JP2002209884A - X-ray ct instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently perform photographing by helical scanning which is synchronized with a body movement phase. SOLUTION: Projection data of multiple views by an X-ray is obtained concerning an object by helical scanning (101), a periodical signal concerning a body movement object is obtained (111), projection data and the periodical signal are stored at each view (103) and the tomographic image of the object in a predetermined phase within the period of the periodical signal is reconstituted based on projection data (105).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an X-ray CT (Xr
More specifically, the present invention relates to an X-ray CT apparatus that captures a tomographic image in synchronization with a periodic body movement of an imaging target.

[0002]

2. Description of the Related Art In an X-ray CT apparatus, transmitted X-ray data of a plurality of views is acquired for an object to be imaged by an X-ray irradiating / detecting apparatus, and an image reconstructing apparatus acquires the object based on the transmitted X-ray data. Reconstruct a tomographic image.

The X-ray irradiator forms a cone-shaped X-ray beam emitted from a focal point of an X-ray tube into a fan-shaped X-ray beam by a collimator and irradiates the X-ray beam to an imaging space.

The X-ray detecting device is a multi-channel device in which a large number of X-ray detecting elements are arranged in an array along a fan-shaped spread of an X-ray beam. ) Is detected by the X-ray detector.
Such an X-ray irradiation / detection device is rotated (scanned) around an object to acquire transmission X-ray data of a plurality of views.

A so-called helical scan is performed by turning the X-ray irradiation / detection device along a spiral orbit. In the helical scan, the object is continuously scanned over a predetermined length in the body axis direction. Therefore, a plurality of tomographic images having different slice positions on the body axis are obtained based on the acquired transmission X-ray data. Can be reconfigured.

[0006] By utilizing such features of the helical scan, a plurality of tomographic images having different slice positions are photographed over the entire length of the heart. Since the heart of a living body is beating, the cross-sectional shape of the heart changes periodically.
Therefore, in order to have consistency among a plurality of tomographic images at different slice positions, all of the plurality of tomographic images are tomographic images having the same phase in the heartbeat cycle.

A technique for obtaining such a tomographic image will be described with reference to FIG. (1) of the figure is a time chart of a heartbeat signal. The heartbeat signal is represented by the R wave of the electrocardiographic signal. The period Tr of R wave generation, that is, the heartbeat period is 500 to 1500 ms.

The phase at a time point Ts after the peak of the R wave is set by the photographer as the phase of the tomographic image. When capturing a tomographic image of the diastole of the heart, the time Ts is set to, for example, 700 ms.

FIG. 2B is a time chart of the helical scan. The cycle of one turn of the helical scan is T
p. The turning cycle Tp is determined by the rotation speed of the X-ray irradiation / detection device, and is about 500 to 1500 ms.

One turn gives 360 ° of projection data. With the progress of the helical scan, projection data for a plurality of turns is obtained. Each projection data has a different position on the body axis. Each projection data also has a different phase.

FIG. 3 (3) is a time chart of image reconstruction. A plurality of vertical lines on the time axis respectively represent time phases of a plurality of reconstructed images. Image reconstruction is a so-called retrospective reconstruction (retroscopic).
restructuring).

[0012] Retrospective reconstruction means that all projection data already obtained by scanning is once transferred to, for example, an HD.
D (Hard Disk Drive) or other memory (m
This is a method of reconstructing a tomographic image by reading out necessary projection data groups from them again. Hereinafter, the retrospective reconstruction is also called retrorecon.

In the retro recon, tomographic images having different time phases can be obtained by changing the configuration of the projection data group used for image reconstruction.
A plurality of tomographic images having a time phase difference corresponding to 10 can be respectively reconstructed.

In such a plurality of tomographic images, a tomographic image I1 having a time phase coincident with a time t1 after a time Ts from the first R wave includes a time t2 after a time Ts from the second R wave. Time T from the tomographic image I2 and the third R wave having the same time phase
Since a tomographic image I3 having a time phase coincident with the time t3 after s is included, a plurality of tomographic images having different positions on the body axis are obtained for the heart in the diastole by extracting these images. be able to.

[0015]

The above-described photographing is inefficient because it is necessary to reconstruct 10 or more times the number of images actually required. Further, since a large number of tomographic images are reconstructed, the time spent for image reconstruction becomes long.

Accordingly, an object of the present invention is to provide an X-ray C-light source for efficiently performing imaging by helical scan synchronized with a body motion phase.
The realization of a T device.

[0017]

(1) In one aspect of the invention for solving the above-mentioned problems, the present invention provides a method of forming a plurality of X-ray views of an object along a spiral trajectory surrounding the object. Means for obtaining projection data; means for obtaining a periodic signal relating to body movement of the subject;
Means for storing the projection data and the periodic signal for each view, and reconstructing the tomographic image of the object at a predetermined phase within a period of the periodic signal based on the stored projection data X-ray CT apparatus.

(2) According to another aspect of the present invention, there is provided a projection apparatus for acquiring projection data of a plurality of views of an object by X-rays along a spiral trajectory surrounding the object. A data acquisition device, a periodic signal acquisition device that acquires a periodic signal related to the body movement of the subject, a storage device that stores the projection data and the periodic signal for each view, and based on the stored projection data. An X-ray CT apparatus, comprising: a tomographic image reconstructing apparatus configured to reconstruct the tomographic image of the target at a predetermined phase within the period of the periodic signal.

(3) According to another aspect of the present invention, there is provided an X-ray irradiating apparatus for irradiating a fan-shaped X-ray beam, and a plurality of X-ray detecting elements. It is arranged in the direction of spread, and the X
Projecting a plurality of views of the object by rotating a detector facing the X-ray irradiation device and an X-ray irradiation / detection system including the X-ray irradiation device and the detector along a spiral trajectory around the object; A projection data acquisition device for acquiring data, a periodic signal acquisition device for acquiring a periodic signal related to the body movement of the object, a storage device for storing the projection data and the periodic signal for each view, A tomographic image reconstruction device for reconstructing the tomographic image of the object at a predetermined phase within the cycle of the periodic signal based on projection data.
Device.

(4) According to another aspect of the present invention, there is provided an X-ray irradiating apparatus for irradiating a fan-shaped X-ray beam, and a plurality of X-ray detecting elements. A plurality of detector element arrays arranged in the direction of spread are arranged in the direction of the thickness of the fan-shaped X-ray beam, and the detector faces the X-ray irradiator with an imaging target interposed therebetween, X
A projection data acquisition apparatus for rotating an X-ray irradiation / detection system including a X-ray irradiation apparatus and the detector along a spiral trajectory around the object to acquire projection data of a plurality of views of the object; A periodic signal acquisition device that acquires a periodic signal related to body movement, a storage device that stores the projection data and the periodic signal for each view, and a period of the periodic signal based on the stored projection data. And a tomographic image reconstructing device for reconstructing the tomographic image of the object at a predetermined phase of the X-ray CT apparatus.

(5) According to another aspect of the present invention, there is provided an X-ray irradiating apparatus for irradiating a fan-shaped X-ray beam, and a plurality of X-ray detecting elements. Two detector element arrays arranged in the direction of spread are arranged in the direction of the thickness of the fan-shaped X-ray beam, and the detector faces the X-ray irradiator with an imaging target interposed therebetween; A projection data acquisition device configured to rotate an X-ray irradiation / detection system including the X-ray irradiation device and the detector along a spiral trajectory around the object to acquire projection data of a plurality of views of the object; A periodic signal acquisition device for acquiring a periodic signal relating to a body movement of a target, a storage device for storing the projection data and the periodic signal for each view, and a sum of projection data respectively acquired through the two detection element arrays Based on previous And tomographic image reconstruction device for reconstructing a tomographic image of the object in the predetermined phase in the period of the periodic signal, an X-ray CT apparatus characterized by comprising a.

In the invention according to each of the aspects (1) to (5), the projection data and the periodic signal are stored for each view, and based on the stored data, the tomographic image of the target at a predetermined phase in the cycle is stored. Is reconstructed, it is possible to efficiently perform imaging by helical scan synchronized with the body motion phase.

(6) According to another aspect of the invention for solving the above-mentioned problem, the present invention is to acquire projection data of a plurality of views of an object by X-rays along a spiral trajectory surrounding the object. Means for acquiring a periodic signal relating to body movement of the object, means for storing information associating view information of the projection data with the periodic signal, and the acquired projection data Means for reconstructing the tomographic image of the object at a predetermined phase within the period of the periodic signal based on the stored information. .

(7) According to another aspect of the present invention, there is provided a projection apparatus for acquiring projection data of a plurality of views of an object by X-rays along a spiral trajectory surrounding the object. A data acquisition device, a periodic signal acquisition device that acquires a periodic signal related to the body movement of the subject, a storage device that stores information that associates the view information of the projection data with the periodic signal, A tomographic image reconstruction device that reconstructs the target tomographic image at a predetermined phase within a cycle of the periodic signal based on the projection data and the stored information. It is a CT device.

(8) According to another aspect of the present invention, there is provided an X-ray irradiating apparatus for irradiating a fan-shaped X-ray beam, and a plurality of X-ray detecting elements. It is arranged in the direction of spread, and the X
Projecting a plurality of views of the object by rotating a detector facing the X-ray irradiation device and an X-ray irradiation / detection system including the X-ray irradiation device and the detector along a spiral trajectory around the object; A projection data acquisition device for acquiring data; a periodic signal acquisition device for acquiring a periodic signal relating to the body movement of the object; and a storage device for storing information that associates the view information of the projection data with the periodic signal. And a tomographic image reconstruction apparatus that reconstructs the target tomographic image at a predetermined phase within a cycle of the periodic signal based on the acquired projection data and the stored information,
An X-ray CT apparatus comprising:

(9) According to another aspect of the present invention, there is provided an X-ray irradiating apparatus for irradiating a fan-shaped X-ray beam, and a plurality of X-ray detecting elements. A plurality of detector element arrays arranged in the direction of spread are arranged in the direction of the thickness of the fan-shaped X-ray beam, and the detector faces the X-ray irradiator with an imaging target interposed therebetween, X
A projection data acquisition apparatus for rotating an X-ray irradiation / detection system including a X-ray irradiation apparatus and the detector along a spiral trajectory around the object to acquire projection data of a plurality of views of the object; A periodic signal acquisition device for acquiring a periodic signal related to body movement, a storage device for storing information that associates the view information of the projection data with the periodic signal, and the acquired projection data and the stored information. And a tomographic image reconstructing device for reconstructing the tomographic image of the target at a predetermined phase within the cycle of the periodic signal based on the tomographic image.

(10) According to another aspect of the present invention, there is provided an X-ray irradiating apparatus for irradiating a fan-shaped X-ray beam, and a plurality of X-ray detecting elements. The detection element array arranged in the direction of spread is
Two detectors arranged in the direction of the thickness of the X-ray beam, the detector being opposed to the X-ray irradiator with the object to be imaged therebetween;
A projection data acquisition apparatus for rotating an X-ray irradiation / detection system including a X-ray irradiation apparatus and the detector along a spiral trajectory around the object to acquire projection data of a plurality of views of the object; A periodic signal acquisition device for acquiring a periodic signal relating to the body movement of the subject, a storage device for storing information in which the view signal of the projection data is associated with the periodic signal, and a storage device for acquiring the periodic signal. A tomographic image reconstruction device that reconstructs the tomographic image of the target at a predetermined phase within the cycle of the periodic signal based on the sum of the projection data and the stored information. It is an X-ray CT apparatus.

In the invention according to each of the above-mentioned aspects (6) to (10), information in which view information of projection data is associated with a periodic signal is stored, and based on the information and the projection data, information in advance in a cycle is stored. Since the tomographic image of the object at the determined phase is reconstructed, it is possible to efficiently perform imaging by helical scan synchronized with the body motion phase.

According to the invention in each of the above aspects, it is preferable to calculate the average period of the periodic signal in terms of facilitating the setting of the phase of the tomographic image to be reconstructed. In that case, displaying the calculated average period is preferable in that the setting of the phase of the tomographic image is further facilitated.

In this case, it is preferable to predict the number of tomographic images to be reconstructed on the basis of the duration and average period of acquisition of projection data, in terms of securing an area for storing tomographic images in advance.

In the invention according to each of the above aspects, calculating the average period of the periodic signal is advantageous in that the number of tomographic images to be reconstructed is determined and the area for storing the tomographic images is easily determined. preferable.

In this case, it is preferable to display the calculated average period in order to make it easier to confirm normal / abnormal of the periodic signal and to confirm the phase setting of the tomographic image. In that case, it is preferable to predict an area to be reserved for storing the projection data based on the average cycle in order to facilitate management of the area for storing the projection data.

According to the invention in each of the above aspects, by using the heartbeat signal as the periodic signal, it is possible to efficiently perform imaging by helical scan synchronized with the heartbeat phase.

[0034]

Embodiments of the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiment. FIG. 1 shows a block diagram of the X-ray CT apparatus. This device is an example of an embodiment of the present invention. The configuration of the present apparatus shows an example of an embodiment relating to the apparatus of the present invention.

As shown in FIG. 1, this apparatus comprises a scanning gantry 2 and a photographing table.
4, an operation console (console) 6 and a periodic signal detecting device 8 are provided.

The scanning gantry 2 has an X-ray tube 20. X
The X-rays (not shown) emitted from the ray tube 20 are shaped by the collimator 22 into, for example, a fan-shaped X-ray beam, that is, a fan beam, and irradiated to the detector 24. The portion including the X-ray tube 20 and the collimator 22 is an example of the embodiment of the X-ray irradiation device according to the present invention. The scanning gantry 2 is an example of an embodiment of the projection data acquisition device according to the present invention.

The detector 24 includes a plurality of X-rays arranged in an array in the direction of the spread of the fan-shaped X-ray beam.
It has a line detection element. The detector 24 is an example of the embodiment of the detector according to the present invention. The configuration of the detector 24 will be described later. The X-ray tube 20, collimator 22, and detector 24 constitute an X-ray irradiation / detection device. The X-ray irradiation / detection device will be described later.

The detector 24 is connected to a data collection unit 26. The data collection unit 26 collects detection data of individual X-ray detection elements of the detector 24. X from X-ray tube 20
Irradiation of X-rays is performed by an X-ray controller
r) controlled by 28. The illustration of the connection relationship between the X-ray tube 20 and the X-ray controller 28 is omitted. The collimator 22 is controlled by a collimator controller 30. The illustration of the connection relationship between the collimator 22 and the collimator controller 30 is omitted.

The components from the X-ray tube 20 to the collimator controller 30 are mounted on the rotating unit 34 of the scanning gantry 2. The rotation of the rotation unit 34 is controlled by a rotation controller 36. The illustration of the connection relationship between the rotation unit 34 and the rotation controller 36 is omitted.

The photographing table 4 carries in and out a photographing target (not shown) into and out of the X-ray irradiation space of the scanning gantry 2. The relationship between the object and the X-ray irradiation space will be described later.

The periodic signal detecting device 8 detects a periodic signal such as a heartbeat signal and a respiratory signal relating to the body movement of the subject to be imaged. The periodic signal detection device 8 is configured using, for example, an electrocardiograph, a respiration monitor (monitor), or the like. The periodic signal detection device 8 is an example of an embodiment of the periodic signal acquisition device according to the present invention.

The operation console 6 has a data processing device 60. The data processing device 60 is constituted by, for example, a computer. The data processing device 60 includes a control interface (interfa).
ce) 62 is connected. Control interface 62
Is connected to the scanning gantry 2 and the imaging table 4. The data processing device 60 controls the scanning gantry 2 and the imaging table 4 through the control interface 62.

The data collection unit 26 in the scanning gantry 2, X
The line controller 28, collimator controller 30, and rotation controller 36 are controlled through a control interface 62. It should be noted that illustration of individual connections between these units and the control interface 62 is omitted.

The data processing device 60 is also connected to a data collection buffer 64. The data collection buffer 64 is connected to the data collection unit 26 of the scanning gantry 2 and the periodic signal detection device 8. Data collection unit 2
The data collected in 6 and the periodic signal detected by the periodic signal detection device 8 are input to the data processing device 60 through the data collection buffer 64.

The data processing device 60 performs image reconstruction using the transmission X-ray data of a plurality of views collected through the data collection buffer 64. Image reconstruction includes, for example, filtered back projection (filtered back projection).
A back projection method or the like is used. The data processing device 60 is an example of an embodiment of the tomographic image reconstruction device according to the present invention.

A storage device 66 is connected to the data processing device 60. The storage device 66 stores various data, reconstructed images, programs for realizing the functions of the present device, and the like. Storage device 66
Is an example of an embodiment of a storage device according to the present invention.

A display device 68 and an operation device 70 are connected to the data processing device 60, respectively. The display device 68 displays the reconstructed image output from the data processing device 60 and other information. The operation device 70 is operated by a user and inputs various instructions and information to the data processing device 60. The user uses the display device 68 and the operation device 70 to interactively operate (interact).
ive).

FIG. 2 shows a schematic configuration of an example of the detector 24. As shown in the figure, the detector 24 is a multi-channel X-ray detector in which a plurality of X-ray detection elements 24 (i) are arranged in an array.

The plurality of X-ray detecting elements 24 (i) form an X-ray incident surface curved in a cylindrical concave shape as a whole. i
Is a channel number, for example, i = 1 to 1000. The X-ray detection element 24 (i) includes, for example, a scintillator and a photodiode (p).
photo diode). The present invention is not limited to this, and may be, for example, a semiconductor X-ray detection element using cadmium tellurium (CdTe) or the like, or an ionization box type X-ray detection element using Xe gas (gas).

FIG. 3 shows an interrelationship between the X-ray tube 20, the collimator 22, and the detector 24 in the X-ray irradiation / detection apparatus. FIG. 3A is a diagram illustrating a state of the scanning gantry 2 viewed from the front, and FIG. 3B is a diagram illustrating a state of the scanning gantry 2 viewed from the side. As shown in FIG.
The line is shaped into a fan-shaped X-ray beam 400 by the collimator 22 and is applied to the detector 24.

FIG. 3A shows a fan-shaped X-ray beam 40.
Indicates a spread of 0. The spreading direction of the X-ray beam 400 is
It matches the arrangement direction of the channels in the detector 24.
(B) shows the thickness of the X-ray beam 400.

With the body axis intersecting the fan surface of the X-ray beam 400, for example, as shown in FIG. 4, the object 8 placed on the imaging table 4 is carried into the X-ray irradiation space. The scanning gantry 2 has a cylindrical structure including an X-ray irradiation / detection device inside.

The X-ray irradiation space is formed inside the cylindrical structure of the scanning gantry 2. An image of the object 8 sliced by the X-ray beam 400 is projected on the detector 24. The detector 24 detects X-rays transmitted through the object 8. The thickness th of the X-ray beam 400 applied to the object 8 is
It is adjusted by the opening of the aperture of the collimator 22.

The X-ray irradiation / detection device including the X-ray tube 20, the collimator 22, and the detector 24 continuously rotates (scans) around the body axis of the object 8 while maintaining their mutual relationship. In parallel with the rotation of the X-ray irradiation / detection device, the imaging table 4 is continuously moved in the body axis direction of the object 8 as indicated by an arrow. As a result, the X-ray irradiation / detection device relatively turns with respect to the target 8 along a spiral trajectory surrounding the target 8, and a so-called helical scan is performed.

Projection data of a plurality of views (for example, about 1000) is acquired per one turn of the helical scan. The collection of the projection data is performed by the detector 24-the data collection unit 2.
6- Performed by the system of the data collection buffer 64.

Based on the projection data collected in the data collection buffer 64, the data processing device 60 performs reconstruction of a tomographic image, that is, image reconstruction. Image reconstruction is
The projection data of, for example, 1000 views obtained by one rotation scan is converted into, for example, a filtered back-projection (filtered back-projection).
on) method.

FIGS. 5 and 6 show more detailed schematic views of the state of irradiation of the detector 24 with the X-ray beam 400. FIG.
As shown in FIG. 5, by displacing the collimator pieces 220 and 222 in the collimator 22 in a direction to narrow the aperture, the slice thickness th of the projected images on the X-ray detectors 242 and 244 is reduced.

Also, as shown in FIG.
By moving 0,222 in the direction in which the aperture is widened, the slice thickness th of the projected image is increased. Such slice thickness adjustment is performed by the collimator controller 30 under the control of the data processing device 60.

FIG. 7 shows a schematic configuration of another example of the detector 24. As shown in the figure, the detector 24 is a multi-channel X-ray detector in which a plurality of X-ray detection elements 24 (ik) are arranged in an array.

The plurality of X-ray detecting elements 24 (ik) form an X-ray incident surface curved in a cylindrical concave shape as a whole.
i is a channel number, for example, i = 1 to 1000. k is a column number, for example, k = 1, 2. The X-ray detection elements 24 (ik) have the same column number k and constitute a detection element row.

The number of detectors 24 is not limited to two. For example, four or more detectors as shown in FIG. 8 may be divided into two groups in the k direction. Hereinafter, an example in which the detector 24 has two rows will be described, but the same applies to a case where a multi-row detector is divided into two groups.

FIG. 9 shows X when the detectors 24 are arranged in two rows.
X-ray tube 20 and collimator 22 in X-ray irradiation / detection device
And the interrelation of the detector 24. FIG. 2A is a diagram showing a state when viewed from the front of the scanning gantry 2, and FIG. 2B is a diagram showing a state when viewed from the side. FIG. 9 is similar to FIG. 3 except that the detectors 24 are in two rows. Note that the thickness direction of the X-ray beam 400 coincides with the direction in which the rows are arranged in the detector 24 (k direction).

With the body axis intersecting the fan surface of the X-ray beam 400, for example, as shown in FIG. 10, the object 8 placed on the imaging table 4 is carried into the X-ray irradiation space.
FIG. 10 is similar to FIG. 4 except that the detectors 24 are in two rows. The two rows of detectors 24 detect X-rays transmitted through the object 8 for two slices. The thickness th of the two-slice X-ray beam 400 that irradiates the target 8 is adjusted by the aperture of the collimator 22.

The X-ray irradiating / detecting device including the X-ray tube 20, the collimator 22, and the detector 24 performs a helical scan around the body axis of the object 8 while maintaining the mutual relationship. Projection data for two slices of a plurality of views (for example, about 1000) is acquired per one rotation of the scan. The collection of the projection data is performed by the detector 24-the data collection unit 2.
6- Performed by the system of the data collection buffer 64.

Based on the projection data of two slices collected in the data collection buffer 64, the data processing device 60
Thus, reconstruction of a tomographic image for two slices, that is, image reconstruction is performed. Image reconstruction is performed, for example, by processing projection data of, for example, 1000 views obtained by one scan of scanning by, for example, a filtered back projection method.

FIGS. 11 and 12 show more detailed schematic views of the state of irradiation of the detector 24 with the X-ray beam 400. FIG. As shown in FIG. 11, the slice thickness th of the projected images on the X-ray detectors 242 and 244 is reduced by displacing the collimator pieces 220 and 222 in the collimator 22 in a direction to narrow the aperture.

Also, as shown in FIG.
The slice thickness th of the projected image is increased by moving 20, 22 in the direction in which the aperture is expanded. Such slice thickness adjustment is performed by the collimator controller 30 under the control of the data processing device 60.

FIG. 13 shows a block diagram of the present apparatus from the viewpoint of capturing a tomographic image of the heart synchronized with the heartbeat phase. As shown in the figure, the present apparatus has a projection data acquisition unit 101. The projection data acquisition unit 101 corresponds to the scanning gantry 2 and acquires projection data of the target 8 by helical scan.

The projection data is input to the data storage unit 103. The data storage unit 103 corresponds to a part of the storage device 66 and stores projection data. Image reconstruction unit 105
Reads the projection data from the data storage unit 103 and reconstructs a tomographic image using the projection data. The image reconstruction unit 105 corresponds to a part of the function of the data processing device 60.

The phase setting section 107 includes an image reconstructing section 105
Sets the phase of the tomographic image to be reconstructed. The phase is set by the user as the phase in the cardiac cycle. The image reconstruction unit 105 corresponds to the operation device 70.

The image storage unit 109 stores the tomographic image reconstructed by the image reconstructing unit 105. The image storage unit 109 corresponds to a part of the storage device 66. The heartbeat detection unit 111 is the target 8
And outputs a heartbeat signal. Heartbeat detection unit 11
1 corresponds to the periodic signal detection device 8. The heartbeat signal is, for example, a signal as shown in FIG. That is, as shown in (2) of the figure, a pulse (pulse) signal corresponding to the R wave of the electrocardiographic signal corresponds to the electrocardiographic signal as shown in (1) of FIG.

The heartbeat signal is input to the average period calculation section 113 and the data storage section 103. The heart rate signal is stored in the data storage unit 103 as a pair with the projection data. FIG. 15 conceptually shows how the data storage unit 103 stores projection data and heartbeat signals. As shown in the figure, a part of a view channel plane for storing projection data includes:
An area for storing a heartbeat signal, that is, the presence or absence of an R wave is provided for each view, and the heartbeat signal is stored in this area in association with projection data for each view.

The time difference between the views is a constant value such as 1 ms determined by the view timing. Therefore, for example, the state of the heartbeat signal every 1 ms is stored.
The heartbeat signal is “1” at a portion where a pulse is generated, and is “0” at other portions. As a result, the generation time of the R wave can be known from the view number in which “1” is stored.

The heartbeat signal may be stored separately from the view channel plane. In this case, for example, as shown in FIG. 16, the logical value of the heartbeat signal in the view is stored in a pair with the view number. From such information, the generation point of the R wave can be known from the view number in which “1” is stored.

By storing the heartbeat signal separately, the view channel plane is a view channel plane that does not store the heartbeat signal, as shown in FIG. 17, for example. In this case, the view numbers k,
It is preferable to store l in order to clarify the correspondence with the view numbers k and l in the heartbeat signal storage area shown in FIG.

When a detector array having two detector rows is used, a view channel plane is provided for each detector row. The heartbeat signal is stored in each of the view channel planes, or is stored in one of the view channel planes.

Alternatively, as shown in FIG. 16, it goes without saying that the information may be stored separately from the view channel plane. It is preferable to store the heart rate signal separately from the view channel plane in that only one heartbeat signal storage area is required regardless of the number of view channel planes.

When a detector array having two detection element arrays is used, for example, as shown in FIG. 18, an addition unit 1 is provided between the projection data acquisition unit 101 and the data storage unit 103.
21 is added, and the addition unit 121 adds the projection data of the same view of the plurality of detection element rows for each same channel,
This addition value may be stored in the data storage unit 103. Thus, the number of view channel planes can be reduced to one. The adding unit 121 is a data processing device 60
It is realized by the function of.

The average period calculator 113 calculates the average period of the heartbeat. The average period is obtained by averaging the periods of a plurality of heartbeats such as the latest four heartbeats. The average period calculator 113 is realized by the function of the data processing device 60. The average period calculator 113 is an example of an embodiment of the period calculator according to the present invention.

The average period of the heartbeat is displayed on the display unit 115. The display unit 115 corresponds to the display device 68. Thereby, for example, the average period of the heartbeat can be displayed on the CRT. The display unit 115 is an example of an embodiment of the periodic display device according to the present invention.

The average period is input to the image number prediction unit 117. The number-of-images prediction unit 117 predicts the number of photographed tomographic images by calculation. For example, the following calculation formula is used for the number prediction.

[0082]

(Equation 1)

Here, Ttotal: helical scan time Tr: average heartbeat period Cg: coefficient The coefficient Cg is for giving a margin to the predicted number of sheets. Because of this allowance, it is possible to cope with a case where the heart rate of the patient becomes faster during the scan. The image number prediction unit 117 is an example of an embodiment of the tomographic image number prediction device according to the present invention. The image number prediction unit 117 is realized by the function of the data processing device 60.

The predicted number is input to the area management unit 119. The area management unit 119 performs area management such as securing an image storage area in the image storage unit 109 in advance in accordance with the input predicted number of sheets. The area management unit 119 is realized by the function of the data processing device 60.

The operation of the present apparatus will be described. FIG. 19 shows a flow chart of the operation of the present apparatus. As shown in the figure, in step 702, a heartbeat cycle calculation is performed. The heartbeat cycle calculation is performed by the average cycle calculation unit 113. For example, the average cycle of the latest four heartbeats is obtained as the heartbeat cycle.

Next, at step 702, a heartbeat period is displayed. The heartbeat cycle is performed by the display unit 115.
The displayed heartbeat cycle is the average cycle of the latest four heartbeats. Next, in step 704, photographing conditions are set. The photographing condition setting is performed by the user through the operation device 70. The imaging conditions include tube voltage, tube current, slice thickness (about 2 to 4 mm), scan time (scan time)
e), a scan pitch (about 1.0), a scan range, a phase of a tomographic image, and the like are set.

The scan time is 1 for the X-ray irradiation / detection device.
It is time to rotate. The scan pitch is a moving distance of the imaging table 4 during one rotation of the X-ray irradiation / detection device. Normally, the scan pitch is set to be equal to the slice thickness (scan pitch 1.0). 2 detection element rows
In the case of a row, twice the slice thickness is set as the scan pitch.

In setting the phase of the tomographic image, the user refers to the heartbeat cycle displayed on the display unit 115 and sets the phase based on the reference. Since the displayed cardiac cycle is the average cycle, the phase of the tomographic image can be easily set by referring to the average cycle.

The phase is set, for example, by the delay time of the heartbeat signal from the R wave. When capturing a tomographic image during the diastole, the delay time is, for example, 700 ms. The delay time is additionally 700 ± 50 ms to 700 ± 100 m
Two or four times of about s may be set. This is preferable in that an optimum phase can be selected again from the reconstructed tomographic images.

The delay time may be set as a percentage of the cardiac cycle. In that case, for example, delay time 8
0% is set. In addition, 80 ± 5% to 8
Of course, two or four times of about 0 ± 10% may be set.

When capturing tomographic images of other phases,
An appropriate delay time is similarly set according to a desired phase. Next, in step 708, the number of images is predicted. The image number prediction is performed by the image number prediction unit 117 using the above equation. The helical scan time Ttotal in the above equation is naturally determined according to the slice thickness, scan time, scan pitch, and scan range.

Next, at step 710, a storage area is secured. The storage area is secured by the area management unit 119 based on the predicted number of images. As a result, the storage area is appropriately secured.

Next, at step 712, a helical scan is performed. The projection data obtained by the helical scan is stored in the data storage unit 103 together with the heartbeat signal. The stored data is shown in FIGS.
The view channel plane and the like shown in FIG.

When the detector 24 has two detection element arrays, a view channel plane is formed for each of the detection element arrays. When the projection data of the two detection element arrays are added in advance by the adder 121 and stored, the number of view channel planes is one regardless of the number of the detection element arrays.

Next, in step 714, image reconstruction is performed. Image reconstruction is performed by the image reconstruction unit 105. Image reconstruction is performed in parallel with the helical scan. Alternatively, reconstruction may be performed by retro-con after completion of the helical scan. The image reconstruction performed in parallel with the helical scan is a prospective reconstruction (prospective reconstruction).
on). Prospective reconstruction is a so-called prospective recon.

In the reconstruction, a segment recon (segment r) using projection data of 180 ° + α is used.
With the use of (construction), the time resolution of the obtained tomographic image is improved. Here, α is the opening angle of the fan-shaped X-ray beam, that is, the so-called fan angle (fan)
angle).

The image reconstruction in step 714 will be described with reference to FIG. (1) of the figure is a time chart of the heartbeat signal. The heartbeat signal represents the R wave of the electrocardiographic signal. The cardiac cycle is Tr (for example, 800 ms).
The phase after the time Ts (for example, 700 ms) from the generation of the R wave is set as the phase of the tomographic image.

As a result, the tomographic image to be reconstructed first becomes the tomographic image of the time phase at time t1 on the time axis. The second tomographic image to be reconstructed is the time t on the time axis.
2 is a tomographic image of the time phase. The third tomographic image to be reconstructed is a time-phase tomographic image at time t3 on the time axis. Similarly, the time phases of other tomographic images are sequentially determined in the same manner.
Each tomographic image is a tomographic image having the same phase at different positions on the body axis.

(2) is a time chart of the helical scan. One turn time of the helical scan is Tp. This corresponds to the scan time. 36 at time Tp
The projection data for 0 ° is obtained.

(3) is a time chart of image reconstruction. The tomographic image I1 of the time phase at the time t1 is reconstructed based on a projection data group obtained in a predetermined time zone centered on the time t1, as shown by oblique lines. The tomographic image I2 in the time phase at the time t2 is reconstructed based on a projection data group obtained in a predetermined time zone around the time t2 as shown by oblique lines. The tomographic image I3 of the time phase at the time t3 is reconstructed based on a projection data group obtained in a predetermined time zone around the time t3 as shown by oblique lines. The same applies to the subsequent tomographic images.

In order to improve the time resolution of a tomographic image, the projection data group is not data for 360 ° but 18 data.
So-called half scan data using projection data of 0 ° + fan angle is used. That is, as shown in FIG. 21, the heartbeat signal (R
In the view channel plane storing the projection data and the projection data, the tomographic image I1 is reconstructed by using a projection data group (shaded portion) corresponding to a half scan centered on the view v1 after Ts from the first R wave. A tomographic image I2 is reconstructed using a projection data group (hatched portion) for a half scan centered on the view v2 after Ts from the second R wave, and the third R wave
A tomographic image I3 is reconstructed using a projection data group (shaded portion) for half scan centering on the view v3 Ts after the wave. Subsequent reconstruction of the tomographic image follows this.

When there are two systems of view channel planes corresponding to two detection element arrays, the same reconstruction is performed using the sum of the projection data of both systems. The projection data group for half scan is a projection data group for 180 ° + fan angle. The projection data group multiplied by a predetermined weight coefficient is used for reconstructing a tomographic image.

FIG. 22 shows an example of the weighting factor as a distribution in the view channel plane. As shown in the drawing, the first view in the projection data group for 180 ° + fan angle is va, the last view is vd, the view after the fan angle fan angle from va is vb, and the fan angle fan angle from vd is vb. Assuming that the previous view is vc, in the views from va to vb, as the view number increases, the number of channels of data multiplied by a weighting factor of 1 is sequentially increased from the first channel, and the weight of other data is set to 0. And so on. vb + 1 to vc
In views up to -1, the weight of all data is set to 1. v
In views from c to vd, as the view number increases, the number of data channels to be multiplied by a weighting factor of 0 is sequentially increased from the first channel, and the weight of other data is set to 1. By performing such weighting, a tomographic image with good time resolution can be reconstructed from the projection data group for half scan.

As described above, since only the set tomographic image is reconstructed and a large number of tomographic images are not reconstructed unlike the conventional art, efficient image reconstruction can be performed. it can.

The reconstructed tomographic image is displayed and stored in step 716. Thereby, the tomographic image is displayed on the display device 68 and the image storage unit 10 is displayed.
9 is stored.

In the above, an example in which a tomographic image synchronized with a heartbeat phase is captured based on a heartbeat signal has been described. However, by using a respiration signal instead of a heartbeat signal, it is possible to capture a tomographic image synchronized with a respiration phase. It goes without saying that you can do it.

In the above description, the latest four heartbeats are used to determine the average period of the heartbeat signal. However, it is of course possible to keep the average period in real time and use the average heartbeat period for a longer time. It is.

Although the present invention has been described based on the preferred embodiments, those skilled in the art to which the present invention pertains may use the techniques of the present invention for the above embodiments. Various changes and substitutions can be made without departing from the scope. Therefore, the technical scope of the present invention includes not only the above-described embodiments but also all the embodiments belonging to the claims.

[0109]

As described above in detail, according to the present invention, it is possible to realize an X-ray CT apparatus that efficiently performs helical scan imaging synchronized with a body movement phase.

[Brief description of the drawings]

FIG. 1 is a block diagram of a device according to an example of an embodiment of the present invention.

FIG. 2 is a schematic view of a detector array in the apparatus shown in FIG.

FIG. 3 is a schematic diagram of an X-ray irradiation / detection device in the device shown in FIG.

FIG. 4 is a schematic view of an X-ray irradiation / detection device in the device shown in FIG.

FIG. 5 is a schematic diagram of an X-ray irradiation / detection device in the device shown in FIG.

6 is a schematic diagram of an X-ray irradiation / detection device in the device shown in FIG.

FIG. 7 is a schematic diagram of a detector array in the device shown in FIG.

FIG. 8 is a schematic view of a detector array in the apparatus shown in FIG.

FIG. 9 is a schematic diagram of an X-ray irradiation / detection device in the device shown in FIG.

10 is a schematic diagram of an X-ray irradiation / detection device in the device shown in FIG.

11 is a schematic diagram of an X-ray irradiation / detection device in the device shown in FIG.

12 is a schematic diagram of an X-ray irradiation / detection device in the device shown in FIG.

FIG. 13 is a block diagram of an apparatus according to an embodiment of the present invention.

FIG. 14 is a graph showing a relationship between an electrocardiographic signal and a heartbeat signal.

FIG. 15 is a conceptual diagram of a view channel plane.

FIG. 16 is a conceptual diagram of a heartbeat signal storage area.

FIG. 17 is a conceptual diagram of a view channel plane.

FIG. 18 is a block diagram of an apparatus according to an embodiment of the present invention.

FIG. 19 is a flowchart showing an operation of the apparatus according to the embodiment of the present invention;

FIG. 20 is a time chart of the operation of the apparatus according to an embodiment of the present invention.

FIG. 21 is a conceptual diagram of a view channel plane.

FIG. 22 is a diagram illustrating weighting of projection data.

FIG. 23 is a time chart of heartbeat phase synchronous imaging by helical scan.

[Explanation of symbols]

 Reference Signs List 2 scanning gantry 4 imaging table 6 operation console 8 target 20 X-ray tube 22 collimator 24 detector array 26 data collection unit 28 X-ray controller 30 collimator controller 34 rotation unit 36 rotation controller 60 data processing device 62 control interface 64 data collection buffer 66 Storage device 68 Display device 70 Operating device 101 Projection data acquisition unit 103 Data storage unit 105 Image reconstruction unit 107 Phase setting unit 109 Image storage unit 111 Heart rate detection unit 113 Average phase calculation unit 115 Display unit 117 Image number prediction unit 119 Area management Part 121 addition part 400 X-ray beam

Continuation of front page (72) Inventor Akihiko Nishiide 127-7 Asahigaoka, Hino-shi, Tokyo 127 GE Inside Yokogawa Medical System Co., Ltd. (72) Inventor Akira Hagiwara 127-7 Asahigaoka 4-chome, Hino-shi, Tokyo Yokogawa Medical System Corporation F-term (reference) 4C093 AA22 BA10 CA13 DA02 FA33 FA47 FC25 FE12

Claims (30)

[Claims] Means for acquiring projection data of a plurality of views of the object along a spiral trajectory surrounding the object to be imaged by X-rays; and acquiring a periodic signal relating to body movement of the object. Means for storing the projection data and the periodic signal for each view; and a tomographic image of the object at a predetermined phase within a cycle of the periodic signal based on the stored projection data. Means for reconstructing an X-ray CT system. 2. A means for acquiring projection data of a plurality of views of the object along an spiral trajectory surrounding the object to be imaged by X-rays, and acquiring a periodic signal relating to body movement of the object. Means for storing information that associates the view information of the projection data with the periodic signal; and based on the acquired projection data and the stored information, Means for reconstructing a tomographic image of the object at a predetermined phase. 3. The X-ray CT apparatus according to claim 1, further comprising means for calculating an average period of the periodic signal. 4. The X-ray CT apparatus according to claim 3, further comprising: means for displaying the average period. 5. The apparatus according to claim 3, further comprising: means for predicting the number of tomographic images to be reconstructed based on a duration of the projection data acquisition and the average period.
An X-ray CT apparatus according to claim 4. 6. The X-ray CT apparatus according to claim 1, wherein the periodic signal is a heartbeat signal. 7. A projection data acquisition apparatus for acquiring projection data of a plurality of views of X-rays of the object along a spiral trajectory surrounding the object to be imaged, and acquiring a periodic signal relating to the body movement of the object. A periodic signal acquisition device, a storage device for storing the projection data and the periodic signal for each view, and a method for storing the projection data and the periodic signal based on the stored projection data in a predetermined phase within a period of the periodic signal. An X-ray CT apparatus comprising: a tomographic image reconstruction device configured to reconstruct a tomographic image. 8. A projection data acquisition apparatus for acquiring projection data of a plurality of views by X-rays of the object along a spiral trajectory surrounding the object to be imaged, and acquiring a periodic signal relating to a body movement of the object. A periodic signal acquisition device; a storage device for storing information that associates the view information of the projection data with the periodic signal; and a period of the periodic signal based on the acquired projection data and the stored information. And a tomographic image reconstructing device for reconstructing the tomographic image of the object at a predetermined phase. 9. The X-ray CT apparatus according to claim 7, further comprising a period calculating device for calculating an average period of the periodic signal. 10. The X-ray CT apparatus according to claim 9, further comprising a period display device for displaying the average period. 11. The tomographic image number predicting apparatus for predicting the number of tomographic images to be reconstructed based on the duration of the projection data acquisition and the average period. An X-ray CT apparatus according to claim 10. 12. The X-ray CT apparatus according to claim 7, wherein the periodic signal is a heartbeat signal. 13. An X-ray irradiator for irradiating a fan-shaped X-ray beam, and a plurality of X-ray detection elements arranged in a direction in which the fan-shaped X-ray beam spreads. A detector facing the X-ray irradiator; and an X-ray irradiator / detector system including the X-ray irradiator and the detector is rotated around the target along a spiral trajectory to project a plurality of views of the target. A projection data acquisition device for acquiring data; a periodic signal acquisition device for acquiring a periodic signal related to the body movement of the object; a storage device for storing the projection data and the periodic signal for each view; An X-ray CT apparatus, comprising: a tomographic image reconstructing apparatus configured to reconstruct the tomographic image of the target at a predetermined phase within a cycle of the periodic signal based on projection data. 14. An X-ray irradiator for irradiating a fan-shaped X-ray beam, and a plurality of X-ray detection elements are arranged in a direction in which the fan-shaped X-ray beam spreads. A detector facing the X-ray irradiator; and an X-ray irradiator / detector system including the X-ray irradiator and the detector is rotated along a spiral trajectory around the object to project a plurality of views of the object. A projection data acquisition device for acquiring data; a periodic signal acquisition device for acquiring a periodic signal relating to the body movement of the object; and a storage device for storing information that associates the view information of the projection data with the periodic signal. And a tomographic image reconstruction apparatus that reconstructs the target tomographic image at a predetermined phase within a cycle of the periodic signal based on the acquired projection data and the stored information. X-ray CT apparatus characterized. 15. The apparatus according to claim 13, further comprising a period calculating device for calculating an average period of said periodic signal.
An X-ray CT apparatus according to claim 14. 16. The X according to claim 15, further comprising a period display device for displaying the average period.
Line CT device. 17. The apparatus according to claim 15, further comprising: a tomographic image number prediction device that predicts the number of tomographic images to be reconstructed based on the duration of the projection data acquisition and the average period. 17. The X-ray CT apparatus according to item 16. 18. The X-ray CT apparatus according to claim 13, wherein the periodic signal is a heartbeat signal. 19. An X-ray irradiator for irradiating a fan-shaped X-ray beam, and a fan-shaped X-ray formed by a plurality of X-ray detection elements arranged in a direction in which the fan-shaped X-ray beam spreads A plurality of detectors arranged in the direction of the thickness of the beam and facing the X-ray irradiator with an imaging target interposed therebetween; and an X-ray irradiator / detector system including the X-ray irradiator and the detector. A projection data acquisition device that acquires a plurality of views of projection data for the object by rotating the object around a spiral trajectory; and a periodic signal acquisition device that acquires a periodic signal related to the body movement of the object. A storage device for storing the projection data and the periodic signal for each view; and reconstructing the tomographic image of the target at a predetermined phase within a cycle of the periodic signal based on the stored projection data. Fault X-ray CT apparatus characterized by comprising a reconstruction device. 20. An X-ray irradiator for irradiating a fan-shaped X-ray beam, and a fan-shaped X-ray formed by arranging a plurality of X-ray detection elements in a direction in which the fan-shaped X-ray beam spreads. A plurality of detectors arranged in the direction of the thickness of the beam and facing the X-ray irradiator with an imaging target interposed therebetween; and an X-ray irradiator / detector system including the X-ray irradiator and the detector. A projection data acquisition device that acquires a plurality of views of projection data for the object by rotating the object around a spiral trajectory; and a periodic signal acquisition device that acquires a periodic signal related to the body movement of the object. A storage device for storing information that associates the view information of the projection data with the periodic signal; and a predetermined phase within a period of the periodic signal based on the acquired projection data and the stored information. Smell X-ray CT apparatus characterized by comprising: a tomographic image reconstruction device for reconstructing a tomographic image of the subject. 21. The apparatus according to claim 19, further comprising a period calculating device for calculating an average period of said periodic signal.
An X-ray CT apparatus according to claim 20. 22. The X according to claim 21, further comprising a period display device for displaying the average period.
Line CT device. 23. The apparatus according to claim 21, further comprising a tomographic image number predicting apparatus for predicting the number of tomographic images to be reconstructed based on a duration of the projection data acquisition and the average period. 23. The X-ray CT apparatus according to 22. 24. The X-ray CT apparatus according to claim 19, wherein the periodic signal is a heartbeat signal. 25. An X-ray irradiator for irradiating a fan-shaped X-ray beam, and a fan-shaped X-ray formed by a plurality of X-ray detection elements arranged in a direction in which the fan-shaped X-ray beam spreads. Two detectors arranged in the direction of the thickness of the beam and facing the X-ray irradiator with an imaging target interposed therebetween; and an X-ray irradiator / detector system including the X-ray irradiator and the detector. A projection data acquisition device that acquires a plurality of views of projection data for the object by rotating the object around a spiral trajectory; and a periodic signal acquisition device that acquires a periodic signal related to the body movement of the object. A storage device that stores the projection data and the periodic signal for each view; and a predetermined phase within a period of the periodic signal based on a sum of the projection data respectively obtained through the two detection element arrays. Oak X-ray CT which is characterized by comprising: a tomographic image reconstruction device for reconstructing a tomographic image of the object
apparatus. 26. An X-ray irradiator for irradiating a fan-shaped X-ray beam, and a fan-shaped X-ray formed by arranging a plurality of X-ray detection elements in a direction in which the fan-shaped X-ray beam spreads. Two detectors arranged in the direction of the thickness of the beam and facing the X-ray irradiator with an object to be imaged therebetween; and an X-ray irradiator / detector system including the X-ray irradiator and the detector. A projection data acquisition device that acquires a plurality of views of projection data for the object by rotating the object around a spiral trajectory; and a periodic signal acquisition device that acquires a periodic signal related to the body movement of the object. A storage device that stores information that associates the view information of the projection data with the periodic signal; and the periodic signal based on the sum of the projection data obtained through the two detection element arrays and the stored information. X-ray CT apparatus characterized by comprising: a tomographic image reconstruction device for reconstructing a tomographic image of the object in the predetermined phase in the cycle. 27. The apparatus according to claim 25, further comprising a period calculating device for calculating an average period of the periodic signal.
An X-ray CT apparatus according to claim 26. 28. The apparatus according to claim 27, further comprising a period display device for displaying the average period.
Line CT device. 29. The apparatus according to claim 27, further comprising: a tomographic image number prediction device that predicts the number of tomographic images to be reconstructed based on the duration of the projection data acquisition and the average period. An X-ray CT apparatus according to Item 28. 30. The X-ray CT apparatus according to claim 25, wherein the periodic signal is a heartbeat signal.