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Ventilated Mouse Lung
The mouse lung images shown below were acquired using a Thorlabs Spectral Radar OCT system with a center wavelength of 930 nm. In general, the Spectral Radar OCT system has a penetration depth of 1 to 2 mm, and an axial resolution of ~10 µm. In these experiments, the imaging depth was 1.6mm with a resolution of 6 µm. Perfundated and ventilated lungs were examined during inspiration and expiration, while the change of volume and shape of alveolar areas was visualized (see Fig. 1a and 1b). The mismatch of the index of refraction between tissue and air-filled structures makes imaging extremely difficult. By filling the lung with an index-matching fluid, imaging down to a depth of 1 mm was possible.
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| Figure 1: Morphological changes in a ventilated mouse lung. |
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These experiments were performed to study the relation between mechanical stress and inflammation, which is important for artificially ventilated patients. The stresses that occur in single alveoli during ventilation are still poorly defined. Based on 3D OCT imaging, it is possible to get detailed structural and spatial information of subpleural contiguous regions of lungs at different alveolar pressure in order to develop appropriate theoretical models of the mechanics of real lung structures under mechanical ventilation.
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| Figure 2: A sequence of 9 B-scans of the mouse lung prefilled with index-matching fluid at pressure equivalent to 3 cm water-ventilation pressure covering a total length of 0.2 mm. Longitudinal resolution in air is 6 µm. The 3D reconstruction of sub-pleural area is also shown in the figure. |
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Image courtesy: Prof. Stefan Uhlig, Dag Friedrichs, Dr. Eva Lankenau and Dr. Gereon Hüttmann, Lübeck, Germany.
Endoscopy
Forward imaging OCT catheters can provide tissue structural information in front of the endoscopic probe, which is essential for guiding surgery or device placement. Unlike side imaging OCT systems, the implementation of forward imaging systems is challenging due to technical difficulties in designing such a narrow probe.
Recently, Yang and his research group developed a new Paired-Angle-Rotating Scanner (PARS) OCT endoscopic probe based on a modified Thorlabs swept source OCT system. The outer diameter of the probe is only 820 µm -small enough to fit in a 21 gauge needle, making it ideal for real-time imaging during ophthalmic surgeries. Placement of the PARS-OCT probe tip near the retinal surface provides cross-sectional images of the retina, unlike standard endoscopes that only provide information along the circumference of the probe.
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| Figure 1. Forward imaging PARS-OCT endoscope for retinal examination though an incision at the PARS plane |
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Feasibility of the new design was demonstrated by obtaining ex vivo porcine retinal images. In a preliminary study, the PARS-OCT probe was used to image the retina of an enucleated porcine eye with cornea, lens, and vitreous removed. The power at the sample was 2.3 mW, and balanced detection was used. Each B-scan consisted of 1984 A-scans, displayed at a rate of 6.9 frames per second. The angular velocity of the PARS-OCT probe and frame rate of the acquisition were matched using custom software. The acquired OCT images are shown in Figure 2 and Figure 3. A remnant vitreous layer was clearly observed (surface rippled due to vibration at the probe tip). The blood vessels in the optic nerve head and the choroidal capillaries can easily be identified with this technology.
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| Figure 2. Images of in vitro porcine retina acquired with the PARS-OCT probe using a circular scan. The image size is 2.5 x 2.3 mm. |
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| Figure 3. PARS-OCT inspection of the retina of in vitro porcine eye using the linear-scanning probe. (left) posterior segment and (right) retinal detachment. |
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Image Courtesy: Prof. Changhui Yang, Department of Electrical Engineering and Bioengineering, California Institute of Technology.
Reference: W. Jigang, M. Conry, G. Chunhui, F. Wang, Z. Yaqoob, and C. Yang Paired-angle-rotation scanning optical coherence tomography forward-imaging probe, Optics Letters , 13, (9), 1265, (2006)
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| Product Links |
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| Swept Source OCT Microscope System |
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| Spectral Radar OCT Imaging System |
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| Rapidly Swept Tunable Laser |
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