A reconstruction method for transillumination laser CT using optical heterodyne detection is proposed. Laser CT does not obey the Radon transform due to surface effects, which occur as results of refractive index mismatch and roughness of surface, and bring about annulus artifact and impair quantitative accuracy of a reconstructed image. Optical attenuation with surface effects is described using a model function with respect to an incident angle. This reconstruction produces a least squares problem incorporating the surface effect, which is solved via the conjugate gradient method. The method is applied to data from a acrylic physical phantom containing Intralipid-10% solution in various concentrations for demonstrating the effectiveness of the proposed method in terms of morphological and quantitative information. The CDI method is proved to have an excellent quantitative accuracy.
In this research, we investigate the imaging properties of tansillumination laser CT system based on the coherent detection imaging (CDI) method, for early diagnosis of rheumatoid arthritis, from the viewpoints of morphological and quantitative imaging. First, to investigate the morphological imaging ability, the index finger PIP joint of a healthy volunteer was imaged with the laser CT, X-ray CT, and MRI. By comparison of these images, we present that the laser CT delineates the bone region with high spatial resolution of sub-millimeters. Next, to investigate the quantitative imaging, three kinds of the physical phantoms simulating bone, made from polyurethane including different concentrations of CaCO3, were imaged. We present that quantitative measurement is possible by demonstrating a satisfactory linear relationship between the averaged pixel value of the reconstructed images and the actual concentrations. These results demonstrate the feasibility of early diagnosis for rheumatoid arthritis.
So far we have shown, through various preliminary imaging experiments with small-animal ankle’s and human finger’s joints both healthy and joint-diseased, that early diagnosis for joint disease such as rheumatoid arthritis (RA) is feasible using a transillumination laser CT. For a practical purpose, we have recently proposed and developed a transillumination laser CT imaging system using optical fibers based on the optical heterodyne detection method for a clinical use. In the proposed system, motion-artifact free images can be obtained because measurements can be performed with the object fixed. In addition, use of fiber-optics enables portability, and robustness against environmental changes in a room, such as variable temperature, air-flow shifts, and unexpected vibrations. The imaging system has the following sensing properties: spatial resolution of 500 μm, a dynamic range of approximately 120 dB, and a minimum-detectable-optical power of 10-14 W as a result of the excellent properties of the heterodyne detection technique. In the present paper, we describe a prototype laser CT imaging system using optical fibers for early diagnosis of joint disease such as rheumatoid arthritis by demonstrating the first in vivo tomographic image of a volunteer’s index finger joint as well as the fundamental imaging properties.
Lasing characteristics of laser-active material-doped microdroplets containing highly scattering fat emulsion Intralipid-10 percent are studied experimentally. Noteworthy findings are than well-defined lasing threshold can be observed and appreciable magnitude-enhancement of emission intensity with suitable conditions of the Intralipid mixing ratio, in comparison with original neat-active-material- doped microdroplets. We present and discuss the measured results of input-output intensities for different Intralipid mixing ratios in these active material-soft scatterer system. It was found that almost no lasing neat- microdroplets can achieve lasing by substituting suitably certain amounts of the Intralipid causing multiple light scattering. Spectral measurements of light emission from the active material-Intralipid microdroplets show the tendency of spectral narrowing with the increase of the pumping intensity and with the optimum Intralipid concentration. It is our belief that the present results make this novel method of active material-Intralipid microsystem very attractive for a variety of future applications including diagnostic tools for highly sensitive detecting and identification of small quantity objects and species embedded or hidden in highly scattering media such as biological tissues and cellular structures.
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