| 摘要 |
For the backprojection of the convoluted measurement signals in a cartesian coordinate system in a computer tomography device, it is necessary to recalculate the weighting factors for each position of the source in order to determine the contribution of a convoluted measurement signal to the attenuation value associated with a given element of the output image matrix. This is a time consuming and hence expensive form of reconstruction, and can be avoided by storing all the weighting factors required; this, however, implies a very large memory, and is also expensive. The invention relates to the use of a matrix of elements organised in polar coordinates, which is stored in the memory, the origin central coordinate of said matrix coinciding with the center of rotation of the X-ray source about the object section. The weighting factors are also stored in a polar organized memory. The angular component of the address of the weighting factors is incremented with a rotational increment in the corresponding position of the X-ray source, so that for each group of measurement values, the same weighting factors can be used. The invention enables all the weighting factors to be stored in a memory of limited capacity, the more so because all weighting factors are mirror-symmetrical with respect to a central axis connecting the X-ray source to the center of rotation, so that the angular coordinates of the memory need only extend from 0 to pi instead of from 0 to 2 pi . |
