JP6556541B2 - Radiation tomography apparatus and program - Google Patents

Description

  The present invention relates to an imaging technique suitable for puncture under image guidance by a radiation tomography apparatus.

  Conventionally, puncture under image guidance has been performed by a radiation tomography apparatus. In puncture under image guidance, an area including a target in a subject is repeatedly imaged and a tomographic image thereof is displayed in almost real time. The surgeon accurately inserts the needle into the target while viewing the tomographic image.

  When a needle enters the imaging area, the needle appears in the tomographic image. The needle is generally made of metal. Therefore, not only needles but also metal artifacts often occur in the tomographic image at the same time. In puncturing, metal artifacts are difficult to specify because it is difficult to specify the position of the target or the needle.

  On the other hand, various proposals have been made for metal artifact reduction processing in tomographic images, and the effects thereof have been confirmed. For example, Patent Document 1 proposes the following metal artifact reduction processing. First, a region of interest is set on a tomographic image where a metal artifact has occurred, and the projection data is generated from a tomographic image obtained by subtracting the average value of the image data (image data) of the region of interest from the current tomographic image and shifting the level. (Projection data) is generated. Then, only the data of the channel where the metal exists is extracted from the projection data to reconstruct the image. By subtracting this from the original tomographic image, the portion hidden by the metal artifact can be reproduced without being disturbed by the metal artifact.

Japanese Patent No. 2814001

  Here, the method that is normally considered is a method in which a tomographic image obtained by repeated imaging is subjected to metal artifact reduction processing and a processed tomographic image is displayed.

  However, the metal artifact reduction processing generally requires a large amount of calculation and requires a certain time or more to complete the processing.

  Therefore, this method cannot be applied to puncture because it takes too much time to process and loses real-time characteristics.

  Under such circumstances, there is a demand for a technique capable of displaying a tomographic image with reduced metal artifacts while maintaining real-time properties during puncture under image guidance by a radiation tomography apparatus.

The invention of the first aspect
By scanning the part of the subject into which the needle is inserted a plurality of times, the first projection data of the part before the insertion of the needle and the second projection data of the part after the insertion of the needle are obtained. First control means for controlling the data collection system to collect;
Subtracting means for subtracting the first projection data from the second projection data to obtain third projection data;
Reconstruction means for reconstructing a first image based on the first projection data and a third image based on the third projection data;
Threshold processing means for obtaining a fourth image composed of pixels having a pixel value exceeding a predetermined threshold in the third image;
There is provided a radiation tomography apparatus comprising: a second control unit configured to control a display device so as to display a composite image formed by superimposing the fourth image on the first image.

The invention of the second aspect is
The radiation tomography apparatus according to the first aspect, in which the threshold value is a pixel value between a pixel value representing a metal artifact and a pixel value representing a metal.

The invention of the third aspect is
The first control means controls the data collection system to continuously scan the site a plurality of times after the start of insertion of the needle;
Provided is the radiation tomography apparatus according to the first aspect or the second aspect, wherein the second control unit performs control so that the composite image is newly displayed each time the second projection data is collected. .

The invention of the fourth aspect is
The first control means controls the data collection system so as to sequentially collect the projection data by repeatedly scanning the part a plurality of times before and after the start of insertion of the needle;
In response to the collection of the projection data, the apparatus further comprises a determination unit that determines whether a change exceeding a certain level (level) has occurred in the temporal change of the projection data or the image based on the projection data.
The first projection data is projection data collected at a time before it is determined that a change exceeding the certain level has occurred;
The radiation tomography apparatus according to the third aspect, in which the second projection data is projection data collected at a time point after it is determined that a change exceeding the certain level has occurred.

The invention of the fifth aspect is
The radiation tomography apparatus according to any one of the first to fourth aspects, wherein the reconstruction unit reconstructs the first and third images by a two-dimensional backprojection process.

The invention of the sixth aspect is
A setting means for setting an area including a path on which the needle is scheduled to be inserted in an image of the part obtained by scanning the part of the subject into which the needle is inserted;
A first control means for controlling a data collection system to sequentially obtain projection data by repeatedly scanning the site several times after the insertion of the needle is started;
Generation means for generating an image in which metal artifacts due to the needle are reduced based on the projection data or a reconstructed image based on the projection data and position information of the region;
A radiation tomography apparatus comprising: a second control unit that controls a display device to display the generated image.

The invention of the seventh aspect
The radiation tomography apparatus according to the sixth aspect, wherein the generation unit searches for the portion corresponding to the needle in the projection data or a reconstructed image based on the projection data based on the position information of the region. To do.

The invention of the eighth aspect
Before and after the start of insertion of the needle, including a first and a second slice adjacent to each other, where the needle is inserted through the first slice to reach the second slice. First control means for controlling the data acquisition system so as to sequentially collect projection data by repeatedly scanning over a plurality of times,
First setting means for setting the first slice as a target slice;
Generation means for generating an image in which metal artifacts due to the needle are reduced using projection data of the slice of interest or a reconstructed image based on the projection data;
Second control means for controlling the display device to display the generated image;
Determining means for determining whether the needle has reached the second slice using the projection data of the first slice or a reconstructed image based on the projection data;
A radiation tomography apparatus comprising: a second setting unit configured to set the second slice as the target slice when the determination unit determines that the needle has reached the second slice. I will provide a.

The invention of the ninth aspect is
In the image obtained by scanning the part before the start of the insertion of the needle, further comprising a third setting means for setting a region including a path where the needle is scheduled to be inserted,
The generation means performs the generation based on position information of the region,
The radiation tomography apparatus according to the eighth aspect, in which the determination unit performs the determination based on position information of the region.

The invention of the tenth aspect is
The generating means searches for a portion corresponding to the needle in a range corresponding to the region in the projection data of the slice of interest or the reconstructed image based on the projection data,
The radiation tomography apparatus according to the ninth aspect, wherein the determination unit performs the determination based on projection data of the first slice or a portion corresponding to the region in a reconstructed image based on the projection data. .

The invention of the eleventh aspect is
The generation unit performs the generation using information related to at least one of the material and thickness of the needle stored in advance, and the generation unit according to any one of the sixth to tenth aspects A radiation tomography apparatus is provided.

The invention of the twelfth aspect is
A program for causing a computer to function as each means in the radiation tomography apparatus according to any one of the first to eleventh aspects is provided.

  According to the above aspect of the invention, the projection data before the insertion of the needle is subtracted from the projection data during the insertion of the needle, and the image in which the needle and the metal artifact are main components is reconstructed based on the difference projection data, Pixel value threshold processing is performed on this to generate an image of almost only the needle, and this is superimposed and displayed on the image reconstructed based on the projection data before the insertion of the needle. An image with reduced artifacts can be displayed.

It is a figure which shows roughly the structure of the hardware of the X-ray CT apparatus which concerns on this embodiment. It is a functional block diagram of the operation console of the X-ray CT apparatus which concerns on 1st Embodiment. It is a figure which shows typically a mode that the subject in 1st Embodiment is scanned. It is a flowchart which shows the flow of a process in the X-ray CT apparatus which concerns on 1st Embodiment. It is a figure for demonstrating the method of obtaining the tomographic image with which the metal artifact which concerns on 1st Embodiment was reduced. It is a functional block diagram of the operation console of the X-ray CT apparatus which concerns on 2nd Embodiment. It is a figure which shows typically a mode that the subject in 2nd Embodiment is scanned. It is a flowchart which shows the flow of a process in the X-ray CT apparatus which concerns on 2nd Embodiment. It is a figure for demonstrating the setting of the puncture root area | region which concerns on 2nd Embodiment. It is a functional block diagram of the operation console of the X-ray CT apparatus which concerns on 3rd Embodiment. It is a figure which shows typically a mode that the subject in 3rd Embodiment is scanned. It is a flowchart which shows the flow of a process in the X-ray CT apparatus which concerns on 3rd Embodiment. It is a figure for demonstrating the setting of the puncture root area | region which concerns on 3rd Embodiment. It is a figure which shows the positional relationship of the slice and biopsy needle in the 1st time, and the tomogram obtained by the scan performed at the time. It is a figure which shows the positional relationship of the slice and biopsy needle in a 2nd time, and the tomographic image obtained by the scan performed at the time. It is a figure which shows the positional relationship of the slice and biopsy needle in the 3rd time, and the tomographic image obtained by the scan performed at the time.

  Embodiments of the invention will be described below. The invention is not limited thereby.

  FIG. 1 is a diagram schematically illustrating a hardware configuration of an X-ray computed tomography system (X-ray computed tomography system) according to the present embodiment.

  As shown in FIG. 1, the X-ray CT apparatus 1 includes a gantry 2, an imaging table 4, and an operation console 6. The gantry 2 and the imaging table 4 are examples of the data collection system in the invention.

  The gantry 2 includes an X-ray tube 21, an aperture 22, a collimator device 23, an X-ray detector 24, a data collection unit 25, a rotation unit 26, a high voltage power supply 27, an aperture drive device 28, and a rotation drive. A device 29 and a gantry table control unit 30 are provided.

  The X-ray tube 21 and the X-ray detector 24 are disposed to face each other with the cavity 2B interposed therebetween.

  The aperture 22 is disposed between the X-ray tube 21 and the cavity 2B. X-rays radiated from the X-ray focal point of the X-ray tube 21 toward the X-ray detector 24 are shaped into a fan beam or a cone beam.

  The collimator device 23 is disposed between the cavity 2B and the X-ray detector 24. The collimator device 23 removes scattered radiation incident on the X-ray detector 24.

  The X-ray detector 24 includes a plurality of two-dimensionally arranged in the spreading direction (referred to as channel direction) and the thickness direction (referred to as column direction) of the fan-shaped X-ray beam emitted from the X-ray tube 21. It has an X-ray detection element. Each X-ray detection element detects transmitted X-rays of the subject 5 arranged in the cavity 2B, and outputs an electrical signal corresponding to the intensity. The subject 5 is a living body such as a human being or an animal.

  The data collection unit 25 receives an electrical signal output from each X-ray detection element of the X-ray detector 24, converts it into X-ray data, and collects it.

  The rotating part 26 is supported so as to be rotatable around the cavity 2B. An X-ray tube 21, an aperture 22, a collimator device 23, an X-ray detector 24, and a data collection unit 25 are mounted on the rotation unit 26.

  The imaging table 4 has a cradle 41 and a cradle driving device 42. The subject 5 is placed on the cradle 41. The cradle driving device 42 puts the cradle 41 into and out of the cavity 2B of the gantry 2, that is, the imaging space.

  The high voltage power supply 27 supplies a high voltage and current to the X-ray tube 21.

  The aperture driving device 28 and the aperture 22 are driven to deform the opening.

  The rotation drive device 29 and the rotation unit 26 are rotationally driven.

  The gantry / table control unit 30 controls each device / unit in the gantry 2, the imaging table 4, and the like.

  The operation console 6 receives various operations from the operator. The operation console 6 includes an input device 61, a display device 62, a storage device 63, and an arithmetic processing device 64. In this example, the operation console 6 is configured by a computer.

  Here, as shown in FIG. 1, the body axis direction of the subject 5, that is, the conveyance direction of the subject 5 by the imaging table 4 is the z direction. The vertical direction is the y direction, and the horizontal direction orthogonal to the y direction and the z direction is the x direction.

(First embodiment)
FIG. 2 is a functional block diagram (block diagram) of the operation console of the X-ray CT apparatus according to the first embodiment.

  The operation console 6 of the X-ray CT apparatus according to the first embodiment includes, as functional blocks, a scan control unit 71, a subtraction processing unit 72, an averaging processing unit 73, an image reconstruction unit 74, a threshold processing unit 75, and a display. A control unit 76 is provided.

  The operation console 6 functions as each functional block when the arithmetic processing unit 64 executes a predetermined program. The predetermined program is stored in, for example, the storage device 63 or an externally connected storage device or storage medium.

  The scan control unit 71 controls the gantry / table control unit 30 so that scanning is performed in accordance with an operation of the operator.

  FIG. 3 is a diagram schematically illustrating a state in which the subject is scanned in the first embodiment. In this example, as shown in FIG. 3, the scanning is performed on the imaging space R1 including the predetermined portion 5a of the subject 5 placed on the cradle 41. The scan is performed by irradiating the subject 5 with X-rays from the X-ray focal point of the X-ray tube 21 while rotating the X-ray tube 21 and the X-ray detector 14 around the subject 5. When scanning is performed, due to the arrangement structure of the X-ray detection elements in the X-ray detector 24, projection data of a plurality of views is collected for each of a plurality of slices obtained by slicing the imaging space in the z-axis direction. Is done. Here, it is assumed that projection data for 24 slices having a thickness of 0.625 mm are collected by performing one scan. In this example, it is assumed that the lesioned part 5c is included in the part 5a. The surgeon performs puncture for inserting the biopsy needle from the surface of the part 5a until reaching the lesioned part 5c while viewing the tomographic image of the part 5a displayed in almost real time by continuous scanning.

  There are two types of scans. The first type is a first scan performed before starting puncturing. The second type is a second scan that is continuously performed repeatedly a plurality of times after the puncture is started. Here, the projection data obtained by the first scan will be referred to as first projection data. The projection data obtained by the second scan is referred to as second projection data. The scan is a so-called half scan in which the view angle range is 180 degrees + fan angle α of the X-ray beam. The scan is performed with the same view angle at which the scan is started. The position of the part 5a in the imaging space is not changed before and after the start of puncturing.

  Each time the second projection data is obtained by the second scan, the subtraction processing unit 72 performs a process of subtracting the first projection data from the obtained second projection data, and represents the difference. 3 projection data is obtained. Therefore, when the second scan is performed and a biopsy needle is included in a slice of the imaging space, the third projection data corresponding to the slice is the amount of change in X-ray absorption due to the presence of the needle. Projection data representing If the biopsy needle is not included in the imaging space when the second scan is performed, the third projection data corresponding to the slice is zero level data excluding noise components. become. The subtraction process is performed between data of the same view, column, and channel. This subtraction process is similarly performed for each slice.

  The averaging processing unit 73 performs averaging processing in the z-axis direction every time a plurality of projection data corresponding to a plurality of slices is obtained, and obtains projection data corresponding to a smaller number of slices. Here, an averaging process is performed in which eight projection data are combined into one for 24 projection data corresponding to 0.625 mm × 24 slices, and three projections corresponding to 5 mm × 3 slices are performed. Projection data is obtained. The averaging processing unit 73 performs this averaging process on the first projection data and the third projection data.

  The image reconstruction unit 74 performs an image reconstruction process based on the projection data that has been averaged, and obtains a tomographic image. For the image reconstruction process, for example, a two-dimensional backprojection process is used. The two-dimensional backprojection process requires less computation than the current mainstream three-dimensional backprojection process. Therefore, an image can be reconstructed in a short time.

  When the first projection data is acquired by performing the first scan, the image reconstruction unit 74 performs an image reconstruction process based on the first projection data that has been subjected to the averaging process. Obtain a tomographic image. Further, when the third projection data is collected by the subtraction process, the image reconstruction unit 64 performs the image reconstruction process based on the averaged third projection data, and the third projection data Obtain a tomographic image. The image reconstruction process is performed in the same manner for each slice.

  The threshold processing unit 75 determines a threshold value of a pixel value (CT value) for each pixel in the third tomographic image, and converts a pixel value equal to or lower than a predetermined threshold value to a 0 level that does not depict anything. That is, only pixels having a pixel value exceeding a predetermined threshold are extracted, and a tomographic image including the extracted pixels is obtained. The predetermined threshold is set to a value smaller than the pixel value representing metal (metal) and larger than the pixel value representing metal artifact. Thus, when the third tomographic image includes a biopsy needle composed of metal and the metal artifact, the metal artifact is removed, and a tomographic image in which only the biopsy needle is extracted can be obtained.

  For each slice, the display control unit 76 obtains a composite tomographic image in which the third tomographic image that has been subjected to threshold processing is superimposed on the first tomographic image. Here, this tomographic image is referred to as a fourth tomographic image. The display control unit 76 controls the display device 62 to display the fourth tomographic image of each slice on the screen. Thereby, even when a biopsy needle is included in each slice, a tomographic image from which metal artifacts have been removed can be displayed.

  Next, the flow of processing in the X-ray CT apparatus according to the first embodiment will be described.

  FIG. 4 is a flowchart showing the flow of processing in the X-ray CT apparatus according to the first embodiment. FIG. 5 is a diagram for explaining a method for obtaining a tomographic image with reduced metal artifacts according to the first embodiment.

  In this case, it is assumed that the subject 5 is already placed on the cradle 41 of the imaging table 4 and conveyed to the cavity 2B, and the part 5a is disposed in the imaging space R1.

  In step S1, a scan before starting puncturing is performed. Specifically, at the stage before puncturing is started, the operator uses the input device 61 to input a command for executing a scan before starting puncturing. The scan control unit 71 detects the input of this command and sends a control signal to the gantry table control unit 30 so as to perform a scan before the puncture is started. The gantry table control unit 30 receives this control signal and controls each part of the gantry 2 and the imaging table 4. Thereby, a scan before the start of puncturing is performed. By performing the scan before the start of puncturing, the first projection data for 24 slices is collected for the imaging space R1 including the region 5a. The scan before the start of puncturing is basically performed only once, but may be performed a plurality of times. When it is performed a plurality of times, the projection data obtained by one of the scans may be processed, or projection data obtained by adding all the projection data obtained by the plurality of scans and adjusting the level is used. It may be a processing target.

  In step S2, a scan after the start of puncturing is performed. Specifically, at the stage immediately before puncturing is started, the operator uses the input device 61 to input a command for performing a continuous scan after puncturing is started. The scan control unit 71 detects the input of this command, and sends a control signal to the gantry table control unit 30 so as to perform a scan after the puncture is started. The gantry table control unit 30 receives this control signal and controls each part of the gantry 2 and the imaging table 4. Thereby, a scan after the start of puncturing is performed. By performing the scan after the start of puncturing, second projection data for 24 slices in the imaging space including the part 5a is collected. The scan after the start of puncture is basically repeatedly performed a plurality of times, and projection data is obtained sequentially.

  In step S3, a projection data subtraction process is performed. Specifically, the subtraction processing unit 72 performs a process of subtracting the first projection data from the second projection data for each of the 24 slices to obtain third projection data representing the difference.

  In step S4, the projection data is averaged. Specifically, the averaging processing unit 73 averages the first projection data corresponding to 24 slices in the z-axis direction, and has already averaged the three slices SL11 to SL13. The first projection data P1 is obtained. This process is performed only once, and the second and subsequent processes are omitted. The averaging processing unit 73 averages the third projection data corresponding to the 24 slices in the z-axis direction and performs the averaging process on the three slices SL11 to SL13. Projection data P3 is obtained.

  The left part of FIG. 5A shows a part 5a and three slices SL11 to SL13 when a scan before starting puncturing is performed. The center of FIG. 5A shows an example of the first projection data P1 obtained by performing the scan before the start of puncturing, corresponding to the slice SL13 and one view. The projection data is expressed with the channel number CH on the horizontal axis and the X-ray absorption μ on the vertical axis. In the scan before the start of puncturing, as shown in the figure, the biopsy needle 9 does not exist in the slice, and therefore, there is no region where the X-ray absorption by the biopsy needle 9 is large in the first projection data P1.

  The left part of FIG. 5B shows a part 5a and three slices SL11 to SL13 when a scan after the start of puncturing is performed. Further, the center of FIG. 5B shows projection data corresponding to slice SL13 and one view as an example of second projection data P2 obtained by performing a scan after the start of puncturing. In the scan after the start of puncturing, as shown in the figure, the biopsy needle 9 may be present in the slice. Therefore, the second projection data P2 includes an area where X-ray absorption by the biopsy needle 9 is high. There is.

  The center of FIG. 5C shows an example of the third projection data P3 obtained by subtracting the first projection data P1 from the second projection data P2 and corresponding to the slice SL13 and one view. Yes. When the biopsy needle 9 is present in any of the slices SL11 to SL13, the third projection data P3 of that slice includes only a region where X-ray absorption by the biopsy needle 9 is high.

  In step S5, an image reconstruction process is performed. Specifically, the image reconstruction unit 74 performs an image reconstruction process on the slices SL11 to SL13 based on the first projection data P1 that has been subjected to the averaging process, and obtains a first tomographic image G1. This process is performed only once, and the second and subsequent processes are omitted.

  The right side of FIG. 5A shows a first tomographic image of the slice SL13 as an example of the first tomographic image G1. The first tomographic image G1 does not include the biopsy needle 9.

  Further, the image reconstruction unit 74 performs an image reconstruction process on the slices SL11 to SL13 based on the third projection data P3 that has been averaged, and obtains a third tomographic image G3.

  The right side of FIG. 5C shows a third tomographic image of the slice SL13 as an example of the third tomographic image G3. When the biopsy needle 9 is present in the slice, the biopsy needle 9 appears in the third tomographic image G3 as shown in the figure. However, the third tomographic image G3 may include metal artifacts that could not be removed.

  The right side of FIG. 5B shows a second tomographic image obtained when the image is reconstructed based on the second projection data P2. When the biopsy needle 9 exists in the slice, not only the biopsy needle 9 but also a metal artifact MA appear in the second tomographic image G2 as shown in the figure.

  In step S6, tomographic image threshold processing is performed. Specifically, for each slice SL11 to SL13, the threshold processing unit 75 extracts only pixels having a pixel value exceeding a predetermined threshold in the third tomographic image G3, and obtains a tomographic image including the extracted pixels. obtain. For example, the threshold value is set to a pixel value between a pixel value representing a metal artifact and a pixel value representing a metal (metal). As a result, when the third tomographic image includes a biopsy needle and a metal artifact that could not be removed, the metal artifact was removed with higher accuracy and only the biopsy needle was extracted. The third tomographic image G3 is obtained.

  In step S7, a tomographic image is synthesized. Specifically, for each slice SL11 to SL13, the display control unit 76 displays the fourth tomographic image G4 as a composite tomographic image obtained by superimposing the third tomographic image G3 subjected to threshold processing on the first tomographic image G1. Generate.

  FIG. 5D is a diagram schematically illustrating a fourth tomographic image G4 obtained by superimposing the third tomographic image G3 subjected to the threshold processing on the first tomographic image G1. The fourth tomographic image G4 includes the part 5a and the biopsy needle 9, but hardly includes metal artifacts.

  In step S8, the synthesized tomographic image is displayed. Specifically, the display control unit 76 displays a composite tomogram for each of the slices SL11 to SL13. Thereby, even when a biopsy needle is included in each slice, a tomographic image from which metal artifacts have been removed can be displayed.

  In step S9, it is determined whether or not to end the scan. Specifically, the scan control unit 71 detects whether or not a scan end command is input, and determines whether or not to end the scan. If it is determined to end, the scanning is ended. If it is determined not to end, the process returns to step S2 to continue scanning.

  According to the first embodiment as described above, the projection data before puncturing is subtracted from the projection data during puncturing, and a tomographic image whose main components are the biopsy needle and the metal artifact is reconstructed based on the difference projection data. Then, pixel value threshold processing is performed on this to generate a tomographic image of almost only the biopsy needle, and this is superimposed and displayed on the tomographic image reconstructed based on the projection data before puncturing. A tomographic image in which metal artifacts are reduced can be displayed. In addition, since information corresponding to biopsy needles and metal artifacts is not detected in projection data and tomographic images, and processing for reducing them is not performed, it is possible to avoid a significant increase in the amount of calculation and display tomographic images. Real-time characteristics can also be maintained.

  In the first embodiment, the following modifications can be considered. The scan control unit 71 controls the gantry / table control unit 30 so as to sequentially and repeatedly scan the region 5a a plurality of times before and after the biopsy needle insertion is started to sequentially obtain projection data corresponding to each slice. To do. The first projection data is the projection data obtained within the most recent fixed period before the change exceeding a certain level occurs in the temporal change of the obtained projection data or the image based on the projection data. Further, the second projection data is the projection data obtained after the obtained projection data or the temporal change of the image based on the projection data is changed exceeding the predetermined level. The determination as to whether or not a change exceeding a certain level has occurred is performed by, for example, obtaining a difference between each channel data value and each pixel value between two temporally adjacent projection data or images, and summing these values or This is performed depending on whether the normalized value exceeds a certain threshold. In this way, the projection data immediately before the biopsy needle enters the slice can be used as the first projection data. As a result, an image obtained by superimposing the tomographic image of the biopsy needle on the normal tomographic image, that is, a metal artifact. A tomographic image including a biopsy needle with reduced can be displayed.

(Second Embodiment)
The X-ray CT apparatus according to the second embodiment has the same hardware configuration as that of the first embodiment, but has different functions.

  FIG. 6 is a functional block diagram of an operation console of the X-ray CT apparatus according to the second embodiment.

  The operation console 6a of the X-ray CT apparatus according to the second embodiment includes, as functional blocks, a scan control unit 81, an averaging processing unit 82, an image reconstruction unit 83, a puncture route (route) region setting unit 84, and a tomographic image. A generation unit 85 and a display control unit 86 are included.

  The scan control unit 81 controls the gantry table control unit so that a scan for collecting projection data is performed.

  FIG. 7 is a diagram schematically illustrating a state in which a subject is scanned in the second embodiment. In this example, as shown in FIG. 7, a scan is performed on the imaging space R2 including the predetermined part 5a of the subject 5 placed on the cradle 41. The scan is performed by irradiating the subject 5 with X-rays from the X-ray focal point of the X-ray tube 21 while rotating the X-ray tube 21 and the X-ray detector 14 around the subject 5. When scanning is performed, due to the arrangement structure of the X-ray detection elements in the X-ray detector 24, projection data of a plurality of views is collected for each of a plurality of slices obtained by slicing the imaging space in the z-axis direction. Here, it is assumed that projection data for eight slices having a thickness of 0.625 mm are collected by performing one scan. In this example, it is assumed that the lesioned part 5c is included in the part 5a. The surgeon performs puncture for inserting the biopsy needle from the surface of the part 5a until reaching the lesioned part 5c while viewing the tomographic image of the part 5a displayed in almost real time by continuous scanning.

  The averaging processing unit 82 averages projection data or tomographic images for a plurality of slices in the imaging space in the z-axis direction, and performs processing for obtaining projection data or tomographic images of a smaller number of slices. Here, eight slices having a thickness of 0.625 mm are combined into one slice having a thickness of 5 mm.

  The image reconstruction unit 83 performs processing for reconstructing a tomographic image based on the projection data.

  The puncture route region setting unit 84 performs a process of setting a planned biopsy needle insertion route at the time of puncture as a puncture route.

  The tomographic image generator 85 performs tomographic image generation processing including limited metal artifact reduction processing.

  The display control unit 86 performs processing for controlling the display device 62 to display a tomographic image or the like on the screen.

  Next, the flow of processing in the X-ray CT apparatus according to the second embodiment will be described.

  FIG. 8 is a flowchart showing the flow of processing in the X-ray CT apparatus according to the second embodiment. FIG. 9 is a diagram for explaining setting of the puncture root region.

  In step A1, a scan before starting puncturing is performed. Specifically, at the stage before puncturing is started, the operator inputs a command for performing a scan before starting puncturing using the input device 61. The scan control unit 81 detects the input of this command, and sends a control signal to the gantry table control unit 30 so as to perform a scan before the puncture is started. The gantry table control unit 30 receives this control signal and controls each part of the gantry 2 and the imaging table 4. Thereby, a scan before the start of puncturing is performed. By performing the scan before the start of puncturing, the first projection data P1 for eight slices is collected for the imaging space R2 including the region 5a.

  In step A2, the projection data is averaged. Specifically, the averaging processing unit 82 averages the first projection data corresponding to the eight slices in the z-axis direction and has already averaged the corresponding one slice SL21. 1 projection data P1 is obtained.

  FIG. 9A shows a part 5a and one slice SL21 when a scan before the start of puncturing is performed. In the scan before the start of puncturing, as shown in the figure, the biopsy needle 9 does not exist in the slice, and therefore there is no region where the X-ray absorption by the biopsy needle 9 is large in the first projection data P1.

  In step A3, image reconstruction processing is performed. Specifically, the image reconstruction unit 83 performs an image reconstruction process based on the first projection data that has been subjected to the averaging process of the slice SL21, and obtains a first tomographic image G1.

  In step A4, a tomographic image is displayed. Specifically, the display control unit 86 controls the display device 62 so that the first tomographic image G1 of the slice SL21 reconstructed in step A3 is displayed on the screen.

  FIG. 9B shows a display example of the first tomographic image G1. The first tomographic image G1 is a tomographic image corresponding to the SL 21 of the part 5a including the lesioned part 5c.

  In step A5, a puncture route area is set. Specifically, the operator designates a route on which the biopsy needle is scheduled to be inserted on the displayed first tomographic image, that is, a route. For example, as shown in FIG. 9 (c), this route is specified by using the input device 61, the center position K11 of the lesioned part 5c, which is a puncture target, and the position of the epidermis of the part 5a where the biopsy needle 9 is inserted. K12 is designated, and a line segment J1 extending from K11 through K12 to the boundary of the slice SL21 is designated. Then, as shown in FIG. 9D, the puncture route region setting unit 84 sets the designated line segment J1 as the puncture route, and sets the local region Q1 including the line segment J1 as the puncture route region.

  In step A6, a scan after the start of puncturing is performed. Specifically, at the stage immediately before puncturing is started, the operator uses the input device 61 to input a command for performing a continuous scan after puncturing is started. The scan control unit 81 detects the input of this command, and sends a control signal to the gantry table control unit 30 so as to perform a scan after the puncture is started. The gantry table control unit 30 receives this control signal and controls each part of the gantry 2 and the imaging table 4. Thereby, a scan after the start of puncturing is performed. By performing the scan after the start of puncturing, second projection data for eight slices in the imaging space including the region 5a is collected. The scan after the start of puncture is basically repeatedly performed a plurality of times.

  In step A7, projection data is averaged. Specifically, the averaging processing unit 82 averages the second projection data corresponding to the eight slices in the z-axis direction, and performs the averaging processing corresponding to one slice SL21. 2 projection data is obtained.

  In step A8, tomographic image generation processing with limited metal artifact reduction is performed. Specifically, metal artifact reduction based on the premise that the biopsy needle (metal; metal) is inserted only in the puncture root region based on the puncture route region set in step A5 by the tomographic image generation unit 85. Performs tomographic image generation processing.

  For example, the following processing is assumed as the tomographic image generation processing with metal artifact reduction. In the second projection data corresponding to the slice SL21, a data region showing high X-ray absorption by the biopsy needle is searched for each view, and if detected, the data region is data in the vicinity thereof or data close thereto. Make corrections to make up for or fit. Such processing is performed to obtain corrected projection data. Next, for each view, the corrected projection data is subtracted from the second projection data corresponding to the slice SL21 to obtain subtraction-processed projection data. When the slice SL21 includes a biopsy needle, the corrected projection data becomes projection data corresponding to the case where there is no biopsy needle, and the subtraction processed projection data is a high X-ray absorption by the biopsy needle. Only the data indicating is extracted projection data. Then, the tomographic image reconstructed based on the subtraction processed projection data is superimposed on the tomographic image reconstructed based on the corrected projection data to obtain a composite tomographic image. Thereby, when the biopsy needle is not included in the slice SL21, a normal tomographic image is obtained, and when the biopsy needle is included, a tomographic image including a biopsy needle with reduced metal artifacts is obtained. be able to.

  Here, in the above-described tomographic image generation processing with metal artifact reduction, a range for searching a data region showing high X-ray absorption by the biopsy needle on the projection data corresponds to a region obtained by projecting the puncture root region from the X-ray focal point. Limited to range. By doing so, it is not necessary to search the entire range of the projection data, the amount of calculation can be reduced, and the time required for the tomographic image generation processing with metal artifact reduction can be shortened. When searching for a data area showing high X-ray absorption by the biopsy needle on the projection data, not only the puncture root area but also information on the material and thickness of the biopsy needle may be used. If the material of the biopsy needle is known, the amount of X-ray absorption of the biopsy needle can be estimated, so the height of data indicating high X-ray absorption by the biopsy needle can be estimated on the profile of the projection data and detected. Accuracy is improved. Further, if the thickness of the biopsy needle is known, the width of the data area showing high X-ray absorption by the biopsy needle can be estimated on the projection data profile, and the detection accuracy is improved. The material and thickness of the biopsy needle are input directly by the operator or stored in advance in the storage device of the X-ray CT apparatus in association with the product name and product number, and the operator selects them. May be determined. As a material of the biopsy needle, for example, a stainless alloy (stainless steal), a tungsten alloy (tungsten steal), or the like can be considered. Further, the thickness (diameter) of the biopsy needle may be 1 mm, 2 mm, 3 mm, or the like.

  Further, for example, the following processing is assumed as the tomographic image generation processing with metal artifact reduction. A tomographic image is reconstructed based on the second projection data corresponding to the slice SL21. Next, in this tomographic image, an image region showing high X-ray absorption by the biopsy needle is searched based on the pixel value (CT value), and if detected, based on the position and shape of the image region. Detect and reduce metal artifacts. Thereby, when the biopsy needle is not included in the slice SL21, a normal tomographic image is obtained, and when the biopsy needle is included, a tomographic image including a biopsy needle with reduced metal artifacts is obtained. be able to.

  Here, in the above-described tomographic image generation processing with metal artifact reduction, the range for searching for an image region showing high X-ray absorption by the biopsy needle on the tomographic image is limited to a range corresponding to the puncture root region. By doing so, it is not necessary to search the entire range of the image area, the calculation amount can be reduced, and the time required for the tomographic image generation processing with metal artifact reduction can be shortened. When searching for an image region showing high X-ray absorption by a biopsy needle on a tomographic image, information on the material and thickness of the biopsy needle as well as the puncture root region may be used. If the material of the biopsy needle is known, the amount of X-ray absorption of the biopsy needle can be estimated, so the size of the pixel value of the pixel showing high X-ray absorption by the biopsy needle on the tomographic image can be estimated, and the detection accuracy is improves. Further, if the thickness of the biopsy needle is known, the size (diameter) of the image region showing high X-ray absorption by the biopsy needle on the tomographic image can be estimated, and the detection accuracy is improved.

  In step A9, a tomographic image is displayed. Specifically, the display control unit 86 controls the display device 62 so that the tomographic image obtained in step A8 is displayed on the screen. If the tomographic image is already displayed, it is displayed in an updated form.

  In step A10, it is determined whether or not to end the scan. Specifically, the scan control unit 81 detects whether or not a scan end command is input, and determines whether or not to end the scan. If it is determined to end, the scanning is ended. If it is determined not to end, the process returns to step A6 to continue scanning.

  According to the second embodiment as described above, by setting the puncture root region, in the tomographic image generation processing with metal artifact reduction, for example, the processing content is reduced such as narrowing the search range of the high X-ray absorption region. The above time can be further shortened.

(Third embodiment)
FIG. 10 is a functional block diagram of the operation console of the X-ray CT apparatus according to the third embodiment.

  The operation console 6b of the X-ray CT apparatus according to the third embodiment includes, as function blocks, a scan control unit 91, an averaging processing unit 92, an image reconstruction unit 93, a puncture route region setting unit 94, and a target slice setting unit 95. A difference determination unit 96, a tomographic image generation unit 97, a needle position determination unit 98, and a display control unit 99.

  The scan control unit 91 controls the gantry table control unit so that a scan for collecting projection data is performed.

  FIG. 11 is a diagram schematically illustrating how a subject is scanned in the third embodiment. In this example, as shown in FIG. 11, scanning is performed on the imaging space R3 including the predetermined part 5a of the subject 5 placed on the cradle 41. The scan is performed by irradiating the subject 5 with X-rays from the X-ray focal point of the X-ray tube 21 while rotating the X-ray tube 21 and the X-ray detector 14 around the subject 5. When scanning is performed, due to the arrangement structure of the X-ray detection elements in the X-ray detector 24, projection data of a plurality of views is collected for each of a plurality of slices obtained by slicing the imaging space in the z-axis direction. Here, it is assumed that projection data for 24 slices having a thickness of 0.625 mm are collected by performing one scan. In this example, it is assumed that the lesioned part 5c is included in the part 5a. The surgeon performs puncture for inserting the biopsy needle from the surface of the part 5a until reaching the lesioned part 5c while viewing the tomographic image of the part 5a displayed in almost real time by continuous scanning.

  The averaging processing unit 92 averages projection data or tomographic images for a plurality of slices in the imaging space in the z-axis direction, and performs processing for obtaining projection data or tomographic images of a smaller number of slices.

  The image reconstruction unit 93 performs processing for reconstructing a tomographic image based on the projection data.

  The puncture route area setting unit 94 performs a process of setting a planned biopsy needle insertion route at the time of puncture as a puncture route.

  The target slice setting unit 95 performs processing for setting a target slice to be subjected to tomographic image generation processing or the like.

  The difference determination unit 96 performs a process of determining whether or not the biopsy needle has moved in the puncture route region based on the difference between time-series data.

  The tomographic image generation unit 97 performs tomographic image generation processing including limited metal artifact reduction processing.

  The needle position determination unit 98 performs a process of determining whether or not the tip of the biopsy needle is in the target slice portion of the puncture root region based on the image in the target slice portion of the puncture root region.

  The display control unit 99 performs processing for controlling the display device 62 to display a tomographic image or the like on the screen.

  Next, the flow of processing in the X-ray CT apparatus according to the third embodiment will be described.

  FIG. 12 is a flowchart showing the flow of processing in the X-ray CT apparatus according to the third embodiment.

  In step B1, a scan before starting puncturing is performed. Specifically, at the stage before puncturing is started, the operator inputs a command for performing a scan before starting puncturing using the input device 61. The scan control unit 91 detects the input of this command, and sends a control signal to the gantry table control unit 30 so as to perform a scan before starting puncturing. The gantry table control unit 30 receives this control signal and controls each part of the gantry 2 and the imaging table 4. Thereby, a scan before the start of puncturing is performed. By performing the scan before the start of puncturing, the first projection data for 24 slices is collected for the imaging space R3 including the region 5a.

  In step B2, image reconstruction processing is performed. Specifically, the image reconstruction unit 93 performs image reconstruction processing on the 24 slices based on the first projection data to obtain a first tomographic image.

  In step B3, an averaging process is performed. Specifically, the averaging processing unit 92 performs the averaging process in the z-axis direction on the first tomographic image corresponding to 24 slices, and performs the first processing corresponding to the three slices SL31 to SL33. Obtain a tomographic image. In addition, the averaging processing unit 92 averages the first projection data in the z-axis direction for 24 slices to obtain first projection data corresponding to the three slices SL31 to SL33.

  In step B4, a tomographic image and a projected image are displayed. Specifically, the display control unit 99 projects the first tomographic image of each slice SL31 to SL33 obtained in step B3 and the first tomographic image of 24 slices obtained in step B2 in the x-axis direction. The display device 62 is controlled to display the projected image.

  FIG. 13A shows a display example of the projection image Gx. The projection image Gx is an image obtained by projecting the first tomographic images of the three slices SL31 to SL33 in the region 5a when the scan before the start of puncturing is performed in the x-axis direction. In the scan before the start of puncturing, the biopsy needle 9 does not exist in the slice, and therefore the biopsy needle 9 is not included in the projection image Gx.

  Instead of the projection image obtained in step B3, a scout image projected in the x-axis direction obtained by performing a scout scan in advance may be displayed on the screen.

  In step B5, a puncture route area is set.

  FIG. 13B shows an example of setting the puncture route and the puncture route region. Specifically, the operator designates a puncture route on which a biopsy needle is scheduled to be inserted on the displayed projection image. As shown in FIG. 13 (b), the puncture route starts from the center position K21 of the lesioned part 5c included in the slice SL32, passes through the position K22 on the surface of the part 5a included in the slice SL33, and the boundary of the projection image Gx A straight route represented by the line segment J2 is assumed. This route is specified by, for example, using the input device 61 to specify the center position K21 of the lesioned part 5c, which is a puncture target, and the epidermis position K22 of the site 5a where the biopsy needle 9 is inserted. Puncturing route region setting unit 94 sets the designated line segment J2 as a puncturing route, and sets a local region Q2 including the line segment J2 as a puncturing route region.

  The lower part of FIG. 13B shows first tomographic images G1 of slices SL31 to SL33. In this example, as shown in FIG. 13B, the puncture root region Q2 is divided into a slice SL31 portion and a slice SL32 portion.

  In step B6, a target slice is set. Specifically, the target slice setting unit 95 sets a slice including the position of the surface of the part 5a where the biopsy needle is inserted, as the target slice ISL based on the set puncture route. In this example, the slice SL31 is set as the target slice.

  In step B7, a scan after the start of puncturing is performed.

  Specifically, at the stage immediately before puncturing is started, the operator uses the input device 61 to input a command for performing a continuous scan after puncturing is started. The scan control unit 91 detects the input of this command and sends a control signal to the gantry table control unit 30 so as to perform a scan after the puncture is started. The gantry table control unit 30 receives this control signal and controls each part of the gantry 2 and the imaging table 4. Thereby, a scan after the start of puncturing is performed. By performing the scan after the start of puncturing, second projection data for 24 slices in the imaging space including the part 5a is collected. The scan after the start of puncture is basically repeatedly performed a plurality of times.

  In step B8, the projection data is averaged. Specifically, the averaging processing unit 92 averages the second projection data corresponding to 24 slices in the z-axis direction, and performs averaging processing corresponding to the three slices SL31 to SL33. Obtained second projection data.

  In step B9, an image reconstruction process is performed. Specifically, the image reconstruction unit 93 performs an image reconstruction process for each slice SL31 to SL33 based on the second projection data, and obtains a second tomographic image.

  In step B10, a difference determination process is performed. Specifically, the difference determination unit 96 uses the image corresponding to the target slice portion of the puncture root region in the second tomographic image of the target slice ISL obtained in step B9 and the tomographic image of the same slice displayed previously. The images of the same part are compared, and it is determined whether or not the difference is a certain level or more. That is, it is determined whether or not the biopsy needle has moved significantly in the target slice portion in the puncture root region. For example, in the image corresponding to the target slice portion of the puncture root region, a pixel that is considered to represent a biopsy needle is identified by pixel value threshold processing, and an increase / decrease in the number of pixels is obtained. If it is, it is determined that the biopsy needle has moved significantly. In addition, although this difference determination process is performed on the image in this example, it can also be performed on projection data.

  In Step B11, a tomographic image generation process with limited metal artifact reduction is performed. Specifically, the tomographic image generation unit 97 reduces metal artifacts on the assumption that the biopsy needle (metal; metal) is inserted only into the puncture root region based on the puncture route region set in step B5. Performs tomographic image generation processing.

  For example, the following processing is assumed as the tomographic image generation processing with metal artifact reduction. In the second projection data corresponding to the slice of interest ISL, for each view, a data region showing high X-ray absorption by the biopsy needle is searched, and if detected, the data region is the data in the vicinity thereof or close thereto. Compensate to make up for or fit with data. Such processing is performed to obtain corrected projection data. Next, for each view, the corrected projection data is subtracted from the second projection data corresponding to the target slice ISL to obtain subtraction-processed projection data. When a biopsy needle is included in the target slice ISL, the corrected projection data becomes projection data corresponding to the absence of the biopsy needle, and the subtraction processed projection data is high X-rays generated by the biopsy needle. Only data indicating absorption is extracted projection data. Then, the tomographic image reconstructed based on the subtraction processed projection data is superimposed on the tomographic image reconstructed based on the corrected projection data to obtain a composite tomographic image. Thereby, when the biopsy needle is not included in the slice of interest ISL, a normal tomographic image is obtained, and when the biopsy needle is included, a tomographic image including the biopsy needle with reduced metal artifacts is obtained. Can be obtained.

  Here, in the tomographic image generation processing with metal artifact reduction described above, a range for searching for a data area showing high X-ray absorption by the biopsy needle on the projection data is determined, and a target slice portion in the puncture root area is determined from the X-ray focus Limited to a range corresponding to the projected area. By doing so, it is not necessary to search the entire range of the projection data, the amount of calculation can be reduced, and the time required for the tomographic image generation processing with metal artifact reduction can be shortened. When searching for a data area showing high X-ray absorption by the biopsy needle on the projection data, not only the puncture root area but also information on the material and thickness of the biopsy needle may be used. If the material of the biopsy needle is known, the amount of X-ray absorption of the biopsy needle can be estimated, so the height of data indicating high X-ray absorption by the biopsy needle can be estimated on the projection data profile, improving detection accuracy To do. Further, if the thickness of the biopsy needle is known, the width of the data area showing high X-ray absorption by the biopsy needle can be estimated on the projection data profile, and the detection accuracy is improved. The material and thickness of the biopsy needle are input directly by the operator or stored in advance in the storage device of the X-ray CT apparatus in association with the product name and product number, and the operator selects them. May be determined.

  Further, for example, the following processing is assumed as the tomographic image generation processing with metal artifact reduction. A tomographic image is reconstructed based on the second projection data corresponding to the target slice ISL. Next, in this tomographic image, an image region showing high X-ray absorption by the biopsy needle is searched based on the pixel value (CT value), and if detected, based on the position and shape of the image region. Detect and reduce metal artifacts. Thereby, when the biopsy needle is not included in the slice of interest ISL, a normal tomographic image is obtained, and when the biopsy needle is included, a tomographic image including the biopsy needle with reduced metal artifacts is obtained. Can be obtained.

  Here, in the tomographic image generation processing with metal artifact reduction, the range for searching for an image region showing high X-ray absorption by the biopsy needle on the tomographic image of the target slice ISL is set as the target slice portion in the puncture root region. Limited to the corresponding range. By doing so, it is not necessary to search the entire range of the image area, the calculation amount can be reduced, and the time required for the tomographic image generation processing with metal artifact reduction can be shortened. When searching for an image region showing high X-ray absorption by a biopsy needle on a tomographic image, information on the material and thickness of the biopsy needle as well as the puncture root region may be used. If the material of the biopsy needle is known, the amount of X-ray absorption of the biopsy needle can be estimated, so the size of the pixel value of the pixel showing high X-ray absorption by the biopsy needle on the tomographic image can be estimated, and the detection accuracy is improves. Further, if the thickness of the biopsy needle is known, the size (diameter) of the image region showing high X-ray absorption by the biopsy needle on the tomographic image can be estimated, and the detection accuracy is improved.

  In step B12, a tomographic image is displayed. Specifically, the display control unit 99 controls the display device 62 so as to display the tomographic image of the slice of interest obtained in step B11 on the screen. If the tomographic image is already displayed, it is displayed in an updated form.

  In step B13, the position of the biopsy needle is determined. Specifically, the needle position determination unit 98 determines whether or not the position of the tip of the biopsy needle is within the target slice portion of the puncture root region in the tomographic image of the target slice ISL obtained in step B11. When it is determined that the position of the tip of the biopsy needle is within the target slice portion of the puncture root region, the process proceeds to step B14. If it is determined that the position of the tip of the biopsy needle is not within the target slice portion of the puncture root region, the process proceeds to step B15.

  In step B14, the target slice is maintained. Specifically, the target slice setting unit 95 performs setting to maintain the current target slice ISL as it is. Then, the process proceeds to Step B16.

  In step B15, the target slice is changed. Specifically, the target slice setting unit 95 sets the adjacent slice that approaches the pathogenic unit 5c from the current target slice ISL as a new target slice ISL. Then, the process proceeds to Step B16.

  In step B16, it is determined whether or not to end the scan. Specifically, the scan control unit 91 detects whether or not a scan end command is input, and determines whether or not to end the scan. If it is determined to end, the scanning is ended. If it is determined not to end, the process returns to step B7 to continue scanning.

  Here, an embodiment according to the flow will be briefly described.

  14 to 16 show the positional relationship between the slices SL31 to SL33 and the biopsy needle 9 at the first to third time points after the start of puncture, and the slices SL31 to SL33 obtained by the scan performed at each time point. A tomographic image is shown.

  At the first time point, as shown in FIG. 14, it is assumed that the tip of the biopsy needle 9 has moved from the outside of the slice SL33 to the inside of the slice SL33 as compared to the scan execution time point when the previously displayed tomographic image was obtained. To do. In step B7, a scan for 24 slices is performed. In step B8, projection data is averaged to be combined into three slices SL31 to SL33. In step B9, a tomographic image of each slice is reconstructed. In this case, in the difference determination in step B10, for the slice SL33 that is the target slice ISL, the difference in the image of the puncture root region Q2 between the tomographic image displayed last time and the tomographic image G2 corresponding to the first time point is obtained. It is determined that it is above a certain level. Therefore, the tomographic image generation process with limited metal artifact reduction is executed for the slice SL33 in step B11, and the display of the tomographic image is updated in step B12. In Step B13, it is determined that the position of the biopsy needle 9 is in the slice SL33 that is the target slice. Therefore, in step B14, the target slice ISL still maintains the slice SL33.

  Next, at the second time point, as shown in FIG. 15, the tip of the biopsy needle 9 is inserted into the region 5a as compared to the scan execution time point when the previously displayed tomographic image was obtained, and the biopsy needle is Assume that the tip of 9 has reached the boundary between the slice SL33 and the slice SL32. In step B7, a scan for 24 slices is performed. In step B8, projection data is averaged to be combined into three slices SL31 to SL33. In step B9, a tomographic image of each slice is reconstructed. In this case, in the difference determination in step B10, for the slice SL33 that is the target slice ISL, the difference in the image of the puncture root region Q2 between the previously displayed tomographic image and the tomographic image G2 corresponding to the second time point is obtained. It is determined that it is above a certain level. Therefore, the tomographic image generation process with limited metal artifact reduction is executed for the slice SL33 in step B11, and the display of the tomographic image is updated in step B12. In Step B13, it is determined that the position of the biopsy needle 9 has reached the boundary between the slice SL33 and the slice SL32 which are the target slice ISL. Therefore, in step B15, the target slice ISL moves to the adjacent slice SL32.

  Next, at the third time point, as shown in FIG. 16, it is assumed that the tip of the biopsy needle 9 has moved from the slice SL33 into SL32 as compared to the scan execution time point when the previously displayed tomographic image was obtained. To do. In step B7, a scan for 24 slices is performed. In step B8, projection data is averaged to be combined into three slices SL31 to SL33. In step B9, a tomographic image of each slice is reconstructed. In this case, in the difference determination in step B10, for the slice SL32 that is the target slice ISL, the difference in the image of the puncture root region Q2 between the previously displayed tomographic image and the tomographic image G2 corresponding to the third time point is obtained. It is determined that it is above a certain level. Therefore, a tomographic image generation process with limited metal artifact reduction is executed for the slice SL32 in step B11, and the display of the tomographic image is updated in step B12. In Step B13, it is determined that the position of the biopsy needle 9 is located in the slice SL32 that is the target slice. Therefore, in step B14, the target slice ISL maintains the slice SL32.

  According to the third embodiment, the tomographic image generation process with metal artifact reduction can be narrowed down to one slice that needs to be updated out of a plurality of slices, and generation of a tomographic image with reduced artifacts is generated.・ Time required for display can be shortened. In addition, by setting the puncture root region, in the tomographic image generation processing with metal artifact reduction, for example, the processing content can be reduced, such as narrowing the search range of the high X-ray absorption region, and the above time can be further reduced. Can do.

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

  A program for causing a computer to function as each means for performing control and processing in the X-ray CT apparatus and a recording medium on which the program is recorded are also examples of embodiments of the invention.

DESCRIPTION OF SYMBOLS 1 X-ray CT apparatus 2 Gantry 2B Cavity part 4 Imaging table 5 Subject 5a Site | part 6,6a, 6b Operation console 21 X-ray tube 22 Aperture 23 Collimator apparatus 24 X-ray detector 25 Data acquisition part 26 Rotation part 27 High voltage power supply 28 Aperture Drive Device 29 Rotation Drive Device 30 Gantry / Table Control Unit 41 Cradle 42 Cradle Drive Device 61 Input Device 62 Display Device 63 Storage Device 64 Arithmetic Processing Device 71 Scan Control Unit 72 Subtraction Processing Unit 73 Averaging Processing Unit 74 Image Reconstruction Unit 75 threshold processing unit 76 display control unit 81 scan control unit 82 averaging processing unit 83 image reconstruction unit 84 puncture route region setting unit 85 tomographic image generation unit 86 display control unit 91 scan control unit 92 averaging processing unit 93 image reconstruction Configuration unit 94 Puncture route region setting unit 95 Attention slice setting unit 96 Min determining unit 97 the tomographic image generator 98 needle position determining unit 99 display control unit SL11~SL13, SL21, SL31~SL33 slice

Claims (5)

By scanning the part of the subject into which the needle is inserted a plurality of times, the first projection data of the part before the insertion of the needle and the second projection data of the part after the insertion of the needle are obtained. First control means for controlling the data collection system to collect;
Subtracting means for subtracting the first projection data from the second projection data to obtain third projection data;
Reconstruction means for reconstructing a first image based on the first projection data and a third image based on the third projection data;
In the third image, a threshold-processed third image is obtained that includes pixels that have a pixel value that exceeds a predetermined threshold that is a pixel value between a pixel value that represents a metal artifact and a pixel value that represents a metal. Threshold processing means;
A radiation tomography apparatus comprising: a second control unit configured to control a display device to display a fourth image that is a composite image formed by superimposing the third image subjected to the threshold processing on the first image. . The first control means controls the data collection system to continuously scan the site a plurality of times after the start of insertion of the needle,
The radiation tomography apparatus according to claim 1, wherein the second control unit performs control so that the composite image is newly displayed each time the second projection data is collected. The first control means controls the data collection system to sequentially scan the part a plurality of times before and after the insertion start of the needle and sequentially collect the projection data,
In response to the collection of the projection data, it further comprises a determination means for determining whether a change exceeding a certain level has occurred in the temporal change of the projection data or the image based on the projection data,
The first projection data is projection data collected at a time point before it is determined that a change exceeding the certain level has occurred,
The radiation tomography apparatus according to claim 2 , wherein the second projection data is projection data collected at a time point after it is determined that a change exceeding the certain level has occurred. Said reconstruction means, the two-dimensional backprojection process to reconstruct the first and third image, the radiation tomography apparatus according to any one of claims 1 to 3. The program for functioning a computer as each means in the radiation tomography apparatus as described in any one of Claims 1-4 .