A system for 3D cone beam computed tomography has been developed. An extension of conventional CT methods is utilized to yield 3D data from 2D radiographic 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. The Feldkamp reconstruction algorithm is used. We have achieved real time reconstructions of large volumes 256³ using parallel processing on clusters of workstations.

The 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. Full width at half maximum resolving power varies with specimen size from 300 µm for 50 mm diameter objects to 70 µm for 10 mm diameter objects. Image resolution is isotropic in three dimensions. We have experimentally determined resolution with a quantitative test.

The 3D nature of the resulting image data can be used to visualize internal structure and compute parameters such as volume, surface area, and surface/volume orientation.

Figure 1. Rat lumbar vertebra rendered using data acquired with the described system.

This system has been used to image bone specimens in studies of human vertebrae, human femoral necks, dog metacarpals, rabbit tibias, and rat tails (see figure). Other applications include imaging small industrial parts, plastics, ceramics, composite materials, and geologic specimens. The 3D nature of this machine can provide accurate measure of surface area and volume.

We are currently working to demonstrate the feasibility of microtomography at a 1 µm scale using an high flux electron impact x-ray source. Other future work includes other specimens, including in vivo scanning of animals at a microscopic scale.

This work was supported in part by NIH grants RO1-AR42101 and R29-AR40776.