Maciej Wojtkowski

Flow velocity measurements by frequency domain short coherence interferometry

A method to measure the longitudinal flow velocity component based on phase resolved frequency domain optical coherence tomography (FDOCT) is introduced. At a center wavelength of 800nm the accessible velocity components ranges from 2 micrometers /s up to 2 mm/s. The upper limit is set by half the maximum frame rate of the CCD detector array. The lower limit is determined by the minimum resolvable phase change in the system, which is set by the system phase noise of 1 deg. First tests of the method include the velocity measurement of a mirror mounted on an oscillating piezo translator, and the flow of 8 micrometers latex spheres dispersed in water through a glass capillary.

Fourier domain OCT imaging of the human eye in vivo

An improved Fourier domain Optical Coherence Tomography (FdOCT) technique is proposed as a new kind of ophthalmic OCT, which enables non-invasive imaging of the retina, the iris and the lens in vivo without an axial mechanical scan of the reference mirror. The FdOCT tomograms of various parts of human eye in vivo, to our knowledge, are the first obtained to date. The detailed images of the human eye are reconstructed from spectral data by the differential method. The tomograms are free of the parasitic autocorrelation terms.

Twenty-five years of optical coherence tomography: the paradigm shift in sensitivity and speed provided by Fourier domain OCT [Invited]

Optical coherence tomography (OCT) has become one of the most successful optical technologies implemented in medicine and clinical practice mostly due to the possibility of non-invasive and non-contact imaging by detecting back-scattered light. OCT has gone through a tremendous development over the past 25 years. From its initial inception in 1991 [Science254, 1178 (1991)] it has become an indispensable medical imaging technology in ophthalmology. Also in fields like cardiology and gastro-enterology the technology is envisioned to become a standard of care. A key contributor to the success of OCT has been the sensitivity and speed advantage offered by Fourier domain OCT. In this review paper the development of FD-OCT will be revisited, providing a single comprehensive framework to derive the sensitivity advantage of both SD- and SS-OCT. We point out the key aspects of the physics and the technology that has enabled a more than 2 orders of magnitude increase in sensitivity, and as a consequence an increase in the imaging speed without loss of image quality. This speed increase provided a paradigm shift from point sampling to comprehensive 3D in vivo imaging, whose clinical impact is still actively explored by a large number of researchers worldwide.

Phase-sensitive interferometry in optical coherence tomography

Optical coherence tomography (OCT) is a noninvasive imaging technique which provides microscopic tomographic sectioning of biological samples. This contribution presents a new spectral OCT technique, which allows to detect the phase of detected signal and thereby to remove the useless low- frequency terms from the registered signal. The basic principle is shown and experimental measurement sin vitro and in vivo are presented.

Autocorrelation free spectral OCT techniques in eye imaging

Two improved spectral Optical Coherence Tomography (OCT)techniques: a differential and complex methods are compared with classical spectral OCT. Both methods enable to eliminate parasitical terms. Additionally the complex spectral OCT doubles the useful depth range. Opthalmic applications of above-mentioned techniques are presented.

Spectroscopic analysis of substances by frequency domain optical coherence tomography

During the last years Optical Coherence Tomography could proof its value as a precise and non-invasive tool for providing morphologic information about biological tissue. Nevertheless there is also a demand for obtaining functional tissue parameters like for instance oxygen saturation of blood. Such information can be accessed by spectroscopic tissue analysis. It is shown how Fourier Domain Optical Coherence Tomography (FDOCT) can serve as a tool for the assessment of spectroscopic object properties. In order to show the feasibility of this method, absorption measurements of a RG830 filter glass plate and of a dye in a glass cuvette are presented.

Depth-resolved spectroscopy by frequency-domain optical coherence tomography

A new spectroscopic OCT technique is introduced, spectroscopic frequency-domain OCT, and its application to measure depth resolved spectral absorption is described. The crucial parameters of this method like transversal, depth, and spectral resolution and their relations are discussed. As preliminary test of the feasibility of this method, a simple absorbing object, in the present case an IR filter glass plate is investigated. Since the filter attenuates shorter wavelengths stronger than longer ones, one expects a shift of the spectral weight to the IR domain, which is absent in the case of a non-absorbing object like a BK7 glass plate. This effect is demonstrated by the measurement. The results are then compared to theoretical calculations based on the well known characteristics of the filter glass plate.

Spectral OCT techniques in eye imaging

This contribution presents examples of images of eye in vitro obtained by spectral optical tomography (OCT). Particular interest was focused on obtaining clear images of the corneo-scleral angle and images of fundus which are both essential for diagnosing and planning of a treatment of glaucoma.

Bessel beam OCM for analysis of global ischemia in mouse brain

We present the in-vivo imaging of the global mouse brain ischemia using Bessel beam optical coherence microscopy. This method allows to monitor changes in brain structure with extra control of blood flow during the process of artery occlusion. The results show the capability and sensitivity of OCM system with Bessel beam to analyze brain plasticity after severe injury within a period of 8 days.

Ultrahigh-sensitivity imaging of the eye by spectral optical coherence tomography

We present theoretical analysis of the sensitivity and signal to noise ratio of spectral of OCT. It will be experimentally demonstrated that Spectral OCT is able to reproduce one line of the tomogram within time shorter than 0.1 ms. This technique has potential to produce images in very demanding conditions like tomograms of the fundus in the cataractous eye.