EP0455001B1 - 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 setting the recording parameters "high voltage", "tube current" and "exposure time" for a diagnostic X-ray generator for an examination of an object to be carried out.

For the control of 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, so it can 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 connection of a consumer or a sudden recovery of the mains voltage by switching off a consumer can result in an unforeseeable change in the high voltage, which changes the dose rate in an unforeseeable manner.

WO-A-8 603 363 (HU) discloses a circuit arrangement for setting the recording parameters such as high voltage, tube current and exposure time for an X-ray examination to be carried out, with an interface, which is provided with input ports, on the one hand for connecting a personal computer and on the other hand for connection to the high-voltage generator of the x-ray system for recording electrical signals, by means of which these recording parameters can be set, a monitoring block being connected upstream of the high-voltage generator, whereby the interface includes a CPU, a ROM and a RAM as program and data storage for storing information that defines the logical conditions for the X-ray exposure, which must be adhered to according to the specifications, a clock for clocking the CPU and its ports with logical states , specified by this CPU, and connection means between these ports and the input ports for converting the logic states into the electrical signals, and a data bus, which is connected via the input ports to the personal computer, for storing the data associated with the parameters of the microcontroll ers are related, wherein the exercise of the monitoring between the monitoring block and the personal computer is divided such that the personal computer is programmed so that the parameters of the X-ray exposure in dialog mode are set by the operator of the X-ray system, while the monitoring block this data used to generate the signals in the manner and sequence determined by the operating needs and conditions of the x-ray system. In this previously published circuit arrangement for an X-ray system, setpoints are predefined, but the further step of checking the actual values by means of feedback of the measured values and influencing the actual values to compensate for such a deviation from the possible setpoint / actual value comparison is avoided. Furthermore, US Pat. No. 4,811,374 describes a circuit arrangement for controlling an X-ray generator for X-ray recordings known in which a processor sets the parameters relevant for the recording, such as tube voltage, tube current, mAs value and recording time, taking into account the load caused by the recording, and the X-ray tube is to be protected against overloading with incorrect parameters, for which the processor prevents the start of a recording in which the X-ray tube can be overloaded. This is achieved in that the processor calculates the power starting from a first current value in an iteration process and the energy with which the anode is loaded for the exposure time resulting for a desired charge transfer. If this value is above the limit, the tube current and tube voltage are reduced in a second step, the procedure is repeated, checked and - if the limit load energy is undershot - the exposure is released, otherwise the procedure is repeated until the first triplet of values is found, at which the limit energy remains below. The functionally related values for tube current and heating current are stored in the memory of the processor. The circuit arrangement leads to an exposure below the limit load.

EP-A-0 001 640 relates to a radiological device which is intended in particular for examining patients and with which the image quality is to be optimized and the service life of the radiation source is to be maximized. For this purpose, a controller with a memory program computer is used used, the application memory contains a number of instruction programs. The factors entered for a recording of tube voltage, tube current and recording time or organ-specific requests are then taken into account by the memory program computer to the maximum tube current, taking into account the direction of radiation and the age and thickness of the patient, in order to achieve a minimum recording time; the resulting loads are compared with the X-ray tube load diagrams stored in the information store, exposure being permitted only if the limit load is not exceeded. If it is exceeded, the program lowers the tube current with a constant charge flow (ie increase in the recording time). These new values are again compared for compatibility with the X-ray tube exposure, etc. A deterioration in the image resolution is accepted. In order to keep this deterioration in image resolution within limits, an upper limit of the recording time can be specified, which must not be exceeded. If this occurs, the power output to the anode is reduced, the tube current is reduced and the tube voltage is increased, while keeping the film blackening factor constant (which is why the decrease in the tube current is disproportionately more important than the increase in the tube voltage), so that the decrease in the power delivered to the anode is reached. According to the publication, this procedure is repeated with other parameters (different focal spot size, higher speed of the rotating anode) until either a suitable triplet of values has been found or the technical feasibility of the recording with the selected or resulting specifications has been proven.

The aim of these arrangements is that the x-ray system can be set to the parameters necessary for the different exposures in such a way that false exposures, which the patients need unnecessarily strain and waste expensive footage, be avoided.

According to the present invention, a circuit arrangement having the features of claim 1 is proposed.

By using a personal computer, the connection to its control technology is achieved in a simple manner; However, this use requires a special interface that takes over the connection between the controller 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, for the high-voltage generator and the electrical supply network to which the high-voltage generator is connected, the current values for the X-ray tube and the present application, such as 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 proposed standard values for the radiation dose rate values for high voltage and heating power for the X-ray tube then takes place in dialogue. 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 special technical knowledge. In addition, (with appropriate specialist knowledge) corrections of these standard values are possible at any time.

It is particularly advantageous that new applications that arise and that have to 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 maintained 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-related operating values of the X-ray tube are stored in the application memory. The personal computer constantly compares the current operating values with the safety-relevant values in the memory which 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 supplied 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 exclude 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 each application on the course of tube voltage and tube current as well as the dose rate and the duration of the application. This means that these printouts can be collected for documentation purposes, for example in the patient file. 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 - referred to here as a 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 takes up the connection of 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 associated 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 according to 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 focusing is adjusted 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 occurs even 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 is roughened during operation). Deviations from these values indicate sudden or permanent (often also insidious) changes, which the PC stores as reference values in the application memory and which the PC can then 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 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 not conclusive, 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 within the valid range. If the parameters are outside, there is a jump back to "input" to enable corrections. If the inputs are recognized as lying in the area, the actual start of the setting of the specified parameters takes place under "Start-up", the settings of which are checked, wherein 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 an error. 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 (5)

1. Circuit arrangement for setting the exposure parameters "high voltage", "tube current" and "exposure time" for a diagnostics X-ray generator for an examination to be carried out on an object, comprising an interface for transferring electric signals which can be used to set these exposure parameters and for sending feedback signals, via the outputs and inputs of which there are connected a personal computer (PC) on the one hand and a high-voltage rectifier having a regulating transformer, a presettable heating voltage generator having a step switch, and an X-ray tube connected with the high voltage rectifier on the other hand, the PC including means for monitoring the exposure parameters as well as an application memory for storing information relating on the one hand to the safety-relevant limit values for the operation of the X-ray tube and on the other hand determining the exposure parameters to be adhered to according to the specification, and wherein the personal computer (PC) first calculates the tube voltage and the heating performance for an X-ray dose of a desired severity, the personal computer (PC) being continuously fed via the interface with actual values of tube voltage and tube current during the time of exposure, the personal computer continuously comparing said measured values with the safety-relevant limit values and keeping the actual values within the range predefined by said limit values, a setting resulting therefrom of the high-voltage rectifier and of the heating voltage generator being provided under consideration of the limit load of the X-ray tube to the regulating transformer and the actuator of the heating voltage generator, so that the exposure time is minimized, while a preselected value for the load value (mAs) is maintained.
2. Circuit arrangement as claimed in Claim 1, characterized in that a program loop is provided for the continuous monitoring of the tube current and the tube voltage, the measured values being displayed and documented upon expiration of the exposure time.
3. Circuit arrangement as claimed in Claim 1 or 2, characterized in that a radiation measuring device is arranged in the beam path downstream of the object for measuring the dose irradiated by the X-ray tube, a power circuit breaker switching the X-ray generator off in a manner known per se once the desired dose value has been reached.
4. Circuit arrangement as claimed in Claim 3, characterized in that deviations in the feedback signals from the measuring chamber, the measuring value of which provides under consideration of the tube voltage and the tube current a standard for the radiation yield of the anode, are stored in the application memory as a reference value and are taken into account for future constancy checks of the X-ray apparatus such that the personal computer (PC) compares these values with the initial values obtained during the acceptance measurement of the X-ray apparatus.
5. Circuit arrangement as-claimed in any one of Claims 1 to 4, characterized in that a printer output of the personal computer (PC) is connected to a printer in a manner known per se, for outputting a complete log of the actual examination, providing information on the course of the actual values of tube voltage and tube current as well as of dose rate and exposure time.

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