JPH08299321A - X-ray CT system - Google Patents

Abstract

(57) [Summary] [Purpose] Imaging is continuously performed by a helical scan on a plurality of imaging areas with different rotation speeds such as an X-ray source. [Structure] The top movement control unit 12 controls the movement of the top, and the rotation control unit 14 controls the rotation of the X-ray source 34 and the like.
The top position detecting unit 11 detects the position information of the top at the time of data collection by the DAS 36, and the rotation position detecting unit 13 triggers each time the rotating X-ray source 34 or the like is rotated by a predetermined angle.
Output R. The DAS 36 collects data each time the trigger TR is given. The rotation controller 14 controls the X-ray source 3
When the rotational speed of 4 or the like is switched, the top movement control unit 12 changes the rotational speed from the trigger TR corresponding to the rotational position information of the X-ray source 34 or the like to the current (actual) X-ray source 34.
Then, the top plate is moved at a moving speed corresponding to the calculated rotation speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a third-generation X-ray C apparatus, and more particularly, an X-ray CT for performing a spiral scan (helical scan) to continuously image a predetermined imaging region of a subject. Regarding the device.

[0002]

2. Description of the Related Art A third-generation X-ray CT apparatus of this type includes a gantry and a bed arranged near the gantry. The gantry is provided with an opening for inserting and removing the subject, and an X-ray source and an X-ray detector are internally provided in the gantry so that the X-ray source and the X-ray detector can be continuously rotated while maintaining a facing state around the central axis of the opening. Has been done. The bed has a top plate on which a subject is mounted, which is horizontally movable above a bed base that can be raised and lowered.

To take a tomographic image of a predetermined portion by this X-ray CT apparatus, the top plate on which the subject is placed is horizontally moved to insert the subject into the gantry opening, and the X-ray source and the X-ray detector are connected. The imaging region of the subject is positioned at the imaging position that connects the two. Then, the X-ray source and the X-ray detector are rotated around the subject,
During this rotation, X-rays are emitted from the X-ray source toward the subject,
An X-ray detector detects transmitted X-ray data transmitted through the subject.

The X-ray detector is connected to data acquisition electronics (DAS) that rotates together with the X-ray detector, and this DAS is detected by the X-ray detector at a predetermined timing. Line data (analog electric signal) is converted into digital data and collected. DA
The data collection timing by S is every time the X-ray source or the like is rotated by a predetermined angle, and the DAS collects data a predetermined number of times while the X-ray source or the like is rotated once around the subject. The collected data for one round from the round of the subject collected by the DAS is sent to the image reconstruction unit, and the image reconstruction unit calculates the tomographic image of the imaging region based on the given collected data by a well-known calculation method. Reconfigure with.

By the way, in recent years, a spiral scan (helical scan) has been performed by using the third generation X-ray CT apparatus.
Proposed implementation is one that is configured to obtain a tomographic image of an arbitrary region within this region by performing continuous imaging of an imaging region consisting of continuous regions (for example, the region from the chest to the upper abdomen). ing.

X-ray CT capable of performing this helical scan
The device is conventionally configured as follows.

For example, an imaging start site (for example, a chest) of an imaging area set from the operation panel or the like is positioned at an imaging position within the gantry opening, and an X-ray source and an X-ray detector are provided while irradiating X-rays. Is continuously rotated at a constant rotation speed, and in synchronization with this rotation, the tabletop is horizontally moved at a constant speed so as to displace the part located at the imaging position toward the imaging end part (eg, abdomen) of the imaging region. The X-ray source and the X-ray detector are moved and scanned so that the rotation loci of the X-ray source and the X-ray detector are spiral with respect to the subject, and the set imaging region is continuously imaged.

The rotation speeds of the X-ray source and the X-ray detector are set, for example, from the operation panel. Thereby, for example, from the state in which the X-ray source is located directly above the subject (the X-ray detector is located directly below the subject) to the state in which the X-ray source is located immediately above the subject. Moreover, the X-ray source and the like move in a spiral manner with respect to the subject, but the DAS collects data for a predetermined number of times.

Further, the horizontal movement of the top plate is performed at a speed corresponding to the rotation speed of the X-ray source or the like. The rotation speed of the X-ray source and the like and the moving speed of the top plate are determined to have a constant ratio. For example, the rotation speed of the X-ray source is 360 ° / 1.
In seconds, if the moving speed of the top is 10 mm / 1 second, X
The rotation speed of the radiation source is 180 ° / 1 second (1 rotation in 2 seconds)
At that time, the moving speed of the top plate is 5 mm / 1 second. Therefore,
It is possible to calculate the moving speed of the tabletop according to the set rotation speed of the X-ray source, etc., and obtain it by this calculation (or from the operation panel etc. according to the rotation speed of the X-ray source etc. The top plate is controlled to move horizontally at the set moving speed.

Further, in order to reconstruct a tomographic image of an arbitrary portion within the imaging region, position information of the tabletop with respect to the data collected by the DAS is necessary. This position information is, for example, an X-ray source. It is calculated based on the rotation speed of the above and the moving speed of the top. During the helical scan, the rotation speed of the X-ray source and the like and the moving speed of the top are constant, so that the position information of the top for each collected data can be uniquely obtained.

In the image reconstructing section, the position information of the tabletop and the collected data for the position are specified, and the orbital collected data (collected data for one round) of the desired portion and the collected data for one round before and after that are collected. Based on the above, the tomographic image of the site is reconstructed by a known calculation method.

[0012]

However, the prior art having such a structure has the following problems. There is a demand to change the imaging condition and perform helical scan because the internal structure varies depending on the imaging site. For example, a case where two adjacent imaging regions (for example, a first imaging region from the chest to the upper abdomen and a second imaging region from the upper abdomen to the lower abdomen) are imaged by a helical scan, and In the first imaging region, the rotation speed of the X-ray source or the like is set to ω1 (for example, 18
In the case where the rotation speed of the X-ray source or the like is imaged at ω2 (for example, 360 ° / 1 second) in the second imaging region, the conventional device has the following inconveniences. .

That is, when the first and second image pickup areas are continuously imaged by the helical scan,
The rotation speed of the X-ray source or the like is switched from ω1 to ω2 at the imaging end portion of the first imaging region (which coincides with the second imaging start portion), but the rotation of the X-ray source or the like depends on the rotation of the motor. Since it is performed, the rotation speed does not change immediately even if the rotation speed is changed, and the rotation speed changes from ω1 to ω
It gradually changes to 2 while decelerating or accelerating. Therefore, in the configuration of the conventional device, during the change of the rotation speed, the position information of the top determined by the calculation with respect to the collected data by the DAS after the start of the change of the rotation and the position information of the actual top are deviated from each other. Therefore, a tomographic image of a desired portion cannot be obtained accurately.

Therefore, when performing the above-mentioned image pickup,
In the conventional apparatus, first, an image is taken by a helical scan at a rotation speed ω1 with respect to the first imaging region, and when this imaging is completed, the rotation of the X-ray source or the like is temporarily stopped, and then the second imaging region is The image is taken by the helical scan at the rotation speed ω2 with respect to. Therefore, the first,
Since the imaging time of the second imaging region is prolonged and the subject is restrained during that time, the pain given to the subject becomes great.

The present invention has been made in view of the above circumstances, and the imaging by the helical scan performed at different rotation speeds of the X-ray source or the like for a plurality of imaging regions is continuously performed in a short time. It is an object of the present invention to provide an X-ray CT apparatus that can be performed.

[0016]

The present invention has the following configuration to achieve the above object. That is, the present invention includes an X-ray source that irradiates an object placed on a top plate with X-rays, and an X-ray detector that is arranged facing the X-ray source with the object interposed therebetween. An X-ray CT apparatus for horizontally imaging the continuous portion (imaging region) of the subject while moving the top plate horizontally while rotating the subject around the subject to perform a helical scan. In (a), a rotation position detecting means for detecting position information (angular position information) of the X-ray source and the X-ray detector during rotation of the X-ray source and the X-ray detector; ) Based on the position information of the X-ray source and the X-ray detector detected by the rotational position detecting means, the transmitted X-ray data detected by the X-ray detector is converted into the X-ray source at predetermined angular intervals. And data collecting means for collecting a predetermined number of times while the X-ray detector makes one round, ( ) And rotation control means for drivable controlling the switching of the rotational speed of the X-ray source and the X-ray detector,
(D) The horizontal movement speed of the top plate is controlled according to the rotation speeds of the X-ray source and the X-ray detector, and at least the rotation speeds of the X-ray source and the X-ray detector are changed. The X-ray source and the X-ray detector position information detected by the rotational position detecting means,
Top movement control means for controlling the horizontal movement speed of the top based on the current rotation speeds of the radiation source and the X-ray detector;
(E) a top position detecting means for detecting position information of the top at the time of data collection by the data collecting means, (f) collected data by the data collecting means, and a top of the top at that time An image reconstructing unit that reconstructs a tomographic image of a predetermined region of the subject based on the position information.

[0017]

The operation of the present invention is as follows. For example,
X for the first imaging region from the chest to the upper abdomen
When the rotation speed of the radiation source is ω1 and the rotation speed of the X-ray source is ω2 for the second imaging region from the upper abdomen to the lower abdomen, first the imaging of the first imaging region is started. The part (chest) is located at the imaging position connecting the X-ray source and the X-ray detector, and the rotation control means rotates the X-ray source or the like at ω1. When the X-ray source or the like is constantly rotated at ω1, the X-ray irradiation is started from the X-ray source, and the top movement control means is positioned at the imaging position at the movement speed of the top corresponding to ω1. From the imaging start part (chest) of the first imaging region to the first part
The tabletop is moved at a constant speed so as to be displaced to the image capturing end portion (upper abdomen) of the image capturing area, and in synchronization therewith, the data collecting unit displays the position information of the X-ray source or the like detected by the rotational position detecting unit. Based on this, the transmitted X-ray data detected by the X-ray detector is collected a predetermined number of times per one revolution at predetermined angular intervals. Further, the position information of the moving top is detected by the top position detecting means at the data collection timing of the data collecting means.

When the portion positioned at the image pickup position becomes the image pickup end portion (upper abdomen) of the first image pickup area, the rotation speed control means switches the rotation speed of the X-ray source or the like from ω1 to ω2. By this switching, the rotation speed of the X-ray source etc.
Switching from ω1 to ω2 while decelerating or accelerating. When the rotation speed is changing, the top control means moves the top (from the imaging start site (upper abdomen) of the second imaging region to the imaging end site (lower abdomen) of the second imaging region). Based on the rotation speed of the current (actual) X-ray source or the like obtained from the position information of the X-ray source or the like detected by the rotation position detecting means, the movement is performed at a movement speed corresponding to this rotation speed. This is done while changing the moving speed of the tabletop. Then, after the rotation speed of the X-ray source or the like has reached ω2, the top movement control means ends the imaging of the portion located at the imaging position in the second imaging area at the movement speed of the top corresponding to ω2. The top plate is moved at a constant speed so as to be displaced in the direction of the part (lower abdomen). As a result, the moving speed of the top plate always corresponds to the rotating speed of the X-ray source or the like.

Even after the rotation speed of the X-ray source or the like is switched from ω1 to ω2, the data collecting means collects the data. This data collection is performed based on the position information of the X-ray source or the like. Therefore, regardless of changes in the rotation speed of the X-ray source or the like, data is always collected a predetermined number of times per revolution. Further, since the top position detecting means detects the position information of the moving top at the data collection timing of the data collecting means, it is collected during the imaging of the first and second imaging regions. The position information of the top plate with respect to the data can be accurately obtained.

When the imaging of the first and second imaging areas is completed, the image reconstructing means is based on the collected data and the position information of the tabletop at the time of collecting each of the data, and the image reconstructing means performs the first and second imaging operations.
To reconstruct a tomographic image of an arbitrary part within the imaging region of.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an X-ray CT according to an embodiment of the present invention.
FIG. 2 is an overall view showing a schematic configuration of the apparatus, FIG. 2 is a diagram showing a configuration of a top plate position detection unit, FIG. 3 is a diagram showing a configuration of a rotation position detection unit, and FIG. 4 is a configuration of a control processing unit. It is a block diagram shown.

The apparatus of this embodiment comprises a bed 1, a gantry 2, a control processing section 3, an operation panel 4, an output device 5 and the like. Further, as shown in FIG. 4, the control processing unit 3 includes a top position detection unit 11, a top movement control unit 12 as a top movement control unit, and a rotation position detection unit 13.
A rotation control unit 14 as rotation control means, an X-ray control device 15, a high voltage generation device 16, and a first memory 17.
A pre-processing unit 18, a second memory 19, an image reconstructing unit 20, and the like.

As shown in FIG. 1, a bed 1 is mounted on a floor surface and is driven up and down by a motor (not shown). A bed base 21 is mounted above the bed base 21 for horizontally moving a subject M. A top plate 22 and the like are provided. The horizontal movement of the top plate 22 is performed by converting the rotation of the motor 23 provided in the bed base 21 into a linear motion. This motor 23
Drive (starting and stopping movement of the top 22) and control of rotation speed (moving speed of the top 22) are performed by the top movement control unit 12, as shown in FIG. Top movement control unit 12
Is a start signal SS1 from the operation panel 4, a positioning instruction signal PS1, imaging conditions (details will be described later), top plate position information CT from the top plate position detection unit 11, and rotation position detection unit 1.
Based on the image pickup start signal SS2 from 3 and the trigger TR, the start and stop of the movement of the top 22 and the movement speed are controlled. In addition, the top movement control unit 12 resets the reset signal RS.
To the top position detector 11, the positioning completion signal PS2 to the rotation position detector 13 and the rotation controller 14, the rotation speed change signal CS to the rotation controller 14, and the imaging end signal ES to the rotation controller 14 and the X-ray. The data is appropriately output to the control device 15.

As shown in FIGS. 1 and 2, a rotary encoder 24 is attached to the motor 23, and outputs a pulse signal psa every time the motor 23 is rotated by a predetermined unit angle (for example, 0.1 °). The counter 11a included in the top position detecting unit 11 counts. Since the horizontal movement amount of the top plate 22 per unit angle rotation of the motor 23 is known, the top plate 22 when the position of the top plate 22 when the counter 11a is reset (“0” is set) is used as a reference.
The relative position of can be recognized by the count value of the counter 11a. This counter 11a is reset
This is performed based on the reset signal RS from the top movement control unit 12. In addition, the count value CT is the top plate movement control unit 12
Is always output to the reading unit 11b by the trigger TR from the rotational position detecting unit 13
Stored in the memory 17. It should be noted that the rotary encoder 24 and the top plate position detecting section 11 constitute the top plate position detecting means in the present invention.

Returning to FIG. 1, a gantry 2 is installed on the floor near the bed 1. Top plate 2 for gantry 2
An opening 31 is provided for inserting / removing the subject M placed on the substrate 2. Also, the gantry 2 has a bearing 3
A pedestal 33 is provided so as to be rotatable around the central axis J of the opening 31 via 2. An X-ray source (X
The (ray tube) 34 and the X-ray detector 35 are attached to face each other, and the DAS 36 is also attached. A belt 37 is hung on the gantry 33, and the rotation of the motor 38 is transmitted through the belt 37, so that the gantry 33 (X-ray source 34, X-ray detector 35, DAS 36) rotates about the central axis J. To be rotated. The drive of the motor 38 (start and stop of rotation around the central axis J of the X-ray source 34) and the rotational speed (rotational speed around the central axis J of the X-ray source 34) are controlled as shown in FIG. Then, the rotation control unit 14 performs this. The rotation control unit 14 receives the positioning completion signal PS2, the rotation speed change signal CS, and the imaging end signal ES from the top movement control unit 12.
Also, based on the imaging conditions from the operation panel 4 (details will be described later), the start and stop of rotation of the X-ray source 34 and the like around the central axis J and the change of the rotation speed are controlled.

The irradiation of X-rays from the X-ray source 34 is controlled by the X-ray controller 15 driven by the image pickup start signal SS2 from the rotational position detector 13 and the image pickup end signal ES from the top movement controller 12. This is performed by supplying a predetermined X-ray tube voltage or X-ray tube current from the high voltage generator 16.
Since the X-ray source 34 and the like are continuously rotated, power is supplied from the high voltage generator 16 to the X-ray source 34 by a brush power transmission / reception mechanism (not shown) (a slip ring provided on the pedestal 33 in the rotation circumferential direction and this slip). It consists of a power transmitting and receiving brush that contacts the ring).

The X-ray detector 35 detects the X-ray transmission data which is emitted from the X-ray source 34 and transmitted through the subject M, and outputs an electric signal (analog data) corresponding to this detection data.
Supply to AS36. The X-ray detector 35 is composed of X-ray detectors for a plurality of channels in the circumferential direction of rotation, and simultaneously detects X-ray transmission data for a plurality of channels by one-time data acquisition described later. It should be noted that C in FIG. 1 indicates an imaging position in the opening 31 of the gantry 1 that connects the X-ray source 34 and the X-ray detector 35.

As shown in FIG. 4, the DAS 36 collects data once by the trigger TR from the rotational position detector 13. Data collection is performed by an A / D (analog to digital) converter (not shown) built in the DAS 36.
This is performed by sequentially A / D converting the electric signal (X-ray transmission data) supplied from the X-ray detector 35 at high speed for each channel. That is, although the electric signal is always supplied from the X-ray detector 35 to the A / D converter, the A / D conversion is performed at a predetermined timing to correspond to the X-ray transmission data for a plurality of channels at that timing. Digital data is collected. The data collected is the above-mentioned top plate 2
2 position information (count value C from the top position detecting unit 11
It is stored in the first memory 17 together with T). Note that D
Data transmission from the AS 36 to the first memory 17 is also performed by the brush power transmission / reception mechanism described above. Also, DAS36
The first memory 17 and the first memory 17 constitute data collecting means in the present invention.

As shown in FIG. 1 and FIG.
The opening hole 33 is provided at a position corresponding to the mounting position of the X-ray source 34.
a is attached, and slits 33b are also formed at predetermined angles along the circumferential direction. And, for example,
When the X-ray source 34 is located directly above the subject M (the X-ray detector 35 is directly below the subject M), it is a transmissive first type including a light projector 41a and a light receiver 41b for detecting the opening hole 33a. No. 1 photodetector 41, and a second transmissive photodetector 42 consisting of a projector 42a and a photoreceiver 42b provided below the first photodetector 41 and sandwiching the slit 33b. And are installed inside the gantry 2.

When the first photodetector 41 detects the opening 33a, the photodetector 41b outputs a pulse signal psb, and the pulse signal psb is counted by the counter 13a constituting the rotational position detector 13. In preparation for start of imaging described later, the count value of the counter 13a is reset by the reading unit 13b based on the positioning completion signal PS2 from the top movement control unit 12, and the count value of the counter 13a thereafter (the X-ray source 34 or the like is The number of rotations of the X-ray source 34 or the like required for the speed to become constant after the rotation of the X-ray source 34 or the like is drive-controlled, for example, 1-2 When the reading unit 13b identifies that the image capturing start signal S
S2 is output to the top movement control unit 12, the X-ray controller 15, and the trigger generation unit 13c.

The second photodetector 42 has a slit 33.
The light receiver 42b outputs the pulse signal psc to the trigger generation unit 13c each time b is detected. Trigger generator 13c
Detects the top position of the trigger TR at the timing of the pulse signal psc supplied from when the imaging start signal SS2 is given by the reading section 13b until the imaging end signal ES is given by the top movement control section 12. It is output to the unit 11, the top movement control unit 12, and the DAS 36. This trigger TR
Corresponds to the data collection timing by the DAS 36, so that the slit 33b is set to [360 / per lap] so that the number of data collections by the DAS 36 per lap becomes a predetermined number (for example, 800 times / lap). DAS3
6 data collection times] ° (for example, (360/80
It is formed on the pedestal 33 at equal intervals of 0 °.

Incidentally, the first and second photodetectors 41, 4
2 and the rotational position detecting section 13 constitute the rotational position detecting means in the present invention.

As shown in FIG. 1, the gantry 2 has a light projector 51 for positioning the imaging region of the subject M, which is provided inside the opening 31 on the side where the top plate 22 is inserted. The slit 52 formed on the top plate 22 insertion side of the opening 31 irradiates the body side surface of the subject M inserted into the opening 31 of the gantry 2. The operator positions the imaging region according to the irradiation position of this light as described later. The projection of light from the projector 51 is started by the start signal SS1 from the operation panel 4, and the projection of light is finished by the positioning instruction signal PS1 from the operation panel 4.

The pre-processing unit 18 performs pre-processing as described below on the collected data stored in the first memory 17 for each of the collected data of a plurality of channels obtained by one collection, and performs the pre-processing. Later collection data and the corresponding top plate 22
The position information of is stored in the second memory 19. This pre-processing may be performed each time data is collected by the DAS 36. For example, the imaging end signal ES from the top movement control unit 12 may be received and all the collected data may be collectively processed after the imaging is completed. May be.

When the image reconstructing section 20 is supplied with a region to be reconstructed and an image reconstructing start signal GS from the operation panel 4, the image reconstructing section 20 is based on the collected data stored in the second memory 19 and its top plate position information. , Reconstructs a tomographic image of the designated region and outputs it to the output device 5 such as a monitor. The preprocessing unit 18, the second memory 19, and the image reconstructing unit 20 constitute the image reconstructing means in this invention.

The operation panel 4 receives an instruction (SS
1), positioning instruction (output of PS1), setting of imaging conditions (details will be described later), setting of a part to be reconfigured and its start (outputting GS).

Next, using the apparatus of the above-mentioned embodiment, when performing imaging by helical scanning with respect to a plurality of (for example, two) imaging areas adjacent to each other, the rotational speed of the X-ray source 34 or the like is different in each area. The operation of will be described.

First, the operator sets the imaging conditions from the operation panel 4. As shown in FIG. 5, the imaging conditions include information for identifying the first and second imaging areas SA1 and SA2, and the X-ray source 3 at the time of imaging each of the imaging areas SA1 and SA2.
The rotation speed such as 4 and the movement speed of the top plate 22 are included. The information for identifying the respective imaging regions SA1 and SA2 is, here, the length (L1) between the start site SP1 and the end site EP1 of the first imaging region SA1 and the second imaging region SA.
The length (L2) between the start portion SP2 of 2 (= end portion EP1 of the first imaging region SA1) and the end portion EP2 is set. The start portion SP1 of the first imaging area SA1 is determined by a positioning instruction from the projector 51, as described later.

Further, the rotation speed RSp of the X-ray source 34, etc. at the time of imaging the respective imaging areas SA1 and SA2 is the first here.
The imaging area SA1 of ω1 is ω1 (for example, 360 ° / 1 second),
The second imaging area SA2 is ω2 (for example, 180 ° / 1
Second), the moving speed TSp of the top 22 is v1 (for example, 10 mm / 1 second) in the first imaging area SA1,
It is assumed that the image pickup area SA2 is set to v2 (for example, 5 mm / 1 second).

When the above imaging conditions are set, L1, L
2, v1, v2, ω1, ω2 are transmitted to the top movement control unit 12,
ω1 and ω2 are provided to the rotation control unit 14, respectively.

Next, with the tabletop 22 lowered, the subject M is placed on the tabletop 22 with its head facing the gantry 2 side, and a motor for raising and lowering the bed base 21 is driven. (Not shown) is driven to raise the top plate 22, and the height of the subject M is adjusted so that the body axis of the subject M coincides with the central axis J of the opening 31 of the gantry 2. The imaging process starts with the height of the subject M adjusted.

When the operator gives an instruction from the operation panel 4 to start the image pickup process, a start signal SS1 is output.
When the projection of the projector 51 for positioning is started,
The top movement control unit 12 horizontally moves the top 22 at a constant speed (predetermined speed). As the top plate 22 moves, the light from the projector 51 emitted from the slit 52 sequentially irradiates the body side surface of the subject M from the head to the feet. The operator observes this irradiation position, and when the light irradiates the start site SP1 of the first imaging region SA1,
An instruction is given from the operation panel 4. By this instruction, the positioning instruction signal PS1 is given to the top movement control unit 12 and the projector 51. The light projector 51 ends the light projection by this signal PS1. Further, the top movement control unit 12 controls the reset signal R
S is given to the top position detector 11. Top position detection unit 11
Then, the count value CT of the counter 11a is reset by the reset signal RS, and the top plate 22 moves to this position (top plate 2
Start site SP of the first imaging region SA1 of the subject M on 2
A count value CT corresponding to the horizontal movement amount of the top 22 based on the state in which 1 is located at the position where the light from the slit 52 is radiated) is given to the top movement controller 12.

As shown in FIG. 6, the length L3 between the slit 52 and the photographing center C is known. Therefore, the top movement control section 12 receives the positioning instruction signal PS1 and then the count value CT from the top position detecting section 11 (the counter 11a outputs the reset signal RS issued at the timing when the positioning instruction signal PS1 is given. Will be reset)
Thus, the movement amount of the top 22 is monitored, and when the top 22 is moved L3 after the positioning instruction signal PS1 is given, the movement of the top 22 is stopped and the positioning completion signal PS2 is output.

By the way, the set image pickup areas SA1 and S
When the tomographic image of an arbitrary site in the region is reconstructed after the imaging of A2 is completed, the collected data for one round of the site and one round before and after the collected data for one round of the site. Collected data is required. Therefore, the set imaging area SA
1, when the image of only SA2 is taken, the first imaging area S
At the start portion SP1 of A1 and the end portion EP2 of the second imaging region SA2, the collected data are insufficient and the tomographic image cannot be reconstructed. Therefore, as shown in FIG. 6, before and after the set imaging areas SA1 and SA2, additional areas PSA and ASA for obtaining collected data for one round are added to perform actual imaging.

Therefore, the amount of movement of the top plate 22 after the positioning instruction signal SP1 is given is shown in FIG. 6 (L4).
= L3-L5), and when the movement of L4 is completed, the positioning completion signal PS2 is output. The above L5
Is 1 before the start site SP1 of the first imaging area SA1.
This is the amount of movement of the top plate 22 enough to obtain the collected data for the circumference, and is specified from ω1 and v1 of the first imaging area SA1. For example, ω1 = 360 ° / 1 second, v1 = 10 mm /
At the time of 1 second, the moving amount (L5) of the top plate 22 for obtaining the collected data for one rotation is 10 mm. Further, when the imaging areas SA1 and SA2 are set including the preceding and following additional areas PSA and ASA, the movement amount of the top plate 22 after the positioning instruction signal PS1 is given is , L3 is acceptable. In the following, the imaging area SA
1, when setting SA2, the additional area PS before and after the above
The operation will be described assuming that A and ASA are set.

The top plate movement control unit 12 causes the positioning completion signal P
FIG. 7 shows the state when S2 is output. As shown in FIG. 7, the start portion SP1 of the first image pickup area SA1 is located at the image pickup position C.

Further, the rotational position detector 13 outputs the signal PS
2, the counter 13a is reset. Further, when this signal PS2 is given, the rotation controller 14 starts rotation of the X-ray source 34 and the like at ω1. It takes some time after the rotation of the X-ray source 34 or the like is started until the X-ray source 34 is rotated at a constant rotation speed of ω1. The reading unit 13b of the rotational position detection unit 13 indicates that the rotation of the X-ray source 34 or the like has been performed for a predetermined number of times after the rotation has been performed. Will be counted up). When the X-ray source 14 and the like have started to rotate a predetermined number of times after being started, the X-ray source 34 and the like are constantly rotating at the rotation speed of ω1.
The number of rotations of the X-ray source 34 and the like from the start of rotation to the constant rotation at the set rotation speed of the first imaging region SAI may be experimentally obtained in advance.

When it is detected that the X-ray source 34 or the like has been rotated by a predetermined number of rotations from the start of rotation, the actual image pickup can be started. Therefore, the reading section 13b of the rotation position detecting section 13 sends the image pickup start signal SS2 to the X-ray. Control unit 15 and top movement control unit 1
2 and trigger generation 13c, and actual imaging is started.

The X-ray controller 15 sends the image pickup start signal SS2.
To generate a predetermined X-ray tube voltage and X-ray tube current by the X-ray source 3
The high voltage generator 16 is controlled so that the X-ray is supplied to the X-ray source 4, and the X-ray irradiation from the X-ray source 34 is started.

When the top panel movement control section 12 receives this signal SS2, the top panel movement control section 12 outputs a reset signal RS to the top panel position detecting section 11.
To the top plate 22 in the start state of this imaging (see FIG. 7).
Preparation is made to monitor the position information (the count value CT from the top plate position detection unit 11) of the top plate 22 to be moved when the position of is used as a reference, and the top plate 22 starts moving at v1.

Based on this signal SS2, the trigger generator 13c causes the trigger TR synchronized with the pulse signal psc from the photodetector 42b of the second photodetector 42 to be DAS36, the top position detector 11, the top movement controller. Output to 12.

As a result, the X-ray source 34 emits X-rays,
While the X-ray source 34 and the like are rotated at ω1, the top plate 22 is v1
Is horizontally moved and the X-ray source 34 and the like are rotated once during that time, for a predetermined number of times (for example, 800 times / 360 times).
°) A lot of X-ray transmission data is collected, and the position information (CT) of the top plate 22 at the time of collection is collected.
Stored in the memory 17 of the first imaging area SA1
The image is captured by a helical scan for the.

The top movement control unit 12 includes the top position detecting unit 1.
Based on the position information (CT) from 1, the top plate 22 is monitored to be moved by L1 from the state of FIG. 7 and is moved by L1, and the end portion EP1 of the first imaging region SA1, that is, the second position When it is detected that the start portion SP2 of the imaging area SA2 has reached the imaging position C, the rotation speed change signal C
S is output to the rotation control unit 14, and the moving speed of the top plate 22 is appropriately changed and adjusted based on the current (actual) rotation speed of the X-ray source 34 or the like obtained from the trigger TR from the rotation position detection unit 13. While controlling.

The rotation controller 14 controls the rotation speed change signal CS.
Is given, the rotation speed of the rotation of the X-ray source 34, etc.
Change from 1 to ω2. However, since the rotation speed of the X-ray source 34 or the like is changed by changing the rotation speed of the motor 38, the rotation of the X-ray source 34 or the like constantly rotates at ω1, as shown in FIG. From this state, the rotational speed gradually decreases (when ω1> ω2: see FIG. 8A) or accelerates (when ω1 <ω2: see FIG. 8B).
Then, it takes some time t to rotate at a constant ω2.

Therefore, in order to adjust the moving speed of the top plate 22 according to the actual rotating speed during the change of the rotating speed from ω1 to ω2, the moving speed of the top plate 22 is as shown in FIG. Need to change to. Note that FIG. 9A shows v1.
> V2 corresponding to FIG. 8A, FIG. 9B shows v1.
<V2 shows a case corresponding to FIG. 8B.

In this embodiment, from the trigger TR from the rotational position detector 13, the current (actual) time during the change
The rotation speed is obtained, and the moving speed of the top 22 is determined based on the obtained current rotation speed. When the rotation speed is changed, the output time interval of the trigger TR is changed. The output time interval of the trigger TR corresponds to the actual rotation speed that is changing. Therefore, the output time interval of the trigger TR and the angular interval of the slit 33b (for example, when 800 slits 33b are formed, [360 /
800] °) and the present (actual) X-ray source 34
It is possible to obtain the rotation speed (denoted as ωx) of the above.
Moving speed of the top plate 22 according to this ωx (denoted as vx)
Can be calculated by the following formula. vx = ωx × (v1−v2) / (ω1−ω2) Note that Tx in FIGS. 8 and 9 all indicate the same time.

When the deceleration or acceleration of the rotation speed is completed and the rotation of the X-ray source 34 or the like is performed at a constant value of ω2, vx obtained by the above equation is also constant at a value of v2. The top movement control unit 12 does not change the movement speed of the top 22 from v2, and the second imaging area S
Imaging is performed up to the end portion ES2 of A2.

Even while the rotational speed and the moving speed of the top 22 are changing, the data collection and the position information of the top 22 are collected each time the trigger TR is output. Therefore, the number of times of data collection is always a predetermined number (80
0 times / 360 °). Further, the position information of the top plate 22 at the time of collecting the data is collected. Since the position information of the top plate 22 is obtained by the count value CT of the pulse signal psa of the rotary encoder 24 or the like, the top plate is obtained. Accurate position information can be obtained without being affected by the moving speed of 22.

Further, while the rotation speed is ω2 and the movement speed of the top plate 22 is constant at v2 and the X-ray source 34 and the like are rotated and the top plate 22 is moved, the top plate 22 is positioned in the second imaging area SA2. Data is collected and position information of the top 22 is collected a predetermined number of times per revolution until the end portion ES2 is moved.

The top movement control section 12 includes the top position detecting section 1
Based on the count value CT from 1, monitor whether the top plate 22 has moved by (L1 + L2) from the state of FIG. 7,
When (L1 + L2) is moved and it is detected that the end site ES2 of the second imaging area SA2 is located at the imaging position C,
The imaging end signal ES is output.

Incidentally, the additional area A after the explanation with reference to FIG.
In the case of adding SA to the set image pickup areas SA1 and SA2, after detecting that the end portion ES2 of the second image pickup area SA2 is located at the image pickup position C, the number of times of data collection for one round is completed. When the trigger TR is output (when data is collected for the number of times of data collection per round)
The imaging end signal ES may be output to the.

When the image pickup end signal ES is output, the X-ray controller 15 stops the irradiation of X-rays, and the rotation controller 14 stops the rotation of the X-ray source 34 and the like. As a result, the imaging by the helical scan in which the rotation speeds of the imaging areas SA1 and SA2 are different is completed.

After outputting the imaging end signal ES, the top movement control section 12 moves the top 12 in the direction opposite to the above-described operation, and the subject M is extracted from the opening 31 of the gantry 2. Then, the top plate 22 is lowered so that the subject M is placed on the top plate 22.
The image pickup process is completed.

By the way, since the first imaging area SA1 is imaged at the rotation speed ω1, while the second imaging area SA2 is imaged at the rotation speed ω2, the X-ray source 34, etc. are respectively imaged in the imaging areas. X-ray source 3 during one revolution of
The X-ray dose irradiated from 4 is different. That is, the X-ray detection amount (value of X-ray transmission data) of each channel when collected with the rotation speed being ω1 is ω1> ω
When 2 (or ω1 <ω2), it becomes larger (or smaller) than the X-ray detection amount of each channel when collected in the state where the rotation speed is ω2.

Therefore, the pre-processing unit 18 uses the collected data of the channels for detecting the X-rays which do not pass through the subject M for each of the collected data of the plurality of channels collected at each data collection timing to obtain the collected data from 0 to 0. 1 is standardized, and the size of the collected data based on the difference in irradiation X-ray dose due to the difference in rotation speed is set to the same ratio.

As shown in FIG. 10, the X-ray detector 35 is constructed by arranging X-ray detectors 35a for a plurality of channels ch in the circumferential direction of rotation, and for example, the X-ray detector 35a for ch0.
Then, X does not pass through the subject M at any position during rotation of the X-ray source 34 and the X-ray detector 35 around the subject M.
Dose is detected. The collected data (detected X-ray dose) at the ch0 X-ray detector 35a is Da.

Assuming that the number of times data is collected from the start to the end of imaging is N, the preprocessing unit 18 calculates the following equation for each i-th (i = 1 to N) M-channel collected data. The collected data Dj of each channel (j = 1 to
M) is normalized to 0 to 1. KDj = Dj / Da (j = 1 to M) KDj indicates collected data standardized by 0 to 1 of each channel.

Further, by using the relationship between the X-ray dose and the data under the condition where Da is set, the collected data during the speed transition can be corrected to the collected data in the constant speed state. The processing result is stored in the second memory 19 together with the position information of the top plate 22. That is, finally, in the second memory 19, the imaging areas SA1 and SA2 (additional area PS
(Including A and ASA), N × M collected data are
It is stored together with the position information of the top plate 22 at the time of each data collection for each collection timing. When the operator gives an image reconstruction instruction from the operation panel 4 to an arbitrary site in the area SA1 or SA2 and the site, the image reconstruction unit 20
The orbital collection data for the position information corresponding to the designated part and the collected data standardized by 0 to 1 for one round before and after that are read from the second memory 19, and the part is calculated based on this data by a well-known calculation method. To reconstruct the tomographic image of and output to the output device 5.

FIG. 11 shows the locus of displacement of the X-ray source 34 and the X-ray detector 35 seen from the subject M in the above-mentioned imaging.
Although only the locus of the X-ray source 34 is shown in FIG. 11, the locus of the X-ray detector 35 has a phase of 1 with respect to the locus of the X-ray detector 34.
It is only offset by 80 °. As shown in the figure, an area in which the rotation speed of the second imaging area SA2 at the beginning of imaging changes (from a start portion SP2 of the second imaging area SA2 to a portion CE where the rotation speed becomes constant at ω2). Area) CA
Also, since the moving speed of the top plate 22 is changed in real time according to the changing rotation speed, the X-ray source 34
Relative displacement amount BX of the subject M in the body axis direction during one rotation such as
Is always constant from the start to the end of imaging, that is, the moving speed of the top plate 22 always corresponds to the rotation speed. In addition, as described above, the number of data collections per one round during imaging and the number of position information collections of the top 22 are always constant without being affected by changes in the rotation speed or the moving speed of the top 22, and The position information of the top plate 22 is not affected by changes in the rotation speed and the moving speed of the top plate 22, and accurate position information can always be obtained. Therefore, even when a plurality of image pickup areas adjacent to each other are picked up by helical scanning with different rotation speeds of the respective image pickup areas, these areas can be continuously picked up.

In the above embodiment, the top movement control section 12 controls the movement speed of the top 22 based on the rotation speed obtained from the rotation position information (trigger TR) only while the rotation speed is changing. Although it is performed, the movement control of the top 22 may be always performed from the start to the end of imaging based on the rotation speed obtained from the rotation position information (trigger TR).

The rotational position information can be detected by means other than the first and second optical sensors 41 and 42 shown in FIG. For example, as shown in FIG. 12 (a), an information slit 63 in which a plurality of openings 61 and light-shielding portions 62 are combined is used, as shown in FIG. 12 (b), instead of the slit 33b of FIG. Provided in the orbiting direction. Then, a transmissive photodetector 66 including a plurality of sets of a projector 64 and a photoreceiver 65 sandwiching each opening 61 and the light shield 62 is provided.
Is replaced with, for example, the first and second photodetectors 41 and 42 in FIG. As a result, when the gantry 33 is rotated, the information slits 63 sandwiched by the photodetectors 66 are sequentially changed, and “ON” and “OF” output from each photodetector 65.
The combination of “F” changes for each information slit 63. If the absolute angle of the gantry 33 is assigned to the combination of “ON” and “OFF”, the rotational position information of the X-ray source 34 and the X-ray detector 35 can be detected by the absolute angle.

Further, in the above operation, the operation at the time of image pickup by the helical scan for the two image pickup areas is described as an example, but the rotation speed is switched for each image pickup area for three or more image pickup areas. Also in the case of capturing images by changing the rotation speed every time the rotation speed is changed, the moving speed of the tabletop 22 is changed and adjusted according to the changing rotation speed. As in the case, continuous imaging becomes possible.

[0073]

As is apparent from the above description, according to the present invention, the rotational speed of the X-ray source or the like can be switched, and the rotational speed of the X-ray source or the like can be decelerated or accelerated by switching the rotational speed. Since the moving speed of the tabletop is changed according to the rotating speed during the change, even if the rotating speed of the X-ray source or the like is switched during imaging by the helical scan, The moving speed of the top plate can be set according to the rotating speed of the X-ray source or the like.

Further, since data collection during imaging by helical scanning is performed based on rotational position information of the X-ray source or the like, even if the rotation speed of the X-ray source or the like is switched during imaging by helical scanning, one revolution is completed. The data collection per hit can always be performed a fixed number of times.

Further, since the position information of the top is detected at the time of data collection, even if the rotation speed of the X-ray source or the moving speed of the top changes during the image pickup by the helical scan, It is possible to obtain an accurate top plate position for the collected data.

Therefore, for example, even when a plurality of image pickup areas adjacent to each other are picked up by a helical scan by changing the rotation speed of the X-ray source or the like for each image pickup area, the helical scan of these image pickup areas is performed. Can be continuously performed, and the overall imaging time can be shortened. This can also reduce the burden on the subject.

[Brief description of drawings]

FIG. 1 is an overall view showing a schematic configuration of an X-ray CT apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a top position detecting unit.

FIG. 3 is a diagram showing a configuration of a rotational position detector.

FIG. 4 is a block diagram showing a configuration of a control processing unit.

FIG. 5 is a diagram for explaining imaging conditions.

FIG. 6 is a diagram for explaining a positioning operation.

FIG. 7 is a diagram showing a startable state of imaging.

FIG. 8 is a graph showing a change in rotation speed when the rotation speed is switched.

FIG. 9 is a graph showing a change in the moving speed of the tabletop in accordance with the rotation speed switching.

FIG. 10 is a diagram showing a relationship between X-rays emitted from an X-ray source during imaging and X-ray detectors of respective channels forming the subject and the X-ray detector.

FIG. 11 is a diagram showing a trajectory of displacement of an X-ray source or the like with respect to a subject.

FIG. 12 is a diagram showing a schematic configuration of a modified example of a sensor for detecting a rotational position.

[Explanation of symbols]

 1 ... Bed 2 ... Gantry 11 ... Top plate position detection unit 12 ... Top plate movement control unit 13 ... Rotation position detection unit 14 ... Rotation control unit 17 ... First memory 18 ... Pre-processing unit 19 ... Second memory 20 ... Image reconstruction unit 22 ... Top plate 23 ... Motor for horizontal movement of top plate 24 ... Rotary encoder 34 ... X-ray source 35 ... X-ray detector 36 ... DAS 38 ... Motors for rotation of X-ray source 41, 42 ... 1st, 2nd photodetector M ... Subject SA1, SA2 ... 1st, 2nd imaging area

Claims (1)

[Claims] 1. An X-ray source for irradiating an object placed on a top plate with X-rays, and an X-ray detector arranged to face the X-ray source with the object interposed therebetween. In an X-ray CT apparatus for horizontally scanning the top plate while rotating around the subject to perform a spiral scan (helical scan) and continuously image a continuous region (imaging region) of the subject. (A) a rotational position detecting means for detecting positional information (angular position information) of the X-ray source and the X-ray detector during rotation of the X-ray source and the X-ray detector; Based on the position information of the X-ray source and the X-ray detector detected by the rotational position detecting means, the transmitted X-ray data detected by the X-ray detector is stored in the X-ray source at predetermined angular intervals. The X
Data collection means for collecting a predetermined number of times during one round of the line detector, (c) rotation control means for drivingly controlling the rotation speeds of the X-ray source and the X-ray detector, and (d)
The horizontal movement speed of the top plate is controlled according to the rotation speeds of the X-ray source and the X-ray detector, and at least when the rotation speeds of the X-ray source and the X-ray detector are changing. A horizontal movement speed of the top plate based on a current rotation speed of the X-ray source and the X-ray detector obtained from position information of the X-ray source and the X-ray detector detected by the rotation position detecting means. And (e) a top position detecting means for detecting position information of the top at the time of data collection by the data collecting means, and (f)
An X-ray CT including an image reconstructing unit that reconstructs a tomographic image of a predetermined region of the subject based on the data collected by the data collecting unit and the position information of the top at that time. apparatus.