X-ray data acquisition system and method for calibration

A method for operating a computerized tomography system of the type which includes a source of x-rays, a plurality of x-ray detectors, a plurality of substantially identical data acquisition channels each connected to receive and process signals from one or more of said x-ray detectors, and a digital computer connected to receive output signals from said data acquisition channels and to extract image information therefrom, which method comprises steps of:

• periodically injecting calibration signals of at least two distinct known levels into each of said data acquisition channels;
• measuring the output signals which are produced by said data acquisition channels in response to said calibration signals;
• calculating a gain parameter and a dc offset parameter, from said output signals, for each of said data acquisition channels;
• utilizing said source of x-rays and said x-ray detectors to measure the characteristics of an unknown body;
• and
• correcting the output signals of said data acquisition channels, which are produced in response to the measurement of said unknown body, with factors relating to the calculated gain and offset parameters of each of said data acquisition channels.

A method for calibrating a computerized tomography system, which system includes (1) means for producing a first plurality of signals, the value of which are representative of the transmissivity of an object;

• (2) one or more data acquisition channels connected to receive said first plurality of signals and to produce therefrom a second plurality of data signals;
• and (3) computer means connected to receive said second plurality of data signals and to generate image data therefrom, said method comprising the steps of sequentially:
• a. injecting two values of a calibrated input signal into each of said data acquisition channels, whereby each of said data acquisition channels are caused to produce two values of a calibration output signal;
• b. determining the values of each of said calibration output signals;
• and
• c. calculating, from the values of each of said calibration output signals, a gain factor and an offset factor for each of said data acquisition channels.

A method for operating a computerized tomography system of the type wherein energy absorption data is transmitted from an array of detector elements to a digital computer via a plurality of parallel data acquisition channels, comprising the steps of:

• a. measuring the gain and dc offset of each data acquisition channel;
• b. measuring the energy absorption data on an unknown body;
• and
• c. correcting the energy absorption data on the body for variations in the gain and dc offset of each data acquisition channel.