Point projection microradiography has established value for imaging large, wet, opaque, and intact specimens in 2D projection views. We have developed a 3D microtomography system by combining the principles of microradiography with computed tomography (CT). An extension of conventional CT methods is utilized to yield 3D data from 2D microradiographic projections. Use of 2D cone beam projections rather than 1D projections of a slice simplifies the specimen motion hardware, and reduces the amount of wasted radiation. Our imaging system consists of a microfocus x-ray source and x-ray image intensifier coupled to a CCD camera. The system is flexible in the size of specimens which can be imaged. Resolving power varies with specimen size from 4 lp/mm for 50 mm diameter objects to 40 lp/mm for 3 mm diameter objects. Image resolution is isotropic in three dimensions. The 3D nature of the resulting image data can be used to visualize internal structure and compute stereologic parameters such as volume, surface area, and surface/volume orientation. This instrument has been used to image bone specimens in studies of human vertebrae, human femoral necks, dog metacarpals, and rabbit tibias. Other applications include imaging small industrial parts, plastics, ceramics, composite materials, and geologic specimens.
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