Low coherence interferometry (LCI), low coherence reflectometry, optical coherence tomography (OCT) or partial coherence reflectometry all refer to the same basic set-up

OCT derives from low-coherence interferometry. This is an absolute measurement technique which was developed for high- resolution ranging and characterisation of optoelectronics components.
[Al-Chalabi SA, Culshaw B, Davies DEN. Partially coherent sources in interferometric sensors. First Internat. Conf. Optical Fibre Sensors 26-28 April 1983, I.E.E. London, 132-135.Youngquist RC, Carr S, Davies DEN. Optical coherence-domain reflectometry: A new optical evaluation technique. Opt Lett 1987;12(3):158-160.]

The first application of low-coherence interferometry in the biomedical optics field was for the measurement of eye length.
[Fercher AF, Mengedoht K, Werner W. Eye length measurement by interferometry with partially coherent light. Opt Lett 1988;13(3):186-189.]b

Adding lateral scanning to a low-coherence interferometer, allows depth resolved acquisition of 3D information from the volume of biologic material.
[Huang D, Swanson EA, Lin CP, Schuman JS, et al. Optical coherence tomography, Science 1991 254:1178-1181.]

The concept was initially employed in heterodyne scanning microscopy.
[Sawatari T. Optical heterodyne scanning microscope Appl Optics. 1973;12(11): 2766 – 2772.]

OCT has the potential of achieving high-depth resolution, which is determined by the coherence length of the source.
[Mandel L, Wolf E. Optical coherence and quantum optics, Cambridge University Press, 1995 (148-150)].

During research on sensing between 1986-1995, the Applied Optics Group (AOG) has contributed towards several avenues which paved the way towards the later development of what is known today as OCT. AOG was involved in all three types of OCT; (i) Time domain OCT (essential a Michelson interferometer), (ii) Spectral or Fourier domain OCT, where the interferometer output is sent to an optical spectrometer and (iii) the Swept source OCT, where a laser source is used which is swept within an equivalent band to that of the broadband source used in the time domain OCT or Fourier domain OCT.

Then we moved the centre of the Newton rings out from the image centre and sampled the target with a grid of line

This report demonstrates for the first time, B-scan OCT images from the retina constructed from T-scans (en-face 1D OCT scans)

The research on flying spot en-face OCT has shown us how to produce OCT images with the same orientation as that in microscopy, or in scanning laser ophthalmoscopy (SLO). This allowed us to devise and assemble a dual imaging system. The system outputs pairs of OCT and confocal images. Several ophthalmoogy groups are now using the OCT/SLO in imaging the eye.

Recognisable patterns in the OCT C-scans could be associated to several diseases for easier diagnostic

Collaboration with New York Eye and Ear Infirmary and the Department of Ophthalmology
Academic Medical Center, University of Amsterdam
M. E. J. Van Velthoven, F. D.Verbraak, L. A. Yannuzzi, R. B. Rosen, A. Gh. Podoleanu, Marc D. De Smet, Imaging the Retina by En-Face Optical Coherence Tomography, RETINA, 26:129–136, 2006. RETINA-THE JOURNAL OF RETINAL AND VITREOUS DISEASES, Issues/Year: 6.

First OCT/ICG instrument for the eye, collaboration with New York Eye and Ear Infirmary

Sequential OCT/confocal
Sequential instead of simultaneous allows all signal to be used in each channel, OCT or confocal (SLO).
(collaboration with New York Eye and Ear Infirmary)

Modulators and scanning methods for OCT

Using two RF modulators, we demonstrated simultaneous acquisition of two C-scans at two different depths

Using a Mach Zehnder integrated modulator with independent RF excitation in each arm, we demonstrated simultaneous acquisition of two C-scans at two different depths, collaboration with University of Besancon

Using two coupled interferometers we devised a novel method for measuring the eye length

Signal to noise ratio analysis
Comparative noise analysis in the two channels of an OCT/SLO system

This reports shows that fast OCT system have to work in excess photon noise regime limitation and not in shot noise regime

Two novel noise bandwidth definitions are introduced to consider the excess photon noise in balanced OCT under wide bandwidth excitation

Corrections of distortions in OCT images
We make distinction between scanning and refractive type distortions in OCT. This report also predicts a distorted elevation of the RPE layer in the fovea in the OCT images of the retina, due to differences in the indeces of refraction of vitreous and retina
(collaboration with University of Central Florida, School of Optics / CREOL and New York Eye and Ear Infirmary)

OCT in ophthalmology
Posterior pole
The majority of reports above referred to examples in imaging the retina.
A novel method for topography using en-face OCT was presented in the following report
(collaboration with Institute of Ophthalmology, London)

The utility of adjustable depth resolution required by en-face OCT method is presented in:

OCT in dentistry
(collaboration with School of Dentistry, University of Liverpool)

OCT in imaging larynx and cochlea
(Collaboration with Otolaryngology-Head & Neck Surgery Department, Guy's Hospital, London)

OCT in imaging breast tissue
(Collaboration with the Department of Histopathology, Imperial College School of Medicine, Hammersmith Hospital, London)

Imaging paintings
En-face OCT allows visualisation of under-drawings
(Collaboration with the Nottingham Trent University, British Museum London and National Gallery, London)

Gallery of some OCT images, others can be viewed by linking to the web pages indicated in the
A. Podoleanu's publication list

Sequence of 100 en-face OCT images from the optic nerve Animation of OCT/SLO (en-face) pair images from the optic nerve	See four clips of 3D en-face OCT images from the optic nerve and 3D en-face OCT images from the finger on Optics Express, Vol. 7, No. 9,Oct. 23, 2000, 292-8
Longitudinal OCT images from the fovea and optic nerve	Longitudinal OCT images from carried teeth Animation of OCT/SLO (en-face) pair images from a carried tooth
Assembly of the OCT/SLO systems	Longitudinal OCT images from the cornea En-faceOCT images from the cornea
Topography and volume measurements of the optic nerve using en-face optical coherence tomography, Optics Express, Vol. 9, No. 10 November 05, 2001 Page: 533 - 545	New Images soon

Prof. A.Gh Podoleanu

Head of Applied Optics Group

Professor of Biomedical Optics

Expertise