JP2014059972A - X-ray ct device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray CT device capable of applying a plurality of kinds of tube voltages having high accuracy and reproducibility to an X-ray tube even when a tube voltage which serves as a base is controlled.SOLUTION: An X-ray CT device comprises a power supply unit, a first and a second inverter, a first and a second transformer, a first and a second rectifier, an X-ray tube, a first and a second divider, and a first and a second inverter control unit. The first inverter converts a DC voltage from the power supply unit to a first AC voltage. The second inverter converts a DC voltage from the power supply unit to a second AC voltage. The first AC voltage is converted to a first DC high voltage by the first transformer and the first rectifier. The second AC voltage is converted to a second DC high voltage by the second transformer and the second rectifier. The first inverter control unit controls the first inverter on the basis of the first divided voltage divided by the first divider. The second inverter control unit controls the second inverter on the basis of the first divided voltage and the second divided voltage divided by the second divider.

Description

  Embodiments described herein relate generally to an X-ray computed tomography apparatus (X-ray CT apparatus).

  For example, in an X-ray CT apparatus, there is a technique called dual energy imaging in which a plurality of output voltages are switched and a subject is diagnosed using a difference in energy characteristics of X-rays generated by the output voltages. In a conventional X-ray CT apparatus capable of performing this dual energy imaging, the high voltage generator switches, for example, two types of high and low tube voltages at high speed and applies them to the X-ray tube, respectively. The X-ray tube emits X-rays generated by the applied tube voltage to the subject while rotating around the subject.

  In a conventional high voltage generator, there is a method using a plurality of high voltage transformers and a plurality of inverters as a method of switching the tube voltage at high speed. The high-voltage generator is generated by the first inverter and the first high-voltage transformer, and is generated by other inverters and other high-voltage transformers with respect to the first tube voltage serving as the reference tube voltage. A plurality of types of tube voltages are generated by synthesizing the high voltages. At this time, the high-voltage generator switches and generates a plurality of types of tube voltages at high speed by switching addition of other high voltages to the first tube voltage at high speed. Moreover, the conventional high voltage generator shares and detects the tube voltage applied to an X-ray tube by a divider. Then, the high voltage generator stably applies a plurality of types of tube voltages by applying feedback control to the first tube voltage and other high voltage values based on the detected tube voltage values. The voltage is applied to the X-ray tube. By the way, when trying to control the first tube voltage in order to reduce the exposure, it is difficult to appropriately control the generation of the high voltage by the high-voltage transformer by the method of detecting the tube voltage by dividing it by the divider. It was.

  As described above, the conventional X-ray CT apparatus has a problem that it is difficult to appropriately control generation of a high voltage by a high-voltage transformer when attempting to control a tube voltage as a base. In particular, in the dual energy imaging method, it is required to apply two types of tube voltages that determine X-ray quality to the X-ray tube with high accuracy and reproducibility.

  Accordingly, the object is to provide an X-ray apparatus having a high voltage generator capable of applying a plurality of types of tube voltages having high accuracy and reproducibility to an X-ray tube even when controlling the tube voltage as a base. The object is to provide a line CT apparatus.

  According to the embodiment, the X-ray CT apparatus includes a power supply unit, first and second inverters, first and second transformers, first and second rectifiers, an X-ray tube, first and second A divider and first and second inverter control units are provided. The first inverter converts a DC voltage supplied from the power supply unit into a first AC voltage. The first transformer boosts the first AC voltage to a first AC high voltage. The first rectifier converts the first AC high voltage into a first DC high voltage. The second inverter converts a DC voltage supplied from the power supply unit into a second AC voltage. The second transformer boosts the second AC voltage to a second AC high voltage. The second rectifier converts the second AC high voltage into a second DC high voltage. The X-ray tube irradiates the subject with X-rays using a tube voltage in which the second DC high voltage is added to the first DC high voltage. The first divider divides the first divided voltage from the first DC high voltage. The first inverter control unit controls a voltage value of the first AC voltage with respect to the first inverter based on the first divided voltage. The second divider divides the second divided voltage from the tube voltage. The second inverter control unit controls a voltage value of the second AC voltage with respect to the second inverter based on a differential voltage between the second divided voltage and the first divided voltage. To do.

It is a block diagram which shows the function structure of the X-ray CT apparatus which concerns on this embodiment. It is a block diagram which shows the function structure of the high voltage generator shown in FIG. FIG. 3 is a schematic diagram illustrating a configuration example of a first divider illustrated in FIG. 2.

  Hereinafter, embodiments will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a functional configuration of an X-ray CT apparatus 10 according to the present embodiment. An X-ray CT apparatus 10 illustrated in FIG. 1 includes a gantry 11 and an information processing unit 12.

  The gantry 11 is configured to collect projection data related to the subject P. The gantry 11 includes a slip ring 111, a gantry driving unit 112, an X-ray tube device 113, an X-ray detector 115, a rotating frame 116, a data collection unit 117, a non-contact data transmission device 118, and a high voltage generator 119.

  The information processing unit 12 generates an X-ray CT image and various types of clinical information using the control of the data collection operation in the gantry 11 and performing predetermined processing on the data collected in the gantry 11. The information processing unit 12 includes a preprocessing unit 122, a memory unit 123, a reconstruction unit 124, an image processing unit 125, a storage unit 126, a control unit 128, a display unit 129, an input unit 1210, a transmission / reception unit 1211, and an X-ray control unit 1212. And a scan plan setting unit 1213.

  The gantry driving unit 112 drives the rotary frame 116 to rotate. By this rotational drive, the X-ray tube device 113 and the X-ray detector 115 are rotated in a spiral manner around the body axis of the subject P while facing each other.

  The X-ray tube device 113 is a vacuum tube that generates X-rays, and is provided on the rotating frame 116. The X-ray tube device 113 is supplied with power (tube current, tube voltage) necessary for X-ray exposure from the high voltage generator 119.

  FIG. 2 is a block diagram showing a functional configuration of the high voltage generator 119 according to the present embodiment. The high voltage generator 119 shown in FIG. 2 includes a power supply unit 21, a first inverter 22, a second inverter 23, a first high voltage transformer unit 24, a second high voltage transformer unit 25, a first divider 26, 2 dividers 27, a first inverter control unit 28 and a second inverter control unit 29.

  The power supply unit 21 supplies DC power (DC current, DC voltage) to the first and second inverters 22 and 23.

  The first inverter 22 converts the DC voltage supplied from the power supply unit 21 into a first AC voltage having a voltage value and frequency according to the control from the first inverter control unit 28. That is, the voltage value of the first AC voltage is changed by the control from the first inverter control unit 28. The first inverter 22 outputs the first AC voltage to the first high-voltage transformer unit 24.

  For example, when the first inverter 22 converts the DC voltage into the first AC voltage by performing pulse width modulation (PWM) on the DC voltage, the first inverter 22 In accordance with the control from the inverter control unit 28, a switch provided in the apparatus is turned on / off, and a pulse signal is generated using the supplied DC voltage. The first inverter 22 changes the “duty ratio” represented by the pulse generation interval / pulse period by turning on / off the switch. The first inverter 22 generates a first AC voltage having a frequency and a voltage value corresponding to the duty ratio of the generated pulse signal.

  The second inverter 23 converts the DC voltage supplied from the power supply unit 21 into a second AC voltage having a voltage value and frequency according to the control from the second inverter control unit 29. That is, the voltage value of the second AC voltage is changed by the control from the second inverter control unit 29. The second inverter 23 outputs the second AC voltage to the second high-voltage transformer unit 25.

  The first high-voltage transformer unit 24 includes a transformer 241 and a rectifier 242.

  The transformer 241 boosts the first AC voltage supplied from the first inverter 22 and converts it to a first AC high voltage. The transformer 241 outputs the converted first AC high voltage to the rectifier 242. The rectifier 242 converts the first AC high voltage supplied from the transformer 241 into the first DC high voltage. The rectifier 242 outputs the converted first DC high voltage to the second high-voltage transformer unit 25.

  The second high voltage transformer unit 25 includes a transformer 251 and a rectifier 252.

  The transformer 251 boosts the second AC voltage supplied from the second inverter 23 and converts it to a second AC high voltage. The transformer 251 outputs the converted second AC high voltage to the rectifier 252. The rectifier 252 converts the second AC high voltage supplied from the transformer 251 into a second DC high voltage. The second high voltage transformer unit 25 applies the first DC high voltage supplied from the first high voltage transformer unit 24 to the X-ray tube 113 as the first tube voltage in accordance with the switching control from the control unit 128. Alternatively, the second DC high voltage converted by the rectifier 252 is combined with the first DC high voltage and switched to be applied to the X-ray tube device 113 as the second tube voltage. As described above, the first or second tube voltage is applied to the X-ray tube device 113.

  The first divider 26 is installed between the output terminal of the first high-voltage transformer unit 24 and the ground, and divides the first DC high voltage output from the first high-voltage transformer unit 24. The first divider 26 outputs the first divided voltage divided from the first DC high voltage to the first and second inverter control units 28 and 29.

  FIG. 3 is a schematic diagram illustrating a configuration example of the first divider 26 according to the present embodiment. The first divider 26 is a resistor connected in series. For example, the first divider 26 divides the first DC high voltage supplied from the first high-voltage transformer unit 24 at a ratio of 100,000: 10. For example, when the first DC high voltage supplied from the first high-voltage transformer unit 24 is 75 kV, the first divided voltage is 7.5V. It should be noted that this partial pressure ratio may be any other value as long as it can be divided to a value that can be easily used for voltage measurement or the like, and is preferably set according to the use environment.

  The second divider 27 is installed between the output terminal of the second high-voltage transformer unit 25 and the ground, and the second DC high voltage is added to the first DC high voltage output from the second high-voltage transformer unit 25. Is divided to obtain a second divided voltage. The second divider 27 outputs the second divided voltage to the second inverter control unit 29.

  The first inverter control unit 28 compares the first divided voltage supplied from the first divider 26 with the first target voltage recorded in advance. The first target voltage is a target voltage of the first divided voltage that is set so that the first tube voltage (that is, the first DC high voltage) has a preset voltage value. The first inverter control unit 28 controls the voltage value of the first AC voltage generated by the first inverter 22 so that the first divided voltage matches the first target voltage.

  For example, when the first inverter 22 generates the first AC voltage by performing pulse width modulation on the DC voltage supplied from the power supply unit 21, the first inverter control unit 28 Control is performed so as to switch on / off of a switch provided in the first inverter 22 in accordance with the difference between the divided voltage and the first target voltage. Specifically, when the first divided voltage is lower than the first target voltage, the first inverter control unit 28 turns on the switch of the first inverter 22 so as to widen the pulse generation period of the pulse signal. Control off / off. Thereby, the voltage value of the 1st alternating voltage output from the 1st inverter 22 increases, and the 1st divided voltage corresponds with the 1st target voltage. When the first divided voltage is higher than the first target voltage, the first inverter control unit 28 turns on / off the switch of the first inverter 22 so as to narrow the pulse generation period of the pulse signal. Control. As a result, the voltage value of the first AC voltage output from the second inverter 22 decreases, and the first divided voltage matches the first target voltage.

  The second inverter control unit 29 takes the difference between the second divided voltage supplied from the second divider 27 and the first divided voltage supplied from the first divider 26. The second inverter control unit 29 compares the differential voltage between the second divided voltage and the first divided voltage with the second target voltage recorded in advance. The second target voltage is a differential voltage target voltage set so that the second tube voltage has a preset voltage value. The second inverter control unit 29 controls the voltage value of the second AC voltage generated by the second inverter 23 so that the differential voltage matches the second target voltage.

  For example, when the second inverter 23 generates the second AC voltage by performing pulse width modulation on the DC voltage supplied from the power supply unit 21, the second inverter control unit 29 outputs the differential voltage. Is controlled so as to switch on / off of a switch provided in the second inverter 23 in accordance with the difference between the second target voltage and the second target voltage. Specifically, when the differential voltage is lower than the second target voltage, the second inverter control unit 29 controls on / off of the switch of the second inverter 23 so as to widen the pulse generation period. Thereby, the voltage value of the 2nd alternating voltage output from the 2nd inverter 23 increases, and a differential voltage corresponds with a 2nd target voltage. When the differential voltage is higher than the second target voltage, the second inverter control unit 29 controls the on / off of the switch of the second inverter 23 so as to narrow the pulse generation interval. As a result, the voltage value of the second AC voltage output from the second inverter 23 decreases, and the differential voltage matches the second target voltage.

  The X-ray tube apparatus 113 is placed in the effective visual field region FOV by accelerating electrons with the first or second tube voltage supplied from the high voltage generator 119 and colliding the accelerated electrons with the target. X-rays are exposed to the subject P.

  Further, the X-ray tube apparatus 113 varies the impedance in accordance with an instruction from the X-ray control unit 1212. As the impedance of the X-ray tube device 113 changes, the power of X-rays exposed to the subject P changes. For example, when the X-ray tube apparatus 113 increases the impedance, the power of X-rays exposed to the subject P is reduced, and as a result, the amount of X-ray exposure to the subject P is reduced. .

  The X-ray detector 115 is a detector system that detects X-rays that have passed through the subject, and is attached to the rotating frame 116 in a direction facing the X-ray tube device 113. The X-ray detector 115 is a single-slice type or multi-slice type detector, and a plurality of detection elements constituted by a combination of a scintillator and a photodiode are one-dimensional or two-dimensional depending on each type. Are arranged.

  The rotating frame 116 is a ring that is driven to rotate about the Z axis, and is equipped with an X-ray tube device 113 and an X-ray detector 115. A central portion of the rotating frame 116 is opened, and a subject P placed on a bed (not shown) is inserted into the opening.

  The data acquisition unit 117 is generally called DAS (Data Acquisition System), converts a signal output from the X-ray detector 115 for each channel into a voltage signal, amplifies it, and further converts it into a digital signal. This data (raw data) is taken into the information processing unit 12 via the non-contact data transmission device 118.

  The preprocessing unit 122 receives raw data from the data collection unit 117 via the non-contact data transmission device 118 and performs sensitivity correction and X-ray intensity correction. The raw data for 360 degrees subjected to various corrections is temporarily stored in the storage unit 126. Note that the raw data preprocessed by the preprocessing unit 122 is referred to as “projection data”.

  The reconstruction unit 124 is equipped with a plurality of types of reconstruction methods, and reconstructs image data by the reconstruction method selected by the operator. The multiple types of reconstruction methods include, for example, a fan beam reconstruction method (also referred to as a fan beam convolution back projection method), and a reconstruction method when a projection ray intersects obliquely with respect to the reconstruction surface. Feldkamp method, Feldkamp method as an approximate image reconstruction method in which convolution is considered as a fan projection beam, and backprojection is processed along the ray at the time of scanning, assuming that the cone angle is small As a method for suppressing the cone angle error, a cone beam reconstruction method for correcting projection data in accordance with the ray angle with respect to the reconstruction surface is included.

  The image processing unit 125 performs image processing for display such as window conversion and RGB processing on the reconstructed image data generated by the reconstructing unit 124, and outputs the image processing to the display unit 129. Further, the image processing unit 125 generates a so-called pseudo three-dimensional image such as a tomographic image of an arbitrary cross section, a projection image from an arbitrary direction, a three-dimensional surface image, and the like based on an instruction from the operator and outputs the generated image to the display unit 129.

  The storage unit 126 stores image data such as raw data, projection data, scanogram data, tomographic image data, a program for an inspection plan, and the like.

  The display unit 129 is an output device that displays CT images such as computer tomographic images and scanogram images supplied from the image processing unit 125. Here, the CT value represents an X-ray absorption coefficient of a substance as a relative value from a reference substance (for example, water).

  The input unit 1210 is a device that includes a keyboard, various switches, a mouse, and the like, and can input various scanning conditions such as a slice thickness and the number of slices through an operator.

  The transmission / reception unit 1211 transmits / receives image data, patient information, and the like via the network N, for example, by communicating with other medical devices based on the DICOM standard.

  The scan plan setting unit 1213 includes an imaging plan (at least one of imaging conditions, imaging ranges, and image conditions) according to an input instruction from the input unit 1210, order information from the clinical department, initial conditions, past information, and the like. Set the scan plan.

  The X-ray control unit 1212 detects the rotation angle of the rotating frame 116 by the gantry driving unit 112 and determines the positional relationship between the X-ray tube device 113 and the X-ray detector 115 and the subject P based on the detected rotation angle. To grasp. For example, the X-ray control unit 1212 assumes in advance that the subject P has an elliptical cross section that is longer in the width direction than in the height direction. The X-ray control unit 1212 increases the tube current when the X-ray is exposed from the width direction, and decreases the tube current when the X-ray is irradiated from the height direction. In addition, the impedance of the X-ray tube is controlled according to the view angle. Thereby, when X-rays are exposed from the height direction, the power of the X-rays is reduced as compared to when X-rays are exposed from the width direction.

  The control unit 128 performs overall control of X-ray CT image imaging processing in the X-ray CT apparatus 10 in scan processing, signal processing, image generation processing, image display processing, and the like. For example, in the scan process, the control unit 128 sets scan conditions based on the patient ID and slice thickness included in the individual data, and based on the scan conditions, the high voltage generator 119, the bed driving unit 12, and the bed Control the amount of feeding of the top plate in the body axis direction, the feeding speed, the rotational speed of the X-ray tube device 113 and the X-ray detector 115, the rotational pitch, the X-ray exposure timing, etc. An X-ray cone beam or an X-ray fan beam is exposed to the region from multiple directions, and X-ray CT image data acquisition (scanning) processing is performed.

  In addition, the control unit 128 switches the output of the second high-voltage transformer unit 25 at a predetermined cycle so that imaging using two types of high and low energy characteristics can be performed in one scan. Switching control is performed for 119. The period at which the second high-voltage transformer unit 25 switches the first and second tube voltages may be any period as long as imaging using two types of high and low energy characteristics can be performed in one scan. Absent.

  As described above, in the above-described embodiment, the high voltage generator 119 has the first divider 26 between the output terminal of the first high-voltage transformer unit 24 and the ground. A first divided voltage is detected from one DC high voltage. Further, the high voltage generator 119 has a second divider 27 between the output terminal of the second high voltage transformer section 25 and the ground, and the second divider converts the second DC voltage to the first DC high voltage. The second divided voltage is detected from the voltage obtained by adding the DC high voltage. Then, the high voltage generator 119 controls the first inverter 22 by the first inverter control unit 28 so that the first divided voltage matches the first target voltage. In addition, the high voltage generator 119 uses the second inverter control unit 29 to change the second inverter so that the differential voltage between the second divided voltage and the first divided voltage matches the second target voltage. 23 is controlled. As a result, the high voltage generator 119 can stabilize the first and second tube voltages at a preset voltage value even when controlling the tube voltage as a base.

  Therefore, according to the X-ray CT apparatus 10 according to the present embodiment, the first and second tube voltages having high accuracy and reproducibility can be obtained from the X-ray tube even when the tube voltage serving as a base is controlled. A high voltage generator that can be applied to the device 113 is provided. Further, according to the X-ray CT apparatus 10 according to the present embodiment, dual energy imaging can be realized while controlling the tube voltage as a base.

  Moreover, in the said embodiment, the X-ray control part 1212 controls the electric power supplied to the X-ray tube apparatus 113 by controlling the impedance of the X-ray tube apparatus 113 according to a patient's body shape. The first inverter control unit 28 controls the first inverter 22 so that the first divided voltage matches the first target voltage even when the impedance of the X-ray tube device 113 changes. . Similarly, even if the impedance of the X-ray tube device 113 changes, the second inverter control unit 29 uses the difference voltage between the second divided voltage and the first divided voltage as the second target voltage. The second inverter 23 is controlled so as to agree with. As a result, the X-ray CT apparatus 10 stabilizes the first and second tube voltages at preset voltage values while reducing the patient exposure by changing the power supplied to the X-ray tube apparatus 113. It becomes possible to make it.

  Moreover, in the said embodiment, the high voltage generator 119 is provided with the 1st inverter 22, the 1st high voltage transformer part 24, the 2nd inverter 23, and the 2nd high voltage transformer part 25, and the 1st and 1st Although the case where the tube voltage of 2 is generated has been described as an example, the present invention is not limited to this. For example, two or more types of tube voltages may be generated and the generated tube voltages may be supplied to the X-ray tube. At this time, the high voltage generator 119 further includes a third inverter, a third high voltage transformer unit, and the like.

  Moreover, although the said embodiment demonstrated to the example the X-ray CT apparatus provided with the above-mentioned high voltage generator, it is not necessarily limited to this. For example, the X-ray diagnostic apparatus may include a high voltage generator as described above.

  Although the embodiment of the present invention has been described, this embodiment is presented as an example and is not intended to limit the scope of the invention. This embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. This embodiment and its modifications are included in the scope of the present invention and the gist thereof, and are also included in the invention described in the claims and the equivalent scope thereof.

  DESCRIPTION OF SYMBOLS 10 ... X-ray CT apparatus, 11 ... Mount, 111 ... Slip ring, 112 ... Mount drive part, 113 ... X-ray tube apparatus, 115 ... X-ray detector, 116 ... Rotating frame, 117 ... Data collection part, 118 ... Non Contact data transmission device, 119 ... high voltage generator, 12 ... information processing unit, 122 ... pre-processing unit, 123 ... memory unit, 124 ... reconstruction unit, 125 ... image processing unit, 126 ... storage unit, 128 ... control unit DESCRIPTION OF SYMBOLS 129 ... Display part, 1210 ... Input part, 1211 ... Transmission / reception part, 1212 ... X-ray control part, 1213 ... Scan plan setting part, 21 ... Power supply part, 22 ... 1st inverter, 23 ... 2nd inverter, 24 DESCRIPTION OF SYMBOLS 1st high voltage transformer part, 241 ... Transformer, 242 ... Rectifier, 25 ... 2nd high voltage transformer part, 251 ... Transformer, 252 ... Rectifier, 26 ... 1st divider, 27 ... 2nd device Da, 28 ... first inverter control unit, 29 ... second inverter control

Claims (3)

A power supply,
A first inverter that converts a DC voltage supplied from the power supply unit into a first AC voltage;
A first transformer that boosts the first alternating voltage to a first alternating high voltage;
A first rectifier for converting the first AC high voltage to a first DC high voltage;
A second inverter that converts a DC voltage supplied from the power supply unit to a second AC voltage;
A second transformer for boosting the second AC voltage to a second AC high voltage;
A second rectifier for converting the second AC high voltage to a second DC high voltage;
An X-ray tube that exposes an X-ray to a subject using a tube voltage in which the second DC high voltage is added to the first DC high voltage;
A first divider for dividing a first divided voltage from the first DC high voltage;
A first inverter control unit for controlling a voltage value of the first AC voltage with respect to the first inverter based on the first divided voltage;
A second divider for dividing a second divided voltage from the tube voltage;
A second inverter control unit that controls a voltage value of the second AC voltage with respect to the second inverter based on a differential voltage between the second divided voltage and the first divided voltage; An X-ray CT apparatus comprising: The first inverter control unit controls the first inverter so that the first divided voltage matches a preset first target voltage;
2. The X-ray CT according to claim 1, wherein the second inverter control unit controls the second inverter so that the differential voltage coincides with a preset second target voltage. apparatus.   The X-ray CT apparatus according to claim 1, further comprising an X-ray tube control unit that controls impedance of the X-ray tube.

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