JP2016168508A - Computed tomography apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a computed tomography apparatus which achieves a tomogram image having no artifacts in real time with a simple configuration.SOLUTION: A computed tomography apparatus includes: projection data collection means for sequentially collecting projection data of a subject while periodically changing a direction of projection to the subject across the subject with respect to an X-ray source; partial image generation means for generating partial image data for each predetermined range set in advance by back-projecting fan beam projection data collected by the projection data collection means; weighting means for performing discontinuous weighting by multiplying at least a plurality of pieces of data among the partial image data by coefficients different from each other; tomogram image generation means for generating a tomogram image of the subject on the basis of the plurality of pieces of partial image data including the partial image data weighted by the weighting means; and weighting change means for changing the coefficients of the weighting to the partial image data by the weighting means.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a computed tomography apparatus capable of instantaneously obtaining a tomographic image and reducing a load on a computer without obtaining a difference in projection data when a tomographic image is obtained with rotation of an X-ray source. .

  A medical image by a CT apparatus is detected by a large number of X-ray detection elements facing each other as an imaging physical quantity by transmitting a transmission amount of an X-ray beam exposed from a direction orthogonal to a human body as a subject, and after A / D conversion, It is obtained by image reconstruction in the processing device.

  Specifically, the X-ray beam is detected at once by a large number of detection elements, and for each detection, an acquisition system including an X-ray tube and a detector facing the X-ray tube rotates by a predetermined degree.

  At this time, as shown in FIG. 12, data (projection data) measured from each direction is a distribution diagram of radiation absorption count values for each tissue when the X-ray beam passes through each surface of the human body (FIG. 11A). ) And is back-projected from each direction ((b) of FIG. 11) to obtain an X-ray CT tomographic image as a two-dimensional image.

  Many X-ray CT apparatuses for performing such reconstruction have been filed. For example, in the X-ray CT apparatus disclosed in Japanese Patent Application Laid-Open No. 9-47449, the projection data group sequentially obtained by the scanning operation overlaps at the first and last at the same angular position (hereinafter collectively referred to as an adjacent portion). Using the projection data for the image, this overlapped part is given a predetermined weight, and the difference between the projection data and the projection data excluding the same projection data is calculated from the weighted projection data corresponding to the previous tomographic image data. Then, only this difference is reconstructed by performing convolution and back projection, and added to the previous tomographic image data to create one tomographic image data.

  This creation method will be described with reference to FIG. FIG. 13 shows an example in which one rotation is divided into six, and the projection data A1, A2, A3, and A4 of the projection data Ai are the first and last to generate moving image tomographic image data. The projection data weighted to the part is shown. The operation in the case of CT fluoroscopy will be described with reference to these drawings.

  First, projection data Ai is sequentially read, and projection data A1 (projection data of numbers 11 to 17 in the example shown in FIG. 13) for one image overlapping at the same angular position at the beginning and at the end is used. I do.

  For example, as shown in FIG. 13, the weighting is performed so that the weighting coefficient is increased for the first part of the projection data, and the weighting coefficient is decreased for the last part of the projection data.

  Thereafter, the first first image (first rotation) is reconstructed by performing convolution and back projection on all of the weighted projection data to generate tomographic image data.

  Next, projection data corresponding to the second image (second rotation) is sequentially read, and projection data A2 for one image overlapping at the same angular position at the beginning and end (projection data of numbers 12 to 18 in the example shown in FIG. 13). A predetermined weight is applied to the overlapping portion.

  After that, when the projection data corresponding to the second image is read, the difference between the weighted projection data A2 and the projection data excluding the same projection data among the previously weighted projection data A1 is obtained.

That is, in FIG.
(Part A in the current projection data but not in the previous projection data)-(Part B in the previous projection data and not in the current projection data)
Ask for.

  Then, when the difference is obtained, only the difference is subjected to convolution and back projection, reconstructed, and added to the previous tomographic image data to create one tomographic image data. This tomographic image data is substantially the same as that obtained by reconstructing the entire projection data A2 in spite of the reconstruction processing time of only the difference.

  As described above, the conventional X-ray CT apparatus uses projection data for one image overlapping at the same angular position at the beginning and the end, performs a predetermined weighting on the overlapping portion, and the projection data and the previously weighted projection. Of the data, the difference between the projection data excluding the same projection data is obtained, and only this difference is reconstructed by convolution and back projection, and added to the previous tomographic image data to create one tomographic image data. By doing so, a tomographic image in which artifacts due to rotation are suppressed is displayed on the screen.

  That is, only a necessary part (data of a part overlapping the tomographic image by the previous rotation) is extracted from the reconstructed data, and the current image data shifted by a predetermined time is weighted again and reconstructed again. The difference between the data of the different parts is obtained, and the difference is reconstructed by performing convolution and back projection.

  However, conventionally, for each predetermined angle range, the difference between the current projection data and the previous projection data shifted by a predetermined time is processed, and the next difference is subjected to convolution and backprojection for reconstruction. And the process of adding the reconstructed data to the previous tomographic image data. That is, an algorithm is obtained in which reconstruction data is obtained by differentiating every predetermined angle range and then multiplying by a weighting factor and backprojecting.

  For this reason, in order to obtain reconstruction data of the adjacent portion, a common portion is found by comparing the previous projection data with the current projection data for each predetermined angle range, and the predetermined projection is again performed on the common projection data. After weighting this time-shifted projection data and reconstructing it again, find the difference data, find the difference, perform convolution and backprojection on this difference, and reconstruct it. The tomographic image per rotation obtained by adding the tomographic image of the adjacent portion obtained by the configuration and the tomographic image of the common portion is obtained and continuously displayed.

  That is, in the adjacent portion, for each predetermined angle range, the process for finding the common portion of the current time and the previous time, and the current projection data shifted by a predetermined time again with respect to the common projection data. A process of performing weighting and reconstructing again, and a process of obtaining a difference between different portions of data are necessary.

  Therefore, since it is necessary to provide a plurality of processing systems for performing each process described above for each angle, the image processing system for obtaining a real-time tomographic image becomes complicated, resulting in an overload state. was there.

Further, in order to obtain a real-time tomographic image by performing high-speed processing, there is a problem that a plurality of processing systems for obtaining the above-described difference must be provided for each angle, which increases the size.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a computer tomography apparatus that realizes a tomogram with no artifacts in real time in a simple configuration.

  The computer tomography apparatus of the present invention includes a projection data collection means for sequentially collecting projection data of the subject while periodically changing the projection direction onto the subject with the subject sandwiched with respect to an X-ray source. , Based on the projection data collected by the projection data collection means, a partial image generation means for generating partial image data for each predetermined rotation angle set in advance, and a plurality of parts generated by the partial image generation means A tomographic image generating unit that generates a tomographic image of the subject based on image data, a weighting unit that performs predetermined weighting on the partial image data, and a weighting coefficient for the partial image data by the weighting unit is changed. It has a gist of having weight change means for performing.

  According to the computed tomography apparatus of the present invention, it is possible to obtain an effect that the tomographic image can be obtained in a simple manner and with high accuracy in real time.

1 is a schematic configuration diagram of a computer tomography apparatus according to Embodiment 1. FIG. It is explanatory drawing explaining the concept of a reconstruction of the computer tomography apparatus of this Embodiment 1. FIG. 3 is a flowchart for explaining the operation of the first embodiment. FIG. 3 is an explanatory diagram illustrating the reconfiguration of the first embodiment. It is a schematic block diagram of the computer tomography apparatus of this Embodiment 2. It is explanatory drawing which illustrated the reconstruction of this Embodiment 2. FIG. 6 is an explanatory diagram for explaining the concept of Embodiment 2. FIG. It is explanatory drawing explaining the problem of this Embodiment 1,2. FIG. 10 is an explanatory diagram for explaining a system according to a third embodiment. 6 is a schematic configuration diagram of a computer tomography apparatus according to Embodiment 3. FIG. FIG. 10 is an explanatory diagram for explaining the operation of the third embodiment. It is explanatory drawing explaining reconstruction of the conventional X-ray CT apparatus. It is explanatory drawing explaining the conventional X-ray CT apparatus of Unexamined-Japanese-Patent No. 9-47449.

<Embodiment 1>
FIG. 1 is a schematic configuration diagram of an X-ray CT image reconstruction apparatus according to the present embodiment. An X-ray CT apparatus 10 in FIG. 1 includes a CT main body 15 including a gantry 14 that rotates while an X-ray source 12 and a detector 13 face each other via a detection object 11, and a rotation pitch of the X-ray source 12. Data acquisition device 16 (DAS) that sequentially collects projection data (m: rotation speed, ψ, θ rotation angle) based on X-ray intensity data for each angle Δαi to obtain a projection data group Ai per rotation unit, and data A data group obtained by adding the previous reconstructed data group to the backprojected data group obtained by performing the back projection on the respective changes of the projection data group Ai from the collection device 16 and the previous projected data group Ai (hereinafter referred to as “reprojected data group”). A predetermined number of first virtual reconstruction data in the first rotation range, a plurality of second virtual reconstruction data to be the next common part, and a predetermined number of first rotation reconstruction data 3 virtual reconstruction data Extracted, and a reconstruction unit 17 to obtain a reconstructed data group Bi which is these virtual reconstructed data on the tomographic images of the rotating unit by multiplying a weighting coefficient corresponding to the projection data.

  In the reconstruction device 17, the projection data (m, ψ, θ) from the data collection device 16 is the projection data (m, ψ, θ) after the second rotation, and the rotation angle range is the rotation within the initial rotation range. In the case of a pitch angle (for example, 0 to 30 degrees) or a rotation pitch angle (for example, 330 to 360 degrees) in the end rotation range (hereinafter collectively referred to as an adjacent angle), projection data (m, ψ) of the adjacent angle , Θ), the difference between the projection data is not obtained, and the first and second virtual reconstruction data of the previous adjacent angle stored in advance are added to the weight coefficients (first and third) corresponding to the adjacent angle. ).

  That is, the convolution and back projection are performed, and the reconstructed data (first and third reconstructed data) of the current adjacent portion multiplied by the weighting coefficient are generated, and the previously generated common portion of the previous time is generated. Generate the reconfiguration data (second reconfiguration data) of the current common part obtained by multiplying the virtual reconfiguration data (second virtual reconfiguration data) by the maximum weight coefficient (third weight coefficient). The current reconstruction data per rotation is obtained by synthesis and displayed as a tomographic image.

  That is, the reconstruction apparatus 17 of the present embodiment is configured to generate virtual reconstruction data (first data) of the adjacent angle generated in advance for the adjacent angle while moving the subject (in the Z-axis direction) and rotating the gantry 14. The first and third virtual reconstruction data) are obtained so that the computer is not overloaded.

  As shown in FIG. 1, the reconstruction device 17 includes a weight function table 18, a rotation speed determination unit 19, a rotation angle determination unit 20, an image temporary reconstruction unit 21 (also referred to as a partial image generation unit), An adjacent part reconstruction unit 24, a common part reconstruction unit 25, and a synthesis unit 26 are provided.

  As shown in FIG. 1, the weighting function table 18 stores a weighting coefficient ωi in association with each rotation angle θi of the gantry 14 (X-ray source 12).

  That is, a rotation pitch angle group of one rotation unit is a predetermined number of first rotation pitch angles of 0 to 30 degrees, which is the first rotation range in one rotation unit, between the end rotation range and the first rotation range. The range is classified into a plurality of second rotation pitch angles ranging from 30 degrees to 330 degrees, and a predetermined number of third rotation pitch angles ranging from 330 degrees to 360 degrees being the end rotation range, and from 0 degrees to 30 degrees For the first rotation pitch angle, the first weighting coefficient ωip of 0.3, 0.7, 0.8 is set to 1.0, 1.0,... The second weighting factor ωik of... Is set to a table structure in which the third weighting factor ωiq of 0.8, 0.7, and 0.3 is assigned to the end rotation range of 330 to 360 degrees. .

  The rotational speed determination unit 19 reads the rotational speed mi of the gantry 14 and determines whether the rotational speed mi is the first or second rotation or more, and the determination result is used as the image temporary reconstruction unit 21 and the adjacent part reconstruction unit 24. , Inform the common part reconfiguration unit 25.

  The rotation angle determination unit 20 detects the rotation angle θi of the gantry 14 and sends the detected rotation angle θi to the temporary image reconstruction unit 21 when the rotation number mi is the first time. When the rotation speed mi is 2 rotations or more, it is determined whether the detected rotation angle θi is an adjacent angle (for example, 0 to 30 degrees, 330 to 360 degrees) or a common image generation angle (for example, 30 to 330 degrees). judge.

  If the determination result is an adjacent angle or a common image generation angle, the detected rotation pitch angle is sent to the adjacent part reconstruction unit 24 or the common part reconstruction unit 24.

  The temporary image reconstruction unit 21 obtains a change from the previous projection data while shifting the current projection data Ai collected by the data collection device 16 by the rotation pitch angle based on the number of rotations. The back projection data group obtained by convolution and back projection is added to the previous reconstruction data group and stored in the file 22.

  When the rotation speed mi is equal to or greater than the second rotation, and the detected rotation angle θi indicates the adjacent angle, the adjacent part reconstruction unit 24 performs virtual reconstruction data and a weight function table corresponding to the adjacent angle. The reconstruction is performed using weighting factors corresponding to 18 adjacent angles.

  That is, for the projection data (m, ψ, θ) of the adjacent angle, the difference between the projection data is not obtained, and the virtual reconstruction data of the previous adjacent angle generated in advance by the temporary image reconstruction unit is added to the adjacent angle. Is multiplied by a weighting coefficient corresponding to, to obtain reconstruction data (first and third reconstruction data) of the current adjacent angle.

  When the rotational speed mi is equal to or greater than the second rotation and the detected rotation angle θ indicates a common image angle, the common unit reconstruction unit 25 determines the weight coefficient corresponding to the common image angle and the image temporary reconstruction. The virtual reconfiguration data (second reconfiguration data) of the previous common portion generated in the configuration unit 21 is multiplied to obtain common unit reconfiguration data.

  The combining unit 26 combines the reconstruction data of the adjacent angle reconstructed by the adjacent unit reconstruction unit 24 and the common unit reconstruction data reconstructed by the common unit reconstruction unit 25, and synthesizes this. While being displayed on the display unit 27 as a tomographic image, the previous reconstruction data group of the file 22 is updated to the reconstruction data group for one rotation added this time.

  That is, in the present embodiment, after the second rotation, as shown in FIG. 2A, the previous reconstruction data Bi is added to the change between the previous projection data A1 and the current projection data A2. From the virtual reconstructed data group Ji obtained by adding the previous reconstructed data group Bi to the backprojected data group obtained by backprojecting, the adjacent angles (for example, 0 to 30 degrees, 330 degrees to 360 degrees) 1 virtual reconstruction data j1, j2, j3 (collectively referred to as the first virtual reconstruction data ja) and third virtual reconstruction data j10, j11, j12 (collectively referred to as the ending virtual reconstruction data jb) As shown in FIG. 2 (c) using the weighting coefficients ω (ω1, ω2, ω3 and ω10, ω11, ω12) corresponding to the angle shown in FIG. Reconstruction data ha and end reconstruction data hb are obtained.

  Then, as shown in FIG. 2 (d), the virtual reconfiguration data jk of the previous common part, which is a plurality of second virtual reconfiguration data, is multiplied by the maximum weighting coefficient, and as shown in FIG. 2 (e). In addition, the reconfiguration data Bk of the common part, the obtained first reconfiguration data ha and the end reconfiguration data hb are synthesized to obtain the current reconfiguration data Bi.

  The operation of the X-ray CT image reconstruction apparatus configured as described above will be described below.

  FIG. 3 is a flowchart for explaining the operation of the X-ray CT image reconstruction apparatus of the present embodiment. FIG. 4 is an explanatory diagram illustrating the operation of the X-ray CT image reconstruction apparatus of the present embodiment. The weighting coefficient for the first rotation data and the weighting coefficient for the second rotation data are changed (weighting coefficient). Is changed with time).

  That is, (d) to (j) in FIG. 4 show the states when rotated by a predetermined angle from (a) to (c) in FIG. 4, and the angles shown in (b) and (f) in FIG. Is exactly different. In this description, the collected projection data group will be described by dividing it into 1/12 equal parts.

  First, X-rays are bombarded from the X-ray source 12 while rotating the gantry 14 at a predetermined speed. The detector 13 (single type, dual type, or multi type) and the X-ray source 12 rotate while maintaining an opposing relationship.

  The X-ray dose transmitted through the subject 11 is detected by each detection element, and projection data based on the X-ray intensity data of each detection element is sequentially collected by the data collection device 16.

  As the projection data Ai is collected, the temporary image reconstruction unit 21, the common unit reconstruction unit 25, and the adjacent unit reconstruction unit 23 of the reconstruction device 17 read the projection data Ai (S1). At the same time, the rotation speed determination unit 19 reads the rotation speed mi of the gantry 14 and determines whether it is the first rotation or the second rotation or more (S3).

  When it is determined in step S3 that the rotation is the first time, every time the temporary projection reconstruction unit 21 collects the current projection data Ai of the data collection device 16, the change between the projection data and the previous projection data is obtained. Is added to the previous virtual reconstruction data, back projection is performed, and this result is multiplied by the corresponding weighting coefficients by the adjacent section reconstruction section 24 and the common section reconstruction section 25 to obtain reconstruction data B1. Is obtained (S5).

  That is, with respect to the projection data for each angle of the first rotation projection data A1 shown in FIG. 4A, the weighting coefficient ωi (for example, ωip) corresponding to each angle of the weighting function table 18 shown in FIG. = 0.3, 0.7, 0.8, ωik = 1.0, 1.0 ..., ωiq = 0.8, 0.7, 0.3), and is shown in FIG. Reconstruction data B1 is obtained.

  Next, the reconstruction data B1 (tomographic image data) is stored in the file 22 (S7) and displayed on the display unit 27 (S9). Next, it is determined whether or not to end (S11), and if it is not ended, the process returns to step S1.

  In step S3, when it is determined that the rotation speed mi of the gantry 14 is the second or more, the image temporary reconstruction unit 21 shifts the current projection data by the rotation pitch angle based on the rotation speed mi, The amount of change between the previous projection data A1 and the current projection data A2 is obtained, back projection is performed on the change, and virtual reconstruction data Ji obtained by adding the previous reconstruction data B1 is obtained (S13).

  For example, after the projection data A2 for the second rotation is shifted as shown in FIG. 4D, the projection data A2 (a1, a2, a3,... A12) and the previous time are changed as shown in FIG. , Projection data A 1 (a 1, a 2, a 3,...) Are obtained, and the previous reconstructed data B 1 is added to the back projection data group back-projected with respect to this change and the virtual reconstruction is performed. Obtain configuration data Ji.

  Next, the common part reconstruction unit 25 and the adjacent part reconstruction unit 24 read the current rotation angle θi from the rotation angle determination unit 20 (S15), and the rotation angle θ is the first adjacent angle θp (0 degrees to 30 degrees). ) Is determined (S17).

  When it is determined in step S17 that the initial adjacent angle θp (0 degrees to 30 degrees) is obtained, the adjacent section reconstruction unit 24 performs the initial adjacent angle θp (0 degrees to 30 degrees) as shown in FIG. The weight coefficient ωip corresponding to (degree) is read from the weight function table 18 (S19). For example, when the initial adjacent angle θp is 10 degrees, the weighting coefficient “0.3” is read, when 20 degrees, the weighting coefficient “0.7” is read, and when it is 30 degrees, the weighting coefficient “0.8” is read.

  Next, the adjacent part reconstruction unit 24 reads the first virtual reconstruction data ja corresponding to the first adjacent angle θp (0 degrees to 30 degrees) in the virtual reconstruction data group Ji obtained in step S13 ( S21). Then, using the read weight coefficient ωip and the virtual reconstruction data of the first adjacent angle θp (0 degrees to 30 degrees) obtained in step S13, the reconstruction data ha of the first adjacent portion in the next round is obtained. Obtain (S23).

  That is, for example, as shown in FIGS. 4E to 4H, the virtual reconstruction obtained based on the change between the previous projection data A1 and the current projection data A1 and the previous reconstruction data B1. Multiplying the first virtual reconstruction data ja of the configuration data group Ji by the weight coefficient ωip (a gradually increasing weight coefficient) of the adjacent angle θp (0 degrees to 30 degrees) corresponding to the first virtual reconstruction data ja Thus, the reconstruction data ha at the beginning of the next round is obtained.

  If it is determined in step S17 that the rotation angle θ is not the first adjacent angle θp, it is determined whether or not it is the end adjacent angle θp (for example, 330 to 360 degrees) (S25).

  If it is determined in step S25 that the adjacent angle θk is the end (for example, 330 degrees to 360 degrees), the process returns to step S19.

  That is, when it is determined in step S19 that the end adjacent angle θk (330 degrees to 360 degrees) is determined, the adjacent portion reconstruction unit 24 sets the weighting coefficient ωiq corresponding to the end adjacent angle θk (330 degrees to 360 degrees). Read from the weight function table 18. For example, when the end adjacent angle θk is 330 degrees, the weight coefficient “0.8” is read, when 350 degrees, the weight coefficient “0.7” is read, and when 360 degrees, the weight coefficient “0.3” is read.

  In steps S21 and S23, the adjacent part reconstruction unit 24 reads and reads the virtual reconstruction data jb of the adjacent angle θk at the end from the virtual reconstruction data group Ji of the second rotation generated in step S13. Convolution and back projection are performed using the weighting factor ωiq and the end virtual reconstruction data jb to obtain the reconstruction data h of the end adjacent portion for the next round.

  That is, for example, as shown in FIG. 4 (e) to FIG. 4 (h), the weighting coefficient ωiq corresponding to the virtual reconstruction data jb at the end of this time is multiplied, and the back projection is performed and the end of the next round is performed. The reconstruction data hb of the adjacent part is obtained.

  In step S25, when the rotation angle determination unit 20 determines that it is not the end adjacent angle θk (330 degrees to 360 degrees), that is, when it is determined that the common image angle θs (30 degrees to 330 degrees), FIG. As shown in FIG. 4 (i), the common part reconstruction unit 25 performs reconstruction using the weighting coefficient ωik corresponding to the common image angle and the virtual reconstruction data jk of the current common part generated in step S13. The current common part image data dk is obtained (S26).

  Then, as shown in FIG. 4 (j), the compositing unit 26 uses the common part image data dk, the reconstruction data ha of the first adjacent part obtained in step S23, and the reconstruction data hb of the last adjacent part. To obtain the current reconstructed image data B2 (current tomographic image) (S27).

  Next, the previous reconstruction data B1 is updated to the reconstruction image data B2 and stored in the file 22 (S29). Then, the process returns to step S9, and the reconstructed data B2 generated this time is displayed on the display unit as a tomographic image by the second rotation.

  Therefore, for the adjacent portion, for each division angle, a process for finding a common portion, and this common projection data are again weighted with respect to the current projection data shifted by a predetermined time, and then again. A process for obtaining a difference and the like for the data of the different part from the process of performing the configuration become unnecessary.

  In particular, when performing multi-slice scanning with a plurality of detector detection elements in parallel, the process for finding a common portion for each of the aforementioned division angles and the common projection data once again for a predetermined time. Since there is no need for a process for weighting the shifted current projection data and reconstructing it, and a process for obtaining a difference between different data, the number of units for reconstruction becomes extremely small. At the same time, since the load on the computer is greatly reduced, the real-time property of tomographic image display is improved.

<Embodiment 2>
The second embodiment is common in that the weighting factor is changed over time. FIG. 5 is a schematic configuration diagram of the X-ray CT apparatus of the second embodiment. The X-ray CT apparatus 30 of FIG. 5 includes a CT main body 15 similar to that of the first embodiment and a data acquisition device 16 (DAS).

  Further, the reconstruction device 32 of the present embodiment is similar to the first embodiment in that the weighting function table 18, the rotation determination unit 19, the rotation angle determination unit 20, the partial image generation unit 29, and the synthesis unit 26, and the second embodiment further includes a change processing unit 33 that temporally changes the weighting coefficient of the weighting function table 18 using the weighting coefficient for the reconstructed data (hereinafter, partial image data) as a table.

  The change processing unit 33 (1) every time a new tomographic image is generated by the synthesizing unit 26 or (2) every time projection data for a predetermined range is collected by the data collecting device 16 (3) Alternatively, every time partial image data is generated by the partial image generation unit 29, the weighting coefficient of the weight function table 18 is changed at any timing. The change of the weighting factor may be performed for every reconstructed partial image, for every predetermined number of partial images, or for each partial image. Here, a case will be described in which the weights for all the reconstructed partial images (for example, a plurality of partial images necessary to construct one tomographic image) are changed.

  For example, as shown in FIG. 6A, the partial image generation unit 29 regenerates the projection data group of 0 to 360 degrees every 10 degrees (in FIG. 6, every predetermined rotation angle collected by the data collection device 16). Reconstruct the projection data (indicating the constructed location) using, for example, a convolution / back projection method to generate a provisional partial image data group, and synthesize these to obtain provisional image data Jn. .

  Then, the synthesized image data Jn is multiplied by a weight function shown in FIG. 6B stored in the weight function table 18 to obtain image data Hn shown in FIG. 6C. The image data Hn is displayed on the display unit 27 as a tomographic image Bn.

  Here, the weighting function ωn shown in (b) of FIG. 6 is 0.3, 0.7, 0.8, 30 to each of the portions corresponding to 0 to 30 degrees of the synthesized image data Jn. It is a function for applying weights of 0.8, 0.7, and 0.3 to a portion corresponding to 330 degrees and 1.0, and a portion corresponding to 330 to 360 degrees.

  Subsequently, as shown in FIG. 6D, when partial image data based on 360-370 degree projection data is newly obtained by the partial image generation unit 29, the newly obtained partial image data and 0 are obtained. A new image data Jn + 1 is generated by combining with the partial image data group Jn of ˜360 degrees.

  Here, the change processing unit 33 changes the weight function of the weight function table 18 at any one of the timings (1), (2), and (3) described above.

  That is, as shown in FIG. 6E, 0, 0.3, 0.7, 0.8, and 40 to 340 degrees with respect to data corresponding to 0 to 40 degrees of the synthesized image data, respectively. The weight function ωn + 1 is changed so that the data corresponding to 1.0, the weight corresponding to 0.8, 0.7, and 0.3 is applied to the data corresponding to 340 to 370 degrees.

  Then, the weighted function ωn + 1 is multiplied by the synthesized image data to obtain image data Hn + 1 shown in FIG. 6F, and this is displayed on the display unit 27 as the tomographic image Bn. Thereafter, each time new projection data, partial image data, or the like is generated, the weight function is changed, and the tomographic image displayed on the display unit 27 is updated.

  On the other hand, when the weight is changed for each reconstructed partial image, the weight function table 18 is preferably provided in the preceding stage of the combining unit 26 instead of being provided in the subsequent stage as shown in FIG.

  In this case, the plurality of partial image data is obtained by reconstructing the projection data for each predetermined rotation angle, as in the case of changing the weighting function for all the reconstructed partial images. Is different in that a weighting factor is applied to each partial image and the weighting factor is changed over time.

  First, as shown in FIG. 7A, a temporary partial image data group Jn in which projection data for each predetermined rotation angle is reconstructed is generated.

  Next, for partial images J1 to J3 of 0 to 30 degrees, 1.0, 330 to 360 degrees for partial images J4 to J33 of 0.3, 0.7, 0.8, and 30 to 330 degrees, respectively. The partial images J34 to J36 are multiplied by weighting factors of 0.8, 0.7, and 0.3, respectively. Then, the partial image data multiplied by the weighting coefficient is combined by the combining unit 18 to obtain a plurality of partial image data Hn. The partial image data Hn is displayed on the display unit 27 as a tomographic image Bn.

  Subsequently, as shown in FIG. 7C, when the partial image data J37 based on the projection data of 360 to 370 degrees is newly obtained by the partial image generation unit 29, the change processing unit 33 displays the weight function table 18. Change the weighting factor. That is, the weighting factor is set to 1.0 for partial images J5 to J34 of 0, 0.3, 0.7, 0.8, and 40 to 340 degrees for partial images J1 to J4 of 0 to 40 degrees, respectively. The partial images J35 to J37 at 340 to 370 degrees are changed to 0.8, 0.7, and 0.3.

  Each partial image is multiplied by the changed weighting coefficient to obtain a weighted partial image group Hn + 1, which is displayed on the display unit 27 as a tomographic image Bn + 1. Thereafter, each time new projection data, partial image data, or the like is generated, the weighting coefficient for each partial image is changed, and the tomographic image displayed on the display unit 27 is updated.

<Embodiment 3>
In the first and second embodiments, the partial image data is described as one, but the number is not limited to one, and a plurality (arbitrary) may be used as one partial image data.

  This is very effective in a real-time X-ray CT apparatus in which scanning (for example, imaging of blood vessels, heart, etc.) starts when a certain CT value is exceeded.

  For example, in the first embodiment, weighting coefficients are applied to one partial image data, and these partial image data are sequentially added. Therefore, the function for converting the density value of the image is slow as shown in FIG. It becomes the nonlinear function. That is, it takes time to reach the threshold value.

  Therefore, in the third embodiment, a threshold value is set (changeable) for each of a plurality of partial image data, so that the plurality of partial image data (hereinafter referred to as setting range image data) as shown in FIG. The desired part is simply obtained in real time by obtaining a function that rises at a time in minutes.

  FIG. 10 is a schematic configuration diagram of the X-ray CT apparatus according to the third embodiment. The X-ray CT apparatus 40 according to the second embodiment includes a gantry rotation mechanism that controls the rotation operation of the gantry (gantry rotation mechanism) 14, a bed control device that controls the bed, a system control device that controls the system, and the like. However, these will be mainly described with reference to the scan control device 42 and the reconstruction device 43 according to the second embodiment, not shown.

  The scan control device 42 connects a button switch 44, and when the button switch 44 is turned on, causes the data collection device 16 to collect projection data associated with the scan of the gantry 14.

  On the other hand, the reconstruction device 43 includes a rotation speed determination unit 19, a rotation angle determination unit 20, a partial image generation unit 29, a partial image range setting unit 45 such as a synthesis unit 26, a weighting table change unit 46, and the like.

  The partial image range setting unit 45 sets the number of partial image data input by the operation unit (not shown) in the memory 47.

  For example, when the range of the partial image of the first embodiment is 5 °, a plurality (for example, 4; angle 20 °) is set in the memory 47 as the current set range.

  The weighting table changing unit 46 stores the angle and the weighting factor in the weighting factor table 18 when a set of the angle and the weighting factor is input by the operation unit.

  For example, when an angle of 20 °, an angle of 40 °, and the like are input with weighting factors of 0.2, 0.32,..., These are stored in correspondence.

  That is, the X-ray CT apparatus 40 according to the second embodiment uses the partial image range setting unit 45 to set one set of, for example, four temporary partial image data ji as shown in FIG. The partial image generation unit 29 generates temporary partial image data Pi based on the projection data for this angle.

  Then, as shown in FIG. 11B, the table 18 changed by the weighting table changing unit 3 is read with respect to these partial image data Pi, and the weighting coefficient wi corresponding to the angle of this table is multiplied. Partial image data PH1, PH2,... Are obtained.

  That is, the partial image data obtained at a time is not reproduced finely, but is reproduced sequentially at a time within the range set by the partial image range setting unit 45, so that the target part can be found quickly, so that it is suitable for a real-time CT apparatus. Is very effective.

  Naturally, the weighting coefficient may be changed for each partial image group as in the above embodiment.

  As described above, if the tomographic image is updated for each of the plurality of partial images during the pre-scan for measuring the timing of performing the main scan, the contrast examination can be easily performed.

  When entering the main scan, observation can be performed in real time by updating the tomographic image for each partial image (for example, for each partial image) smaller than that for the pre-scan.

  In the second embodiment, the button switch 44 is connected to the scan control device 42. However, the data collection timing may be controlled by respiratory synchronization or electrocardiographic synchronization. That is, a specific respiratory phase or cardiac phase is monitored from the respiratory waveform or electrocardiographic waveform, and a synchronization signal is output to the scan control device 42 when a specific respiratory phase or cardiac phase appears.

  Further, after the images are sequentially reproduced within the range set by the partial image range setting unit 45 and the target part is found and the scan control apparatus is operated, as shown in the first embodiment, each one The partial image data may be multiplied by a weighting coefficient.

  Furthermore, in the above embodiment, one or a plurality of partial image data has been described. However, in a slice image composed of a plurality of tomographic images, a single tomographic image is simply used as partial image data, and the partial image data May be weighted.

  In each of the above embodiments, the weighting coefficient table has been described. However, the weighting coefficient and the angle may be stored as a function, and the partial image data may be weighted using this function.

  In the above embodiment, the predetermined range angle is described as the partial image data, but a finer angle range may be used as the partial image data.

  In the above-described second embodiment, it has been described that the weight for the partial image is changed temporally. However, the weight for the projection data may be changed temporally.

DESCRIPTION OF SYMBOLS 10 X-ray CT apparatus 11 Detected object 12 X-ray source 13 Detector 14 Gantry 15 CT main body part 16 Data collection apparatus 17 Reconstruction apparatus 18 Weight function table 19 Rotational speed judgment part 20 Rotation angle judgment part 21 Temporary image construction part 24 Adjacent part image generation part 25 Common part image generation part 26 Composition part

Claims (1)

Projection data collection means for sequentially collecting projection data of the subject while periodically changing the projection direction onto the subject with the subject sandwiched with respect to an X-ray source;
Partial image generation means for generating partial image data for each predetermined rotation angle based on the projection data collected by the projection data collection means;
A tomographic image generating means for generating a tomographic image of the subject based on a plurality of partial image data generated by the partial image generating means;
Weighting means for performing predetermined weighting on the partial image data;
A computer tomography apparatus comprising: a weight changing unit that changes a weighting coefficient for the partial image data by the weighting unit.

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