Utilizing spatial wavelength encoding, spectrally encoded endoscopy (SEE) makes it possible to create miniature, small diameter endoscopic probes that can allow easy access to hard-to-reach locations within the body. Previously described SEE probes have been side-viewing, which limits their use for guiding the navigation of narrow passages. Forward-viewing SEE (FVSEE) probes are advantageous as they provide a look ahead that facilitates navigation and surveillance of a wider field of view (FOV). In this work, we present a novel FVSEE probe. The 500-µm illumination optics are designed in such a way that the shortest wavelength (460 nm) propagates along the optical axis, while an angle of approximately 56° is formed between the longest wavelength (720 nm) and the optical axis. Two-dimensional illumination was accomplished by rotating the illumination optics at a speed of 15 rps using a miniature torque coil. Reflected light from the sample was collected by 8 multimode detection fibers that were arranged into a circular array around the illumination optics. The proximal ends of the detection fibers were polished at a 17° angle, resulting in a total angle of detection of approximately 100°. Light coming out from the distal end of the detection fibers, which were rearranged into a linear array, was detected using a custom spectrometer with a tall-pixel linear CCD camera. The FVSEE probe was used to conduct a preclinical imaging of a swine joint. The results were compared to a commercial chip-on-the-tip mini-endoscope and showed a better spatial resolution and a wider FOV using the FVSEE probe.
Utilizing spatial wavelength encoding, spectrally encoded endoscopy (SEE) makes it possible to create miniature, small diameter endoscopic probes that can allow easy access to hard-to-reach locations within the body. Previously described SEE probes have been side-viewing, which limits their use for guiding the navigation of narrow passages. Forward-viewing SEE probes are advantageous as they provide a look ahead that facilitates navigation and surveillance of a wider field of view. In this work, we present a novel forward-viewing SEE probe. The 500-µm illumination optics are designed in such a way that the shortest wavelength (460 nm) propagates along the optical axis, while an angle of approximately 56° is formed between the longest wavelength (720 nm) and the optical axis. Two-dimensional illumination was accomplished by rotating the illumination optics at a speed of 15 rps using a miniature torque coil. Reflected light from the sample was collected by 8 multimode detection fibers that were arranged into a circular array around the illumination optics. The proximal ends of the detection fibers were polished at a 17° angle, resulting in a total angle of detection of approximately 100°. Light coming out from the distal end of the detection fibers, which were rearranged into a linear array, was detected using a custom spectrometer with a tall-pixel linear CCD camera. Similar to the theoretical value, an effective FOV of 23 mm at a focal distance of 10 mm was measured by imaging a grid pattern. Preliminary results demonstrate the potential of the forward-viewing SEE probe for a variety of medical imaging applications.
White blood cells (WBC) analysis is an important part of the complete blood count, providing good indication of the patient’s immune system status. The most common types of WBCs are the neutrophils and lymphocytes that comprise approximately 60% and 30% of the total WBC count, respectively; differentiating between these cells at the point of care would assist in accurate diagnosis of the possible source of infection (viral or bacterial) and in effective prescription of antibiotics. In this work, we demonstrate the potential of spectrally encoded flow cytometry (SEFC) to non-invasively image WBC in human patients, allowing morphology characterization of the main types of WBCs. The optical setup includes a broadband light that was diffracted and focused onto a single transverse line within the cross section of a small blood vessel at the inner patient lip. Light backscattered from the tissue was measured by a high-speed spectrometer, forming a two-dimensional reflectance confocal image of the flowing cells. By imaging at different depths into vessels of different diameters, we determine optimal imaging conditions (i.e. imaging geometry, speed and depth) for counting the total amount of WBCs and for differentiating between their main types. The presented technology could serve for analyzing the immune system status at the point of care, and for studying the morphological and dynamical characteristics of these cells in vivo.
During a sickle cell crisis in sickle cell anemia patients, deoxygenated red blood cells may change their mechanical properties and block small blood vessels, causing pain, local tissue damage and even organ failure. Measuring these cellular structural and morphological changes is important for understanding the factors contributing to vessel blockage and developing an effective treatment. In this work, we use spectrally encoded flow cytometry for confocal, high-resolution imaging of flowing blood cells from sickle cell anemia patients. A wide variety of cell morphologies were observed by analyzing the interference patterns resulting from reflections from the front and back faces of the cells’ membrane. Using numerical simulation for calculating the two-dimensional reflection pattern from the cells, we propose an analytical expression for the three-dimensional shape of a characteristic sickle cell and compare it to a previous from the literature. In vitro spectrally encoded flow cytometry offers new means for analyzing the morphology of sickle cells in stress-free environment, and could provide an effective tool for studying the unique physiological properties of these cells.
The properties of red blood cells are a remarkable indicator of the body's physiological condition; their density could indicate anemia or polycythemia, their absorption spectrum correlates with blood oxygenation, and their morphology is highly sensitive to various pathologic states including iron deficiency, ovalocytosis, and sickle cell disease. Therefore, measuring the morphology of red blood cells is important for clinical diagnosis, providing valuable indications on a patient’s health. In this work, we simulated the appearance of normal red blood cells under a reflectance confocal microscope and discovered unique relations between the cells’ morphological parameters and the resulting characteristic interference patterns. The simulation results showed good agreement with in vitro reflectance confocal images of red blood cells, acquired using spectrally encoded flow cytometry (SEFC) that imaged the cells during linear flow and without artificial staining. By matching the simulated patterns to the SEFC images of the cells, the cells’ three-dimensional shapes were evaluated and their volumes were calculated. Potential applications include measurement of the mean corpuscular volume, cell morphological abnormalities, cell stiffness under mechanical stimuli, and the detection of various hematological diseases.
Values of blood oxygenation levels are useful for assessing heart and lung conditions, and are frequently monitored during routine patient care. Independent measurement of the oxygen saturation in capillary blood, which is significantly different from that of arterial blood, is important for diagnosing tissue hypoxia and for increasing the accuracy of existing techniques that measure arterial oxygen saturation. Here, we developed a simple, non-invasive technique for measuring the reflected spectra from individual capillary vessels within a human lip, allowing local measurement of the blood oxygen saturation. The optical setup includes a spatially incoherent broadband light that was focused onto a specific vessel below the lip surface. Backscattered light was imaged by a camera for identifying a target vessel and pointing the illumination beam to its cross section. Scattered light from the vessel was then collected by a single-mode fiber and analyzed by a fast spectrometer. Spectra acquired from small capillary vessels within a volunteer lip showed the characteristic oxyhemoglobin absorption bands in real time and with a high signal-to-noise ratio. Measuring capillary oxygen saturation using this technique would potentially be more accurate compared to existing pulse oximetry techniques due to its insensitivity to the patient’s skin color, pulse rate, motion, and medical condition. It could be used as a standalone endoscopic technique for measuring tissue hypoxia or in conjunction with conventional pulse oximetry for a more accurate measurement of oxygen transport in the body.
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