Abstract: The present invention, in one form, is a method for determining and applying a ZCAL correction vector to the channel outputs from the detector array in a multi-slice CT system. More specifically, and in accordance with one embodiment of the present invention, the signal gain for each detector cell, or channel, at multiple z-axis locations is measured. For each channel, a correction polynomial Q.sub.n is fitted to the signal variation curve as a function of z-axis position so that the correction polynomial value multiplied by its channel signal produces a constant value over the operational range of z-axis positions. Beam positions (Z.sub.r) are measured as a function of each position reference signal (D.sub.r) and the Z position of the beam at the sensor channel and the location of the focal spot are determined. The z-axis location for each channel and the ZCAL correction vector are then determined. The ZCAL correction vector is then multiplied by the channel signal to calibrate the channel signal.