JP6313051B2 - X-ray computed tomography system - Google Patents

Description

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

  The X-ray computed tomography apparatus is equipped with a rotating frame to which an X-ray tube and an X-ray detector are attached. Each time the rotating frame rotates a predetermined angle, a view trigger signal is generated. The X-ray computed tomography apparatus generates X-rays from the X-ray tube in synchronization with the generation of the view trigger signal while rotating the rotating frame. X-rays generated from the X-ray tube are detected by an X-ray detector. The X-ray detector is equipped with a plurality of X-ray detection elements arranged two-dimensionally. The plurality of X-ray detection elements are connected to a data acquisition circuit. The X-ray computed tomography apparatus reads out electrical signals generated in a plurality of detection elements by a data acquisition circuit in synchronization with the generation of a view trigger signal. A method of reading electrical signals from a plurality of X-ray detection elements at different timings in units of X-ray detection element arrays is called a sequential reading method. Further, as an X-ray irradiation method, there is a pulse X-ray irradiation method in which pulse X-rays are intermittently generated from an X-ray tube in order to reduce the exposure dose of a subject.

JP 2005-349187 A

  FIG. 8 is a diagram showing a typical scan sequence using the pulse X-ray irradiation method and the sequential readout method. As shown in FIG. 8, the view trigger signal is repeatedly turned on and off at regular intervals. The pulse X-ray is switched ON and OFF in synchronization with the rise time of the view trigger signal at an interval of 1 view from the X-ray tube. The view is a unit sampling period of the electric signal by the data acquisition circuit, and corresponds to the generation period of the view trigger signal. The data acquisition circuit sequentially reads out the electrical signals sequentially from the element row Row1 in synchronization with the rise time of the view trigger signal.

  The X-ray irradiation period spans both the readout period of the processing target view and the readout period of the view temporally prior to the processing target view due to the fact that the readout time is different for each X-ray detection element array. Yes. For example, in the case of the element row Row4 in FIG. 8, the irradiation period of the X-ray pulse targeting the view view2 extends over the readout period of the view view1 and the readout period of the view view2. As a result, the electrical signal that should originally be read as the view view 2 is divided into the electrical signal related to the view view 1 and the electrical signal related to the view view 2. In order to correct the division of the electric signal, the output value must be added in the subsequent data processing, which complicates the data processing. In addition, the S / N ratio is deteriorated due to the division of the electric signal and the image quality of the reconstructed image is deteriorated. Further, even if the electrical signals are related to the same view by the sequential readout method, the spatial sampling position of the electrical signals is shifted. The image quality of the reconstructed image is deteriorated due to the deviation of the sampling position.

  An object of the embodiment is to provide an X-ray computed tomography apparatus capable of preventing image quality deterioration due to the combined use of a pulse X-ray irradiation method and a sequential readout method.

An X-ray computed tomography apparatus according to this embodiment includes an X-ray tube that repeatedly generates pulsed X-rays repeatedly, a high voltage generator that generates a high voltage supplied to the X-ray tube, and a two-dimensional shape. A plurality of X-ray detection elements arranged in the X-ray detector, each of the plurality of X-ray detection elements repeatedly detecting pulse X-rays from the X-ray tube, the X-ray tube and the X-ray detector A rotating frame provided with a line detector, a support mechanism that supports the rotating frame so as to be rotatable about a rotation axis, a signal generating unit that generates a trigger signal each time the rotating frame rotates a predetermined angle, and Synchronizing with the generation of the trigger signal, a collection unit that sequentially executes read processing of electric signals from the plurality of X-ray detection elements for each view in units of element rows, the high voltage generation unit, the collection unit, Controls the signal generator to the target view A control unit to irradiate the pulsed X-ray from the X-ray tube is limited to between the end of the reading process of the first element rows beginning with relates to the subject views over the reading process of the last element array to Are provided.

The figure which shows the structure of the X-ray computed tomography apparatus which concerns on this embodiment. FIG. 2 is a diagram showing an appearance of the X-ray detector of FIG. The figure which shows typically the structure of the X-ray detection system which concerns on this embodiment. The figure which shows typically the flow of the read-out process of the electrical signal from each X-ray detection element row | line | column by the data acquisition circuit of FIG. The figure which shows an example of the scan sequence in the 1st control mode which concerns on this embodiment. The figure which shows an example of the scan sequence in the 2nd control mode which concerns on this embodiment. The figure which shows an example of the scan sequence in the 3rd control mode which concerns on this embodiment. A diagram showing a typical scan sequence using a pulse X-ray irradiation method and a sequential readout method

  The X-ray computed tomography apparatus according to this embodiment will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of an X-ray computed tomography apparatus 1 according to the present embodiment. As shown in FIG. 1, the X-ray computed tomography apparatus 1 includes a gantry 10 and a console 30.

  The gantry 10 is equipped with a rotating frame 11. The rotating frame 11 is supported by the gantry 10 so as to be rotatable around the rotation axis Z. The rotating frame 11 is mounted with an X-ray tube 13 and an X-ray detector 15 that are arranged to face each other. An FOV (field of view) is set in an opening (bore) of the rotating frame 11. The top 17 is positioned so that the FOV includes the imaging area of the subject S. The rotating frame 11 is connected to the rotation driving unit 19. The rotation drive unit 19 rotates the rotating frame 11 around the rotation axis Z at a predetermined angular velocity according to a control signal from the gantry control unit 21. Specifically, the rotation drive unit 19 is realized by a motor that generates power for rotating the rotary frame 11 in accordance with a control signal from the gantry control unit 21. A trigger signal generator 23 is attached to the rotation drive unit 19. The trigger signal generator 23 repeatedly generates an electric pulse signal (hereinafter referred to as a view trigger signal) every time the rotating frame 11 rotates by a predetermined angle. The generation period of the view trigger signal by the trigger signal generator 23 is set according to the control signal from the gantry control unit 21. The view trigger signal is supplied to the gantry control unit 21.

  The X-ray tube 13 generates X-rays in response to application of a high voltage from the high voltage generator 25 and supply of a filament current. The high voltage generator 25 applies a high voltage to the X-ray tube 13 in accordance with a control signal from the gantry control unit 21 and supplies a filament current to the X-ray tube 13. Specifically, the X-ray tube 13 is equipped with an anode and a cathode. A high voltage is applied by a high voltage generator 25 between the anode and the cathode. A filament current from the high voltage generator 25 is supplied to the cathode. Electrons (thermoelectrons) are emitted from the cathode heated by the supply of the filament current. The thermoelectrons fly toward the anode by a high voltage applied between the anode and the cathode. X-rays are generated when thermionic electrons collide with the anode. A bias electrode is provided between the anode and the cathode. The high voltage generator 25 applies a bias voltage to the bias electrode. The number of thermionic electrons that collide with the anode changes by adjusting the potential with respect to the cathode potential by the bias voltage. That is, the high voltage generator 25 can switch ON (irradiation) and OFF (irradiation stop) of X-rays from the X-ray tube 13 by alternately switching two kinds of voltage values of the bias voltage. . Thereby, pulse X-rays are repeatedly generated from the X-ray tube 13.

  The X-ray detector 15 detects the pulse X-ray generated from the X-ray tube 13 and generates an electrical signal corresponding to the intensity of the pulse X-ray. FIG. 2 is a diagram showing the appearance of the X-ray detector 15. As shown in FIG. 2, the X-ray detector 15 is equipped with a plurality of X-ray detection elements arranged two-dimensionally. In FIG. 2, for example, the plurality of X-ray detection elements are arranged along an arc centered on the rotation axis Z of the rotating frame 11. The arrangement direction of the X-ray detection elements along the arc is called a channel direction. A plurality of X-ray detection elements arranged along the channel direction is called an element array. The plurality of element rows are arranged along the row direction along the rotation axis Z. Each X-ray detection element detects a pulse X-ray generated from the X-ray tube 13 and generates an electric signal corresponding to the intensity of the detected pulse X-ray. The generated electrical signal is read out by a data acquisition circuit (DAS: data acquisition system) 27.

  The data collection circuit 27 reads out the electrical signal from the X-ray detector 15 by the sequential readout method in accordance with the control signal from the gantry control unit 21. Specifically, the data acquisition circuit 27 sequentially executes the reading process of the electrical signal from the X-ray detection element for each view in synchronism with the generation of the view trigger signal. The data collection circuit 27 converts the read analog electrical signal into digital data. Digital data is called raw data. Raw data is transmitted to the console 30.

The gantry control unit 21 supervises control of various devices mounted on the gantry 10 in accordance with instructions from the system control unit 45 in the console 30. Specifically, the gantry control unit 21 controls the rotation drive unit 19, the trigger signal generator 23, the high voltage generator 25, and the data collection circuit 27. Specifically, the gantry control unit 21 controls the rotation driving unit 19 so that the rotating frame 11 rotates at a predetermined angular velocity. The gantry control unit 21 controls the trigger signal generator 23 so as to generate a view trigger signal at a generation cycle (angular interval) according to a command from the console 30. The gantry control unit 21 controls the high voltage generator 25 and the data collection circuit 27 based on the generation time of the view trigger signal from the trigger signal generator 23. Specifically, the gantry control unit 21 is configured so that pulse X-rays corresponding to predetermined X-ray conditions are repeatedly generated from the X-ray tube 13 at a predetermined timing based on the generation time of the view trigger signal. The voltage generator 25 is controlled. The gantry control unit 21 controls the data acquisition circuit 27 so that electrical signals are sequentially read out from a plurality of X-ray detection elements at a predetermined timing based on the generation time of the view trigger signal. In the present embodiment, the gantry control unit 21, for a plurality of element rows included in the X-ray detector 15, is another view in which the irradiation period of each pulse X-ray from the X-ray tube 13 is temporally adjacent to the irradiation target view. The trigger signal generator 23, the high voltage generator 25, and the data acquisition circuit 27 are controlled so as not to overlap with the reading processing relating to the above. Specifically, by controlling the trigger signal generator 23 and the high voltage generator 25 and a data acquisition circuit 27, the first about the beginning and the irradiation target views over the reading process of the last element string related irradiation target view The pulse X-rays are emitted from the X-ray tube 13 only during the end of the reading process of the element array. The gantry control unit 21 has three types of control modes as control modes for avoiding overlap. The control mode is set by a control mode setting unit 35 described later. Note that the gantry control unit 21 may be provided in the console 30.

  The console 30 includes a preprocessing unit 31, a reconfiguration unit 33, a control mode setting unit 35, an I / F unit 37, a display unit 39, an input unit 41, a storage unit 43, and a system control unit 45.

  The preprocessing unit 31 performs preprocessing such as logarithmic conversion on the raw data transmitted from the gantry 10. The raw data after the preprocessing is also called projection data. The preprocessing includes various correction processes such as logarithmic conversion, X-ray intensity correction, and offset correction.

  The reconstruction unit 33 generates a CT image representing the spatial distribution of CT values related to the subject S based on the raw data after preprocessing. Image reconstruction algorithms include analytical image reconstruction methods such as FBP (filtered back projection) and CBP (convolution back projection), ML-EM (maximum likelihood expectation maximization), and OS-EM (ordered subset). An existing image reconstruction algorithm such as a statistical image reconstruction method such as an expectation maximization method may be used.

  The control mode setting unit 35 selects any one of the three control modes for avoiding the overlap according to an instruction from the user via the input unit 41 or a predetermined control mode setting algorithm. Set. The setting of the control mode is performed at the time of scan planning, for example. The three control modes will be described later.

  The I / F unit 37 is an interface for communication between the console 30 and the gantry 10. For example, the I / F unit 37 transmits a signal indicating the type of control mode set by the control mode setting unit 35 (hereinafter, control mode signal) to the gantry 10. In addition, the I / F unit 37 transmits preset shooting conditions to the gantry 10. Examples of imaging conditions include X-ray conditions and the rotational speed of the rotating frame. The imaging conditions characteristic of the present embodiment include the time from generation of a view trigger signal to X-ray irradiation (irradiation standby period), the irradiation period of each pulse X-ray, the number of wait times for view trigger signals (number of irradiation triggers). ), The generation period (angle interval) of the view trigger signal, and the like. Details of these photographing conditions will be described later.

  The display unit 39 displays a CT image, a scan plan setting screen, and the like on a display device. As the display device, for example, a CRT display, a liquid crystal display, an organic EL display, a plasma display, or the like can be used as appropriate.

  The input unit 41 receives various commands and information input from the user by the input device. As an input device, a keyboard, a mouse, various switches, and the like can be used.

  The storage unit 43 is a storage device that stores various information. For example, the storage unit 43 stores raw data before preprocessing, raw data after preprocessing, and CT image data. The storage unit 43 stores a scan plan program for a scan plan according to the present embodiment, a scan program corresponding to various control modes, and the like.

  The system control unit 45 functions as the center of the X-ray computed tomography apparatus 1. The system control unit 45 reads the scan plan program according to the present embodiment from the storage unit 43 and controls various components according to the scan plan program. Thereby, the scan plan according to the present embodiment is performed. In addition, the system control unit 45 reads the scan program according to the present embodiment from the storage unit 43 and controls various components according to the scan program. Thereby, scanning according to the control mode according to the present embodiment is performed.

  Next, an operation example of the X-ray computed tomography apparatus according to this embodiment will be described.

  First, the configuration of the X-ray detection system according to the present embodiment will be described. FIG. 3 is a diagram schematically showing the configuration of the X-ray detection system according to the present embodiment. As shown in FIG. 3, the X-ray detection system includes an X-ray detector 15 and a data acquisition circuit 27. As described above, the X-ray detector 15 has a plurality of element rows, and each element row has a plurality of X-ray detection elements 151 arranged along the channel direction. Here, the number of channels is Cm (m is an integer), and the number of element rows is Rn (n is an integer).

  The data collection circuit 27 has a plurality of read channels 27Cm and an output device 277. It is assumed that the read channel 27Cm is provided for each channel. The read channel 27Cm reads electric signals related to the plurality of X-ray detection elements 151-Rn included in one channel. The read channel 27 </ b> Cm includes an integrator 271 -Rn, a multiplexer 273, and an A / D converter 275. An integrator 271 -Rn is connected to each X-ray detection element 151 -Rn. Each integrator 271 -Rn integrates (stores) the electric signal supplied from the connected X-ray detection element 151 -Rn over a predetermined sampling period (view), and generates an integrated signal. A single multiplexer 273 is connected to the plurality of integrators 271 -Rn included in each readout channel 27Cm. An A / D converter 275 is connected to the multiplexer 273. The multiplexer 273 is a switch that switches connections between the plurality of integrators 271 -Rn and the A / D converter 275. The multiplexer 273 sequentially reads integration signals for each view from the plurality of integrators 271 -Rn to be connected at a timing according to control by the gantry control unit 21. The A / D converter 275 performs A / D conversion on the analog integrated signal from the multiplexer 273 and converts the analog integrated signal into digital peak value data representing the peak value of the integrated signal. A single output device 277 is connected to the plurality of read channels 27Cm. The output unit 277 generates, for each view, raw data in which the peak value data is arranged according to the channel number Cm and the column number Rn, based on the peak value data from the plurality of readout channels 27Cm to be connected.

  Next, the details of the process of reading electrical signals from each element array will be described. FIG. 4 is a diagram schematically showing the flow of a process for reading an electrical signal from each element row Row by the data collection circuit 27. As shown in FIG. 4, the electrical signal readout process for each view is divided into an electrical signal integration process and an integral signal readout process. First, the integrator 271 integrates (stores) the electric signal supplied from the X-ray detection element 151 at the connection destination. The integration period is assigned to all integrators 271 regardless of the element row Row. The supply start time of the electric signal from the X-ray detection element 151 to the integrator 271 differs depending on the element row Row to which the X-ray detection element 151 belongs. The integrator 271 belonging to the element row Row1 to be read first in each view starts the integration process of the electric signal from the X-ray detection element 151 in synchronization with the generation time Ttri of the view trigger signal. The integration period (storage period) by each integrator 271 is set to be shorter than one view period. The multiplexer 273 triggers the element row Row in response to the elapse of a standby time (referred to as a read waiting time) in the element row Row with reference to the time Ttri when the trigger signal generator 23 generates the view trigger signal. The integrated signal is read from the integrator 271 to which it belongs, and the read integrated signal is supplied to the subsequent A / D converter 275. In other words, the multiplexer 273 reads the integration signal from the integrator 271 when the predetermined integration period has elapsed for each element row Row. In the readout period of the integration signal, the same time is assigned to all the element rows Row. The read standby time for each element row Row is set so that the integration signal read periods do not overlap between different element rows Row. In this way, the sequential readout method is realized by shifting the start time of the integration signal readout processing from the integrator 271 in units of element rows. The integration signal reading process is completed within a minute time as compared with the electrical signal integration process. Therefore, the integration period is dominant in one view period, and the integration signal readout period is set sufficiently shorter than the integration period. When the reading process is completed in each view, each integrator 271 starts integration of the electric signal from the connected X-ray detection element 151 again. The A / D converter 275 performs A / D conversion on the integrated signal from the multiplexer 273 to generate peak value data, and the output unit 277 integrates the peak value data from all the read channels to generate raw data on each view. Is generated.

  The configuration of the data collection circuit 27 is an example, and the present embodiment is not limited to the configuration described above. For example, a plurality of A / D converters 275 may be connected to the multiplexer 273. Thereby, the load of the A / D conversion process of the integral signal by each A / D converter 275 can be reduced. In the above description, one integrator 271 is connected to each X-ray detection element 151. However, this embodiment is not limited to this. For example, two integrators 271 may be connected to each X-ray detection element 151. The electric signal from the X-ray detection element 151 is alternately supplied to the subsequent two integrators 271 for each view, whereby the electric signal can be processed efficiently. In the above configuration, one multiplexer 273 controls the reading process of the integration signal from the integrator 271 of all the element rows Rn related to each reading channel Cm. However, this embodiment is not limited to this. For example, a plurality of multiplexers 273 may be provided for each read channel Cm. As a result, the integration signal readout process for each readout channel Cm is shared by a plurality of multiplexers 273, reducing the burden on each multiplexer 273, and improving the processing speed of the integration process readout process for one view. .

  Next, the scan sequence for each of the three control modes performed under the control of the system control unit 45 according to the present embodiment will be described. In the following description of the scan sequence, for convenience of explanation, it is assumed that the element rows are four rows from Row1 to Row4. However, the element columns according to the present embodiment are not limited to this, and may be any number of columns such as 8 columns, 16 columns, 64 columns, 256 columns, 512 columns, and the like.

  In the first control mode, the gantry control unit 21 adjusts the irradiation timing and the irradiation time of the pulse X-rays, thereby reading out the other views in which the irradiation period of each pulse X-ray is temporally adjacent to the target view. Avoid overlapping processing.

  FIG. 5 is a diagram illustrating an example of a scan sequence in the first control mode. As shown in FIG. 5, the trigger signal generator 23 repeats ON and OFF of the view trigger signal at a preset generation cycle (angular interval) while the rotating frame 11 is rotating. In the first control mode, the generation period of the view trigger signal coincides with the view period. The gantry control unit 21 includes a view memory, and manages the current view number based on the count number recorded in the view memory. The gantry control unit 21 adds 1 to the count number of the view memory every time the trigger signal is turned ON. The count number corresponds to the view number. In other words, the gantry control unit 21 controls the data collection circuit 27 in synchronization with the rise of the view trigger signal in response to the view trigger signal being turned on. Read electrical signals sequentially. Further, the gantry control unit 21 controls the high voltage generator 25 to irradiate the pulse X-rays from the X-ray tube 13 every predetermined number of views. For example, in the case of FIG. 5, pulse X-rays are generated every other view. The predetermined number of views can be set to an arbitrary value by the user.

As shown in FIG. 5, the gantry control unit 21 controls the high voltage generator 25, and in the irradiation target view of the pulse X-ray, the start time of the reading process of the last element row related to the irradiation target view and the irradiation target limited to be irradiated with pulsed X-rays from the X-ray tube 13 between the end of the reading process of the first element array about the view. More specifically, the gantry control unit 21 waits for a predetermined irradiation standby time Twx to elapse with reference to the time Ttri when the view trigger signal is turned ON in the irradiation target of the pulse X-ray. The gantry controller 21 supplies an irradiation instruction signal to the high voltage generator 25 when the irradiation standby time Twx has elapsed. The high voltage generator 25 that has been supplied with the irradiation instruction signal irradiates the pulse X-ray from the X-ray tube 13 for a preset irradiation time Trx. The irradiation time Trx is set to a time shorter than one view period. For example, as shown in FIG. 5, when pulse X-rays are irradiated in the view View2 , between the start time of the read process of the element row Row4 of the view View2 and the end time of the read process of the element row Row1 of the view View2 Pulse X-rays are irradiated for a limited period. Irradiation time Trx is set to be shorter than the time interval between the end of the reading process of the first element array about the beginning and the irradiation target views over the reading process of the last element array about the irradiation target view Is done. The irradiation standby period Twx may be set to a value obtained by subtracting the irradiation time Trx from the view period. The irradiation standby time Twx and the irradiation time Trx can be set by the user via the input unit 41 as imaging conditions.

  When the scan ends, the reconstruction unit 33 reconstructs a CT image related to the subject S based on the collected projection data. In the first control mode, there is a view that is not irradiated with X-rays. For example, as shown in FIG. 5, views View2 and View4 are irradiated with X-rays, but views View1 and View3 are not irradiated with X-rays. Raw data relating to views not irradiated with X-rays cannot be used for image reconstruction. Therefore, the reconstruction unit 33 reconstructs a CT image based on raw data regarding a view irradiated with X-rays (hereinafter referred to as an X-ray ON view) in the collected raw data. Specifically, the reconstruction unit 33 classifies the collected raw data into raw data related to an X-ray ON view and raw data related to a view not irradiated with X-rays (hereinafter referred to as an X-ray OFF view). . The reconstruction unit 33 may classify the raw data related to the X-ray ON view and the raw data related to the X-ray OFF view by referring to the view number associated with the raw data. By referencing, the raw data related to the X-ray ON view and the raw data related to the X-ray OFF view may be classified. Then, the reconstruction unit 33 reconstructs the CT image based on the raw data regarding the X-ray ON view. Thus, by excluding the raw data related to the X-ray OFF view from the reconstruction target, it is possible to prevent the image quality of the CT image from being reduced.

  As described above, in the first control mode, the gantry control unit 21 adjusts the irradiation timing and the irradiation time of the pulse X-rays, thereby starting the reading process of the last element row related to the irradiation target view and the irradiation target. The pulse X-rays are emitted from the X-ray tube 13 only between the end of the reading process of the first element row relating to the next view of the view. Thus, the irradiation period of each pulse X-ray can be overlapped only in the reading period of the irradiation target view without overlapping the reading period of the next view of the irradiation target view. Further, according to the first control mode, the X-ray irradiation time can be shortened as compared with the conventional example. Therefore, in the first control mode, the exposure dose to the subject S is reduced as compared with the conventional example.

  Next, the second control mode will be described. In the second control mode, the gantry control unit 21 avoids the irradiation period of each pulse X-ray from overlapping the readout process related to another view temporally adjacent to the target view by thinning out the views.

  FIG. 6 is a diagram illustrating an example of a scan sequence in the second control mode. As shown in FIG. 6, the trigger signal generator 23 repeats turning on and off the view trigger signal at a preset generation cycle while the rotating frame 11 is rotating. The gantry control unit 21 controls the high voltage generator 25 to irradiate pulse X-rays from the X-ray tube 13 when the view trigger signal is turned ON a predetermined number of times (hereinafter referred to as the number of irradiation triggers). The irradiation time Trx of each pulse X-ray is set to the view period as in the conventional example of FIG. In addition, the gantry control unit 21 controls the data collection circuit 27 when the view trigger signal is turned on by the number of irradiation triggers, and sequentially reads electrical signals from a plurality of element rows in order from the element row Row1. That is, in the second control mode, the generation period of the view trigger signal does not match the view period.

  As shown in FIG. 6, the gantry control unit 21 controls the data collection circuit 27 to execute the sequential reading process each time the trigger signal generator 23 generates two or more irradiation trigger number of view trigger signals. . For example, as illustrated in FIG. 6, the gantry control unit 21 controls the data collection circuit 27 when the view trigger signal is first turned ON in the irradiation target view, and starts sequential reading processing for the view View1. During execution of the sequential reading process, the gantry control unit 21 counts the number of times the view trigger signal is generated from the start of the sequential reading process, in other words, the number of times the view trigger signal is switched to ON. The gantry control unit 21 stands by until the number of generations of the view trigger signal reaches the preset number of irradiation triggers. The number of irradiation triggers can be arbitrarily set as an imaging condition by the user via the input unit 41. In the case of FIG. 6, the number of irradiation triggers is set to two. When the view trigger signal is generated and the number of times the view trigger signal is generated is less than the number of irradiation triggers, the gantry control unit 21 extends the sequential reading process for the processing target view View1 to the data collection circuit 27. . As described above, the reading process is divided into an electric signal integration process and an integration signal reading process. The sequential reading process is extended by extending the electric signal integration process. Regardless of whether the sequential readout process is extended, there is no change in the processing period of the integral signal readout process. Then, when the number of times the view trigger signal is generated reaches the number of irradiation triggers, the gantry control unit 21 causes the data collection circuit 27 to switch the processing target view to the next view View2 and starts the sequential reading process regarding the view View2.

  In this way, in the second control mode, the gantry control unit 21 switches the view every time the view trigger signal is generated for the number of irradiation triggers, and starts the sequential reading process. Therefore, compared with the case where the view is switched every time the view trigger signal is generated, the electrical signal reading process of each view can be expanded. As a result, from the X-ray tube 13 only between the start time of the reading process of the last element row related to the irradiation target view and the end time of the reading process of the first element row related to the next view of the irradiation target view. Pulse X-rays are irradiated. Therefore, the irradiation period of each pulse X-ray can be overlapped only in the reading period of the irradiation target view without overlapping the reading period of the next view of the irradiation target view. In the second control mode, the X-ray OFF view does not exist. Therefore, it is not necessary to classify the raw data related to the X-ray OFF view and the raw data related to the X-ray ON view, and the data processing can be simplified. In the second control mode, since the number of views can be reduced as compared with the conventional example, the data collection speed by the data collection circuit 27 can be reduced, and circuit noise can be reduced.

  Next, the third control mode will be described. In the third control mode, the gantry control unit 21 extends the generation interval of the view trigger signal, so that the irradiation period of each pulse X-ray overlaps with the readout period related to another view temporally adjacent to the target view. Avoid that.

  FIG. 7 is a diagram illustrating an example of a scan sequence in the third control mode. FIG. 7 is a diagram illustrating an example of a scan sequence in the third control mode. As shown in FIG. 7, the trigger signal generator 23 repeats ON and OFF of the view trigger signal at a preset generation cycle while the rotating frame 11 is rotating. As shown in FIG. 7, the generation period of the view trigger signal in the third control mode, that is, the view period is extended as compared with the initial view period. The gantry control unit 21 controls the high voltage generator 25 to irradiate pulse X-rays from the X-ray tube 13 in synchronization with the view trigger signal. The irradiation time Trx of each pulse X-ray is set to the view period as in the conventional example of FIG. The gantry control unit 21 controls the data collection circuit 27 when the view trigger signal is turned on, and sequentially reads electrical signals from a plurality of element rows in order from the element row Row1.

  More specifically, the gantry control unit 21 sets a generation period in the trigger signal generator 23 before the start of scanning. The actual generation period of the view trigger signal can be changed to an arbitrary value by the user via the input unit 41. More specifically, the actual generation period of the view trigger signal is preferably set to an integer multiple of the initial switching period of the view trigger signal between ON and OFF. In the case of FIG. 7, the actual generation period of the view trigger signal is set to twice the initial generation period of the view trigger signal. Note that the actual generation period of the view trigger signal is not limited to an integral multiple of the initial generation period of the view trigger signal, and can be set to any half integer multiple such as 1.5. The trigger signal generator 23 repeatedly generates a view trigger signal with a set generation cycle during scanning. The gantry control unit 21 controls the high voltage generator 25 when the irradiation standby time Twx with reference to the generation time of the view trigger signal has elapsed in the irradiation target view, and the irradiation time Trx is the only time from the X-ray tube 13. X-rays are irradiated. In the case of FIG. 7, the irradiation standby time Twx and the irradiation time Trx are set to the generation time or non-generation time of the view trigger signal, that is, the ON time or OFF time of the view trigger signal. In addition, the gantry control unit 21 controls the data collection circuit 27 to sequentially execute the reading process in synchronization with the generation of the view trigger signal.

  As described above, in the third control mode, the gantry control unit 21 can extend the readout period of the electrical signal of each view by extending the generation period of the view trigger signal. As a result, from the X-ray tube 13 only between the start time of the reading process of the last element row related to the irradiation target view and the end time of the reading process of the first element row related to the next view of the irradiation target view. Pulse X-rays are irradiated. Accordingly, the irradiation period of each pulse X-ray can be overlapped only in the reading period of the irradiation target view without overlapping the reading period of the next view of the irradiation target view. In the third control mode, the X-ray OFF view does not exist. Therefore, it is not necessary to classify the raw data related to the X-ray OFF view and the raw data related to the X-ray ON view, and the data processing can be simplified. In the third control mode, since the number of views can be reduced as compared with the conventional example, the data collection speed by the data collection circuit 27 can be reduced, and the circuit noise can be reduced.

  This is the end of the description of the scan sequence for each of the three control modes.

  Next, a scan plan performed under the control of the system control unit 45 will be described. In the scan plan, the system control unit 45 causes the control mode setting unit 35 to perform control mode setting processing. The control mode setting unit 35 has a manual setting mode and an automatic setting mode as control mode setting processing.

  In the manual setting mode, the control mode setting unit 35 sets the control mode selected by the user via the input unit 41 from the above three control modes. The user can select an arbitrary control mode from the above three control modes.

  In the automatic setting mode, the control mode setting unit 35 determines whether or not the X-ray irradiation time of each pulse X-ray in the first control mode can be secured longer than a predetermined value. The predetermined value is set to a time during which an X-ray dose necessary and sufficient for image reconstruction can be secured. The predetermined value can be set to an arbitrary value via the input unit 41 by the user. When it is determined that the X-ray irradiation time of each pulse X-ray can be secured longer than a predetermined value, the control mode setting unit 35 sets the first control mode as the control mode. When it is determined that the X-ray irradiation time of each pulse X-ray can be secured longer than the predetermined value, the control mode setting unit 35 selects the user among the second control mode and the third control mode as the control mode. To set a control mode designated in advance via the input unit 41.

  The identifier of the set control mode is stored in the storage unit 43. When a scan start instruction is given, the system control unit 45 reads the control mode identifier from the storage unit 43 and sends a control mode signal corresponding to the control mode identifier to the gantry control unit 21 via the I / F unit 37. Send. The gantry control unit 21 controls the trigger signal generator 23, the high voltage generator 25, and the data collection circuit 27 in accordance with the transmitted control mode signal as described above, and the control set by the control mode setting unit 35. Scan in mode.

  This is the end of the description of the scan plan.

As described above, the X-ray computed tomography apparatus according to the present embodiment includes the X-ray tube 13, the high voltage generator 25, the X-ray detector 15, the rotating frame 11, the gantry 10, the trigger signal generator 23, and the data. A collection circuit 27 and a gantry control unit 21 are included. The X-ray tube 13 repeatedly generates pulse X-rays intermittently. The high voltage generator 25 generates a high voltage supplied to the X-ray tube 13. The X-ray detector 15 has a plurality of X-ray detection elements arranged two-dimensionally, and each of the plurality of X-ray detection elements repeatedly detects pulse X-rays from the X-ray tube 13. The rotating frame 11 is provided with an X-ray tube 13 and an X-ray detector 15. The gantry 10 supports the rotary frame 11 so as to be rotatable about the rotation axis Z. The trigger signal generator 23 generates a view trigger signal every time the rotating frame 11 rotates by a predetermined angle. The data acquisition circuit 27 sequentially executes readout processing of electric signals from a plurality of X-ray detection elements for each view in synchronism with the generation of the view trigger signal. The gantry control unit 21 controls the high voltage generator 25, the data acquisition circuit 27, and the trigger signal generator 23 to start the reading process of the last element column for the target view and read the first element column for the target view. The pulse X-rays are irradiated from the X-ray tube 13 only during the end of the process.

  With the above configuration, the irradiation period of each pulse X-ray is prevented from overlapping with the readout period related to another view temporally adjacent to the target view without significantly changing the structure of the data acquisition circuit 27. . Therefore, in the present embodiment, the irradiation period of each pulse X-ray occurs in the conventional example in which both the readout period for the target view and the readout period for another view temporally adjacent to the target view overlap. The problem that the raw data related to the target view is divided into the raw data related to the target view and the raw data related to the next view is solved. By eliminating this problem, extra processing such as addition of raw data output values, which was necessary in the conventional example, becomes unnecessary, and raw data processing is simplified. In addition, with the reduction of surplus processing, the present embodiment improves the S / N ratio as compared to the conventional example, and improves the image quality of the CT image. Further, in comparison with the conventional example in which the irradiation period of each pulse X-ray overlaps both the readout period related to the target view and the readout period related to another view temporally adjacent to the target view, Deviation of the spatial sampling position of the raw data is reduced, and the image quality of the CT image is improved.

  Thus, according to the present embodiment, it is possible to prevent deterioration in image quality due to the combined use of the pulse X-ray irradiation method and the sequential readout method.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 10 ... Mount, 11 ... Rotating frame, 13 ... X-ray tube, 15 ... X-ray detector, 17 ... Top plate, 19 ... Rotation drive part, 21 ... Mount control part, 23 ... Trigger generator, 25 ... High voltage generation 27 ... Data collection circuit, 30 ... Console, 31 ... Pre-processing unit, 33 ... Reconfiguration unit, 35 ... Control mode setting unit, 37 ... I / F unit, 39 ... Display unit, 41 ... Input unit, 43 ... Storage unit, 45 ... system control unit

Claims (8)

An X-ray tube that repeatedly generates pulsed X-rays intermittently;
A high voltage generator for generating a high voltage supplied to the X-ray tube;
An X-ray detector having a plurality of X-ray detection elements arranged two-dimensionally, each of the plurality of X-ray detection elements repeatedly detecting pulse X-rays from the X-ray tube;
A rotating frame provided with the X-ray tube and the X-ray detector;
A support mechanism for rotatably supporting the rotating frame around a rotation axis;
A signal generator for generating a trigger signal each time the rotating frame rotates by a predetermined angle;
Synchronizing with the generation of the trigger signal, a collection unit that sequentially executes, for each view, readout processing of electric signals from the plurality of X-ray detection elements,
Controls and the collecting unit and the high voltage generating unit, based on the generation period or the number of occurrences of the trigger signal, the first element row concerning the start of the reading process of the last element string related object view to the subject views over A control unit for irradiating the pulsed X-ray from the X-ray tube limited to the end point of the reading process;
An X-ray computed tomography apparatus comprising: The collector is
An integrator for integrating electrical signals from the plurality of X-ray detection elements;
An A / D converter for A / D converting the integration signal from the integrator;
A switch for switching the connection between the integrator and the A / D converter,
The collection unit sequentially executes the integration process of the electrical signal by the integrator and the readout process of the integration signal from the integrator to the A / D converter as the readout process of the electrical signal,
The control unit controls the high voltage generation unit, the collection unit, and the signal generation unit so that an irradiation period of the pulse X-ray does not overlap with a processing period of the electrical signal reading process of the other view. To
The X-ray computed tomography apparatus according to claim 1. The control unit controls the high voltage generation unit, and is limited between a start time of the reading process of the last element column related to the target view and an end time of the reading process of the first element column related to the target view. The X-ray computed tomography apparatus according to claim 1, wherein an irradiation timing and an irradiation period of the pulse X-ray are adjusted so that the pulse X-ray is irradiated from the X-ray tube.   The control unit controls the acquisition unit, and two or more from the signal generation unit so that the irradiation period of the pulse X-rays from the X-ray tube does not overlap the processing period of the readout process related to the other view. The X-ray computed tomography apparatus according to claim 1, wherein a reading process of the electrical signal is executed every time a predetermined number of trigger signals are generated.   The control unit controls the signal generation unit to increase the generation interval of the trigger signal so that the irradiation period of the pulse X-rays from the X-ray tube does not overlap with the processing period of the readout process related to the other view. The X-ray computed tomography apparatus according to claim 1. A setting unit,
The control unit has a first control mode, a second control mode, and a third control mode,
The setting unit sets the first control mode, the second control mode, or the third control mode according to an instruction from a user,
In the first control mode, the control unit controls the high voltage generation unit to start a read process for the last element column related to the target view and a read process for the first element column related to the target view. Adjusting the irradiation timing and irradiation period of the pulse X-ray so as to irradiate the pulse X-ray from the X-ray tube limited to the end point of
The control unit controls the collection unit in the second control mode, and executes the reading process of the electric signal every time a predetermined number of trigger signals of 2 or more are generated from the signal generation unit,
The control unit controls the signal generation unit in the third control mode to expand a generation interval of the trigger signal.
The X-ray computed tomography apparatus according to claim 1. A setting unit,
The control unit has a first control mode, a second control mode, and a third control mode,
In the first control mode, the control unit controls the high voltage generation unit to start a read process for the last element column related to the target view and a read process for the first element column related to the target view. Adjusting the irradiation timing and irradiation period of the pulse X-ray so as to irradiate the pulse X-ray from the X-ray tube limited to the end point of
The control unit controls the collection unit in the second control mode, and executes the reading process of the electric signal every time a predetermined number of trigger signals of 2 or more are generated from the signal generation unit,
The control unit controls the signal generation unit in the third control mode, and expands the generation interval of the trigger signal,
The setting unit sets the first control mode when the irradiation period of the pulse X-rays in the first control mode can be secured more than a threshold, and sets the pulse X-rays in the first control mode. If the irradiation period cannot be secured more than the threshold value, the second control mode or the third control mode is set.
The X-ray computed tomography apparatus according to claim 1.   Further comprising a reconstruction unit,
  For each view, the collection unit collects raw data based on the electrical signal on which the reading process has been performed,
  The reconstruction unit classifies raw data related to a view irradiated with the pulse X-ray and raw data related to a view not irradiated with the pulse X-ray, and is based on the raw data related to the view irradiated with the pulse X-ray. To reconstruct the CT image,
  The X-ray computed tomography apparatus according to claim 1.

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