Automatic exposure control for dental panoramic and cephalographic x-ray equipment

A dental x-ray device having an x-ray radiation source and image receptors for panoramic and cephalographic radiography of bone structure of a patient, and for performing multiple projections where the density of the latent image is controlled by the imaging parameters, comprising an apparatus for the automatic control of the exposure (AEC) comprising:

• an x-ray radiation detector located behind an image receptor and providing a signal corresponding to the x-ray absorption characteristic of the bone structure;
• a control unit for analysing the radiation detector signal and providing adjustment of the imaging parameters by incorporating as functional units:
• (a) A programmed kV profile unit (PKP) being the functional unit providing pre-programmed modulated profile of the x-ray source tube voltage (kV) during the imaging process, correlated to the standard patient anatomy;
• said PKP being a reference for the AEC operation during the imaging process in the panoramic projections;
• (b) a density simulation unit (DSU) being the functional unit providing simulation of the density of the latent image on the x-ray receptor, and processing a radiation detector-amplified signal by combining it with the speed of the cassette drive in case of panoramic projections, or by integrating it in the time in case of cephalographic projections;
• (c) a density correction unit (DCU) being the functional unit processing the DSU density simulation output by comparing with a reference value, and generating a density error, and translating the density error into a correction of the applicable imaging parameter using a computational unit;
• in panoramic projections said density error is translated into a correction of the tube voltage, by applying to it a proportional control or an integrative control (PSC);
• in panoramic projections correction is applied with upper and lower limits over said PKP, within an ARU functional unit;
• in cephalographic projections said density error is translated into a correction of the exposure time, by comparing the actual integrated density level generated by the DSU with a threshold value, and generating a stop of x-ray emission when said threshold is exceeded;
• (d) said PSC being a patient size correction functional unit operating in panoramic projections and performing on selected portions of the anatomy corresponding to a region of measurement an integration of the density error generated by the DCU and generating in real-time a correction quantity to be added to said PKP;
• in the region of measurement the density correction values are analysed and samples within a selected range are integrated;
• (e) said ARU being an artefacts rejection unit and being a functional unit providing rejection of spurious correction of the imaging parameter, as generated by artefacts of non-anatomical structures inserted into the bone structure;
• in panoramic projections said ARU analyses the correction of the imaging parameter generated by the DCU and its derivative, and rejects samples exceeding threshold limits both in absolute value and in slew rate, by clipping them to a predefined level;
• in cephalographic projections it prevents the exposure time to exceed a predefined maximum level, by generating a stop of x-ray emission when such maximum level would be exceed.