| Popis: |
This paper presents a modification of the z-slope algorithm introduced in the accompanying paper 'An algorithm to correct for z-detector gain variations in multislice volumetric CT.' The x-expansion coefficients found by SVD are plugged into the equation describing the final estimate of the error vector. It is then found that the algorithm can be expressed in vector form as a matrix equation relating the final error estimate to the initial error estimate, where the final error vector estimate e is subtracted from the projection data for correction. In this form, the matrix coefficients, but not the size, are dependent on the correction order. Also, the final correction matrix MXF (size Nchan by N, where Nchan is the number of channels corrected) is calculated channel-by- channel, by evaluating MX as above for a segment of N channels (with N odd), and extracting the central row to define the corresponding row of MXF. The segment of N channels is then slid by one channel, and the process is iterated till completion of MXF. Although the number of calculations required to obtain the correction matrix is greatly increased, as MXF depends only on the detector cell gains, these calculations can be performed off-line in calibrations. The scan data-dependent calculations are greatly streamlined. |
