JP2010131215A - X-ray ct apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To subject X-ray projection data to the X-ray tube discharge correction in the X-ray computerized tomography for scanning by controlling an X-ray tube to repeatedly change the X-ray tube voltage to a plurality of set values by several views. <P>SOLUTION: The set value Vp (view) and the measured value Vm (view) of the X-ray tube voltage at each time in the plurality of views when X-ray projection data are collected are specified, and the difference between the set value and the measured value is found. The projection data of the views in which the difference is in at least a prescribed level are subjected to the X-ray tube discharge correction. The set view Vp (view) of the X-ray tube voltage in each view is specified, for example, based on control information of the X-ray voltage directly acquired from an X-ray controller of a scanning gantry, or predicted, for example, based on the relations between a changing pattern of the set value of the X-ray tube voltage and the temporal change of the measured value of the X-ray tube voltage. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an X-ray CT (Computed Tomography) apparatus.

  Conventionally, in X-ray CT imaging, X-ray tube discharge generated during CT scan (hereinafter simply referred to as scan) is detected, and X-ray projection data (data X-ray tube discharge correction is known in which X is approximated to X-ray projection data that should be obtained.

  The X-ray tube discharge is an abnormal discharge in which an electric current flows instantaneously in a different path from the electrode that is the original current path in the X-ray tube. In a general scan, the X-ray tube voltage is controlled to be substantially constant while the X-ray projection data is collected. However, when an X-ray tube discharge occurs, the X-ray tube voltage drops greatly instantaneously.

  Therefore, for example, an X-ray tube voltage can be measured in an X-ray CT apparatus, and X-ray tube discharge can be corrected by detecting an X-ray tube discharge by simple threshold determination of the measured value.

  On the other hand, using the X-ray CT apparatus, X-ray projection data based on a plurality of X-ray tube voltages is obtained by scanning the same part of the subject with different X-ray tube voltages, and based on these X-ray projection data An imaging method (for example, a dual energy imaging method) for reconstructing a tomographic image in which a predetermined substance is emphasized or suppressed, a tomographic image corresponding to a certain X-ray tube voltage, or the like is known.

  As one of the imaging methods, an imaging method is known in which scanning is performed while repeatedly switching the set value of the X-ray tube voltage to a plurality of voltage values in units of one or several views (for example, Patent Documents). 1).

According to such an imaging method for switching the set value of the X-ray tube voltage, the X-ray projection data corresponding to the view angle range necessary for the reconstruction of the tomographic image can be quickly obtained for each set value of the X-ray tube voltage. The imaging can be performed while suppressing the movement of the subject.
JP 2008-125900 A

  However, in the above-described imaging method for switching the X-ray tube voltage, the X-ray tube voltage changes during the scan, so that the X-ray tube discharge is detected from a simple threshold judgment of the measured value of the X-ray tube voltage as in the past. It is impossible to correct the X-ray tube discharge correctly.

  In view of the above circumstances, the present invention can perform X-ray tube discharge correction while using an imaging method of scanning while repeatedly switching a set value of an X-ray tube voltage to a plurality of voltage values in units of several views. An object is to provide a line CT apparatus.

  In a first aspect, the present invention scans an object while repeatedly switching a set value of an X-ray tube voltage to a plurality of voltage values in units of one or several views, and collects X-ray projection data of a plurality of views. An X-ray CT apparatus including a line data collection unit, a set value specifying unit for specifying a set value of an X-ray tube voltage in the plurality of views, and a tube voltage measuring unit for measuring the X-ray tube voltage in the plurality of views. , An abnormal view detection means for detecting an abnormal view in which the difference between the set value and the measured value of the X-ray tube voltage is equal to or higher than a predetermined level among the plurality of views, and correction of the X-ray projection data of the abnormal view Provided is an X-ray CT apparatus including a correcting means.

  In a second aspect, the present invention provides the correction means, wherein the X-ray projection data of the abnormal view is close to the abnormal view of the plurality of views, and the set value of the X-ray tube voltage is the abnormal view. An X-ray CT apparatus according to the first aspect of the present invention that corrects based on X-ray projection data of a view that is the same and different from the detected abnormal view is provided.

  In a third aspect, the present invention acquires X-ray projection data of a plurality of views by scanning a subject while repeatedly switching a set value of an X-ray tube voltage to a plurality of voltage values in units of one or several views. An X-ray CT apparatus provided with a line data acquisition means, which detects X-rays generated from an X-ray tube and outputs a signal corresponding to the intensity of the X-rays, and X-rays in the plurality of views Setting value specifying means for specifying a setting value of the tube voltage; output signal estimating means for estimating an output signal value of the reference detector in the plurality of views based on a setting value of the X-ray tube voltage of the view; Output signal measuring means for measuring the output signal value of the reference detector in the plurality of views, and the difference between the estimated value and the measured value of the output signal value of the reference detector in the plurality of views is a predetermined level. An anomaly view that is above Providing an abnormal view detection means for detecting the X-ray CT apparatus and a correcting means for correcting the X-ray projection data of the abnormality view.

  In a fourth aspect, the present invention provides the X-ray projection data of the abnormal view that is continuous or discontinuous with less than a predetermined number, and the correction means is close to the abnormal view of the plurality of views, There is provided an X-ray CT apparatus according to the third aspect, wherein a set value of a tube voltage is the same as that of the abnormal view, and correction is performed based on X-ray projection data of a view different from the detected abnormal view.

  In a fifth aspect, the present invention provides the correction means, wherein X-ray projection data of an abnormal view that is continuous in a predetermined number or more is an estimated value of the output signal value in the abnormal view, or of the plurality of views. The X-ray CT apparatus according to the third aspect or the fourth aspect is provided that corrects based on a measured value of the output signal value in a view that is close to an abnormal view and is different from the detected abnormal view.

  In a sixth aspect, according to the present invention, the correction unit performs first-order weighted addition processing on the X-ray projection data of the abnormal view, and projection data of views different from the detected abnormal view among the plurality of views. The X-ray CT apparatus according to the second aspect, the fourth aspect, or the fifth aspect that replaces the X-ray projection data obtained by multi-order weighted addition processing is provided.

  In a seventh aspect, according to the present invention, the set value specifying unit specifies the set value of the X-ray tube voltage in the plurality of views based on the control information of the X-ray tube voltage obtained from the data collecting unit. An X-ray CT apparatus according to any one of the first to sixth aspects is provided.

  In an eighth aspect of the present invention, the set value specifying means assigns a set value switching pattern (pattern) of the set X-ray tube voltage from a predetermined number of views of the plurality of views. An X-ray CT apparatus according to any one of the first to sixth aspects that specifies a set value of an X-ray tube voltage in a view is provided.

  In a ninth aspect, the present invention provides the set value specifying means in the plurality of views based on a switching pattern of a set value of the set X-ray tube voltage and a time change of the measured value of the X-ray tube voltage. An X-ray CT apparatus according to any one of the first to sixth aspects that specifies a set value of an X-ray tube voltage is provided.

  In a tenth aspect, the present invention provides the set value specifying means based on a change pattern of a set value of the set X-ray tube voltage and a time change of a measured value of the output signal value of the reference detector. Provided is the X-ray CT apparatus according to any one of the third to fifth aspects, which specifies set values of the X-ray tube voltage in the plurality of views.

  In an eleventh aspect, the present invention scans a subject while repeatedly switching a set value of an X-ray tube voltage to a plurality of voltage values in units of one or several views, and collects X-ray projection data of a plurality of views. An X-ray CT apparatus comprising line data collection means, wherein a set value specifying means for specifying a set value of an X-ray tube voltage in at least one of the plurality of views, and an X-ray tube voltage in the at least one view are measured. A tube voltage measuring means for detecting, an abnormal view detecting means for detecting an abnormal view in which a difference between a set value and a measured value of the X-ray tube voltage is not less than a predetermined level in the at least one view, and the X of the abnormal view An X-ray CT apparatus is provided that includes correction means for correcting line projection data.

  In a twelfth aspect, the present invention acquires X-ray projection data of a plurality of views by scanning a subject while repeatedly switching a set value of an X-ray tube voltage to a plurality of voltage values in units of one or several views. An X-ray CT apparatus comprising a line data acquisition means, detecting a X-ray generated from an X-ray tube and outputting a signal corresponding to the intensity of the X-ray, and at least one of the plurality of views A set value specifying means for specifying a set value of the X-ray tube voltage in the two, and an output signal value of the reference detector in the at least one view based on the set value of the X-ray tube voltage in the view Output signal estimation means; output signal measurement means for measuring an output signal value of the reference detector in the at least one view; and output signal value of the reference detector in the at least one view. The difference between the value and the measured value to provide an X-ray CT apparatus including an abnormality view detector for detecting an abnormality view a predetermined level or more, and a correction means for correcting the X-ray projection data of the abnormality view.

  In the present invention, “measuring the X-ray tube voltage” includes the case of specifying the X-ray tube voltage with high probability, for example, information used when directly controlling the X-ray tube voltage. Etc. may be specified. Moreover, the measurement method (specific method) does not ask a contact and non-contact.

  According to the present invention, a set value and a measured value of an X-ray tube voltage are specified in a plurality of views from which X-ray projection data is collected or at least one of the plurality of views, and the set value and the measured value of the X-ray tube voltage are specified. X-ray projection data of a view in which the difference from the above becomes a predetermined level or more is corrected, so that an X-ray tube discharge can be detected based on a deviation from the X-ray tube voltage setting value as a reference. X-ray tube discharge correction can be performed using an imaging method in which scanning is performed while repeatedly switching the set value of the tube voltage to a plurality of voltage values in units of several views.

(First embodiment)
Embodiments according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing an X-ray CT apparatus 100 according to an embodiment of the present invention. The X-ray CT apparatus 100 includes an operation console 1, an imaging table 10, and a scanning gantry (X-ray data collection means) 20.

  The operation console 1 includes an input device 2, a central processing unit 3, a data collection buffer (buffer) 5, a monitor 6, and a storage device 7.

  The input device 2 includes a keyboard (not shown), a mouse, and the like, and receives input of various information from an operator. The input device 2 accepts input of information for setting shooting conditions in dual energy shooting, for example.

  The data collection buffer 5 collects X-ray projection data for each view transferred from the data collection device 25 of the scanning gantry 20 and its accompanying information. The incidental information includes a view number in the view, a view angle position, a set value and a measured value of the X-ray tube voltage, a measured value of the X-ray tube current, and the like. 22 and the rotating unit controller 26. Or it collects via the X-ray controller 22 and the data collection device 25 which are mentioned later.

  The monitor 6 includes a CRT (cathode ray tube), a liquid crystal panel (panel), and the like, and displays an operation screen, a tomographic image, and the like.

  The storage device 7 includes a hard disk, an IC memory, and the like, and stores various data, programs, and the like.

  The central processing unit 3 executes a scan control process for performing dual energy imaging. In addition, the central processing unit 3 stores data input by the input device 2, X-ray projection data collected by the data collection buffer 5 and its incidental information in the storage device 7, or causes the monitor 6 to display an operation screen or a tomogram. Display an image, etc.

  As shown in FIG. 2, the central processing unit 3 includes a tube voltage set value specifying unit (set value specifying unit) 31, an abnormal view detecting unit (abnormal view detecting unit) 32, a correcting unit (correcting unit) 33, and an image generating unit. 34.

  The tube voltage set value specifying unit 31 specifies a set value of the X-ray tube voltage in a plurality of views where X-ray projection data is collected by scanning.

  The abnormal view detection unit 32 detects, as an abnormal view, a view in which the difference between the set value and the measurement value of the corresponding X-ray tube voltage among the plurality of views is equal to or higher than a predetermined level.

  The correction unit 33 corrects the X-ray projection data of the detected abnormal view.

  The imaging table 10 has a cradle 12. The subject is placed on the cradle 12, and the cradle 12 is moved in the body axis direction of the subject (hereinafter referred to as the z direction). The subject is transported to the opening of the scanning gantry 20.

  The scanning gantry 20 has an opening including an imaging space, and includes a rotating unit 15 that rotates about the central axis of the opening and a scanning gantry body 20a that rotatably supports the rotating unit 15. The rotating unit 15 and the scanning gantry main body 20 a are electrically connected via a slip ring 30.

  The rotating unit 15 includes an X-ray tube 21, an X-ray controller (tube voltage measuring means) 22, an X-ray collimator 23, an X-ray detector 24, a data acquisition device (DAS) (detection signal measuring means) 25, And the rotation part controller 26 is mounted.

  FIG. 3 is a diagram illustrating a data collection system of the rotation unit 15.

  As shown in FIG. 3, the X-ray tube 21 and the X-ray detector 24 are arranged to face each other with the opening interposed therebetween.

  The X-ray tube 21 is of a rotating anode type, and the thermoelectrons emitted from the cathode filament are accelerated by the X-ray tube voltage generated between the cathode and the rotating anode so as to collide with the rotating anode. X-rays are emitted from the X-ray focal point F on the rotating anode.

  The X-ray detector 24 slices a detector array in which a plurality of detection elements that detect X-rays and output signals corresponding to the X-ray dose, that is, X-ray intensity, are arranged in the channel direction. This is a multi-row detector having a plurality in the slice) direction. The X-ray detector 24 includes, as a part thereof, a first reference detector 24a and a second reference amount detector 24b for measuring the dose of X-rays generated from the X-ray tube 21. As shown in FIG. 3, the first reference detector 24 a is composed of a plurality of detection elements arranged in the slice direction at one end in the channel direction of the X-ray detector 24, and the second reference detector 24b is composed of a plurality of detection elements arranged in the slice direction at the other end in the channel direction. The X-ray dose measured using these reference detectors is used for X-ray dose correction for correcting the level of the data value of the X-ray projection data based on the X-ray dose. The first and second reference detectors 24a and 24b may double as the X-ray detector 24 as in the present embodiment, or may be provided independently.

  The X-ray controller 22 receives information such as an X-ray tube voltage setting value switching pattern and an X-ray tube current setting value determined by the set imaging conditions from the rotating unit controller 26, and receives the X-ray tube voltage and the X-rays. The high voltage generator of the X-ray tube 21 is controlled so that the tube current follows these settings. Further, the X-ray controller 22 controls the X-ray generation timing (timing) by a control signal from the rotating unit controller 26 via the controller 29. Further, the X-ray controller 22 monitors the X-ray tube voltage and the X-ray tube current in substantially real time to control the X-ray tube voltage and the X-ray tube current, and the measured values are monitored. Output.

  The X-ray collimator 23 controls the position and width of the opening by a control signal from the rotating unit controller 26 via the controller 29. The X-ray generated from the X-ray focal point F of the X-ray tube 21 is shaped into a fan beam X-ray or a cone beam X-ray by the X-ray collimator 23, and the detection surface of the X-ray detector 24. dp is irradiated.

  The data collection device 25 collects X-ray projection data by performing analog-digital conversion on the output signal of each detection element of the X-ray detector 24. The X-ray projection data includes output data from the first and second reference detectors 24a and 24b. Further, the data collection device 25 receives, from the X-ray controller 22, for each view, information indicating the set value and measured value of the X-ray tube voltage and the measured value of the X-ray tube current at the time corresponding to the view. In addition to the X-ray projection data, the data collection device 25 sends information representing the set value and measurement value of the X-ray tube voltage and the measurement value of the X-ray tube current to the data collection buffer 5 as incidental information.

  The rotation unit controller 26 controls a motor (not shown) of the rotation unit 15, an X-ray controller 22, an X-ray collimator 23, a data collection device 25, and the like.

  The scanning gantry body 20 a includes a rotation controller 26 and a controller 29 that controls the imaging table 10. The controller 29 is controlled by a control signal from the central processing unit 3.

  FIG. 4 is a flowchart showing the flow of dual energy imaging processing in the X-ray CT apparatus according to the present embodiment.

  In step S11, shooting condition setting processing is executed. Specifically, the central processing unit 3 sets shooting conditions for dual energy shooting based on information input from the operator via the input device 2. The imaging conditions include an X-ray tube voltage and its switching pattern, an X-ray tube current, a scan speed (rotation speed of the rotating unit 15), the number of views to be scanned, a scan area, a slice thickness, and the like. Here, two types of 140 kV and 80 kV are set as examples of set values that are X-ray tube voltage switching targets. In addition, as a switching pattern of the set value of the X-ray tube voltage, a pattern for repeating 140 kV for 2 views and then 80 kV for 3 views, a total of 5 views for 1 cycle, and repeating this periodically is set. . Further, as the number of views to be scanned, the number of views corresponding to one rotation of the rotation unit 15, for example, 1000 views is set.

  In step S12, dual energy imaging is performed.

  First, the central processing unit 3 controls the imaging table 10 via the controller 29 and transports the subject placed on the cradle 12 to the opening of the scanning gantry 20.

  Next, the central processing unit 3 controls the motor of the rotating unit 15 via the controller 29 based on the set scan speed, and rotates the rotating unit 15 at a predetermined speed. In addition, the central processing unit 3 sends information on the set photographing conditions to the rotating unit controller 26 via the controller 29. The rotating unit controller 26 sends a control signal to the X-ray controller 22 based on information such as a set value of the X-ray tube voltage, its switching pattern, and a set value of the X-ray tube current determined by the imaging conditions. Based on the control signal, the X-ray controller 22 controls the high-voltage generator of the X-ray tube 21 so that the X-ray tube voltage and the X-ray tube current approach the set values. In addition, the rotation unit controller 26 sends a control signal to the X-ray collimator 23 based on information such as a scan area and a slice thickness determined by the imaging conditions. The X-ray collimator 23 controls the position and width of the opening of the X-ray collimator 23 based on the control signal. Further, the rotating unit controller 26 sends a control signal to the data collection device 25. The data collection device 25 collects X-ray projection data from the X-ray detector 24 at a predetermined timing based on the control signal, and transfers the X-ray projection data for each view.

  In this manner, the subject is scanned by controlling the X-ray tube 21 so as to repeatedly switch the set value of the X-ray tube voltage between a high voltage value and a low voltage value in units of several views.

  FIG. 5 is a diagram conceptually showing a state of scanning while repeatedly switching the set value of the X-ray tube voltage to a plurality of voltage values in units of several views. As shown in FIG. 5, the position of the X-ray focal point F corresponding to each view moves so as to draw a circular orbit centered on the iso center ISO, and at the time corresponding to each view, the X-ray beam Xb is irradiated from the X-ray focal point F toward an imaging field of view (SFOV). The set value of the X-ray tube voltage changes according to the set value switching pattern of the X-ray tube voltage. Here, the set value Vp (view) of the X-ray tube voltage in the view of the view number view is Vp (a), Vp (a + 1) = 140 kV, Vp (a + 2), Vp (a + 3), Vp (a + 4) = 80 kV, Vp (a + 5), Vp (a + 6) = 140 kV, Vp (a + 7), Vp (a + 8), Vp (a + 9) = 80kV, and so on.

  On the other hand, when the data collection device 25 collects the X-ray projection data, the rotating unit controller 26 obtains the control information Vs (view) of the control information of the X-ray tube 21, that is, the set value of the X-ray tube voltage at the present time. The data is sent to the data collection device 25. In parallel with this, the X-ray controller 22 receives from the X-ray tube 21 information indicating the current measured value Vm (view) of the X-ray tube voltage and the measured value Im (view) of the X-ray tube current, These pieces of information are sent to the data collection device 25 via the rotating unit controller 26 or directly. For each view, the data acquisition device 25 converts the X-ray projection data in the view into the X-ray tube voltage control value Vs (view) and the measured value Vm (view) and the X-ray tube current at the time corresponding to the view. Information indicating the measurement value Im (view) is attached and sent to the data collection buffer 5. The central processing unit 3 stores the X-ray projection data sent to the data collection buffer 5 and its accompanying information in the storage device 7.

  By performing such a scan, X-ray projection data for a plurality of views in which two types of X-ray tube voltage set values, that is, 140 kV and 80 kV are mixed, are collected together with the accompanying information.

  FIG. 6 is a diagram conceptually illustrating an example of the X-ray projection data stored in the storage device 7 and its accompanying information. As shown in FIG. 6, X-ray projection data PD (view, i, j) (i is a channel number of a detection element, j is a column number of the detection element) and associated information AD (view) are associated with each other. Remembered. The X-ray projection data PD (view, i, j) includes output data PDa (view) of the first reference detector 24a and output data PDb (view) of the second reference detector 24b. The accompanying information AD (view) includes data DVs (view) representing the control value Vs (view) of the X-ray tube voltage, data DVm (view) representing the measured value of the X-ray tube voltage, and the X-ray tube current. Data DIm (view) representing the measured values of are included.

  Note that the X-ray tube voltage setting value data DVs (view) may be information indicating the voltage value itself such as 140 kV or 80 kV, or the voltage value such as H or L (here, 140 kV is high). , 80 kV is low). Further, unlike the present embodiment, the rotation unit controller 26 generates an X-ray projection of a data file representing the control value and measurement value of the X-ray tube voltage and the measurement value of the X-ray tube current at the time corresponding to each view. The data may be created separately and sent to the central processing unit 3 via the controller 29, and the central processing unit 3 may store it in the storage device 7.

  In step S13, a tube voltage set value specifying process is executed.

  FIG. 7 is a flowchart showing an example of the tube voltage set value specifying process. The tube voltage set value specifying process (S13) is executed according to a flow as shown in FIG. 7, for example.

  First, the control value Vs (view) of the X-ray tube voltage in each view obtained by the X-ray controller 22 is read from the incidental information of the X-ray projection data (SA131).

  Next, the read control value Vs (view) of the X-ray tube voltage is determined as it is as the set value Vp (view) of the X-ray tube voltage at the time corresponding to the view (SA132).

  In step S14, an abnormal view detection process is executed.

  FIG. 8 is a flowchart illustrating an example of the abnormal view detection process. The abnormal view detection process (S14) is executed according to a flow as shown in FIG. 8, for example.

  First, the abnormal view detection unit 32 selects a view to be processed (view number is represented by q) from a plurality of views from which X-ray projection data has been collected (S141).

  Next, the abnormal view detector 32 reads the set value Vp (q) and the measured value Vm (q) of the X-ray tube voltage in the target view (S142).

ここで、ｑは対象ビューのビュー番号、Ｖp(ｑ)は対象ビューにおけるＸ線管電圧の設定値、Ｖm(ｑ)は対象ビューにおけるＸ線管電圧の測定値、ε(ｑ)は対象ビューにおけるＸ線管電圧の誤差率である。Ｘ線管電圧の誤差率は、Ｘ線管電圧の設定値と測定値との差分を設定値または測定値で割ることにより算出される。 Next, the abnormal view detection unit 32 calculates the error rate of the X-ray tube voltage in the target view according to the following equation (S143).

Here, q is the view number of the target view, Vp (q) is the set value of the X-ray tube voltage in the target view, Vm (q) is the measured value of the X-ray tube voltage in the target view, and ε (q) is the target view. Is the error rate of the X-ray tube voltage. The error rate of the X-ray tube voltage is calculated by dividing the difference between the set value of the X-ray tube voltage and the measured value by the set value or the measured value.

  Then, the abnormal view detection unit 32 determines whether or not the error rate ε (q) is equal to or greater than a predetermined threshold value (S144). Here, as an example, the threshold value is set to 10%. If this determination condition is satisfied, it is considered that X-ray tube discharge has occurred at the time corresponding to the target view, and the target view is registered as an abnormal view (S145). On the other hand, if this determination condition is not satisfied, it is considered that the X-ray tube discharge has not occurred at the time corresponding to the target view, and the target view is registered as a normal view (S146).

  Thereafter, the abnormal view detection unit 32 determines whether there is a view to be selected next as a processing target (S147). If this determination condition is satisfied, the process returns to step S141 to continue the abnormal view detection process. On the other hand, if this determination condition is not satisfied, the abnormal view detection process is terminated.

  In step S15, correction processing is executed.

  FIG. 9 is a flowchart illustrating an example of the correction process. The correction process (S15) is executed according to a flow as shown in FIG. 9, for example.

  First, the correction unit 33 selects an abnormal view to be processed (view number is represented by r) from the registered abnormal views (S151).

  Next, the correction unit 33 sets the X-ray tube voltage setting value as the target abnormal view for the view number increasing direction and the view number decreasing direction centering on the target abnormal view in the plurality of views from which the X-ray projection data is collected. The normal view that is the same is searched (S152).

  Next, the correcting unit 33 registers the normal view first detected on the view number increasing direction side as the first normal view and the normal view detected first on the view number decreasing direction side as the second normal view. (S153).

  Then, the correcting unit 33 converts the X-ray projection data PD (r, i, j) in the target abnormal view, the X-ray projection data PD (s1, i, j) in the first normal view, and the second normal view. The X-ray projection data PD (s2, i, j) at is replaced with the X-ray projection data PD ′ (r, i, j) calculated by weighted addition processing (S154). Thereby, a so-called X-ray tube discharge correction process is performed.

  Here, an example of the X-ray tube discharge correction process will be described.

  FIG. 10 is a diagram conceptually illustrating an example of the X-ray tube discharge correction process. In the lower graph in this figure, the horizontal axis is the view number view, the vertical axis is the X-ray tube voltage, and the change of the set value and the measured value of the X-ray tube voltage for the view in which the view number view ranges from a to a + 14 ( (Time change). In addition, the upper small circle in the figure schematically represents the X-ray projection data collected in the view in the above range.

その後、補正部３３は、処理対象として次に選択すべき異常ビューがあるか否かを判定する（Ｓ１５５）。この判定条件が成立する場合には、ステップＳ１５１に戻って補正処理を続行する。 Here, for example, as shown in FIG. 10, the set value Vp (view) of the X-ray tube voltage is a switching pattern of 140 kV for the first and second views and 80 kV for the third to fifth views for one cycle. As described above, the view number view = a is periodically repeated. The measured value Vm (view) changes so as to take a value close to the set value Vp (view). However, for the three views in which the view numbers view are a + 6 to a + 8, an error from the set value set value Vp (view). The value is significantly lower than 10%. In this example, three views with view numbers view = a + 6 to a + 8 are detected as abnormal views. Then, the X-ray projection data of each abnormal view is corrected to be replaced with the X-ray projection data PD ′ (view) calculated using the primary weighted addition process, for example, as in the following equation.

Thereafter, the correction unit 33 determines whether there is an abnormal view to be selected next as a processing target (S155). If this determination condition is satisfied, the process returns to step S151 to continue the correction process.

  On the other hand, when this determination condition is not satisfied, the correction unit 33 targets each of the plurality of views as output data PDa (view) and PDb (view) of the first and second reference detectors in the target view. ) Is read out, and the output signal value of the reference detector in the target view is obtained. Then, based on the output signal value, an X-ray dose correction process for correcting the level of the data value of the X-ray projection data in the target view is performed (S156). When the X-ray dose correction processing is completed for all of the plurality of views, the correction processing (S15) is ended. Note that the output signal value of the reference detector can be, for example, the sum (count value) or the average value of the data values obtained from each detection element constituting the reference detector.

  In step S16, an image generation process is executed.

  FIG. 11 is a flowchart illustrating an example of image generation processing. The image generation process (S16) is executed according to a flow as shown in FIG. 11, for example.

  First, X-ray projection data is extracted for each set value of the X-ray tube voltage (S161). Here, the image generation unit 34 extracts the X-ray projection data of the view whose X-ray tube voltage setting value is 140 kV as the first group, and the X-ray tube voltage setting value is 80 kV. The X-ray projection data of the view is extracted as the second group.

  Next, the X-ray projection data of the missing view is interpolated in the view direction (S162). Here, for the first group with a set value of 140 kV, X-ray projection data of the same view as the view with the set value of 80 kV is not collected and is missing. Therefore, the image generation unit 34 interpolates the X-ray projection data of the missing view by performing weighted addition processing on the X-ray projection data of the view located in the vicinity of the missing view and having a setting value of 140 kV. Similarly, for the second group with the setting value of 80 kV, X-ray projection data of the same view as the view with the setting value of 140 kV is not collected and is missing. Therefore, the image generation unit 34 interpolates the X-ray projection data of these missing views by performing a weighted addition process on the X-ray projection data of the view located near the missing view and having a setting value of 80 kV.

  Next, an image reconstruction process is executed (S163). Here, based on the X-ray projection data of each interpolated view belonging to the first group whose set value is 140 kV, the image generation unit 34 uses the first tomogram G140 when the X-ray tube voltage is 140 kV. Reconstruct the image. Similarly, the image generation unit 34 uses the second tomogram when the X-ray tube voltage is 80 kV based on the X-ray projection data of each interpolated view belonging to the second group whose setting value is 80 kV. The image G80 is reconstructed.

  Then, a ratio image / difference image generation process is executed (S164). Here, the image generation unit 34 obtains a pixel value ratio for each corresponding pixel between the first tomographic image G140 and the second tomographic image G80, and sets the pixel value ratio at the same position as the corresponding pixel. A ratio image having pixel values of pixels is generated. Alternatively, after the image generation unit 34 performs level adjustment of the pixel value between the first tomographic image G140 and the second tomographic image G80, the difference between the pixel values is obtained for each corresponding pixel, and the pixel value A difference image is generated in which the difference between the two pixels is the pixel value of the pixel at the same position as the corresponding pixel. The ratio image is an image that can separately represent each substance in the tomographic image, and the difference image is an image in which a predetermined substance is emphasized or suppressed. The central processing unit 3 displays these images on the monitor 6 or outputs them to other devices.

  As described above, according to the present embodiment, the set value and the measured value of the X-ray tube voltage in the plurality of views in which the X-ray projection data is collected are specified, and the difference between the set value and the measured value of the X-ray tube voltage is predetermined. Since the X-ray projection data of the view exceeding the level is corrected, the X-ray tube discharge can be detected based on the deviation from the X-ray tube voltage setting value as a reference, and the X-ray tube voltage setting value. X-ray tube discharge correction can be performed by using an imaging method in which scanning is performed by repeatedly switching a plurality of voltage values in units of several views.

  In the present embodiment, the set value of the X-ray tube voltage corresponding to each view is specified based on the X-ray tube voltage control information obtained from the rotating unit controller 26 that performs high-voltage control of the X-ray tube 21. Therefore, a slight delay or the like occurs in the control of the rotation speed of the rotating unit 15 and the timing for reading the output of the X-ray detector 24, and the correspondence between each view and the set value of the X-ray tube voltage is initially set. Even if it is delayed from what was planned, it is possible to accurately grasp the correspondence and detect an abnormal view with high reliability.

(Second Embodiment)
The present embodiment is an X-ray CT apparatus having substantially the same configuration as that of the first embodiment, but also executes a reference detector shielding correction process in addition to the X-ray tube discharge correction process. It is different.

  In the present embodiment, the central processing unit 3 further includes a reference detector output signal value estimation unit (output signal estimation means) 35 as shown in FIG.

  The reference detector output signal value estimation unit 35 is based on the set value of the X-ray tube voltage specified by the tube voltage set value specifying unit 31 and corresponds to each of a plurality of views from which X-ray projection data is collected. The output signal value of the reference detector at the time is estimated.

  Further, the abnormal view detection unit 32 includes the estimated output signal value of the reference detector at the corresponding time among the plurality of views, and the output signal value of the reference detector measured by the data collection device 25. A view whose difference is equal to or greater than a predetermined level is detected as an abnormal view.

  In addition to the X-ray tube discharge correction process, the correction unit 33 executes a reference detector shielding correction process. As shown in FIG. 13, the reference detector shielding correction process is generated from the X-ray tube 21, and the X-ray Xb to be incident on the first and second reference detectors 24 a and 24 b is caused by the subject H. This is a process of correcting the X-ray projection data collected when the X-ray intensity cannot be properly specified due to shielding.

  More specifically, the correcting unit 33 sets, among the detected abnormal views, abnormal views belonging to an abnormal view group in which abnormal views are continuously arranged over a predetermined number or more as a continuous abnormal view, and does not belong to this abnormal view group. The abnormal view is a discontinuous abnormal view. Although details will be described later, the discontinuous abnormal view can be considered as an abnormal view due to X-ray tube discharge, and the continuous abnormal view can be considered as an abnormal view due to shielding of the reference detector.

  Then, the correction unit 33 brings the projection data of the discontinuous abnormal view close to the discontinuous abnormal view among the plurality of views, and the set value of the X-ray tube voltage is the same as that of the discontinuous abnormal view. The correction is made based on the projection data of the normal view different from the abnormal view. Thereby, X-ray tube discharge correction processing is executed.

  In addition, the correction unit 33 makes the projection data of the continuous abnormal view close to the estimated value of the output signal value of the reference detector in the continuous abnormal view or the continuous abnormal view of the plurality of views. The correction is made based on the measured value of the output signal value of the reference detector in the normal view different from the abnormal view. Thereby, the reference detector shielding process is executed.

  The data collection device 25 is an example of an output signal value measurement unit in the present invention.

  FIG. 14 is a flowchart showing the flow of dual energy imaging processing in the X-ray CT apparatus according to the present embodiment.

  In steps S21 to S23, as in steps S11 to S13 in the first embodiment, the imaging condition setting process, dual energy imaging, and the tube voltage setting value specifying process are executed.

  In step S24, reference detector output signal value estimation processing is executed. Specifically, the reference detector output signal value estimation unit 35 collects X-ray projection data based on the specified X-ray tube voltage setting value, X-ray tube current setting value or measurement value, and the like. The output signal values of the first and second reference detectors 24a and 24b at each time point corresponding to each of the plurality of views are estimated. Note that the estimated value RLa, p (view) of the output bell of the first reference detector 24a and the estimated value RLb, p (view) of the output signal value of the second reference detector 24b are the data collection system. When there is left-right symmetry in the channel direction, it is usually the same.

  In step S25, an abnormal view detection process is executed.

  FIG. 15 is a flowchart illustrating an example of an abnormal view detection process. The abnormal view detection process (S25) is executed according to a flow as shown in FIG. 15, for example.

  First, the abnormal view detection unit 32 selects a view to be processed (view number is represented by q) from a plurality of views from which X-ray projection data has been collected (S251).

  Next, the abnormal view detection unit 32 reads the estimated value RLa, p (q) of the output signal value of the first reference detector in the target view. Further, the abnormal view detection unit 32 reads the output data PDa (q) of the first reference detector, and calculates the measured value RLa, m (q) of the output signal value (S252).

ここで、ｑは対象ビューのビュー番号、ＲＬa,p(ｑ)は対象ビューにおける第１の参照用検出器の出力信号値の推定値、ＲＬa,m(ｑ)は対象ビューにおける第１の参照用検出器の出力信号値の測定値、εRL,a(ｑ)は対象ビューにおける第１の参照用検出器の出力信号値の誤差率である。第１の参照用検出器の出力信号値の誤差率は、第１の参照用検出器の出力信号値の推定値と測定値との差分を推定値または測定値で割ることにより算出される。 Next, the abnormal view detection unit 32 calculates the error rate of the output signal value of the first reference detector in the target view according to the following equation (S253).

Here, q is the view number of the target view, RLa, p (q) is an estimated value of the output signal value of the first reference detector in the target view, and RLa, m (q) is the first reference in the target view. The measured value of the output signal value of the detector for detector, εRL, a (q) is the error rate of the output signal value of the first reference detector in the target view. The error rate of the output signal value of the first reference detector is calculated by dividing the difference between the estimated value of the output signal value of the first reference detector and the measured value by the estimated value or the measured value.

  Then, the abnormal view detection unit 32 determines whether or not the error rate εRL, a (q) is equal to or greater than a predetermined threshold value (S254). Here, as an example, the threshold value is set to 10%.

  If this determination condition is satisfied, the process proceeds to step S255. On the other hand, if this determination condition is not satisfied, the target view is registered as a normal view, and the measurement value RLa, m (q) of the output signal value of the first reference detector is detected for reference of the target view. Is registered as an output signal value RL (q) (S259), and then the process proceeds to step S2511.

  In step S255, the output data PDb (q) of the second reference detector is read, and the measured value RLb, m (q) of the output signal value is calculated (S255).

そして、異常ビュー検出部３２は、この誤差率εRL,b(ｑ)が所定のしきい値以上であるか否かを判定する（Ｓ２５７）。なお、ここでは、その一例として、しきい値を１０％に設定する。 Next, the abnormal view detection unit 32 calculates the error rate of the output signal value of the second reference detector in the target view according to the following equation (S256).

Then, the abnormal view detection unit 32 determines whether or not the error rate εRL, b (q) is equal to or greater than a predetermined threshold value (S257). Here, as an example, the threshold value is set to 10%.

  If this determination condition is satisfied, the target view is registered as an abnormal view (S258), and the process proceeds to step S2511. On the other hand, if this determination condition is not satisfied, the target view is registered as a normal view, and the measurement value RLb, m (q) of the output signal value of the second reference detector is detected for reference in the target view. Is registered as an output signal value RL (q) of the device (S2510), and then the process proceeds to step S2511.

  In step S2511, the abnormal view detection unit 32 determines whether there is a view to be selected next as a processing target. If this determination condition is satisfied, the process returns to step S251 to continue the abnormal view detection process. On the other hand, if this determination condition is not satisfied, the abnormal view detection process is terminated.

  In step S26, correction processing is executed.

  FIG. 16 is a flowchart illustrating an example of the correction process. The correction process (S26) is executed according to a flow as shown in FIG. 16, for example.

  First, the correction unit 33 selects an abnormal view to be processed (view number is represented by r) from the registered abnormal views (S261).

  Next, the correcting unit 33 determines whether or not the target abnormal view is a continuous abnormal view belonging to an abnormal view group in which the abnormal views are continuously arranged over a predetermined number (S262). Here, as an example, the predetermined number is 40.

  In general, the time during which the X-ray tube discharge occurs is relatively short, and corresponds to, for example, several views to a dozen views under general imaging conditions. In contrast, the time during which the reference detector is shielded is relatively long, and corresponds to, for example, several tens to several hundred views under general imaging conditions. Therefore, by determining whether or not the target abnormal view is a continuous abnormal view belonging to an abnormal view group in which the abnormal views are continuously arranged over a predetermined number or more, the target abnormal view is caused by X-ray tube discharge. It is possible to determine whether it is due to the shielding of the reference detector.

  When this determination condition is satisfied, that is, when it is determined that the target abnormal view is a continuous abnormal view, the process proceeds to step S263, and the reference detector shielding correction process is executed. On the other hand, when this determination condition is not satisfied, that is, when it is determined that the target abnormal view is a discontinuous abnormal view, the process proceeds to step S264 and X-ray tube discharge correction processing is executed.

  In step S263, the correction unit 33 displays the estimated value RLa, p (r) or RLb, p (r) of the output signal value of the first or second reference detector in the target abnormal view or the target abnormal view. The output signal value RL (r + α) or RL (r−α) of the reference detector in the adjacent normal view is read out. Then, the read output signal value of the reference detector is registered as the output signal value RL (r) of the reference amount detector in the target abnormality view (S263). As a result, the estimated value in the abnormal view or the measurement value in another normal view is substituted as the output signal value of the reference detector that should have been originally obtained in the abnormal view due to the reference detector shielding. Thereafter, the process proceeds to step S267.

  On the other hand, in step S264, the correction unit 33 targets the set values of the X-ray tube voltage in the view number increasing direction and the view number decreasing direction centering on the target abnormal view in the plurality of views from which the X-ray projection data is collected. A normal view that is identical to the abnormal view is searched (S264).

  Next, the correcting unit 33 registers the normal view first detected on the view number increasing direction side as the first normal view and the normal view detected first on the view number decreasing direction side as the second normal view. (S265).

  Then, the correcting unit 33 converts the X-ray projection data PD (r, i, j) in the target abnormal view, the X-ray projection data PD (s1, i, j) in the first normal view, and the second normal view. The X-ray projection data PD (s2, i, j) in is replaced with the X-ray projection data PD ′ (r, i, j) obtained by the primary weighted addition process or the multi-order weighted addition process (S266). In particular, in the multi-order weighted addition process, there is an advantage that beam hardening correction can be performed simultaneously. Thereafter, the process proceeds to step S267.

  In step S267, the correction unit 33 determines whether there is an abnormal view to be selected next as a processing target (S267). If this determination condition is satisfied, the process returns to step S261 to continue the correction process.

  On the other hand, when this determination condition is not satisfied, the correction unit 33 corrects the level of the data value of the X-ray projection data in the view using the output signal value of the reference detector in the view for each view. A dose correction process is performed (S268), and the correction process is terminated.

  The reference detector shielding correction process is executed in steps S263 and S268, and the X-ray tube discharge correction process is executed in steps S264 to S266.

  Here, an example of the X-ray tube discharge correction process and the reference detector shielding correction process will be described.

  FIG. 17 is a graph showing an example of changes in the estimated value and the measured value of the output signal value of the reference detector with respect to the view. In the graph of this figure, the horizontal axis is the view number view, the vertical axis is the output signal value of the reference detector, and the output signal of the reference detector for views in the range of the view number view from 0 to N (≈1000). It represents changes in the estimated value RLp (view) and the measured value RLm (view).

  Here, for example, as shown in FIG. 17, the estimated value RLp (view) of the output signal value of the reference detector fluctuates somewhat as the set value of the X-ray tube voltage is switched, but is at a substantially constant level. I take the. The measurement value RLm (view) basically changes so as to take a value close to the estimated value, but the view number view is a view with a to a + m (m <40) and b to b + n (n> 40). Takes a value significantly lower than the estimated value with an error rate of 10% or more.

  In this example, views with view numbers view = a to a + m and b to b + n are detected as abnormal views. Then, the X-ray tube discharge correction process similar to that in the first embodiment is performed on the X-ray projection data of the abnormal view having the view numbers view = a to a + m. On the other hand, the above-described reference detector shielding correction process is performed on the X-ray projection data of the abnormal views with the view numbers view = b to b + n.

  As described above, according to the present embodiment, the estimated value and the measured value of the output signal value of the reference detector at each time point of each of the plurality of views from which the X-ray projection data has been collected are specified, Since the error between the estimated value of the output signal value of the reference detector and the measured value is obtained and the X-ray projection data of the view in which the error exceeds a predetermined level is corrected, the estimated value of the output signal value of the reference detector The X-ray tube discharge can be detected on the basis of the deviation from the reference, and the CT scan is performed by controlling the X-ray tube to repeatedly switch the X-ray tube voltage to a plurality of set values in units of several views. X-ray tube discharge correction processing can be performed while using the imaging method.

  In addition, according to the present embodiment, since an abnormal view is detected based on the output signal value of the reference detector, X-rays generated from the X-ray tube and incident on the reference detector are shielded by the subject. An abnormal view due to the reference detector shielding can also be detected, and the X-ray dose correction processing for the X-ray projection data can be appropriately performed.

(Third embodiment)
FIG. 18 is a flowchart illustrating an example of the tube voltage setting value specifying process. In the first and second embodiments, the tube voltage set value specifying unit 31 may execute the tube voltage set value specifying process (S13 or S23) according to a flow as shown in FIG. 18, for example.

  First, based on the set imaging conditions, one cycle of the switching pattern of the set value of the X-ray tube voltage is specified (SB131).

  Next, one cycle of the specified switching pattern is periodically allocated from a predetermined number of views (which may be the first view) to a plurality of views from which X-ray projection data has been collected (SB132). .

  According to the present embodiment, when the temporal correspondence between the change in the view for collecting X-ray projection data and the change in the set value of the X-ray tube voltage is constant, the correspondence is predicted in advance. Therefore, the set value of the X-ray tube voltage corresponding to each view can be specified without complicated calculation.

(Fourth embodiment)
FIG. 19 is a flowchart illustrating an example of the tube voltage setting value specifying process. In the first and second embodiments, the tube voltage set value specifying unit 31 may execute the tube voltage set value specifying process (S13 or S23) according to a flow as shown in FIG. 19, for example.

  First, based on the set imaging conditions, one cycle of the switching pattern of the set value of the X-ray tube voltage is specified (SC131).

  Next, the first view of the plurality of views from which the X-ray projection data has been collected is set as the target view, and the measured value of the X-ray tube voltage in this target view is read (SC132).

  Next, it is determined whether or not the set value of the first view for one cycle of the specified switching pattern matches the measured value of the read target view within a predetermined error range (SC133).

  When this determination condition is satisfied, one cycle of the specified switching pattern is periodically allocated from the target view to the plurality of views (SC134).

  On the other hand, if this determination condition is not satisfied, the target view in the plurality of views is updated to the next view. Then, the number of views corresponding to one cycle of the specified switching pattern is designated from the updated target view, and the measured value of the X-ray tube voltage in the designated view is read (SC135).

  Then, it is determined whether or not the change pattern of the measured value of the X-ray tube voltage in the designated view matches the specified switching pattern within a predetermined error range (SC136).

  If this determination condition is satisfied, one cycle of the specified switching pattern is periodically assigned to the plurality of views from the head view in the designated view (SC137). On the other hand, if this determination condition is not satisfied, the process returns to step SC135 to update the target view to the next view and continue the processing.

  According to the present embodiment, the temporal correspondence between the change in the view for collecting the X-ray projection data and the change in the set value of the X-ray tube voltage, the change in the measured value of the X-ray tube voltage and the X-ray tube voltage Even when there is a possibility that this temporal correspondence relationship may be shifted for each scan, the set value of the X-ray tube voltage corresponding to each view Can be specified.

(Fifth embodiment)
FIG. 20 is a flowchart illustrating an example of the tube voltage setting value specifying process. In the first and second embodiments, the tube voltage set value specifying unit 31 may execute the tube voltage set value specifying process (S13 or S23) according to a flow as shown in FIG. 20, for example.

  First, based on the set imaging conditions, one cycle of the switching pattern of the set value of the X-ray tube voltage is specified (SD131).

  Next, the first view of the plurality of views from which the X-ray projection data is collected is set as a target view, and the measurement value of the output signal value of the reference detector in this target view is read (SD132).

  Next, the measured value of the X-ray tube voltage in the target view is estimated by referring to the set value of the X-ray tube current and the like based on the measured output signal value of the reference detector in the read target view. (SD133).

  Next, the set value of the first view for one cycle of the specified switching pattern and the measured value in the estimated target view (hereinafter, the estimated measured value is referred to as an estimated measured value) are within a predetermined error range. It is determined whether or not they match (SD134).

  When this determination condition is satisfied, one cycle of the specified switching pattern is periodically assigned from the target view to the plurality of views (SD135).

  On the other hand, if this determination condition is not satisfied, the target view in the plurality of views is updated to the next view. Then, the number of views corresponding to one cycle of the specified switching pattern is designated from the updated target view, and the measured value of the output signal value of the reference detector in this designated view is read (SD136).

  Next, the measured value of the X-ray tube voltage in the designated view is estimated by referring to the set value of the X-ray tube current and the like based on the measured value of the output signal value of the reference detector in the designated view read out. (SD137).

  Then, it is determined whether or not the change pattern of the estimated measurement value of the X-ray tube voltage in the designated view matches the specified switching pattern within a predetermined error range (SD138).

  When this determination condition is satisfied, one cycle of the specified switching pattern is periodically assigned to the plurality of views from the head view in the designated view (SD139). On the other hand, if this determination condition is not satisfied, the process returns to step SD136 to update the target view to the next view and continue the processing.

  According to the present embodiment, the temporal correspondence between the change in the view for collecting the X-ray projection data and the change in the set value of the X-ray tube voltage is estimated from the measured value of the reference detector output signal value. When it can be inferred by matching the change in the estimated measurement value of the obtained X-ray tube voltage and the switching pattern of the set value of the X-ray tube voltage, and this temporal correspondence may be shifted for each scan The set value of the X-ray tube voltage corresponding to each view can be specified.

  The present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention.

  In each of the embodiments described above, the correction unit 33 calculates the X-ray projection data to be replaced when performing the X-ray tube discharge correction by performing a primary weighted addition process on the X-ray projection data of normal views. However, for example, the normal view X-ray projection data may be calculated by multi-order weighted addition processing.

  Further, in each of the above embodiments, the X-ray tube voltage has two types of set values, but may be three or more types.

  In each of the above embodiments, the reference detector is a part of the X-ray detector 24, but may be provided independently of the X-ray detector 24. Further, the position where the reference detector is installed may be a place closer to the X-ray tube 21. The number of reference detectors may be only one, but in this case, the threshold processing for the error rate of the output signal value of the reference detector is performed only once.

  In the second embodiment, both the X-ray tube discharge correction process and the reference detector shielding correction process can be corrected. However, only the X-ray tube discharge correction process or the reference detector shielding correction can be performed. It may be configured to allow only processing.

Further, in each of the above embodiments, the image generation unit 34 generates a ratio image or a difference image, but the image to be generated is not limited to such an image. For example, an image corresponding to a tomographic image of an X-ray tube voltage different from the set value may be used.

  Further, in each of the embodiments described above, the switching pattern of the set value of the X-ray tube voltage is a pattern in which a predetermined pattern is periodically repeated. However, such a periodic pattern may not be used.

  In each of the above-described embodiments, the set values of the X-ray tube voltage in all the views from which X-ray projection data has been collected are specified and an abnormal view is detected from all the views. The set value of the X-ray tube voltage in the partial view from which data is collected may be specified, and an abnormal view may be detected from the partial view. For example, an X-ray tube voltage setting value in a view obtained by thinning a part from all the views may be specified, and an abnormal view may be detected from the view. Alternatively, based on the control information of the X-ray tube voltage, a view in which the set value of the X-ray tube voltage is a specific voltage value may be specified in reverse, and an abnormal view may be detected in the specified view. The specific voltage value is, for example, a voltage value equal to or higher than a predetermined voltage value or a maximum voltage value among a plurality of voltage values to be switched. In this case, since the X-ray tube discharge is more likely to occur as the voltage value is higher, an abnormal view due to the X-ray tube discharge can be detected efficiently.

It is a block diagram which shows the X-ray CT apparatus which is one Embodiment of this invention. It is a figure which shows the structure of the central processing unit in 1st Embodiment. It is a figure which shows the data collection system of a rotation part. It is a flowchart which shows the flow of the dual energy imaging process in the X-ray CT apparatus by 1st Embodiment. It is a figure which shows notionally a mode that it scans, changing the setting value of X-ray tube voltage to several voltage value repeatedly in several view units. It is a figure which shows notionally an example of X-ray projection data and its incidental information. It is a flowchart which shows an example of the tube voltage setting value specific process in 1st Embodiment. It is a flowchart which shows an example of the abnormal view detection process in 1st Embodiment. It is a flowchart which shows an example of the correction process in 1st Embodiment. It is a figure which shows notionally an example of the X-ray tube discharge correction process in 1st Embodiment. It is a flowchart which shows an example of the image generation process in 1st Embodiment. It is a figure which shows the structure of the central processing unit in 2nd Embodiment. It is a figure which shows the state of the reference detector shielding. It is a flowchart which shows the flow of the dual energy imaging process in the X-ray CT apparatus by 2nd Embodiment. It is a flowchart which shows an example of the abnormal view detection process in 2nd Embodiment. It is a flowchart which shows an example of the correction process in 2nd Embodiment. It is a graph which shows an example of the change with respect to the view of the estimated value and measured value of the output signal value of a reference detector. It is a flowchart which shows an example of the tube voltage setting value specific process in 3rd Embodiment. It is a flowchart which shows an example of the tube voltage setting value specific process in 4th Embodiment. It is a flowchart which shows an example of the tube voltage setting value specific process in 5th Embodiment.

Explanation of symbols

100 X-ray CT apparatus 1 Operation console 2 Input device 3 Central processing unit 5 Data collection buffer 6 Monitor 7 Storage device 10 Imaging table 12 Cradle 20 Scanning gantry 20a Scanning gantry main body 21 X-ray tube 22 X-ray controller 23 X-ray collimator 24 X Line detector 24a First reference detector 24b Second reference detector 25 Data collection device 26 Rotation unit controller 29 Control controller 30 Slip ring 31 Tube voltage set value identification unit 32 Abnormal view detection unit 33 Correction unit 34 Image Generation unit 35 Reference detector output signal value estimation unit

Claims (12)

X-ray CT apparatus provided with X-ray data collection means for scanning a subject and collecting X-ray projection data of a plurality of views while repeatedly switching a set value of an X-ray tube voltage to a plurality of voltage values in units of one or several views Because
Setting value specifying means for specifying a setting value of the X-ray tube voltage in the plurality of views;
Tube voltage measuring means for measuring X-ray tube voltage in the plurality of views;
An abnormal view detecting means for detecting an abnormal view in which a difference between a set value and a measured value of the X-ray tube voltage is a predetermined level or more among the plurality of views;
An X-ray CT apparatus comprising correction means for correcting X-ray projection data of the abnormal view.   The correction means has X-ray projection data of an abnormal view close to the abnormal view of the plurality of views, the set value of the X-ray tube voltage is the same as the abnormal view, and the detected abnormal view The X-ray CT apparatus according to claim 1, wherein correction is performed based on X-ray projection data of a view different from that of the first view. X-ray CT apparatus provided with X-ray data collection means for scanning a subject and collecting X-ray projection data of a plurality of views while repeatedly switching a set value of an X-ray tube voltage to a plurality of voltage values in units of one or several views Because
A reference detector for detecting X-rays generated from the X-ray tube and outputting a signal corresponding to the intensity of the X-ray;
Setting value specifying means for specifying a setting value of the X-ray tube voltage in the plurality of views;
Output signal estimation means for estimating an output signal value of the reference detector in the plurality of views based on a set value of an X-ray tube voltage of the view;
An output signal measuring means for measuring an output signal value of the reference detector in the plurality of views;
An abnormal view detection means for detecting an abnormal view in which the difference between the estimated value and the measured value of the output signal value of the reference detector is a predetermined level or more among the plurality of views;
An X-ray CT apparatus comprising correction means for correcting X-ray projection data of the abnormal view.   The correction unit is configured to make X-ray projection data of abnormal views that are continuous or discontinuous less than a predetermined number close to the abnormal view of the plurality of views, and the set value of the X-ray tube voltage is the abnormal view. The X-ray CT apparatus according to claim 3, wherein correction is performed based on X-ray projection data of a view different from the detected abnormal view.   The correction unit is configured to detect X-ray projection data of abnormal views that are continuous in a predetermined number or more, an estimated value of the output signal value in the abnormal views, or close to the abnormal view among the plurality of views, and the detection The X-ray CT apparatus according to claim 3 or 4, wherein correction is performed based on a measurement value of the output signal value in a view different from the abnormal view.   The correction means obtains X-ray projection data of an abnormal view by performing a primary weighted addition process or a multi-order weighted addition process on projection data of views different from the detected abnormal view among the plurality of views. 6. The X-ray CT apparatus according to claim 2, wherein the X-ray CT apparatus is replaced with line projection data.   The setting value specifying unit specifies the setting value of the X-ray tube voltage in the plurality of views based on the control information of the X-ray tube voltage obtained from the data collection unit. The X-ray CT apparatus according to Item 1.   The set value specifying means specifies the set value of the X-ray tube voltage in the plurality of views by assigning a switching pattern of the set value of the set X-ray tube voltage from a predetermined number of views of the plurality of views. The X-ray CT apparatus according to any one of claims 1 to 6.   The set value specifying means specifies the set value of the X-ray tube voltage in the plurality of views based on a switching pattern of the set value of the set X-ray tube voltage and a time change of the measured value of the X-ray tube voltage. The X-ray CT apparatus according to any one of claims 1 to 6.   The set value specifying means is configured to determine the X-ray tube voltage in the plurality of views based on a switching pattern of the set value of the set X-ray tube voltage and a time change of the measured value of the output signal value of the reference detector. The X-ray CT apparatus according to any one of claims 3 to 5, wherein a set value is specified. X-ray CT apparatus provided with X-ray data collection means for scanning a subject and collecting X-ray projection data of a plurality of views while repeatedly switching a set value of an X-ray tube voltage to a plurality of voltage values in units of one or several views Because
Set value specifying means for specifying a set value of an X-ray tube voltage in at least one of the plurality of views;
Tube voltage measuring means for measuring an X-ray tube voltage in the at least one view;
An abnormal view detecting means for detecting an abnormal view in which a difference between a set value and a measured value of the X-ray tube voltage is a predetermined level or more in the at least one view;
An X-ray CT apparatus comprising correction means for correcting X-ray projection data of the abnormal view. X-ray CT apparatus provided with X-ray data collection means for scanning a subject and collecting X-ray projection data of a plurality of views while repeatedly switching a set value of an X-ray tube voltage to a plurality of voltage values in units of one or several views Because
A reference detector for detecting X-rays generated from the X-ray tube and outputting a signal corresponding to the intensity of the X-ray;
Set value specifying means for specifying a set value of an X-ray tube voltage in at least one of the plurality of views;
Output signal estimation means for estimating an output signal value of the reference detector in the at least one view based on a set value of an X-ray tube voltage of the view;
Output signal measuring means for measuring an output signal value of the reference detector in the at least one view;
An abnormal view detection means for detecting an abnormal view in which the difference between the estimated value and the measured value of the output signal value of the reference detector is a predetermined level or more in the at least one view;
An X-ray CT apparatus comprising correction means for correcting X-ray projection data of the abnormal view.

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