X-ray system exposure control with ion chamber

Claim 1

An X-ray exposure control system for an X-ray diagnostic installation including an X-ray generator and an X-ray tube directing X-rays through the patient to an X-ray film, said exposure control system comprising in combination means providing kVp and mA settings for said X-ray generator, the kVp and mA settings affecting the exposure time required to produce desired images on said film, an ion chamber including a plurality of selectively energizable ironizable fields for monitoring the amount of radiation provided to an X-ray film by said X-ray generator, and said ion chamber fields being electrically coupled to said X-ray generator selectively terminating the output of said X-ray generator, electronic circuitry for monitoring and controlling the time of operation of said X-ray generator, said circuit receiving a first voltage proportional to the kVp being applied to the associated tube, means for providing a reference voltage, means for combining said first voltage with said reference voltage to provide a first control signal, means for combining a voltage proportional to a density selection factor to said first control signal to obtain a second control signal, means for obtaining a voltage dependent on the radiation impinging on the selected fields of said ion chamber and means for comparing the said dependent voltage with said second control signal to provide an output control signal to terminate the radiation from said X-ray generator, said ion chamber including a plurality of discrete fields which may be selectively energized, said fields comprising an emitter electrode extending over a limited area, a collector electrode of substantially the same size as said emitter electrode spaced from said emitter electrode, spacer material positioned between said electrodes and having apertures formed therein adjacent said fields to form air chambers, a second emitter electrode of substantially the same size as said collector electrode spaced from said collector electrode, the X-rays passing through said apertures ionizing the air thereon, and holes in said fields adjacent said apertures for balancing the ionizing potential.