EP0455001A2 - Circuit arrangement for X-ray generators, especially for diagnostic applications - Google Patents

Abstract

In order to develop a circuit arrangement for X-ray generators which are used especially for diagnostic purposes, having a high-voltage rectifier, whose preselectable tube voltage can be matched to the requirements, with a variable transformer and an X-ray tube connected thereto whose heating power provided by a heating voltage generator can be preset, the preselection of the tube voltage and the presetting of the heating power of the tube being capable of being carried out by means of a controller in accordance with the desired or necessary X-ray dose, such that the presetting can be carried out in accordance with the desired radiation dose power, radiation hardness and exposure duration in a simple manner even by personnel who have only been instructed, it being intended that the setting should be capable of being carried out in a simple manner using logos and symbols, it is proposed that a personal computer (PC) which is known per se be used for the presetting, which PC is connected via an interface to the controller of the X-ray generator in such a manner that the personal computer (PC) initially calculates the tube voltage and heating power for a desired X-ray dose of desired hardness, transmits this voltage and power via the interface to the controller and the time duration, tube voltage and heating current of the X-ray tube is set in accordance with the guidelines by the controller, with the aid of the actuating elements. <IMAGE>

Description

The invention relates to a circuit arrangement for X-ray generators used in particular for diagnostic purposes with a high-voltage rectifier which can be adapted to the requirements in its preselectable tube voltage, with a variable transformer and an X-ray tube connected to it, the heating power of which is provided by a heating voltage generator can be preset, the preselection of the tube voltage and the presetting of the heating power of the tube using a control according to the desired or necessary X-ray dose can be carried out.

To control X-ray generators, on the one hand the voltage of the X-ray tube (tube voltage) is preselected in order to ensure that the radiation is sufficiently soft or sufficiently hard for the intended use; on the other hand, the heating current of the hot cathode of the X-ray tube is preselected in order to obtain a desired cathode current and thus a certain radiation yield, which also depends on the condition of the anode; Finally, the duration of the radiation is preselected in order to be able to apply the desired radiation dose required for diagnosis or therapy at a dose rate given by the radiation hardness and radiation yield. In the known X-ray generators, these values are set on the control panel, this being done by preselecting the high voltage on the variable transformer of the high-voltage rectifier and by setting the heating current. While the heating current already flows before the high voltage is switched on (preheated cathode) and so the measurement of the actually flowing heating current with corresponding converters does not cause any problems, the high voltage is only applied during the application time, it can therefore only be preset "cold", a procedure that is different from plant to plant due to the load dependency of the high voltage with flowing cathode current depending on the manageable internal resistances of the high-voltage rectifiers and the unmanageable source resistances of the network and brings considerable difficulties especially for trained personnel. In addition, especially during longer application times, a drop in due to a sudden switching on of a consumer or a sudden recovery of the mains voltage by switching off a consumer can result in an unpredictable change in the high voltage, which seriously changes the dose rate in an unpredictable manner.

This is where the invention comes in, which is based on the object of further developing the circuit arrangement for controlling X-ray generators in such a way that even simply instructed personnel do so the presetting can be carried out in accordance with the desired radiation dose rate, radiation hardness and duration of exposure, the setting should be able to be carried out in a simple manner with logos and symbols.

This object is achieved according to the invention with the features specified in claim 1; advantageous further developments and preferred embodiments describe the subclaims.

By using a personal computer, the connection to the control technology with a personal computer is achieved in a simple manner; However, this application requires a special interface that takes over the connection between the control and the personal computer PC. This interface is constructed in such a way that, on the one hand, it transfers the analog (or already digitally converted on the encoder) feedback of the states of the actuators and the electrical and / or radiation measurements to the personal computer, which takes into account the technical data permanently stored in its application memory Values for the X-ray tube, the high-voltage generator and for the electrical supply network to which the high-voltage generator is connected, the current values for the X-ray tube and the present application determine the heating power to be provided and the required high voltage (excessive due to the network load). For this purpose, the input informs the personal computer which application is present, the selection (and possibly the change) of the standard values proposed for this application for the values for the radiation dose rate for high voltage and heating power for the X-ray tube is then carried out in dialog. The dialogue is carried out on a screen connected to the personal computer; the input is made via a keyboard connected to it. The program required for this is provided by the on-screen menu, which offers the operator sufficient options with logos and entries offers. Since the application memory has stored the values for the standard setting for these use cases, the “setting” of the X-ray generator can be carried out in a simple manner and without any special expertise. In addition, corrections to these standard values are possible at any time (with the appropriate specialist knowledge).

It is particularly advantageous that new applications that occur and that must be handled "by hand" according to the known setting methods also run on the personal computer; This gives you the option of storing this setting for the new use cases in the application memory for further use when such cases occur again. This makes the proposed configuration capable of learning to a sufficient extent for routine practice. This also applies to the correction values that the personal computer provides for the source resistance of the high-voltage generator, including the source resistance of the electrical supply network, or for the condition of the X-ray tube: if these values change, for example due to aging processes, the changes can be made in the application memory in the same way filed and taken into account in the following use cases in a corrected manner.

The constant monitoring of tube voltage and tube current takes place over the entire application time. On the one hand, this gives a value for the instantaneous load on the X-ray tube, and on the other hand also the time integral of this load. From this, the radiation doses required for the application can be calculated and the tube voltage can be kept for a preselected charge value (mAs) in such a way that the maximum permissible load on the anode is not exceeded, the application time being a minimum (the latter is important for recordings in the diagnosis) , because with increasing recording time, motion-related blurring increases the evaluability of the Deteriorate recording).

In addition, safety-relevant operating values of the x-ray tube can be stored in the application memory. The personal computer constantly compares the current operating values with the safety-relevant values in the memory that are to be regarded as limit values and keeps the current values in the range specified by these limit values. Security problems are inevitably avoided. Storing these values also allows these values to be adjusted if changes need to be made, for example due to a change in the safety concept. This also applies to the application-specific values stored in the application memory. While these are constantly updated by simply overwriting or adding, those require special treatment because of the security-related problems: The files must be secured against unauthorized overwriting; It is advantageous to use EPROMs, which require special treatment for deletion and rewriting (which is particularly important with regard to future changes to the security regulations).

Since the radiation yield of the X-ray tube depends on the condition of its anode and this changes with increasing age, it is necessary to monitor the radiation yield continuously or from time to time. This is done with a measuring device switched into the beam path, which triggers the load switch when the desired dose value is reached and thus switches off the high voltage. This switch-off pulse is also used as an acknowledgment pulse for the personal computer PC and is fed to it via the interface. This tells the personal computer that the application is complete. This message causes a switching state that, for example, rules out a new application without confirmation. This is necessary to avoid double exposures when taking pictures; the need for such a blocking circuit also results from safety requirements.

In addition to its interface to the input keyboard and the screen, the personal computer has further interfaces, one of which is used as a printer interface, to which a printer is connected as a further output unit. With the help of this printer, the personal computer is able to output a protocol for the application of the tube voltage and tube current as well as the dose rate and the duration of the application. This means that these printouts can be used for documentation purposes e.g. in which patient records are collected. It goes without saying that electronic storage can also be carried out and a printout can only be made if necessary. A connection to a higher-level computer (host) is also possible with this or another interface. This higher-level computer can transmit the application data for the selected application, it can contain the security-relevant data and, finally, it can also take over the task of the memory for the data to be documented.

The essence of the invention is explained in more detail with reference to the block diagram attached in FIG. 1.

The personal computer PC - referred to here as the computer PC, has at least three interfaces, one of which is occupied by an input unit, the keyboard, and another by the output unit, the screen. The interface with which the connection to the individual components of the X-ray generator is established is connected to the third interface. The third interface, which connects the interface, is set up as an IN / OUT port, via which position feedback and measured value signals, as well as acknowledgment signals to the computer, and control commands to the connected components run.

If the desired application is selected via the input unit "keyboard" with the help of a corresponding menu provided by the program, and if the computer has also calculated the necessary high voltage and the heating power required for the necessary tube current based on this program, the corresponding control commands are issued by the Part "tube voltage" of the interface to the "control transformer" and part "tube current" of the interface to the "tap changer for heating", the actuators of which then execute the control commands. The high voltage selected by the PC is then applied to the "load switch", with a value that is excessive under the expected reduction under load.

The heating is started up with an undervoltage as preheating, the switch "preheating / heating" is still in the position (not shown) "preheating with unstabilized voltage". The dose rate calculated by PC also affects the anode load, it should also be monitored.

In order to keep the anode load below the permissible limit load, the rotating anode is activated via the "dose automat" part of the interface, the beam bundling is set in the desired or necessary manner via "focus" and finally the feedback of the measuring chamber is recorded via the "dose control" locks the PC for further applications without a new confirmation. Such feedback also takes place after the rotating anode has started, without this feedback the switching on of the load switch and thus the application of the high voltage to the X-ray tube is excluded. The dose machine connected to the interface itself is generally not part of the X-ray generator, but is to be seen as an autonomously working part of the X-ray system.

The "load switch" part of the interface activates the high-voltage load switch, coupled with the changeover from "preheating with unstabilized voltage" to "heating with stabilized voltage". The use of a stabilized voltage ensures the desired heating power and thus the temperature of the heated cathode required for a specific tube current. Switching in the heating circuit allows adaptation to the different requirements, for example for exposure or fluoroscopy.

Finally, the interface also has measured value inputs, some of which go to the interface via the A / D converter of the "measured value converter" and partly directly via the "preparation for recording". The incoming measured values serve on the one hand to monitor the progress of the entire application, but on the other hand the measured values provide feedback e.g. about changes in the source resistance of the high-voltage rectifier (including the electrical connection network) and thus about the overvoltage to be set without load or the emissivity of the cathode as a function of the temperature of the cathode and thus the cathode heating power supplied. The same also applies to the feedback from the measuring chamber, the measured value of which, depending on the tube voltage and tube current, provides a measure of the radiation yield of the anode (which roughened up during operation). Deviations from these values indicate sudden or permanent (often also insidious) changes that the PC stores as reference values in the application memory and which the PC can take into account in the periodically prescribed constancy tests of the X-ray system and compare them with the initial values obtained during the acceptance measurement of the X-ray system.

The control takes place via the personal computer PC, which is loaded with a program, the structure of which can be seen in the flow diagram attached as an x-ray to FIG. After the start, a system test is carried out under "INIT" and set all variable values to the starting position. The system is then ready to accept the values determined for the given circumstances under "Input". These values are checked for their conclusiveness under "Verify" and in the following YES / NO decision under "Start" the further program sequence is triggered given the start command. If the specifications are inconclusive or if the start command is not given, the system jumps back to the input and thus also allows an input correction.

If "Start" is released, the next step "Check" is used to check whether all parameters of the specification are in the valid range. If the parameters are outside, there is a return to "input" to enable corrections. If the inputs are recognized as being in the range, the actual start of the setting of the specified parameters takes place under "Start-up", the settings of which are checked, whereby errors occurring during the setting lead to an error message associated with a return to "input".

If there are no errors, the automatic exposure starts under "Exposure", during which the high voltage at the tube, the tube current, the heating current and the exposure time are measured. Errors that occur, i.e. Deviations from the specifications are identified by the system and reported as 6 errors. If necessary, termination and return to "input". During the exposure this test is repeated continuously by querying the parameters in a loop. After the passage of time, i.e. At the end of the exposure time, the measured values are displayed, including the current-time product in mAs that is important for the dose, which can also be documented, if necessary, by transmission to a higher-level computer, the personal computer PC hosted. The system then jumps back to "Enter" and is ready to accept new parameters.

Claims (8)

Circuit arrangement for X-ray generators used in particular for diagnostic purposes with a preselectable tube voltage which can be adapted to the requirements with a high-voltage rectifier with a variable transformer and an X-ray tube connected to it, the heating power of which is provided by a heating voltage generator can be preset, the preselection of the tube voltage and the presetting of the heating power of the tube using a controller in accordance with desired or necessary X-ray dose can be carried out, characterized in that a personal computer (PC) known per se is used for the presetting, which is connected via an interface to the control of the X-ray generator in such a way that the hardness of the personnel required for a desired X-ray dose Computer (PC) first calculates the tube voltage and heating power, transmits them via the controller interface and from the controller using the actuators Duration, tube voltage and heating current of the X-ray tube is set according to the specifications. Circuit arrangement according to claim 1, characterized in that the personal computer (PC) is provided with an application memory in which the characteristic curve of the x-ray tube is stored and that the primary network load resulting from the specifications is calculated and based on the input source resistance of the high-voltage rectifier including the Source resistance of the network determines the resulting reduction in the network voltage and compensates for it by increasing the transformation ratio of the variable transformer of the high-voltage rectifier in the sense of increasing the tube voltage and provides the heating power required for the tube current. Circuit arrangement according to claim 1 or 2, characterized in that in the application memory of the personal computer (PC) the data required for the usual applications for radiation dose, radiation hardness and radiation duration are stored as retrievable stored values and related data can be called up in the manner of a menu control, with over the input unit of the personal computer (PC) new applications can be entered and stored in the application memory. Circuit arrangement according to one of claims 1 to 3, characterized in that the interface is constructed in such a way that the high voltage applied to the x-ray tube and the current tube current are measured during the application period and the measured values are fed to the personal computer (PC), and that resulting setting of the high-voltage transformer and the heating power generator are preferably given to the actuators of the high-voltage transformer and the heating power generator, taking into account the limit load on the X-ray tube. Circuit arrangement according to one of Claims 1 to 4, characterized in that the safety-relevant limit values for the operation of the X-ray tube are stored in the application memory and can be specified as limit values for the personal computer (PC) when determining the control values. Circuit arrangement according to one of claims 1 to 5, characterized in that a radiation measuring device is arranged in the region of the beam path downstream of the object for measuring the dose emitted by the X-ray tube, which switches off the load switch in a manner known per se when the desired dose is reached and by it as an acknowledgment signal via the interface to the personal computer (PC) output signal when switching off a safety circuit, for example against a new triggering can be triggered without confirmation. Circuit arrangement according to one of claims 1 to 6, characterized in that the personal computer (PC) is provided in a manner known per se with a printer output, via which the entire protocol of the current application can be output as a document via a printer. Circuit arrangement according to one of claims 1 to 7, characterized in that the personal computer (PC) has an additional interface via which the latter is connected to a higher-level computer, which takes over the evaluation of the data of the application and its documentation and / or has data available for use cases and security technology.

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