attempted to lend "eyes and ears" to 3D printing powered by artificial intelligence (AI) through the use of OCT scanners.
To provide a high-level overview, performance metrics, uses and application, as well as recent developments in OCT technology, the research team began by looking through industry commentary by practitioners and dedicated websites. A majority of the findings were garnered from Optical+Biomedical Engineering Laboratory (OBEL) and Review Education Group's paper, as the research team deemed this relevant to the brief. Review Education Group's paper was the earliest dated in 2017, but it is noted on its web page that the information remains relevant to September 2020.