Endoscopic Confocal Scanning Microscopic Imaging

Confocal microscopy has been widely applied to the field of biological science due to its great advantages in high resolution and 3-D imaging. However it is incapable of getting the image of inner tissue in vivo. Thus endoscopic confocal microscopy has been proposed. Combined confocal microscopy and fiber technique, it not only has advantage of confocal microscopy, but also can obtain the image of tissue of inner organ in vivo. In recent years, it has become the hot spot of study and will be widely used in clinical medicine.The theory on confocal microscopy is known to us. But the theory on endoscopic confocal microscopy has not been studied intensively, and the influence of optical parameters on imaging quality is not analyzed systematically. Therefore in this paper, we will deduce the imaging equations of the new system and analyze the impact of optical parameters on imaging quality.There are some reports on the experiments of endoscopic confocal microscopic imaging, but the imaging quality is poor and need to be improved. Therefore in this paper, we will design the endoscopic confocal microscopic system based on theoretical analysis and digital simulation, and carry out the related experiments and discussion.Major work of this dissertation is as follows:First, the optical path model of the endoscopic confocal microscopic system is established in this paper, and the imaging equations are also derived on the basis of both the optical wave-guide theory and the scalar diffusion theories. Such researchachievements lay a solid groundwork on the following system design.Second, the coherent transmission function of the system is deduced, and further, the influence of fiber radius on axial resolution is simulated. It is shown that (1) the whole imaging process belongs to the coherent imaging and can be described by coherent transmission function; (2) the fiber radius has distinct impact on resolution:the half-width of the axial response increases with higher A, i.e., the axial resolution decreases with higher A .Third, the influence of confocal pinhole radius, the objective NA and pupil function on the imaging intensity and resolution is simulated based on endoscopic confocal microscopic theory. According to the computing results, the optimumnormalized pinhole radius vd = 3 and the optimization approach of axial resolutionare proposed in this paper, which lay a solid groundwork on the following systemdesign.Fourth, according to theoretical analysis and numerical simulation, the endoscopic confocal microscopic system is designed and the corresponding experimental platform for measurement is also established. The half-width of axial response is measured in the following cases: pinhole radius rd = 5jum -, 25jum > 50,0m;the central obstruction rate s - 0 > 0.5. It is shown that (l)the higher pinhole radius, the higher half-width,i.e., the higher pinhole radius,the lower axial resolution, (2) when rd = 5/um -, 25jum , the application of circular lens leads to higher axialresolution, (3) when rd = 50/jm , the application of annular lens leads to higher axial resolution. In the meanwhile, the in-focus and out-of-focus 4/jm images of the discriminator plate are obtained by combining fiber bundle and CCD technique, which is shown that the in-focus image has higher contrast and better visual effect than that of the out-of-focus image.Fifth, a method for edge-enhancement is proposed by using photorefractive two-wave coupling. Based on two-wave coupling theory, the gain coefficient is derived on the basis of two-wave coupling theories, and further the feasility of such method is demonstrated. Edge-enhancement is obtained by decreasing the low-frequency information in the conventional method. While in the method proposed in this paper, the low-frequency information and high-frequency information is separated firstly, then the high-frequency information is increased using low-frequency. Compared with the conventional method, it can utilize energy effectively.