JP6054036B2 - X-ray CT apparatus and data processing method of X-ray CT apparatus - Google Patents

Description

  FIELD Embodiments described herein relate generally to an X-ray computed tomography apparatus (hereinafter referred to as an X-ray CT apparatus), and an X-ray CT apparatus and an X-ray CT apparatus that reduce a misdiagnosis probability due to a failure of a multichannel X-ray detector. The present invention relates to a data processing method for a line CT apparatus.

A conventional X-ray CT apparatus irradiates a subject with X-rays from an X-ray tube and detects X-rays transmitted through the subject with an X-ray detector to obtain projection data of the subject. Yes. In the X-ray CT apparatus, an image in the subject is reconstructed based on the projection data.
On the other hand, X-ray detectors are becoming multi-row and multi-channel, and the number of detection elements constituting the detector increases, so that the probability of failure due to defective detection elements increases. When a failure of the detection element occurs, an abnormality of the CT value occurs, and the reconstructed tomographic image also becomes abnormal. For example, a missing portion of information becomes a white ring and affects as a ring artifact.

 When an X-ray detector fails, a method of apparently avoiding the failure of the element is used by replacing the data of the failure detection element with the data interpolated from the data of the surrounding detection elements (channel replacement). Yes. Alternatively, as shown in Patent Document 1, when an X-ray detection element includes a failure detection element, data may be collected by the remaining columns excluding the column including the failure detection element.

  However, when performing channel replacement, it is necessary to recognize a defective portion after a problem occurs and then specify a failed detection element. For this reason, it becomes a factor which becomes misdiagnosis at the time of the image diagnosis by system down, generation | occurrence | production of a ring artifact, CT value abnormality, etc.

  Further, in the X-ray CT apparatus, X-rays are detected through an X-ray detector and a data collection unit. X-ray detection sensitivity is X-ray light conversion characteristics, light-to-electricity photoelectric conversion characteristics, It is determined by the amplification accuracy of the electrical signal. However, these characteristics and the like may vary from channel to channel due to the surrounding environment such as temperature and changes over time. For this reason, correction for removing the influence of changes in sensitivity characteristics is performed for each channel.

  Since the change in sensitivity characteristic occurs due to the ambient environment such as temperature and a change with time, correction of the X-ray detection sensitivity is periodically performed, and correction data corresponding to the change in sensitivity characteristic needs to be created. The correction data is called calibration data and is generally generated based on data obtained by scanning a phantom (pseudo model).

  However, when collecting calibration data, if there is a defective channel in the X-ray detector, an abnormal CT value or a ring may occur during the main scan.

JP 2004-49303 A

  The problem to be solved by the invention is to provide an X-ray CT apparatus which copes with a failure of an X-ray detector, automatically identifies a failure channel and performs data replacement.

An X-ray CT apparatus according to an embodiment includes an imaging unit that includes an X-ray tube that irradiates a subject with X-rays, and a multi-channel X-ray detector disposed opposite to the X-ray tube, and the imaging unit When the calibration model is generated by photographing the pseudo model by using the X-ray detector, the output value in the channel direction of the X-ray detector is compared with a preset threshold value, and a channel exhibiting an output value exceeding the threshold value is determined as a failure channel. A failure channel determination unit that collects output data of the X-ray detector obtained by imaging the pseudo model, generates calibration data, and is based on calibration data of a plurality of channels adjacent to the failure channel generating calibration data for the faulty channel Te, and upon shooting a subject by the imaging unit, the output data of the X-ray detector Processing the generated output data of the faulty channel based on the faulty channel to the output data of a plurality of channels adjacent, anda data processing unit for correcting the output data the generated by the calibration data of the faulty channel To do.

1 is a block diagram showing a configuration of an X-ray CT apparatus according to an embodiment. The perspective view which shows schematically the relationship between the X-ray tube and X-ray detector in one Embodiment. Explanatory drawing of operation | movement of the failure channel determination part in one Embodiment. Explanatory drawing which shows CT value for every structure | tissue which made the human body the object in one Embodiment. Explanatory drawing which shows the operation | movement of the replacement process of the data with respect to the failure channel in one Embodiment. 6 is a flowchart showing calibration data creation operation according to an embodiment.

  Hereinafter, an X-ray CT apparatus according to an embodiment will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected about the same location.

(First embodiment)
FIG. 1 is a block diagram illustrating a configuration of an X-ray CT apparatus according to an embodiment. The X-ray CT apparatus 100 includes a gantry 10 and a computer system 20. The gantry 10 collects projection data related to the subject P, and includes a rotating frame 11, an X-ray tube 12, an X-ray detector 13, a data collection unit 14, a non-contact type data transmission device 15, a slip ring 16, and a gantry. A drive unit 17 is included.

  The rotating frame 11 is a ring that is driven to rotate, and is equipped with an X-ray tube 12 and an X-ray detector 13. The central portion of the rotating frame 11 is open, and the subject P placed on the top 18 of a bed (not shown) is inserted into the opening.

  The X-ray tube 12 is a vacuum tube that generates X-rays. In the X-ray tube 12, electric power (tube current, tube voltage) necessary for X-ray exposure is slip-ringed from a high voltage generator 28 (described later). 16 is supplied. The X-ray tube 12 exposes X-rays to the subject P placed in the effective visual field region by accelerating electrons by the supplied high voltage and colliding with the target.

  The X-ray detector 13 detects X-rays transmitted through the subject P, and is attached to the rotating frame 11 so as to face the X-ray tube 12. The X-ray detector 13 is, for example, a multi-slice type detector, and a plurality of detection elements configured by combining a scintillator and a photodiode are two-dimensionally arranged. The X-ray tube 12 and the X-ray detector 13 constitute an imaging unit.

  The data acquisition unit 14 is called DAS (Data Acquisition System), converts a signal output from the X-ray detector 13 for each channel into a voltage signal, amplifies it, and further converts it into a digital signal. This digital data is sent to the computer system 20 via the non-contact type data transmission device 15.

  The gantry driving unit 17 drives the rotary frame 11 to rotate. By rotating the rotary frame 11, the X-ray tube 12 and the X-ray detector 13 face each other and rotate about the body axis of the subject P. If the top plate 18 is moved along the opposite axis direction of the subject P simultaneously with this rotation, so-called helical scanning that scans the subject in a spiral shape becomes possible.

  The computer system 20 includes a preprocessing unit 21, a system control unit 22, a storage unit 23, a reconstruction processing unit 24, a data processing unit 25, a display unit 26, an input unit 27, a high voltage generation unit 28, a failure channel determination unit 29, An auxiliary storage unit 30 is included. In addition, a bus line 201 and a network interface 31 are included.

  The preprocessing unit 21 receives the raw data from the data collection unit 14 via the non-contact data transmission device 15 and performs sensitivity correction and X-ray intensity correction. The system control unit 22 is connected to the bus line 201, performs overall control of the X-ray CT apparatus 100, and performs scan processing, signal processing, image generation processing, image display processing, and the like.

  The raw data subjected to various corrections by the preprocessing unit 21 is called “projection data” and is temporarily stored in the storage unit 23 via the bus line 201. The reconstruction processing unit 24 is equipped with a plurality of kinds of reconstruction methods, and reconstructs image data by the reconstruction method selected by the operator.

  The data processing unit 25 performs image processing for display such as window conversion and RGB processing on the reconstructed image data generated by the reconstruction processing unit 24 and outputs the processed image data to the display unit 26. Further, the data processing unit 25 generates a tomographic image of an arbitrary cross section, a projection image from an arbitrary direction, a three-dimensional image, and the like based on an instruction from the operator and outputs the generated image to the display unit 26. In addition to the raw data, the storage unit 23 stores image data such as reconstructed tomographic image data.

  The display unit 26 displays a CT image such as a computer tomographic image input from the data processing unit 25. The input unit 27 includes a keyboard, various switches, a mouse, and the like, and inputs various scanning conditions such as a slice thickness and the number of slices by an operator. The high voltage generator 28 supplies power necessary for X-ray exposure to the X-ray tube 12 via the slip ring 16.

  The failure channel determination unit 29 checks the output characteristics of the X-ray detector 13 and identifies a defective detection element. Since the output value of the defect detection element is extremely low or high compared to the output characteristics of the surrounding detection elements, the defect detection element is determined by setting a threshold value for such an abnormal output value. The auxiliary storage unit 30 stores calibration data.

  Further, in the scanning process, the system control unit 22 feeds and feeds the high voltage generation unit 28, the gantry driving unit 17, and the top plate 18 in the body axis direction based on the input scanning conditions such as slice thickness. The rotational speed, rotational pitch, and X-ray exposure timing of the X-ray tube 12 and the X-ray detector 13 are controlled. Therefore, it is possible to perform X-ray CT image data collection (scanning) processing by exposing an X-ray cone beam or an X-ray fan beam from multiple directions to a desired imaging region of the subject. Examples of the scan include a one-turn conventional scan and a helical scan.

  FIG. 2 shows the X-ray tube 12 and the X-ray detector 13. The X-ray tube 12 and the X-ray detector 13 are arranged to face the rotating frame 11 with the subject P interposed therebetween. The X-ray detector 13 is formed by arranging a plurality (n × m) of detector modules in the slice direction and the channel direction, and has an arc shape. The slice direction is substantially parallel to the body axis direction of the subject. The channel direction is substantially orthogonal to the body axis direction of the subject.

  The detector module of the X-ray detector 13 includes a plurality of detection elements each composed of a scintillator array and a photodiode array, and the plurality of detector modules are arranged in a matrix in two directions of a channel direction and a slice direction. . The plurality of detector modules are arranged along an arc centered on the focal point of the X-ray tube 12.

  There is also a multi-tube type X-ray CT apparatus in which a plurality of pairs of the X-ray tube 12 and the X-ray detector 13 are mounted on the rotating frame 11. In this embodiment, a single-tube type X-ray CT apparatus is provided. Alternatively, a multi-tube type X-ray CT apparatus can be applied. In the following description, a single tube type will be described.

  As described above, the X-ray detector 13 includes a plurality of detector modules arranged two-dimensionally in the channel direction and the slice direction, and each module includes a plurality of X-ray detection elements. In the following description, one X-ray detection element is described as constituting one channel. However, the present invention is not limited to this, and a plurality of adjacent X-ray detection elements may constitute one channel. .

  When the X-ray detector 13 is multi-rowed and multi-channeled, the number of detection elements constituting the X-ray detector 13 is increased, so that the probability that a failure will occur due to a defect in the detection elements increases. When a failure of the detection element occurs, an abnormality in the CT value occurs, and an abnormality also occurs in the reconstructed tomographic image, which hinders diagnosis.

  In this embodiment, when a failure of the detection element occurs, the failure channel is determined, and the failure channel data is replaced with replacement data obtained from data of a plurality of adjacent channels to reduce CT value abnormality. is there.

  FIG. 3 is an explanatory diagram of the operation of the failure channel determination unit 29. In FIG. 3, the horizontal axis indicates the channel direction of the X-ray detection elements in a certain column, and the vertical axis indicates an example of the output value (CT value) detected by the detection element of each channel. When determining the failure channel, the phantom (pseudo model) is scanned during calibration or warm-up scan, the output characteristics of the X-ray detector 13 are checked, and the output profile A of each channel is generated. As for the output profile A, when photographing the same type of phantom with the same size as an object, a certain output profile can be obtained.

  FIG. 4 shows a CT value for each tissue for the human body. For example, the CT value of water is zero and the CT value of air is -1000. The CT value of bone is +1000. Therefore, when a phantom corresponding to a specific CT value (for example, air or water) is prepared and this phantom is photographed, an almost constant output profile A is obtained.

  On the other hand, when the X-ray detection element is out of order, it exhibits an output value different from the output value indicated by a certain output profile. Therefore, when the upper and lower thresholds B1 and B2 are set for the output profile A shown in FIG. 3 and there are output values exceeding the thresholds B1 and B2, the detection element exhibiting the output values is faulty. Is determined. The upper and lower thresholds B1 and B2 are set according to an empirical rule or the like. Alternatively, the inspector arbitrarily sets it. In this way, it is possible to automatically determine the detection element that has failed.

  The data processing unit 25 replaces the data of the channel determined as a failure by the failure channel determination unit 29 with other data (replacement data). As the replacement processing, for example, the data of the failed channel determined to have a failure is replaced with replacement data obtained from data of a plurality of surrounding channels adjacent to the failed channel.

  For example, as shown in FIG. 3, when a channel exhibiting an output value exceeding the threshold B2 is c0, interpolation processing is performed based on the output values of the adjacent channels c1 and c2 before and after that, for example, the channels c1 and c2 The average value c0 ′ of the output values is calculated, and the data of the failure channel c0 determined as having a failure is replaced with the data c0 ′. Information indicating which channel is faulty is stored in the auxiliary storage unit 30.

  FIG. 5 is a diagram for explaining the operation of the replacement processing, showing detection elements arranged two-dimensionally in the channel direction and the slice direction, and adjacent channels in the channel direction centering on the failure channel (black channel n24). An example is shown in which replacement data is obtained by performing interpolation processing based on the output values of (n23 and n25). As shown in FIG. 3, for example, the replacement data is calculated by calculating the average value c0 'of the output values of the adjacent channels c1 and c2 as replacement data.

  Note that the replacement data may be obtained by calculating an average value from data of a plurality of surrounding channels with respect to the two directions of the channel direction and the slice direction with the failure channel as the center.

  Further, the detection sensitivity of X-rays is caused by the ambient environment such as temperature and changes with time. Therefore, correction data (calibration data) is periodically generated according to the change of sensitivity characteristics, and the calibration data is stored in the auxiliary storage unit 30. To remember. Calibration data is collected using a phantom, and correction data corresponding to changes in sensitivity characteristics is created based on the collected data.

  For example, as in FIG. 5, the auxiliary storage unit 30 two-dimensionally arranges calibration files in the same channel direction and slice direction as each detection element of the X-ray detector 13, and stores correction data for each channel in each file. Remember. If there is a faulty channel, the average value is obtained using correction data of a plurality of adjacent channels, and the correction data is stored in a file corresponding to the faulty channel.

  Therefore, when photographing an actual patient (subject P) in place of the phantom, the failure channel determination unit 29 has already found the failure channel. The replacement data may be calculated from the channel data and replaced, and the correction value (calibration data) of the corresponding failure channel may be read from the auxiliary storage unit 30 and corrected.

  FIG. 6 is a flowchart showing the calibration data creation operation. In FIG. 6, step S0 is a start step, and in step S1, collection of calibration data is started using a phantom. In step S2, a fault channel is checked. That is, as shown in FIG. 3, threshold values B1 and B2 are set for profile A to determine the presence or absence of a faulty channel.

  In step S3, it is determined whether or not the X-ray detection element is normal. If normal, calibration data is created and stored based on the normal value in step S4. If it is determined in step S3 that there is an abnormal value, that is, there is a faulty channel, interpolation is performed using data of surrounding normal channels (channel interpolation) in step S5. In step S4, calibration data for the failed channel is created and stored based on the interpolated data, and the process ends in step S6.

  Thus, in the first embodiment, the failure channel can be identified by checking the output characteristics of the X-ray detector at the time of collecting calibration data performed before actual inspection or at the warm-up scan. Therefore, in the actual patient examination, if there is a failed channel, the replacement data can be calculated from the data of the surrounding channels and replaced. Further, the change with time and the surrounding environment can be corrected using the calibration data, and the failure channel can also be corrected based on the calibration data obtained from the correction data of the surrounding channels.

  As described above, according to the embodiment of the present invention, it is possible to avoid a clinical problem even if a specific channel becomes faulty or abnormal. Further, even if calibration data collection is performed unintentionally at the time of a channel failure, CT values do not become abnormal in clinical examinations.

  In the above embodiment, the network interface 31 may communicate with an external terminal device (such as the PC 32) via the network NW. In this case, the failure and the failure location can be notified to the PC 32 when the failure channel is determined in the X-ray detector 13.

  As mentioned above, although several embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the invention described in the claims and equivalents thereof as well as included in the scope and gist of the invention.

DESCRIPTION OF SYMBOLS 100 ... X-ray diagnostic imaging apparatus 10 ... Base 11 ... Rotating frame 12 ... X-ray tube 13 ... X-ray detector 14 ... Data collection part 15 ... Data transmission apparatus 20 ... Computer system 21 ... Pre-processing part 22 ... System control part 23 ... Storage unit 24 ... Reconfiguration processing unit 25 ... Data processing unit 26 ... Display unit 27 ... Input unit 28 ... High voltage generation unit 29 ... Fault channel determination unit 30 ... Auxiliary storage unit

Claims (8)

An imaging unit including an X-ray tube that exposes an X-ray to a subject, and a multi-channel X-ray detector disposed opposite to the X-ray tube;
When imaging the pseudo model by the imaging unit and generating calibration data, the output value in the channel direction of the X-ray detector is compared with a preset threshold value, and a channel exhibiting an output value exceeding the threshold value fails. A failure channel determination unit for determining a channel;
Collecting output data of the X-ray detector obtained by imaging the pseudo model, generating calibration data, and calibrating the failed channel based on calibration data of a plurality of channels adjacent to the failed channel Output data of the X-ray detector when data is generated and the subject is imaged by the imaging unit , and output of the failed channel based on output data of a plurality of channels adjacent to the failed channel A data processing unit for generating data and correcting the generated output data with the calibration data of the failed channel ;
An X-ray CT apparatus comprising:   The X-ray CT apparatus according to claim 1, further comprising a storage unit that stores the failure channel determined by the failure channel determination unit.   The X-ray CT apparatus according to claim 1, wherein the failure channel determination unit determines a failure channel based on output data of the X-ray detector obtained by imaging a phantom having a specific CT value as the pseudo model. . The X-ray CT apparatus according to claim 1, wherein the data processing unit generates calibration data of the failed channel by interpolating calibration data of a plurality of peripheral channels adjacent to the failed channel. And X-ray tube irradiating X-rays to a subject when generating the calibration data by photographing a result pseudo model the imaging unit including the X-ray detector of a multichannel disposed the X-ray tube and the opposite In addition, the output value in the channel direction of the X-ray detector is compared with a preset threshold value, and a channel exhibiting an output value exceeding the threshold value is determined as a failure channel,
Collecting the output data of the X-ray detector obtained by photographing the pseudo model, generating calibration data,
Generating calibration data for the failed channel based on calibration data for a plurality of channels adjacent to the failed channel;
Processing the output data of the X-ray detector when the subject is imaged by the imaging unit, and generating the output data of the failed channel based on the output data of a plurality of channels adjacent to the failed channel. The data processing method of the X-ray CT apparatus correct | amends the output data by the calibration data of the said failure channel .   6. The data processing method of the X-ray CT apparatus according to claim 5, wherein when the failed channel is determined, the failed channel is stored in a storage unit.   6. The data processing method of an X-ray CT apparatus according to claim 5, wherein the failure channel is determined using output data of the X-ray detector obtained by imaging a phantom having a specific CT value as the pseudo model. 6. The data processing of the X-ray CT apparatus according to claim 5, wherein when the failed channel is determined, calibration data of a plurality of surrounding channels adjacent to the failed channel is interpolated to generate calibration data of the failed channel. Method.

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