JP5897262B2 - X-ray computed tomography system - Google Patents

Description

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

  Conventionally, there is an X-ray computed tomography apparatus (hereinafter referred to as an X-ray CT apparatus) that reconstructs an image related to a subject based on the number of X-ray photons output from an X-ray detector. A plurality of X-ray detection elements (for example, FIG. 6) having a size capable of achieving the minimum necessary resolution are respectively connected to the plurality of counters. When the number of photons of X-rays incident on the X-ray detection element increases under such connection, charge pulses may overlap in time (hereinafter referred to as a pile-up phenomenon) as shown in FIG. . The pile-up phenomenon makes it difficult to discriminate each charge pulse and causes the photon count to be missed. If the charge output exceeds the overflow output, the number of photons is not counted. If the number of photons is not counted correctly, artifacts will occur in the reconstructed image.

  When the irradiation dose to the subject is reduced so as not to cause a pile-up phenomenon, photon noise appears in the reconstructed image. In order to ensure a sufficient S / N (signal to noise ratio), it is necessary to increase the imaging time. Extension of the imaging time is a burden on the subject and the operator.

  Further, if the X-ray detection element is subdivided so as not to cause a pile-up phenomenon, the following problem occurs. As the number of X-ray detection elements increases, the number of counters connected to the X-ray detection elements increases (for example, FIG. 8), so that the amount of heat generation increases compared to the conventional case. In addition, the cost increases as the counter increases. As the number of counters increases, the size becomes larger than the conventional one. This makes it difficult to mount on an X-ray CT apparatus.

  An object is to provide an X-ray computed tomography apparatus that reduces the occurrence of a pile-up phenomenon without increasing the calorific value, size, and cost.

An X-ray computed tomography apparatus 1 according to the present embodiment includes an X-ray generation unit that generates X-rays and a plurality of X-ray detection elements that detect X-rays generated from the X-ray generation unit and transmitted through a subject. A number of X-rays based on outputs from the plurality of X-ray detection elements, a plurality of counters smaller than the number of the plurality of X-ray detection elements, A connection switching unit that is provided between the plurality of X-ray detection elements and the plurality of counters and switches connection of the plurality of counters to the plurality of X-ray detection elements; a first threshold value related to the number of photons; a range sandwiched between the threshold greater than the second threshold value, and the X-ray detecting elements respectively corresponding to said second threshold value is larger than the range and a plurality of connection patterns between the counter and the number of photons, the first Threshold , On the basis of the second threshold value, and the connection determination unit which determines the connection to be switched out of connection of said plurality of counters, a switching control unit that controls the connection switching part to switch to the determined connection A reconstruction unit that reconstructs a medical image based on outputs from the plurality of counters, and a scan information storage unit that stores the plurality of connection patterns determined for each view angle in a past scan for the subject. The connection determination unit determines, for each view angle, a connection to be switched among the connections of the plurality of counters based on the stored connection pattern and the view angle .

FIG. 1 is a diagram illustrating a configuration of an X-ray computed tomography apparatus according to the first embodiment. FIG. 2 is a diagram illustrating a plurality of X-ray detection elements that can be connected to one counter together with a connection switching unit according to the first embodiment. FIG. 3 is a flowchart illustrating an example of a procedure for switching connection of a plurality of counters to a plurality of X-ray detection elements based on an output from the counter according to the first embodiment. FIG. 4 is a flowchart illustrating an example of a procedure for switching the connection of a plurality of counters to a plurality of X-ray detection elements based on the scan information of the subject according to the first modification of the first embodiment. FIG. 5 is a flowchart illustrating an example of a procedure for correcting the count number output from the counter according to the second modification of the first embodiment. FIG. 6 is a diagram showing a conventional photon counting circuit. FIG. 7 is a schematic diagram illustrating an example of a pile-up phenomenon. FIG. 8 is a diagram showing a plurality of conventional subdivided X-ray detection elements together with a plurality of counters.

  An embodiment of an X-ray computed tomography apparatus (Computed Tomography: hereinafter referred to as an X-ray CT apparatus) will be described with reference to the drawings. In the X-ray CT apparatus, a Rotate / Rotate-Type in which the X-ray tube and the X-ray detector are integrally rotated around the subject, and a large number of X-ray detection elements arrayed in a ring shape are fixed. There are various types such as Stationary / Rotate-Type in which only the X-ray tube rotates around the subject, and any type is applicable to the present embodiment. Further, in order to reconstruct an image, projection data for 360 ° around the subject and projection data for 180 ° + fan angle are required for the half scan method. The present embodiment can be applied to any reconfiguration method. In recent years, the so-called multi-tube type X-ray CT apparatus in which a plurality of pairs of X-ray tubes and X-ray detectors are mounted on a rotating ring has been commercialized, and the development of peripheral technologies has been advanced. In the present embodiment, both a conventional single-tube X-ray CT apparatus and a multi-tube X-ray CT apparatus are applicable. Here, a single tube type will be described.

  In the following description, components having substantially the same function and configuration are denoted by the same reference numerals, and redundant description will be given only when necessary.

(First embodiment)
FIG. 1 is a diagram illustrating a configuration of an X-ray CT apparatus according to the first embodiment. The X-ray computed tomography apparatus 1 according to the first embodiment includes a high voltage generation unit 5, a gantry 7, a counter monitor unit 9, a connection determination unit 11, a scan information storage unit 13, a switching control unit 15, and a correction data storage unit. 17, a correction unit 19, a projection data generation unit 21, a reconstruction unit 23, an image storage unit 24, an interface 25, a display unit 27, an input unit 29, and a control unit 31.

  The high voltage generator 5 supplies a filament current to the cathode filament of the X-ray tube 71 and a high-voltage power source (not shown) for applying a high voltage between the anode target and the cathode filament of the X-ray tube 71. And a filament current generator (not shown).

  The gantry 7 houses a rotation support mechanism. The rotation support mechanism includes a rotation ring 73, a ring support mechanism that supports the rotation ring 73 so as to be rotatable about the rotation axis Z, and a drive unit 79 that drives the rotation of the ring. The rotating ring 73 is equipped with an X-ray tube 71 and an X-ray detector 75 also called a two-dimensional array type or a multi-row type. At the time of imaging or scanning, the subject P is placed on the top plate 31 and inserted into a cylindrical imaging area 719 between the X-ray tube 71 and the X-ray detector 75 in the gantry 7. A connection switching unit 753 is connected to the output of the X-ray detector 75. A plurality of counters 757 are connected to the output of the connection switching unit 753.

  The X-ray tube 71 radiates X-rays from the X-ray focal point 715 upon receiving a voltage application (hereinafter referred to as tube voltage) and a filament current from the high voltage generator 5 via the slip ring 81. . X-rays emitted from the X-ray focal point 715 are shaped into, for example, a cone beam shape (pyramidal shape) by a collimator unit (not shown) attached to the X-ray emission window of the X-ray tube 71. The X-ray emission range 717 is indicated by a dotted line. The X axis is a straight line that is orthogonal to the rotation axis Z and passes through the focal point 715 of the emitted X-ray. The Y axis is a straight line orthogonal to the X axis and the rotation axis Z. The X-ray tube 71 in the present embodiment is a rotary anode type X-ray tube. It should be noted that other types of X-ray tubes other than the fixed anode type X-ray tube can be applied to the present embodiment. Hereinafter, the high voltage generator 5 and the X-ray tube 71 are collectively referred to as an X-ray generator.

  The X-ray detector 75 is attached at a position and an angle facing the X-ray tube 71 across the rotation axis Z. The X-ray detector 75 has a plurality of X-ray detection elements. Each of the plurality of X-ray detection elements is provided with a collimator for reducing the directionality of incident X-rays. Each of the plurality of X-ray detection elements detects X-rays generated from the X-ray tube 71 and transmitted through the subject. The output from each of the plurality of X-ray detection elements is output to the counter 757 via the connection switching unit 753 and the amplifier.

  The connection switching unit 753 has a plurality of switches respectively connected to a plurality of X-ray detection elements. The connection switching unit 753 may be a multiplexer connected to a plurality of X-ray detection elements. The connection switching unit 753 switches connection of a plurality of counters to a plurality of X-ray detection elements according to an output from a switching control unit 15 described later. Specific switching regarding connection of a plurality of counters to a plurality of X-ray detection elements will be described in detail in the switching control unit 15. The amplifier amplifies a signal before being input to each of the plurality of counters.

  The counter counts the number of X-rays that have passed through the subject based on the output from the X-ray detection element. The plurality of counters is smaller than the number of the plurality of X-ray detection elements. Each of the plurality of counters has a wave height discriminator (or a comparator) (not shown). The signal output from the amplifier is input to the wave height discriminator. The pulse height discriminator generates a specific output pulse only when an input signal having an amplitude exceeding a specified value is received. The counter counts the pulses output by the wave height discriminator. The counter outputs the number of X-ray photons incident on the X-ray detector 75 (hereinafter referred to as a count number) to the correction unit 19 or the projection data generation unit 21 described later.

  Hereinafter, for convenience of explanation, an amplifier and connection switching unit 753 connected to one counter, a plurality of X-ray detection elements connectable to one counter via the connection switching unit 753, and the plurality of X-ray detection elements A module having a collimator attached to the is called an X-ray detection module. The number of counters in one X-ray detection module is smaller than the number of X-ray detection elements. Further, the size of the X-ray detection element in the X-ray detection module is smaller than the size of the conventional X-ray detection element. In addition, the size of the X-ray detection module in the present embodiment is a size having a minimum necessary spatial resolution.

  FIG. 2 is a diagram illustrating an example of an X-ray detection module together with a plurality of X-ray detection elements connectable to one counter and a connection switching unit 753. For example, each X-ray detection module has a structure as shown in FIG. In FIG. 2, d is the X-ray detection module pitch, and d 'is the subdivision detection element pitch. The X-ray detection module pitch d is a pitch related to the minimum necessary spatial resolution. The subdivision detection element pitch d ′ is, for example, one third (d = 3 × d ′) of the X-ray detection module pitch d as shown in FIG. Note that the subdivision detection element pitch d ′ is less than the X-ray detection module pitch d (d ′ <d), and can be set to any length that reduces the pile-up phenomenon.

  An output from at least one of the plurality of X-ray detection elements (7511 to 7519) in FIG. 2 is input to the amplifier 755 via a plurality of switches (indicated as SW in FIG. 2) in the connection switching unit 753. . An output from the amplifier 755 is input to the counter 757. Note that the connection switching unit 753 provided between the X-ray detection elements 7511 to 7519 and the counter 757 may be a multiplexer. The connection switching unit 753 switches connection of the plurality of X-ray detection elements (7511 to 7519) to the counter to connection to a ground or bias power source (not shown) under the control of the switching control unit 15 described later. The determination of the connection to be switched will be described in connection determination unit 11. Hereinafter, the X-ray detection module 751 will be described as having the structure of FIG.

  In the following description, it is assumed that a single X-ray detection module 751 constitutes a single channel. The plurality of X-ray detection modules are orthogonal to the rotation axis Z and have a radius from the center to the center of the light receiving unit of the X-ray detection module for one channel from the center of the emitted X-ray focal point 715. They are arranged two-dimensionally with respect to the two directions of the arc direction (channel direction) and the Z direction. The X-ray detector 75 may be configured by arranging a plurality of X-ray detection modules in one row. At this time, the X-ray detection modules are arranged one-dimensionally in a substantially arc direction along the channel direction. The two-dimensional array may be configured by arranging a plurality of X-ray detection modules arranged in a one-dimensional manner along the channel direction in a plurality of rows in the slice direction. The X-ray detector 75 having an array of two-dimensional X-ray detection modules may be configured by arranging a plurality of X-ray detection modules arranged in a one-dimensional shape in a substantially arc direction in a plurality of rows in the slice direction.

  The counter monitor unit 9 monitors the output of the counter 757 in the X-ray detector 75. Specifically, the counter monitor unit 9 outputs the count number output from the counter 757 to the connection determination unit 11 described later.

  The scan information storage unit 13 stores scan information related to the subject. The scan information is, for example, a plurality of connection patterns determined in past CT scans related to the subject. The plurality of connection patterns are respectively associated with the plurality of X-ray detection modules by the cone angle and the channel number. Further, the plurality of connection patterns may be different for each view angle. The view angle represents each position of the circular orbit around which the X-ray tube 71 circulates around the rotation axis Z as an angle in a range of 360 ° with the uppermost portion of the circular orbit vertically upward from the rotation axis Z as 0 °. It is. The scan information storage unit 13 corresponds to a connection pattern corresponding to a scanogram taken before the CT scan is performed on the subject or a plurality of tube voltage change patterns determined based on the scanogram. The connection pattern may be stored. Further, the scan information storage unit 13 may store a correspondence table between the imaging region of the subject and the connection pattern as the scan information of the subject.

  Based on the output from the count monitor unit 9, the connection determination unit 11 determines a connection to be switched among the connections of the counter 757 to the plurality of X-ray detection elements (7511 to 7519). The connection determination unit 11 outputs a switching signal corresponding to the determined connection to the switching control unit 15 described later. The switching signal is, for example, a signal for switching the connection of the counter to the X-ray detection element to the connection of the ground or bias power source to the X-ray detection element. Specifically, the connection determination unit 11 stores a plurality of threshold values for determining a connection to be switched. The plurality of threshold values are values related to the count number. The connection determination unit 11 stores a connection (hereinafter referred to as a connection pattern) corresponding to a range determined by the two closest thresholds among a plurality of thresholds.

  Hereinafter, as an example, two types of connection patterns will be described with reference to FIG. In addition, it is assumed that there are two types of threshold values for determining two types of connection patterns: a first threshold value and a second threshold value. The first threshold value is smaller than the second threshold value (first threshold value <second threshold value). The plurality of threshold values and the plurality of connection patterns can be set by the operator via the input unit 29 described later. In addition, the connection determination unit 11 may store a correspondence table between a plurality of ranges based on a plurality of threshold values and a plurality of connection patterns.

  In the first connection pattern, 7511, 7513, 7515, 7517, and 7519 X-ray detection elements are connected to the counter 757, and the 7512, 7514, 7516, and 7518 X-ray detection elements are connected to a ground or bias power source (not shown). A connection pattern to be connected (hereinafter referred to as a first connection pattern). Specifically, the first connection pattern is obtained when the number of counts output from the counter 757 is greater than or equal to the first threshold and less than the second threshold when the X-ray detection elements 7511 to 7519 are connected to the counter 757 (first It is a connection pattern applied to 1 threshold value <count number <2nd threshold value). At this time, the connection determination unit 11 determines the connection of the counter 757 to the X-ray detection elements 7512, 7514, 7516, and 7518 among the connections of the counter 757 to the X-ray detection elements 7511 to 7519 as the connection to be switched. . The connection determination unit 11 outputs a switching signal corresponding to the determined connection to the switching control unit 15 described later.

  In the first connection pattern, 7512, 7514, 7515, 7516, and 7518 X-ray detection elements are connected to the counter 757, and the X-ray detection elements 7511, 7513, 7517, and 7519 are not shown. It may be a connection pattern to connect to. For example, the first threshold value is a value that causes the pile-up phenomenon by the output of the counter 757 in a state where the X-ray detection elements 7511 to 7519 are connected to the counter 757. Note that the first threshold value may be a value that causes the output of the counter 757 to overflow in a state where the X-ray detection elements 7511 to 7519 are connected to the counter 757.

  In the second connection pattern, 7515 X-ray detection elements are connected to the counter 757, and 7511, 7512, 7513, 7514, 7516, 7517, 7518, and 7519 X-ray detection elements are connected to a ground or bias power supply not shown. A connection pattern to be connected (hereinafter referred to as a second connection pattern). Specifically, in the second connection pattern, the X-ray detection elements 7511 to 7519 are connected to the counter 757, or the X-ray detection elements 7511, 7513, 7515, 7517, and 7519 are connected to the counter 757. The connection pattern applied when the count number output from the counter 757 is greater than or equal to the second threshold value (second threshold value ≦ count number). At this time, the connection determination unit 11 connects the counter 757 to the X-ray detection elements 7511, 7512, 7513, 7514, 7516, 7517, 7518, and 7519 among the connections of the counter 757 to the X-ray detection elements 7511 to 7519. Is determined as the connection to be switched. In addition, the connection determination unit 11 switches the connection of the counter 757 to the X-ray detection elements 7511, 7513, 7517, and 7519 among the connections of the counter 757 to the X-ray detection elements 7511, 7513, 7515, 7517, and 7519. Determined as a connection. The connection determination unit 11 outputs a switching signal corresponding to the determined connection to the switching control unit 15 described later.

  The second threshold value is a value that causes an output of the counter 757 to cause a pile-up phenomenon in a state where the X-ray detection elements 7511, 7513, 7515, 7517, and 7519 are connected to the counter 757. Note that the second threshold value may be a value that causes the output of the counter 757 to overflow when the X-ray detection elements 7511, 7513, 7515, 7517, and 7519 are connected to the counter 757.

  The connection determination unit 11 is output from the counter 757 in a state where the X-ray detection elements 7511, 7513, 7515, 7517, and 7519 are connected to the counter 757, or in a state where the X-ray detection elements 7515 are connected to the counter 757. When the count number is less than the first threshold value (count number <first threshold value), a switching signal for connecting the X-ray detection elements 7511 to 7519 to the counter 757 is output to the switching control unit 15 described later. In a state where 7515 X-ray detection elements are connected to the counter 757, the connection determination unit 11 has a count number output from the counter 757 that is greater than or equal to the first threshold value and less than the second threshold value (first threshold value ≦ count number < (Second threshold value), a switching signal for matching the connection of the counter 757 with the X-ray detection element to the first connection pattern is output to the switching control unit 15 described later.

  The connection determination unit 11 determines the connection to be switched among the connections of the counter 757 to the plurality of X-ray detection elements (7511 to 7519) based on the scan information of the subject stored in the scan information storage unit 13. The connection determination unit 11 outputs a switching signal corresponding to the determined connection to the switching control unit 15.

  Specifically, the connection determination unit 11 reads the scan information of the subject from the scan information storage unit 13 based on the subject information input via the input unit 29 described later. Hereinafter, in order to simplify the description, it is assumed that the read scan information of the subject is a plurality of connection patterns determined in the past CT scan related to the subject. The connection determining unit 11 determines a connection to be switched for each view angle based on the plurality of read connection patterns. The connection determination unit 11 outputs a switching signal corresponding to the determined connection to the switching control unit 15 described later in association with the view angle.

  The switching control unit 15 controls the connection switching unit 753 based on a connection switching signal corresponding to the connection pattern determined by the connection determination unit 11. Specifically, the switching control unit 15 controls switching by the connection switching unit 753 so that the connection of the counter 757 to the X-ray detection element matches the connection pattern. If the connection to be switched is determined for each view angle, the switching control unit 15 controls switching by the connection switching unit 753 for each view angle.

  The correction data storage unit 17 stores correction data (hereinafter referred to as element correction data) corresponding to each of the plurality of X-ray detection elements. The correction data storage unit 17 stores correction data (hereinafter referred to as pattern correction data) corresponding to each of the plurality of connection patterns. The element correction data is data for correcting a deviation related to the output characteristics of each X-ray detection element. The element correction data is associated with each X-ray detection element. Specifically, the element correction data is set based on the calibration data of each corresponding X-ray detection element, the influence of the collimator, and the like. Note that the correction data storage unit 17 may store a correspondence table between each of the ranges based on a plurality of threshold values and the correction data.

  The pattern correction data is associated with each of the plurality of connection patterns stored in the connection determination unit 11. For example, the correction data storage unit 17 stores first and second pattern correction data corresponding to the first and second connection patterns, respectively. Specifically, the first pattern correction data is a ratio of the sum of the areas of the X-ray detection elements 7511 to 7519 to the area of the X-ray detection elements connected to the counter 757 in the first connection pattern (hereinafter referred to as the first area). Called the ratio). The first area ratio is 9/5 according to FIG. The first pattern correction data includes the first area ratio (9/5), the calibration data of each of the plurality of X-ray detection elements connected to the counter 757 in the first connection pattern, and the collimator of each X-ray detection element. It may be a value to which the influence of is added.

  The second pattern correction data is a ratio of the sum of the areas of the X-ray detection elements 7511 to 7519 to the area of the X-ray detection elements connected to the counter 757 in the second connection pattern (hereinafter referred to as a second area ratio). is there. The second area ratio is 9/1 according to FIG. The second pattern correction data includes the second area ratio (9/1), the calibration data of the X-ray detection element connected to the counter 757 in the second connection pattern, the influence of the collimator of each X-ray detection element, and the like. It is good also as a value which added.

  The correction unit 19 corrects the count number output from the plurality of counters based on element correction data corresponding to each of the plurality of X-ray detection elements connected to the plurality of counters. Hereinafter, for the sake of simplicity, description will be given with reference to FIG. For example, it is assumed that the first connection pattern is applied to the X-ray detection module 751. That is, the X-ray detection elements connected to the counter 757 are 7511, 7513, 7515, 7517, and 7519 X-ray detection elements. A plurality of element correction data respectively corresponding to the X-ray detection elements 7511, 7513, 7515, 7517, and 7519 are referred to as first, second, third, fourth, and fifth element correction data. The correction unit 19 corrects the count number output from the counter 757 using the first to fifth element correction data.

  The correction unit 19 uses the pattern correction data corresponding to the connection pattern applied to each of the plurality of X-ray detection modules to correct the count number output from the counter in each of the plurality of X-ray detection modules. Also good. Hereinafter, for the sake of simplicity, description will be given with reference to FIG. For example, when the first connection pattern is applied to the X-ray detection module 751, the correction unit 19 multiplies the first pattern correction data (9/5) by the count number output from the counter 757. Thereby, the count number expected when the X-ray detection elements 7511 to 7519 are connected to the counter 757 is calculated. When the second connection pattern is applied to the X-ray detection module 751, the correction unit 19 multiplies the second pattern correction data (9/1) by the count number output from the X-ray detection module 751. Thereby, the count number expected when the X-ray detection elements 7511 to 7519 are connected to the counter 757 is calculated.

  The correction unit 19 may correct the projection data generated by the projection data generation unit 21 described later based on the correction data stored in the correction data storage unit 17.

  The projection data generation unit 21 generates projection data based on the count number output from the correction unit 19 or the count number output from the counter 757. Specifically, the projection data generation unit 21 generates projection data by performing preprocessing on the count number. Projection data is data immediately before reconstruction processing (raw data), and is a set of data values according to the intensity of X-rays that have passed through the subject. The projection data is stored in a storage unit (not shown) including a magnetic disk, a magneto-optical disk, or a semiconductor memory in association with data representing a view angle when data is collected. Here, for convenience of explanation, a set of projection data over all channels having the same view angle collected almost simultaneously in one shot is referred to as a projection data set. The projection data for each channel in the projection data set is identified by the view angle, cone angle, and channel number.

  The reconstruction unit 23 reconstructs a substantially cylindrical three-dimensional image based on a projection data set having a view angle of 360 ° or 180 ° + fan angle.

  The image storage unit 24 stores the volume data generated by the reconstruction unit 23. The image storage unit 24 stores a cross-sectional image of the subject generated by an image processing unit (not shown).

  The interface 25 connects the X-ray computed tomography apparatus 1 to an electronic communication line (hereinafter referred to as a network). A radiation department information management system and a hospital information system (not shown) may be connected to the network.

  The display unit 27 displays the image reconstructed by the reconstruction unit 23, the image stored in the image storage unit 24, conditions set for X-ray computed tomography, and the like.

  The input unit 29 inputs X-ray computed tomography imaging conditions desired by the operator, subject information, and the like. Specifically, the input unit 29 captures various instructions / commands / information / selections / settings from the operator into the X-ray computed tomography apparatus 1. Although not shown, the input unit 29 includes a trackball, a switch button, a mouse, a keyboard, and the like for setting a region of interest. The input unit 29 detects the coordinates of the cursor displayed on the display screen, and outputs the detected coordinates to the control unit 31. The input unit 29 may be a touch panel provided to cover the display screen. In this case, the input unit 29 detects the coordinates instructed by touch on the principle of coordinate reading such as electromagnetic induction type, electromagnetic distortion type, and pressure sensitive type, and outputs the detected coordinates to the control unit 31. The input unit 29 can also input a plurality of threshold values and a plurality of connection patterns used in the connection determination unit 11.

  The control unit 31 functions as the center of the X-ray computed tomography apparatus 1. The control unit 31 includes a CPU and a memory (not shown). The control unit 31 includes a bed unit and a gantry unit (not shown) for X-ray computed tomography, and a high voltage generation unit 5 based on examination schedule data and a control program stored in a storage unit (not shown). To control. Specifically, the control unit 31 temporarily stores information such as operator instructions and image processing conditions sent from the input unit 29 in a memory (not shown). The control unit 31 controls the bed unit, the gantry unit, and the high voltage generation unit 5 based on these pieces of information temporarily stored in the memory. The control unit 31 reads a control program for executing predetermined image generation / display and the like from a storage unit (not shown), develops it on its own memory, and executes calculations / processings related to various processes.

  Next, in the X-ray computed tomography apparatus 1, a function for switching connection of a plurality of counters to a plurality of X-ray detection elements based on the output of the count monitor unit 9 with reference to the flowchart shown in FIG. The operation of the first switching function will be described. In order to simplify the description below, the connection patterns stored in the connection determination unit 11 are first and second connection patterns, and the plurality of threshold values stored in the connection determination unit 11 are first and second threshold values. . The following description is given for one X-ray detection module 751 among the plurality of X-ray detection modules.

  Prior to scanning the subject by the X-ray computed tomography apparatus 1, the operator inputs patient information and sets or updates scanning conditions using the input unit 29. These settings and updates are stored in a storage unit (not shown). When these inputs / selections / settings are completed, the control unit 31 performs a scan (step Sa1). It is assumed that the X-ray detection elements 7511 to 7519 in the X-ray detection module 751 are connected to the counter 757 at the start of scanning. The count number is output from the counter 757 (step Sa2). Until the scanning is completed, the processing of the following steps Sa4 to Sa10 is repeated for each output of the counter for each of the plurality of X-ray detection modules (step Sa3).

  The output count number is compared with the first threshold value (step Sa4). If the output count number is less than the first threshold value (count number <first threshold value), all the X-ray detection elements (for example, 7511 to 7519) in the X-ray detection module 751 that output the count number less than the first threshold value. The X-ray detection element) is connected to the counter 757 (step Sa5).

  When the output count number is not less than the first threshold value and less than the second threshold value (first threshold value ≦ count number <second threshold value) (step Sa6), the connection to be switched is determined based on the first connection pattern ( Step Sa7). For example, if the X-ray detection elements 7511 to 7519 in the X-ray detection module 751 are connected to the counter 757 before the processing of step Sa7, the connections to be switched are the X-ray detection elements 7512, 7514, 7516, and 7518. Is a counter connection.

  When the output count number is equal to or greater than the second threshold (second threshold ≦ count number) (step Sa6), the connection to be switched is determined based on the second connection pattern (step Sa8). For example, when the X-ray detection elements 7511 to 7519 in the X-ray detection module 751 are connected to the counter 757 before the process of step Sa8, the connection to be switched is 7511, 7512, 7513, 7514, 7516, 7517, The counter is connected to the X-ray detection elements 7518 and 7519. The determined connection is switched from the connection to the counter to the connection to the ground or the bias power supply (step Sa9).

(First modification)
The difference from the first embodiment is that the connection to be switched is determined based on the scan information related to the subject. In the X-ray computed tomography apparatus 1, a function for switching connection of a plurality of counters to a plurality of X-ray detection elements based on the scan information of the subject with reference to the flowchart shown in FIG. The operation of this function will be described. The following description is given for one X-ray detection module 751 among the plurality of X-ray detection modules.

  The operator inputs information about the subject via the input unit 29. Information about the subject may be transferred from the radiation department information management system or the hospital information system via the network. Prior to scanning the subject by the X-ray computed tomography apparatus 1, scan information related to the subject is read from the scan information storage unit 13 based on the inputted information about the subject (step Sb1). It is assumed that the read scan information related to the subject is a plurality of connection patterns determined in the past CT scan related to the subject. The plurality of connection patterns correspond to a plurality of view angles, respectively.

  A connection to be switched for each view angle is determined based on the read scan information (step Sb2). After the process of step Sb2, scanning is started (step Sb3). The determined connection is switched by the connection switching unit 753 in association with the view angle (step Sb4). Note that step Sb4 may be omitted when there is no connection switched between the viewing angles. When the connection is switched, X-rays are emitted from the X-ray tube 71, and the count number is output from the counter 757 of the X-ray detection module 751 (step Sb5). If the scan is not completed, the view angle is rotated by a predetermined angle. Until the scanning is completed, the processes of step Sb4 and step Sb5 are repeated (step Sb6).

(Second modification)
The difference between the first embodiment and the first modification is that correction is performed on the count number output in the first embodiment and the first modification. In the X-ray computed tomography apparatus 1, a function for correcting the count number output from the counter 757 based on element correction data or pattern correction data (hereinafter referred to as an element correction function and an element correction function) while referring to the flowchart shown in FIG. Will be described. The following description is given for one X-ray detection module 751 among the plurality of X-ray detection modules.

  After the start of scanning, the count number is output from the counter 757 in the X-ray detection module 751 (step Sc1). Element correction data corresponding to the X-ray detection element relating to the output of the count number is read from the correction data storage unit 17 (step Sc2). For example, when the plurality of X-ray detection elements relating to the output of the count number are 7511, 7513, 7515, 7517, and 7519 X-ray detection elements, they correspond to the X-ray detection elements of 7511, 7513, 7515, 7517, and 7519, respectively. The element correction data is read from the correction data storage unit 17. Note that pattern correction data corresponding to connection patterns applied to each of the plurality of X-ray detection modules may be read from the correction data storage unit 17. Using the read element correction data, the output count number is corrected (step Sc3). When the pattern correction data is read from the correction data storage unit 17, the output count number is corrected by multiplying the read pattern correction data.

According to the configuration described above, the following effects can be obtained.
According to the X-ray computed tomography apparatus 1 of the present embodiment, the connection determined based on the output from the counter 757 and a plurality of threshold values can be switched. Further, the connection determined based on the scan information of the subject can be switched. Thereby, the X-ray computed tomography apparatus 1 can reduce the pile-up phenomenon and the overflow output. In addition, an increase in the amount of generated heat, size, and cost can be suppressed by suppressing an increase in the counter associated with subdivision of the X-ray detection element. For these reasons, mounting on an X-ray computed tomography apparatus becomes easy. Further, the X-ray computed tomography apparatus 1 can correct the output from the counter 757 to a count number expected by connecting a plurality of X-ray detection elements to the plurality of counters, respectively. Thereby, the minimum necessary spatial resolution can be achieved.

  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 1 ... X-ray computed tomography apparatus, 5 ... High voltage generation part, 7 ... Gantry, 9 ... Count monitor part, 11 ... Connection determination part, 13 ... Scan information storage part, 15 ... Switching control part, 17 ... Correction data storage , 19 ... correction unit, 21 ... projection data generation unit, 23 ... reconstruction unit, 24 ... image storage unit, 25 ... interface, 27 ... display unit, 31 ... top plate, 71 ... X-ray tube, 73 ... rotating ring 75 ... X-ray detector, 79 ... drive unit, 81 ... slip ring, 715 ... X-ray focal point, 717 ... X-ray emission range, 719 ... imaging region, 751 ... X-ray detection module, 753 ... connection switching unit 755 ... Amplifier, 757 ... Counter, 7511 ... X-ray detection element, 7512 ... X-ray detection element, 7513 ... X-ray detection element, 7514 ... X-ray detection element, 7515 ... X-ray detection element, 7516 ... X-ray detection element , 7517 ... X-ray detecting elements, 7518 ... X-ray detecting elements, 7519 ... X-ray detecting elements

Claims (2)

An X-ray generator for generating X-rays;
An X-ray detector having a plurality of X-ray detection elements for detecting X-rays generated from the X-ray generator and transmitted through the subject;
Counting the number of photons according to the intensity of X-rays based on outputs from the plurality of X-ray detection elements, a plurality of counters less than the number of the plurality of X-ray detection elements;
A connection switching unit that is provided between the plurality of X-ray detection elements and the plurality of counters and switches connection of the plurality of counters to the plurality of X-ray detection elements;
Multiple connections and ranges sandwiched between the first threshold value relating to the number of photons and the first threshold value greater than the second threshold value, and the X-ray detecting elements respectively corresponding to the second threshold value is larger than the range to the counter a pattern, and the number of photons, and the first threshold value, on the basis of the second threshold value, and the connection determination unit which determines the connection to be switched out of connection of said plurality of counters,
A switching control unit for controlling the connection switching unit to switch to the determined connection;
A reconstruction unit for reconstructing a medical image based on an output from the counter;
Aforementioned ingredients Bei the scan information storage unit for storing the plurality of connecting pattern determined past scan smell Te every bi Yuanguru relative to the subject,
The connection determination unit is an X-ray computed tomography apparatus that determines, for each view angle, a connection to be switched among the connections of the plurality of counters based on the stored connection pattern and the view angle. Correction data storage for storing, as correction data, the ratio of the area of the X-ray detection element that can be connected to the counter to the maximum with respect to the area of the X-ray detection element connected to each of the counters in each of the plurality of connection patterns And
A correction unit that corrects the outputs of the plurality of counters for each of the connection pattern and the view angle using the correction data;
X-ray computed tomography apparatus of claim 1, further comprising a.

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