JP4472818B2 - High pressure generator and X-ray imaging apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-voltage generator and an X-ray imaging apparatus, and more specifically, prevents an overshoot from occurring when a micro discharge occurs in an X-ray tube and the tube voltage drops to return to a steady voltage. The present invention relates to a high-voltage generator that can be used, an X-ray imaging apparatus that uses the high-voltage generator, and an X-ray imaging apparatus that can suppress deterioration in image quality when a minute discharge occurs.
[0002]
[Prior art]
FIG. 10 is a schematic block diagram of a high-pressure generator disclosed in Japanese Patent Application Laid-Open No. 11-283789.
The high voltage generator 500 includes a high voltage generator 11 that generates a high voltage Vo (for example, 1 kV) to be supplied to the X-ray tube XT, and a tube voltage that measures a tube voltage applied to the X-ray tube XT and outputs a measurement voltage Vm. A measurement unit 12 and a high voltage control unit 501 that sends a voltage control signal R to the high voltage generator 11 based on the measurement voltage Vm are provided.
[0003]
FIG. 11 is a graph showing the operation of the high-voltage generator 500 when a micro discharge occurs.
When a minute discharge occurs, the measurement voltage Vm drops rapidly from the steady voltage Vh, and is detected by the high voltage controller 501. The time to required for this detection is, for example, about several tens of μs.
Then, the high voltage controller 501 temporarily stops the high voltage generator 11 and starts to return to normal operation after a predetermined time t1 ′ (for example, 100 μs).
The measurement voltage Vm returns to the steady voltage Vh after the rising time t2 determined by the characteristics of the high voltage control unit 501, the high voltage generator 11, and the X-ray tube XT.
Here, the returning tube current is monitored, and if the tube current is larger than the reference, the high voltage control unit 501 temporarily stops the high voltage generator 11 again and returns to normal operation again after a predetermined time (for example, 1 ms). Let it begin. When this re-return operation is repeated a predetermined number of times, the high-pressure control unit 501 is stopped.
[0004]
[Problems to be solved by the invention]
In the conventional high-voltage generator 500, the steady voltage Vh may be smoothly restored as shown in FIG. 11, but an overshoot may occur as shown in FIG.
However, when an overshoot occurs, an excessive voltage is applied to the X-ray tube XT and the high voltage generator 11, which causes a problem that causes damage and shortens the service life.
Accordingly, a first object of the present invention is to use a high voltage generator capable of preventing the occurrence of overshoot when a micro discharge occurs and the tube voltage decreases to return to a steady voltage, and the high voltage generator. It is to provide an X-ray imaging apparatus.
[0005]
In addition, the conventional X-ray imaging apparatus has a problem in that the image quality deteriorates because data in a period from when the micro discharge occurs and the tube voltage decreases to when it returns to the steady voltage is lost.
Accordingly, a second object of the present invention is to provide an X-ray imaging apparatus capable of suppressing deterioration in image quality when a minute discharge occurs.
[0006]
[Means for Solving the Problems]
In a first aspect, the present invention detects high voltage generating means for generating a high voltage supplied to an X-ray tube, tube voltage measuring means for measuring a tube voltage applied to the X-ray tube, and a sudden drop in the tube voltage. Return delay means for temporarily stopping the high-voltage generating means or lowering the generated voltage and starting a return to normal operation after a return delay time of 300 μs or more from the detection, and determining whether the tube voltage after the return start after the return monitoring time is abnormal And a protective means for continuing the state in which the high voltage generating means is stopped or the generated voltage is lowered when it is lower than the threshold value for use.
In the high voltage generator according to the first aspect, when a sudden drop in the tube voltage is detected, the high voltage generator is temporarily stopped for a return delay time of 300 μs or longer, or the normal operation is performed after the voltage generated by the high voltage generator is temporarily reduced. Return to start. Conventionally, this return delay time is about 100 μs, and since there was little time for the X-ray tube to return to a stable state after a minute discharge occurred, overshoot may occur. Since the return delay time is set to 300 μs or more, there is sufficient time for the X-ray tube to return to a stable state after a minute discharge occurs, and the occurrence of overshoot can be prevented. Thus, it is possible to avoid the disadvantage that an excessive voltage is applied to the X-ray tube and the high voltage generating means.
Furthermore, if the tube voltage after the return monitoring time from the start of recovery is lower than the abnormality determination threshold, the high voltage generating means is stopped or the generated voltage is lowered, and the forced recovery is not performed. The generating means can be protected.
[0007]
In a second aspect, the present invention detects high voltage generating means for generating a high voltage supplied to the X-ray tube, tube voltage measuring means for measuring the tube voltage applied to the X-ray tube, and a sudden drop in the tube voltage. Return delay means for temporarily stopping the high-voltage generating means or lowering the generated voltage and starting a return to normal operation after a return delay time of 300 μs or more from the detection, and determining whether the tube voltage after the return start after the return monitoring time is abnormal A re-retry trial means for temporarily stopping the high-voltage generating means when it is lower than the threshold value, or temporarily reducing the generated voltage again and starting re-return to normal operation after the return re-delay time, and A protective means for stopping the high-voltage generating means when the number of re-restarting start times by the re-recovery trial means reaches the number of protection times or continuing the state in which the generated voltage is lowered. Providing high pressure apparatus according to symptoms.
In the high voltage generator according to the second aspect, when a sudden drop in the tube voltage is detected, the high voltage generator is temporarily stopped for a return delay time of 300 μs or longer, or the normal operation is performed after the voltage generated by the high voltage generator is temporarily reduced. Return to start. Conventionally, this return delay time is about 100 μs, and since there was little time for the X-ray tube to return to a stable state after a minute discharge occurred, overshoot may occur. Since the return delay time is set to 300 μs or more, there is sufficient time for the X-ray tube to return to a stable state after a minute discharge occurs, and the occurrence of overshoot can be prevented. Thus, it is possible to avoid the disadvantage that an excessive voltage is applied to the X-ray tube and the high voltage generating means.
In addition, when the tube voltage after the return monitoring time from the start of recovery is lower than the abnormality determination threshold, the high voltage generating means is stopped or the generated voltage is lowered and the forced recovery is not performed. The generating means can be protected.
Furthermore, even if the recovery fails, the recovery is attempted again, so that even if a micro discharge having a relatively long discharge time occurs, it is possible to return to a steady voltage.
[0008]
In a third aspect, the present invention provides a high-pressure generator having the above-described configuration, wherein the high-pressure generator includes an abnormality notification means for notifying abnormality when the protection means is activated.
In the high pressure generator according to the third aspect, the abnormality is notified when the protection means is operated, so that the operator can quickly cope with the abnormality.
[0009]
In a fourth aspect, the present invention provides an X-ray imaging apparatus comprising the high-pressure generator configured as described above.
Since the X-ray imaging apparatus according to the fourth aspect includes the high-voltage generator, it is possible to avoid the disadvantage that an excessive voltage is applied to the X-ray tube and the high-voltage generator. In addition, since it is possible to suitably recover from a decrease in tube voltage due to minute discharge, data loss can be suppressed.
[0010]
In a fifth aspect, the present invention provides an X-ray imaging apparatus comprising the high voltage generator configured as described above for each of a positive voltage and a negative voltage.
The X-ray imaging apparatus according to the fifth aspect can avoid the disadvantage that an excessive voltage is applied to the X-ray tube and the high voltage generating means for each of the positive voltage high voltage generator and the negative voltage high voltage generator. In addition, since it is possible to suitably recover from a decrease in tube voltage due to minute discharge, data loss can be suppressed.
[0011]
In a sixth aspect, the present invention detects high voltage generating means for generating a high voltage supplied to an X-ray tube, tube voltage measuring means for measuring a tube voltage applied to the X-ray tube, and a sudden drop in the tube voltage. The high-voltage generating means is temporarily stopped or the generated voltage is temporarily reduced, and the return delay means for starting the return to the normal operation after the return delay time from the detection. The high voltage generating means is stopped or the generated voltage is lowered when the voltage is lower, and the tube voltage applied to the X-ray tube suddenly drops during data acquisition and then returns to the original high voltage. There is provided an X-ray imaging apparatus characterized by comprising interpolation means for interpolating missing data that could not be acquired before and after using data acquired before and after that.
In the X-ray imaging apparatus according to the sixth aspect, when a sudden drop in tube voltage is detected, the high voltage generating means is temporarily stopped for the return delay time or the generated voltage of the high voltage generating means is temporarily reduced and then returned to normal operation. However, if the tube voltage after the return monitoring time after the start of recovery is lower than the abnormality determination threshold, the high voltage generating means is stopped or the generated voltage is lowered, and the forced recovery is not performed. And high pressure generating means can be protected. In addition, since the missing data that cannot be acquired during the period from when the tube voltage suddenly drops to when the voltage returns to the original high voltage is interpolated, it is possible to minimize deterioration in image quality.
[0012]
Examples of the X-ray imaging apparatus according to the fourth to sixth aspects include an X-ray CT apparatus and an X-ray line sensor TV.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to embodiments shown in the drawings. Note that the present invention is not limited thereby.
[0014]
-First embodiment-
FIG. 1 is a block diagram of an X-ray CT (Computed Tomograhy) apparatus 1000 according to the first embodiment of the present invention.
The X-ray CT apparatus 1000 includes an operation console 20, an imaging table 30, and a scanning gantry 40.
The operation console 20 includes an input device 22 that accepts an operator's instruction input and information input, a central processing unit 23 that performs control to perform imaging processing and interpolation processing by helical scan, and a control signal and the like. 30, a control interface 24 that communicates with the scanning gantry 40, a data collection buffer 25 that collects data acquired by the scanning gantry 40, a CRT 26 that displays an X-ray image reconstructed from the data, and a program And a storage device 27 for storing data.
The imaging table 30 carries the subject and moves it in the body axis direction.
The scanning gantry 40 rotates the X-ray tube XT, the high-pressure generator 100 according to the present invention, the detector array 47, the data collection unit 48, and the X-ray tube XT around the body axis of the subject. And a rotation controller 49.
[0015]
FIG. 2 is a block diagram of the high pressure generator 100.
The high voltage generator 100 includes a high voltage generator 11 that generates a high voltage Vo (for example, 1 kV) to be supplied to the X-ray tube XT, and a tube voltage that measures a tube voltage applied to the X-ray tube XT and outputs a measurement voltage Vm. A voltage control signal R corresponding to the measurement voltage Vm is sent to the measurement unit 12, a microcomputer 13 that detects a sudden drop in the measurement voltage Vm, and the voltage level of the high voltage Vo is set to the high voltage generator 11. And a high voltage control unit 101 for sending a voltage drop signal Rlow for reduction.
The high voltage control unit 101 includes a regulator circuit 14 that outputs a voltage control signal R based on a difference between the measurement voltage Vm and a reference voltage Vref, and a switch 15 that selectively outputs the voltage control signal R or the voltage drop signal Rlow. It has. The selection state of the switch 15 is switched by a switching signal S from the microcomputer 13. Note that, instead of selecting the voltage drop signal Rlow, the high voltage generator 11 may be stopped.
[0016]
FIG. 3 is a flowchart showing a high pressure control process by the high pressure generator 100.
The high-voltage control process is started when the microcomputer 13 detects a minute discharge (for example, a phenomenon in which the measured voltage Vm decreases to 10% or less of the reference voltage Vref during a period of 1 μs). In the initial state, the switch 15 is in a state of selectively outputting the voltage control signal R.
[0017]
In step ST1, the repetition number n is initialized to “1”.
In step ST2, the switch 15 is switched to the selected output state of the voltage drop signal Rlow for a return delay time t1 of about 300 μs to 1 ms.
In step ST3, the switch 15 is returned to the selection output state of the voltage control signal R.
[0018]
In step ST4, the process waits until the return monitoring time t3 elapses, and then proceeds to step ST5. The return monitoring time t3 is longer than the time required for the measurement voltage Vm to rise to 90% or more of the reference voltage Vref when the X-ray tube XT is normal.
In step ST5, the tube voltage measuring unit 12 measures the tube voltage.
In step ST6, it is determined whether or not the measured voltage Vm is 90% or more of the reference voltage Vref. If the measured voltage Vm is 90% or more of the reference voltage Vref, the high voltage control process is terminated (in this case, a stable high voltage is supplied to the X-ray tube XT). If the measured voltage Vm is not 90% or more of the reference voltage Vref, the process proceeds to step ST7.
[0019]
In step ST7, it is determined whether the number of repetitions n is “3” or more. If the repetition number n is smaller than “3”, the process proceeds to step ST8, and if the repetition number n is “3” or more, the process proceeds to step ST9.
[0020]
In step ST8, the repetition number n is incremented by “1”. Thereafter, the process returns to step ST2.
[0021]
In step ST9, it is determined that an abnormality (such as an abnormal short circuit) other than a minute discharge has occurred, and the switch 15 is switched to the selected output state of the voltage drop signal Rlow. Thereby, damage to X-ray tube XT and the high voltage | pressure generator 11 can be prevented.
In step ST10, the occurrence of abnormality is notified. For example, an alarm sound is emitted, a warning lamp is turned on, or a warning message is displayed on the CRT 26. Thereafter, the high pressure control process is terminated.
[0022]
4 to 6 are graphs showing changes in the measured voltage Vm when the high voltage control process of FIG. 3 is performed.
FIG. 4 shows a case where the measurement voltage Vm rises to the steady voltage Vh at the stage where the number of repetitions n = 1 when a micro discharge with a short discharge time (for example, a micro discharge between the anode and the cathode) occurs. That is, at the time of the first step ST6 in FIG. 3, the measured voltage Vm is determined to be 90% or more of the reference voltage Vref (abnormality determination threshold value Vt), so that the switch 15 is set to the selected output state of the voltage control signal R. A stable steady voltage Vh is obtained after a predetermined time t2 (for example, 1 ms to 5 ms) after returning.
Thus, since the return delay time t1 is 300 μs or more, there is a sufficient time margin from the occurrence of the minute discharge until the X-ray tube XT returns to a stable state, and the occurrence of overshoot can be prevented. Thus, it is possible to avoid the disadvantage that an excessive voltage is applied to the X-ray tube and the high voltage generating means.
[0023]
FIG. 5 shows that the measurement voltage Vm rises to the steady voltage Vh when the number of repetitions n = 2 due to the occurrence of a minute discharge with a long discharge time (for example, a minute discharge between the anode and the ground or between the cathode and the ground). Show the case. That is, it is determined that the measured voltage Vm is not greater than or equal to the abnormality determination threshold Vt at the time of the first step ST6 in FIG. 3, and the measured voltage Vm is determined to be greater than or equal to the abnormality determination threshold Vt at the second time of step ST6. Thereafter, the measurement voltage Vm becomes a stable steady voltage Vh.
As described above, even if the initial restoration fails, the restoration is resumed. Therefore, even when a micro discharge having a relatively long discharge time occurs, it is possible to restore the steady voltage.
[0024]
FIG. 6 shows a case where an abnormal short circuit or the like that is not a minute discharge occurs and the abnormal termination occurs at the stage where the number of repetitions n = 3. That is, it is determined that the measured voltage Vm is not equal to or higher than the abnormality determination threshold Vt at the time of the first, second, and third step ST6 in FIG. 3, and the switch 15 is switched to the selected output state of the voltage drop signal Rlow in step ST9. It ends in the state. Thereafter, the state where a low voltage is supplied to the X-ray tube XT continues, and an abnormality is notified.
In this way, the voltage generated by the high voltage generator 11 is reduced (or the high voltage generator 11 is stopped), and the forced recovery is not performed, so that the X-ray tube XT and the high voltage generator 11 can be protected.
In addition, since the abnormality is notified, the operator can quickly cope with the abnormality.
[0025]
FIG. 7 is a flowchart showing CT image display processing by the X-ray CT apparatus 1000.
In step SU1, data of the number of views capable of reconstructing one CT image is acquired while rotating the X-ray tube XT around the subject (CT scan), or the X-ray tube XT is not rotated. The number of data that can generate one scout image that covers a necessary range while moving in the body axis direction of the subject is acquired (scout scan).
In step SU2, it is determined whether or not there is a period during which data acquisition is interrupted (a period from when the tube voltage suddenly drops until a stable high voltage is supplied to the X-ray tube XT). If there is a period in which data acquisition is interrupted, the process proceeds to step SU3, and if there is no period in which data acquisition is interrupted, the process proceeds to step SU4.
[0026]
In step SU3, as shown in FIG. 8, using the data D (i) ⁻ and D (i) ⁺ for each detector channel number i acquired before and after the period when the data acquisition is interrupted, the missing raw data D (I) 'is interpolated.
[0027]
In step SU4, a CT image or a scout image is generated from the acquired data or the interpolated data.
In step SU5, the generated CT image or scout image is displayed on the CRT 26.
[0028]
According to the X-ray CT apparatus 1000 described above, since an image is generated by interpolating missing data that could not be acquired due to the occurrence of minute discharge, image quality deterioration can be suppressed.
[0029]
In the first embodiment, the return delay time t1 when n = 1 is applied as the return delay time when n = 2, 3. However, the return delay time may vary depending on the value of n. .
[0030]
-Second Embodiment-
FIG. 9 is a principal block diagram of an X-ray CT apparatus 2000 according to the second embodiment of the present invention.
The X-ray Ct device 2000 includes a positive high pressure generator 200-1 that supplies a positive high voltage + Vo (for example, + 500V) to the anode of the X-ray tube XT ', and a negative high pressure -Vo to the cathode of the X-ray tube XT'. A negative high pressure generator 200-2 for supplying (for example, -500V).
[0031]
The positive high voltage generator 200-1 includes a positive high voltage generator 11-1 that generates the positive high voltage + Vo, and a tube that measures a positive tube voltage applied to the X-ray tube XT 'and outputs a measured voltage + Vm. A voltage control unit 12-1, a microcomputer 13-1 that detects a sudden drop in the measured voltage + Vm, and a voltage control signal + R corresponding to the measured voltage + Vm are sent to the positive and high voltage generator 11-1, or the high voltage + Vo And a positive and high voltage control section 201-1 for sending a voltage drop signal Rlow for lowering the voltage level of the power supply. The positive and high voltage controller 201-1 selects and outputs the voltage control signal + R or the voltage drop signal Rlow, and a regulator circuit 14-1 that outputs a voltage control signal + R based on the difference between the measured voltage + Vm and a reference voltage + Vref. And a switch 15-1. The selection state of the switch 15-1 is switched by a switching signal S1 from the microcomputer 13-1.
The operation of the microcomputer 13-1 is the same as that in the first embodiment.
[0032]
The negative high voltage generator 200-2 measures the negative tube voltage applied to the negative high voltage generator 11-2 for generating the negative high voltage -Vo and the X-ray tube XT 'and outputs the measured voltage -Vm. A voltage control signal -R corresponding to the measured voltage -Vm to the tube voltage measuring unit 12-2, the microcomputer 13-2 that detects a sudden rise in the measured voltage -Vm, and the negative high voltage generator 11-2 Or a negative high voltage control unit 201-2 for sending a voltage increase signal Rhigh for increasing the voltage level of the high voltage -Vo.
The negative high voltage control unit 201-2 includes a regulator circuit 14-2 that outputs a voltage control signal -R based on a difference between the measurement voltage -Vm and a reference voltage -Vref, and the voltage control signal -R or the voltage increase signal. And a switch 15-2 for selectively outputting Rhigh. The selection state of the switch 15-2 is switched by a switching signal S2 from the microcomputer 13-2.
The operation of the microcomputer 13-2 is the same as that of the first embodiment.
[0033]
According to the X-ray CT apparatus 2000 described above, the occurrence of overshoot can be prevented in both the positive and high pressure generators 200-1 and 200-2.
[0034]
【The invention's effect】
According to the high voltage generator and the X-ray imaging apparatus of the present invention, when a micro discharge occurs, the generation of the high voltage is stopped for the return delay time of 300 μs or more, or the voltage level is lowered and then returned to the normal high voltage. Therefore, the X-ray tube becomes stable during that time, and overshooting can be prevented. Therefore, damage to the X-ray tube and the high pressure generating means can be avoided and the life can be extended.
[0035]
In addition, according to the X-ray imaging apparatus of the present invention, an image is generated by interpolating missing data that could not be acquired between the occurrence of a minute discharge and the return to the normal high voltage. Even in such a case, a high-quality image can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram of an X-ray CT apparatus according to a first embodiment of the present invention.
FIG. 2 is a block diagram of a high pressure generator in the X-ray CT apparatus of FIG.
FIG. 3 is a flowchart showing high-pressure control processing by the high-pressure generator in FIG. 2;
4 is a graph showing changes in measured voltage when the high voltage control process of FIG. 3 is performed. FIG.
FIG. 5 is another graph showing a change in measured voltage when the high voltage control process of FIG. 3 is performed.
6 is another graph showing a change in measured voltage when the high voltage control process of FIG. 3 is performed. FIG.
7 is a flowchart showing image generation / display processing by the X-ray CT apparatus of FIG. 1; FIG.
FIG. 8 is an explanatory diagram illustrating an example of interpolation processing in the image generation / display processing of FIG. 7;
FIG. 9 is a principal block diagram of an X-ray CT apparatus according to a second embodiment of the present invention.
FIG. 10 is a block diagram of an example of a conventional high pressure generator.
11 is a graph showing the operation of the high-voltage generator of FIG. 10 when a minute discharge occurs.
FIG. 12 is a graph showing a change in measured voltage when an overshoot occurs.
[Explanation of symbols]
11, 11-1, 11-2 High voltage generator 12, 12-1, 12-2 Tube voltage measuring unit 13, 13-1, 13-2 Microcomputer 14, 14-1, 14-2 Regulator circuit 15, 15- DESCRIPTION OF SYMBOLS 1,15-2 Switch 100,200 High voltage generator 101 High voltage controller 200-1 Positive high voltage generator 200-2 Negative high voltage generator 201-1 Positive high voltage controller 201-2 Negative high voltage controller 1000,2000 X-ray CT Equipment XT, XT 'X-ray tube

Claims (6)

A high voltage generating means for generating a high voltage to be supplied to the X-ray tube, a tube voltage measuring means for measuring a tube voltage applied to the X-ray tube, and the high voltage generating means is temporarily stopped when a sudden drop in the tube voltage is detected, or A return delay means for temporarily reducing the generated voltage and starting a return to normal operation after a return delay time of 300 μs or more from the detection, and generating a high voltage when the tube voltage after the return start time after the return start is lower than an abnormality determination threshold. A high-voltage generator characterized by comprising protection means for continuing the state in which the means is stopped or the generated voltage is lowered. A high voltage generating means for generating a high voltage to be supplied to the X-ray tube, a tube voltage measuring means for measuring a tube voltage applied to the X-ray tube, and the high voltage generating means is temporarily stopped when a sudden drop in the tube voltage is detected, or A return delay means for temporarily reducing the generated voltage and starting a return to normal operation after a return delay time of 300 μs or more from the detection, and generating a high voltage when the tube voltage after the return start time after the return start is lower than an abnormality determination threshold. Re-restart trial means for temporarily stopping the means again or reducing the generated voltage again and starting re-return to normal operation after the return re-delay time, and the number of re-restart starts by the re-retry trial means The high-voltage generator is provided with a protection unit that stops the high-voltage generation unit when the number of protections reaches the number of protections or continues the state in which the generated voltage is lowered. 3. The high pressure generator according to claim 1, further comprising an abnormality notifying unit for notifying an abnormality when the protection unit is activated. An X-ray imaging apparatus comprising the high-pressure generator according to any one of claims 1 to 3. An X-ray imaging apparatus comprising the high-voltage generator according to claim 1 for each of a positive voltage and a negative voltage. A high voltage generating means for generating a high voltage to be supplied to the X-ray tube, a tube voltage measuring means for measuring a tube voltage applied to the X-ray tube, and the high voltage generating means is temporarily stopped when a sudden drop in the tube voltage is detected, or A return delay means for temporarily lowering the generated voltage and starting return to normal operation after the return delay time from the detection, and stopping the high voltage generating means when the tube voltage after the return monitoring time after the return start is lower than the abnormality determination threshold Protection means that keeps the state in which the generated voltage is reduced, or missing data that could not be acquired between the time when the tube voltage applied to the X-ray tube suddenly drops during data acquisition and the return to the original high voltage Interpolating means for interpolating using the data acquired before and after the X-ray imaging apparatus.

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