JP3402722B2 - X-ray computed tomography apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray computed tomography apparatus for collecting projection data of a subject from multiple directions and reconstructing a tomographic image based on these projection data.

[0002]

2. Description of the Related Art In an X- ray computed tomography apparatus (hereinafter abbreviated as "X-ray CT") , a thin slide
Imaging the area near the center of the lesion area with the thickness of the
Very effective at. Conventionally, the slice position is in the lesion
Thick slice thickness, 10 mm spacing to align with the heart
The rice thickness is roughly scanned while scanning the periphery of the lesion with multiple slices.
After confirming the slice position at the center of the crab lesion,
Is a thin slice thickness, and a slice thickness of 1 mm makes it possible to scan multiple faults.
While observing the tomographic image,
It was In this way, the conventional alignment work requires time and labor.
In addition to being exposed to radiation, the amount of radiation exposure is increased because scanning is repeated on multiple faults
Could increase.

[0003]

[0004]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to reduce the labor and time required for aligning a slice position having a thin slice thickness with the center of a lesion, and to suppress the radiation dose during this alignment work. It is to provide an X-ray computed tomography apparatus capable of performing the above.

[0005]

SUMMARY OF THE INVENTION The present invention is an X-ray computed tomography apparatus for reconstructing multi-directional projection data of an object to obtain a tomographic image of the object, the X-ray being directed toward the object. And an X-ray tube for irradiating the X-ray and a channel direction for detecting the X-ray transmitted through the subject.
And the X-ray detection means having a plurality of X-ray detection element, said slit for limiting a bed that move can and in the slice direction of the object, the X-rays exposure from said X-ray tube with respect to the slice direction, a slit moving unit for moving said slit in said slice direction, the range wherein the slit comprises a site of interest of the subject by the slit moving means
Corresponding to the region of interest while being moved in the slice direction
Repeated detection by a specific X-ray detection element of the X-ray detection means
Based on a plurality of detected signals having different slice positions, a determination unit that determines the position of the region of interest in the slice direction, and the X-ray tube according to the position in the slice direction of the region of interest determined by the determination unit A control means for controlling the bed so that the slit, the region of interest, and the X-ray detection means are arranged in a straight line.

[0006]

According to the X-ray computed tomography apparatus of the present invention, the slit covers the range including the region of interest of the subject.
X-ray detection corresponding to the region of interest while moving in the chair direction
Slices repeatedly detected by a specific X-ray detection element of the means
Based on multiple detection signals with different position
Determine the position in the slice direction. Find this slice position
Conventionally, in order to search for
Rough slice position while scanning the periphery with multiple slices
After confirming, check again with thin slice thickness
The precise position is specified while looking at the tomographic image while scanning the layers.
And gradually cut the slice thickness in this way
It was necessary to repeat the layer scan. However, in the present invention
Is due to the repetition of multiple tomographic scans as in the past
Instead, the slit is slid over the range including the region of interest of the subject.
X-rays are emitted only while moving in the chair direction, and detection is performed during that time.
Since it is sufficient to collect the output signal repeatedly, the position of the site of interest
The time required for matching work can be reduced, and
Reduced exposure dose required for slice position determination
can do.

[0007]

Embodiments will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram of an X-ray computed tomography apparatus (hereinafter abbreviated as “X-ray CT”) according to the first embodiment.
The X-ray CT uses detection signals at each of a plurality of angles with respect to the object detected by the X-ray detection means while the X-ray tube and the X-ray detection means are relatively moving while facing each other in a predetermined imaging plane. In the third generation, the X-ray tube and the X-ray detection means rotate while facing each other, and in the fourth generation, the X-ray detection means is fixed and the X-ray is reconstructed. Only the tube rotates.

An X-ray tube 2 for exposing X-rays to the gantry 1.
And a multi-channel X-ray in which a plurality of X-ray detection elements for converting the X-rays transmitted through the subject P installed on a bed (not shown) near the center O of the imaging region into electric signals are arranged one-dimensionally. The detector 3 is housed therein. The X-ray tube 2 and the multi-channel X-ray detector 3 are held on a rotary mount (not shown) so as to face each other across the imaging region and to be rotatable about the center O as indicated by an arrow. In this rotating coordinate system,
Hereinafter, the arrangement direction of the plurality of X-ray detection elements will be appropriately used as the channel direction X, the direction orthogonal to the channel direction X in the rotation plane as the X-ray projection direction Y, and the direction orthogonal to the rotation plane as the slice direction Z.

A high voltage generating circuit 7 is connected to the X-ray tube 2, and a high voltage is applied to the X-ray tube 2 to irradiate the X-ray tube 2 with X-rays. A bed platform control mechanism 8 is connected to the above-described rotary platform and the bed that moves the subject along the slice direction Z (body axis) and inserts the subject into the imaging region.
It controls the rotation of the rotating gantry and the movement of the bed. The bed platform control mechanism 8 includes a bed platform control circuit 9 for controlling this.
Are connected.

In front of the X-ray emission window of the X-ray tube 2, a slit device 4 for limiting the X-ray irradiation range is arranged. In the slit device 4, for example, two rectangular X pieces are formed so as to form a rectangular slit along the channel direction X.
The line shields are arranged in parallel. These X-ray shields are held by the slit control mechanism 5 and can be moved along the slice direction. As a result, the width of the slit in the slice direction Z is variably adjusted within the range of 10 mm to 1 mm. Further, when the two X-ray shields are moved in parallel along the slice direction Z while keeping a constant interval, the slits are moved in parallel along the slice direction Z. The slit width and parallel movement are controlled by the slit control circuit 6.

The individual detection signals detected by the respective X-ray detection elements of the multi-channel X-ray detector 3 are independently amplified by the data acquisition circuit 10 and converted into digital signals to be processed by the data preprocessing section. Then, the image data is sent to the image reconstruction circuit 11 and subjected to preprocessing such as sensitivity correction, and then sent to the image reconstruction circuit 12 directly or via the data storage circuit 13 such as an external disk device. The tomographic image reconstructed by the image reconstruction circuit 12 is sent to the display circuit 15 via the image memory 14 and displayed.

The cross-shaped pointer (cursor) displayed on the display circuit 15 moves in association with the operation of the operator of the ROI input section 16 such as a trackball or a joystick. The region of interest (RO
I) is designated on the tomographic image. The position of the pointer in the coordinate system of the tomographic image, that is, the ROI position is calculated by the ROI position calculation circuit 17. This ROI position is sent to the channel position calculation circuit 18. Channel position calculation circuit 1
8 is an X at a predetermined position (for example, 0 ° (topmost position))
One X-ray detection element (channel) on the extension line passing through the actual ROI of the subject in the imaging region is specified from the ray tube 2. That is, when the X-ray tube 2 is at the predetermined position, the X-rays that have transmitted through the actual ROI in the subject are detected by the channel specified by the channel position calculation circuit 18.

When the X-ray tube 2 is in a predetermined position, the X-ray tube 2
X-rays are continuously or intermittently emitted. In the meantime, the width of the slit of the slit device 4 is set to amm (a <Amm), and along the slice direction Z, for example, bmm (b <Bm).
m) is translated. As a result, the region before and after the actual ROI in the subject is scanned in the Bmm range along the slice direction Z with the X-ray having a thin slice thickness of Amm. a: A and b: B are set so as to match the distance from the X-ray focus to the slit: the distance from the slit to the subject. For example, A = 1mm, B = 10m
It is set to m, a = 0.2 mm and b = 2 mm. The following describes these settings.

While the X-ray tube 2 is in place and the slit is translated in a range of 2 mm with a width of 0.2 mm, X
X-rays are repeatedly emitted from the ray tube 2. X-ray detection element (channel) specified by the channel position calculation circuit 18
Only the detection signal detected by the data collection preprocessing circuit 1
The data is selected from 1 by the slice thickness direction scanning data collection circuit 19 and sent to the target position determination circuit 20 one after another.

In the target position determination circuit 20, a plurality of detection signals detected while the slits are translated in the slice direction Z, the vertical axis represents intensity, and the horizontal axis represents distance (slice center of the X-ray detection element). Distance) from the data space. In the target position determination circuit 20, a characteristic point in the change of the detection signal intensity depending on the distance, for example, a minimum point (generally, the lesion part has a larger X-ray absorption amount than the healthy part, and thus the detection signal intensity is low) or Maximum point (cyst in the brain, etc.)
Is recognized and the distance (target position) is determined. The determined target position is sent to the central control circuit 21 as a determination signal. The central control circuit 21 determines the distance from the slice center of the X-ray detection element determined by the target position determination circuit 20,
The distance on the subject is converted based on the ratio of the distance from the X-ray focus to the slit and the distance from the slit to the subject. The bed is controlled according to the conversion result. As a result, the subject moves in the slice direction by the distance on the subject. This allows the X-ray tubes 2 and 1 to be placed on the imaging surface.
The slit of mm width, the actual ROI (region of interest (lesion)) of the subject, and the detector 3 are aligned in a straight line, and the alignment is completed. At this position, a 1 mm thick plane including the ROI center is scanned to reconstruct a tomographic image of the lesion.

Next, a procedure for aligning the scan position of the thin slice thickness according to the present embodiment configured as described above with the center of the ROI (region of interest (lesion)) will be described. First, as shown in FIG. 2A, the slit device 4
The slit width d is thick and is set to, for example, 10 mm. this
With a slice thickness of 10 mm, multiple slices are scanned while the bed moves intermittently or continuously. That is, while the X-ray tube 2, the multi-channel X-ray detector 3 and the slit device 4 continuously rotate around the subject, the X-ray irradiation is performed intermittently or continuously for every minute angle, and Multi-directional projection data for the specimen is detected. This detection signal is sent to the image reconstruction circuit 1 via the data acquisition circuit 10 and the data preprocessing circuit 11.
2 and is reconstructed into a tomographic image. The tomographic image is displayed on the display circuit 15 via the image memory 14. This operation is repeated by changing the slice position while the bed moves intermittently or continuously, and the tomographic image showing the ROI (region of interest (lesion)) is specified by the operation of the operator of the ROI input unit 16. Under the control of the central control circuit 21, the bed moves backward and the scan position of the subject when the specified tomographic image is captured is set in the imaging region.

Further, as shown in FIG. 3, the operator operates the ROI input unit 16 on the specified tomographic image to specify the lesion area as the ROI with a pointer. Position of the pointer in the coordinate system of the tomographic image, that is, R
The OI position is calculated by the ROI position calculation circuit 17. This ROI position is sent to the channel position calculation circuit 18. As shown in FIG. 4, the channel position calculation circuit 18
Thus, one X-ray detection element (channel ch _n ) on the extension line that passes through the actual ROI of the subject in the imaging region from the X-ray tube 2 located at the predetermined position is specified.

The X-ray tube 2 is controlled by the central control circuit 21.
The rotation of the X-ray tube 2 is stopped, the X-ray tube 2 is fixed at a predetermined position of 0 °, and the slit width d ′ is thinly adjusted to 1 mm here as shown in FIG. 2 (b). Slit device 4
The width of the slit of 1mm remains 1mm,
As shown in (b), for example, 10 along the slice direction Z
Translated by mm. At this time, X-rays are continuously or intermittently emitted from the X-ray tube 2, and the multi-channel X-ray detector 3 repeats the X-ray detection. As a result, a range of 10 mm in front of and behind the actual ROI in the subject is scanned along the slice direction Z with an X-ray having a thin slice thickness of 1 mm.

By this scan, a plurality of detection signals having different slice positions detected by the X-ray detection element (channel) specified by the channel position calculation circuit 18 are acquired from the data acquisition preprocessing circuit 11 in the slice thickness direction scan data acquisition. It is sent to the target position determination circuit 20 via the circuit 19.

In the target position determination circuit 20, as shown in FIG. 6, these detection signals indicate that the slit is in the slice direction Z.
A plurality of detection signals with different slice positions detected while being translated along the axis are intensity on the vertical axis and distance (X
The distance from the slice center of the line detection element) is distributed in the data space. In the target position determination circuit 20, a characteristic point in the change of the detection signal intensity according to the distance, for example, a minimum point (generally, the lesion part has a larger X-ray absorption amount than the healthy part,
Therefore, the detected signal intensity is low) or the maximum point (cyst in the brain) is recognized, and the distance (target position) is determined. The determined target position is sent to the central control circuit 21 as a determination signal. The central control circuit 21 determines the distance from the slice center of the X-ray detection element determined by the target position determination circuit 20 based on the ratio between the distance from the X-ray focal point to the slit and the distance from the slit to the subject described above. And convert it to the distance on the subject. The bed is controlled according to the conversion result. As a result, the subject moves in the slice direction by the distance on the subject. As a result, the X-ray tube 2, the slit with a width of 1 mm, the actual ROI (region of interest (lesion)) of the subject, and the detector 3 are linearly arranged on the imaging surface,
The alignment is complete.

At this slice position, 1 m including the ROI center
An m-thick plane is scanned to reconstruct a tomographic image containing the lesion. In the above description, when the lesion area is scanned along the slice direction Z with a thin slice thickness of 1 mm, the rotation of the X-ray tube 2 and the like is stopped, and the X-ray tube 2 is at a predetermined position of 0 °. Although the position is fixed, if the parallel movement of the slit is sufficiently fast with respect to the rotation speed of the X-ray tube 2 or the like, the above scanning can be performed while the X-ray tube 2 or the like is rotating. For this purpose, the moving speed V of the slit is X
The number of times of data collection repeated during one rotation of the tube 2 (this number is generally called a sample number, and the position of each data collection is called a sample point) is set to 900,
If the time required for the X-ray tube to make one rotation is t, and the area around the lesion is to be scanned with a thin slice thickness of 1 mm along the slice direction Z is 10 mm, the following equation (1) is satisfied without do it.

10 mm / V ≦ t / 900 (1) That is, as shown in FIG. 7, in the time interval in which the X-ray tube 2 moves from one sample point P ₀ to the next sample point P ₁ ,
The slit has completed at least the planned movement of 10 mm along the slice direction Z. Even if the X-ray tube 2 etc. rotates, the lesion area is scanned along the slice direction Z with a thin slice thickness of 1 mm. It is a prerequisite that can be done.

Further, in the above description, the lesion area is detected on the basis of "change in detection signal intensity according to distance" measured at one place when the X-ray tube 2 is at a predetermined position (for example, 0 ° position). The position is determined, but this causes a problem that this determination becomes difficult when the lesioned part is shadowed by ribs or the like. Therefore, as shown in FIG. 8, the X-ray tube 2 is placed at the predetermined position P.
Not only when it is at ₀ , but at another angle, for example, the predetermined position P
_The “change in detection signal intensity according to distance” is measured at each of a plurality of angles such as the position P ₄₅ rotated from ₀ to 45 °, and the lesion area of the lesion site is measured based on the plurality of “changes in detection signal intensity according to the distance”. It is desirable to determine the position. The “change in detection signal intensity according to distance” in FIG. 9A corresponds to P ₀ in FIG.
The “change in detection signal intensity according to distance” in FIG. 9B corresponds to P ₄₅ in FIG. A plurality of “changes in the detection signal intensity depending on the distance” may be selected to have one local minimum value and used for the determination of the lesion position, or a plurality of “detection depending on the distances”. It may be used for determining the lesion position based on a new “change in detected signal strength according to distance” as a result of average addition of “change in signal strength”. The present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

[0024]

According to the X-ray computed tomography apparatus of the present invention, the range in which the slit includes the region of interest of the subject
While moving in the slice direction, X corresponding to the region of interest
Repeatedly detected by a specific X-ray detecting element of the line detecting means.
Interest based on multiple detection signals with different slice positions
The position of the part in the slice direction is determined. This slice
Traditionally, to search
Slice roughly while scanning the area around the site with multiple faults
Check the position of the slice, and after checking, the same with a thin slice thickness
Accurate position while observing tomographic images while scanning with multiple tomography
Location, and gradually reduce the slice thickness in this way.
It was necessary to repeat multiple tomographic scans. But the book
In the present invention, by repeating the multi-slice scan as in the past,
Instead of the slit, the slit covers the range including the region of interest of the subject.
Exposure to X-rays only while moving in the slice direction, during that time
Since it is sufficient to collect the detection signal repeatedly,
The time required for alignment work can be shortened and
Dose required to determine the slice position of
Can be reduced.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an X-ray CT according to an embodiment of the present invention.

FIG. 2 is a diagram showing a change in slit width.

FIG. 3 is a diagram showing a tomographic image and a pointer displayed on the display circuit of FIG.

4 is a diagram showing channels specified by the channel position calculation circuit of FIG. 1. FIG.

FIG. 5 is a diagram showing parallel movement of slits.

FIG. 6 is a diagram showing an example of changes in the detection signal intensity measured by the target position determination circuit of FIG. 1 along the slice direction.

FIG. 7 is a diagram showing two adjacent sample points.

FIG. 8 is a diagram showing a plurality of angles for measuring a change in detected signal intensity along a slice direction.

9 is a diagram showing an example of changes in the detected signal intensity at each angle in FIG. 8 along the slice direction.

[Explanation of symbols]

1 ... Gantry, 2 ... X-ray tube, 3 ... Multi-channel type X-ray detector, 4 ... Slit device, 5 ... Slit control mechanism, 6 ...
Slit control circuit, 7 ... High-voltage generating circuit, 8 ... Sleeping bed control mechanism, 9 ... Sleeping bed control circuit, 10 ... Data collecting circuit, 11 ... Data preprocessing circuit, 12 ... Image reconstruction circuit,
13 ... Data storage circuit, 14 ... Image memory, 15 ... Display circuit, 16 ... ROI input section, 17 ... ROI position calculation circuit, 18 ... Channel position calculation circuit, 19 ... Slice thickness direction scanning data collection circuit, 20 ... Target position Judgment circuit, 2
1 ... Central control circuit.

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) A61B 6/00-6/14

Claims (5)

(57) [Claims] 1. An X-ray computed tomography apparatus for reconstructing multi-directional projection data of a subject to obtain a tomographic image of the subject, comprising an X-ray tube for irradiating the subject with X-rays. A channel for detecting X-rays transmitted through the subject
X having a plurality of X-ray detection elements arranged in the direction
And line detecting means, the a bed which enables moving the object in the slice direction, a slit <br/> restrictions on slice direction the X-rays exposure from said X-ray tube, the slice direction the slit in a slit moving unit for moving said slit by the slit moving means said subject
The area including the region of interest of the body is moved in the slice direction.
Of the X-ray detecting means corresponding to the region of interest during
Of the slice position repeatedly detected by the X-ray detection element of
Made on the basis of a plurality of detection signals, judging means for judging the position in the slice direction of the pre-Symbol Seki heart site, according to the position of the determined slice direction of the region of interest by the determination means, the X-ray tube, said slit An X-ray computed tomography apparatus comprising: a control unit that controls the bed so that the region of interest and the X-ray detection unit are aligned in a straight line. 2. The X according to claim 1, wherein the determination unit determines a position where the output change of the X-ray detection unit is characteristic as a position in the slice direction of the region of interest.
Line computed tomography equipment. 3. The determination means is based on a change in output of the X-ray detection means when each of the X-ray tube and the X-ray detection means is in a predetermined position with respect to the subject. X-ray computed tomography apparatus according to claim 1, wherein determining the slice direction position of the site. 4. The determination means is based on a plurality of changes in output of the X-ray detection means when the X-ray tube and the X-ray detection means are at respective predetermined plurality of positions with respect to the subject. Te, X-rays computed tomography system according to claim 1, wherein determining the slice direction position of the region of interest. Wherein said determining means claims on the basis of a plurality of the output change to a new output change obtained by adding the X-ray detecting means, and judging the slice direction position of said region of interest The X-ray computed tomography apparatus according to 4.