Abstract: A tomographic x-ray imaging system comprises a large plurality of parallel data acquisition channels which integrate and digitize signals from an array of x-ray detectors. Calibration pulses are injected into each data acquisition channel to permit measurement of drift in electronic gain and dc offset parameters. Separate x-ray detectors continuously monitor the intensity of the x-ray source.The measured values for channel gains, dc offsets, and source intensity are fed to a digital computer where they are automatically combined with x-ray transmission data to compensate for system drift and extend the period between calibration measurements.