Patent Number: 052456480
Section: summary

FIELD OF THE INVENTION The present invention relates to an x-ray tomographic image magnification process, to microscopy systems and to apparatus for use therein. More particularly, it relates to an x-ray tomographic microscopy system containing an image magnifier which enables three-dimensional images of high resolution to be achieved. BACKGROUND OF THE INVENTION Computerized axial tomography systems or machines, i.e., CAT scanners, have been used for a number of years to obtain three-dimensional images from two-dimensional data. These systems have been used primarily by the medical profession to obtain three-dimensional pictures of the body, but they also have been used in industry for a variety of purposes. Typically, the system comprises a source of x-rays, a sample positioned in the path of the x-rays, a detection system and an analyzing computer. Conventional computerized tomography (CT) measurements for industrial purposes involve collecting absorption information for a single cross-sectional slice through a material. Spatial resolution is achieved by either collimating an incident beam using a pinhole and then rastering the beam across the sample, or by using a position sensitive-linear photodiode array to measure all the projection data for a single angular view in parallel. There are disadvantages to both of these systems. The primary disadvantage of using the pinhole is that most of the incident radiation is thrown away. As a consequence, the rastering technique is extremely time consuming. Acquiring the data for reconstruction of a single sample takes upwards to twelve hours. The photodiode array is noisy and subject to non-linearities. The noise limits the dynamic range, and therefore, the maximum contrast that can be studied in a sample. The non-linearities also introduce ring-like artifacts in the reconstructions which can further reduce the usefulness of the information obtained. Finally, it still requires days to obtain enough information for three-dimensional sample visualization. THE PRIOR ART A high resolution tomography system with chemical specificity is described by Bonse et al., in an article in Nucl. Instrum. Methods A246,644 (1986). This system utilizes parallel beam synchrotron x-rays from an electron storage ring. The beams are passed sequentially through a double crystal monochromator, a collimator, the sample to be analyzed, a second monochromator, a scintillator which converts the x-rays to visible light, and a lens which Projects the light onto a charge coupled device. The charge coupled device records the intensity of the light and this value is stored in a computer. The sample is then rotated by a small angle and another two-dimensional absorption image is obtained. The process continues until 180.degree. of sample rotation has been recorded and the information stored in a computer. Tomographic software converts x-ray absorption profile data into two-dimensional reconstructions of the linear attenuation coefficients in the sample interior. These values are rendered into a three-dimensional view by means of high-speed, digital, image processing computers. The system described is a vast improvement over previous techniques, achieving spatial resolution of the order of 2-5 .mu.m. This order of resolution is sufficient for many purposes. However, even finer resolution is needed when the object is to discriminate between micrometer size objects and flaws in such materials as mineralized tissues or man-made composite microstructures. Higher resolution can be achieved by magnifying the x-ray images after the x-rays have passed through a sample. It is, therefore, an object of this invention to provide a process for magnifying x-ray images in a computerized axial tomography system. It is a further object of this invention to provide a computerized x-ray tomographic microscopy process having improved signal to noise ratios and improved spatial resolutions of x-ray images. It is a still further object of this invention to provide an improved computerized x-ray tomographic microscopy system having improved signal to noise ratios and spatial resolution as compared to the systems of the prior art. It is yet another object of this invention to provide an improved computerized x-ray tomographic microscopy system containing an image magnifier which enables three-dimensional images of high resolution to be achieved. It is a still another object of this invention to provide an x-ray image magnifier for use in a computerized tomography system. Other objects and advantages of the invention will be apparent from the description, drawings and claims to follow.