JPH11218578A - Solid detector for computed tomography - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid detector for CT in which a strong artifact does not appear in the center part even if the focus point of X-ray tube moves in the slice direction. SOLUTION: The X-ray beam in the X-ray incidence direction 5 from the initial focus position is limited at the lower end of a wedge shape collimator 14, goes in a detector 2 which takes in the signal at the opening of X-ray incidence width 7 from the focus position. On the other hand, the' X-ray beam in the X-ray incidence direction 6 after moving the focus slantingly goes in; however, it goes in the detector 2 limited at the lower end of wedge shape collimator 14 without being cut at the upper edge of the collimator by the shape of the wedge shape collimator 14 which takes in the signal at the opening of X-ray incidence width 8 after moving the focus. This wedge shape collimator 14 is designed to converge in the X-ray source direction for whole channel and the X-ray beam goes in all detectors without cut-off and so no detector output variation due to the focus movement exists and no strong artifact generated in the center part (corresponding image of ϕ30-ϕ50) is seen.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solid state detector for CT used in an X-ray CT apparatus.

[0002]

2. Description of the Related Art An X-ray CT apparatus emits X-rays from an X-ray tube while rotating in a circumferential direction around a subject, and transmits the subject through a plurality of detectors arranged in a circular configuration facing the tube. X-rays are detected, and the signals are processed by a computer to form an image. A plurality of the detectors are two-dimensionally arranged in an arc shape. The direction is called a slice direction, and a direction perpendicular to the slice direction is called a channel direction (the direction in which the subject lies). X-rays emitted from the X-ray tube
There are two types: one that travels straight through the subject and one that is scattered by the subject.A collimator is installed in front of the detector to capture only the former information, remove scattered rays entering obliquely, and prevent crosstalk. Is provided. In this collimator, an X-ray shielding wall is formed in front of detectors arranged two-dimensionally in a slice direction and a channel direction using a material that is hard to transmit X-rays.

[0003] The detector is an X-ray tube comprising an X-ray detecting element comprising a scintillator element for converting X-rays into light and a photodiode for detecting the light converted by the scintillator element and outputting it as an electric signal. And about 500 to 1000 channels arranged in an arc with the center as the center.

As shown in FIG. 11, an X-ray radiated from an X-ray tube focal point A is focused on a fan-shaped X-ray beam 4 by a collimator provided on the front surface of the X-ray tube and transmitted through a subject. The mask is masked in the body axis direction according to the slice thickness by the collimator 3 on the front surface of the detector 2 and enters the detector 2. In the collimator 3, the height of the shielding plate is constant over all the channels, and the direction thereof converges in the direction of the X-ray tube focal point A. Therefore, scattered radiation obliquely other than that direction can be removed.

[0005]

The conventional solid-state detector for an X-ray CT apparatus is constructed as described above.
While the X-ray tube of the T device is rotating, the position of the X-ray tube focal point A moves in the slice direction (tomographic plane direction) to the position of the moved X-ray tube focal point A 'as shown in FIG. When the X-ray tube focal position moves in this manner, the X-ray beam incident from the X-ray incident direction 5 from the initial focal position as shown in FIG.
The entire amount (X-ray incident width 7 from the initial focus position) determined by the pitch of the collimator 3 enters the detector 2, but the X
The X-ray beam incident from the line incident direction 6 is
(The upper end of the right collimator and the lower end of the left collimator), and the X-ray incident width 8 after the focal point shift is smaller than the aforementioned 7.

FIG. 9 shows the relationship between the X-ray tube focal position and the output of the detector as an angle dependency (polar response) with respect to the output of an arbitrary detector 2. As shown in FIG. 11, the position of the output peak of each of the detectors 2 and the collimator 3 is set to θ (the angle between the normal line of the detector 2 and the straight line connecting the X-ray tube focal point A and the detector 2) = 0. If the focal point of the X-ray tube moves from the central axis XX of the detector in FIG. 11, the X-ray beam is missing at the corner of the collimator 3.
The output of the detector decreases accordingly.

However, as shown in FIG. 8, at this time, although ΔIa is reduced in the first detector D 1, the second detector D 2
In this case, a phenomenon occurs that ΔIb increases, and if these channels exist adjacent to each other, a difference in the output change rate of the detector occurs. This is the central part (φ30 to φ50 in the image)
, There is a problem that it appears as a particularly strong artifact on the image.

The present invention has been made in view of such circumstances, and even when the focal position of the X-ray tube moves in the slice direction, a CT image in which a strong artifact does not appear at the center.
An object of the present invention is to provide a solid-state detector for use.

[0009]

In order to achieve the above object, a solid-state detector for CT according to the present invention comprises a collimator for preventing X-ray crosstalk and a two-dimensional array at an X-ray aperture. In the CT solid-state detector provided with the X-ray detecting element described above, the cross-sectional shape of the collimator shielding plate in the two-dimensional array direction is wedge-shaped.

A collimator for preventing X-ray crosstalk and a two-dimensional array of X-rays are provided at the X-ray opening.
In a solid state detector for CT equipped with a line detecting element, a collimator shielding plate in a two-dimensional array direction is arranged to be inclined at a predetermined angle with respect to the X-ray incident direction.

A collimator for preventing X-ray crosstalk and a two-dimensional array of X-rays are provided at the X-ray opening.
In a CT solid-state detector provided with a line detecting element, a collimator shielding plate is stacked and arranged with two or more types of plates whose thickness is increased in the direction of the detector from the side closer to the X-ray source.

The solid-state detector for CT according to the present invention is configured as described above, and the collimator shielding plate in the two-dimensional array direction (slice direction) has a wedge-shaped cross-sectional shape.
The difference in the rate of change in the output of the detector can be reduced by using one that has a predetermined inclination with respect to the X-ray source direction or one that has two or more types of plates whose thickness has increased from the side closer to the X-ray source. A good image without strong artifacts in the center of the image can be obtained.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the solid state detector for CT according to the present invention will be described with reference to FIG.

As shown in FIG. 1, the solid-state detector for CT comprises a plurality of detectors 2 arranged in a circular arrangement facing an X-ray source, a separator 16, and a wedge-shaped collimator 14 on the upper part thereof. It is configured. This wedge-shaped collimator 14,
Are supported at equal intervals by a support plate in the channel direction, the direction of which converges in the direction of the X-ray source (X-ray incident direction 5 from the initial focal position), and is made of a material that is difficult to transmit X-rays.
A line shielding wall is formed to remove scattered radiation, and is provided so that the X-ray beam incident on the detector 2 is maximized. The detector 2 includes a scintillator element for converting X-rays into light, and an X-ray detection element including a photodiode for detecting the light converted by the scintillator element and outputting it as an electric signal. It has a configuration in which about 500 to 1000 channels are arranged by being partitioned by an arc-shaped separator 16.

An X-ray beam from the X-ray incident direction 5 from the initial focus position is incident on the detector 2 and X-rays from the initial focus position.
It enters the line incident width 7. On the other hand, the X-ray beam from the X-ray incident direction 6 after the focal point shift is missing at the corner of the collimator 3 before being incident on the detector 2 as shown in FIG. The collimator 14 has the X-ray incident width 8 after the focal point movement without any chipping. These 7 and 8
Is determined by the width limited by both lower ends of the wedge-shaped collimator 14, and is the same. Therefore, because the collimator is wedge-shaped,
Since the x-ray beam is always restricted at the lower end of the wedge collimator 14 in all channels, there is no change in the detector output. For this reason, a strong artifact occurring at the center (φ30 to φ50 in the image) is not observed.

FIG. 2 shows an arrangement in which the wedge-shaped collimator 14 is arranged in a direction opposite to that of the wedge-shaped collimator 14.
In this case, the X-ray beam is limited by the upper end corner of the wedge-shaped collimator 14 before and after the focal point movement, and the detector 2
The X-ray incident width 7 from the initial focal position and the X
The line incident width becomes 8, and the detector output is the same.

FIG. 3 shows an arrangement in which the direction of the wedge-shaped collimator 14 is alternately changed upside down. In this case, the left end of the X-ray beam is applied to all the channels both before and after the focal point movement. There is a similar detector output change since the upper end of the wedge collimator 14 is truncated at the lower right end of the wedge collimator 14. Therefore, no artifact is generated.

One embodiment of the solid-state detector for CT according to the second aspect of the present invention will be described with reference to FIG.

In this CT solid-state detector, as shown in FIG. 4, the collimators of all channels are inclined by a predetermined inclination angle 24 with respect to the X-ray incident direction 5 (reference axis) from the initial focal position. This is one in which an inclined collimator 15 is arranged. The detector 2 has the same structure as in FIG.

In this case, the left end of the X-ray beam is cut off at the lower end of the inclined collimator 15 and the right end is cut off at the upper end of the inclined collimator 15 in all the channels before and after the focal point shift. There is a change in the detector output. Therefore, no artifact is generated.

One embodiment of the solid-state detector for CT according to claim 3 of the present invention will be described with reference to FIGS. 5, 6, and 7. FIG.

In this solid state detector for CT, as shown in FIG. 5, the collimator is composed of an upper thin plate collimator 22 and a lower thick plate collimator 21, and the thick plate collimator 21 outputs an X-ray beam. The structure is such that it has a function of collimating and removing scattered radiation by a plate collimator 22 having a small thickness. As described above, when the thicknesses t1 and t2 and the heights h1 and h2 of the two-layer structure of the upper plate and the lower plate are respectively set, t1 <
t2, h1> h2 are set. The detector 2 has the same structure as in FIG.

In this case, the X-ray beam is always chipped at the lower end of the lower thick plate collimator 21 before and after the focal point movement in all channels, so that the X-ray incident widths 7 and 8 are the same for each channel. Equivalent X
A line beam will be incident on the detector 2. Also, since the height of the lower thick plate collimator 21 is set very low, even if the X-ray beam is cut off at the upper corner or cut off at the lower corner, the output change amount of the detector 2 is extremely small. , Negligible. Therefore, no harmful artifact is generated on the image.

FIG. 6 is an assembled sectional view when this collimator is used, and FIG. 7 is a groove plate 1 in which a thin plate collimator 22 and a thick plate collimator 21 are inserted.
It is a perspective view of the groove part of No. 9. In general, ceramics with high processing and cutting accuracy are used. First, a narrow groove for a thin plate is subjected to all-channel dicing, and then a wide groove for a thick plate is subjected to all-channel dicing. Even if the positional relationship between the two grooves does not completely match, there is no problem as long as the pitch accuracy is obtained.

[0025]

The solid-state detector for CT of the present invention is constructed as described above. Even if the focal point of the X-ray tube moves in the slicing direction, the X-ray beam is almost always occluded by the collimator shielding plate, and is always removed. Since the light enters the detector, there is no change in the output change rate of each channel due to the polar response of the detector. Therefore, a good image free from artifacts can be obtained without special adjustment.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a solid state detector for CT of the present invention.

FIG. 2 is a diagram showing another embodiment of the solid-state detector for CT of the present invention.

FIG. 3 is a diagram showing another embodiment of the solid-state detector for CT of the present invention.

FIG. 4 is a diagram showing another embodiment of the solid state detector for CT of the present invention.

FIG. 5 is a view showing another embodiment of the solid-state detector for CT of the present invention.

FIG. 6 is an assembled sectional view of the two-stage collimator of the present invention.

FIG. 7 is a perspective view of a groove plate for a two-stage collimator of the present invention.

FIG. 8 is a diagram for explaining a conventional detector output change.

FIG. 9 is a diagram showing a conventional detector polar response.

FIG. 10 is a diagram for explaining a conventional detector.

FIG. 11 is a diagram showing a geometric structure of an X-ray CT apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 X-ray tube 2 Detector 3 Collimator 4 X-ray beam 5 X-ray incidence direction from initial focus position 6 X-ray incidence direction after focus shift 7 X-ray incidence width from initial focus position 8 X-ray incidence after focus shift Width 14 wedge collimator 15 inclined collimator 16 separator 18 support plate 19 groove plate 20 groove for thin plate 21 thick plate collimator 22 thin plate collimator 23 groove for thick plate 24 scintillator element 25 photodiode

Claims (3)

[Claims] 1. A CT solid-state detector having a collimator portion for preventing X-ray crosstalk and a two-dimensional array of X-ray detecting elements in an X-ray opening thereof, wherein the collimator shields in the two-dimensional array direction. A solid-state detector for CT, wherein a plate has a wedge-shaped cross section. 2. A CT solid-state detector including a collimator portion for preventing X-ray crosstalk and a two-dimensional array of X-ray detection elements in an X-ray opening thereof. The plate is moved with respect to the X-ray incidence direction.
A solid state detector for CT, wherein the solid state detector is arranged to be inclined at a predetermined angle. 3. A CT solid-state detector having a collimator portion for preventing X-ray crosstalk and a two-dimensional array of X-ray detection elements in an X-ray opening thereof, wherein a collimator shielding plate is provided with an X-ray source. A solid state detector for CT, wherein the solid state detector is configured by stacking and arranging two or more types of plates whose thickness is increased in the direction of the detector from the side closer to.