JP4542256B2 - X-ray CT system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray CT apparatus, and more specifically, an X-ray tube and an X-ray detector array are opposed to each other with a subject interposed therebetween, the subject is scanned in advance, and the accumulated projection data is reused. The present invention relates to an X-ray CT apparatus capable of reconstructing a CT tomogram.
[0002]
The image reconstruction method of the X-ray CT apparatus includes a prospective recon (Prospective Recon.) And a retrorecon (Retro. Recon.). In the prospective recon, image reconstruction is performed immediately after the scan according to the reconstruction conditions (slice position, slice thickness, reconstruction algorithm, etc.) set immediately before the scan. In retrorecon, image reconstruction is performed again according to the reconstruction conditions set after the scan. Do. The present invention relates to an improvement of this retrorecon.
[0003]
[Prior art]
In the conventional prospective recon, a scout image (corresponding to a two-dimensional X-ray image) of the subject taken immediately before the scan is displayed on the console, and the operator cuts the scan line (scan position / slice) displayed on the scout image. By referencing (confirming / changing etc.) the position, etc., it is possible to enter graphical settings for scan conditions (scan position, tube voltage kV, tube current mA, etc.) and prospective recon conditions (slice position, slice thickness, etc.) I was trying.
[0004]
[Problems to be solved by the invention]
However, in the case of the conventional retro-recon, the scout image as described above is not displayed, which causes inconvenience in setting the retro-recon condition.
[0005]
The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide an X-ray CT apparatus that enables a graphical setting input of retrorecon conditions.
[0006]
[Means for Solving the Problems]
The above problem is solved by the configuration of FIG. That is, the X-ray CT apparatus of the present invention (1) is based on projection data obtained by X-ray CT imaging of a subject, and the CT tomography of the subject according to reconstruction conditions set after the X-ray CT imaging. An X-ray CT apparatus capable of retrospective reconstitution for reconstructing an image, wherein the scout corresponds to a scout image based on projection data obtained by X-ray CT imaging of the subject or reconstruction data based on the projection data Scout image data generating means for generating image data, display control means for displaying the generated scout image data on a display screen for setting a reconstruction condition of a reconstruction condition set after the X-ray CT imaging, Setting means for setting the reconstruction condition using the display screen .
[0007]
Therefore, the operator can easily and appropriately set the retro-recon parameters by a graphical operation referring to the scout image on the display screen 13b.
[0008]
Preferably, in the present invention (2), in the present invention (1), the scout image data generating means 1 generates the scout image data using the projection data of the required view angle and / or the opposite view angle.
[0009]
Therefore, particularly when using helically scanned projection data, it is possible to easily generate scout image data dense in the body axis direction of the subject by using the projection data of the required view angle and the opposite view angle. .
[0010]
Preferably, in the present invention (3), in the present invention (2), the scout image data generating means 1 adds the projection data of the view angle near the required view angle and / or the view angle near the opposite view angle. Generate scout image data.
[0011]
For the purpose of generating scout image data (two-dimensional X-ray data) of the subject, even if the projection data of the required view angle is the projection data of the near view angle that is slightly deviated from the required view angle, A fluoroscopic image at a required view angle (particularly, a fluoroscopic image of a subject outline) is well represented. Moreover, when using helically scanned projection data, the projection data is shifted in the direction of the body axis even if there is a slight difference in view angle. Scout image data that is denser in the body axis direction can be generated. The same applies to projection data near the opposite view angle.
[0012]
Preferably, in the present invention (4), in the present invention (2) or (3), the scout image data generating means 1 generates the projection data at the intermediate position at the same and / or opposite view angle adjacent in the body axis direction. Generated by data interpolation calculation using a plurality of projection data. Therefore, it is possible to generate scout image data that is smooth in the body axis direction of the subject.
[0013]
In the present invention (5) , in the present inventions (1) to (4), the scout image data generating means generates the data corresponding to the scout image by cutting out the reconstructed data at the tomographic plane having the required view angle. .
[0014]
A plurality of reconstructed data (CT tomographic image data) dense in the body axis direction cut out by a tomographic plane (plane parallel to the body axis) of the required view angle is the cross-sectional shape of the subject (particularly the shape of the contour portion) ). Therefore, this is used as data equivalent to a scout image. In this case, particularly when three-dimensional reconstruction data is present, an accurate sectional view image can be displayed.
[0015]
Preferably, in the present invention (6), in the present inventions (1) to (5), the display control means displays a line indicating each slice position superimposed on the scout image data. The setting means sets the slice position.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. Note that the same reference numerals denote the same or corresponding parts throughout the drawings.
[0017]
FIG. 2 is a configuration diagram of a main part of an X-ray CT apparatus according to the embodiment. The apparatus includes a scanning gantry unit 30 that performs axial / helical scanning / reading of the subject 100 by an X-ray fan beam XLFB, and a subject 100. An imaging table 20 that is placed and moved in the direction of the body axis CLb and a remote operation console unit 10 operated by an operator are provided.
[0018]
In the scanning gantry 30, 40 is a rotary anode type X-ray tube, 40 A is an X-ray controller, 50 is a collimator for limiting the X-ray exposure range (mainly in the body axis CLb direction), and 50 A is a collimator controller. , 90 is an X-ray detector array (multi-detector) in which a large number (n = 1000) of X-ray detectors arranged in the channel CH direction are arranged in, for example, four rows L1 to L4 in the body axis CLb direction, and 91 is an X-ray detector A data collection unit (DAS) that generates and collects projection data g ₁ (X, θ) to g ₄ (X, θ) of the subject 100 based on the detection signal of the line detector array 90, and 30A is a scanning gantry (X The rotation control unit rotates the line imaging system around the body axis CLb of the subject 100.
[0019]
In the operation console unit 10, 11 is a central processing unit for performing main control and processing (scan control, CT tomographic reconstruction processing, retrorecon processing according to the present invention, etc.) of the X-ray CT apparatus, 11a is its CPU, and 11b is CPU 11a. Main memory (MM) composed of RAM, ROM, etc. used by the computer, 12 is a command and data input device including a keyboard, mouse, etc. 13 is a scan plan, a recon plan, and a CT tomogram reconstructed image, etc. A display device (CRT) 14, a control interface 14 for exchanging various control signals CS and monitor signals MS between the CPU 11 a, the scanning gantry unit 30 and the imaging table 20, and 15 a projection data from the data collecting unit 91. A data collection buffer for temporarily storing 16 is a projection data RAD (scanned data) from the data collection buffer 15. 2) and various application programs necessary for the operation of the X-ray CT apparatus, various calculation / correction data files, and the like. Secondary storage device (hard disk device or the like).
[0020]
With this configuration, the X-ray fan beam XLFB from the X-ray tube 40 passes through the subject 100 and enters the detection rows L1 to L4 of the X-ray detector array 90 all at once. The data collection unit 91 generates projection data g ₁ (X, θ) to g ₄ (X, θ) corresponding to each detection output of the X-ray detector array 90 and stores them in the data collection buffer 15. Here, X represents the detection channels 1 to n of the X-ray detector array 90, and θ represents the view angle around the body axis. Further, projection similar to that described above is performed at each view angle θ slightly rotated by the scanning gantry, and thus projection data for one rotation of the scanning gantry is collected and accumulated. At the same time, the imaging table 20 is moved intermittently / continuously in the body axis direction of the subject 100 according to the axial / helical scan method, and thus all projection data for the required imaging region of the subject 100 is collected and accumulated. Then, after all the scans are completed or following (in parallel with) the execution of the scan, the CPU 11a reconstructs the CT tomogram of the subject 100 based on the obtained projection data (prospective recon) and displays it. Display on the device 13. It is also possible to reconstruct (retro-recon) a CT tomogram of a subject by reusing the scanned / reconstructed data. Hereinafter, the operation will be described in detail.
[0021]
FIG. 3 is a flowchart of the X-ray CT imaging process according to the embodiment. Preferably, this process is performed after a scout scan of the subject 100 is performed in advance. In step S11, a scan parameter for the subsequent axial / helical scan of the subject 100 is set.
[0022]
FIG. 4 shows an image of scan parameter input processing in the embodiment. After the previous scout scan is completed, a scan setting screen 13a for the subsequent axial / helical scan is displayed on the display screen 13A, and the operator clicks or inputs a necessary scan parameter with a mouse. An example scan plan for acquiring image Q is as follows.
[0023]
Scan type [Scan Type] = Scan start position on the axial scan body axis [Start Loc] = Z1
Scan end position on body axis [End Loc] = Z10
Number of scans [NO.of Images] = 10 slice thickness of specimen [Thick] = 2 mm
Scan time [Sec] = 1 second / tube voltage of gantry 1 rotation X-ray tube [kV] = 120 kV
X-ray tube current [mA] = 280 mA
Further, when the operator clicks the [Show Localizer] icon on the scan setting screen, a scout image 100A of the subject 100 as shown in the figure is displayed in the image display area 13b of the display screen 13A, and each slice is displayed thereon. A line indicating the position (cut line) is displayed in an overlapping manner. The solid bold lines in the figure represent the scan start and end positions, and the dotted lines represent the intermediate slice positions. The operator can check the cut line or the like by looking at the scout image 100A on the image display area 13b, and can change it with a mouse or a keyboard if necessary.
[0024]
Although not shown, the operator clicks on the prospective recon “P-RECON” tag on the display screen 13a, so that the prospective recon parameters (slice position to be reconstructed, slice thickness, reconstruction algorithm, image filter, etc.) Can be set and input.
[0025]
Returning to FIG. 3, in step S12, the input of the confirmation “CONFIRM” button is awaited. When the “CONFIRM” button is input, the scan control of the subject 100 is performed in step S13 according to the set scan parameter. In step S14, projection data of the subject 100 is collected and accumulated. In step S15, it is determined whether or not scanning of the required imaging area is complete. If not, the process returns to step S13. Thus, when the scanning is completed, the X-ray CT tomographic image of the subject 100 is reconstructed in accordance with the prospective recon parameter in step S16. In step S17, the obtained X-ray CT tomogram is displayed on the display device 13. The prospective recon processing and the display of the reconstruction data may be performed in parallel with the progress of the scan control. The obtained scout image data, scanned projection data, reconstructed CT tomographic image data, and the like are stored in the secondary storage device 16.
[0026]
FIG. 5 is a flowchart of retrorecon processing according to the embodiment. When the operator wants to execute retro-recon, click the retro-recon “R-RECON” tag on the display screen 13a and input a desired image number (for example, image H). Thereby, it inputs into the process of FIG.
[0027]
In step S21, it is determined whether or not there is scout shooting data for the image H. If there is scout shooting data for the image H, the scout shooting data for the image H is read from the disk 16, and the process proceeds to step S25 described later. In general, a scout image is captured in advance when performing a wide scan of the chest and abdomen, but a scout image is often not captured when scanning a narrow range such as the head.
[0028]
When there is no scout shooting data of the image H, scout image data corresponding to the scout shooting data is created from the reconstruction data or projection data (scan data) of the image H. That is, in step S22, it is determined whether or not there is reconstruction data for the image H. If there is, the scout image data is generated from the reconstruction data in step S23. If not, scout image data is generated from the projection data of the image H in step S24. Hereinafter, a method for generating scout image data will be described in detail.
[0029]
FIGS. 7 to 9 are image diagrams (1) to (3) of scout image data generation processing according to the embodiment. FIG. 7 shows a case where scout image data is generated from reconstruction data of a subject. When there is reconstruction data reconstructed with a plurality of small slice pitches SP, these are superimposed on each slice position in the body (z) axis direction to obtain a substantially three-dimensional image as shown in the figure. It is done. When this is cut out on a yz plane (view angle 90 °) including the body axis CLb, for example, cross-sectional image data 100B of the subject 100 including a two-dimensional set of X-ray CT values is obtained. Although this image is different from the original scout (X-ray) image, it sufficiently includes graphical information (particularly, information on the contour of the subject) necessary for setting and inputting retrorecon information. Therefore, the scout image data 100B corresponding to the scout image is obtained by a simple image cut-out process.
[0030]
It should be noted that scout image data 100B from the front of the subject can be obtained by cutting out on the xz plane including the body axis CLb. Further, as shown in the figure, there are cases where reconstruction data of a three-dimensional image exists, and in this case as well, the scout image data 100B having a desired view angle can be cut out in the same manner as described above.
[0031]
FIG. 8 shows a case where scout image data is generated from the projection data of the subject, and FIG. 8A shows a side view when the subject 100 is helically scanned by the multi-detector 90. In the figure, the X-ray fan beam XLFB exposed from the X-ray tube 40 passes through the subject 100 and enters the X-ray detector array 90 all at once, and the corresponding projection data g ₁ from each detection row L1 to L4. (X, θ) to g ₄ (X, θ) are obtained. Here, X represents the detection channels 1 to n of the X-ray detector array 90, and θ represents the view angle of the scanning gantry.
[0032]
In the helical scan using the multi-detector 90, the scanning gantry (X-ray imaging system 40, 90, etc.) is rotated around the body axis CLb, and the imaging table 20 is continuously moved in the direction opposite to the z axis. The resulting scan trajectory is spiral as shown. The figure shows the helical scan trajectory of the detection rows L1 to L4, the solid line corresponds to the trajectory of the view angle θ = 0 ° to 180 ° (front side of the paper), and the dotted line the view angle θ = 180 ° to 360 ° ( Corresponds to the locus on the back side of the paper.
[0033]
When generating scout image data when the subject 100 is viewed from the side, each projection data g ₁ (X, 90 °) to g ₄ (X, 90 °) with a view angle of 90 ° and its opposing view angle Each projection data g ₁ (X, 270 °) to g ₄ (X, 270 °) of 270 ° can be used as it is. In the following description, the projection data g ₁ (X, 270 °) to g ₄ (X, 270 °) at the opposite view angle 270 ° are referred to as detection row data C1 to C4, and the projection data at the view angle 90 °. g ₁ (X, 90 °) to g ₄ (X, 90 °) are also referred to as detection row data C5 to C9. In this way, by first extracting the required view angle and the respective detection row data C1 to C9 of the opposite view angle, it is possible to generate scout image data 100B that is relatively dense in the body axis direction.
[0034]
However, the actual scout image is continuous in the z-axis direction. Therefore, preferably, each projection data that fills the space between the respective detection string data C1 to C9 is generated by data interpolation calculation. FIG. 8B shows a partially enlarged view in which a part of FIG. 8A is enlarged in the z-axis direction. In the figure, the generation of projection data of the intermediate column H1 at a view angle of 90 ° is now performed by using each of the detection column data C6 and C7 for two columns adjacent in the z-axis direction, for example, for each channel data X _j (j = 1 to n) is obtained by weighted data interpolation according to the distances a and b in the z-axis direction. For example, if both projection data of the detection channel X _j are g ₂ (X _j , 90 °) = A, g ₃ (X _j , 90 °) = B, the projection data H1 _j of the intermediate row H1 is
H1 _j = A + {a / (a + b)} * (B−A)
It is obtained by. Here, H1 _j = A when the distance a = 0, and H1 _j = B when the distance b = 0, and the luminance smoothly transitions from A to B at these intermediate positions. The same applies to other detection rows. Similarly, the data can be interpolated between the detection row data C1 to C4 having the opposing view angle of 270 °.
[0035]
On the other hand, each projection data of the intermediate row H2 at the boundary between the view angle 90 ° and the opposite view angle 270 ° is obtained by using the detection row data C5 and C6 for two rows that are also adjacent in the z-axis direction. It is obtained by weighted data interpolation calculation according to the distance in the z-axis direction for each of the channel data X _i and X _j . However, the channel numbers i and j in this case are in symmetrical positions about the body axis CLb. That is, for example, when i = 1, j = n, when i = n / 2, j = n / 2, and when i = n, j = 1.
[0036]
When generating scout image data when the subject 100 is viewed from the front, projection data g ₁ (X, 0 °) to g ₄ (X, 0 °) with a view angle of 0 ° and the opposite view thereof are displayed. Using the projection data g ₁ (X, 180 °) to g ₄ (X, 180 °) at an angle of 180 °, scout image data can be generated in the same manner as above. Scout image data for other arbitrary view angles can be similarly generated.
[0037]
Preferably, the scout image data can be generated by adding projection data of a view angle near the required view angle and / or a view angle near the opposite view angle. This will be specifically described below.
[0038]
FIG. 9A is a front view when the scanning gantry is viewed in the z-axis direction. Here, the relationship between the X-ray tube 40 and the X-ray detector array 90 at a view angle of 90 ° is indicated by a solid line and the vicinity thereof. The same relationship in view angle (90 ° + α) / (90 ° −β) is indicated by a dotted line / broken line, respectively. In the figure, now focusing attention on the projection data distribution with a view angle of 90 °, the projection data o that has passed through the body axis CLb of the subject 100 is centered, and the both ends P and Q of the subject 100 have passed through the upper and lower sides. Projection data p and q are expanded. The projection data p and q corresponding to the both ends P and Q of the subject well represent the shape of the contour of the subject, and can be important graphic information when setting and inputting the retro-recon parameters.
[0039]
Next, paying attention to the projection data distribution of the near view angle (90 ° + α) / (90 ° −β), the projection data o ′ transmitted through the body axis CLb is above and below the substantially opposite ends P of the subject. , Q through the projection data p ′, q ′, and above and below the projection data o ″ transmitted through the body axis CLb, up to the projection data p ″, q ″ transmitted through substantially both ends P, Q, respectively. The projection data p ′, p ″, q ′, q ″ respectively corresponding to the substantially both ends P, Q of these well represent the shape of the contour of the subject, and as shown in the figure. The fluoroscopic images of both ends P and Q of the subject are quite similar between the view angle 90 ° and the vicinity view angle (90 ° + α) / (90 ° −β). Projection data of not only ° but also its near view angle (90 ° + α) / (90 ° −β) (especially data on the contour of the subject) ) Can also be important graphic information for setting and inputting retro-recon parameters.
[0040]
FIG. 9B shows a side view when the scanning gantry is viewed in the x-axis direction. Now, focusing attention on the detection row data C5 with a view angle of 90 °, the position of the detector 90 is displaced in the z-axis direction within this section even in the case of a slight difference in view angles + α, −β in the helical scan. This displacement increases as the helical pitch HP increases. As a result, detection sequence data C5 ″ and C5 ′ are obtained before and after the detection sequence data C5 in the z-axis direction, and projection data (p ″, p, p ′) (q ″) at least at both ends of the subject. , Q, q ′) are very similar.
[0041]
Therefore, preferably, a view angle (90 ° + α) in the vicinity of the required view angle 90 °, (90 ° −β) and / or a view angle (270 ° + α) in the vicinity of the opposite view angle 270 °, Scout image data is generated in consideration of each projection data of (270 ° −β). For example, the detection string data C5 ″ and C5 ′ are used by being offset in the direction of the arrows in the figure.
[0042]
Returning to FIG. 5, in step S <b> 25, the read or generated scout image data 100 </ b> A / 100 </ b> B is displayed in the image display area 13 b of the display unit 13. In step S26, the operator sets retrorecon parameters.
[0043]
FIG. 6 shows an image of retrorecon parameter input processing in the embodiment. An example plan for a retro-recon of head image H is as follows.
[0044]
Recon start position on the body axis [Start Loc] = Z1
Recon end position on the body axis [End Loc] = Z10
Number of Recons [NO.of Images] = 10 Reconstruction Algorithm = Default Image Filter = Default Recon Area Matrix Size = 256 × 256 Pixels The operator sees the scout image on the image display area 13b, and is described in the scan plan above. You can set up a retro recon plan in the same way as above, and if necessary, you can operate (change) and check the cut lines that are overlaid.
[0045]
In the above embodiment, an example of application to a medical X-ray CT apparatus has been described. However, the present invention can also be applied to an industrial X-ray CT apparatus.
[0046]
Moreover, although the data interpolation method of the above example was shown, it is not limited to this. In addition, for example, various well-known two-dimensional image processing (two-dimensional intermediate pixel prediction processing, two-dimensional pixel filter processing, etc.) is performed on scout elephant data on the yz plane obtained from each extracted projection data. As a result, smooth scout elephant data can be generated as a whole. This also applies to scout image data generated from reconstruction data (X-ray CT values).
[0047]
In the above embodiment, the scout image data of the entire desired region is generated from the corresponding scout image data, projection data, or reconstruction data. However, the present invention is not limited to this. Scout image data generated by different methods (different types of accumulated data) for each partial region may be combined to generate scout image data for the entire region. Therefore, the accumulated data in various forms can be effectively used, and retrorecon planning with reference to a larger subject area can be performed.
[0048]
In the above embodiment, the scout image data is generated from the projection data obtained by the helical scan, but may be generated from the projection data obtained by the axial scan.
[0049]
Further, although the preferred embodiment of the present invention has been described, it goes without saying that various changes in the configuration, control, processing, and combination of each part can be made without departing from the spirit of the present invention.
[0050]
【The invention's effect】
As described above, according to the present invention, since a required scout image can be displayed at the time of retro-recon planning, the operator can easily and appropriately set the recon parameters based on the graphical operation referring to the scout image.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating the principle of the present invention.
FIG. 2 is a configuration diagram of a main part of an X-ray CT apparatus according to an embodiment.
FIG. 3 is a flowchart of X-ray CT imaging processing according to the embodiment.
FIG. 4 is an image diagram of scan parameter input processing according to the embodiment.
FIG. 5 is a flowchart of retrorecon processing according to the embodiment.
FIG. 6 is an image diagram of retrorecon parameter input processing in the embodiment.
FIG. 7 is an image diagram (1) of scout image data generation processing according to the embodiment;
FIG. 8 is an image diagram (2) of scout image data generation processing according to the embodiment;
FIG. 9 is an image diagram (3) of scout image data generation processing according to the embodiment;
[Explanation of symbols]
10 Operation console 11 Central processing unit 11a CPU
11b Main memory (MEM)
12 Input device 13 Display device (CRT)
14 Control interface 15 Data collection buffer 16 Secondary storage device (disk device, etc.)
20 Imaging table 30 Scanning gantry unit 30A Rotation control unit 40 X-ray tube 40A X-ray control unit 50 Collimator 50A Collimator control unit 30A Rotation control unit 90 X-ray detector array 91 Data collection unit (DAS)

Claims (6)

X-ray CT that enables retrospective recon reconstruction that reconstructs a CT tomogram of the subject in accordance with reconstruction conditions set after the X-ray CT imaging based on projection data obtained by X-ray CT imaging of the subject A device,
  Scout image data generation means for generating scout image data corresponding to a scout image based on projection data obtained by X-ray CT imaging of the subject or reconstruction data based on the projection data;
  Display control means for displaying the generated scout image data on a display screen for setting a reconstruction condition of a reconstruction condition set after the X-ray CT imaging;
  Setting means for setting the reconstruction condition using the display screen;
  An X-ray CT apparatus comprising: Scout image data generating means, X-rays CT apparatus according to claim 1, wherein the using the projection data of the required viewing angle and or its opposite view angle and generates a scout image data. Scout image data generating means, according to claim 2, characterized in that the addition of projection data of the view angle and or view angle of the opposing view angle near the desired view angle near and generates a scout image data X-ray CT system. Scout image data generating means, according to claim, characterized in that those generated by data interpolation calculation using a plurality of projection data of the same and or opposite view angle adjacent the projection data in the intermediate positions in the body axis direction 2 Or the X-ray CT apparatus of 3. The X-ray CT according to any one of claims 1 to 4, wherein the scout image data generation unit generates data corresponding to a scout image by cutting out the reconstruction data at a tomographic plane having a required view angle. Equipment . The display control means is a display in which a line indicating each slice position is displayed over the scout image data,
  The X-ray CT apparatus according to claim 1, wherein the setting unit sets the slice position.

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