Our Technology

The Science

Optical coherence tomography (OCT) is analogous to ultrasound imaging, except that light, instead of sound, is used noninvasively to provide 10-100 times better resolution compared to ultrasound. OCT can image tissue microstructure with resolutions approaching that of standard histopathology by microscopy. Even in highly scattering biological tissues, e.g., skin, OCT can achieve an imaging depth of up to 1-2 mm. To date, OCT has been used in a wide range of clinical applications in humans, including ophthalmology, cardiology, endoscopy, urology, dermatology, and dentistry.

Compares Favorably with Other Imaging Modalities

Advantages of OCT:

  • No ionizing radiation
  • Real-time 3D imaging
  • Millimeter spatial resolution; 50- to 100-times greater compared to ultrasound
  • Millimeter depth image penetration
    • Sufficient to see through epithelium tissue
    • 20-times deeper compared to confocal microscopy
Resolution comparisons

Why Faster is Better

High speed, resolution, and sensitivity are desirable for optical coherence tomography (OCT) no matter the application. For use in imaging of the eye, ultra‑highspeed scanning is the next step in the evolution of OCT. Current ophthalmic OCT technology offers significant improvement over earlier generation devices with today's most advanced devices offering scanning speeds of <100,000 scans/second. Regrettably, even this high scan rate is not fast enough as issues related to the need for higher imaging speeds for the eye include:

Due to blinking, tear film degradation, and involuntary sacchidic movements, all things being equal, reducing the scanning time should result in images with fewer motion artifacts. The efforts used in today's OCT technology to increase scanning speeds include faster raster speeds (side to side and up and down) of the laser system and/or combined with imaging software such as eye tracking and mosaicing of multiple images to reduce motion artifacts in the final image. These methods increase the complexity of both the mechanical and the software of diagnostic eye scanners and are approaching the limit of their usefulness.

Our technology: Space-division multiplexing optical coherence tomography (SDM-OCT)

Importantly, our technology is patented: US 2014/0160488 A1, WO 2014/088650 A1. Using a prototype system, we have demonstrated a space division multiplexing (SDM) technology that translates long coherence length of a commercially-available wavelength tunable laser into high OCT imaging speed. We achieved an effective 800,000 A-scans/s imaging speed using a 100,000 Hz tunable vertical cavity surface-emitting laser (VCSEL). A sensitivity of 94.6 dB and a roll-off of <2 dB over ~30 mm imaging depth were measured from a single channel in the prototype SDM-OCT system. An axial resolution of ~11 μm in air (or ~8.3 μm in tissue) was achieved throughout the entire depth range.

SDM technology provides:

Thus, SDM-OCT improves upon existing uses and enables new biomedical and other industrical applications.

SDM-OCT Concept

The following diagrams describe the basic principals of the technology as initially demonstrated in a benchtop system.2

Follow-on improvements have included the development of a photonic chip that eliminates optical fibers to improve performance, reduce costs, and to simplify manufacture and implementation by device companies. SDMI is currently focused on the refinement of the photonic chip and overall system performance.

Diagram A

Overview

Schematic diagram of the prototype SDM-OCT system. The key of the technology is to create multiple illumination beams on the sample simultaneously, while having different optical delays for each beam (see the red rectangular region). A single detection channel is used to simultaneously collect signals from all beams.

Diagram B

Fiber Spacing

A 1 x 8 fiber array with 300 µm spacing between individual fibers are used in a prototype system.

Diagram C

Optical Delay

Each beam is optically delayed. Signals from different beams (different sample locations) are presented at different frequency range, i.e., imaging depth. For simplicity, only four beams are shown in this diagram.


References

1 Boris Považay, Bernd Hofer, Cristiano Torti, Boris Hermann, Alexandre R. Tumlinson, Marieh Esmaeelpour, Catherine A. Egan, Alan C. Bird, and Wolfgang Drexler, "Impact of enhanced resolution, speed and penetration on three-dimensional retinal optical coherence tomography," Opt. Express 17, 4134-4150 (2009).

2 Zhou et al, Optics Express, 21(16): 19219-19227, 2013.