JP2007207542A - X-ray irradiation device, and irradiation control method for x-ray diagnostic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology making an actual irradiation period conform with a set intended irradiation period on the basis of responding property of a driving system by grasping the responding property before starting radiographic irradiation. <P>SOLUTION: On the X-ray irradiation device provided with an X-ray tube and a driving means responding to a control signal and irradiating X-ray by driving tube voltage of the X-ray tube, a time measuring means receives the tube voltage or a tube current of the X-ray tube driven by the driving means, measures actual irradiation time by comparing the size of received signal with a reference value, and obtains responding period of rising time and falling time of the tube voltage driven by the driving means. A time correction means corrects the input intended irradiation period by the measured responding period, and transmits the control signal to the driving means so as to irradiate the X-ray during the corrected irradiation period. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an X-ray irradiation apparatus and an X-ray irradiation control method for imaging an X-ray image obtained by irradiating (exposing and radiating) X-rays to a subject and using the X-ray image obtained by imaging. In particular, the present invention relates to a technique for controlling the actual irradiation time to be the original desired irradiation time in consideration of the influence of the response time of the drive system including the X-ray tube on the irradiation time.

  The X-ray irradiation apparatus irradiates a subject with X-rays, detects transmitted X-rays from the subject with an X-ray detection unit, and based on the detected data, the image processing means determines the structure inside the subject. It has a configuration that can be visualized by a display means after being imaged. At that time, irradiation is performed so as to obtain a necessary X-ray image by reducing an unnecessary amount of X-ray irradiation as much as possible.

  However, in general, an X-ray irradiation apparatus is driven by heating a filament (cathode) of an X-ray tube with a filament power source and applying a high voltage between the anode and the filament (cathode) of the X-ray tube with a high voltage power source. ing. In supplying the high voltage, a high voltage cable is often used (Patent Document 1). For this reason, the drive system configured including the stray capacitance expected in the high-voltage cable, further the circuit configuration of the X-ray tube and the high-voltage power supply has response characteristics at the rise and fall, so the irradiation start signal or irradiation end signal When the X-ray tube is irradiated in response, the actual irradiation of the X-ray tube has passed a predetermined rise time or a predetermined fall time (hereinafter referred to as “response time” of the drive system). X-ray irradiation starts or ends.

  On the other hand, the irradiation time is preferably as short as possible in consideration of the exposure of the subject. However, the irradiation time is an appropriate time for imaging or observation (hereinafter collectively referred to as “imaging time”). There is a need to secure.

  In the above example, even if the desired irradiation time T is set, there is a deviation from the actual irradiation time due to the response time of the drive system as described above, and it is difficult to perform irradiation according to the set irradiation time. It was. For this reason, there has been a problem that it is not possible to ensure adequate time for imaging.

  Therefore, conventionally, the designer measured the amount of deviation between the desired irradiation time and the actual actual irradiation time under various irradiation conditions, and determined the correction value for each condition to perform irradiation. An appropriate imaging time is ensured.

JP 2001-46363 A

  However, it took a very long time to determine the correction value by measuring under various conditions. Further, although it was difficult to cope with variations in the X-ray irradiation apparatuses, fine adjustment was performed when necessary.

  In order to solve the above problem, the present invention knows the response characteristic of a drive system that drives an X-ray tube before the start of irradiation for imaging, and sets a desired irradiation time based on the response characteristic. The purpose is to provide a technique for combining the actual irradiation time with the actual irradiation time.

The invention described in claim 1 is an X-ray irradiation apparatus comprising: an X-ray tube; and a driving unit that drives a tube voltage of the X-ray tube in response to a control signal to irradiate the X-ray.
Operation means for inputting a desired irradiation time;
The response time of the rise and fall of the tube voltage by the pre-driving means is acquired, the input desired irradiation time is corrected by the response time, and the control signal for irradiating the corrected irradiation time is the driving unit. And a time correction means to be sent to.

  According to a second aspect of the present invention, in the first aspect of the present invention, the time correction unit receives a signal corresponding to a tube voltage or a tube current of the X-ray tube when driven by the driving means. A time measuring means for measuring and acquiring the actual irradiation time including the response time by comparing the magnitude of the received signal with a reference voltage, and correcting the desired irradiation time based on the measured actual irradiation time And correction means for sending the corrected irradiation time and a control signal for irradiation.

  According to a third aspect of the present invention, in the first aspect of the present invention, the time correction unit is an irradiation time based on response characteristics of the rise and fall of the tube voltage with respect to a change in irradiation conditions including a change in tube voltage. When a desired irradiation condition is input together with the storage means for storing a correction function and the desired irradiation time, the desired irradiation time is corrected and corrected by the desired irradiation condition and the irradiation time correction function. And correction means for sending the control signal to be irradiated for irradiation time.

  According to a fourth aspect of the present invention, in the first, second, or third aspect, a desired tube current value can be input, and the driving means detects and inputs the tube current of the X-ray tube. Tube current control means for calculating a difference from the desired tube current value and controlling the tube current of the X-ray tube so as to eliminate the difference.

The invention according to claim 5 is an input stage in which a desired irradiation time is input by an operating means;
A test irradiation stage in which X-ray irradiation is performed by driving a tube voltage of the X-ray tube to irradiate the driving means having an X-ray tube for the desired irradiation time;
When a signal corresponding to the tube voltage or tube current of the X-ray tube when driven by the driving means is received, the magnitude of the received signal is compared with a reference voltage, and the signal is driven by the driving means A time measurement stage for measuring the response time of the rise and fall of
An actual irradiation step of correcting the desired irradiation time based on the measured response time by a correcting unit, and sending the corrected irradiation time and a control signal for irradiation to the driving unit;

  According to the configuration of the present invention, the set desired irradiation time and the actual irradiation time can be matched. In particular, when intermittent irradiation is performed, irradiation can be performed with a planned irradiation time. Furthermore, an appropriate imaging time can be secured. In the invention of claim 2, since the irradiation time is corrected by measurement, irradiation can be performed for a desired irradiation time regardless of conditions such as tube voltage. In addition, since measurement is performed including variations, variations can be absorbed and corrected. In the invention of claim 3, since irradiation is performed based on the correction function stored in advance, irradiation can be performed immediately for a desired irradiation time.

  Embodiments of an X-ray irradiation apparatus and an irradiation control method thereof according to the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a functional configuration of the present embodiment. FIG. 2 is a diagram showing a modification of the time correction unit 20 in the embodiment of FIG. FIG. 3 is a diagram illustrating a functional configuration of another embodiment. FIG. 4 is a diagram showing a functional configuration of the driving means 40 in FIGS. 1 and 3. FIG. 5 is a diagram schematically illustrating the timing in the embodiment of FIG. FIG. 6 is a diagram for explaining correction in another embodiment of FIG.

  An embodiment will be described with reference to FIG. In FIG. 1, as described in the background art, an X-ray detection unit that detects transmitted X-rays, an image processing unit that generates image data for reconstruction as an image, and an image based on the image data are displayed. A display means for displaying is provided but omitted.

  In FIG. 1, a high voltage, for example, 75 KV, is applied to the X-ray tube 50 from the driving means 40 between the anode 51 and the filament 52 (cathode) through the high voltage cable 46.

  The driving means 40 receives a time control signal instructing to irradiate for a predetermined irradiation time, and turns on the switch Sp for the irradiation time to apply a high voltage to the X-ray tube 50. On the other hand, the driving means 40 receives a tube voltage raw control signal and a tube current control signal corresponding to the tube voltage and tube current desired by the operator, and applies them to the X-ray tube 50 along these control signals. Adjust the voltage and flowing tube current. The voltage dividing means 41 is a means for reducing the high voltage to a low voltage, for example, dividing it to m = 1/10 and taking it out for use in measuring the actual irradiation time by the time measuring means 21 described later. is there.

  A detailed example of the driving means 40 is shown in FIG. The high voltage power supply unit 42 generates a high voltage corresponding to the tube voltage control signal and applies it to the X-ray tube 50 at the timing of the time control signal. The tube current detecting means 43 detects a tube current flowing through the anode 51 when a high voltage is applied to the X-ray tube 50. The tube current control means 44 compares the detected tube current with a tube current control signal representing a desired tube current, so that a large filament current flows when the tube current is smaller than the tube current control signal. When it is larger than the tube current control signal, the filament power supply unit 45 is controlled so that a small filament current flows. The filament power supply unit 45 generates a pulse having a pulse width according to the control from the tube current control unit 44 by the pulse generation unit 45a, and controls the current of the filament 52 via the transformer 45b. The reason why the filament 52 is pulse-driven by the transformer 45b is to drive the filament 52 separately from the high voltage. As a result, the tube current control means 44 performs feedback control so that the tube current control signal matches the tube current.

  Returning to FIG. 1, the user interface 10 includes an operation unit 11 and a display unit 12, and a desired tube voltage, a desired tube current, and a desired irradiation time (including irradiation start time and irradiation end time). The input setting is enabled.

  The tube voltage information and the tube current information input by the operation unit 11 are sent to the drive unit 40 by the irradiation control unit 30 as a tube voltage control signal and a current sensitive control signal that interface with the drive unit 40. The desired irradiation time information input by the operation unit 11 is sent to the time correction unit 20 in FIG. 1 and to the time correction unit 70 via the time control signal generation unit 60 in FIG. Are corrected (1)], [irradiation time correction (2)] or [irradiation time correction (3)].

[Correction of irradiation time (1)]
In the example of FIG. 1, a time control signal corresponding to the irradiation time information set by the operation unit 11 is generated and the driving unit 40 is driven to measure the actual irradiation time by trial irradiation, and the measured actual irradiation. By correcting the irradiation time information set based on the time and irradiating with the irradiation time corrected from the next actual irradiation, the problem of the response time of the driving means 40 is cleared and desired irradiation time = actual irradiation time It is to make. A description will be given based on the timing waveforms of FIG. 1 and FIG.

  (A) When the irradiation time information is set by the operation means 11, the correction means 22 passes as it is, and the time control signal generation means 60 is used for the first irradiation (for measurement shown in FIG. 5A). A time control signal based on the set irradiation time information is generated, and the driving means 40 is operated based on the time control signal. Irradiation conditions such as tube voltage when operating the driving means 40 are performed based on the conditions during main irradiation.

(B) The reference voltage generating means generates the following reference voltage from the desired tube voltage information E.
Reference voltage = n × m × E
However, n: If the ratio of the set tube voltage to the reference voltage is 0.5 <n <1, that is, within (1-n)% of the set tube voltage E, it is determined as the actual irradiation voltage. It is a thing. n is a predetermined value.
m: Voltage division ratio of the voltage dividing means 41 In the following description, the coefficient p = n × m will be described.
Therefore, the reference voltage is described as p × E.

(C) The actual irradiation time is measured by the time measuring means 21.
The counter 21d and the counter 21e are counters (or timers) that count time at the rising edge of the input pulse. In either case, the count starts at the rise of the first time control signal. The comparison means 21b and the comparison means 21c both receive the reference voltage from the reference voltage generator 21a and the tube voltage detection signal from the voltage dividing means 41, and compare their magnitudes. The comparison means 21b generates a pulse that rises when the tube voltage detection signal becomes larger than the reference voltage (at Δt1 in FIG. 5), and stops the count value of the counter 21d at Δt1. When the reference voltage becomes smaller than the tube voltage detection signal (when [T + Δt2] in FIG. 5), the comparison means 21c generates a rising pulse and stops the count value of the counter 21e at [T + Δt2]. Thus, the counter 21d and the counter 21e measure the actual irradiation time affected by the response time (response characteristic) of the rise or fall by the driving unit 40. The actual irradiation time is indicated by [T−Δt1 + Δt2] as shown in FIG.

  (D) The correction means 22 receives the response time elements of the drive means 40 received from the counter 21d and the counter 21e, that is, Δt1 (rising response time) and T + Δt2 (Δt2 is the falling response time) shown in FIG. The desired irradiation time information T initially set by the operating means 11 is corrected to irradiation time information [T + Δt1−Δt2] and output.

  (E) Based on the corrected irradiation time information [T + Δt1−Δt2], the time control signal generation means 60 generates a time control signal for the second irradiation (main irradiation) as shown in FIG. It is sent to the means 40 for irradiation. Other conditions at the time of irradiation, such as conditions such as tube voltage, are the same as those at the time of test irradiation. In particular, if the tube voltage changes, the response time may also change.

  (F) Next, the tube voltage detection signal after correction shown in FIG. 5B is observed, and the actual irradiation time is equal to the initially set desired irradiation time. In actual irradiation after the second time excluding the first trial irradiation, the actual irradiation time is not measured by the time measuring means 21. The actual irradiation time is measured and corrected by the time measuring means 21 when a new desired irradiation time is set or changed again.

  As a numerical example, if the desired irradiation time T = 100 ms and Δt1 = 1 ms and T + Δt2 = 110 ms are measured, the actual irradiation time at this time is [T−Δt1 + Δt2] = 109 ms. Therefore, if the desired irradiation time T is then corrected to [T + Δt1−Δt2] = 91 ms and actual irradiation is performed, the actual irradiation time T = 100 ms is obtained as a result.

[Correction of irradiation time (2)]
FIG. 2 shows the second correction unit 22 after the time control signal generating unit 60 generates the first irradiation time control signal waveform of FIG. 5A based on the irradiation time information set from the operation unit 11. It is an example which correct | amends to the time control signal waveform of the 2nd irradiation by the instruction | indication from. This is substantially the same as changing the desired irradiation time input to the time control signal generating means 60 to correct, and generating the time control signal after correction as in the correction of FIG.

[Correction of irradiation time (3)]
Another embodiment of correction will be described with reference to FIG. FIG. 3 shows a form in which the time control signal generator 60 generates a time control signal on the basis of the irradiation time information from the operation unit 11 and then corrects the correction by the corrector 72. The opposite form may be used as described. The form of FIG. 3 is different from the form of FIGS. 1 and 2 because the response time (characteristics) of the driving means 40 when the irradiation conditions such as the tube voltage are changed is obtained in advance and obtained. A correction function corresponding to the irradiation condition is stored based on the data, and the time control signal from the time control signal generation means 60 is corrected by the correction function, and is sent to the drive means 40 for control.

FIG. 6A shows a time control signal reflecting the irradiation time information and the tube voltage (the vertical axis is the tube voltage) set from the operation means 11. FIG. 6B shows an actual tube voltage waveform when irradiation is actually performed with the control signal of FIG. At this time, the rise time Δt1 and the fall time Δt2 change according to the tube voltage E. As described above, this change is caused when the response time is strongly influenced by the passive element such as the high voltage cable 46 or when the tube voltage E output from the high voltage power supply unit 42 is different. When not shown, it can be expressed as shown in the following equation.
Rising characteristics: Er = Fr (E, t)
Falling characteristics: Ed = −Qd (E, t−T) + E,
Where E is the desired tube voltage and t-T is positive.
Here, Er = Ed = p × E, where p × E is a reference voltage and p is a coefficient, the above-described rising characteristics are expressed by the following equations.
(Formula 1) Fr (E, tp) / E = p,
(Formula 2) Qd (E, tp−T) / E = 1−p
When the coefficient p is fixed, the rising function Fr (E, tp) and the falling function Qd (E, tp−T) are proportional to the desired tube voltage E.

  Therefore, for each coefficient p (or n), the rising function Fr (E, tp), the falling function Qd (E, tp−T), or an approximate function thereof is obtained by empirical investigation and used as a correction function. When the tube voltage E and the coefficient p are specified, the calculation is performed by calculating the values tp and tp-T by substituting them into the above-described equations 1 and 2, and corresponding to the desired tube voltage E. Response times Δt1 and Δt2 can be obtained.

  The correction function storage unit 74 in FIG. 3 stores correction functions such as the above-described formulas 1 and 2 as the correction function, and the correction value calculation unit 73 sets the desired function set from the operation unit 11. In response to the tube voltage E and the desired irradiation time T, the coefficient p (or n) for determining the reference voltage in the correction function stored in the correction function storage means 74, the desired tube voltage E, and the desired irradiation time T are obtained. By substituting, response times Δt1 and Δt2 are calculated. The correction value calculation means 73 can be constituted by a CPU.

  The correction unit 72 receives the response times Δt1 and Δt2, corrects the time control signal of the irradiation time T from the time control signal generation unit 60 to the time control signal of the irradiation time [T + Δt1−Δt2], and drives the driving unit 40. To drive. By doing so, the irradiation time of the actual tube voltage when driven by the time control signal of the irradiation time [T + Δt1−Δt2] becomes the desired tube voltage and the desired irradiation time T.

  In addition, in addition to conditions such as high voltage and reference voltage, if the correction function has an element that changes the response time continuously and changes along a certain function, the related function ( (Approximate function) may be stored and corrected.

  As a form for correcting the irradiation time in this way, there are mainly [Irradiation time correction (1)] and [Irradiation time correction (3)]. Since the correction is made based on the measured value, it is not necessary to make correction depending on the setting conditions such as the tube voltage, but it is necessary to perform a trial irradiation once for the measurement. However, the trial irradiation need not be irradiation of the subject. In the former case, the variation in the correction value for each X-ray irradiation apparatus is also absorbed by the correction value obtained by automatic measurement, and fine adjustment for that is unnecessary. On the other hand, in the latter case, it is necessary to prepare a function for estimating the response time in accordance with the conditions such as the tube voltage in advance. In the latter case, by preparing an average function of a variation range assumed for each X-ray irradiation apparatus as a correction function, it is possible to suppress variation in actual irradiation time within an allowable value.

  Since the correction due to the tube voltage response time by the driving means 41 is independent from the tube current control as described above, the correction according to the present invention is performed as shown in FIG. Even a drive system having

It is a figure which shows the function structure of this embodiment. It is a figure which shows the function structure of embodiment which deform | transformed the time correction | amendment part in embodiment of FIG. It is a figure which shows the function structure of other embodiment. FIG. 4 is a functional configuration diagram for explaining in detail the drive means of FIGS. 1 and 3. It is a figure for demonstrating the timing in embodiment of FIG. It is a figure for demonstrating the timing in embodiment of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 User interface 20 Time correction part 30 Irradiation control part 40 Driving means 50 X-ray tube 60 Time control signal generation means 70 Time correction part

Claims (5)

In an X-ray irradiation apparatus comprising: an X-ray tube; and a driving unit that drives a tube voltage of the X-ray tube in response to a control signal to irradiate X-rays.
Operation means for inputting a desired irradiation time;
The response time of the rise and fall of the tube voltage by the pre-driving means is acquired, the input desired irradiation time is corrected by the response time, and the control signal for irradiating the corrected irradiation time is the driving means. An X-ray irradiation apparatus comprising a time correction unit for sending to   The time correction unit receives a signal corresponding to the tube voltage or tube current of the X-ray tube when driven by the driving means, compares the received signal magnitude with a reference voltage, and compares the response time. Measuring means for measuring and acquiring the actual irradiation time, and correcting means for correcting the desired irradiation time based on the measured actual irradiation time and sending the corrected irradiation time and a control signal for irradiation. The X-ray irradiation apparatus according to claim 1, comprising:   The time correction unit includes storage means for storing an irradiation time correction function based on response characteristics of rise and fall of the tube voltage with respect to a change in irradiation condition including a change in tube voltage, and a desired irradiation together with the desired irradiation time. A correction unit that corrects the desired irradiation time according to the desired irradiation condition and the irradiation time correction function when a condition is input, and sends the control signal for irradiation with the corrected irradiation time; The X-ray irradiation apparatus according to claim 1, wherein the apparatus is an X-ray irradiation apparatus.   A desired tube current value can be input, and the driving means detects a tube current of the X-ray tube, calculates a difference from the input desired tube current value, and eliminates the difference. The X-ray irradiation apparatus according to claim 1, 2 or 3, further comprising tube current control means for controlling the tube current of the X-ray tube. An input stage in which a desired irradiation time is input by operating means;
A test irradiation stage in which X-ray irradiation is performed by driving a tube voltage of the X-ray tube to irradiate the driving means having an X-ray tube for the desired irradiation time;
When a signal corresponding to the tube voltage or tube current of the X-ray tube when driven by the driving means is received, the magnitude of the received signal is compared with a reference voltage, and the signal is driven by the driving means A time measurement stage for measuring the response time of the rise and fall of
An actual irradiation step of correcting the desired irradiation time based on the measured response time by a correction unit, and sending the corrected irradiation time and a control signal for irradiation to the driving unit; X-ray irradiation time control method.

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