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Optical coherence tomography

A method of subsurface optical coherence tomographic (OCT) imaging in highly scattering and relatively weakly absorbing media has been developed. Near IR radiation sources were used to create optical tomographs for non-invasive diagnostics (endoscopic one inclusive) of biological tissues at a depth of 2 mm. The measurement of a structure on the 10-µm scale, which is typical in OCT, corresponds to a time resolution of ~30 fsec. We were pioneers in obtaining tomograms of human internal organs, normal and pathologic including oncologic diseases. An algorithm was developed for reconstructing parameters of scattering of biological tissues by OCT images and qualitative description of the state of the tissues. The acquired information cannot be obtained by any other available technique of medical diagnostics, including computer tomography and ultrasonography.

General view of the tomograph
Endoscopic probe inserted into a biopsy canal of fibrogastroscope
Tomogram of healthy esophagus
Tomogram of larynx at the tumor border malignant growth (on the right); benign hyperplastic epithelium (on the left)
Fig. 1.

Development of the OCT technique as one of the most promising fields of low-coherence fiber interferometry is the main scientific trend of the High-sensitivity Optical Measurements Laboratory and the Biophotonics Laboratory at the IAP RAS Department of Coherent Optics starting with the mid-nineties of the XX-th century up to the present time and for the near future. Looking for additional sources of information, OCT polarization methods as well as optical coherence microscopy (OCM) have also been developed in the recent years. The OCM modality that combines the methods of OCT and confocal microscopy enhanced the spatial resolution up to the cellular level (about 4 mcm). The principles of creating a compact device for clinical applications as well as the principles of acquiring images of real biotissue in vivo are studied now. The photo of the OCM device is given in fig. 2.

Fig. 2. Optical coherence microscope

The OCT and OCM images of plants (tradescantia and tomato leaves) are shown for comparison in fig. 3. Analysis of the images demonstrates that a much higher spatial resolution was obtained by the OCM technique.

Fig. 3. OCT and OCM images of the internal structure
of Tradescantia (a) and tomato (b) leaves

Figure 4 presents OCT and OCM images of human mucosa (Uterine cervix) acquired after removal ex vivo, in norm and in the case of oncology.

Fig. 4. Comparative OCT (a) and OCM (b) images of the same section of human mucosa in norm;
(c) OCM image of mucosa of the same organ in the case of oncology.

Currently, works aimed at developing and advancing novel OCT techniques, enhancing sensitivity, resolution, penetration depth and speed are under way at the IAP RAS Department of Coherent Optics. IAP RAS has top-level achievements in this field, including development of highly sensitive tomographs for different branches of medicine. Development of the OCT and OCM techniques facilitates realization of the idea of optical biopsy.