JPH119588A - X-ray ct equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make possible to reduce total time during which a subject is retained for tomography by recomposing a coarse X-ray tomogram by carrying out recomposition by thinning out X-ray projection data stored by a data collection means and displaying immediately the coarse X-ray tomogram retained during preparation. SOLUTION: After a subject M is placed on a top plate 4, X-ray projection data necessary for obtaining an X-ray tomogram are stored in a memory area of a computer 6 by rotating an imaging section 3. And then a temporary X-ray tomogram is prepared for an X-ray tomogram by proceeding with recomposition by thinning out on the basis of selected X-ray projection data selected every four sets of data for instance, using the memory area. On the other hand, when the next imaging region for X-ray tomography is matched with an imaging position and a collection start signal is outputted, the computer 6 suspends the recomposition of an X-ray tomogram, stores a temporary X-ray tomogram in the memory area and holds, and displays immediately the temporary X-ray tomogram on a monitor 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a computer
X-ray tomography of subject using tomography
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line CT apparatus, and more particularly to a technique for reducing the restraint time of a subject during imaging.

[0002]

2. Description of the Related Art Conventional X-ray CT used in hospitals and the like
The device maintains the X-ray tube and X-ray detection array equipped with the X-ray tube and X-ray detection array facing each other with the X-ray tube and X-ray detection array facing each other with the patient placed on the top plate. While rotating around the patient's body axis while keeping it in the same position, a fan-shaped X-ray beam is emitted from the X-ray tube to the patient every time the rotation position of the imaging unit becomes an appropriate position. The transmitted X-ray detection signal output from the X-ray detection
This is an apparatus that, after collecting and storing X-ray projection data, reconstructs an X-ray tomographic image by computer processing on the collected X-ray projection data.

Normally, in X-ray tomography, one X-ray tomographic image is obtained.
It is rare that only a single image is obtained. In many cases, a plurality of X-ray tomographic images are obtained at a time by continuously performing imaging while changing the imaging region of the same patient. In this way, a plurality of X
When obtaining a tomographic X-ray image at a time, after collecting and storing one X-ray projection data, the X-ray tomographic image is reconstructed based on the collected one X-ray projection data and displayed on a screen of a monitor or the like. When it is displayed and it is confirmed that one X-ray tomographic image has been properly captured, the imaging region is changed, and a one-by-one processing method for the next imaging is employed, or the imaging region is sequentially changed for the same patient. While continuously changing all data for the planned number of shots while changing the
A parallel processing method for sequentially executing reconstruction of an X-ray tomographic image based on line projection data is employed.

[0004]

However, in the above-mentioned conventional X-ray CT apparatus, there is a problem that the restraint time of the patient during imaging is long in any case. In the former one-by-one processing method, the patient can be lowered from the top of the table only after it has been confirmed that all X-ray tomographic images have been properly obtained. Even with the latter parallel processing method, the patient can be lowered from above the tabletop after confirming that all X-ray tomographic images have been obtained accurately. If an X-ray tomographic image cannot be obtained accurately, the patient must be re-taken, and the patient must remain on the tabletop until it is confirmed that all X-ray tomographic images have been obtained accurately. You will have to wait.

[0005] In a recent X-ray CT apparatus, the acquisition time of X-ray projection data is much shorter than before. For example, about one second is sufficient for collecting data for one X-ray tomographic image. However, the reconstruction processing time of the X-ray tomographic image is not much shorter than before. The reconstruction processing time required to obtain one X-ray tomographic image is, for example, about 7 seconds, and the reconstruction processing time for all X-ray tomographic images is quite long in recent years when the number of images to be photographed is increasing. Therefore, although the data acquisition is fast in either method, the patient remains restrained on the table for a considerable time until the reconstruction of the last X-ray tomogram is completely completed.

In view of the above problems, an object of the present invention is to provide an X-ray CT apparatus that can reduce the restraint time of a subject during imaging.

[0007]

X-ray CT according to the present invention
The device is configured as follows to achieve the above object. That is, the present invention provides an imaging means in which an X-ray generation means and an X-ray detection means are arranged to face each other with a subject interposed therebetween.
An imaging system rotating unit that rotates around the body axis of the subject while maintaining the opposed arrangement state of the line detection unit; an X-ray irradiation control unit that performs X-ray beam irradiation on the X-ray generation unit;
A data collection unit that collects and stores a transmission X-ray detection signal output from the X-ray detection unit in association with the X-ray beam irradiation as X-ray projection data, and starts imaging to start collecting data for one X-ray tomographic image A start signal generating means for outputting an acquisition start signal for giving a timing; an image reconstructing means for reconstructing an X-ray tomographic image by computer arithmetic processing on the X-ray projection data acquired and stored by the data acquiring means; Image output means for displaying an X-ray tomographic image, wherein the progress of data acquisition by the data acquisition / storage means and reconstruction of the X-ray tomographic image by the image reconstruction means are controlled based on the acquisition start signal from the start signal generation means. In the X-ray CT apparatus configured as described above, the image reconstructing means is configured to select, from among the X-ray projection data stored in the data collecting means,
First, a reconstruction process by a thinning process based on intermittently selected data is executed to reconstruct a coarse X-ray tomographic image, and based on the next acquisition start signal, the ongoing reconstruction process is interrupted and is being created. While the X-ray tomographic image is held, the reconstruction processing by the thinning processing for the next X-ray tomographic image is executed, and the reconstruction processing by the thinning processing is executed for all the X-ray tomographic images. The interrupted reconstruction processing is restarted to sequentially complete a dense X-ray tomographic image, and the image output means is configured to immediately display a coarse X-ray tomographic image held during the creation. ing.

[Operation] The operation when tomography is performed by the X-ray CT apparatus of the present invention is as follows. The imaging system rotating means rotates the imaging means around the body axis of the subject while maintaining the opposed arrangement of the X-ray generation means and the X-ray detection means. The X-ray generator irradiates the subject with a fan-shaped X-ray beam according to the control of the irradiation controller. At the same time, a transmitted X-ray detection signal is output from the X-ray detecting means on which the transmitted X-ray of the subject enters, and the data is collected and stored as X-ray projection data by the data collecting means. Then, an X-ray tomographic image is reconstructed by a computer operation on the collected and stored X-ray projection data by the image reconstructing means, and after the X-ray tomographic image is obtained, it is displayed by the image output means. The progress of the data collection and the reconstruction processing of the X-ray tomographic image is appropriately performed based on the acquisition start signal from the start signal generation means for instructing the imaging start timing so as not to be disturbed and not to waste time. Is controlled by

On the other hand, in the X-ray CT apparatus of the present invention, in the reconstruction processing of the X-ray tomographic image performed by the image reconstruction means, the reconstruction processing by thinning-out processing based on the selected data which is discretely selected is first executed. And then executes a reconstruction process by a replenishment process based on the remaining unselected data 2
Although a step processing method is adopted, the data acquisition time is shorter than the total reconstruction processing time of the X-ray tomographic image, so that the next data acquisition is performed while the reconstruction processing is performed on the data obtained earlier. At the beginning, the next acquisition start signal is output.
Upon receiving the next acquisition start signal, the image reconstructing means suspends the currently executing reconstructing process and holds a coarse X-ray tomographic image being created (hereinafter abbreviated as “temporary X-ray tomographic image” as appropriate). The execution of the reconstruction process by the thinning process of the next X-ray tomographic image is started as it is. After the reconstruction process by the thinning process is completed for all the X-ray tomographic images, the reconstruction processes interrupted so far are sequentially restarted, and dense X-ray tomographic images are completed one after another.

The provisional X-ray tomographic image displayed by the image output means is an overall image even though it is a coarse image based on the thinned-out data. Judgment as to whether or not it is obtained can be made sufficiently. Therefore, when it is determined that an accurate X-ray tomographic image can be obtained for the last provisional X-ray tomographic image, the patient can be dropped from the table at that time. At the time when the last temporary X-ray tomographic image is displayed, the reconstruction processing is interrupted one after another, so that
The time point is far before the time point when the entire reconstruction process ends, and the timing for lowering the patient from the tabletop is much earlier than before.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a medical X according to the present invention will be described.
One embodiment of the line CT apparatus will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of an X-ray CT apparatus according to an embodiment. FIG. 2 is a graph showing X-ray projection data, a reconstruction function, and convolution corrected data.
FIG. 8 is a schematic diagram illustrating a memory area division state in a storage unit of the example device.

As shown in FIG. 1, an X-ray CT apparatus according to an embodiment includes an X-ray tube (X-ray generating means) 1 for irradiating a fan-shaped X-ray beam FB, and a large number (several hundred channels to about 1,000 channels). ), An X-ray detection array (X-ray detection means) 2 in which X-ray detection elements 2a are arranged along an arc corresponding to a fan shape of an X-ray beam is used to detect a subject (patient) M on a top plate 4. An arrow A1 is provided around the body axis Z of the subject M (integrally) while maintaining the opposed arrangement state of the X-ray tube 1 and the X-ray detection array 2 while holding the imaging unit 3 opposed to each other. An imaging system rotation mechanism (imaging system rotation means) 5 for rotating the imaging unit 3 in the direction shown is provided. This imaging system rotation mechanism 5
Controls the operation of the imaging unit 3 in accordance with a command from the computer 6.

Further, the apparatus of the embodiment is an X-ray irradiation control section (X-ray irradiation control means) for causing the X-ray tube 1 to perform X-ray irradiation.
7 and a DAS (data collecting means) for collecting and storing a transmitted X-ray detection signal output from the X-ray detection array 2 with the X-ray irradiation as X-ray projection data in the storage unit 10 via the AD conversion unit 9. 8 is provided. The X-ray irradiation controller 7 mainly includes a high-voltage power supply and the like, and supplies a high-voltage power required for X-ray irradiation to the X-ray tube 1 according to a command from the computer 6. The DAS 8 has a group of amplifiers and the like, and performs a data collection operation in accordance with a command from the computer 6.

While the imaging section 3 makes one rotation around the subject M, for example, data is collected 700 to 800 times. For example, when data is collected every time the imaging unit 3 rotates 0.5 °, a total of 72 X-ray tomographic images are required to obtain
This is an account where zero data collection is performed. In the following description, the number of times of data collection is set to 720 for convenience. When X-ray irradiation is performed on the subject M, X-ray projection data Da is obtained from the X-ray detection array 2 as shown in FIG. In the X-ray projection data Da, the vertical axis corresponds to the signal intensity, and the horizontal axis corresponds to the arrangement of each X-ray detection element 2a. In order to obtain one X-ray tomographic image, X-ray irradiation is performed from different 720 directions around the body axis Z of the subject M, and X-ray irradiation is performed.
A total of 720 line projection data Da are obtained, one for each direction.

As shown in FIG. 3, the 720 pieces of X-ray projection data Da thus obtained are stored in a memory area 21a of the X-ray projection data, and the stored X-ray projection data Da is being collected. The data is sequentially read out by the computer 6, and a preliminary correction process is performed using the memory area 22a and the like for processing working to eliminate the variation in the detection sensitivity of the X-ray detection element 2a and the error due to the aging of the amplifier. The original memory area 21a
Is stored again. Similarly, 720 pieces of X-ray projection data Da of the next imaging region are stored using the memory areas 21b and 22b. Similarly, 720 X-ray projection data Da of the next imaging region are similarly stored in the memory areas 21c and 21c.
It is stored using 2c. The same is repeated for the number of shots.

Further, the apparatus of the embodiment is provided with a start signal generating unit 11 for outputting a collection start signal for instructing a photographing start timing at which data collection for one image must be started. The start signal generation unit 11 is equipped with a photoelectric reader-type rotation position detection mechanism and the like, and the imaging unit 3 is positioned at a reference position (for example, as shown in FIG.
At the lowest point), a collection start signal (pulse signal) is output to the computer 6. Since the imaging unit 3 is rotated at such a high speed as to rotate around the subject M in one second, after the rotation of the imaging unit 3 is started, the rotation speed stably rotates at a predetermined constant speed, and then the imaging unit 3 is moved to the reference position. , An acquisition start signal is output. Based on the acquisition start signal, the computer 6 outputs a command signal for controlling the X-ray exposure timing and the progress of data acquisition and reconstruction processing from the computer 6 to each unit in a timely manner. During one rotation of M, 720 data collections are performed in a timely manner, and the X-ray projection data Da is correctly stored in the storage unit 10.

The top board 4 can be moved by the top board moving mechanism 12 in the forward and backward directions (parallel to the body axis Z), in the left and right directions, and further in the up and down directions while the subject M is placed thereon. I have. The top moving mechanism 12 controls the movement of the top 4 according to a command from the computer 6. The operator is also configured to be able to input various commands such as a command to move the top 4 to a desired position from the operation unit 13.

In the X-ray CT apparatus of the embodiment, DA
An X-ray tomographic image is reconstructed by the processing of the computer 6 with respect to the X-ray projection data collected and stored in the storage unit 10 in S8, and the obtained X-ray tomographic image is displayed on the monitor 1.
4 is displayed. In the computer operation processing for reconstructing the X-ray tomographic image, as shown in FIG. 2B, a correction operation using a reconstruction function (convolution function) Db is performed on each X-ray projection data Da. Convolution processing (convolution integration processing) is executed to obtain convolution corrected data (processing result) Dc as shown in FIG. The convolution processing is performed using the processing working memory areas 22a, 22b, 22c and the like shown in FIG.
As a whole reconstruction process, the convolution corrected data D for all of the 720 pieces of X-ray projection data Da
c is obtained.

Next, the convolution corrected data D
A back projection process for performing a linear operation based on c is executed by the computer 6. That is, in the backprojection processing, as shown in FIG. 4, memory cells are arranged vertically and horizontally (for example, 512 columns vertically) so as to correspond to each pixel of the reconstructed X-ray tomogram.
FIG. 3 shows a memory matrix 25 having 512 horizontal rows).
Processing working memory areas 22a, 22 shown in FIG.
b, 22c, etc., and associated with the X-ray irradiation direction for each of the 720 convolution-corrected data Dc, and 72 in the memory matrix 25.
Zero radial directions RD1 to RDn to RD720 are set. Then, each data of each convolution corrected data Dc is stored in each memory cell in such a manner that the same data is allocated to the memory cells arranged in the radial direction of the corresponding memory matrix 25. If there is already stored data, the sum of the already stored data and the new data is stored. That is, the backprojection processing is a primary linear addition processing. For example, in the case of the radial direction RD1, the convolution corrected data Dc is stored in each cell of a memory cell row continuing vertically in each memory matrix 25.
Corresponding to the same data is stored. Specifically, data Dc1 is stored in all memories in the memory cell column Mn.

From the above, in the case of the X-ray CT apparatus of the embodiment, the image reconstructing means is mainly composed of the computer 6 and the control program and the storage section 10, and the image output means is the computer 6, the control program and the storage section. 10 and the monitor 14. The calculation processing for reconstructing an X-ray tomographic image by these image reconstructing means is as outlined above. However, in the embodiment apparatus, a configuration specific to the present invention is further added. The specific configuration will be specifically described.

That is, the image reconstructing means first executes a reconstruction process by a thinning process based on selected X-ray projection data selected every several (currently four) of all X-ray projection data. Then, a tentative X-ray tomographic image is obtained, which is an overall image even though the image is coarse. Since the X-ray projection data to be used is 1/4, a provisional X-ray tomographic image is obtained in about 1/4 of the time required to obtain a complete X-ray tomographic image.

On the other hand, while the X-ray tomographic image reconstruction processing is in progress, the data acquisition processing that is shorter than the reconstruction processing starts with the next X-ray tomographic image data acquisition. When the computer 6 receives the next acquisition start signal, the currently executing reconstruction processing is interrupted, and the temporary X-ray tomographic image is retained in the reconstructed image retaining memory area 23a shown in FIG. Then, the process proceeds to the reconstruction reconstruction process by the thinning process based on the newly acquired selected X-ray projection data.

On the other hand, the held provisional X-ray tomographic image is immediately displayed on the monitor 14 by the image output means. In the case of the embodiment, the respective reconstruction processes are interrupted one after another as described above, and the provisional X-ray tomographic images are stored in the memory areas 23b, 23c,... And displayed on the monitor 14 one by one. In addition, since the next acquisition start signal is not output for the last one, the reconstruction process is temporarily stopped at the stage where the reconstruction process by the thinning process is completed, the temporary X-ray tomographic image is held, and the monitor 14 To be displayed. And
After the last provisional X-ray tomographic image is displayed, the reconstruction processing interrupted so far is restarted, and the reconstruction processing is performed for each provisional X-ray tomographic image by the supplemental processing based on the remaining unselected X-ray projection data. To complete the complete X-ray tomographic image in order.

Next, the operation of the X-ray CT apparatus of the embodiment having the above-described configuration when X-ray tomography is performed will be described with reference to FIG. FIG. 5A shows the progress of data collection and image reconstruction by the apparatus of the embodiment.
FIG. 5B shows the progress of data collection and image reconstruction by the conventional one-by-one processing system, and FIG. 5C shows the progress of data collection and image reconstruction by the conventional parallel processing system. Here, a total of three X-ray tomographic images A to C are obtained one by one for three imaging sites of the subject M. First, after placing the subject M on the top 4, the top 4 is moved so that the first imaging region is aligned with the imaging position, and then the rotation of the imaging unit 3 is started.

After the rotation of the imaging unit 3 is stabilized, when an acquisition start signal is output to the computer 6 when the imaging unit 3 reaches the reference position for the first time, 720 acquisitions of X-ray projection data are performed. All 720 pieces of X-ray projection data Da required to obtain the X-ray tomographic image A (with various preliminary correction processes performed as necessary) are all stored in the memory area 21a.

Following the completion of the acquisition of the X-ray projection data Da, reconstruction processing by thinning processing based on the selected X-ray projection data selected every fourth is advanced using the memory area 22a, and the X-ray tomographic image is obtained. A provisional X-ray tomographic image of A is created.

On the other hand, with the completion of the data collection for the X-ray tomographic image A, the top 4 is moved again, and when the imaging part for the next X-ray tomographic image B is adjusted to the imaging position, the collection is performed. The start signal is output to the computer 6 and the acquisition of the X-ray projection data Da necessary for obtaining the X-ray tomographic image B is started.

The computer 6 receiving the collection start signal
Suspends the reconstruction processing of the X-ray tomographic image A, stores the temporary X-ray tomographic image in the memory area 23a, and immediately displays the temporary X-ray tomographic image on the screen of the monitor 14. The operator confirms that the X-ray tomographic image A of the desired part can be obtained from the temporary X-ray tomographic image displayed on the monitor 14. The provisional X-ray tomographic image is less dense than a complete X-ray tomographic image, but does not hinder whether or not a desired portion is correctly photographed.

With the completion of the collection of the X-ray projection data Da in the memory area 21b, reconstruction processing by thinning processing based on the selected X-ray projection data is performed in the memory area 22b.
And a tentative X-ray tomographic image of the X-ray tomographic image B is created.

On the other hand, with the completion of the data collection for the X-ray tomographic image B, the top board 4 is moved again, and when the imaging part for the next X-ray tomographic image C is adjusted to the imaging position, the collection is performed. The start signal is output to the computer 6 and the acquisition of the X-ray projection data Da necessary for obtaining the X-ray tomographic image C starts.

The computer 6 receiving the collection start signal
Suspends the reconstruction processing of the X-ray tomographic image B, stores the temporary X-ray tomographic image in the memory area 23b, and immediately displays the temporary X-ray tomographic image on the screen of the monitor 14. The operator confirms that an accurate X-ray tomographic image B can be obtained from the temporary X-ray tomographic image displayed on the monitor 14.

Further, with the completion of the collection of the X-ray projection data Da in the memory area 21c, reconstruction processing by thinning processing based on the selected X-ray projection data is performed in the memory area 22c.
When a temporary X-ray tomographic image is obtained by using b, it is immediately displayed on the monitor 14. The operator monitors 14
It is confirmed that an accurate X-ray tomographic image C can be obtained by the provisional X-ray tomographic image displayed in.

When the final tentative X-ray tomographic image is confirmed,
The subject M is lowered from the top 4. In the case of the apparatus according to the embodiment, the subject M is lowered from the top 4 by the arrow B in FIG.
This is the time point indicated by 1. On the other hand, in the case of the conventional one-by-one processing system, the subject M is dropped from the top 4
At the time indicated by arrow B2 in FIG. 5B, and in the case of the conventional parallel processing system, the subject M is lowered from the top 4 at the time indicated by arrow B3 in FIG. Yes, in all cases, the reconstruction processing is completed and complete X-ray tomographic images A to
This is after C was obtained. As described above, the apparatus of the embodiment confirms that an accurate X-ray tomographic image can be obtained by the provisional X-ray tomographic image, thereby moving the subject M to the top 4.
Since the subject M can be lowered earlier, the restraint time of the subject M is much shorter than in the conventional case.

The present invention is not limited to the above embodiment, but can be modified as follows. (1) In the above embodiment, a temporary X-ray tomographic image is obtained only based on the selected X-ray projection data, and then the provisional X-ray tomographic image is supplemented with the remaining unselected X-ray projection data to complete the processing. However, for example, convolution processing is first performed on all the X-ray projection data, and a temporary X-ray tomographic image is obtained using data that is randomly selected from all the convolution processing results. As a modified example, in the replenishment process, a back projection process based on the thinned convolution process result is performed, and only the back projection process is performed in a two-stage process.

Further, a thinned-out memory matrix consisting of only specific memory cells regularly extracted without using all the memory cells of the memory matrix 25 at the time of the back projection processing is set in the memory matrix 25, and the skipped memory matrix is set. As a modified example, a configuration in which a temporary X-ray tomographic image is obtained by storing data only in a cell and data is stored in a thinned-out memory cell in the replenishment process.

(2) In the above embodiment, the ratio of the selected X-ray projection data is 1/4, but the ratio of the selected X-ray projection data is not limited to 1/4. However, if the ratio of the selected X-ray projection data is too large, it takes a long time to obtain a temporary X-ray tomographic image. Therefore, the ratio of the selected X-ray projection data is within a range in which a reconstructed image having acceptable accuracy can be created. Is preferably minimized.

[0037]

According to the X-ray CT apparatus according to the first aspect of the present invention, it is confirmed that an accurate X-ray tomographic image can be obtained by obtaining and displaying a coarse image by thinning processing, and the reconstruction processing is completely completed. Because the configuration is such that the patient can be taken off the tabletop earlier than before, the restraint time of the subject at the time of imaging can be reduced because the timing of lowering the patient from the tabletop can be much earlier than before.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a main configuration of an X-ray CT apparatus according to an embodiment.

FIG. 2 is a graph showing X-ray projection data, a reconstruction function, and data subjected to convolution correction by the reconstruction function.

FIG. 3 is a schematic diagram illustrating a memory area division state in a storage unit of the embodiment device.

FIG. 4 is a schematic diagram showing a memory matrix configuration for back projection processing.

FIG. 5 is a diagram showing data collection by the embodiment apparatus and the conventional apparatus;
FIG. 7 is a sequence diagram showing the progress of image reconstruction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... X-ray tube 2 ... X-ray detection array 2a ... X-ray detection element 3 ... Imaging part 5 ... Imaging system rotation mechanism part 6 ... Computer 7 ... X-ray emission control part 8 ... DAS (data collection part) 10 ... Storage Part 14: Monitor

Claims (1)

[Claims] An imaging unit in which an X-ray generation unit and an X-ray detection unit are arranged to face each other across a subject;
The imaging system rotating means for rotating the imaging means around the body axis of the subject while maintaining the X-ray generation means and the X-ray detection means facing each other, and causing the X-ray generation means to perform X-ray beam irradiation X-ray irradiation control means, data collection means for collecting and storing transmitted X-ray detection signals output from the X-ray detection means in association with X-ray beam irradiation as X-ray projection data, and one X-ray tomographic image Start signal generation means for outputting an acquisition start signal for giving an imaging start timing for starting data collection for an image, and image reconstruction for reconstructing an X-ray tomographic image by computer arithmetic processing on the X-ray projection data collected and stored by the data acquisition means. And an image output unit for displaying a reconstructed X-ray tomographic image. X-ray CT the progress of reconstruction of X-ray tomographic image by reconstructing means is configured to be Kontoru
In the apparatus, the image reconstructing means first executes a reconstructing process by a thinning process based on the selected data which is discretely selected from the X-ray projection data stored in the data collecting means, and executes a coarse X-ray tomography. An image is reconstructed, the reconstruction process in progress is interrupted based on the next acquisition start signal, and a reconstruction process by thinning-out process for the next X-ray tomogram is performed while the X-ray tomogram being created is kept. Is performed, and reconstruction processing by thinning processing is performed for all X-ray tomographic images. Then, the reconstruction processing interrupted up to that point is resumed, and fine X
It is configured to complete line tomographic images in order, and
An X-ray CT apparatus, wherein the image output means is configured to immediately display a coarse X-ray tomographic image held during creation.