Ichiro Sogawa

A near infrared angioscope visualizing lipid within arterial vessel wall based on multi-spectral image in 1.7 μm wavelength band

We have developed a near infrared (NIR) angioscope that takes multi-wavelength images in 1.7μm band for visualizing lipid-rich coronary plaques. The angioscope comprises light source, camera, and angioscopic catheter. The light source, containing a supercontinuum source and a switching optical filter, emits 1.60, 1.65, 1.73 and 1.76μm wavelengths sequentially in synchronization to the camera frame. The supercontinuum is seeded by 1.55μm wavelength pulses, whose spectrum is spread by an optical fiber with ring loops for reducing peak power so that light in 1.7μm band is generated efficiently. The switching filter contains 1×4 fiber-optic path switches and interferometric band-pass filters. The camera detects NIR images by an InGaAs/GaAsSb type-II quantum well sensor at 100 frames/s. The source wavelength and the camera frame are synchronized with each other by an FPGA. The angioscopic catheter, based on a silica-based image-guide designed for 1.7 μm wavelength, transmits 1300-pixel NIR images and has 0.73 mm outer diameter, which is compatible with the conventional angioscope and suited for continuous flushing to displace blood. We have also developed image processing software that calculates spectral contribution of lipid as lipid score at each pixel and create lipid-enhanced color images at 12 frames/s. The system also includes conventional visible light source and camera, and takes visible light images synchronously with the lipid-enhanced images. The performance of the angioscope for detecting lipid-rich plaque has been verified in bench tests using a plaque model made by injecting lard into excised swine carotid arterial vessel. The plaque models are imaged in water at working distances of 0 to 2 mm, and significantly distinguished from normal vessels.

Lipid distribution imaging in in-vitro artery model by 1.7-μm spectroscopic spectral-domain optical coherence tomography

We demonstrate visualization of lipid distribution in in-vitro artery model by 1.7-μm spectroscopic spectral-domain optical coherence tomography (SD-OCT). In the demonstration, we measure spectral fringes by a spectrometer with an extended InGaAs line sensor and a super-continuum (SC) light source whose spectrum is arranged to have its maximum intensity in 1.7-μm band. The OCT system has an axial resolution of 21μm, a measurement range of 5mm and a sensitivity of 108dB with an A-scan rate of 0.96kHz, which is limited by the noise of the available SC light source. The in-vitro model is made by injecting lipid into swine carotid artery, which is compared to intact artery. We perform Bscan of the model in water by connecting an OCT probe to the OCT system and pulling the probe back at 0.027mm/sec with a rotation rate of 112rpm. For visualizing lipid distribution, we adopt a spectroscopic OCT algorism where the detected spectral fringe is divided into six sub-bands, the set of the sub-band A-scans are fitted to a model accounting absorption characteristics of lipid with its peak at 1726nm, and the content of lipid is estimated as lipid score. As a result, the p-value of the lipid score between normal artery and plaque one is less than 1E-10 in 1-mm depth from the surface, which is significant of visualization of lipid distribution.

Laser Angioplasty With Excimer Laser :Animal Experiment

Excimer laser is able to destruct tissue with less thermal effect. This characteristics was considered to prevent thermal perforation in laser angioplasty. In order to realize coronary laser angioplasty with excimer laser under the visual condition, the basic studies were performed to evaluate the tissue reactions of excimer laser on atheroma and to develop laser endoscopic system for the coronary arteries. The tissue reactions of excimer laser in atheroma were evaluated with rabbits atherosclerotic aorta, which was made with 1.5% high cholesterol diet. The bigger tissue destruction was obtained in accordance with the increase of the oscillating frequency. Excimer laser indused rather selective destruction of atheroma with high oscillating frequency. The fiber transmission of excimer laser was tried and atheroma was destructed through 400 μm core diameter fiber. Atheroma was observed as like as small lump under endoscopic obsevation, and excimer laser could be irradiated through the fiber under endoscopic view. In order to realize endoscopic application of excimer laser to the coronary arteries, the endoscope was designed from the point of percutaneous approach method to the coronary arteries, and 1.5 mm diameter of endoscope with the channel for laser fiber was developed experimentally. The endoscope could be inserted deeply into the coronary arteries of goat, and the laser irradiation could be performed under endoscopic observation. The possibility of visual coronary laser angioplasty with the combination of excimer laser and coronary endoscope was demonstrated with the endoscope.