Novel OCT technique incorporates gold-coated probes to monitor biological tissues

Compared with other image-guiding modalities such as MRI, CT, and ultrasound, optical coherence tomography (OCT) is more compact and portable, allowing for integration with surgical tools. Recognizing this fact, researchers from the Johns Hopkins School of Medicine and the Whiting School of Engineering have been working to design and develop ultra-high resolution (~1 µm), high-speed (10 fps) functional spectral-domain OCT for real-time guided microsurgery.

Their common-path optical coherence tomography (CPOCT) system promises to simultaneously monitor depth properties of biological tissues. And their scanning (2D) and non scanning (1D) micro probes aim for full integration with the targeted surgical tools (endoscope and biopsy/therapeutic injection needles), followed by evaluation and validation of the integrated system performance.

The goal of the research is to design a CPOCT system and fabricate micro-fiber probes that can be fully integrated with micro-retinal surgical instruments working in close proximity to the tissue. This will provide a tool for measuring tissue distances, and for obtaining cross-sectional images of the internal retinal tissue planes.

OCT has emerged as a noninvasive, optical imaging technique that can be used to perform high-resolution, cross-sectional in-vivo and in situ imaging of microstructure in biological tissues. Particularly, CPOCT has garnered interest recently due to its robust and stable configuration, resulting from the fact that sample and reference arms share the same fiber-optic path. The CPOCT configuration has a couple of unique, advanced characteristics, such as the freedom to use any arbitrary sample probe length and insensitivity to temperature and strain variations. In addition, it eliminates the need for dispersion and polarization matching between the reference and sample arms. Thus, CPOCT systems are inherently simpler and more robust, which results in easier-to-obtain, high-resolution OCT images. 

For ophthalmic applications, there have been many successful efforts to obtain high-resolution retinal images using non-intruding probes for 2D or 3D optical cross-sectional imaging scanning tools. However, these OCT imaging probes are not designed to be inserted into eyes and can obstruct both the surgeon’s view and the use of surgical tools. Therefore, there is a need for minimally invasive OCT probes that can be inserted directly into various organs and be compatible with commercial biomedical devices. The diameters of most current catheters or surgical needles are around 0.3 to 1.6 mm. In addition to the compatibility issue, the imaging should not exhibit performance degradation while it is in situ or in-vivo conditions. In the case of eye, for instance, which is filled with vitreous humor, the imaging probe should perform equally well both inside and outside the eye. For a typical CPOCT probe, which uses probe tip reflection as the reference, when the fiber is submerged in the water, the reflected signal is reduced due to the reduced index difference at the interface of fiber end.

As a preliminary result, the researchers have fabricated gold-coated micro-fiber probes (Au-µFP) and demonstrated their imaging capability using a North American bullfrog (Rana catesbeiana) eye as an imaging sample. Au-µFP allows a strong reference reflection from the probe tip, even when the probe is submerged in the liquid or in contact with the tissue. No focusing lens was implemented with Au-µFP in order to limit the probe size to the current fiber diameter of 125 µm.

Source: Johns Hopkins University

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Posted by Lee Mather

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