Abstract:
An X-ray apparatus has a radiation source, an interchangeable radiation filter and an area dose measuring device having a measurement chamber with an allocated evaluation device for determining the area dose product on the basis of a measured signal provided by the measurement chamber. The measurement chamber is arranged preceding the filter in the beam path with reference to the radiation propagation direction. A detector recognizes the nature and/or the type of radiation filter that is currently inserted in the beam path. The evaluation device corrects the area dose product that is calculated from the measured signal from the measurement chamber on the basis of at least one filter-specific correction value that is selected as a result of the detection of the filter nature and/or type.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention is directed to an X-ray apparatus of the type having a radiation source, an interchangeable radiation filter and an area dose measuring device with a measurement chamber and an allocated evaluation device for determining the area dose product on the basis of the measured signals provided by the measurement chamber, with the measurement chamber arranged preceding the filter in the beam path with reference to the radiation propagation direction. 
   2. Description of the Prior Art 
   Measurement of the area dose product allows determination of the amount of X-radiation applied to the examination subject, for example a patient. This measurement is conventionally undertaken with an area dose-measuring device having a measurement chamber that is arranged in the beam path. This measurement chamber usually is an ionization chamber through which the X-rays pass and at which an output signal dependent on the amount of radiation can be obtained. The applied, surface area-dependent dose can be determined from this signal, usually in μGym 2  units. 
   Radiation filters are often employed in known X-ray apparatuses in order to attenuate or entirely blank the X-rays in certain filter-specific ranges. A large variety of interchangeable and employable filters are known, for example shoulder filters, foot filters, pelvis filters or skull filters. These filters, that are usually fashioned in the form of essentially rectangular plates, are inserted into the beam path. These insertion guides usually are arranged outside the housing containing the measurement device and further parts of the area dose-measuring device, such as, the evaluation device. The measurement chamber lies in front of the filter with reference to the radiation propagation direction. The measurement chamber often is integrated into a diaphragm device that follows the radiation source in the propagation direction, particularly in the depth diaphragm, and which has an outer housing section at which the insertion guides for the plate-like radiation filters are located. 
   Due to this arrangement wherein the radiation filters follow the measurement chamber, the problem arises that the filter effect does not enter into the determination of the area dose product. The filter performance that attenuates the X-rays that are actually applied to the subject is not taken into consideration since the measurement occurs preceding the radiation filter. Ultimately, thus, the applied dose is lower than that indicated by the “unfiltered” measured result. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide an X-ray apparatus that eliminates the aforementioned disadvantage associated with known X-ray apparatus in the determination of the area dose. 
   This object is achieved in accordance with the invention in an X-ray apparatus of the type initially described having a detector for recognizing a filter characteristic of the filter currently in use, such as the nature and/or the type of filter, and an evaluation fashioned for correcting the calculated surface dose product on the basis of at least one filter-specific correction value dependent on the identification of the filter in use. 
   In the inventive X-ray apparatus, the detector makes it possible to determine what filter type or what kind of filter is inserted into the beam path following the measurement chamber. On the basis of this knowledge, which is forwarded to the evaluation device, the evaluation device is able to suitably correct the area dose product that is calculated in the evaluation device based on the signal acquired by the measurement chamber preceding the radiation filter. This correction is undertaken using at least one filter-specific correction value, i.e. a correction value that takes the filter properties of the recognized filter into consideration. As a result, it is possible to calculate the filter effect of the following radiation filter and to include this in the calculated area dose product. This product thus indicates the actually applied X-rays as accurately as possible, rather than the unattenuated amount of radiation. 
   In order to recognize the nature or type of filter, it is necessary to be able to identify each inserted or insertable filter so that its filter-specific features or characteristics can be likewise identified. In a first embodiment of the invention, the detector for recognizing the nature and/or type of filter can be a transponder arranged at the filter and an acquisition device that picks up the transponder signal. This acquisition device, which can also be the corresponding excitation device, activates the transponder to emit the transponder signal. The acquisition device can be external to the surface dose-measuring device or the evaluation device itself can be fashioned for this purpose. Each radiation filter has its own filter-specific transponder, so that a simple acquisition and discrimination are possible. 
   As an alternative, the detector for recognizing the nature and/or type of filter can include at least one identification specifying the nature and/or type of filter and an acquisition device that acquires the identification. Expediently, the identification is a coding. According to a first alternative of the invention, this can be an electronic coding that can be interrogated via the acquisition device. For example, the evaluation device itself also can be employed as the acquisition device. Each radiation filter can have a small integrated chip associated therewith that, for example, is automatically contacted by a corresponding connector plug upon insertion of the filter, the connection to the acquisition device being closed through the chip/plug connection. 
   As an alternative, the identification can be acquired by an optical reader device. For example, a label or an imprint can be used, particularly a bar code or the like. Further, specific reflection patterns at the filter can be employed as the identification, these being acquired via the optical reader device. Another alternative is to provide the identification as a structure applied to the radiation filter, particularly in the form of notches or the like. This structure likewise can be acquired by the optical reader device. 
   A further alternative for fashioning the identification in accordance with the invention is to provide projections or depressions, for example in the form of notches, at the radiation filter which activate switch or sensor elements when the radiation filter is introduced. The projections or depressions are specifically fashioned for each radiation filter, so that a specific switch or sensor element actuation occurs for each radiation filter. The respective filter type or kind of filter can then be recognized from the combination of actuated switch or sensor elements. 
   Magnetic identifications also can be used that, for example, can be acquired via Hall sensors that detect the generated magnetic field. For example, a number of magnetic identifications can be filter-specifically arranged here along a side of the filter, the positioning or the magnetic fields of these identifications in turn representing a coding for the filter type and/or kind of filter. Dependent on the output signals of the Hall sensor or sensors, the kind of filter or the filter type can be identified. 
   As already described, it is expedient to integrate the surface dose measuring device in a diaphragm device that follows the radiation source, particularly in the depth diaphragm, so that an overall closed system is achieved. The evaluation device also can be integrated; however, it is also possible to externally position the evaluation device. 
   Although a specific correction value can be allocated to each radiation filter which always is utilized for correction given employment of that radiation filter, it is expedient for the correction value employed for correction to be dependent on at least one parameter representing a criterion for the generated X-rays. The applied X-rays are variable within broad ranges by means of a corresponding setting of the operating parameters, i.e., for example, the operating voltage or the operating current. In order to be able to design the correction of the area dose product even more exactly, it is expedient to employ a correction value that is adapted to the employed parameters that influence the X-rays. For example, a number of correction values can be stored in the evaluation device that are allocated or dependent on specific parameters that influence the X-rays such as, for example, the tube voltage or the tube current. Dependent on which operating parameters are set by the physician or the radiology technician, the evaluation device that has the corresponding operating parameter information available to it then selects the appropriate correction value from the stored, filter-specific family of correction values. The resulting thus takes the actual operating conditions into consideration. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic illustration of an inventive X-ray apparatus as well as a releasably introducible radiation filter. 
       FIG. 2  is a schematic illustration of the relevant parts of the inventive surface dose measuring device. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows an inventive X-ray apparatus  1 , with only the radiation source  2  being shown, this being arranged at a telescoping arm  3  of a ceiling-mounted stand (not shown in detail). A diaphragm device  4 , for example a depth diaphragm, is provided under the radiation source  2  in the illustrated example; the shape of the beam in the x-direction and y-direction, or in the plane defined by those directions, can be shaped by this diaphragm device  4 , which shall be discussed in brief below. 
   At its housing, the depth diaphragm  4  has receptacles  5  for the acceptance of one or more radiation filters  6 . In the illustrated example, the receptacles are fashioned as lateral insertion channels  7  into which an essentially rectangular, plate-shaped radiation filter  6  is inserted. As shown in  FIG. 2 , the inserted filter  6  is then located in the beam path of the X-rays generated by the radiation source  2 , which is not shown in detail in FIG.  2 . Only the focus  8  of the radiation source  2  is shown, the X-ray beam  9  expanding as it proceeds from said focus  8 . The shape of the X-ray beam is defined by x and y diaphragms  10 ,  11 . The X-ray beam  9  likewise passes through the radiation filter  6 , so it is attenuated in the regions wherein the radiation filter  6  includes an X-ray filter medium  12 . 
   In order to determine the area dose product, an area dose measuring device  13  is provided that has a measurement chamber  14 , such as an ionization chamber, that is arranged in the beam path and precedes the radiation filter  6 , and also has an evaluation device  15  that is external therefrom in the illustrated example. The X-rays penetrate into the ionization chamber  14 , which leads to a particle ionization dependent on the radiation dose and ultimately leads to an output signal that is dependent on the degree of ionization. The functioning of such an ionization chamber as well as the calculation of the area dose product dependent on the output signal are well-known. The calculation ensues in the evaluation device  15  that receives the output signal of the ionization chamber  14 . A suitable calculating unit  16  is provided for the calculation. As warranted, a partial system control can ensue via the evaluation device  15  or the calculating unit  16  when an adequate area dose product is reached, but this shall not be discussed in detail. This is also well-known and need not be presented herein. 
   The evaluation device  16  also has a memory device  17  available to it wherein a number of filter-specific correction value families K F1  . . . K Fn  are stored. A filter-specific correction value for the area dose product exists for each radiation filter  6  that is employed (a large variety of radiation filters can be employed) and the correction of this area dose product is necessary because the measurement chamber  14  is situated in front of the radiation filter  6  and the output signal at the side of the ionization chamber consequently is not influenced by the filter effect, and thus the beam attenuation produced by the radiation filter would not otherwise be taken into consideration. 
   In order to be able to select the right correction value from the stored correction values, it is necessary to be able to identify the inserted radiation filter  6  in terms of its nature or its type. Suitable means for recognizing the nature or type are provided for this purpose. First, a unique identification of each radiation filter  6  is required. The radiation filter  6  shown in  FIG. 1  shows some identification versions. A transponder  18  can be used, with each radiation filter having its own specific transponder  18 . For example, a suitable drive device  19  can be provided in the evaluation device  15 , for driving the transponder  18  such that it transmits its transponder signal, which is in turn received and interpreted by the drive device  19  and the corresponding filter can be recognized in this way. Each filter has its own transponder that emits a filter-specific transponder signal, so that a definitive discrimination and recognition is possible. 
   A further, alternative identification version is a number of specifically shaped indentations  20  at the edge of the radiation filter  6  that, for example, can be acquired via an optical device  21  that is integrated in the diaphragm device  4 . The identification and coding of the respective filter type ensues by means of the shape of the employed indentations  20  and their arrangement and positioning relative to one another. Arbitrary codings are possible in this version. 
   Alternatively, reflection fields can be applied to the filter  6  that are acquired via the optical read device  21 . 
   Another possibility shown in  FIG. 1  is the employment of an electronic identification  22 , for example in the form of a small microchip, that is automatically coupled via its terminal pins  23  to a suitable acquisition device  24  in the diaphragm, that then emits a corresponding output signal that is forwarded to the evaluation device  15 . Only one identification version need be provided at a radiation filter  6 ; the employment of the three different identification possibilities in  FIG. 2  is only for explaining a number of exemplary alternatives. The same is true of the employment of the detector for the recognition of the identification. Only one of the drive device  19 , the optical reader device  21  or the electronic reader device  24  is to be provided. 
   In any case, the evaluation device  15  receives an information signal that describes the filter type or the kind of filter. In addition, the evaluation device  15  is provided with information data about the operating parameters of tube voltage U and tube current I that have been set for generating the X-rays. In addition to the information about the filter being utilized, these serve the purpose of selecting the correct filter-specific correction for the inserted filter value from the family of correction values. 
   Two correction value families for two specific radiation filters, namely the filters F 1  and Fn, are shown as an example in the memory area  17  in FIG.  2 . The respective correction values in the two families are a 1 , b 1  . . . f 1  and b n  . . . f n , whereby the index  1  indicates the correction value family for the filter F 1  and the index n indicates the correction value family for the filter Fn. 
   Further, respective operating parameters U/I are indicated, namely U 1 /I 1 , U 2 /I 2 , . . . , U 6 /I 6 . 
   The respective correction value family K F1  . . . K Fn  is selected on the basis of the pending information signal about the introduced filter. Let it be assumed that the radiation filter F 1  is introduced, so that one of the correction values a 1 , . . . f 1  will thus be employed for the correction. 
   The exact determination of the correction value to be employed ensues on the basis of the pending voltage and current signals. Let it be assumed that the voltage and the current lie in respective value ranges around U 3  and I 3 . In this case, thus, the correction value c 1  would be utilized for the correction of the originally calculated area dose product without taking the filter attenuation into consideration. For example, the correction value c1 can be a defined value, for example in a μGym 2  unit, that is subtracted from the calculated area dose product. Alternatively, it can be a suitable percentage by which the calculated area dose product is to be reduced, etc. Different forms of correction values are employed as appropriate. When the pending voltage and current values do not lie in a prescribed interval range, i.e. when, for example, they are not to be allocated to U 4  and I 4  but, for example, to U 2  and I 5 , it is also possible to make a defined selection for determining the specific correction value, so that, for example, c 1  is selected given such a combination. Alternatively, there is the possibility of calculating, for example, an average value from b 1  and e 1  (with respect to U 2  or I 5 ). Different approaches are also possible. 
   The area dose product calculated in this way is then, for example, either output by the calculating device  16  and displayed at a monitor, or is forwarded to a central control device, which takes the area dose product into consideration in the framework of the higher-ranking control of the calculating device  16 . 
   Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of his contribution to the art.