JP5995491B2 - X-ray CT system - Google Patents

Description

  The present invention relates to an X-ray CT apparatus, and more particularly to a failure element detection technique for a multi-element type X-ray detector and a data acquisition apparatus.

  An X-ray CT apparatus is an X-ray source that irradiates a subject with X-rays, an X-ray detector that detects an X-ray dose that has passed through the subject and outputs it as analog data, and data that converts analog data into digital data The tomographic image of the subject is reconstructed using measurement data from a plurality of angles obtained by rotating the collection device around the subject, and the reconstructed tomographic image is displayed. The image displayed by the X-ray CT apparatus describes the shape of an organ in the subject and is used for image diagnosis.

  In recent X-ray CT apparatuses, the number of X-ray detectors is increasing, and the number of elements constituting the X-ray detector and the data acquisition apparatus is increasing. If there is no output among the elements constituting the X-ray detector or the data acquisition device or there is a faulty element whose output is significantly different from that of the peripheral element, the X-ray CT of the subject without appropriate correction or treatment When imaging is performed, it may cause the appearance of image artifacts, image quality degradation, and invalid exposure of the subject. For this reason, in a multi-element type X-ray detector or data acquisition device, it is important to find and identify the location of the failed element at an early stage, and to perform appropriate correction and treatment.

  In Patent Document 1, as a technique for detecting a faulty element, a “standard” collected in advance under predetermined scanning conditions (a group of parameters related to scanning such as tube voltage, tube current, and scan time) at the time of shipment or adjustment of the device. An X-ray CT apparatus is disclosed in which failure detection is performed by comparing two data, “data” and “measurement data” collected under the same scanning conditions as at the time of reference data collection at the time of maintenance and inspection.

JP 63-222742 A

  However, “reference data” is only “one of the measurement data without failure”, and in the process of collecting reference data at the time of shipment or adjustment, the measurement data must first be collected and there is no failure in the measurement data. It was necessary to record the “measurement data without failure” confirmed as having no failure as “reference data” in the apparatus. When the confirmation work is performed visually, the number of work steps is expected to increase with the increase in the number of elements, and there is a risk of overlooking the abnormality. However, in Patent Document 1, no consideration is given to such reference data collection work. It was. Further, in Patent Document 1, since it is necessary to collect data twice for reference data and for measurement data, the opportunities that can be used for failure detection are limited when data is collected under the same scanning conditions. No consideration has been given to the early detection and identification of faulty devices under arbitrary conditions such as those used for daily diagnosis.

  Therefore, the object of the present invention is at the time of shipment, adjustment, maintenance, at the time of daily Air correction data collection for correcting the sensitivity characteristics of the X-ray detector, at the time of offset data measurement without X-ray irradiation, etc. It is to provide a technique for detecting a failed element at an arbitrary stage.

In order to achieve the above object, an X-ray CT apparatus according to the present invention includes an X-ray source that irradiates X-rays, and an X-ray detection that detects the X-rays and outputs analog data corresponding to the detected X-ray dose. An X-ray detector having a plurality of elements, and a data collection element provided corresponding to each of the X-ray detection elements, for converting the analog data output from each X-ray detection element into digital data and collecting the data A data collection device having the same number as the X-ray detection elements, and a faulty element detection unit that detects a fault of a measurement element composed of a pair of combinations of the X-ray detection elements and the data collection elements corresponding thereto. The failure element detection unit generates measurement data to be used for failure determination using measurement data including an output value of digital data of each measurement element for each measurement element, Versus Based on determination measurement data of peripheral elements located around the measurement element, determination reference data used for the failure determination is generated, and based on a comparison result between the determination measurement data of the target measurement element and the determination reference data Then, it is determined whether or not the target measurement element is a faulty element . Further, the faulty element detection unit generates an approximate function based on measurement data of the peripheral element for the measurement element at the end of the X-ray detector, and the peripheral element sandwiches the measurement element. On the opposite side, an element having a virtual output value based on the approximate function is virtually set by extrapolation, and the determination is performed using the output value of the element set by the extrapolation and the output value of the peripheral element Generate reference data.

  According to the present invention, at the time of shipment, adjustment, maintenance and inspection, daily Air correction data collection for correcting the sensitivity characteristics of the X-ray detector, offset data measurement without X-ray irradiation, etc. In this stage, a technique for detecting a failed element can be provided.

Overall configuration diagram of an X-ray CT apparatus 1 according to the present embodiment Explanatory drawing which shows the whole structure of a X-ray detector and a data acquisition device The flowchart which shows the flow of the failure element detection process which concerns on 1st embodiment. Explanatory drawing which shows the output value calculation process (step S102 of FIG. 3) of the extrapolation element 205 Explanatory drawing which shows failure determination processing (step S104 of FIG. 3) The flowchart which shows the flow of the failure element detection process which concerns on 2nd embodiment. The flowchart which shows the flow of a failure location determination process (step S204 of FIG. 6). The flowchart which shows the whole flow of the failure element detection process which concerns on 3rd embodiment. Flowchart showing the flow of preprocessing (step S402 in FIG. 8) A flowchart showing the flow of output value correction (step S501 in FIG. 9) according to the element area. Flowchart showing the flow of module end element output value correction (step S502 in FIG. 9) Explanatory drawing which shows the calculation process of the judgment reference data used for module end element correction Flowchart showing the flow of failure module detection processing (step S503 in FIG. 9)

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same reference numerals are given to the procedures having the same functions and the same processing contents, and the description thereof will not be repeated.

First, based on FIG. 1, the whole structure of the X-ray CT apparatus which concerns on this embodiment is demonstrated.
FIG. 1 is an overall configuration diagram of an X-ray CT apparatus 1 according to the present embodiment.

  The X-ray CT apparatus 1 shown in FIG. 1 includes a scan gantry unit 100 and an operation console 120.

  The scan gantry unit 100 includes an X-ray tube 101 that is an X-ray source, a rotating disk 102, a collimator unit 103, an X-ray detector 106, a data collection device 107, a bed 105, a gantry control device 108, A couch control device 109 and an X-ray control device 110 are provided.

  The X-ray tube 101 is an apparatus that irradiates a subject placed on a bed 105 with X-rays. The collimator unit 103 includes a mechanism for limiting the X-ray irradiation range irradiated from the X-ray tube 101 and an X-ray compensator for adjusting the X-ray dose distribution.

  The rotating disk 102 includes an opening 104 into which a subject placed on a bed 105 enters, and an X-ray tube 101 and an X-ray detector 106 are mounted to rotate around the subject.

  The X-ray detector 106 is a device that is arranged opposite to the X-ray tube 101 and measures the spatial distribution of transmitted X-rays by detecting X-rays transmitted through the subject. The rotating disk 102 is arranged in the rotating direction, or the rotating disk 102 is arranged two-dimensionally in the rotating direction (channel direction) and the rotating shaft direction (slicing direction). Each X-ray detection element detects X-rays transmitted through the subject and outputs analog data corresponding to the transmitted X-ray dose.

  The data collection device 107 is a device that converts analog data output from the X-ray detector 106 into digital data and collects it, and includes the same number of data collection elements as X-ray detection elements. One data collection element is connected to each X-ray detection element. Hereinafter, a combination of one X-ray detection element and one data collection element connected thereto is referred to as a “measurement element”.

  The gantry control device 108 is a device that controls the rotation of the rotary disk 102. The bed control device 109 is a device that controls the vertical movement of the bed 105. The X-ray control device 110 is a device that controls electric power input to the X-ray tube 101.

  The console 120 includes an input device 121, an image reconstruction device 122, a display device 125, a storage device 123, a system control device 124, and a failure element detection unit 126 that detects a failure of a measurement element. Yes.

  The input device 121 is a device for inputting a subject name, examination date and time, imaging conditions, and the like. Specifically, a keyboard or a pointing device may be used. The image reconstruction device 122 is a device that uses the digital data sent from the data collection device 107 as measurement data and performs a reconstruction calculation process based on this data to generate a CT image. The display device 125 is a device that displays the CT image reconstructed by the image reconstruction device 122. Specifically, a CRT (Cathode-Ray Tube), a liquid crystal display, or the like may be used. The storage device 123 is a device that stores the measurement data collected by the data collection device 107 and the image data of the CT image created by the image reconstruction device 122. Specifically, the storage device 123 uses an HDD (Hard Disk Drive) or the like. Also good. The system control device 124 includes components of the console 120 (input device 121, image reconstruction device 122, storage device 123, display device 125, failure element detection unit 126), gantry control device 108, bed control device 109, and X. This is a device for controlling the line control device 110.

  By controlling the power input to the X-ray tube 101 by the X-ray control device 110 based on the imaging conditions input from the input device 121, particularly the X-ray tube voltage and X-ray tube current, the X-ray tube 101 The subject is irradiated with X-rays according to imaging conditions. The X-ray detector 106 detects X-rays irradiated from the X-ray tube 101 and transmitted through the subject with a large number of X-ray detection elements, and measures the distribution of transmitted X-rays. The rotating disk 102 is controlled by the gantry control device 108 and rotates based on the photographing conditions input from the input device 121, particularly the rotation speed. The bed 105 is controlled by the bed control device 109 and operates based on the photographing conditions input from the input device 121, in particular, the helical pitch.

  Measurement data from various angles (views) is acquired by repeating the X-ray irradiation from the X-ray tube 101 and the measurement of the transmitted X-ray distribution by the X-ray detector 106 along with the rotation of the rotating disk 102. . The acquired measurement data from various angles is transmitted to the image reconstruction device 122. The image reconstruction device 122 reconstructs the CT image by performing back projection processing on the transmitted measurement data from various angles. The CT image obtained by the reconstruction is displayed on the display device 125.

  The faulty element detection unit 126 operates between the data collection device 107 and the system control device 124. A failure of the X-ray detector 106 and the data collection device 107 is diagnosed from the digital data collected by the data collection device 107, and a failed element is specified. If there is a faulty element, the system controller 124 is notified of information regarding the faulty element. For example, the system control device 124 instructs the gantry control device 108 to stop scanning, instructs the image reconstruction device 122 to correct faulty element data, registers the faulty element in the storage device 123, displays the faulty element on the display device 125, and service center. 127 to perform a notification or the like.

  Next, the configurations and names of the X-ray detector 106 and the data acquisition device 107 will be described with reference to FIG. FIG. 2 is an explanatory diagram showing the overall configuration of the X-ray detector and the data collection device.

  As shown in FIG. 2, the X-ray detector 106 is configured by two-dimensionally arranging a large number of X-ray detector elements 201 in the channel direction and the slice direction. The X-ray detector element 201 is unitized for each of a plurality of elements. Each unit is referred to as an X-ray detection module 202. Elements located at both ends of the X-ray detection module 202 in the channel direction are referred to as module end elements 203. One or more elements located at both ends in the channel direction of the X-ray detector 106 are referred to as detector end elements 204. Furthermore, one or more elements virtually created outside the X-ray detector 106 in the channel direction are referred to as extrapolation elements 205.

  Each of the X-ray detector elements 201 is connected to each data collection element of a pair of data collection devices. Therefore, it can be said that FIG. 2 illustrates an end face on the X-ray detector element side of the measurement element in which the X-ray detector element 201 and the data collection element are paired.

<First embodiment>
Based on FIGS. 3-5, the content of the failure element detection process which concerns on 1st embodiment is demonstrated. FIG. 3 is a flowchart showing the flow of the faulty element detection process according to the first embodiment. FIG. 4 is an explanatory diagram showing an output value calculation process (step S102 in FIG. 3) of the extrapolation element 205. FIG. 5 is an explanatory diagram showing the failure determination process (step S104 in FIG. 3). Hereinafter, it demonstrates along each step of FIG.

(Step S101)
The faulty element detection unit 126 generates determination measurement data for each measurement element (S101). The determination measurement data means data used for failure determination generated using measurement data including output values of each measurement element at the time of X-ray irradiation or non-X-ray irradiation. In the first embodiment, determination measurement data is generated from measurement data at the time of X-ray irradiation. In addition, although the measurement data at the time of X-ray non-irradiation are used in 2nd embodiment, the detail is mentioned later.

  In the measurement of the faulty element detection, it is desirable to scan the Air without inserting an X-ray compensator in order to suppress the change of the output value due to factors other than the fault. Therefore, in this step, the measurement data D (s, c, v) in each slice, each channel, and each view of the X-ray detector 106 collected by the data acquisition device 107 with no X-ray compensator inserted. Read. Here, s is a slice number of the detection element, c is a channel number of the detection element, and v is a view number.

式（１）の判定計測データＶ（ｓ，ｃ）は、計測データＤ（ｓ，ｃ，ｖ）の全ビュー方向標準偏差、あるいはビュー方向最大出力値と最小出力値との差としても良い。 The determination measurement data may be measurement data of one view, but is preferably calculated from measurement data of a plurality of views in order to correct variations between views. For example, as shown in the following equation (1), the view direction average output value V (s, c) is used as determination measurement data.

The determination measurement data V (s, c) of the equation (1) may be the total deviation in the view direction of the measurement data D (s, c, v), or the difference between the maximum output value and the minimum output value in the view direction.

(Step S102)
The faulty element detection unit 126 generates reference data (hereinafter referred to as “determination reference data”) M (s, c) for use in failure determination based on the determination measurement data (S102). For example, the determination reference data M (s, c) is a moving average output value of determination measurement data of peripheral elements located around the measurement element (hereinafter referred to as “target measurement element”) c [channel] to be determined. And use. Peripheral elements may be the channel direction, slice direction, combinations thereof, and the like.

The calculation method of the determination reference data M (s, c) includes a method of calculating using both the output values of the target measurement element and the peripheral element, and a method of calculating using only the output value of the peripheral element. For example, when taking the average of the output value of the target measurement element and the output value of the peripheral element w ₁ as the determination reference data M (s, c), it can be calculated by the following equation (2). Further, when the output value of the target measurement element is not included and only the peripheral element w ₁ minute is averaged, it can be calculated by the following equation (2) ′. However, _{w 1} is the odd number of 3 or more.

Here, in each slice, for the left end (w ₁ −1) / 2 elements and the right end (w ₁ −1) / 2 elements in the channel direction of the X-ray detector 106, the moving average represented by the equation (2) is used. The number of elements for calculating the output value is insufficient.

Therefore, as shown in FIG. 4, the tendency of the output value of the detector end element 204 (the number of elements is not limited) is fitted with an approximate curve 210 such as a linear function at both the left and right ends, and the left and right ends (w ₁₎ according to the approximate curve 210. -1) / 2 Calculates the virtual output value of each extrapolation element 205. By using the output value of the extrapolation element 205, the expression (2) also applies to the left end (w ₁ −1) / 2 and the right end (w ₁ −1) / 2 elements in the channel direction of the X-ray detector. Applicable.

但し、Ｎ：Ｘ線検出器を構成するチャネル方向の素子数 The determination reference data M (s, c) may be the average output value in all channels or the average output value in all slices of the determination measurement data V (s, c). For example, the average output value M (s, c) = M (s) in all channel directions of the determination measurement data V (s, c) can be written as the following equation (3).

N: Number of elements in the channel direction constituting the X-ray detector

  Further, the determination reference data M (s, c) may be an approximate value when the tendency of the determination measurement data V (s, c) in the slice direction or the channel direction is fitted with an approximate curve such as a polynomial function.

(Step S103)
The faulty element detection unit 126 determines a determination value R (s, c) for determining whether or not it is a faulty element from the determination measurement data V (s, c) of the target measurement element c and the determination reference data M (s, c). c) is calculated (S103). The determination value R (s, c) is calculated as a ratio of a difference between the determination reference data M (s, c) and the determination measurement data V (s, c), for example, as in the following equation (4).

(Step S104)
The faulty element detection unit 126 determines a faulty element (S104). For example, as shown in the following equation (5), the threshold value determination is performed with the allowable fluctuation rate of the determination value R (s, c) as d ₁ .

As shown in FIG. 5, is not satisfied equation (5), namely the determination value R (s, c) of the target measurement element, if it exceeds the allowable variation rate d ₁ determines the corresponding element as a failure element . The allowable variation rate d ₁ may be a value (for example, a constant multiple) set based on the specification value of the apparatus or the standard deviation in the channel direction or slice direction of the determination measurement data V (s, c).

(Step S105)
If there is an element determined to be a failed element, information about the failed element such as the slice number, element number, and module number of the failed element is notified to the system control device 124 (S105). For example, the system control device 124 instructs the gantry control device 108 to stop scanning, instructs the image reconstruction device 122 to correct faulty element data, registers the faulty element in the storage device 123, displays the faulty element on the display device 125, and services. Take measures such as notification to the center 127.

  In addition, the output value of the failed element is multiplied by a coefficient so that it approaches the criterion data, or the output value of the failed element is replaced with the criterion data, and the subsequent image reconstruction calculation is performed. May be.

  According to the present embodiment, it is possible to detect a faulty element of an X-ray detector or a data acquisition device without requiring two data acquisitions of determination reference data and determination measurement data.

  Moreover, if it is incorporated so that the above-mentioned failure element detection processing is executed not only during maintenance and inspection but also during daily Air correction data collection, the failure element of the X-ray detector or the data collection device is detected before inspection. Corrections and actions can be taken. In the unlikely event that the number of faulty elements is large and it is judged that image quality degradation cannot be prevented unless the scan itself is stopped and the faulty elements are replaced, real-time measures such as stopping the scan urgently before X-ray irradiation are performed. Therefore, invalid exposure of the subject can be prevented.

  In the above formulas (2) and (3), an example in which the average in the channel direction is taken is shown, but the same processing may be performed by taking the average in the slice direction.

<Second embodiment>
The second embodiment is an embodiment in which a failure location is detected by combining measurement data with X-ray irradiation and measurement data without X-ray irradiation as determination measurement data.

  If measurement data when X-rays are irradiated is input, it can be detected whether either the X-ray detector or the data collection device is out of order, but whether the failure is caused by the X-ray detector or the data collection device. It cannot be specified. Therefore, the cause of failure is determined using measurement data when X-rays are not irradiated and measurement data when X-rays are irradiated. Hereinafter, based on FIG.6 and FIG.7, 2nd embodiment is described. FIG. 6 is a flowchart showing the flow of a faulty element detection process according to the second embodiment. FIG. 7 is a flowchart showing the flow of the failure location determination process (step S204 in FIG. 6). Hereinafter, although it demonstrates along each step of FIG. 6, since it is the same process as 1st embodiment from step S101 to step S103, description is abbreviate | omitted.

(Steps S201 to S203).
The faulty element detection unit 126 acquires the measurement data output from the data collection device 107 without irradiating X-rays, and performs the same processing as step S101 using this measurement data (S201). In steps S202 and S203, processing similar to that in steps S102 and S103 is performed using the determination measurement data calculated in step S201 (S202 and 203). Subsequently, the processes of steps S101 to S103 described in the first embodiment are performed.

  In FIG. 6, it is described that the processing of steps S101 to S103 is executed after steps S201 to S203, but the execution order is not limited to the above. That is, steps S101 to S103 may be performed first, and then steps S201 to S203 may be performed. Steps S201 to S203 may be executed in parallel.

(Step S204)
The faulty element detection unit 126 determines a fault location using the determination values calculated in Step S103 and Step S203 (S204). The failure location determination process will be described in the order of steps in FIG.

(Step S301)
Failure element detection unit 126, the determination value calculated in step S203, i.e., the determination value calculated based on the determination reference data for determining the measurement data and the X-ray non-irradiation during X-ray non-irradiation is the allowable variation rate d ₂ It is determined whether it exceeds (S301). The determination measurement data at the time of non-X-ray irradiation is not an output value from the X-ray detection element but an output value from the data collection element. Therefore, when the determination value using the output value of the determination measurement data exceeds the allowable fluctuation rate d ₂ , it can be understood that the cause of the failure is derived from the data collection device 107. If exceeding, the process proceeds to step S302, and if not exceeding, the process proceeds to step S303.

(Step S302)
The faulty element detection unit 126 determines that the data collection element is faulty because the determination measurement data using the measurement data at the time of non-irradiation of X-rays exceeds the allowable fluctuation rate d ₂ (S302). Thereafter, the process proceeds to step S205.

(Steps S303 and S304)
Or failure element detection unit 126, the calculated determination value in step S103, i.e., the determination value calculated based on the determination reference data at the time of determining the measurement data and the X-ray irradiation at the time of X-ray irradiation is more than the allowable variation rate d ₁ It is determined whether or not (S303). When not exceeding, it progresses to step S304, it determines with "no failure", and complete | finishes a failure location determination process (S304). When exceeding, it progresses to step S305.

(Step S305)
Failure element detection unit 126 is determined measurement data using the measurement data during X-ray irradiation is more than the allowable variation rate d _1, X-ray non-irradiation of the measurement data determined measurement data using an allowable variation rate d ₂ Therefore, the failure of the X-ray detector element is determined (S305). Thereafter, the process proceeds to step S205.

(Step S205)
The system controller 124 is notified of the result of specifying the failure location (S205). Upon receiving the notified result, the system control device 205 performs the same processing as step S105.

  According to the present embodiment, the failure of the failed element detected by executing the failed element detection process while properly using X-ray irradiation or non-irradiation at the time of shipment, adjustment, maintenance inspection, and Air correction data collection. The cause can be identified, and more appropriate measures can be taken. That is, when a faulty element is detected in a state where X-rays are not irradiated, it can be determined that the data collection element is faulty. In addition, when a failure element is not detected in a state where X-ray irradiation is not performed and a failure element is detected in a state where X-ray irradiation is performed, it can be determined that the X-ray detection element is in failure.

  In the scan of the X-ray CT apparatus, offset data that does not irradiate X-rays every time is collected immediately before X-ray irradiation in the scan. When this offset data is measured, if it is incorporated so as to execute the faulty element detection process according to the present embodiment, the faulty element of the data collection device generated immediately before the start of the inspection imaging from the offset data collected under an arbitrary condition can be obtained. It can be detected. In the unlikely event that the number of faulty elements is large and it is judged that image quality degradation cannot be prevented unless the scan itself is stopped and the faulty elements are replaced, real-time measures such as stopping the scan urgently before X-ray irradiation are performed. Therefore, invalid exposure of the subject can be prevented.

<Third embodiment>
The third embodiment is an embodiment in which preprocessing for increasing the accuracy of failure detection processing is performed between step S101 and step S102 of the first embodiment. Pre-processing is a variety of processes for preventing erroneous detection of normal elements and improving the detection accuracy of faulty elements by correcting output value changes due to factors other than faults prior to faulty element detection. . By performing the preprocessing, for example, erroneous detection of the module end element 203 and elements around the failure module can be prevented, and the failure detection accuracy of the X-ray detector element 201 and the X-ray detection module 202 can be improved.

  Hereinafter, the third embodiment will be described with reference to FIGS. 8 to 13. FIG. 8 is a flowchart showing the overall flow of the faulty element detection process according to the third embodiment. FIG. 9 is a flowchart showing the flow of preprocessing (step S402 in FIG. 8). FIG. 10 is a flowchart showing the flow of output value correction (step S501 in FIG. 9) according to the element area. FIG. 11 is a flowchart showing the flow of module end element output value correction (step S502 in FIG. 9). FIG. 12 is an explanatory diagram illustrating calculation processing of determination reference data used for module end element correction. FIG. 13 is a flowchart showing a flow of detection of a failure module (step S503 in FIG. 9).

  8 will be described below in the order of steps in FIG. 8. Step S401 in FIG. 8 corresponds to step S101 in the first embodiment, and steps S403 to S406 correspond to steps S102 to S105 in the first embodiment. To do. Therefore, description of the same processing is omitted.

(Step S402)
After obtaining the determination measurement data of each measurement element (S401), the failure detection unit 126 performs preprocessing for increasing the accuracy of the failure detection processing (S402). In the present embodiment, as shown in FIG. 9, three types of output value correction (S501) according to the element area, output value correction of the module end element (S502), and failure module detection (S503) are included. Although preprocessing is performed, all these processes may be performed as preprocessing, or may be selectively performed as necessary.

  Further, the execution order is not limited to the order shown in FIG. 9, but the order shown in FIG. 9 is recommended in view of the purpose and effect of the preprocessing.

  Hereinafter, the contents of each process will be described in the order of output value correction according to the element area (S501), module end element output value correction (S502), and failure module detection (S503).

(Step S501)
Output value correction according to the element area of the X-ray detector element 201 (the area of the light receiving surface of the X-ray detector 201) is performed (S501). When the scanning conditions other than the element area of the X-ray detector element 201 are exactly the same, the element area of the X-ray detector element 201 and the detector output are in a proportional relationship. When X-ray detector elements 201 having different element areas coexist in the X-ray detector, it is expected that the output values in the channel direction and the slice direction will change due to the difference in element area. In order not to erroneously detect such an output value change due to the difference in element area as an output value change due to a failure, output value correction is performed in accordance with the element area. Hereinafter, the content of the output value correction according to the element area of the X-ray detector element 201 will be described with reference to FIG.

(Step S601)
The faulty element detection unit 126 reads the element area ratio α (s, c) stored in advance in the device (for example, stored in the storage device 123) (S601). Here, α (s, c) is the element area specification value S (s, c) of each X-ray detector element 201 and the element area specification value S of a typical element of the X-ray detector 106. It is a ratio and is a value calculated as in the following equation (6).

(Step S602)
As shown in the following equation (7), the faulty element detection unit 126 performs correction for standardizing the determination measurement data V (s, c) using the element area ratio α (S602).

  By unifying the determination measurement data V (s, c) as an output value with respect to the element area S by the expression (7), it is possible to correct the output value change due to the element area. In the processing after step S602, the corrected V ′ (s, c) is handled as determination measurement data V (s, c).

(Step S502)
The faulty element detection unit 126 corrects the output value of the module end element (S502). In the module end element 203, the output value may change due to a decrease in crosstalk events between adjacent elements or the influence of the scattered radiation prevention grid. In order not to erroneously detect such an output value change of the module end element 203 as an output value change due to a failure, the output value of the module end element 203 is corrected. In the course of this processing, the module end element failure is also detected. Hereinafter, the output value correction of the module end element 203 will be described with reference to FIG.

(Step S701)
The failure element detection unit 126 sets the determination reference data M (s, c _edge ) in the module end element 203 (represented as c = c _edge ) based on the determination measurement data V (s, c) (S701). As the determination reference data M (s, c _edge ), for example, a moving average output value of peripheral elements of the corresponding module end element c _edge [channel] is calculated. Peripheral elements may be the channel direction, slice direction, combinations thereof, and the like.

In FIG. 12, in one module of the same slice, the number of peripheral elements is w ₂ = 4 [channel], and the average of the peripheral element w ₂ [channel] in the channel direction in the same module as the module end element is taken. Indicates processing. However, _{w 2} is an integer of 1 or more. In FIG. 12, the determination measurement data of the module end element is not used for calculating the moving average output value.

  In the case of the module left end element V (c), the average value of the output values of V (c + 1), V (c + 2), V (c + 3), and V (c + 4) as the peripheral elements is obtained as determination reference data M (c). In the case of the module right end element V (c), the average value of the output values of V (c-1), V (c-2), V (c-3), and V (c-4) as peripheral elements is determined as reference data. Obtained as M (c).

The moving average output value calculation process shown in FIG. 12 can be expressed by the following equation (8). In the above description, the output value of the module end element is not used for calculating the moving average output value for the determination reference data M (c). However, as in the equation (2) of the first embodiment, The moving average output value may be calculated including the output value of the module end element. The moving average output value calculation process in this case can be expressed by the following equation (8) ′.

(Step S702)
The faulty element detection unit 126 calculates a determination value R (s, c _edge ) in the module end element 203 using the determination measurement data and the determination reference data (S702). For example, the determination value R (s, c _edge ) is calculated as in the following equation (9).

(Step S703)
The faulty element detection unit 126 determines a faulty element in the module end element 203 (S702). For example performs threshold decision the allowable variation ratio determination value by the following equation (10) as d _3.

  If the expression (10) is not satisfied, the corresponding module end element 203 is determined as a failed element, and the process proceeds to step S704. If the expression (10) is satisfied, the corresponding module end element 203 is determined not to be a failed element. Then, the process proceeds to step S705.

(Step S704)
When there is a module end element 203 determined as a failed element, the failed element detection unit 126 notifies the system control device 124 of information on the failed element such as a slice number, an element number, and a module number of the failed element (S704). . For example, the system control device 124 instructs the gantry control device 108 to stop scanning, instructs the image reconstruction device 122 to correct faulty element data, registers the faulty element in the storage device 123, displays the faulty element on the display device 125, and services. Take measures such as notification to the center 127.

(Step S705)
The faulty element detection unit 126 performs correction for replacing the determination measurement data V (s, c _edge ) of the module end element 203 with the determination reference data (S705). The processing in this step can be expressed by the following equation (11).

  The correction of Expression (11) is a correction for increasing the failure detection accuracy of the X-ray detector element 201 in the processing after S503, and therefore, for all module end elements 203 regardless of the failure state of the module end elements 203. Run. In the processing after S705, V (s, c) corrected by Expression (11) is handled as determination measurement data V (s, c).

  By performing the above processing, the failure of the module end element 203 is accurately detected, and the change in the output value of the module end element 203 due to a factor other than the failure is corrected to improve the detection accuracy of the X-ray detector element 201 after S503. Increase.

(Step S503)
The faulty element detection unit 126 detects a faulty module (S503). In this step, failure detection is performed in units of the X-ray detection module 202. When the determination reference data M (s, c) is calculated by the moving average of the peripheral elements as in the above-described equation (2) without performing this step, the moving average width w is set to be sufficiently wider than n. Otherwise, all elements in the failed module may not be detected. Moreover, there is a possibility that a non-failed element around the failed module is erroneously detected. Therefore, a faulty module is detected prior to faulty element detection.

  The number of elements in the channel direction constituting the X-ray detection module 202 is n, and a module showing an abnormal output value over all n elements constituting the X-ray detection module 202 is defined as a failure module. Hereinafter, the failure module detection process will be described along each step of FIG.

ただしｍはモジュール番号である。 (Step S801)
The faulty element detection unit 126 generates determination measurement data W (s, m) for each module for each X-ray detection module 202 (S801). The determination measurement data W (s, m) for each module is assumed to be an average output value in the channel direction of elements constituting the X-ray detection module 202, for example, as in the following equation (12).

Where m is the module number.

  The determination measurement data W (s, m) for each module may be the maximum output value or the minimum output value in the X-ray detection module 202.

  Thereafter, the same processing as that of the first embodiment is performed using W (s, m) as determination measurement data. The difference lies in handling determination measurement data in units of modules, not in units of elements.

(Step S802)
Determination reference data is set using determination measurement data of peripheral modules located around the module to be measured (S802). That is, the process similar to step S102 of 1st embodiment is performed using the determination measurement data W (s, m) of a module unit.

(Step S803)
Using the determination measurement data of the module to be measured calculated in step S801 and the determination reference data calculated in step S802, the same processing as in step S103 of the first embodiment is performed to calculate the determination value R (s, m). (S803).

(Step S804)
If the determination value R (s, m) obtained in step S804 exceeds a preset allowable variation rate, the failure element detection unit 126 determines that the module is a failure module, and proceeds to step S805. If the allowable variation rate is not exceeded, the failure module detection process is terminated.

(Step S805)
The faulty element detection unit 126 notifies the system controller 124 of the result of detecting the faulty module (S805), and ends the faulty module detection process. Then, it progresses to step S403.

  With the above processing, the failure module can be detected with high accuracy, and the processing target after step S403 in FIG. 8 can be reduced to elements other than the failure module, thereby reducing the processing.

  As mentioned above, although embodiment of this invention was described, embodiment of this invention is not limited to these. There may be various modifications that do not depart from the object of the present invention. Although the foregoing has been illustrated in order to describe the present invention in detail, they are intended to be illustrative and exemplary and not limiting.

  According to the present embodiment, since it is not necessary to collect measurement data for determination reference data, it is possible to reduce the labor and time of an operator at the time of shipment or adjustment. In addition, failure element detection can be performed at any timing, so that oversight of abnormalities in the X-ray detector and data collection device can be prevented, and failure determination can be performed at any stage during maintenance inspection, Air correction data collection, and offset data measurement. The failure can be detected at an early stage. And even if a faulty element occurs just before the start of inspection imaging, it is detected and the imaging is stopped, so that it is possible to provide an X-ray CT apparatus that prevents invalid exposure and ensures image quality.

DESCRIPTION OF SYMBOLS 1: X-ray CT apparatus, 100: Scan gantry part, 101: X-ray tube, 102: Rotary disk, 103: Collimator unit, 104: Opening part, 105: Bed, 106: X-ray detector, 107: Data acquisition apparatus 108: Gantry control device 109: Bed control device 110: X-ray control device 120: Console console 121: Input device 122: Image reconstruction device 123: Storage device 124: System control device 125: Display device 126: Faulty element detection unit 201: X-ray detector element 202: X-ray detection module 203: Module end element 204: X-ray detector end element 205: Extrapolation element

Claims (9)

An X-ray source that emits X-rays;
An X-ray detector comprising a plurality of X-ray detection elements for detecting the X-ray and outputting analog data corresponding to the detected X-ray dose;
Data provided corresponding to each of the X-ray detection elements and having the same number of data collection elements as the X-ray detection elements for converting the analog data output from each X-ray detection element into digital data and collecting the data A collecting device;
A failure element detection unit that detects a failure of a measurement element comprising a pair of combinations of the X-ray detection element and the data collection element corresponding to the X-ray detection element;
The failure element detection unit generates, for each measurement element, determination measurement data for use in failure determination using measurement data including an output value of digital data of each measurement element, and a target for failure determination Based on determination measurement data of peripheral elements located around the measurement element, determination reference data used for the failure determination is generated, and based on a comparison result between the determination measurement data of the target measurement element and the determination reference data Te, the target measurement element is determined whether the failure element,
The faulty element detection unit generates an approximate function based on the measurement data of the peripheral element for the measurement element at the end of the X-ray detector, and the opposite side of the peripheral element across the measurement element In addition, an element having a virtual output value based on the approximate function is virtually set by extrapolation, and the determination reference data is set using the output value of the element set by the extrapolation and the output value of the peripheral element. Generate
An X-ray CT apparatus characterized by that. The faulty element detection unit determines that the faulty element is present when a comparison result between the determination measurement data and the determination reference data exceeds a predetermined allowable fluctuation rate.
The X-ray CT apparatus according to claim 1. The failure element detection unit is configured to compare the determination measurement data based on the measurement data obtained by irradiating the X-ray and the determination reference data using the measurement data and the measurement data obtained without irradiating the X-ray. Based on the determination measurement data based on and the comparison result of the determination reference data using the determination data, it is determined which of the X-ray detection element or the data collection element included in the failure element is defective,
The X-ray CT apparatus according to claim 1 or 2 , wherein Prior to the determination of the faulty element, the faulty element detection unit performs preprocessing for correcting output value changes due to factors other than faults ,
The X-ray CT apparatus according to any one of claims 1 to 3 . The faulty element detection unit corrects an output value change according to an element area of the X-ray detection element for the determination measurement data as the preprocessing.
The X-ray CT apparatus according to claim 4 . An X-ray source that emits X-rays;
An X-ray detector comprising a plurality of X-ray detection elements for detecting the X-ray and outputting analog data corresponding to the detected X-ray dose;
Data provided corresponding to each of the X-ray detection elements and having the same number of data collection elements as the X-ray detection elements for converting the analog data output from each X-ray detection element into digital data and collecting the data A collecting device;
A failure element detection unit that detects a failure of a measurement element comprising a pair of combinations of the X-ray detection element and the data collection element corresponding to the X-ray detection element;
The failure element detection unit generates, for each measurement element, determination measurement data for use in failure determination using measurement data including an output value of digital data of each measurement element, and a target for failure determination Based on determination measurement data of peripheral elements located around the measurement element, determination reference data used for the failure determination is generated, and based on a comparison result between the determination measurement data of the target measurement element and the determination reference data Determining whether the target measurement element is a faulty element,
The X-ray detector is configured by arranging a plurality of X-ray detection modules including a plurality of the X-ray detection elements,
Prior to the determination of the faulty element, the faulty element detection unit corrects the output value of the X-ray detection element located at the end of the X-ray detection module as pre-processing for correcting a change in the output value due to a factor other than the fault. Do,
X-ray CT apparatus you wherein a. The X-ray detector is configured by arranging a plurality of X-ray detection modules including a plurality of the X-ray detection elements,
The faulty element detection unit generates determination measurement data and determination criterion data using the X-ray detection module unit as the preprocessing, and uses the determination measurement data and determination criterion data using the determination measurement data. It is determined whether or not there is a failure in the X-ray detection module unit.
The X-ray CT apparatus according to claim 4 . The determination reference data is generated using only the determination measurement data of the peripheral element, or is generated using the determination measurement data of the peripheral element and the determination measurement data of the target measurement element.
X-ray CT apparatus according to any one of claims 1 to 7, characterized in that. The determination measurement data is generated based on measurement data obtained in an arbitrary plurality of views.
X-ray CT apparatus according to any one of claims 1 to 8, characterized in that.

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