Circuit for controlling X-ray exposure with monopolar or bipolar power supplies using grid current.

Abstract

Circuit for controlling X-ray exposure with monopolar or bipolar power supplies using grid current. A circuit for controlling X-ray exposure by an intermediate or feedback current directly proportional to a grid current (IG), which controls the anode current of the tube and is ultimately responsible for the emission of X-ray photons, the circuit comprising an anode (A), a grounded cathode (K), and a grid (G) connected to a control circuit for the grid current (IG). The control circuit for the grid current (IG) comprises a DC-DC converter (CONV) or "step-down converter" to which a supply voltage (Vsup) is connected, the output of which is connected to an inverter (INV), which is further connected to a transformer (TR), the output of which is connected to a rectifier (RECT), the output of which is connected to the grid (G) and to ground. The control circuit further comprises a control circuit (CONT).

Description

[Technical Field]

[0001] (Object of the invention) The object of the present invention, as indicated in the title of the invention, is a circuit for controlling X-ray exposure by the grid current of a cold cathode X-ray tube.

[0002] The invention is characterized in that each and every element that is part of the control circuit is specially designed and constructed so that the X-ray exposure can be controlled by an intermediate or "feedback" current that is directly proportional to the grid current that controls the current in the tube anode and ultimately is responsible for the emission of X-ray photons.

[0003] This circuit feature results in less voltage ripple between the anode and cathode, more precise control, and therefore more effective control of the delivered dose, and does not require elements that are part of the circuit to withstand high voltages.

[0004] The present invention is therefore within the scope of X-ray devices, in particular cold cathode devices. [Background technology]

[0005] It is known in the art that the energy of X-ray radiation depends on the applied kV, and the amount of radiation depends on the current and exposure time. One way to control such radiation is to control the temperature of the filament, known as thermionic emission control.

[0006] In currently used cold cathode X-ray tubes, a grid is placed between the cathode and anode, and electron emission is controlled by a cold cathode made of a series of carbon nanotubes.

[0007] Figure 1 shows a schematic diagram of a cold cathode X-ray device, including an anode (A), a cathode (K) formed from a series of carbon nanotubes and positioned opposite the anode (A), and a grid (G) interposed between them. There is a first loop formed by the anode (A), the cathode (K), and a voltage-controlled power supply, which can be monopolar or bipolar. In the bipolar power supply configuration (Figure 1a), the power supply is grounded at its midpoint, halving the stress on the power supply itself and the X-ray tube's insulation relative to earth. There is also a second loop formed by the grid (G), the cathode (K), and a current-controlled power supply. Both loops share a common section; current IA flows through the first loop, current IG flows through the second loop, and current IA+IG flows through the common section.

[0008] Figure 2 is a graph showing that the anode current (IA) is linear with respect to the grid current (IG), whereas Figure 3 shows that the relationship between the anode current (IA) and the grid current (IG) with respect to the grid voltage (VG) is exponential, and therefore controlling the anode current (IA) via the grid voltage is very complicated.

[0009] Figure 4 shows a circuit diagram for controlling the anode current (IA) via voltage: the anode is grounded via a power supply (VAG), the grid (G) is directly grounded, and the cathode (K) is grounded via a power supply (Vsup) and a MOSFET switch, where a voltage (Vcont) is dropped, controlling the signal of the current demanded by the cathode.

[0010] The control method shown in FIG. 4 satisfies the following:

[0011] VGK=Vsup-Vcont VAK=VAG+VGK VAK=VAG+Vsup-Vcont

[0012] This control scheme provides linear control of the cathode current (IK), but is very complex and requires a MOSFET capable of operating at several thousand volts, which results in a very large voltage drop between the source and drain.

[0013] Another major drawback of this type of control is that the voltage between the anode and cathode of the X-ray tube depends on the grid voltage (which changes as the X-ray tube ages), and directly affects the energy of the emitted radiation. Summary of the Invention [Problem to be solved by the invention]

[0014] The object of the present invention is therefore to develop a circuit for controlling X-ray exposure by means of the grid current in a separate and independent manner, thereby establishing a constant voltage VAK between the anode and the cathode that is independent of the grid control, and to develop a control circuit as described below, the essence of which is contained in the first claim. [Means for solving the problem]

[0015] Description of the Invention The object of the invention is essentially contained in the independent claims, with different embodiments being contained in the dependent claims.

[0016] The purpose of the circuit is to control the X-ray exposure by the IFB current, which is directly proportional to the grid current (IG), which controls the anode current of the tube and is ultimately responsible for the emission of X-ray photons.

[0017] The circuitry controlling the x-ray exposure can be configured for monopolar or bipolar x-ray tube power supplies. In a monopolar configuration, the circuitry controlling the x-ray exposure includes an anode connected to a power supply grounded through a shunt that measures the anode current, a cathode also grounded, and a grid with control circuitry for grid current, where the power supply voltage is connected to a DC-DC converter or "step-down converter," the output of which is connected to an inverter, the output of which is connected to a transformer, the output of which is connected to a rectifier, the output of which is connected to the grid and to ground.

[0018] In a bipolar power supply configuration for an x-ray tube, the x-ray exposure control circuit includes an anode connected to a grounded power supply through a shunt that measures the anode current, a cathode also connected to a grounded power supply, and a grid with control circuitry for grid current whose power supply voltage is connected to a DC-DC converter or "step-down converter," the output of which is connected to an inverter, the output of which is connected to a transformer, the output of which is connected to a rectifier, and the output of the rectifier is connected to the grid and to the cathode.

[0019] Furthermore, the control circuit includes a feedback current (I FB ) a signal from the required current, a preload, and an exposure signal, and outputs a first signal to the DC-DC converter and a second signal to the inverter.

[0020] In a preferred non-limiting embodiment, the DC-DC converter is formed by a first diode and coil, a capacitor in parallel with a first switch, and a return diode in parallel with the assembly formed by the first switch and coil.

[0021] The inverter is formed by a bridge including a second switch, a third switch, a fourth switch and a fifth switch, the second switch and the fifth switch are connected in series to form a first branch, the third switch and the fourth switch are connected in series to form a second branch, and both branches are in parallel with each other.

[0022] A transformer is connected to the middle of each branch, and the output of the transformer is connected to a rectifier bridge, where the grid current is obtained. Meanwhile, a feedback current signal (I FB ) is obtained from the DC-DC converter and the lower ends of both branches of the inverter.

[0023] Because controlling the grid voltage is very complex to implement, the control of the grid is achieved by current rather than voltage thanks to the control circuit described. Furthermore, controlling the grid by applied voltage requires the use of large components, such as MOSFET switches, which must be able to handle up to 15 kV if necessary. Furthermore, the voltage drop between source and drain is very large. This voltage changes depending on the aging state of the X-ray tube, changing the total voltage applied between the anode and cathode, which directly affects the X-ray exposure dose. This is because a change in this voltage (VAK) changes the energy of the emitted photons and therefore the total emitted dose.

[0024] All these drawbacks are overcome by a control circuit with a grid current that controls the anode current that is ultimately responsible for the emission of X-ray photons.

[0025] Unless otherwise indicated, all technical and scientific elements used herein have the meaning commonly understood by one of ordinary skill in the art to which this invention belongs. Methods and materials similar or equivalent to those described herein can be used in the practice of the present invention.

[0026] In the present specification and claims, the word "comprises" and variations thereof are not intended to exclude other technical features, additives, components or steps. For those skilled in the art, other objects, advantages and features of the invention will be inferred in part from the specification and in part from the practice of the invention. [Brief explanation of the drawings]

[0027] To supplement the description given herein, and with the purpose of facilitating a better understanding of the characteristics of the present invention, according to its preferred practical embodiments, said description is accompanied, as an integral part thereof, by a series of drawings in which, by way of example and not of limitation, the following are represented:

[0028] FIG. 1 is a schematic diagram of a cold cathode X-ray device with a monopolar power supply for the X-ray tube.

[0029] Figure 1a shows the same X-ray device, but in this case with a bipolar power supply.

[0030] FIG. 2 is a graph showing that the anode current (IA) is linear with the grid current (IG).

[0031] FIG. 3 shows the relationship between the anode current (IA) and the grid current (IG) and the grid voltage (VG).

[0032] FIG. 4 is a schematic diagram of a prior art circuit for controlling the anode current (IA) via the cathode current (IK), which affects the voltage between the anode and cathode (VAK) (and therefore the energy of the emitted radiation).

[0033] FIG. 5 shows a circuit for controlling X-ray exposure by the grid current (IG) using a monopolar power supply for an X-ray tube.

[0034] Figure 5a shows the same control circuit, but with the X-ray tube power supply bipolar.

[0035] A possible embodiment of such a circuit is shown in FIG.

[0036] FIG. 7 shows the operating cycle of the first operating mode, or preload and exposure mode.

[0037] FIG. 8 shows the operating cycle of the second operating mode, or direct exposure mode.

[0038] FIG. 9 shows a possible embodiment of the current control circuit. DETAILED DESCRIPTION OF THE INVENTION

[0039] (Preferred embodiment of the present invention) With reference to the figures, preferred embodiments of the proposed invention are described below.

[0040] 1 to 4 correspond to the description of the prior art of X-ray exposure control.

[0041] Figure 5 shows an X-ray exposure control circuit using a monopolar power supply for an X-ray tube. The anode (A) is connected to a grounded power supply (VAK) via a shunt to measure the current at the anode (IA), and the cathode (K) is also grounded. Meanwhile, the grid (G) is connected to a grid current (IG) control circuit, in which the power supply (Vsup) is connected to a DC-DC converter (CONV), also known as a "step-down converter," which is connected to an inverter (INV). The output of the inverter (INV) is connected to a transformer (TR). The output of this transformer (TR) is connected to a rectifier (RECT), and the output of the rectifier (RECT) is connected to the grid (G) and grounded.

[0042] Figure 5a shows an X-ray exposure control circuit for a bipolar power supply of an X-ray tube. The anode (A) is connected to a grounded power supply (VAK / 2) via a shunt for measuring the anode current (IA), and the cathode (K) is connected to another power supply (VAK / 2), also grounded. Furthermore, the grid (G) is connected to a grid current (IG) control circuit, where the power supply voltage (Vsup) is connected to a DC-DC converter (CONV), also known as a "step-down converter," which is connected to an inverter (INV). The output of the inverter (INV) is connected to a transformer (TR). The output of this transformer (TR) is connected to a rectifier (RECT), and the output of the rectifier (RECT) is connected to the grid (G) and the cathode (K).

[0043] Furthermore, the control circuit includes a current (I FB ) signal, the required current (I demThere is a control circuit (CONT) that receives the signals from the control circuit 100, as well as a preload signal (PRE) and an exposure signal (EXP), and has as outputs a first signal (S1) going to the DC-DC converter and a second signal (S2) going to the inverter (Inv). This circuit has three states: OFF, preload, and exposure, and therefore requires two control signals: a preload signal (PRE) and an exposure signal (EXP).

[0044] FIG. 6 shows a non-limiting preferred embodiment of the control circuitry, where the DC-DC converter is formed by a diode (D1) and a coil (L), a capacitor (C) in parallel with a first switch (Q1), and a return diode (D2) in parallel with the assembly formed by the first switch (Q1) and the coil (L).

[0045] The inverter is formed by a bridge including a second switch (Q2), a third switch (Q3), a fourth switch (Q4) and a fifth switch (Q5), the second switch (Q2) and the fifth switch (Q5) being connected in series to form a first branch, and the third switch (Q3) and the fourth switch (Q4) being connected in series to form a second branch, the two branches being parallel to each other.

[0046] A transformer (TR1) is connected to the middle of each branch, and the output of the transformer (TR1) is connected to a rectifier bridge, from which the grid current (IG) is obtained. FB ) is obtained from the DC-DC converter and the lower ends of both branches of the inverter.

[0047] FIG. 7 shows a first operation mode of the X-ray exposure control circuit, which corresponds to the preload mode.

[0048] This diagram shows the different cycles (C1, C2, C3, C4, C5, C6, C7, C8), the state of the different switches (Q1, Q2, Q3, Q4, Q5) and the current demand (I dem ) and current (I FB ) is shown.

[0049] During the C1 cycle, all five transistors (Q1, Q2, Q3, Q4, Q5) are on. The current (I FB ) rises linearly and is limited by the value of inductance (L).

[0050] In the C2 cycle, everything remains the same because the current (IFB) has not yet reached the required value (IDEM).

[0051] In the third cycle C3, the current (I FB ) is the value (I dem ), Q1 stops conducting, so the current (I FB ) starts to fall. In the next cycle, (Q1) turns on again and (I FB ) again becomes the value (I dem ) is reached. This preload state occurs when the four inverter bridge transistors (Q2, Q3, Q4, Q5) are on and transistor (Q1) is conducting a current (I FB ) can be maintained indefinitely.

[0052] At some point, the system controller decides to start the exposure by signal (EXP) and transfers the current stored in (L) to the grid circuit. To start this new state, the inverter bridge transistors (Q2, Q3, Q4, Q5) open their short circuits and begin operating as an inverter, i.e., a DC to AC converter. To do this, (Q2) and (Q4) are turned on and (Q3) and (Q5) are turned off. In the next cycle, (Q2) and (Q4) are turned off and (Q3) and (Q5) are turned on, and this alternating cycle is maintained indefinitely as long as the X-ray exposure is active. In each cycle, and regardless of the preload or exposure state, transistor (Q1) transfers a current (I FB ) to the value (I DEM ) and continue to maintain it.

[0053] When the system controller decides to end the X-ray exposure by signal (EXP), the five transistors (Q1, Q2, Q3, Q4, Q5) are turned off simultaneously in an instant. At that moment, the current circulation to the grid stops and the X-ray exposure is immediately turned off. The energy stored in the inductance (L) is transferred to the power supply (Vsup) via diodes (D1) and (D2).

[0054] Another way to terminate the X-ray exposure is by turning on the current (I FB ), while maintaining control of the inverter bridge, turning on four transistors (Q2, Q3, Q4, Q5) in preload mode, allowing a new exposure to be made at any time without delay.

[0055] FIG. 8 shows a second operating mode of the circuit for controlling X-ray exposure, which corresponds to the direct mode.

[0056] The purpose of Direct Mode is to start the X-ray exposure immediately, without waiting for the grid to obtain the optimum current. In this mode, the exposure time is slightly longer than in Preload Mode.

[0057] As can be seen from Figure 8, the transistor (Q1) is in current control mode (I FB ) is the required value (I DEM ) and then it turns off. Then the transistors (Q2, Q3, Q4, Q5) start to operate in inverter mode and transfer all the current to the grid from the very first moment.

[0058] In cycle C1, I FB still has value(I DEM ) has not been reached, so Q1 conducts 100%. Then Q2 and Q4 turn on, while Q3 and Q5 remain off. In the next cycle C2, the value (I dem ) has not yet been reached, so (Q1) continues to conduct permanently, while transistors (Q2) and (Q4) are turned off and (Q3) and (Q5) are turned on, reversing the polarity of the magnetic field in the core of (TR1) and preventing saturation.

[0059] Finally (I FB ) is the value (I dem ) and Q1 begins to regulate the current.

[0060] As can be seen from Figure 8, in direct mode, the value (I dem ) because in direct mode, the inductance (L) starts transmitting energy from the very first moment, whereas in preload mode, the energy is stored until it reaches the optimum value and then suddenly discharged during X-ray exposure.

[0061] As in the preload mode, when the system controller decides to end the X-ray exposure, the five transistors (Q1, Q2, Q3, Q4, and Q5) are turned off simultaneously and instantaneously. At that moment, the current circulating toward the grid stops, and the X-ray exposure is immediately turned off. The energy stored in the inductance (L) is transferred to the power supply (V) through the diodes (D1) and (D2). sup ) is transmitted.

[0062] Also, as in the preload mode, the current (I FB The X-ray exposure can be stopped by turning on the four inverter bridge transistors (Q2, Q3, Q4, Q5) while maintaining control of the FET, which enters preload mode and allows a new exposure to be made at any time without delay.

[0063] Finally, Figure 9 shows the current (I FB ) shows a control circuit for the FET 100. This control circuit, as shown, includes a flip-flop (FF1), preferably a positive edge triggered D-type flip-flop (FF1), which activates its output (Q) to turn on Q1 when both of its inputs (AND1) are "1", i.e., when it receives a signal (Clock) requesting that a preload (PRE) be initiated.

[0064] Current (I FB ) is output to the comparator (COMP1) with the value (I dem ), the output of the comparator (COMP1) goes to "0", the output Q of (FF1) restarts, and the transistor (Q1) turns off until it turns on again in the next clock cycle (Clock).

[0065] It is worth noting that the grid current (IG) ripple, which depends on the amount of photons generated at the tube anode, i.e. the integral of the anode current over the exposure time (internationally known as mAs), is directly proportional to the anode current, but has no effect on dose control of X-ray exposure. In contrast, the VA-K voltage ripple is of great importance, as it generates photons of different energies, which has a very important direct effect on the emitted dose.

[0066] Having fully described the essence of the invention as well as the manner in which it can be carried out, it is noted that the invention may be carried out in other embodiments which differ in their essence from those shown by way of example in detail, and to which protection likewise applies, provided that its main principles are not altered, changed or modified.

Claims

1. An X-ray exposure control circuit using a grid current, It includes an anode (A) connected to a grounded power supply (VAK) or (VAK / 2) and a cathode (K) connected to ground; a grid (G) connected to a control circuit of a grid current (IG), said control circuit of said grid current (IG) comprising a DC-DC converter (CONV) or "step-down converter" to which a supply voltage (Vsup) is connected; an output of the DC-DC converter (CONV) connected to an inverter (INV), an output of the inverter (INV) connected to a transformer (TR), an output of the transformer (TR) connected to a rectifier (RECT), an output of the rectifier (RECT) connected to the grid (G) and grounded; The control circuit includes a control circuit (CONT), which outputs a current signal (I ＦＢ ), requested current signal (I ＤＥＭ ), a preload signal (PRE), and an exposure signal (EXP), and has as outputs a first signal (S1) to the DC-DC converter and a second signal (S2) to the inverter (INV).

2. 2. The grid current X-ray exposure control circuit of claim 1, wherein the DC-DC converter is formed by a diode (D1) and a coil (L), a capacitor (C) in parallel with a first switch (Q1), and a return diode (D2) in parallel with the assembly formed by the first switch (Q1) and the coil (L).

3. The inverter (INV) is formed by a bridge including a second switch (Q2), a third switch (Q3), a fourth switch (Q4) and a fifth switch (Q5), the second switch (Q2) and the fifth switch (Q5) are connected in series to form a first branch; The third switch (Q3) and the fourth switch (Q4) are connected in series to form a second branch, and the two branches are parallel to each other, and each branch is connected to a transformer (TR1) at its midpoint, and the output of the transformer (TR1) is connected to a rectifier bridge, from which the grid current (IG) is obtained, and the current signal (I ＦＢ 3. The X-ray exposure control circuit using grid current according to claim 1, wherein the power supply voltage Vcc is obtained from the lower ends of the branches of both the DC-DC converter and the inverter.

4. The control circuitry switches on five transistors (Q1, Q2, Q3, Q4 and Q5) in the first cycle, and the current (I ＦＢ 4. The grid current X-ray exposure control circuit of claim 3, which operates in a preload mode in which the rise of the grid current is limited by an inductance (L).

5. 4. The grid current X-ray exposure control circuit of claim 3, wherein the control circuit operates in a direct mode in which X-ray exposure begins immediately without waiting for the grid to have an optimal current intensity.

6. The current intensity (I ＦＢ The control circuit of the flip-flop (FF1), preferably of the D type, includes a flip-flop (FF1) triggered by a positive edge, which activates its output (Q) to turn on the flip-flop (FF1) when the inputs (AND1) of the gate are both "1", i.e., when the start of the preload (PRE) is requested and a (Clock) signal is received; The current intensity (I ＦＢ ) control circuit controls the required current (I ｄｅｍ ) and the reversed current (I ＦＢ ) as an input, and ＦＢ ) is output to the comparator (COMP1) as a value (I ｄｅｍ 6. An X-ray exposure control circuit using grid current according to claim 1, wherein when the grid current reaches a predetermined value, the output of the comparator (COMP1) becomes "0", the output Q of the (FF1) restarts, and the transistor (Q1) turns off until it turns on again in the next clock cycle (Clock).

7. 7. An X-ray exposure control circuit using a grid current according to claim 1, wherein the power supply is a monopolar power supply from the power supply (VAK), the anode (A) is connected to the power supply (VAK) which is grounded via a shunt for measuring an anode current IA, and the cathode (K) is also grounded.

8. 7. An X-ray exposure control circuit using a grid current according to claim 1, wherein the power supply is a bipolar power supply, the anode (A) is connected to the power supply (VAK / 2) that is grounded via a shunt for measuring an anode current (IA), and the cathode (K) is connected to the other power supply (VAK / 2) that is grounded.

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