Made in AOG


Master Slave Optical Coherence Tomography

  • Master Slave optical coherence tomography1 (MS-OCT) operates like a time domain OCT1, selecting signal from a selected depth while scanning the laser beam across the sample.
    Master Slave is a spectral (Fourier) domain OCT method, hence benefits from the sensitivity and speed advantage of the spectral (Fourier) domain methods in comparison with time domain method1, 3-5.
  • Master Slave method allows collection of signals from any number of depths, as required by the user, ie of any number of en-face OCT images, from any depths, separated by any distance from the neighboring en-face slices1, 3-5. MS-OCT does not require resampling of data, hence no linearization, no calibration necessary, no clock needed in the
    swept source OCT, no linearized spectrometer in spectrometer based OCT1, 3-5.
  • MS-OCT is tolerant to dispersion7, so no need to optimize the quantity of glass in the interferometer. Since no data re-sampling is required, the sensitivity at large depths provided by the method proposed is slightly superior to that provided by the FFT based technique1, 3-5. The depth resolution does not depend on the way in which data are sampled, and reaches the theoretical expected limit1, 3-5.
  • The Master Slave method is ideally suited to production of en-face OCT images from any tissue, including the eye, to satisfy the recent revival of interest in the en-face orientation7,8.
  • The MS method is ideally suited for parallel computing algorithms on GPUs due to its parallel nature. Recently, we have demonstrated realtime production of MS based B-scan images of the human retina9 as well as a dual modality imaging system en-face SLO/OCT entirely based on MS method 10.

Principle of operation of the MS method illustrated here using a multi-layered object. Decoding of the depth information can be obtained by comparing the reference (mask) channeled spectrum (mask) with the three channeled spectra (CS1, CS2, CS3) produced by interference between the reference beam and the back-reflected light by the three reflecting structures in the object.

  References

  1. A. Gh. Podoleanu and A. Bradu, “Master-slave interferometry for parallel spectral domain interferometry sensing and versatile 3D optical coherence tomography,” Opt. Express 21, 19324-19338 (2013).
  2. A. Gh. Podoleanu, “Principles of en-face optical coherence tomography: real time and post-processing en-face imaging in ophthalmology,” (in Clinical en-face OCT atlas, B. Lambruso, D. Huang, A. Romano, M. Rispoli, G. Coscas eds., J.P. Medical Ltd 2013), Chap. 1.
  3. A. Bradu and A. Gh. Podoleanu, “Calibration-free B-scan images produced by master/slave optical coherence tomography,” Opt. Lett. 39, 450-453 (2014).
  4. A. Bradu and A. Gh. Podoleanu, “Imaging the eye fundus with real-time en-face spectral domain optical coherence tomography,” Biomed. Opt. Express 5, 1233-1249 (2014).
  5. K. Kapinchev, F. Barnes, A. Bradu, A. Gh. Podoleanu, “Approaches to General Purpose GPU Acceleration of Digital Signal Processing in Optical Coherence Tomography Systems,” IEEE International Conference on Systems, Man, and Cybernetics (SMC), 2013, 2576-2580, (2013).
  6. A. Bradu, M. Maria, and A. Podoleanu, “Demonstration of tolerance to dispersion of master/slave interferometry,” Opt. Express 23, 14148-14161 (2015).
  7. First international congress of en-face OCT, Rome 2013.
  8. Second International Congress on “En-Face” OCT imaging New Developments in OCT, OCT Angiography, Rome, 2014.
  9. Adrian Bradu, Konstantin Kapinchev, Frederick Barnes, and Adrian Podoleanu, “On the possibility of producing true real-time retinal cross-sectional images using a graphics processing unit enhanced master-slave optical coherence tomography system,” J. Biomed. Opt., 20, 076008 (2015).
  10. Adrian Bradu, Konstantin Kapinchev, Frederick Barnes, and Adrian Podoleanu, “Master slave en-face OCT/SLO,” Biomed. Opt. Express 6, 3655-3669 (2015).

En-face OCT

Researchers in the Applied Optics Group were the first to demonstrate en-face images from the retina, now known as C-scans. To mark the event, a special brick has been engraved in the Footstep project (part of the new Crab & Winkle Path alongside the Templeman Library in the campus).

The image was made possible by realizing that scattering in combination with a fixed coherence gating, can generate a C-scan. There is no need for an external phase modulator if the object to be imaged is scattering and the image size is sufficiently large. The modulation is, interestingly, created by scanning the beam over the target.

OCT/SLO

The OCT/SLO instrument was invented in 1998 by Adrian Podoleanu and David Jackson.

Reading:

Our first OCT/SLO ever was an en-face OCT/SLO system, where the OCT channel operates based on en-face time domain OCT. After 2002, spectral domain OCT technology took off, and the SLO channel was then paired sequentially with a spectral domain OCT channel. Such a system is now sold by Optos Plc., based on the patent:

Optical imaging apparatus with spectral detector
United States Patent 7649629 B2 · Filed: 10/05/2007 · Published: 01/19/2010

The acronym OCT/SLO lives on meaning now different formats of OCT. Spectral domain OCT technology is now so fast, that a fundus image can be created using spectral domain OCT. Several groups have by now reported generation of a fundus type image to guide the B-scan imaging based by the spectral domain OCT, and labelled their instruments as OCT/SLO.

The output from a joint OCT/SLO system, with the SLO image on the left and the OCT on the right. The top of the optic nerve, then the RPE and at the end the lamina cribrosa are seen in the OCT image. In the SLO image, these are visible all the time. The animation is made up from forty 3 mm x 3 mm images collected from the optic nerve in 20 seconds, with a total exploration depth of 1.5 mm.

Key publications on the OCT/SLO in the Applied Optics Group