Where Does OCT Go From Here?

MARCIA STAMELL, ASSOCIATE MANAGING EDITOR, marcia.stamell @photonics.com

OCT-A — optical coherence tomography angioplasty — which allows imaging without dye, is a promising breakthrough in the detection of early-stage glaucoma. And swept-source OCT has opened new possibilities for diagnosing diabetic retinopathy and early macular degeneration.

Although ophthalmology continues to dominate the OCT landscape, this imaging technology also has seen new adaptations outside that field. In dermatology, it is used for the diagnosis and treatment of nonmelanoma skin cancer, and in cardiology it’s being used for intravascular imaging.

An OCT-A image of a basal cell carcinoma skin lesion. Image courtesy G. Jemec/L. Themstrup, University of Copenhagen, Roskilde Hospital and Michelson Diagnostics.

No wonder then that market researchers continue to predict robust growth. One such 2016 projection, by the firm Research and Markets, puts the global OCT market at approximately $1.32 billion by 2020, as the result of a projected five-year compound annual growth rate of 12 percent.

In a reprise of a BioPhotonics story from January 2014, we asked three industry experts to help fill in the portrait of OCT’s current state and future prospects. They include:

Jon Holmes, CTO and acting CEO of Michelson Diagnostics in Kent, England. Michelson produces the VivoSight scanner that allows dermatologists to analyze nonmelanoma skin cancers without biopsies. Holmes trained as a physicist at the University of Cambridge and has 30 years’ experience in applying laser scanning and imaging to real-world problems.

One of the newer uses of OCT is for the diagnosis and treatment of nonmelanoma skin cancer. Courtesy of Michelson Diagnostics.

Nishant Mohan, vice president of the OCT division at Wasatch Photonics in Durham, N.C. Mohan has participated in research, development and commercialization of OCT for over a decade. He was affiliated in the past with Bausch+Lomb and Massachusetts General Hospital, and is a judge for the annual Prism Awards.

Adrian Podoleanu, head of the applied optics group of the School of Physical Sciences at the University of Kent in England. Widely published and a frequent speaker at conferences, he is also a fellow of SPIE, OSA and IOP, and a recipient of the Royal Society Wolfson Research Merit Award.

Q: Has the technical development of OCT lived up to your expectations? If not, what have been the critical obstacles?

Holmes: Yes and no. On one hand, the development of low-cost, high-bandwidth swept-source lasers was slower than I hoped in 2014. This is still holding back the market in my opinion. There are some promising developments, but we are not quite there yet; nevertheless I am optimistic for 2017-18. On the other hand, the development and commercial availability of OCT-A has been rapid and very encouraging, and has given OCT a “shot in the arm” due to the explosion of clinical interest.

Mohan: OCT is a fast-developing field with continuous improvements in hardware and software. However, the field hasn’t been able to make a major impact outside ophthalmology and, to some degree, interventional cardiology. A critical factor in adaption across other domains has been the cost of technology.

Ophthalmology remains the primary application area of OCT. Pictured here, an image of the anterior segment of the eye showing the cornea, iris and top surface of the lens. Courtesy of Nishant Mohan, vice president, Wasatch Photonics.

Podoleanu: Although research has advanced in terms of speed, novel tuneable lasers and wider-band spectrometers, the cost of imaging systems is still high. The increase in the demand for OCT technology is still not matched by more affordable technology. We have witnessed continuation of spectral separation of OCT technologies, spectrometer-based for short infrared wavelengths and tuneable lasers for longer infrared wavelengths. There is an interest to expand the tuneable laser technology to shorter wavelengths, but fast-tuning-rate lasers that can cope with eye movement are not available so far. Therefore, investigating the retina is mainly performed with spectrometer-based devices, while for the investigation of skin and internal organs, tuneable laser technology is preferred. The optical source, spectrometer, digitizer and scanning devices compound into a cost exceeding five figures.

The speed of OCT imaging systems has grown exponentially over the past two decades. Courtesy of Nishant Mohan, vice president, Wasatch Photonics.

Q: How has the market adoption of OCT changed in the past three years?

Holmes: Outside ophthalmology, market adoption of OCT has continued to grow slowly. The driving factors are the availability of clinical data that prove efficacy, and, coupled with that, whether there is reimbursement for performing the scan. Although there are hundreds of small clinical studies of OCT for numerous interesting applications, the awarding of reimbursement codes and widespread clinical adoption only occurs when there are published multi-center prospective trials with convincing results. These must be done!

Mohan: OCT has shown continuous growth in ophthalmology and is being adapted in optometry practice as well. OCT is becoming an essential part of several other ophthalmic instruments like surgical lasers and others. OCT has shown adaption in intravascular imaging, dermatology and nondestructive testing as well.

Podoleanu: An interesting evolution was the progress in imaging the vessels with no dye — OCT angiography (OCT-A). This has quickly moved from research to commercialization. Quick evolution has been matched by dedicated conferences, such as the Rome Congress on en-face OCT and OCT-A, each in December. These promote the transition from fluorescein angiography to OCT-A by educating the ophthalmologists in using OCT-A. However, the cost of OCT-A systems for ophthalmology is in the same range as that of other commercial OCT systems. There is also a trend in extending OCT-A to fields outside ophthalmology. In terms of other directions, there are still several avenues successfully reported by numerous academic teams, but still not embraced by the market, such as polarization OCT.

A 3D rendering of an OCT image of vessels in a port-wine stain skin lesion. Image courtesy J. Waibel, Miami Dermatology & Laser Institute and Michelson Diagnostics.

Q: Which application areas would you say are thriving and why?

Holmes: In OCT imaging of skin, the thriving area is to aid diagnosis and monitoring of treatment of nonmelanoma skin cancer. This is because we have three large-scale studies published that show the benefits and advantages of OCT over the standard techniques of clinical assessment and biopsy, because OCT works well when used with noninvasive treatments so the patient avoids being cut, and, finally, because the patients and doctors love OCT!

Mohan: Ophthalmology is still the primary application for OCT. There is certainly growth in intravascular imaging, however OCT hasn’t moved beyond research hospitals in this domain. There are several factors for success in ophthalmology. OCT images provide actionable information for practitioners — with about 20 years of experience behind them there is a strong database for physicians. OCT also falls more comfortably in the workflow for ophthalmology compared to the cardiovascular setting, resulting in greater adaption. OCT has very positive brand association in ophthalmology.

Podoleanu: The main application continues to be imaging the eye. Imaging the retina with high axial resolution practically led to the OCT discovery as a better choice than improving the focus capabilities of simple microscopy. The first OCT image was that of a retina tissue. OCT became a widespread tool in eye diagnosis, and OCT is unbeatable by any other technology in performing optical biopsy. This is the application that still draws more than 55 percent of research publications in OCT. The other two markets are cardiovascular and dermatology, but with less intakes, and there is dental OCT looming. We have also witnessed various combinations of OCT with niche bioscience applications, as well as the spread of OCT applications reported in meetings that were not dedicated to OCT only. There is a phenomenon of OCT diffusion to many sectors of science and engineering, such as microfluidics and nondestructive testing. This keeps the OCT research efforts on track while their heterogeneity and low number makes market adoption difficult.

Q: Where is the next new frontier?

Holmes: I am very interested in extracting measurements from OCT, as well as images. I think that it will be possible to relate measurements obtained from OCT datasets, such as the optical attenuation coefficient, blood vessel density, surface roughness, epidermal thickness and so forth, to skin physiology, in ways that will open up new possibilities to accurately measure skin health and skin aging. This might lead to development of improved treatments for skin rejuvenation that really work!

Mohan: OCT technology continues to thrive at several levels. The next major breakthroughs are likely to come in the form of technologies that convert OCT images to information. Given the amount of data produced by OCT images and the growth in data analysis methods over the last few years, one can expect great value creation by their marriage.

Podoleanu: I envisage two opposing frontiers that will be impacted by further progress of research. We still do not have a smartphone delivering high-quality OCT images. We expect smaller and lower-cost devices that can be used by a larger community of ophthalmic practices. One possibility is integration of several components to improve reliability and reduce the cost of manufacturing, together with adjacent progress in principles of optical sources and spectrometers. This will happen more in the commercial world than in the academic lab.

Figure 1. Forty en-face OCT images, two cross-section OCT images, and a fundus image produced from 400 images acquired and processed simultaneously from 400 depths in the optic nerve of the human eye. Courtesy of A. Bradu et al. from “Master slave en-face OCT/SLO,” Biomed Opt Express, 6, 2015.

The other frontier is the push toward higher performance by research in academic labs, with potential in two main areas. The first is resolution enhancement by embracing large bandwidth sources, adaptive optics and digital refocusing for medical imaging to achieve smaller resolving 3D volumes (voxels). The other is topography and 3D visualization of large objects using long coherence tuning lasers, such as for visualization, orientation and robotics. By extra efforts, these high-performance avenues may become more attractive to industry. Both industry and academia are involved in combinations of imaging with novel tracking methods to eliminate the effects of movement, as well as to create real-time presentation, for a market that already exists. Industry and academia are also involved with enhanced methods for 3D delivery of tissue volume and their visualization to serve surgery for markets that just started to form. Novel processing methods adopt a parallel approach using graphic cards to obtain images for each depth of interest in parallel¹, as shown in Figure 1 where 400 en-face images from 400 depths are produced in parallel with 40 images displayed in real time.

Reference

1. A. Bradu et al. (2016). Master/slave interferometry — ideal tool for coherence revival swept source optical coherence tomography. Biomed Opt Express, Vol. 7, pp. 2453-2468. doi: 10.1364/BOE.7.002453.