JPH05196584A - Ct scanner - Google Patents

Abstract

PURPOSE:To obtain a CT scanner of which detection channels are used very effectively and which is appropriate for making inspection of object, about which date processing is very simple, to be performed by online processing. CONSTITUTION:An object 3 to be inspected, which is placed on rotation tables 10a to 10f on a revolution table 11 provided along with surface of fan beam irradiation, making an X-ray tube 1 which generates X-ray fan beam 2 having 180 deg. fan angle, to be a center point thereof, is made just to revolve without any rotation, and, while keeping this situation, the object 3 is made to pass through in the fan beam irradiation. X-ray passing through the object 3 is detected by a multichannel detector 4 consisting of a plurality of detection elements which are arranged in a semicircle shape making a center point thereof to be the X-ray tube 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CT scanner capable of inspecting an object online by taking a tomographic image of the object such as an industrial product or its material.

[0002]

2. Description of the Related Art Conventionally, this type of CT scanner has been widely used as a medical diagnostic apparatus for taking a tomographic image of a human body. The most popular medical CT scanner at present is a system called the third generation, in which an X-ray tube and an X-ray detector are provided so as to face each other across a subject, and both are integrated. The projection data of the subject is acquired while rotating around the subject.

On the other hand, a widely used industrial CT scanner is a system called a second generation as shown in FIG. In the CT scanner shown in FIG.
The X-ray tube 101 and the X-ray detector 104 are provided so as to face each other with 9 interposed therebetween, and the traverse (straight line) operation and the rotating operation are alternately performed on the subject while the X-ray tube 101 is narrower than the subject imaging region. Irradiate a fan-shaped X-ray fan beam 103,
The detector 104 detects X-rays transmitted through the subject, collects the detection data, and reconstructs a tomographic image of the subject.

In the CT scanner shown in FIG. 5, the fan angle θ of the X-ray fan beam 103 is about 15 °, and it is necessary to perform the traverse operation 12 times, that is, 6 reciprocations to image one cross section. It takes ~ 3 minutes and is not suitable for on-line testing of subjects.

Therefore, for example, Japanese Patent Laid-Open No. 61-155739.
C for online inspection as disclosed in Japanese Patent Publication
T-scanners have been developed. This CT scanner has an X-ray tube 211 at the center of the scanner 210, as shown in FIG.
Is installed, and a fan-shaped X-ray beam is generated along the horizontal plane.
It is radiated in the direction of 60 °. Further, a revolution table 215 that rotates along the fan beam around the X-ray tube 211 is provided, and on this revolution table 215, a plurality of rotation tables 2 are equidistant from the center of the X-ray tube.
13A to 213D are provided. A subject is placed on these rotation tables, and the X-ray beam that has passed through the subject is detected with angular resolution by a detector 212 provided in a ring shape around the subject, and while the subject revolves once, the X-ray beam is detected. Since the tomographic image of the subject is reconstructed by the collected detection data, the subject can be inspected one after another in a short time, which is suitable for online inspection. The conventional CT scanner shown in FIG. 6 can perform a scanning method similar to the second generation, third generation, and fourth generation by changing the combination of revolution and rotation.

FIG. 7 (a) shows the movement of one rotation table over time when second generation data acquisition is performed using the CT scanner shown in FIG. In the same figure, while rotating 180 degrees clockwise in the direction indicated by arrow 220, the rotation table rotates so that the direction does not change when viewed from the outside of the device. That is, it rotates 180 degrees counterclockwise on the revolution table. The detector detects data using M detection channels corresponding to 180 ° in the 360 ° direction, and the data is time t = 0 in FIG.
To t = T. Of this data, the data in the shaded area as shown in FIG. 7 (b) is used, and if this data is rearranged and arranged,
As shown in FIG. 7C, since a second generation sinogram in which the horizontal axis is the traverse position L and the vertical axis is the beam azimuth angle θ, a cross-sectional image can be obtained by the second generation reconstruction method. Composed.

FIG. 8 (a) shows the movement of one rotation table over time when third generation data acquisition is performed using the CT scanner shown in FIG. In the CT scanner shown in the figure, data of N channels for the angle α in the detector 360 ° direction is used. While rotating in the clockwise direction in the X-ray fan beam measured by the detectors of channels 0 to N, the rotating table rotates 360 ° in the counterclockwise direction on the rotating table. The data is collected from t = 0 to t = T in FIG. 8 (a). Of the collected data, the data in the shaded area shown in FIG. 8B is used. When the data is rearranged in the vertical direction, as shown in FIG. 8C, the vertical axis shows X-rays. Since the 3rd generation sinogram positioned at the position angle φ within the fan centered on the generation point and the rotation angle θ of the fan on the horizontal axis is obtained, the sectional image is constructed by the 3rd generation reconstruction method thereafter. It Note that in FIG. 8A, the angle α can be set arbitrarily and may be 180 ° or less, but it is necessary that the angle α be large enough to cover the minimum photographing area.

FIG. 9A shows the movement of one rotation table over time when the fourth generation acquisition is performed using the CT scanner shown in FIG. In this case 360
Data of N channels for the angle α in the ° direction is used. While revolving clockwise by the angle α, the rotation table rotates 360 ° -α counterclockwise as viewed from the outside of the apparatus. In other words, 36
Rotate 0 °. The data is collected from t = 0 to t = T in FIG. 9 (a). Figure 9 of this data
The data shown by hatching in (b) is used. When the data is arranged while being shifted in the horizontal direction, the position angle φ in the fan centered on the virtual detector position on the horizontal axis as shown in FIG. 9 (c). , A fourth-generation sinogram positioned at the fan rotation angle θ on the vertical axis is obtained, and thereafter, a cross-sectional image is constructed by the fourth-generation reconstruction method. It should be noted that the virtual detector position is α · r / (360 ° from the center of rotation when the revolution radius is r.
It is a point separated by the distance calculated by -α), and the data is such that one detector channel is provided at this point viewed from one detector channel, and the X-ray focus S is rotated about this point. It is collected in various physical relationships. In FIG. 9 (a),
α can be set arbitrarily and may be 180 ° or less. The setting limit of α is determined by the condition that the virtual detector position does not fall within the imaging area, and α · r / (360 ° −α)>
It can be calculated from the relationship of the imaging area radius.

[0009]

The conventional C shown in FIG. 6 is used.
The T-scanner was developed as a device suitable for online inspection, but when performing online inspection one after another,
Since it is necessary to finish the inspection within one rotation for one subject and it is necessary to have a margin to replace the subject, the X-ray beam fan angle α used cannot be 360 °. However, there is a problem in that it is wasted because some of the detector channels installed in the entire circumferential direction are not used because they need to be about 300 ° or less.

Also, when performing third generation data acquisition, artifacts may occur if the detector channels are not arranged in a uniform manner. For example, 1 for 8 channels
If you create a detector with a unit structure that is a unit,
It is unavoidable that the pitch between channels becomes inhomogeneous at the seam between units, that is, the pitch becomes larger than that in the unit, which causes artifacts. Therefore, the detector cannot be made into a unit structure, and since the whole is continuously manufactured, it is difficult to manufacture the detector, and there is a problem that the yield is reduced. In contrast, the second generation and the fourth
In the case of generational data acquisition, there is no problem even if the arrangement between channels is not uniform.

Furthermore, since it is compatible with the data generation methods of three generations, there is a problem that data collection becomes complicated. It should be noted that comparing the data collections of the second generation, the third generation, and the fourth generation, the data collection is easy to collect and the image quality is second.
It has been found that the CT scanner shown in FIG. 6 currently requires substantially only second generation data acquisition because generation is the most advantageous.

Further, the conventional CT scanner shown in FIG. 6 has a problem that the inspection must be interrupted when offset data is collected. The offset data is data output from the detector at 0 point (no incident X-ray), and is data used for offset correction. Since the offset data changes with the temperature of the detector,
It is necessary to collect the data frequently, but in the conventional device, the inspection is interrupted each time, and the X-ray is turned off to perform the offset collection, which is a problem as an online inspection device.

The present invention has been made in view of the above,
It is an object of the present invention to provide a CT scanner that has no waste of detector channels and is simple in data processing and suitable for online inspection of a subject.

[0014]

In order to achieve the above object, a CT scanner of the present invention mounts a radiation source for generating fan beam radiation having a predetermined fan angle and a subject, and the radiation source A subject moving means for passing the inside of the fan beam radiation while only revolving the subject without rotating the subject along the plane of the fan beam radiation at the center, and for detecting the fan beam radiation transmitted through the subject. And a multi-channel detector including a plurality of detection elements arranged in a semicircle centered on the radiation source.

[0015]

In the CT scanner of the present invention, the radiation source for generating the fan beam radiation having a predetermined fan angle is used as the center of the fan beam radiation while revolving the object along the plane of the fan beam radiation without rotating. Through
Radiation that has passed through the subject is detected by a multi-channel detector including a plurality of detection elements arranged in a semicircular shape around the radiation source.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of a CT scanner according to an embodiment of the present invention. In the figure, the X-ray tube 1 is provided substantially at the center, and a fan angle of 180 °
The X-ray fan beam 2 is emitted. X
A revolution table 11 which rotates about a vertical axis passing through the X-ray focal point S of the X-ray tube 1 is provided so as to make the table surface horizontal, and six revolution tables 11 are arranged on the revolution table 11 at positions equidistant from the vertical axis. The rotation tables 10a to 10f are provided so as to rotate about the rotation axis C in the horizontal plane.

The revolution table 11 and the rotation tables 10a to 10f are controlled by the mechanism controller 6, whereby the revolution table 11 rotates clockwise at a constant speed, and the rotation tables 10a to 10f are placed on the rotating revolution table 11. Each of them rotates in the counterclockwise direction at the same speed as the revolution. And the rotation table 10
The subject 3 placed on a to 10f crosses the X-ray fan beam 2 in the horizontal plane, respectively, but in this case, the rotation tables 10a to 10f are focused on the X-ray so that their directions do not change when viewed from the outside of the apparatus. Revolve around S.

The X-ray fan beam 2 transmitted through the subject 3 is detected with angular resolution by a detector 4 provided outside the revolution table 11. The detector 4 is connected to the data collector 7, and the X-ray detection signal from the detector 4 is supplied to the data collector 7. The data collecting device 7 has a fixed minute angle of the revolution table 11, about 0.03 °.
A collection pulse output from the mechanism control device 6 is received for each rotation of, and data collection is performed in synchronization with this collection pulse.

The X-ray detection signal from the detector 4 is AD-converted by the data acquisition device 7 and supplied to the reconstruction device 8 as digital data. The reconstructing device 8 temporarily stores this data in the internal memory, picks up the data for the beam set passing through the imaging region corresponding to one rotation table, rearranges the data, and outputs the data corresponding to the parallel beam set in the 180 ° direction. Convert to. Then, based on the data thus converted, a cross-sectional image is constructed by a normal second-generation reconstruction method and displayed on the display device 9.

An X-ray shield 12 is fixedly provided on the revolution table 11 so as to block a part of the X-ray fan beam 2 as the revolution table 11 revolves. The data collected when the X-ray fan beam 2 is blocked by the X-ray shield 12 is performed by the reconstructing device 8 as output data 0 (no incident X-ray) for the detector channel, that is, as offset data. Used for offset correction.

FIG. 2 (a) shows the internal structure of the detector 4. The detector 4 comprises a detector unit 20 which is composed of 8 detector channels and is compatible with each other.
It is arranged at a position equidistant from the line focus S, facing the direction of the X-ray focus S. There are 132 detector units 20 and there are 1056 channels in total. Each detector unit 20 is connected to one relay unit 21.

The internal structure of the detector unit 20 is shown in FIG.
It is shown in FIG. 2B, and its sectional structure is shown in FIG. In FIGS. 2A and 2B, the collimator 24 has eight openings 24 a directed toward the X-ray focal point S, and the X-ray beam 2 passing through the openings 24 a is formed at the rear of the collimator 24. Eight scintillators 22 provided
It is supposed to hit. A separator 23 is provided between the scintillators 22 to block scattered X-rays.

Further, a photodiode 25 is joined to the lower portion of the scintillator 22 and the scintillator 2 is
The light from 2 is received. The output signal from the photodiode 25 is supplied to the relay unit 21 via a preamplifier 27, an integrator 28, a sample and hold 29, a multiplexer 30, and a buffer amplifier 31 mounted on the detection substrate 26. The relay unit 21 has a function of multiplexing the signal from the detector unit 20.

The structures of the detector 4 and the detector unit 20 of the CT scanner configured as described above are the same as those of the ordinary second
The same as the detector of the next generation CT scanner, with the X-ray focus S
However, it is not necessary to arrange them at equal intervals, and the intervals between the detector units 20 are wider than the angular pitch within the detector units 20 in order to provide clearance. That is, unlike the third generation, the second generation CT scanner has an advantage that an artifact does not occur in a cross-sectional image even if the inter-channel pitch is inhomogeneous.

The overall operation of the CT scanner configured as above will be described. First, the X-ray controller 5 is activated to start irradiation of the X-ray fan beam 2 from the X-ray tube 1. Then, the mechanism control device 6 controls the revolution table 1
1 and the rotation tables 10a to 10f are rotated. Then, the data collection device 7 receives a collection pulse generated at every rotation of a fixed angle from the mechanism control device 6, and collects data in synchronization with this collection pulse. That is, when the data acquisition device 7 receives one acquisition pulse, the outputs from the detectors of all channels are time-divisionally switched before receiving the next acquisition pulse, and each detector output signal is converted into digital data one after another. It is converted and supplied to the reconstruction device 8.

Further, during such a data detection state, the subject 3 is successively placed on the rotation table while the rotation table is out of the area of the X-ray fan beam 2. That is, the subject that has passed through the region of the X-ray fan beam 2 is replaced with a new subject one after another outside the region, so that the examination can be continued as an online examination device.

The data supplied to the reconstruction device 8 is reconstructed and displayed on the display device 9 while sequentially switching the cross-sectional images of the subject on the rotation table. Therefore, the quality of the subject is judged by looking at the cross-sectional image of the subject displayed on the display device 9.

On the other hand, in the detector 4 shown in FIG.
The X-ray beam 2 that has passed through the subject passes through the opening 24a of the collimator 24 and is absorbed by the scintillator 22 to become visible light. This visible light enters the photodiode 25 and becomes a current signal, and this current output signal is the preamplifier 2
It is amplified at 7 and supplied to the integrator 28. In this state, when the data acquisition device 7 receives the acquisition pulse,
The data acquisition device 7 immediately supplies a reset signal to the detector 4. As a result, the reset signal is supplied to the integrator 28 through the relay unit 21 to reset the integrator. Therefore, the integrator starts integration immediately after this reset. When the data collection device 7 receives the next collection pulse in this state, the data collection device 7 immediately supplies the hold signal and the reset signal to the detector 4 sequentially. The hold signal is supplied to the sample and hold 29 to hold the output of the detector unit 20 immediately before it is reset. All channels are held at the same timing as above. The output of the integrator held before the next acquisition pulse is input is sequentially switched by the multiplexer 30 on the detector substrate 26 and the multiplexer in the relay unit 21 and supplied to the data acquisition device 7. The data collection device 7 sequentially converts this signal into digital data and supplies it to the reconstruction device 8.

Next, the relationship between the detector channel and the beam will be observed with reference to FIG. FIG. 3A shows the movement of the rotation table 10a over time, but at time t =
The beam measured by the channel 1 from t ′ to t = t ₁ ′ scans the imaging area in parallel at the installation angle θ ₁ of the channel 1 as shown in FIG. 3B. Then, it can be seen that the transition of time corresponds to the transition of the traverse position L. The same applies to the other channels, and the installation angle is equal to the azimuth angle of the parallel beam.

In FIG. 4B, the data supplied to the reconstruction device 8 is shown with the vertical axis representing the channel number (ch) and the horizontal axis representing the time (t). The reconstructing device 8 sequentially stores the supplied data in the buffer memory, and when the memory area becomes full, the oldest data is sequentially erased and replaced with new data. In this memory, the data (Tb.10a to Tb.10f) of each table is a hatched portion. For example, the data of the rotation table 10a (Tb.10a) is collected from the time t = t ₁ to T _M, the position at this time of the table is shown in Figure 4 (a). In FIG. 4B, A indicates air data (air transmission data), which is collected when the X-ray beam passes between the tables. Further, Of represents offset data (data without incident X-rays), which is collected when the X-ray fan beam 2 is hitting the X-ray shield 12. As shown in FIG. 4B, the data in the buffer memory is read for each table before being updated, and the interpolation calculation is performed while shifting the time axis direction, and the vertical axis indicates the beam azimuth angle θ and the horizontal axis indicates the beam. The traverse position L is taken and arranged. At this time, the air data before and after and the offset data closest in time are also attached to this organized data. The offset data is used for offset correction (0-point correction), and the air data is used for air correction (gain correction).

The rearranged data is parallel beam data in the 180 ° direction, and a cross-sectional image is formed by the normal second-generation reconstruction method. Then, cross-sectional images are sequentially formed for each table and are supplied to the display device 9. The display device 9 updates the display each time the cross-sectional image is supplied.

In addition to the above embodiment, a vertical movement mechanism is further provided to move the X-ray tube 1 and the detector 4 up and down, or the revolution table 11 or the rotation table is moved up and down. The slice plane position of can be changed. Further, it is effective in the case of an unstable X-ray tube to provide a comparative detector for monitoring the intensity of the source in the vicinity of the X-ray tube 1 so as to correct the intensity of the source.

In the CT scanner configured as described above, the scan is completed while the subject is rotated about half a turn, so the scan time is short. Measurements are simultaneously performed on a large number of specimens, and the examination efficiency is good. It is suitable for online inspection because it can be inspected while moving the subject. Since the X-ray tube has a fan angle of 180 °, the radiation source utilization rate is high. All detectors are always used, so there is no waste in detector channels. Since the data is collected in parallel beams, the second generation simple reconstruction method can be applied. Since it is the second-generation data collection, the quality of the cross-sectional image does not deteriorate even if the channel arrangement of the detector is inhomogeneous. Therefore, the detector can have a unit structure. Since it is the second-generation data collection, even if the characteristics of the channels of the detector vary, the quality of the cross-sectional image is unlikely to deteriorate. Since the offset data and the air data can be obtained during the inspection without interrupting the inspection, it is easy to perform, the inspection efficiency is good, and it is suitable for online. Since the inspection can be performed without turning on / off the X-ray, the X-ray tube is not overpowered and the life is extended. Since the X-ray beam is used only for 180 °, sufficient space and time for exchanging the subject can be secured. Since the X-ray shield 12 is fixed to the revolution table 11, a mechanism for moving the X-ray shield 12 is not required. It is a 2nd generation CT scanner with a fan angle of 180 ° and is the fastest as the 2nd generation. Fan angle 180 °
Since it is the second generation of, the traverse (arc shape) only needs to be done once, and the acceleration during deceleration is not applied to the subject.

[0035]

As described above, according to the present invention,
A radiation source that generates a fan-beam radiation having a predetermined fan angle is passed through the fan-beam radiation while revolving the subject along the plane of the fan-beam radiation but not revolving around the radiation source. Since the radiation that has passed through the object is detected by the multi-channel detector that consists of multiple detection elements arranged in a circle, it is possible to perform an examination in a short time continuously without interrupting many objects. It is suitable for online, and all detectors are always used, so there is no waste in the detectors and there is no deterioration in the quality of cross-sectional images.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a CT scanner according to an embodiment of the present invention.

FIG. 2 is a diagram showing an internal structure of a detector.

FIG. 3 is an explanatory diagram showing an operation of the CT scanner shown in FIG.

FIG. 4 is an explanatory diagram showing the operation of the CT scanner shown in FIG. 1.

FIG. 5 is a configuration diagram of a conventional CT scanner.

FIG. 6 is another configuration diagram of a conventional CT scanner.

FIG. 7 is an explanatory diagram showing the operation of the conventional CT scanner shown in FIG.

FIG. 8 is an explanatory diagram showing the operation of the conventional CT scanner shown in FIG.

FIG. 9 is an explanatory diagram showing the operation of the conventional CT scanner shown in FIG.

[Explanation of Codes] 1 X-ray tube 2 X-ray fan beam 3 Subject 4 Detector 5 X-ray controller 6 Mechanism controller 7 Data collector 8 Reconfiguring device 10a to 10f Rotation table 11 Revolution table 12 X-ray shield

Claims (1)

[Claims] 1. A radiation source that generates a fan beam radiation having a predetermined fan angle and a subject are placed on the radiation source, and the subject is not rotated about the radiation source along the plane of the fan beam radiation. Object moving means for passing through the fan beam radiation while only revolving around, and a plurality of detections arranged in a semicircular shape centered on the radiation source so as to detect the fan beam radiation transmitted through the object. A multi-channel detector composed of elements, and a CT scanner.