JP2010252951A - X-ray ct apparatus and data acquisition method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray CT apparatus which is suitable for an operation in clinical practice and acquires highly accurate CT images without a ring artifact. <P>SOLUTION: An air calibration calculation part 165 subtracts air calibration data stored in a storage device 114 from photographing data acquired by a photographing data acquisition part 163 and performs calibration processing, and an image reconstruction calculation part 166 inputs data after the calibration processing is performed, reconstructs and calculates image data and outputs them to an image display device 116. When a ring artifact is detected in the outputted image, an air calibration data acquisition part 164 acquires new air calibration data, and an air calibration data exchange part 167 replaces the air calibration data used until the point of time with the new air calibration data. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an X-ray CT apparatus and a data acquisition method using the same, and more particularly to a technique for removing ring artifacts from a tomographic image taken by an X-ray CT apparatus.

  In the X-ray CT apparatus, an X-ray source and an X-ray detector are installed in opposing positions with a rotation center in a rotatable gantry. The subject is placed near the center of rotation of the gantry, the subject is irradiated with X-rays while rotating the gantry, and the X-ray detector detects the dose of transmitted X-rays that have passed through the subject. The detected X-ray dose is used as imaging data, and the imaging data is subjected to a calculation process called image reconstruction to create a tomographic image perpendicular to the body axis of the subject.

Conventionally, one tomographic image has been obtained by one rotation of the gantry. However, in recent years, by arranging a plurality of X-ray detectors in the body axis direction, a plurality of tomographic images can be obtained once by one rotation of the gantry. The method of getting to is becoming widespread. As a result, the three-dimensional information inside the subject can be obtained in a short time, and at the same time, even if there is a movement in the subject, for example, a heart beat, it is possible to take an image so that the image is not substantially blurred. It was.
On the other hand, since a plurality of X-ray detectors are used, there is a problem in that uneven sensitivity occurs. Due to the uneven sensitivity of the X-ray detector, arc-shaped noise called ring artifact appears in the tomographic image reconstructed.

  Therefore, in order to remove ring artifacts, a calibration process called air calibration is performed. The air calibration data acquired by imaging in the absence of the subject represents the sensitivity unevenness of the X-ray detector itself. Since the sensitivity data is added to the radiographed data when the subject is imaged, air calibration is a calibration process that subtracts the air calibration data obtained from the radiographed data and cancels the sensitivity irregularity. is there.

  Here, the X-ray detector deteriorates unevenly every time it is irradiated with X-rays. Therefore, when the number of imaging is increased to some extent, the distribution of sensitivity unevenness changes. Therefore, it is necessary to periodically acquire air calibration data necessary for image calibration. In clinical practice, it is ideal to perform air calibration once every morning for every imaging condition (protocol) and acquire air calibration data necessary for calibration, but it takes time and effort, Actually, air calibration for specific imaging conditions is performed.

  For example, in Patent Document 1, air calibration is performed, the data and the time when the data is performed are stored, and the operator of the X-ray CT apparatus is warned immediately before imaging of the patient if the time is longer than a predetermined period. And an X-ray CT apparatus for notifying an operator of the necessity of air calibration is described.

JP-A-2005-237422

However, in the X-ray CT apparatus described in Patent Document 1, the air calibration was performed only recently, that is, the time from the time when the last air calibration was performed to the current time when the patient is imaged. Even within the predetermined period, the sensitivity variation of the X-ray detector appears, and ring artifacts may occur.
In addition, if the X-ray source or X-ray detector is adjusted for any reason after air calibration, re-air calibration is required, but the calibration time must also be initialized. That's how much maintenance it takes.
Further, even when air calibration is performed periodically, there is a problem that it is not known whether this is an appropriate period for performing calibration. For example, there are cases where air calibration is performed more than necessary, manpower and time are used more than necessary, and the deterioration of the device is accelerated.Therefore, it is difficult to determine the appropriate time for air calibration even in the operation of the device. is there.
The present invention has been made in view of the above points, and an object of the present invention is to provide an X-ray CT apparatus that is suitable for apparatus operation in a clinical field and that acquires a high-accuracy CT image without ring artifacts.

  In order to achieve the above-described object, the present invention provides an X-ray source that irradiates a subject with X-rays, an X-ray detector that is disposed opposite to the X-ray source and detects transmitted X-rays that have passed through the subject, A gantry that includes an X-ray source and an X-ray detector, rotates around the subject, a storage device that stores the transmitted X-ray amount detected by the X-ray detector by rotating the gantry as imaging data, and based on the imaging data An X-ray CT apparatus comprising: an image reconstruction device that reconstructs a tomographic image of a subject; and an image display device that displays a tomographic image reconstructed by the image reconstruction device, wherein the subject is not disposed An air calibration data acquisition unit that acquires X-ray dose data detected by the X-ray detector by rotating the gantry as air calibration data, and an air calibration storage unit that stores the air calibration data The air calibration data read from the air calibration storage unit is subtracted from the imaging data of the subject, and the air calibration calculation unit for executing the air calibration and the air calibration execution result by the air calibration calculation unit are used. Detecting a ring artifact in the tomographic image reconstructed by the image reconstructing apparatus, and when the ring artifact is detected by the detecting means, the air calibration data acquisition unit obtains new air calibration data. The air calibration calculation unit obtains the air calibration data by subtracting the new air calibration data from the imaging data, and executes the air calibration using the new air calibration data by the detection unit. In the tomographic image by the image reconstruction unit based on air calibration execution result is reconstituted, if you ring artifact is not detected, the air calibration storage unit, and to store the new air calibration data.

  In other words, air calibration is performed by subtracting existing air calibration data from imaging data obtained by CT imaging of a subject, and when a ring artifact is detected in a tomographic image reconstructed based on the execution result, the air calibration is performed again. Calibration data is acquired, and air calibration is executed using newly acquired air calibration data to obtain a tomographic image excluding the influence of ring artifacts.

  According to the present invention, since an image free from ring artifacts can be obtained, it is possible to improve the efficiency of device operation in a clinical field.

It is a hardware block diagram of a X-ray CT apparatus. It is a functional block block diagram of a central controller. It is a flowchart which shows the flow of the imaging | photography process by a X-ray CT apparatus. It is a functional block block diagram of the central control apparatus of 2nd Embodiment. It is a flowchart which shows the flow of the air calibration time prediction process by X-ray CT apparatus. It is a figure which shows an example of the time series data of imaging | photography conditions and air calibration implementation time. It is a functional block block diagram of the central control apparatus of 3rd Embodiment. It is a flowchart which shows the flow of the detector replacement time prediction process by X-ray CT apparatus. It is a functional block block diagram of the central control apparatus of 4th Embodiment. It is a flowchart which shows the flow of the air calibration time determination process by X-ray CT apparatus.

  Hereinafter, preferred embodiments of an X-ray CT apparatus according to the present invention will be described in detail with reference to the accompanying drawings. In the following description and the accompanying drawings, the same reference numerals are given to components having substantially the same functional configuration, and redundant description is omitted.

<First Embodiment>
First, a first embodiment of the present invention will be described.
FIG. 1 is a hardware configuration diagram of the X-ray CT apparatus 1.
The X-ray CT apparatus 1 shown in FIG. 1 includes a scanner 101 and a computer system 111. The scanner 101 acquires CT imaging data, and the computer system 111 processes the CT imaging data.

  The scanner 101 includes a gantry 102, an opening 103, an X-ray source 104, an X-ray beam collimator 105, a bed 107, an X-ray detector 108, an amplifier 109, and a scanner control device 110. Inside the gantry 102, an X-ray source 104, an X-ray beam collimator 105, an X-ray detector 108, and an amplifier 109 are installed. The gantry 102 rotates at a predetermined speed with an internal device around a rotation axis perpendicular to the surface of the opening 103. The subject 106 is placed on a bed 107 that is parallel to the rotation axis and movable in the opening 103 along the rotation axis.

  Photographing is performed while rotating the gantry 102. The X-ray source 104 emits X-rays, and the X-ray beam collimator 105 narrows the irradiated X-rays into a predetermined beam shape. The beam-shaped X-rays pass through the subject 106 and the bed 107 in the opening 103, and the X-ray detector 108 detects the transmitted X-rays. The amplifier 109 amplifies the detection signal detected by the X-ray detector 108 and transfers it to the scanner controller 110 and the central controller 113 of the computer system 111 as imaging data.

  The scanner control device 110 controls each unit installed in the scanner 101. For example, the scanner control device 110 controls the rotation of the gantry 102 and the movement of the bed 107. During imaging by the X-ray CT apparatus 1, the bed 107 moves in the direction of the rotation axis from the front of the paper or from the back of the paper. It is moved at a predetermined speed toward you. The X-ray CT apparatus 1 captures imaging data in a spiral shape with respect to the subject 106 by combining the rotation of the gantry 102 and the movement of the bed 107. The scanner control device 110 controls the dose of the X-ray source 104 and the shape of the diaphragm of the X-ray beam collimator 105.

  Note that the air calibration data is imaging data obtained by performing CT imaging in the same manner as described above without placing the subject 106 and the bed 107. The signal obtained by the X-ray detector 108 becomes air calibration data (calibration value) representing the sensitivity unevenness of the X-ray detector 108.

  The computer system 111 is a computer or the like, and includes an input device 112, a central control device 113, a storage device 114, a buffer 115, and an image display device 116. The input device 112 is an input device such as a keyboard and a mouse, and accepts operation command input, data input, and the like by an operator. The central control unit 113 is a central processing unit (CPU), a microprocessor, or the like, has a main memory, controls each unit, and executes processing described later. The storage device 114 is a storage device such as a nonvolatile memory, a volatile memory, or a hard disk drive device, and stores shooting data transmitted from the scanner 101 and the like. The buffer 115 is a memory that temporarily stores photographing data transmitted from the scanner 101, data to be displayed on the image display device 116, and the like. The image display device 116 is a display that displays a tomographic image or the like.

FIG. 2 shows a functional block configuration diagram of the central controller 113.
The central controller 113 includes an interface 161, a scanner control signal calculation unit 162, an imaging data acquisition unit 163, an air calibration data acquisition unit 164, an air calibration calculation unit 165, an image reconstruction calculation unit 166, and an air calibration data exchange unit. 167.
Here, the central control device 113 is configured to include each calculation unit. However, the central control device 113 may be configured to read a program for executing each calculation from the storage device, and the central control device 113 executes each program.

  The input device 112, the storage device 114, the buffer 115, and the image display device 116 are connected to the central control device 113. The central control device 113 has an interface 161, and exchanges information with each internal function and each external device via this interface 161. Here, the internal functions are each processing unit, scanner control signal calculation unit 162, imaging data acquisition unit 163, air calibration data acquisition unit 164, air calibration calculation unit 165, image reconstruction calculation unit 166, air calibration. A data exchange unit 167 and external devices include an amplifier 109, a scanner control device 110, an input device 112, a buffer 115, an image display device 116, and a storage device 114.

  The scanner control signal calculation unit 162 calculates a control signal to be sent to the scanner control device 110 based on an operation command, data, or the like received from the input device 112. The imaging data acquisition unit 163 acquires imaging data of the subject 106 transmitted from the amplifier 109 and outputs it to the buffer 115 and the storage device 114. The air calibration data acquisition unit 164 acquires the air calibration data obtained by the amplifier 109 and outputs it to the buffer 115 and the storage device 114. The air calibration calculation unit 165 reads the air calibration data and the imaging data of the subject 106 from the buffer 115 and the storage device 114, and performs conversion and calibration processing.

  The image reconstruction calculation unit 166 performs the reconstruction calculation of the tomographic image using the calibration image data after the calibration processing as an input, and outputs the result to the buffer 115, the storage device 114, and the image display device 116. When new air calibration data is acquired after a ring artifact is found in the tomographic image, the air calibration data exchanging unit 167 performs processing to replace it with the air calibration data that has been used up to that point. .

Next, the operation of the X-ray CT apparatus 1 will be described.
FIG. 3 is a flowchart showing the flow of calibration processing of the X-ray CT apparatus 1 (see FIGS. 1 and 2 as appropriate).
In this case, the initial value of the air calibration data is acquired in advance, and attribute data such as information on the subject 106 (patient ID, etc.), imaging region, imaging mode, acquisition date and time is added to the storage device 114. Assume that it is stored.

  After placing the subject 106 (patient) on the bed 107, an imaging start command input from the operator of the X-ray CT apparatus 1 by the input device 112 is converted into a control signal by the scanner control signal calculation unit 162, and the scanner The data is transmitted to the control device 110, and the scanner 101 performs CT imaging (step S201). The shooting data acquisition unit 163 temporarily stores the acquired shooting data in the main memory of the central control device 113, adds attribute data to the acquired shooting data, and stores the attribute data in the storage device 114 (step S202).

  The air calibration calculation unit 165 reads the existing air calibration data (calibration value) from the storage device 114 into the main memory (step S203). The air calibration calculation unit 165 performs predetermined conversion such as removal of attribute data from the shooting data in the main memory and the air calibration data, and generates calibration shooting data by subtracting the air calibration data from the shooting data. To do. The image reconstruction calculation unit 166 reconstructs an image based on the calibration photographing data (step S204), and displays a tomographic image on the image display device 116 together with information that the air calibration data is used.

  Next, the presence or absence of ring artifacts in the displayed tomographic image is determined (step S205). In this determination process, a ring artifact may be detected by an automatic image recognition process, or the operator of the X-ray CT apparatus 1 may detect it visually on the image display device 116.

  Referring to FIG. 2, for example, in the case of automatic image recognition processing, the central control device 113 includes an automatic recognition processing unit (not shown), and a reference image of a typical tissue or the like is stored in the storage device 114. Then, the tomographic image displayed by the automatic recognition processing unit is compared with a typical reference image of the same part as the tomographic image, and the presence or absence of ring artifacts in the tomographic image displayed on the image display device 116 is determined. The automatic image recognition processing unit displays the determination result, that is, the presence or absence of a ring artifact on the image display device 116.

When the operator of the X-ray CT apparatus 1 visually detects a ring artifact, the input device 112 receives input information regarding the presence or absence of the ring artifact.
It is also possible to use both automatic image recognition processing and visual observation by the operator of the X-ray CT apparatus 1. For example, when ring artifacts cannot be detected by automatic recognition processing, the X-ray CT apparatus 1 It is also possible for the operator to visually confirm on the image display device 116.

  Returning to FIG. 3, when no ring artifact is present in the tomographic image displayed on the image display device 116 (“No” in step S205), the process ends.

When a ring artifact exists in the tomographic image displayed on the image display device 116 (“Yes” in step S205), the air calibration data acquisition unit 164 performs air calibration, and the obtained air calibration data ( (Calibration value) is measured (step S206), and the air calibration data exchange unit 167 replaces the air calibration data stored in the main memory with the measured air calibration data (step S207), and uses the measured air calibration data. The attribute data is added, and the existing air calibration data stored in the storage device 114 is overwritten and stored (step S208).
Then, the process returns to step S204, and an image is reconstructed using new air calibration data.

As described above, in the present embodiment, the presence or absence of ring artifacts is detected every time tomographic imaging by the X-ray CT apparatus 1 is performed, and when a ring artifact is detected in a tomographic image, air calibration is performed, and a new air Obtain calibration data and use it to recalibrate tomograms.
According to the present embodiment, air calibration is performed at the time when a ring artifact is detected, and air calibration data may be acquired. The air calibration is performed from imaging data of a patient (subject 106) from which the ring artifact is detected. If the motion data is subtracted, a tomographic image with little influence of ring artifacts can be obtained. Therefore, the patient does not perform CT imaging many times, and the exposure dose does not increase. In addition, since air calibration is performed when necessary, extra time and effort are not required, and efficiency can be achieved in the operation of the X-ray CT apparatus 1 in a clinical field. Note that each process of the flowchart of FIG. 3 is appropriately executed by each calculation unit included in the central control device 113, but a program for executing each process of the flowchart is read from the storage device, and the central control device 113 may execute each program.

<Second Embodiment>
Next, a second embodiment of the present invention will be described.
In the method of using the X-ray CT apparatus 1 according to the first embodiment, when ring artifacts occur when the CT tomographic image of a patient is taken more frequently than usual using the X-ray CT apparatus 1. In order to perform the air calibration, the subsequent patient's CT imaging is waited for a while. Therefore, in the second embodiment, a time when a ring artifact occurs is predicted, and air calibration is performed prior to CT imaging performed in succession to avoid interruption of CT imaging.

  The hardware configuration of the second embodiment is the same as that shown in FIG.

  FIG. 4 is a functional block configuration diagram of the central controller 113 according to the second embodiment. The functional block configuration of the central controller 113 shown in FIG. 4 is substantially the same as the functional block configuration shown in FIG. 2, but differs in that an air calibration time prediction unit 171 is provided.

FIG. 5 is a flowchart showing a processing flow of the X-ray CT apparatus 1 of the second embodiment.
The air calibration time prediction unit 171 determines whether or not the current time coincides with the prediction time (step S301). The air calibration time prediction unit 171 reads out the prediction time of execution of air calibration under a desired photographing condition from the storage device 114, and the read prediction time within a predetermined time range in which the time is around the current time. Is entered, it is determined that “the current time coincides with the predicted time”. Here, it is assumed that the initial value and the predetermined time value of the prediction time are input in advance from the input device 112 by the operator and stored in the storage device 114 or the like.

If the air calibration time prediction unit 171 determines that the current time does not coincide with the prediction time (“No” in step S301), the process proceeds to step S303. The processing from step S303 to step S307 is the same as the processing from step S201 to step S205 shown in FIG.
If the air calibration time prediction unit 171 determines that the current time coincides with the prediction time (“Yes” in step S301), the air calibration time prediction unit 171 displays the fact on the image display device 116, or The operator is notified of the necessity of air calibration by making a warning sound or the like, and the operator's determination as to whether or not to perform calibration (air calibration) is accepted from the input device 112 (step S302).

If it is determined that air calibration is not performed (“No” in step S302), the process proceeds to step S303, and CT imaging is performed.
When it is determined that air calibration is to be performed (“Yes” in step S302), the process proceeds to step S308, where the air calibration data acquisition unit 164 acquires new air calibration data (step S308), and the air calibration data. The exchange unit 167 replaces the air calibration data in the main memory with new air calibration data (step S309). The details of the processes in steps S308 and S309 are the same as those in steps S206 and S207 shown in FIG.
The air calibration data exchange unit 167 adds attribute data to the measured air calibration data and stores the attribute data separately from the existing air calibration data stored in the storage device 114 (step S310).

  Next, the air calibration time prediction unit 171 reads the time-series data of the air calibration execution time from the storage device 114, adds the newly performed air calibration time to the time calibration data, and then performs the air calibration. The required time is predicted (step S311).

  FIG. 6 is a diagram illustrating an example of time-series data of the air calibration execution time stored in the storage device 114. As shown in FIG. 6, the time series data of the air calibration execution time is composed of the ID of the imaging condition associated with the imaging condition and the time series of the execution time of the air calibration performed under the imaging condition.

There are several methods for predicting the timing of air calibration.
For example, from time series data, find all the time intervals of the air calibration execution time adjacent on the time axis, calculate their average value, add the average value to the time when the air calibration was last performed, There is a method for setting a predicted time for the next air calibration.
In addition, there is a method of obtaining the standard deviation of the time interval of the air calibration execution time as the predetermined time used for the determination in step S301 and designating it by a value that is a multiple of the standard deviation, but this is not restrictive.

  Returning to FIG. 5, the air calibration time prediction unit 171 stores both the predicted prediction time and the imaging conditions in the storage device 114, and returns to step S <b> 301.

  As described above, according to the second embodiment, it is possible to predict the time when the ring artifact occurs, so that CT imaging is not interrupted and air calibration is not performed, and the operator knows the predicted time. It is also possible to plan the execution time of air calibration, and it is possible not only to improve the accuracy of the CT image, but also to improve the efficiency of operation of the X-ray CT apparatus 1 at the clinical site. Each process of the flowchart of FIG. 5 is appropriately executed by each calculation unit included in the central control device 113, but a program for executing each process of the flowchart is read from the storage device, and the central control device 113 may execute each program.

<Third Embodiment>
Next, a third embodiment of the present invention will be described.
The hardware configuration of the third embodiment is the same as the configuration shown in FIG.
The X-ray CT apparatus 1 according to the third embodiment stores the obtained air calibration data in the storage device 114 each time air calibration is performed, and the deterioration of the X-ray detector 108 from the air calibration data. Means for predicting the time when becomes a predetermined value or more.
FIG. 7 is a functional block configuration diagram of the central controller 113 according to the third embodiment. The functional block configuration of the central controller 113 shown in FIG. 7 is substantially the same as the functional block configuration shown in FIG. 2, but differs in that a detector replacement time prediction unit 181 is provided.

FIG. 8 is a flowchart showing a processing flow of the X-ray CT apparatus 1 of the third embodiment (see FIG. 1 and the like as appropriate).
The processing from step S401 to step S407 is the same as that from step S201 to S207 shown in FIG.
The air calibration data exchange unit 167 adds attribute data to the new air calibration data measured in step S406, and stores the attribute data separately from the existing air calibration data stored in the storage device 114 (step S408).

  The detector replacement time prediction unit 181 predicts the replacement time of the X-ray detector 108 using all the air calibration data including the new air calibration data (step S409).

  Referring to FIGS. 1 and 7, the detector replacement time prediction unit 181 reads all of the air calibration data stored in the storage device 114, and also acquires the air calibration execution time from the attribute data. The detector replacement time predicting unit 181 obtains the sensitivity of each X-ray detector 108 from the main part of the air calibration data, and predicts the time when the sensitivity becomes a predetermined value or less from the time series change.

  When performing air calibration, the gantry 102 rotates around the bed 107 several times, and during that time, the X-ray detector 108 measures the X-ray dose at a predetermined time interval. Accordingly, time-series data of the dose for each X-ray detector 108 is obtained until the scan is completed.

The detector replacement time predicting unit 181 calculates the average value of the time series data of the dose for each X-ray detector 108, and obtains the average value for each X-ray detector 108 obtained by one air calibration. To do. Here, since the execution time of air calibration is known, a time series of sensitivity is obtained for each X-ray detector 108. The detector replacement time prediction unit 181 linearly approximates the time series of sensitivity obtained for each X-ray detector 108 by the least square method, and predicts the time when the sensitivity is equal to or lower than a predetermined value as the replacement time.
Note that the prediction method by the X-ray detector 108 is not limited to this.

  Returning to FIG. 8, in step S409, the detector replacement time prediction unit 181 predicts the replacement time of the X-ray detector 108 and displays the predicted replacement time on the image display device 116. Then, the process returns to step S404.

  According to the third embodiment, it is possible to predict the replacement time of the X-ray detector 108. For example, the medical institution side can request the supplier to replace the X-ray detector 108 systematically. Is possible. Therefore, not only the imaging sensitivity of the X-ray CT apparatus 1 can be improved, but also the operation efficiency of the X-ray CT apparatus 1 can be improved. Note that each process of the flowchart of FIG. 8 is appropriately executed by each calculation unit included in the central control device 113, but a program for executing each process of the flowchart is read from the storage device, and the central control device 113 may execute each program.

<Fourth Embodiment>
Next, a fourth embodiment of the present invention will be described.
In the method of using the X-ray CT apparatus 1 according to the first embodiment, when ring artifacts occur when the CT tomographic image of a patient is taken more frequently than usual using the X-ray CT apparatus 1. In order to perform the air calibration, the subsequent patient's CT imaging is waited for a while. Therefore, in the fourth embodiment, there is provided means for setting a timing for performing air calibration, and air calibration is performed prior to CT imaging performed in succession to avoid interruption of CT imaging.

  The hardware configuration of the fourth embodiment is the same as the configuration shown in FIG.

  FIG. 9 is a functional block configuration diagram of the central controller 113 according to the fourth embodiment. The functional block configuration of the central controller 113 shown in FIG. 9 is substantially the same as the functional block configuration shown in FIG. 2, but differs in that an air calibration time determination unit 191 is provided.

FIG. 10 is a flowchart showing a processing flow of the X-ray CT apparatus 1 of the fourth embodiment.
After placing the subject 106 (patient) on the bed 107, the scanner 101 performs CT imaging (step S501). The shooting data acquisition unit 163 temporarily stores the acquired shooting data in the main memory of the central controller 113, adds attribute data to the acquired shooting data, and temporarily stores it in the buffer 115 (step S502). ). Here, the shooting data is stored in different locations in the buffer 115 for each shooting data.

  The air calibration calculation unit 165 reads the existing air calibration data (calibration value) from the storage device 114 into the main memory (step S503). The air calibration calculation unit 165 performs predetermined conversion such as removing attribute data from the shooting data in the buffer 115 and the air calibration data in the main memory, and subtracts the air calibration data from the shooting data for calibration. Generate shooting data. The image reconstruction calculation unit 166 reconstructs an image based on the calibration photographing data (step S504), and displays a tomographic image on the image display device 116 together with information that the air calibration data is used.

Next, it is determined whether or not there is a ring artifact in the displayed tomographic image (step S505). This determination processing method is the same as that in step S205 shown in FIG.
If no ring artifact is confirmed in step S505 (“No” in step S505), the air calibration calculation unit 165 stores the imaging data after the air calibration is performed in the storage device 114 (step S506).

When a ring artifact is confirmed in step S505 (“Yes” in step S505), the air calibration time determination unit 191 receives an input of the time for performing calibration from the input device 112 and stores it in the storage device 114. However, if the air calibration time has already been stored in the storage device 114, no processing is performed in this step S507.
The air calibration time determination unit 191 determines whether the current time is the configuration time based on the air calibration execution time that has been input or is already stored in the storage device 114 (step S508).

If it is not determined in step S508 that the air calibration has been performed (“No” in step S508), the process returns to step S504 to perform the next shooting.
When it is determined in step S508 that the air calibration is performed (“Yes” in step S508), the air calibration data acquisition unit 164 performs air calibration and measures the obtained air calibration data (step S508). S509). The air calibration data exchange unit 167 replaces the air calibration data stored in the main memory with the measured air calibration data (step S510), adds attribute data to the measured air calibration data, and stores the attribute data in the storage device 114. The existing air calibration data is overwritten and stored (step S511).
Then, returning to the processing of step S501, the image reconstruction calculation unit 166 reconstructs an image using new air calibration data.

  In the fourth embodiment, when a ring artifact is found, if a number of patients have to perform CT scans continuously, air calibration is performed after the CT scans of a series of patients are completed. It is effective to postpone the air calibration execution time. In the operation of the X-ray CT apparatus 1 in the clinical field, there may be a situation where CT imaging of a number of patients must be performed continuously, and even in such a situation, by performing air calibration at a later set time It is possible to obtain a CT tomogram with high accuracy. Each process of the flowchart of FIG. 10 is appropriately executed by each calculation unit included in the central control device 113, but a program for executing each process of the flowchart is read from the storage device, and the central control device 113 may execute each program.

  As described above, according to the embodiment of the present invention, an image free from ring artifacts can be obtained. In addition, since the air calibration that was performed regularly only needs to be performed when a ring artifact occurs, the air calibration that was performed more or less than the original was matched to the operation of the X-ray CT system. It can be done at the timing, making it possible to improve the efficiency of device operation in the clinical field.

  The preferred embodiments of the X-ray CT apparatus according to the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to such examples. It will be apparent to those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea disclosed in the present application, and these naturally belong to the technical scope of the present invention. Understood.

The embodiment of the present invention relates to an air calibration method in an X-ray CT apparatus, but can be used for an imaging apparatus such as PET using radiation other than X-rays.
In addition, since the subject to be imaged is not limited to the human body, the present invention is applied even in the case where there is a plurality of detectors and nonuniformity of sensitivity occurs and air calibration is effective in an image inspection apparatus using radiation intended for non-destructive inspection of machinery. It is possible.

DESCRIPTION OF SYMBOLS 1 ... X-ray CT apparatus 101 ... Scanner 102 ... Gantry 103 ... Opening part 104 ... X-ray source 105 ... X-ray beam collimator 106 ... Subject 107 ... Bed 108 ... X-ray detector 109 ... Amplifier 110 ... Scanner control apparatus 111 ... Computer system 112 ... Input device 113 ... Central control device 114 ... Storage device 115 ... Buffer 116 ... Image display device 161 ... Interface 162 ... Scanner control signal calculation unit 163 ... Shooting data acquisition unit 164 ... Air calibration data acquisition unit 165 ... Air Calibration calculation unit 166 ... Image reconstruction calculation unit 167 ... Air calibration data exchange unit

Claims (12)

An X-ray source that irradiates the subject with X-rays, an X-ray detector that is disposed opposite to the X-ray source and detects transmitted X-rays that have passed through the subject, and the X-ray source and the X-ray detection A gantry that rotates around the subject, a storage device that stores the transmitted X-ray dose detected by the X-ray detector by rotating the gantry as imaging data, and a tomogram of the subject based on the imaging data An X-ray CT apparatus comprising: an image reconstruction device that reconstructs an image; and an image display device that displays a tomographic image reconstructed by the image reconstruction device,
An air calibration data acquisition unit that acquires, as air calibration data, X-dose data detected by the X-ray detector by rotating the gantry in a state where the subject is not disposed;
An air calibration storage unit for storing the air calibration data;
An air calibration calculation unit that subtracts the air calibration data read from the air calibration storage unit from the imaging data of the subject, and executes air calibration;
Detecting means for detecting ring artifacts in a tomographic image reconstructed by the image reconstruction device based on an air calibration execution result by the air calibration calculation unit;
With
When a ring artifact is detected by the detection means,
The air calibration data acquisition unit acquires new air calibration data,
The air calibration calculation unit performs air calibration so as to subtract the new air calibration data from the imaging data,
When no ring artifact is detected in the tomographic image reconstructed by the image reconstruction device based on the result of air calibration performed using the new air calibration data by the detection unit, the air calibration storage unit Is an X-ray CT apparatus which stores the new air calibration data.   The detection means detects the ring artifact by comparing a tomographic image reconstructed by the image reconstruction device based on the air calibration execution result and a reference image stored in the storage device. The X-ray CT apparatus according to claim 1, wherein:   The detecting means detects the ring artifact based on input information received from an operator who visually confirms a tomographic image reconstructed by the image reconstruction device based on the air calibration execution result. The X-ray CT apparatus according to claim 1.   The air calibration data storage unit stores time information on the air calibration data and the air calibration execution time from which the air calibration data was acquired, and predicts the next air calibration execution time using the time information. The X-ray CT apparatus according to claim 1, further comprising an air calibration time prediction unit that performs the operation.   The air calibration data storage unit stores the air calibration data and time information related to an air calibration execution time from which the air calibration data is acquired, and uses the air calibration data and the time information to The X-ray CT apparatus according to claim 1, further comprising a detector replacement timing prediction unit that obtains individual sensitivities of the X-ray detectors and predicts the replacement timing of each X-ray detector. A scheduled execution time storage unit for storing a scheduled air calibration execution time for performing the next air calibration;
An air calibration time determination unit that determines whether or not the current time is the air calibration execution scheduled time;
The X-ray CT apparatus according to claim 1, further comprising: An X-ray source that irradiates the subject with X-rays, an X-ray detector that is disposed opposite to the X-ray source and detects transmitted X-rays that have passed through the subject, and the X-ray source and the X-ray detection A gantry that rotates around the subject, a storage device that stores the transmitted X-ray dose detected by the X-ray detector by rotating the gantry as imaging data, and a tomogram of the subject based on the imaging data A data acquisition method for acquiring data in an X-ray CT apparatus comprising: an image reconstruction device that reconstructs an image; and an image display device that displays a tomographic image reconstructed by the image reconstruction device,
An acquisition step of acquiring, as air calibration data, X-ray dose data detected by the X-ray detector by rotating the gantry in a state where the subject is not disposed;
A storage step of storing the air calibration data;
An execution step of subtracting the air calibration data from the imaging data of the subject and performing air calibration;
A detection step of detecting a ring artifact in a tomogram reconstructed by the image reconstruction device based on an air calibration execution result;
With
If a ring artifact is detected in the detection step,
Acquiring new air calibration data;
Performing air calibration so as to subtract the new air calibration data from the imaging data;
A step of storing the new air calibration data when a ring artifact is not detected in a tomographic image reconstructed by the image reconstruction device based on an air calibration execution result executed using the new air calibration data; A method for obtaining data, characterized in that   In the detection step, the ring artifact is detected by comparing the tomographic image reconstructed by the image reconstruction device based on the air calibration execution result and the reference image stored in the storage device. The data acquisition method according to claim 7, wherein:   In the detection step, the ring artifact is detected based on input information received from an operator who visually confirms a tomographic image reconstructed by the image reconstruction device based on the air calibration execution result. The data acquisition method according to claim 7.   The storing step stores the air calibration data and time information related to the air calibration execution time at which the air calibration data was acquired, and predicts the next air calibration execution time using the time information. The data acquisition method according to claim 7, further comprising a time prediction step.   The storing step stores the air calibration data and time information related to an air calibration execution time at which the air calibration data is acquired, and uses the air calibration data and the time information to detect the plurality of X-ray detections. 8. The data acquisition method according to claim 7, further comprising a detector replacement time prediction step of obtaining individual sensitivity of the detector and predicting replacement time of each X-ray detector. A scheduled execution time storage step for storing a scheduled air calibration execution time for performing the next air calibration;
An air calibration time determination step for determining whether or not the current time is the air calibration execution scheduled time;
The data acquisition method according to claim 7, further comprising:

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