Claims
- 1. In panoramic and cephalographic dental x-ray equipment having a x-ray radiation source and image receptors for panoramic and cephalographic radiography, which are capable of performing multiple projections where the density of the latent image can be controlled by the imaging parameters, an apparatus for the automatic control of the exposure comprising:
1.1. a x-ray radiation detector located behind the image receptor in a useful location to provide a signal corresponding to the x-ray absorption characteristic of the bone structure; and 1.2. a control unit analysing the radiation detector signal and providing adjustment of the imaging parameters, by incorporating the following functional units:
(a) PKP (Programmed kV profile).
Functional unit providing pre-programmed modulated profile of the tube voltage (kV) during the imaging process, correlated to the standard patient anatomy. It is used as a reference for the AEC operation during the imaging process in the panoramic projections. (b) DSU (Density Simulation Unit).
Functional unit providing simulation of the density of the latent image on the x-ray receptor. It processes the radiation detector amplified signal either 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) DCU (Density Correction Unit).
Functional unit processing the DSU density simulation output by comparing with a reference value, and generating a density error. Then the computational unit translates the density error into a correction of the applicable imaging parameter. In case of panoramic projections the density error is translated into a correction of the tube voltage, by applying to it a proportional control and/or an integrative control named PSC and described below. In panoramic projections such correction is applied with certain upper and lower limits over the Programmed kV Profile, as further described below within the ARU functional unit. In cephalographic projections the 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 in case that the threshold is exceeded. (d) PSC (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 the Programmed kV Profile. In the region of measurement the density correction values are analysed and samples within the acceptance range are integrated. (e) ARU (Artefacts rejection unit)
Functional unit providing rejection of spurious correction of the imaging parameter, as may be generated by artefacts of non-anatomical structures inserted into the patient denture, such as amalgam fillings, implants, etc. In panoramic projections it analyses the correction of the imaging parameter generated by the DCU and its derivative, and rejects those 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. and a method for the automatic control of the exposure in panoramic projections, including the steps of: A) selecting by the user interface the patient size, by which the initial setting of the imaging parameter and the programmed kV profile (PKP) are defined; and B) initiating the imaging process, where the PKP corresponding the patient size selected by the user is applied; the DSU, DCU and ARU functions are active; the PSC control is inactive, while the P control (proportional) of the DCU may be active. C) activating in the applicable region of measurement the PSC function, to provide a real time correction of the PKP corresponding to the actual patient size. At the end of this phase the PKP will result shifted upwards or downwards depending on the values of the integrated samples; the PKP, DSU, DCU and ARU are active; The P control of the DCU may be inactive. D) Disabling the PSC function, while the PKP corrected with the additive term generated by the PSC is applied; the DSU, DCU and ARU functions are active. The PSC control is inactive, while the P control of the DCU may be active to provide further correction in specific anatomical regions, such as the spine. and a method for the automatic control of the exposure in cephalographic projections, including the steps of: A) selecting through the user interface the imaging parameters (tube voltage, tube current, exposure time), either manually or pre-programmed depending on the selection of the patient size; and B) initiating the imaging process, where the tube voltage and current are kept stable at the values pre-set by the user; DSU and DCU and ARU are active; the density simulation generated by the DSU is analysed by the DCU and compared with the threshold value. C) Terminating the imaging process by generation of a stop of exposure signal. If the integrated density simulation generated by the DSU is exceeding the threshold level, then the DCU generates the stop of the exposure. If the exposure time exceeds the programmed maximum limit then the ARU generates the stop of x-ray emission. After the end of exposure all functions get inactive.
- 2. The apparatus and method as set forth in claim 1 wherein a different PKP may be programmable for each panoramic projection, and eventually for each patient size.
- 3. The apparatus and method as set forth in claim 1 wherein a range of acceptable density values is applied to the DSU density simulation, and such range of acceptable density values is programmable for each projection.
- 4. The apparatus and method as set forth in claim 1 wherein the parameters for the DSU simulation (e.g. the gain) are programmable for each projection.
- 5. The apparatus and method as set forth in claim 1 wherein the parameters for the DSU simulation (e.g. the gain) are programmable for each compatible image detector type, by taking into account its particular sensitivity (e.g. the speed of the applied screen-film combination).
- 6. The apparatus and method as set forth in claim 1 wherein the parameters for the DSU simulation (e.g. the gain) are programmable for each compatible image detector holder type (e.g. the film cassette), by taking into account its particular x-ray transmission characteristic.
- 7. The apparatus and method as set forth in claim 1 wherein the parameters for the proportional control of the DCU correction (e.g. the gain) are programmable for each projection.
- 8. The apparatus and method as set forth in claim 1 wherein the parameters for the PSC operation (e.g. start and end of region of measurement, gain of the integrator, range of acceptable values of samples) are programmable for each projection.
- 9. The apparatus and method as set forth in claim 1 wherein the start of the PSC region of measurement may be located automatically during the imaging process, by performing an analysis of the density simulation generated by the DSU and its derivative, and identifying the negative transition of the derivative corresponding to start of the bone structure.
- 10. The apparatus and method as set forth in claim 1 wherein the parameters for the ARU operation (e.g. threshold limits of the imaging parameter generated by the DCU and its derivative in panoramic projections, exposure time limit in cephalographic projections) are programmable for each projection.
RELATED APPLICATION
[0001] This application is a continuation application to U.S. application Ser. No. 09/679,768 filed on Oct. 5, 2000.
Provisional Applications (1)
|
Number |
Date |
Country |
|
60158706 |
Oct 1999 |
US |
Continuations (1)
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Number |
Date |
Country |
Parent |
09679768 |
Oct 2000 |
US |
Child |
10024873 |
Dec 2001 |
US |