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Abstract

Computed tomographic ('CT') x-ray scanning yields a discrete set of measurement values that are line integrals of attenuation coefficients .mu.(r), which attenuation coefficients may be obtained using suitable reconstruction techniques. Electronic beam computed tomograph ('EBCT') systems add error to the reconstructed attenuation coefficients owing to their unique cone geometry. A method is provided that reduces such errors. At least two scans, 'tilted' by the system cone angle, collect data in the neighborhood of a reference plane normal to the system z-axis. These scans are rebinned into parallel projections, and a series expansion is considered for variation of .mu.(r) in the vicinity of the reference plane. If a first order series is considered sufficient, then two scans are required to estimate the slope A of the variation in data. The data can then be corrected for the 'tilt' and line integrals on the reference plane normal to the z-axis obtained. If a second order series is necessary, two parameters A and B need to be determined from three suitably spaced scans, and the data corrected to obtain line integrals on the reference plane. The data can be corrected in the spatial domain by integration or preferably in the transform domain by differentiation. Once the line integrals are obtained on the reference plane, standard two-dimensional CT reconstruction be carried out to obtain the correct attenuation coefficients. The result is to provide a reconstructed image with reduced cone beam error.

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