JP3249088B2 - X-ray irradiation alignment method and X-ray tomographic imaging 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 irradiation positioning method and an X-ray tomography method and apparatus, and more particularly to X-ray irradiation for irradiating an X-ray generated from an X-ray tube to an X-ray detector through a collimator. The present invention relates to an X-ray irradiation position alignment method for a detection device, and an X-ray tomography method and apparatus for performing X-ray irradiation position alignment and imaging.

[0002]

2. Description of the Related Art X-ray computed tomography (CT)
(Graphy), an X-ray irradiation / detection device for irradiating an X-ray detector with X-rays generated from an X-ray tube through a collimator is rotated (scanned) around the subject to scan around the subject. Projection data (data) of the subject by X-rays is measured in each of a plurality of view directions, and a tomographic image is generated (reconstructed) based on the projection data.

An X-ray irradiator irradiates an X-ray beam having a width that encompasses an imaging range and a predetermined thickness in a direction perpendicular thereto. The thickness of the X-ray beam is set by the degree of opening of the X-ray passage aperture (aperture) of the collimator.

The X-ray detector detects X-rays by a multi-channel X-ray detector in which a large number of X-ray detection elements are arranged in an array in the direction of the width of the X-ray beam. The multi-channel X-ray detector has a length (width) corresponding to the width of the X-ray beam in the direction of the width of the X-ray beam. In the direction of the thickness of the X-ray beam, X
It has a length (thickness) larger than the thickness of the line beam.

[0005] Some X-ray detectors have an array of X-ray detecting elements in two rows so that projection data for two slices can be obtained at one time. There, two rows of arrays are arranged adjacent to and parallel to each other, and the X-ray beam is uniformly distributed in the thickness direction and irradiated. The thickness of the X-ray beam applied to the two rows of arrays at the isocenter of the subject determines the slice thickness of the tomographic image.

In the X-ray tube, the focal point of the X-ray moves due to thermal expansion or the like due to a rise in temperature during use, and this shift appears as a displacement in the thickness direction of the X-ray beam through the aperture of the collimator. When the X-ray beam is displaced in the thickness direction, 2
The distribution ratio of the thickness of the X-ray beam in the row array changes, and the slice thickness of the subject projected on the two arrays is not uniform.

[0007] Therefore, reference channels provided in two-row arrays are respectively provided.
monitor the ratio of x-ray counts
Since the ratio is no longer 1, the deviation of the X-ray irradiation position is recognized, and the position of the collimator is adjusted to control the X-ray irradiation position to be a fixed position.

[0008]

Since the above-described irradiation position control does not start unless X-ray irradiation is performed to start scanning, it is considered that the X-ray irradiation position coincides with the fixed position immediately after the start of scanning. Not necessarily, but rather more often than not. For this reason, there was a problem that the quality of the initially obtained image tends to be poor.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an X-ray irradiation position alignment method for making an X-ray irradiation position coincide with a fixed position from the beginning of scanning, and a method of adjusting the position. An object of the present invention is to realize an X-ray tomography method and apparatus for performing X-ray irradiation position alignment and imaging.

[0010]

Means for Solving the Problems (1) According to a first aspect of the present invention, an X-ray irradiating / detecting device irradiates an X-ray generated from an X-ray tube to an X-ray detector through a collimator. In performing tomography by scanning a sample, the position of an X-ray focal point in the X-ray tube is predicted based on the temperature of the X-ray tube before the start of scanning and a scan condition to be performed, and the position of the X-ray tube generated from the X-ray tube is calculated. Adjusting the position of one or both of the collimator and the X-ray detector in accordance with the predicted position so that the X-rays emitted irradiate a fixed position in the X-ray detector, X-ray irradiation position adjustment method.

(2) According to a second aspect of the present invention, an X-ray radiating / detecting device for irradiating an X-ray generated by an X-ray tube through a collimator to an X-ray detector scans a subject tomography. In performing imaging, the position of the X-ray focal point in the X-ray tube is predicted based on the temperature of the X-ray tube before the start of scanning and the scan conditions to be performed from now on. Adjust the position of one or both of the collimator and the X-ray detector according to the predicted position to irradiate a fixed position in the X-ray detector, the X-ray irradiation after the position adjustment An X-ray tomography method characterized by performing tomography by scanning with a detection device.

(3) According to a third aspect of the present invention, a subject is scanned by an X-ray irradiating / detecting device which irradiates an X-ray generated by an X-ray tube through a collimator to an X-ray detector. An X-ray tomography apparatus for performing imaging, wherein focus position estimating means for estimating a position of an X-ray focal point in the X-ray tube based on a temperature of the X-ray tube before a scan is started and a scan condition to be performed; One or both of the collimator and the X-ray detector according to the predicted position of the X-ray focal point so that the X-ray generated from the X-ray tube irradiates a fixed position in the X-ray detector. And a position adjusting means for adjusting the position of the X-ray tomography apparatus.

[0013] In any one of the first to third inventions, it is preferable that the scan condition includes at least a tilt angle and a scan time of the X-ray irradiation / detection device. This is preferable in that the position is appropriately predicted.

[0014] In any one of the first to third inventions, the scan condition includes at least a tilt angle and an azimuth angle of the X-ray irradiation / detection device. This is preferable in that the line focus position is appropriately predicted.

[0015] In the above case, X is further added to the scan condition.
It is preferable to include the size of the X-ray focal point from the viewpoint of appropriately predicting the X-ray focal position when the size of the X-ray focal point is changed. (Operation) In the present invention, the positions of the collimator and the X-ray detector are adjusted in accordance with the position of the X-ray focal point predicted before the start of the scan, and the X-rays are moved to the home position of the X-ray detector from the beginning of the scan. Be irradiated.

[0016]

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. An example of an embodiment of the method of the present invention is shown by the operation of the present apparatus.

As shown in FIG. 1, this apparatus comprises a scanning gantry 2 and a photographing table 4.
And an operation console (console) 6. The scanning gantry 2 has an X-ray tube 20. X-ray tube 20
Is an example of an embodiment of an X-ray tube according to the present invention.
The X-ray tube 20 is provided with a temperature detector (not shown). An X-ray (not shown) emitted from the X-ray tube 20 is shaped by the collimator 22 into, for example, a fan-shaped X-ray beam, and is applied to the detector array 24. The collimator 22 is an example of an embodiment of the collimator according to the present invention. The detector array 24 is an example of an embodiment of the X-ray detector according to the present invention. The detector array 24 has a plurality of X-ray detection elements arranged in an array in the direction in which the fan-shaped X-ray beam spreads. The configuration of the detector array 24 will be described later.

The X-ray tube 20, collimator 22 and detector array 24 constitute an X-ray irradiation / detection device. The X-ray irradiation / detection device is an example of an embodiment of the X-ray irradiation / detection device in the present invention. The configuration of the X-ray irradiation / detection device will be described later. A data collection unit 26 is connected to the detector array 24. Data collection unit 2
6 collects the detection data of the individual X-ray detection elements of the detector array 24. The data collection unit 26 also includes the X-ray tube 20
Collect temperature data.

The irradiation of X-rays from the X-ray tube 20 is controlled by an X-ray controller (controller) 28. The illustration of the connection relationship between the X-ray tube 20 and the X-ray controller 28 is omitted. The collimator 22
It is controlled by the collimator controller 30. The illustration of the connection relationship between the collimator 22 and the collimator controller 30 is omitted.

The above-mentioned X-ray tube 20 or collimator controller 30 is mounted on the rotating unit 32 of the scanning gantry 2. The rotation of the rotation unit 32 is controlled by a rotation controller 34. The rotation unit 32
The illustration of the connection relationship between the motor and the rotation controller 34 is omitted. The scanning gantry 2 also has a tilt (til)
t) having a controller 36; Tilt controller 3
Reference numeral 6 controls the tilt operation of the scanning gantry 2.

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

The operation console 6 has a central processing unit 60. The central processing unit 60 is constituted by, for example, a computer. The central processing unit 60 has a control interface (interfac).
e) 62 is connected. The scanning gantry 2 and the imaging table 4 are connected to the control interface 62.

The central processing unit 60 has a control interface 6
2, the scanning gantry 2 and the imaging table 4 are controlled. A data acquisition unit 26, an X-ray controller 28, a collimator controller 30, a rotation controller 34, and a tilt controller 36 in the scanning gantry 2 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 central processing unit 60
It is an example of embodiment of a focus position prediction means in the present invention. The part consisting of the central processing unit 60, the control interface 62 and the collimator controller 30 is an embodiment of the position adjusting means in the present invention.

A data acquisition buffer 64 is also connected to the central processing unit 60. Data collection buffer 6
4 is connected to the data collection unit 26 of the scanning gantry 2. The data collected by the data collection unit 26 is input to the data collection buffer 64. Data collection buffer 6
4 temporarily stores the input data.

The central processing unit 60 also has a storage device 6
6 are connected. The storage device 66 stores various data, reconstructed images, programs, and the like. The display device 68 and the operation device 70 are also connected to the central processing unit 60. Display device 68
Displays the reconstructed image and other information output from the central processing unit 60. The operation device 70 is operated by an operator, and inputs various instructions and information to the central processing unit 60.

FIG. 2 shows a schematic configuration of the detector array 24. The detector array 24 forms two rows of multi-channel X-ray detectors 242 and 244 in which a large number (for example, about 1000) of X-ray detection elements 24 (i) are arranged in an arc shape. i is a channel number, for example, i = 1 to 100
0. The X-ray detectors 242 and 244 are adjacent to each other in parallel. A predetermined number of channels at both ends of the detector array 24 are reference channels in each row. The reference channel is outside the range where the subject is projected during imaging.

FIG. 3 shows an interrelationship between the X-ray tube 20, the collimator 22, and the detector array 24 in the X-ray irradiation / detection apparatus. (A) of the same figure is a front view, (b) is a side view. Here, three coordinate axes perpendicular to each other in a geometric space formed by the X-ray irradiation / detection device are defined as x, y, and z. The same applies to other figures shown below. As shown in the figure, the X-ray emitted from the X-ray tube 20 is
Is shaped into a fan-shaped X-ray beam 40 so that the detector array 24 is irradiated. In FIG. 3A, the spread of the fan-shaped X-ray beam 40, that is, X
The width of the line beam 40 is shown. The fan surface of the X-ray beam 40 is xy
Parallel to the plane. FIG. 3B shows the thickness of the X-ray beam 40. The X-ray beam 40 has two rows of X-ray detectors 24.
2, 244 are irradiated with the thickness evenly distributed. X
The thickness direction of the line beam 40 is the z direction. The z direction is also the direction of the rotation axis of the X-ray irradiation / detection device.

The fan axis of the X-ray beam 40 is crossed with the body axis, and for example, as shown in FIG.
Is placed in the X-ray irradiation space. The body axis of the subject 8 matches the z direction. X-ray beam 40
The projection image of the subject 8 sliced by the above is projected on the detector array 24. Each half of the thickness of the X-ray beam 40 at the isocenter of the subject 8 gives two slice thicknesses th of the subject 8. Slice thickness th
Is determined by the aperture of the collimator 22.

X-ray beam 40 for detector array 24
FIG. 5 shows a more detailed schematic diagram of the irradiation state of FIG. As shown in FIG.
By displacing 0, 222 in the direction to narrow the aperture, the slice thickness th of the projected image in the X-ray detectors 242, 244 can be reduced. Further, by moving the collimator pieces 220 and 222 in the direction in which the aperture is widened, the slice thickness th of the projected image can be increased. In addition, by simultaneously moving the collimator pieces 220 and 222 with the slice thickness th set in the z direction while maintaining the relative positional relationship, the irradiation position in the z direction on the detector array 24 can be adjusted.

The slice thickness adjustment and the irradiation position adjustment are performed by the collimator controller 30.
The irradiation position in the z direction is detected based on the output ratio of two rows of reference channels in the detector array 24, and based on this detection signal, the collimator 22 is adjusted so that the slice thickness becomes equal on the two detector rows. The position is adjusted. As a result, the change in the irradiation position due to the movement of the focal point of the X-ray tube is corrected, and the X-ray beam 40 is always irradiated to the fixed position. Hereinafter, this function is referred to as an auto collimator.

The adjustment of the irradiation position in the z direction is performed by displacing the detector array 24 relative to the collimator 22 in the z direction, as indicated by a broken arrow, instead of moving the collimator pieces 220 and 222. You may do it.
In this way, two separate systems for adjusting the slice thickness and controlling the irradiation position in the thickness direction can be provided.
Multilateral control becomes possible. On the other hand, if all the operations are performed by the collimator 22 as described above, the control system can be unified into one system, and it is possible to meet the demand for simplifying the configuration. It is needless to say that the irradiation position may be adjusted by combining these two means.

The X-ray irradiating / detecting device comprising the X-ray tube 20, the collimator 22, and the detector array 24 rotates around the body axis of the subject 8 while maintaining their mutual relationship (axial scan). I do. Projection data of the subject is collected at a plurality of (eg, about 1000) view angles per rotation of the scan. The collection of projection data is performed by a system including the detector array 24, the data collection unit 26, and the data collection buffer 64.

Based on the projection data for two slices collected in the data collection buffer 64, the central processing unit 60 generates tomographic images for two slices, that is, performs image reconstruction. Image reconstruction is performed, for example, by using projection data of, for example, 1000 views obtained by one rotation scan, for example, with filtered back projection (filteredba).
The processing is performed by, for example, a ck-projection method.

The scanning gantry 2 is controlled by the tilt controller 36.
Is tilted, the rotation axis (z
Axis) is inclined with respect to the body axis of the subject 8. Thus, scanning can be performed on the slice plane tilted counterclockwise or clockwise in FIG.

The X-ray irradiating and detecting device is irradiated with X-rays while the rotation of the X-ray irradiating / detecting device is stopped, and the projection table is collected while moving the imaging table 4 in the body axis direction of the object 8, thereby obtaining the object 8 The perspective image of is taken. Such fluoroscopy is used in stationary scans.
can). As the perspective image, a front image, a side image, or an oblique side image at an arbitrary angle is obtained according to the position of the X-ray tube 20 on the rotational orbit. The position on the rotational trajectory of the X-ray tube 20 during fluoroscopic imaging is represented by an angle (azimuth) with respect to the y direction.

FIG. 6 shows a schematic configuration of a main part of the X-ray tube 20. (A) of the same figure is a front view, (b) is a side view.
As shown in the figure, a rotating anode (anode) 200
And a cathode 202 are provided facing each other in a vacuum tube (not shown). A predetermined high voltage is applied between the rotating anode 200 and the cathode 202. The rotating anode 200 is driven by a driving unit (not shown) and rotates at high speed. The rotating anode 200 has an inclined surface facing the cathode 202, and the inclined surface is irradiated with an electron beam from the cathode 202, and generates an X-ray beam 40 by the collision energy of the electron beam.

Here, the irradiation area of the electron beam on the surface of the rotating anode 200 can be switched between a small area 204 and a large area 204 'by switching the cathode 202, for example. The small area 204 is the X-ray beam 40
Form a small X-ray focus to generate
4 'forms a large x-ray focus for generating an x-ray beam 40'. Hereinafter, the X-ray focal point is simply referred to as a focal point.

The temperature of the rotating anode 200 rises due to the collision energy of the electron beam, and as a result, the temperature of the X-ray tube 20 rises. The temperature of the X-ray tube 20 increases according to the duration of the X-ray irradiation. The position of the focal point in the z direction changes due to thermal expansion accompanying the temperature rise. The direction of displacement is a direction in which the rotation axis of the rotating anode 200 extends. Hereinafter, this direction is defined as +, and the opposite direction is defined as-.

Although the absolute amount of the displacement is very small, it is enlarged by an optical lever with the aperture of the collimator 22 as a fulcrum, so that the displacement of the X-ray irradiation surface of the detector array 24 becomes a considerable distance. The same applies to the focus movement due to other factors described below.

The movement of the focal point in the z direction is also caused by the tilt of the scanning gantry 2. That is, when tilted counterclockwise (+ direction) in FIG. 4, the focal point is displaced, for example, in the + direction, and when tilted clockwise (− direction), for example, −.
Displace in the direction. The focal position in the z direction is affected by the rotation speed of the scanning gantry 2 during scanning. The centrifugal force due to the rotation of the scanning gantry 2 acts on the X-ray tube 20 and the force changes depending on the rotation speed.
Move in the direction.

As shown in FIG. 6, when the size of the focal point is changed by changing the electron beam irradiation area on the rotating anode 200, the electron beam irradiation surface of the rotating anode 200 is tilted. The focus position in the direction changes. In addition, when performing stationary scans,
The azimuth of the X-ray tube 20 affects the position of the focal point in the z direction instead of the scan time being independent. That is, when the azimuth is 0 degree, the maximum displacement occurs in the + direction, for example, and
At 0 degrees, for example, a maximum displacement occurs in the negative direction. In the middle of azimuth, an intermediate displacement occurs between the two.

As described above, the position of the focal point in the z direction changes at least due to the temperature of the X-ray tube 20, the tilt angle of the scanning gantry 2, the scanning time, the magnitude of the focal point, and the azimuth. Therefore, when starting the scan, the central processing unit 60 predicts the amount of displacement of the focal point based on these factors, and adjusts the irradiation position of the X-ray beam 40 to the fixed position of the detector array 24. The movement distance in the z direction 22 is calculated. Alternatively, when a position adjusting mechanism of the detector array 24 is provided, the moving distance of the detector array 24 in the z direction for making the irradiation position of the X-ray beam 40 coincide with the fixed position of the detector array 24 is obtained. May be. Then, the position of the collimator 22 (or the detector array 24 or both) is adjusted according to the calculated value, and scanning is started.

FIG. 7 is a conceptual diagram showing the movement of the focal point and the corresponding position adjustment of the collimator. As shown in FIG.
The state where the focal point is located at a position 206 on a perpendicular line set in the center of the detector array 24 in the direction is set as a reference state. In this reference state, the position 230 of the collimator 22 that irradiates the center of the detector array with the X-ray beam 40 is defined as This is the reference position of the collimator.

The focal point moves from the reference state to the left (+
Direction), the collimator 22 must be moved from the reference position 230 to the + direction position 230 'in order to cause the detector array 24 to irradiate the center with the X-ray beam 40' emitted therefrom. There is. Similarly,
When the focal point moves from the reference state to a position 206 ″ in the right direction (−direction) in the figure, the collimator 22 is moved to the center in order to irradiate the detector array 24 with the X-ray beam 40 ″ emitted therefrom. It is necessary to move from the position 230 to the position 230 ″ in the − direction. Collimator 22
Is proportional to the focal distance z,

[0045]

(Equation 1)

Is as follows. Proportional constant G1 (gain: gai
n) is a positive value smaller than 1. FIG. 8 shows a conceptual diagram of the focus movement and the corresponding position adjustment of the detector array. When the focal point moves from the reference state to a position 206 'in the left direction (+ direction) in the figure, in order to cause the X-ray beam 40' emitted therefrom to be applied to the center of the detector array 24, the detector array 24 must be moved. It is necessary to move from the reference position 240 to the position 240 ′ in the − direction. Similarly, the focus is located at a position 20 in the right direction (−direction) in the figure from the reference state.
When the beam moves to 6 '', the X-ray beam 4
In order to illuminate the detector array 24 with 0 '' in the center,
The detector array 24 is moved from the reference position 240 to the position 2 in the + direction.
Need to move to 40 ''. Detector array 24
Is proportional to the focal distance z,

[0047]

(Equation 2)

Is as follows. Proportional constant G2 (gain: gai
n) is a negative value whose absolute value is greater than one. As a result of intensive studies, the present inventor has found that in the case of axial scanning, the following relationship exists between the focal point moving distance and the above-described factors.

[0049]

(Equation 3)

Here, T: temperature of X-ray tube, but percentage of operating temperature range T1: upper limit of temperature range, eg, 90% T2: lower limit of temperature range, eg, 10% U: tilt angle U1: tilt angle + Upper limit of direction, for example, 30 degrees U2: Upper limit of negative direction of tilt angle, for example, 30 degrees V: Scan time V1: Longest scan time, for example, 3 seconds V2: Shortest scan time, for example, 0.8 seconds W: Focus size, Large = 1, small = 0 a, b, c, d, k: constants In the case of stationary scanning, it has been found that the following relationship exists between the focal distance and each factor.

[0051]

(Equation 4)

Here, T: temperature of X-ray tube, but percentage of operating temperature range T1: upper limit of temperature range, eg, 90% T2: lower limit of temperature range, eg, 10% U: tilt angle U1: tilt angle + Upper limit of direction, for example, 30 degrees U2: Upper limit of-direction of tilt angle, for example, 30 degrees X: Azimuth W: Large or small of focus, large = 1, small = 0 a ', b', c ', d', k ' : Constant The central processing unit 60 predicts the focus moving distance z according to the equation (3) in the case of the axial scan, and according to the equation (4) in the case of the stationary scan. The collimator 22 according to the equation
Is determined, and the position is adjusted through the collimator controller 30 based on the distance Z. When adjusting the position of the detector array 24, the distance Z is obtained by the equation (2).

However, equation (1) is an equation in the case where the initial position of the collimator 22 coincides with the reference position, and is generally expressed by the following equation including a deviation z0 of the current position of the collimator 22 from the reference position. The moving distance Z 'of the collimator 22 is obtained. The current position of the collimator 22 is always recognized by the central processing unit 60. The same applies to the case where the position of the detector array 24 is adjusted.

[0054]

(Equation 5)

The present inventor has also found a relational expression for obtaining the moving distance of the collimator 22 at once based on the above factors. It is shown below. Although no distinction is made in the following expression, it is natural that prediction of focus movement is included.

For the axial scan,

[0057]

(Equation 6)

Here, A, B, C, D, and K are constants.

[0059]

(Equation 7)

Here, A, B, C, D, and K: constants The constants A to K are used for calibration (cali
b). Calibration is performed by scanning with different scanning conditions one by one. Needless to say, the scan for calibration is performed without mounting the subject 8.

The scan order and conditions for the axial scan are as shown in FIG. 9, for example. First, the collimator 22 is set to the reference position, and the first scan 1 is performed in this state. As shown in the figure, the scan conditions are as follows: the temperature of the X-ray tube is 10% or less of the operating temperature range, the tilt angle is -30 degrees, the scan time is 3 seconds, and the size of the focal point is small. Scanning is performed with the autocollimator function activated. Therefore, the position of the collimator 22 is automatically adjusted so that the irradiation position of the X-ray beam 40 becomes a fixed position. Then, the automatically adjusted collimator position Z
Find 1 The focal position affected by the scan condition of scan 1 is reflected on Z1.

Next, scan 2 is performed. The scan conditions are the same as scan 1 except that the tilt angle is +30 degrees. In this scan, the position Z2 of the collimator 22 automatically adjusted by the autocollimator is obtained. Z2 reflects the focal position affected by the scan conditions of scan 2. Note that only the effect of the tilt angle differs from Z1.

Next, scan 3 is performed. The scan conditions are the same as in scan 2 except that the size of the focal point is increased.
In this scan, the position Z3 of the collimator 22 automatically adjusted by the autocollimator is obtained. The focal position affected by the scan condition of scan 3 is reflected in Z3. It differs from Z2 only in the effect of the size of the focal point.

Next, scan 4 is performed. The scan conditions are the same as for scan 3 except that the scan time was 0.8 seconds. In this scan, the position Z4 of the collimator 22 automatically adjusted by the autocollimator is obtained. Z4 reflects the focal position affected by the scan conditions of scan 4. It differs from Z3 only in the effect of the scan time.

Thereafter, idle scan (idle s)
can) is performed continuously to raise the temperature of the X-ray tube.
However, the autocollimator does not work during that time. Scan 5 is performed when the temperature of the X-ray tube becomes 90% or more of the operating temperature range. The scan conditions are the same as in scan 4, except that the temperature of the X-ray tube was set to 90% or more of the operating temperature range. In this scan, the position Z5 of the collimator 22 automatically adjusted by the autocollimator is obtained. Scan 5 for Z5
The focal position affected by the scan condition is reflected. It differs from Z4 only in the effect of the temperature of the X-ray tube 20.

The data Z1 to Z5 obtained as described above
Are used, constants A to K are obtained by the following equations.

[0067]

(Equation 8)

Here, T1, T2, U1, U2, V1,
V2 is the same as in equation (3). The order of scanning and the conditions for stationary scanning are as follows.
For example, as shown in FIG. First, the collimator 22
Is set to the reference position, and the first scan 1 is performed in this state. As shown in the figure, the scanning conditions are as follows: the temperature of the X-ray tube is 10% or less of the operating temperature range, the tilt angle is -30 degrees,
Azimuth is 0 degrees and the size of the focus is small. Scanning is performed with the autocollimator function activated. Therefore, so that the irradiation position of the X-ray beam 40 becomes a fixed position,
The position of the collimator 22 is automatically adjusted. Therefore, the position Z1 of the automatically adjusted collimator is obtained.

Next, scan 2 is performed. The scan conditions are the same as scan 1 except that the tilt angle is +30 degrees. In this scan, the position Z2 of the collimator 22 automatically adjusted by the autocollimator is obtained.

Next, scan 3 is performed. The scan conditions are the same as in scan 2 except that the size of the focal point is increased.
In this scan, the position Z3 of the collimator 22 automatically adjusted by the autocollimator is obtained.

Next, scan 4 is performed. The scan conditions were the same as scan 3 except that the azimuth was set to 180 degrees. In this scan, the position Z4 of the collimator 22 automatically adjusted by the autocollimator is obtained.

Thereafter, X-ray irradiation is continuously performed to raise the temperature of the X-ray tube. However, the autocollimator does not work during that time. Scan 5 is performed when the temperature of the X-ray tube becomes 90% or more of the operating temperature range. The scan conditions are the same as in scan 4, except that the temperature of the X-ray tube was set to 90% or more of the operating temperature range. In this scan, the position Z5 of the collimator 22 automatically adjusted by the autocollimator is obtained.

The data Z1 to Z5 obtained as described above
Are used, constants A to K are obtained by the following equations.

[0074]

(Equation 9)

Here, T1, T2, U1, and U2 are (4)
Same as in the formula. The above (5), (6),
Equation (7) is an equation in the case of irradiating the X-ray beam 40 so that the slice thicknesses in the two detector rows are equal, but the slice thickness ratio in the two detector rows is generally 1: n (n ≧ 1), the collimator 2 is placed on the side where the slice thickness ratio is larger by the following distance zn.
Correction for shifting the position of No. 2 may be added.

[0076]

(Equation 10)

Here, M: full width of the aperture of the collimator The operation of the present apparatus will be described. The operation of this device proceeds under the control of the central processing unit 60 based on an instruction from the operator. The operator inputs shooting conditions through the operation device 70. Imaging conditions include tube voltage, tube current, slice thickness,
The information includes a slice position, a tilt angle, a scan time, a focus size, and the like. In the case of the stationary scan, azimuth is included instead of the scan time. Hereinafter, an example of an axial scan will be described, but the same applies to a stationary scan. Also, an example in which the position of the collimator 22 is adjusted will be described. In the case where the position of the detector array 24 is adjusted, or when the collimator 22 and the detector array 2 are adjusted.
Adjusting the position of No. 4 is in accordance with this.

The central processing unit 60 predicts the position of the focal point of the X-ray tube 20 in the z-direction at the start of scanning based on the scanning condition and the temperature measurement value of the X-ray tube 20 based on the equation (3). From the expression 5), the position Z ′ of the collimator 22 in the z direction is obtained.
Ask for. Alternatively, based on equation (6), collimator 2
2, the position Z ′ in the z direction is obtained at a glance.

Next, based on a command from the operator, after positioning the imaging table 4 on which the subject 8 is mounted, the rotating unit 32 of the scanning gantry 2 is rotated to emit X-rays, and axial scanning starts. Since the position Z ′ of the collimator 22 in the z direction is adjusted to correspond to the focal position z of the X-ray tube 20 at the beginning of the scan, the X-ray beam 40 irradiates the fixed position of the detector array 24 from the beginning. Is done. The irradiation position is stabilized by the autocollimator function with respect to the focus movement based on the X-ray tube temperature that rises with the start of scanning.

The central processing unit 60 performs image reconstruction based on the view data collected by the scan. Image reconstruction is performed by processing view data by, for example, a filtered back projection method. A tomographic image of the subject 8 is obtained by image reconstruction. Since the X-ray irradiation is performed at the fixed position of the detector array 24 from the beginning, a high quality reconstructed image can be obtained from the beginning.

Since the detector array 24 has two rows of X-ray detectors in parallel, tomographic images of two adjacent slices can be obtained at once by one scan. Thereby, a multi-slice scan (multi-sli) is performed.
ce scan and helical scan (helical)
scan) is performed more efficiently. The reconstructed image is displayed on the display device 68 and stored in the storage device 66.

As described above, prior to the start of scanning,
The collimator 22 predicts the position of the focal point of the X-ray tube 20 and emits the X-ray beam 40 to a fixed position of the detector array.
Adjust the initial position such as It is preferable to perform such position adjustment whenever the scan pause time is longer than one hour, for example, in order to obtain a high-quality image. Also,
Even if the downtime is within one hour, it should be performed if the temperature of the X-ray tube has dropped below 10% of the operating temperature range.

In other cases, if the difference between the predicted movement amount obtained from the scan condition to be performed now and the predicted movement amount obtained from the previous scan condition exceeds a predetermined limit, the position adjustment is performed. It is better to go. Further, it is preferable to perform the photographing every time the photographing series (series) or the examination (examination) is changed, in order to always perform photographing with high quality.

While the example in which the detector array is composed of two rows of X-ray detectors has been described above, the detector array may be a multi-row of three or more rows. Of course, a single-row detector array may be used.

[0085]

As described above in detail, according to the present invention, an X-ray irradiation position alignment method for making an X-ray irradiation position coincide with a fixed position from the beginning of scanning, and such an X-ray irradiation position adjustment X-ray tomography method and apparatus for performing imaging by performing the above method can be realized.

[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.

FIG. 6 is a schematic view of a main part of an X-ray tube in the apparatus shown in FIG.

FIG. 7 is a schematic diagram showing displacement of a focal point of an X-ray tube and corresponding position adjustment of a collimator in the apparatus shown in FIG.

8 is a schematic diagram showing displacement of a focal point of an X-ray tube and corresponding adjustment of a position of a detector array in the apparatus shown in FIG. 1;

9 is a diagram showing scan conditions at the time of calibration of the apparatus shown in FIG.

FIG. 10 is a diagram showing scan conditions at the time of calibration of the apparatus shown in FIG. 1;

[Explanation of symbols]

 2 Scanning gantry 20 X-ray tube 22 Collimator 24 Detector array 26 Data collection unit 28 X-ray controller 30 Collimator controller 32 Rotating unit 34 Rotation controller 36 Tilt controller 4 Imaging table 6 Operation console 60 Central processing unit 62 Control interface 64 Data collection buffer 66 storage device 68 display device 70 operating device 242,244 X-ray detector 40 X-ray beam 8 subject 220,222 collimator piece

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-10-118058 (JP, A) JP-A-6-169914 (JP, A) JP-A-7-116157 (JP, A) JP-A 10-108 211199 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) A61B 6/03

Claims (13)

(57) [Claims] 1. An X-ray irradiating / detecting device that irradiates an X-ray detector with X-rays generated from an X-ray tube through a collimator to scan a subject and perform tomography. X-rays are emitted from the X-ray tube without rotating around the subject, and projection data is collected while moving the subject in the body axis direction, and a stationary scan for capturing a perspective image is performed. At this time, the position of the X-ray focal point in the X-ray tube is predicted based on the temperature of the X-ray tube before the start of scanning and at least the tilt angle and the azimuth angle of the X-ray irradiation / detection device in a stationary scan to be performed from now on. The collimator and the collimator according to the predicted position so that the X-ray generated from the X-ray tube irradiates a fixed position in the X-ray detector. Adjusting the position of one or both of the X-ray detectors. 2. An X-ray irradiating / detecting device that irradiates an X-ray generated by an X-ray tube to a X-ray detector through a collimator to scan a subject and perform tomography. X-rays are emitted from the X-ray tube without rotating around the subject, and projection data is collected while moving the subject in the body axis direction, and a stationary scan for capturing a perspective image is performed. At this time, the position of the X-ray focal point in the X-ray tube is predicted based on the temperature of the X-ray tube before the start of scanning and the scanning conditions of the stationary scan to be performed from now on, and the X-rays generated from the X-ray tube are When adjusting the position of the collimator according to the predicted position so as to irradiate a fixed position on the X-ray detector, the moving distance Z of the collimator is expressed by the following equation (1). Represented by, Z = G1 · z (1) (however, z is the moving distance z of the focal point of the X-ray tube,
G1 (gain) is a proportionality constant and a positive value smaller than 1. The moving distance z of the focal point of the X-ray tube is represented by the following equation (4): (However, T: temperature of X-ray tube, but percentage of operating temperature range T1: upper limit of temperature range T2: lower limit of temperature range U: tilt angle U1: upper limit of tilt angle in the positive direction U2: tilt angle of the negative direction Upper limit X: azimuth angle W: magnitude of focus, large = 1, small = 0 a ', b', c ', d', k ': constants.) The position of the collimator based on the above equation (1) Is adjusted. 3. An X-ray irradiating / detecting device for irradiating an X-ray detector with X-rays generated from an X-ray tube through a collimator to scan a subject and perform tomography. X-rays are emitted from the X-ray tube without rotating around the subject, and projection data is collected while moving the subject in the body axis direction, and a stationary scan for capturing a perspective image is performed. At this time, the position of the X-ray focal point in the X-ray tube is predicted based on the temperature of the X-ray tube before the start of scanning and the scanning conditions of the stationary scan to be performed from now on, and the X-rays generated from the X-ray tube are When adjusting the position of the X-ray detector according to the predicted position so as to irradiate a fixed position on the X-ray detector, the moving distance Z of the X-ray detector is expressed by the following equation (2). Represented by, Z = G2 · z (2) (although, z is the moving distance z of the focal point of the X-ray tube,
G2 (gain: gain) is a proportional constant, and is a negative value whose absolute value is larger than 1. The moving distance z of the focal point of the X-ray tube is represented by the following equation (4): (However, T: temperature of X-ray tube, but percentage of operating temperature range T1: upper limit of temperature range T2: lower limit of temperature range U: tilt angle U1: upper limit of tilt angle in the positive direction U2: tilt angle of the negative direction Upper limit X: azimuth angle W: magnitude of focus, large = 1, small = 0 a ', b', c ', d', k ': constants.) X-ray detection based on the above equation (2) X-ray irradiation positioning method, wherein the position of the vessel is adjusted. 4. An X-ray irradiating / detecting device for irradiating an X-ray detector with X-rays generated from an X-ray tube through a collimator to scan a subject and perform tomography. When performing an axial scan that rotates around the body axis of the subject while irradiating X-rays from an X-ray tube while maintaining the mutual relationship and collects projection data while moving the subject in the body axis direction. The temperature of the X-ray tube before the start of the scan and at least the X-ray in the axial scan to be performed.
The position of the X-ray focal point in the X-ray tube is predicted based on the tilt angle and the scan time of the X-ray irradiation / detection device, so that the X-ray generated from the X-ray tube irradiates a fixed position in the X-ray detector. Adjusting the position of one or both of the collimator and the X-ray detector according to the predicted position. 5. An X-ray irradiating / detecting device that irradiates an X-ray detector with X-rays generated from an X-ray tube and scans a subject with an X-ray irradiating / detecting device. When performing an axial scan that rotates around the body axis of the subject while irradiating X-rays from an X-ray tube while maintaining the mutual relationship and collects projection data while moving the subject in the body axis direction. The position of the X-ray focal point in the X-ray tube is predicted based on the temperature of the X-ray tube before the start of scanning and the scanning conditions in an axial scan to be performed. When adjusting the position of the collimator according to the predicted position so as to irradiate a fixed position in the line detector, the moving distance Z of the collimator is expressed by the following equation (1). Is, Z = G1 · z (1) (however, z is the moving distance z of the focal point of the X-ray tube,
G1 (gain) is a proportionality constant and a positive value smaller than 1. The moving distance z of the focal point of the X-ray tube is represented by the following equation (3): (However, T: temperature of X-ray tube, but percentage of operating temperature range T1: upper limit of temperature range T2: lower limit of temperature range U: tilt angle U1: upper limit of tilt angle in the positive direction U2: tilt angle of the negative direction Upper limit V: scan time V1: longest scan time V2: shortest scan time W: focus size, large = 1, small = 0 a, b, c, d, k: constants.) Based on equation (1) above. The position of the collimator is adjusted by the method. 6. An X-ray irradiating / detecting device for irradiating an X-ray detector through which an X-ray generated from an X-ray tube passes through a collimator to scan a subject and perform tomography. When performing an axial scan that rotates around the body axis of the subject while irradiating X-rays from an X-ray tube while maintaining the mutual relationship and collects projection data while moving the subject in the body axis direction. The position of the X-ray focal point in the X-ray tube is predicted based on the temperature of the X-ray tube before the start of scanning and the scanning conditions in an axial scan to be performed. When adjusting the position of the X-ray detector according to the predicted position so as to irradiate a fixed position in the X-ray detector, the moving distance Z of the X-ray detector is expressed by the following equation (2). Is, Z = G2 · z (2) (although, z is the moving distance z of the focal point of the X-ray tube,
G2 (gain: gain) is a proportional constant, and is a negative value whose absolute value is larger than 1. The moving distance z of the focal point of the X-ray tube is represented by the following equation (3): (However, T: temperature of X-ray tube, but percentage of operating temperature range T1: upper limit of temperature range T2: lower limit of temperature range U: tilt angle U1: upper limit of tilt angle in the positive direction U2: tilt angle of the negative direction Upper limit V: Scan time V1: Longest scan time V2: Shortest scan time W: Focus size, large, large = 1, small = 0 a, b, c, d, k: constants.) Based on equation (2) above. Adjusting the position of the X-ray detector by adjusting the position of the X-ray detector. 7. An X-ray tomography apparatus for performing tomography by scanning a subject with an X-ray irradiation / detection apparatus that irradiates an X-ray detector with X-rays generated from an X-ray tube through a collimator, X-rays are emitted from the X-ray tube without rotating the X-ray irradiation / detection device around the subject, and projection data is collected while moving the subject in the body axis direction, and a fluoroscopic image is obtained. When performing a stationary scan for imaging the X-ray tube, the X-ray in the X-ray tube based on the temperature of the X-ray tube before the start of the scan and at least the tilt angle and azimuth angle of the X-ray irradiation / detection device in the stationary scan to be performed from now on Focus position predicting means for predicting the position of a line focus; and the X-ray generated from the X-ray tube is predicted to irradiate a fixed position on the X-ray detector. An X-ray tomography apparatus, comprising: a position adjusting unit that adjusts one or both of the collimator and the X-ray detector in accordance with the position of an X-ray focal point. 8. An X-ray tomography apparatus for performing tomography by scanning a subject with an X-ray irradiating / detecting apparatus that irradiates an X-ray generated through an X-ray tube to a X-ray detector through a collimator, X-rays are emitted from the X-ray tube without rotating the X-ray irradiation / detection device around the subject, and projection data is collected while moving the subject in the body axis direction, and a fluoroscopic image is obtained. Focus position estimating means for estimating the position of the X-ray focal point in the X-ray tube based on the temperature of the X-ray tube before the start of the scan and the scanning conditions of the stationary scan to be performed when performing a stationary scan for imaging A position for adjusting the position of the collimator according to the predicted position of the X-ray focal point such that the X-rays generated from the X-ray tube irradiate a fixed position on the X-ray detector. Adjusting means, wherein in the focus position estimating means, the moving distance Z of the collimator is obtained by the following equation (1): Z = G1 · z (1) (where z is the focal point of the X-ray tube) The travel distance z,
G1 (gain) is a proportionality constant and a positive value smaller than 1. In addition, the moving distance z of the focal point of the X-ray tube is represented by the following equation (4). (However, T: temperature of X-ray tube, but percentage of operating temperature range T1: upper limit of temperature range T2: lower limit of temperature range U: tilt angle U1: upper limit of tilt angle in the positive direction U2: tilt angle of the negative direction Upper limit X: azimuth angle W: magnitude of focus, large = 1, small = 0 a ', b', c ', d', k ': constants.) The collimator is obtained by the focus position predicting means. An X-ray tomography apparatus characterized by being moved by the position adjusting means by a distance based on the above equation (1). 9. An X-ray tomography apparatus that scans a subject with an X-ray irradiation / detection apparatus that irradiates an X-ray generated from an X-ray tube through a collimator to an X-ray detector and performs tomography. X-rays are emitted from the X-ray tube without rotating the X-ray irradiation / detection device around the subject, and projection data is collected while moving the subject in the body axis direction, and a fluoroscopic image is obtained. Focus position estimating means for estimating the position of the X-ray focal point in the X-ray tube based on the temperature of the X-ray tube before the start of the scan and the scanning conditions of the stationary scan to be performed when performing a stationary scan for imaging A position for adjusting the position of the X-ray detector according to the predicted position of the X-ray focal point so that the X-rays generated from the X-ray tube irradiate a fixed position on the X-ray detector. Adjusting means, wherein the focal position predicting means obtains a moving distance Z of the X-ray detector by the following equation (2): Z = G2 · z (2) (where z is the X-ray tube) Is the moving distance z of the focal point of
G2 (gain: gain) is a proportional constant, and is a negative value whose absolute value is larger than 1. In addition, the moving distance z of the focal point of the X-ray tube is represented by the following equation (4). (However, T: temperature of X-ray tube, but percentage of operating temperature range T1: upper limit of temperature range T2: lower limit of temperature range U: tilt angle U1: upper limit of tilt angle in the positive direction U2: tilt angle of the negative direction Upper limit X: azimuth angle W: magnitude of focus, large = 1, small = 0 a ', b', c ', d', k ': constants.) The X-ray detector is controlled by the focus position predicting means. An X-ray tomography apparatus characterized by being moved by the position adjusting means by a distance based on the obtained equation (2). 10. An X-ray tomography apparatus that scans a subject with an X-ray irradiation / detection apparatus that irradiates an X-ray detector with X-rays generated from an X-ray tube through a collimator, and performs tomography. While rotating the X-ray irradiating / detecting device around the body axis of the subject while irradiating X-rays from the X-ray tube while maintaining the correlation between the X-ray irradiating and detecting devices, the projection data is transferred while moving the subject in the body axis direction. When performing an axial scan to be collected, the temperature of the X-ray tube before the start of scanning and at least the X in the axial scan to be performed from now on
Focus position predicting means for predicting a position of an X-ray focal point in the X-ray tube based on a tilt angle and a scan time of the X-ray irradiation / detection device; and X-rays generated from the X-ray tube are fixed positions in the X-ray detector. And a position adjusting means for adjusting the position of one or both of the collimator and the X-ray detector in accordance with the predicted position of the X-ray focal point so as to irradiate the X-ray. Line tomography equipment. 11. An X-ray tomography apparatus that scans a subject with an X-ray irradiation / detection apparatus that irradiates an X-ray detector with X-rays generated from an X-ray tube through a collimator, and performs tomography. While rotating the X-ray irradiating / detecting device around the body axis of the subject while irradiating X-rays from the X-ray tube while maintaining the correlation between the X-ray irradiating and detecting devices, the projection data is transferred while moving the subject in the body axis direction. Focus position estimating means for estimating the position of the X-ray focal point in the X-ray tube based on the temperature of the X-ray tube before the start of the scan and the scan condition of the axial scan to be performed, Position adjusting means for adjusting the position of the collimator according to the predicted position of the X-ray focal point so that the X-rays generated from the X-ray tube irradiate a fixed position on the X-ray detector. In the focus position predicting means, the moving distance Z of the collimator is obtained by the following equation (1): Z = G1 · z (1) (where z is the moving distance z of the focal point of the X-ray tube. Yes,
G1 (gain) is a proportionality constant and a positive value smaller than 1. In addition, the moving distance z of the focal point of the X-ray tube is represented by the following equation (3). (However, T: temperature of X-ray tube, but percentage of operating temperature range T1: upper limit of temperature range T2: lower limit of temperature range U: tilt angle U1: upper limit of tilt angle in the positive direction U2: tilt angle of the negative direction Upper limit V: Scan time V1: Longest scan time V2: Shortest scan time W: Focus size, large, large = 1, small = 0 a, b, c, d, k: constants.) The collimator predicts the focus position. X-ray tomography apparatus characterized in that the apparatus is moved by the position adjusting means by a distance based on the above equation (1) obtained by the means. 12. An X-ray tomography apparatus that scans a subject with an X-ray irradiation / detection apparatus that irradiates an X-ray detector with X-rays generated from an X-ray tube through a collimator, and performs tomography. While rotating the X-ray irradiating / detecting device around the body axis of the subject while irradiating X-rays from the X-ray tube while maintaining the correlation between the X-ray irradiating and detecting devices, the projection data is transferred while moving the subject in the body axis direction. Focus position estimating means for estimating the position of the X-ray focal point in the X-ray tube based on the temperature of the X-ray tube before the start of the scan and the scan condition of the axial scan to be performed, Position adjusting means for adjusting the position of the X-ray detector in accordance with the predicted position of the X-ray focal point so that the X-ray generated from the X-ray tube irradiates a fixed position on the X-ray detector. In the focus position predicting means, the moving distance Z of the X-ray detector is obtained by the following equation (2): Z = G2 · z (2) (where z is the shift of the focal point of the X-ray tube) The distance z,
G2 (gain: gain) is a proportional constant, and is a negative value whose absolute value is larger than 1. In addition, the moving distance z of the focal point of the X-ray tube is represented by the following equation (3). (However, T: temperature of X-ray tube, but percentage of operating temperature range T1: upper limit of temperature range T2: lower limit of temperature range U: tilt angle U1: upper limit of tilt angle in the positive direction U2: tilt angle of the negative direction Upper limit V: scan time V1: longest scan time V2: shortest scan time W: large and small of focus, large = 1, small = 0 a, b, c, d, k: constants.) An X-ray tomography apparatus characterized in that the X-ray tomography apparatus is moved by the position adjusting unit by a distance based on the above equation (2) obtained by the focal position estimating unit. 13. The X-ray irradiation / detection device, wherein the position adjusting means predicts the position of the X-ray focal point such that the X-ray generated from the X-ray tube irradiates a fixed position on the X-ray detector. After adjusting the position of one or both of the collimator and the X-ray detector according to
The X-ray tomography apparatus according to any one of claims 7 to 12, wherein the tomography is performed by scanning the subject.