EP0529505A1 - Procédé de production de prises de vues radiographiques à haut contraste pour le diagnostic et arrangement de circuit à cette fin - Google Patents

Procédé de production de prises de vues radiographiques à haut contraste pour le diagnostic et arrangement de circuit à cette fin Download PDF

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Publication number
EP0529505A1
EP0529505A1 EP92114171A EP92114171A EP0529505A1 EP 0529505 A1 EP0529505 A1 EP 0529505A1 EP 92114171 A EP92114171 A EP 92114171A EP 92114171 A EP92114171 A EP 92114171A EP 0529505 A1 EP0529505 A1 EP 0529505A1
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EP
European Patent Office
Prior art keywords
voltage
converter
tube
ray tube
frequency
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EP92114171A
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German (de)
English (en)
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EP0529505B1 (fr
Inventor
Klaus-Peter Bork
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BORK KLAUS PETER
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BORK KLAUS PETER
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05G—X-RAY TECHNIQUE
    • H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
    • H05G1/08—Electrical details
    • H05G1/10—Power supply arrangements for feeding the X-ray tube
    • H05G1/20—Power supply arrangements for feeding the X-ray tube with high-frequency ac; with pulse trains
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05G—X-RAY TECHNIQUE
    • H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
    • H05G1/08—Electrical details
    • H05G1/26—Measuring, controlling or protecting
    • H05G1/30—Controlling
    • H05G1/32—Supply voltage of the X-ray apparatus or tube
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05G—X-RAY TECHNIQUE
    • H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
    • H05G1/08—Electrical details
    • H05G1/26—Measuring, controlling or protecting
    • H05G1/30—Controlling
    • H05G1/46—Combined control of different quantities, e.g. exposure time as well as voltage or current
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05G—X-RAY TECHNIQUE
    • H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
    • H05G1/08—Electrical details
    • H05G1/60—Circuit arrangements for obtaining a series of X-ray photographs or for X-ray cinematography

Definitions

  • the invention relates to a method for increasing the contrast of diagnostic X-ray recordings with an X-ray generator connected to an electrical AC voltage network with a high-voltage rectifier and an X-ray tube connected to it and with a switching unit that controls the tube current and tube voltage as well as exposure time, in particular those with a converter, on the one of which is provided with a charging capacitor High-voltage output, the X-ray tube is connected, the converter as frequency converter to the frequency of the alternating current supplied to the rectifier Converter frequency and as a voltage converter whose voltage is increased to a value corresponding to the desired high voltage; it also relates to a circuit arrangement therefor.
  • X-ray generators for diagnostic purposes are operated in different voltage ranges and with different current intensities and with different switch-on times, the level of the voltage applied to the X-ray tube determining the spectral composition of the X-ray radiation and radiation yield, the current strength determining the radiation intensity and both together determining the dose rate, while the switch-on duration determines the Exposure time and thus the dose is given. All three factors determine the exposure of the X-ray film and thus influence the quality of the X-ray images. This influence is essentially due to the change in the spectral composition of the radiation and thus in connection with the different absorption capacities of the types of tissue lying in the beam path with their different absorption behavior characterized by the half-value layer thickness.
  • the rib structure with a lower tube voltage and the soft tissue structure with a higher tube voltage will appear more clearly in a chest scan, the latter because the radiation of the strongly absorbing ribs with the harder radiation is otherwise present due to the absorption Compensates for loss of information.
  • an increase in the tube voltage leads to a reduction in the duty cycle and thus avoids blurring due to movement; it allows the focal spot on the tube anode to be reduced, with the success of a greater sharpness of the image due to improved radiation geometry; it enables a greater distance between the X-ray tube and the patient, which is associated with less distortion, less geometric blur and less secondary radiation.
  • Lowering the tube voltage means an increase in the duty cycle.
  • a reduction in the tube voltage also means a shift in the spectral energy distribution towards a softer radiation, which increases the stress on the skin.
  • Optimal image quality will therefore have to start from a tube voltage that corresponds to the organ to be displayed and the thickness of the patient to be irradiated.
  • This object is achieved according to the invention in that the voltage applied to the X-ray tube is reduced at least once from a predeterminable upper limit value to a likewise predeterminable lower limit value during the exposure time.
  • the tube voltage thus runs through all voltage values between an upper limit value and a lower limit value in an exposure interval, the spectral composition of the emitted X-rays follows this voltage change, so that the spectral composition required for the exposure situation and necessary for maximum contrast is thereby achieved.
  • the lowering is advantageously carried out several times, preferably quasi-periodically, with the tube voltage being raised to the upper limit value after the lowering. It is advantageous if the interruptions of the higher-frequency alternating current supplied to the rectifier during the exposure time take place quasi-periodically, the frequency to be assigned to this quasi-periodic interruption being in the range from 1/100 to 1/5 of the converter frequency. At normal converter frequencies of 20-40 kHz, this means an interruption to which a frequency of 0.2-8 kHz can be assigned. With recording times in the millisecond range, this ensures that the tube voltage runs through the entire voltage interval at least once during the exposure, that is, it oscillates between the specified maximum and the likewise specified minimum value.
  • the time constants for the drop in the tube voltage and its increase are chosen to be the same.
  • the inductance which interacts with the charging capacitor in general the load-dependent leakage inductance of the high-voltage transformer, forms an oscillating circuit, the switching elements in the oscillating circuit also being controllable.
  • the higher-frequency alternating current which causes the charging of the charging capacitor and is fed to it at the converter frequency is interrupted quasi-periodically and this interruption is canceled when the predetermined upper limit value of the tube voltage has been reached, or when the predetermined one is also reached lower limit of the tube voltage has been reached.
  • the negative grid bias of one of the X-ray tubes is used to lower and re-raise the tube voltage upstream electron tube quasi-periodically increased and decreased when the predetermined upper or the likewise predetermined lower limit value of the tube voltage is reached.
  • the negative grid bias of a grid control of the x-ray tube is increased or decreased quasi-periodically to lower and raise the tube voltage when the predetermined upper or the likewise predetermined lower limit value of the tube voltage has been reached. If the charging voltage of the charging capacitor or the voltage on the X-ray tube is measured, when the maximum value of the anode voltage of the X-ray tube is reached, either the oscillation can be suppressed so that the charging capacitor discharges to the lower limit value, or the measured value is converted into a grid bias, which either controls the electron tube upstream of the x-ray tube or controls the x-ray tube itself.
  • the charging capacitor is charged so that the upper limit is reached even under load; the variation of the voltage is brought about by the discharge of the charge through the X-ray tube and the inflow of charge from the high-voltage rectifier, the duration of a reduction interval, together with that determined by the temperature of the cathode of the X-ray tube, determining the amount of the reduction, given the capacitance of the charging capacitor.
  • the interruption is canceled and the charging capacitor starts charging again.
  • the upstream grid-controlled tube acts as a series resistor
  • the current flowing in the high-voltage circuit is a saturation current determined by the temperature of the cathode of the X-ray tube
  • the grid bias changes the internal resistance of the upstream electron tube, so that its voltage drop causes the voltage across the X-ray tube changed
  • the charge of the charging capacitor is kept constant and adjusted so that in the time interval the lowering to the desired lower Limit of the tube voltage is reached.
  • the third alternative can be used:
  • the variation of the grid bias causes an increase or decrease in the tube current, so that the charging capacitor more or unloaded less quickly. Since the voltage at the charging capacitor is equal to the tube voltage and this is due to the respective balance between charging (or recharging) and removal, this must fluctuate between a predefinable upper and a likewise predeterminable lower limit value.
  • the desired degree of ripple in the anode voltage of the X-ray tube is achieved with these variants:
  • the tube voltage passes through a voltage interval which specifies the spectral compositions of the X-ray radiation.
  • the short-wave cutoff frequency of the radiation spectrum is shifted towards longer wavelengths, and the radiation becomes softer.
  • this interplay of lowering and raising is referred to here as ripple or modulation, the degree of ripple (or modulation) being assumed as the ratio of maximum voltage to minimum voltage. It is also advantageous if means are provided with which the curve shape of lowering and increasing the voltage can be influenced.
  • the values for the lowering and re-raising of the tube voltage, for its quasi-periodic frequency and / or for the "modulation" degree of the X-ray tube voltage and thus for the ripples that can be achieved in accordance with the type of Desired x-ray image are stored in an application memory and retrieved from the memory and are preferably fed to the processor for controlling the interruption in preparation for the image. Automation is thus achieved, which enables exposures or fluoroscopes to be carried out in a simple manner, even under special circumstances, with only the exposure situation having to be specified based on the stored values.
  • the application memory of the processor additionally contains correction values which can be called up in connection with a desired x-ray image in addition to the application data for superimposing them.
  • this prevents the X-ray tube from being overloaded, on the other hand, the radiation exposure of the patient can be kept clearly within limits, especially since repeated procedures can generally be dispensed with in the procedure.
  • monitoring of the x-ray system itself is also possible if the measured values for voltage variation and degree of ripple are fed back to the control unit, for comparison with the preset values for the upper and lower limit values, taking into account the maximum values of the x-ray tube voltage and current as well as the permissible current flow time and to correct them.
  • a circuit arrangement which is advantageous for carrying out the method is provided in that the converter has at least one measurement input for the tube voltage, which forwards the measured tube voltage as a control signal to a modulator generating the control signal for lowering and raising the tube voltage, which is connected to the control part or to the Grid of the electron tube upstream of the X-ray tube or connected to the grid of the X-ray tube.
  • the signal necessary for the control of the tube voltage can be obtained and either to interrupt the converter frequency, to generate the grid bias of the grid-controlled electron tube upstream of the x-ray tube or finally to generate the grid bias of the x-ray tube self.
  • control connections of the thyristors of the converter are connected to the outputs of a phase control, the current pulses which ignite the thyristors are phase-shiftable with respect to the converter oscillation in accordance with the desired upper limit value of the voltage for setting their upper limit value, and that the phase control has means which each after reaching this upper limit value blocks the delivery of these ignition pulses until the lower limit value of the voltage is reached, for which purpose the phase gating control on the one hand provides a connection for taking over the in-phase converter frequency and on the other hand makes a connection for taking over the anode of the x-ray tube, preferably the one connected to the high-voltage rectifier Charging capacitor applied voltage is supplied directly or via a voltage converter.
  • Such a circuit arrangement operates under the specified conditions as a frequency generator and is thus able to control the thyristors of the converter accordingly, its frequency being specified by a series resonant circuit contained in the converter.
  • the quasi-periodic charging and discharging of the charging capacitor results in voltage fluctuations which extend from the predetermined upper limit value to the likewise predetermined lower limit value. These voltage fluctuations run with their own time constants, which depend on the external and internal resistances.
  • This type of circuit leads to a type of "modulation" of the converter frequency, since the converter alternating current of higher frequency, which charges the charging capacitor via the high-voltage rectifier, is only present quasi-periodically.
  • the converter has a timer for setting the opening time and thus the charging time of the smoothing capacitor. With this timer, the time constant acting for charging the charging capacitor can be changed.
  • the x-ray tube circuit has a controllable resistor, preferably a triode, connected upstream of the anode of the x-ray tube, the internal resistance of which and thus the time constant of the discharge of the charging capacitor can be controlled.
  • the x-ray tube have a control grid for controlling its internal resistance and thus the time constant of the discharge of the charging capacitor via the grid bias.
  • the time constant determining the discharge of the charging capacitor can be changed. If both changes are combined, the two time constants can be adjusted to each other. This creates an at least sine-like voltage curve on the charging capacitor.
  • an inductor be provided in the line carrying the charging current of the charging capacitor, for deforming the waveform of the current emitted by the converter, the inductor and the capacitor forming a resonant circuit with a resonance frequency close to that Break frequency.
  • the resonance frequency of this resonant circuit determines the frequency with which the charging and discharging of the charging capacitor take place, and thus the repetition frequency for the "ripple".
  • the converter or the modulation stage is preferably one Assigned to a microprocessor to control the interruption frequency and thus the "modulation" level of the X-ray tube voltage. It is also advantageously provided that the microprocessor is assigned a working memory and a further mass memory, the mass memory containing files in which recording or fluoroscopy parameters are stored, which are required for a desired recording in the working memory for comparison with the set or measured values Values are transferable.
  • the device is brought so far that it can interact with a computer or even contains an integrated computer.
  • the connections are made via parallel bus structures, whereby serial connections are not excluded. With the help of the stored values, the usual recording situations can be specified so far that they can be called up and are thus available.
  • a computer for example a personal computer, the keyboard of which enables the necessary commands to be entered and the monitor of which allows the entire recording or screening process to be monitored.
  • the computer can also be integrated, with a keyboard and monitor.
  • the processor is connected via at least one internal connection bus to an internal mass memory designed as a permanent memory, the output signals of which are carried out together with those of the working memory via an internal data bus, these being connected to the inputs and the output the intended digital / analog or digital / analog converter.
  • an internal mass memory designed as a permanent memory
  • the output signals of which are carried out together with those of the working memory via an internal data bus, these being connected to the inputs and the output the intended digital / analog or digital / analog converter.
  • FIGS. 1 and 2 show the typical course of the high voltage on the X-ray tube when using a conventional rectification with a 3-phase full-wave rectifier to generate the DC voltage applied to the anode (FIG. 1) and when using a converter known per se ( Fig. 2).
  • the main difference lies in the ripple of the DC voltage (also "humming"), which the 6-pulse voltage from the 50 Hz three-phase network is around 30%, and the converter drops to below 10%. This is due to the use of a (relatively) high frequency of around 20-30 kHz, with which the high voltage is generated here.
  • FIGS. 3 and 4 show the curve shapes of voltages applied to X-ray tubes and generated by means of a converter, which are provided with a ripple according to the invention. These curves consist of the rising charging branches and the falling discharging branches of the charging capacitor (each related to the voltage at the X-ray tube anode). For the sake of clarity, the ripple resulting from the converter frequency, which overlaps the charging branches in accordance with the illustration in FIG. 2, has not been drawn in, although it goes without saying that the falling branches do not show any such ripple. While FIG. 3 shows a curve shape with a degree of ripple (or modulation) of approximately 50% (FIG. 3a) or approximately 75% (FIG.
  • the interruption frequency lies in the voltage curve according to FIG 4 significantly higher at about 3 kHz, the degree of ripple (or modulation) corresponding approximately to that of FIG. 3a.
  • the choice of the interruption frequency and degree of ripple determine external parameters, which depend on the type of recording situation and the X-ray generator, the maximum voltage at the X-ray tube also being able to be determined via the charging pulses resulting from the higher-frequency AC voltage, which for a few pulses when the anode voltage reaches the maximum value suspend until the anode voltage has dropped slightly below the value of this maximum value.
  • FIG. 5 shows basic circuits for the connection of X-ray tubes, in which a converter takes over the generation of the "modulated" anode voltage (Fig. 5), in which the discharge and thus the anode voltage of the X-ray tube is achieved by control with a lattice-controlled high-vacuum tube ( 6a, 6b).
  • voltage is supplied from a three-phase network (not designated in more detail) via the circuit breaker 1, which can also be designed with controlled semiconductor switching elements.
  • the voltage is fed to the converter 2, in which the voltage converted in the vibration generator 2.1 to the converter frequency in the transformer and rectifier part 2.3 is converted into the anode voltage of the x-ray tube 3.
  • a controlled converter FIG.
  • the voltage applied to the charging capacitor connected downstream of the rectifier is detected by the voltage measuring set 4 and reported to the modulator 5, which in turn releases the modulation control 2.2 until the maximum voltage value at the charging capacitor as specified is reached, then the converter oscillation stops and only releases it again when the voltage has reached a (likewise predetermined) lower voltage value at the charging capacitor.
  • a triode 7 is connected upstream of the x-ray tube as a grid-controlled high vacuum tube, the voltage at the output corresponding to the anode voltage of the x-ray tube 3 7.1 is removed from the triode and fed to the voltage measuring set 4, which evaluates the value of the applied voltage as described above and reports to the modulator 5, which then in turn adjusts the grid bias of the triode 7 so that the internal resistance of the triode 7 and thus the voltage drop across it the anode voltage of the X-ray tube 3 assumes the desired value.
  • an X-ray tube 3 'with a control grid their anode current can be controlled with the grid voltage, the anode current representing a load for the charging capacitor and, depending on the excess charge or deficit, increasing or decreasing the anode voltage.
  • the grid control intervenes in the discharge of the charge capacitor, the discharge of the charge capacitor predominating when the grid is "open” and its charge predominating when the grid is sufficiently biased negatively, the grid control itself acting as a "switch” that interrupts the Converter vibration and thus charging voltage replaced.
  • the anode voltage of the x-ray tube 3 is set by means of the control described so that the x-ray radiation lies in the desired spectral range.
  • FIG. 7 shows a (schematic) circuit of a converter which can be controlled by a PC and is supplied from the three-phase network via the connections U, V, W.
  • the center conductor M P ensures a connection to the neutral point of the three-phase network and also allows a corresponding AC voltage to decrease, for controlling the main switching relay HR or the heating circuit HK for heating the cathode of the X-ray tube RR.
  • the entire control of the X-ray generator is effected with the aid of a computer, for example a PC with an input terminal and monitor as an output unit with a comprehensive control panel STP.
  • a voltage is provided for the heating circuit HK, and further the voltage for switching through the main switching relay HR for activating the X-ray tube RR.
  • the tube voltage required for the present case is preselected on the control panel STP and the heating current required for the required tube current is set, which - since the cathode must be preheated due to its inertia - flows before the start of the recording, since the cathode temperature for the anode current of the X-ray tube is decisive.
  • the main switching relay HR When the recording is triggered, the main switching relay HR then connects the mains voltage to the high-voltage generator, which is then converted directly into the mains rectifier NGL, which is designed as a 3-phase double-path rectifier, and fed to the current transformer part STW.
  • the voltage symmetrized by the same capacitors C1, C2 is applied to the thyristors Th1 and Th2, to which the diodes D1 and D2 are connected antiparallel, the circuit via one of the capacitor C3 and the (leakage) inductance of the power transformer TR1 formed resonant circuit is closed.
  • the direct voltage is converted into a higher-frequency alternating voltage, the frequency of which is determined by the capacitor capacitance C3 and the leakage inductance of the transformer TR, which is large when idling and decreases with increasing load, which causes an increase in frequency with increasing Load and thus a reduction in ripple means.
  • the AC voltage is converted in the power transformer TR to the voltage required for the desired operation of the X-ray tube RR, which is then rectified in the high-voltage rectifier HGL (indicated only as a diode) and smoothed with the capacitor C4.
  • the increasing frequency with increasing load together with this smoothing causes the (relatively) low ripple of the curve shape of the direct voltage generated by a conventional converter circuit (see FIG. 2).
  • the converter circuit is not limited to the use of a thyristor pair, but in the same way e.g. can also be implemented with a bridge circuit.
  • the phase of the control current pulses which control the thyristors Th1 and Th2 is shifted with the aid of a phase shifter PHS corresponding to a phase control, so that in the end result an output voltage corresponding to the desired voltage at the charging capacitor C4 results.
  • the high voltage available for the X-ray tube RR to the smoothing capacitor HGL drops after each interruption until it is recharged by opening the thyristors Th1 and Th2.
  • the switch-off interval can take place both via the fall time of the voltage at the charging capacitor HGL (time constant of the charging capacitor and internal resistance of the X-ray tube) and via the direct determination of the value of the falling voltage at the charging capacitor.
  • the preselected heating system When determining the time interval, the preselected heating system must be taken into account, which determines the saturation current of the X-ray tube via the cathode temperature, which thus receives an internal resistance that is dependent on the heating current.
  • the upper voltage value is measured and monitored; In order to achieve the ripple that is favorable for high-contrast recording, this monitoring is extended to the lower voltage value.
  • the opening of the thyristors Th1 and Th2 is advantageously coupled to this voltage measurement and thus the way is opened via the control panel STP the upper and lower limits to specify for the voltage so that during the recording or fluoroscopic interval the tube voltage drops at least once from the high voltage specified on the control panel STP to the likewise specified low voltage.
  • These specifications also allow the circuit to be adapted to the circuits of X-ray generators which work with a grid-controlled vacuum tube (see FIG. 6a) connected upstream of the anode of the X-ray tube, or in which the X-ray tube RR 'itself has a grid control (see FIG. 6b ). In these cases there is no need to interrupt the converter oscillation, the charging voltage is constant here.
  • the anode voltage is changed here by reducing or increasing the discharge of the charging capacitor, since here the current flowing in the anode circuit is not the saturation current corresponding to the temperature of the cathode of the x-ray tube, but is determined by the grid bias.
  • FIGS. 8 show the computer-aided control of the converter in a schematic basic circuit.
  • the microcontroller U1 as CPU with external power supply (here indicated by a mains rectifier NGL with outputs for the supply voltage VCC and for a reference voltage VRZ) and external clock generator (with quartz TG) is the heart of the control; it works according to a program stored in a ROM memory U4, which is read in via an external I / O connection, this I / O connection being connected to a computer, for example a PC, but at least to a mass storage device (with the latter, the CPU also controls this mass storage as a microprocessor).
  • the externally incoming commands lead to the activation of the CPU U1, which issues the corresponding commands via the control bus output "S" and the bus outputs "C” and “B".
  • the outgoing signals via the address bus ADB are fed to the latch U2 and the ROM U4.
  • the corresponding control commands are output via the data bus DDB, which on the one hand go back to the CPU U1 and on the other hand are fed to the inputs and outputs.
  • the signals arriving at a first, programmable logic gate U3 are converted into control signals for the ROM U4, the RAM of the RAM U5, the I / O unit U6 and the general read / write signal R / W and via appropriate bus or line connections output:
  • the ROM U4 receives the control signal via the control line ROSL, the RAM U5 via RASL and the I / O unit U6 via IOSL.
  • the read / write signals for all are output via the control line RWSL.
  • a second programmable logic gate U6 receives the corresponding signals for measurement and setpoints via the data bus DDB and via the signal which switches the converter on and off.
  • the second programmable logic gate U6 derives both the START signal, which is output via a separate START line, and the input / output signal, which runs over the input / output bus and the input and output units U7, U9, U11 and U14 activated.
  • the input connections E1, E2 and E3 for the actual values of tube voltage U tube , tube current I tube and heating current I heating (or in general Heating power N heating ) are essentially of the same design: each has an operational amplifier connected to the supply voltage and to the reference voltage, the two inputs of which are provided with a resistance network, for adaptation to the connected circuit, the operational amplifier adjusting the signal level at the desired output impedance manufactures that can be processed by the downstream analog / digital converters U7, U9, U11.
  • the input signals from E1, E2 and E3 digitized in this way run via the data bus DDB to the CPU U1 and to the RAM U4, in order to be compared there as actual values with the desired values.
  • the CPU U1 calculates the necessary control commands that are sent to the digital / analog converter U14 and, via this, a process amplifier U13 as an adaptation element and level converter, from the deviation detected in this comparison is connected to the converter via output A1.
  • the number of inputs and outputs need not be limited to 3 or 1 in accordance with the selected exemplary embodiment.
  • the corresponding continuations of the control lines and the data bus are indicated by dashed lines in FIG. 8b.
  • the address bus can also continue to be used if further RAMs are used (indicated by dashed lines).
  • the general rule here is that the operation of the microcontroller U1 takes place according to the operating system stored in the ROM U4 in connection with the program stored in it and called up or a program read into the RAM U5 from an external source.
  • the ROM U4 also has the current program as well as the limit values for tube voltage, tube current and anode power loss that apply to the connected X-ray tube or the upstream control triode (or tetrode) are stored so that they can be called up. It goes without saying even that operating values for constantly recurring exposure situations are stored as such, advantageously with a short command.
  • the microcontroller U1 is controlled via a (possibly externally connected) control bus (with the individual control lines for RESET, IQR, R / W, E; START, WR, RD, LOAD, MSB, LSB), which controls the microprocessor U1 with the connected electronic components, the (edge-triggered) latch U2, the first programmable logic gate PAL U3, the ROM U4 for the operating system of the microprocessor U1, the RAM U5 with those read in by the PC via the I / O connection Program parts, the second programmable logic gate PAL U6, and the analog / digital converters U7, U9, and U11 as well as the digital / analog converter U15 and their OP amplifiers U8, U10 provided in the input and output for adaptation, U12, U16 connects with them and with each other.
  • a control bus with the individual control lines for RESET, IQR, R / W, E; START, WR, RD, LOAD, MSB, LSB
  • An input bus (A-Bus of the MC U1), which is connected to an input terminal, allows the selection of the operating state of the X-ray tube desired for the next exposure and the entry of specifications that deviate from the standard values.
  • the data exchange between the CPU U1, the ROM U5 and the main memory as well as the input A / D converters U7, U9, U11, U13 and the output D / A converter U15 takes place via an internal data bus connecting these modules DDB (B-Bus of the CPU U1), the associated memory addresses via an internal data bus ADB (C-Bus of the CPU U1) at least to the latch U2, which generates address information from the data information, which allows the read-only memory of the Addressing the ROM U4 and the RAM of the RAM U5 address-wise.
  • the values for the tube voltage kV-IN (E1), the tube current mA-IN (E2), the heating current A H -IN (E3) and for in are also fed via the internal input bus DDB via the analog inputs of the control RAM U5 for comparison with the specifications obtained from the ROM U4 or entered via the terminal, these representing the TARGET values and that of the ACTUAL values. It goes without saying that further inputs E4 to EN can be provided, wherein the number of which could only be given by an address limit.
  • the control system For X-ray generators that are equipped with a converter generator and that already work in X-ray systems and that are to be converted by installing a modulation stage, the control system must be varied: The maximum high voltage that builds up with the highest charging frequency (approx. 25 kHz) is achieved via a certain time measured by the control unit. The steepness of the voltage rise in the voltage on the charging capacitor gives the possibility of calculating the interruption frequency with which the high voltage can be modulated (and thus the charging of the charging capacitor can be interrupted). The average voltage at the charging capacitor corresponds to the equilibrium between charging and discharging, the ripple or modulation being determined by the individual time constants.
  • the freely oscillating converter is blocked for a number of recharging pulses. The drop in the voltage at the charging capacitor is monitored, so that this means for the converter that the charging of the charging capacitor stops up to a lower discharge point corresponding to the minimum value of the anode voltage (FIGS. 3a, 3b).
  • the modulation unit now holds the high-voltage value kV-OUT at the maximum value for a calculated time, it pretends to the converter that the voltage is above the value at which reloading must begin; therefore there is no reloading as long.
  • the actual high voltage thus drops more or less quickly to a point specified by the modulation unit in accordance with the specification, for example to 30% of the high voltage value kV-OUT, in relation to the flowing tube power which is taken from the charging capacitor.
  • the modulation unit measures the course of the high voltage, it can recognize when this point has been reached.
  • the "real" ACTUAL value of the high voltage kV-ACTUAL is output as the kV-OUT value, which influences the recharge control of the converter in such a way that the high voltage is brought back to its maximum value as quickly as possible or depending on the preselected ripple, the waveform and / or steepness of the voltage rise can also be selected.
  • the modulation unit can of course be integrated into the basic concept.
  • the duration of exposure is obtained via a timing element (not shown in more detail), which acts on a switching element which generates or deactivates the medium-frequency low voltage.
  • a timing element not shown in more detail
  • both further input A / D converters can be provided for further input parameters and further output D / A converters if there is a need for this.
  • Such a need can be given, for example, by the fact that the setting of the exposure duration is also taken over by the converter controller, with the dose rate sensed by a radiation indicator being additionally used as an input parameter for limitation.
  • the second output signal would act on the converter in such a way that the higher-frequency low voltage is only generated during the "open" time specified by this output signal, or that the pulses necessary for conversion to the high voltage are generated outside of this "open” Time be suppressed.
  • this can also be done with a Grid control of the X-ray tube can be achieved, in which the current flow is suppressed when a permissible dose rate is exceeded via a far negative bias of the grating, this far negative grid bias being reduced during the "open” time, so that the X-ray tube has tube current during this time leads, which can itself be regulated via the amount of the grid bias.

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  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • X-Ray Techniques (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)
EP92114171A 1991-08-23 1992-08-20 Procédé de production de prises de vues radiographiques à haut contraste pour le diagnostic et arrangement de circuit à cette fin Expired - Lifetime EP0529505B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE4127983 1991-08-23
DE4127983A DE4127983A1 (de) 1991-08-23 1991-08-23 Verfahren zur erzeugung kontrastreicher diagnostischer roentgenaufnahmen sowie schaltungsanordnung dafuer

Publications (2)

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EP0529505A1 true EP0529505A1 (fr) 1993-03-03
EP0529505B1 EP0529505B1 (fr) 1996-06-12

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EP (1) EP0529505B1 (fr)
AT (1) ATE139404T1 (fr)
DE (2) DE4127983A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998021625A3 (fr) * 1996-11-10 1998-11-05 Smartlight Limited Film a latitude etendue

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19933537B4 (de) * 1998-08-18 2005-03-17 Siemens Ag Röntgen-Computertomographie-Gerät mit Mitteln zur Modulation der Röntgenleistung einer Röntgenstrahlenquelle
DE102021108456A1 (de) 2021-04-01 2022-10-06 Energy Resources International Co.,Ltd. Antriebsvorrichtung zum Fahren einer Hochspannungsröntgenröhre und Verfahren zum Fahren derselben

Citations (6)

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Publication number Priority date Publication date Assignee Title
DE2224366A1 (de) * 1972-05-18 1973-11-29 Siemens Ag Roentgendiagnostikapparat zur anfertigung von roentgenaufnahmen mit einem belichtungsautomaten
US3904874A (en) * 1973-01-30 1975-09-09 Siemens Ag X-ray diagnosing device with means for changing X-ray tube voltage
EP0096843A1 (fr) * 1982-06-11 1983-12-28 Kabushiki Kaisha Toshiba Appareil de diagnostic par rayons X
EP0102532A2 (fr) * 1982-09-09 1984-03-14 General Electric Company Appareil de polarisation en tension pour un tube à rayons X
US4763343A (en) * 1986-09-23 1988-08-09 Yanaki Nicola E Method and structure for optimizing radiographic quality by controlling X-ray tube voltage, current, focal spot size and exposure time
US5007073A (en) * 1989-12-20 1991-04-09 Gendex Corporation Method and apparatus for obtaining a selectable contrast image in an X-ray film

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Publication number Priority date Publication date Assignee Title
US4851983A (en) * 1988-01-27 1989-07-25 Gendex Corporation KVP regulator and resonant circuit for high frequency medical x-ray generator

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Publication number Priority date Publication date Assignee Title
DE2224366A1 (de) * 1972-05-18 1973-11-29 Siemens Ag Roentgendiagnostikapparat zur anfertigung von roentgenaufnahmen mit einem belichtungsautomaten
US3904874A (en) * 1973-01-30 1975-09-09 Siemens Ag X-ray diagnosing device with means for changing X-ray tube voltage
EP0096843A1 (fr) * 1982-06-11 1983-12-28 Kabushiki Kaisha Toshiba Appareil de diagnostic par rayons X
EP0102532A2 (fr) * 1982-09-09 1984-03-14 General Electric Company Appareil de polarisation en tension pour un tube à rayons X
US4763343A (en) * 1986-09-23 1988-08-09 Yanaki Nicola E Method and structure for optimizing radiographic quality by controlling X-ray tube voltage, current, focal spot size and exposure time
US5007073A (en) * 1989-12-20 1991-04-09 Gendex Corporation Method and apparatus for obtaining a selectable contrast image in an X-ray film

Non-Patent Citations (1)

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Title
MEDICAL PHYSICS. Bd. 6, Nr. 2, 1. März 1979, NEW YORK US Seiten 134 - 136 M.G. ORT ET AL. 'RADIOGRAPHIC QUALITY, TUBE POTENTIAL, AND PATIENT DOSE' *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998021625A3 (fr) * 1996-11-10 1998-11-05 Smartlight Limited Film a latitude etendue

Also Published As

Publication number Publication date
ATE139404T1 (de) 1996-06-15
DE59206536D1 (de) 1996-07-18
EP0529505B1 (fr) 1996-06-12
DE4127983A1 (de) 1993-02-25

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