JP3442494B2 - X-ray CT system - 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 scattering component correcting method and an X-ray CT (Computed Tomograpy) apparatus. More specifically, the present invention relates to an X-ray CT component correction method that can improve the correction accuracy and can be suitably implemented with a labor-saving method of correcting an X-ray scattering component.

[0002]

2. Description of the Related Art FIG. 13 is an explanatory diagram of a situation in which an object is scanned by an X-ray CT apparatus. X-ray tube T
The X-rays emitted from the collimator K are focused into a fan-shaped X-ray beam (Beam) Xr having a thickness w, pass through the subject H, become a transmission component Xp, and become the thickness of the detector D ′. Direction (= thickness direction of the X-ray beam Xr) is incident on a region having a width w in the central portion. However, when passing through the subject H, the subject H scatters the X-ray beam Xr.
Therefore, the scattered component Xs is incident on the entire surface of the detector D ′.

FIG. 14 is a schematic perspective view of the detector D '. The detector D ′ has a large number of channels Ci arranged in the width direction (B direction in the drawing). Number of channels is 8
00. The width t of one channel is, for example, 0.5 mm
And the thickness d is, for example, 25 mm. The transmission component Xp and the scattering component Xs are incident on the central portion P of the detector D ′ in the thickness direction. Further, the scattered component Xs is incident on the vicinity S1 and S2 of the end portion in the thickness direction of the detector D ′.

As described above, since the count value (detection data) of each channel of the detector D'is the sum of the transmission component Xp and the scattering component Xs, in order to correctly reconstruct an image, Correction for removing the scattered component Xs is required.

Next, an example of a conventional method of correcting the X-ray scattering component will be described. Before scanning the subject H, the relational expression Q between the area of the projected image and the amount of scattered components is obtained. As shown in FIG. 15, with respect to phantoms F having different diameters and different sizes, the detector D ′ is displaced in the thickness direction and only the scattered component Xs is made incident to obtain the count value. Each count value at this time is phantom F of various sizes.
Is the amount of each scattering component. Next, as shown in FIG. 16, the area A of the projected image of each phantom F is calculated. Next, FIG.
As shown in FIG. 7, the relational expression Q between the area A of the projected image of each phantom F and the measured scattered component amount is obtained. Note that FIG.
7, wtr15 to wtr30 represent phantoms F having a diameter of 15 cm to 30 cm, and Air represents no phantom. When scanning the subject H, the area of the projected image of the subject H in each view is obtained, the X-ray scattering component is obtained from the area of the projected image of the subject H using the relational expression Q, and the Correct the count value.

FIG. 17 shows a flowchart of a conventional scattered component correction process. In step B1, the subject H is scanned, and the count value α in each channel Ci of the detector D ′ is
To get. In step B2, the area Ah of the projected image of the subject H is calculated from the count value α. In step B3, the scattered component amount βh of the subject H is obtained based on the projected image area Ah and the relational expression Q (see FIG. 17).

At step B4, the scattered component amount βh is subtracted from the count value α, and the subtraction result is used as transmission X-ray data γ.

[0008]

In the above-described conventional method for correcting the X-ray scattering component, it is assumed that the scattering characteristic of the phantom F and the scattering characteristic of the subject H are the same, but in reality they are the same. is not. In some cases, the relational expression Q may not be appropriate due to changes in the characteristics of the detector T with time. Therefore, there is a problem that the correction accuracy is not sufficient. Further, in order to obtain the relational expression Q, it is necessary to measure the phantoms F having various sizes, which causes a problem that the operation is troublesome. Therefore,
An object of the present invention is to provide an X-ray CT apparatus which can improve the correction accuracy and can suitably perform the method of correcting the X-ray scattering component and the correction method of the X-ray scattering component, which does not require any trouble.

[0009]

According to a first aspect of the present invention, a plurality of channels among a large number of channels arranged in a width direction of a detector of an X-ray CT apparatus are arranged between channels or between channels for X-ray scattering components. The monitor channels having different detection areas between the groups are set, the detection values of the respective channels of the detector are acquired by scanning the object, and the amount of scattered components per channel is calculated based on the detection values acquired by the monitor channels. A method for correcting an X-ray scattered component, which is calculated and subtracted from the detected value of each channel to obtain transmission X-ray data of each channel. In the above configuration, “having different detection areas between channels or channel groups” may mean different detection areas for each channel, or two or more channels as one channel group and different detection areas for each channel group. Means good.

According to a second aspect of the present invention, in the X-ray CT apparatus having a detector in which a large number of channels are arranged in the width direction, a plurality of the plurality of channels are X-rays.
Calculate the amount of scattered components per channel based on the detectors that are the monitor channels having different detection areas for each channel or channel group for the line scattered components and the detection values acquired by the monitor channels by the scan of the subject. And a scattering component amount correcting unit that subtracts the amount of the scattering component from the detection value acquired in each channel of the detector by scanning the subject and acquires the transmission X-ray data of each channel. There is provided an X-ray CT apparatus characterized by being provided.

According to a third aspect of the present invention, in the X-ray CT apparatus having a detector in which a large number of channels are arranged in the width direction, a plurality of the plurality of channels are at least the ends in the thickness direction of the detector. A detector having a detection surface in the vicinity of the part and having a detection area different for each channel or channel group, and for each channel based on the detection value acquired by the monitor channel by scanning the subject. Scattering component amount calculation means for calculating the amount of scattering component, and a scattering component for obtaining transmission X-ray data of each channel by subtracting the amount of the scattering component from the detection value acquired in each channel of the detector by scanning the subject. Provided is an X-ray CT apparatus characterized by comprising an amount correction means.

According to a fourth aspect of the present invention, in the X-ray CT apparatus having the above-mentioned structure, the vicinity of the end portions in the thickness direction of the detection surfaces of the plurality of channels is shielded by a lead block and the shielded area is set for each channel or. There is provided an X-ray CT apparatus characterized in that the monitor channel is configured by changing between channel groups.

According to a fifth aspect of the present invention, in the X-ray CT apparatus having the above-mentioned structure, a plurality of channels near a width direction end of a large number of channels arranged in the width direction of the detector are the monitor channels. X characterized by being
A line CT apparatus is provided.

[0014]

In the X-ray scattering component correction method according to the first aspect and the X-ray CT apparatus according to the second aspect, the detection areas of a plurality of detector channels are different for each channel or channel group for the X-ray scattering component. As a monitor channel. Then, the subject is scanned to acquire the detection value of each channel of the detector, and then the amount of scattered component per channel is calculated based on the detection value acquired by the monitor channel. Each monitor channel or channel group has a different detection area for the X-ray scattered component. Therefore, the relational expression between the size of the detection area and the amount of scattered components can be obtained from the detection value of the monitor channel. Since the detection area of the channel which is not the monitor channel is constant, the amount of scattered component per channel can be calculated from the detection area and the relational expression. Then, the calculated scattered component amount is subtracted from the detection value of the channel other than the monitor channel to obtain the transmission X-ray data of each channel. The detected value of the channel that is not the monitor channel is the sum of the transmitted component and the scattered component. Further, the amount of scattered component per channel can be regarded as constant (experimentally known that the amount of scattered component does not change significantly depending on the channel). Therefore, by subtracting the amount of scattered component per channel from the detection value of the channel other than the monitor channel, the detection value of only the transmission component, that is, the transmission X-ray data is obtained. According to the above, the scattering component amount is calculated from the detection value obtained by scanning the subject itself instead of the phantom, so that there is no problem of scattering characteristic mismatch. Further, since the relational expression is obtained at the time of scanning, there is no problem that the relational expression becomes improper due to changes in the characteristics of the detector over time. Therefore, the correction accuracy can be sufficiently improved. Further, it is not necessary to measure phantoms of various sizes, and the operation is easy. In the method of correcting the X-ray scattering component having the above configuration, if the relational expression is a linear expression, the calculation process becomes simple.

In the X-ray CT apparatus according to the third aspect,
The plurality of channels of the detector are set as monitor channels each having a detection surface at least in the vicinity of the end in the thickness direction and having different detection areas between each channel or channel group. Other than that, the configuration is the same as that of the X-ray CT apparatus according to the second aspect. Since each of the monitor channels has a detection surface in the vicinity of the end in the thickness direction, their detection values are only scattered components. In addition, each channel or channel group of the monitor channels has a different detection area. Therefore, the relational expression between the size of the detection area and the amount of scattered components can be obtained from the detection value of the monitor channel. Since the detection area of the channel which is not the monitor channel is constant, the amount of scattered component per channel can be calculated from the detection area and the relational expression. The other functions are the same as those of the X-ray CT apparatus according to the second aspect. Note that, for example, if the detector has a large thickness, it is possible to obtain the detection value of only the scattering component even if it is not near the end in the thickness direction.

In the X-ray CT apparatus according to the fourth aspect,
A monitor channel is configured by shielding the vicinity of the ends in the thickness direction of the detection surface of a plurality of channels with a lead block and changing the shielding area between channels or between channel groups. This allows a portion of the normal detector to be used for the monitor channel, simplifying the configuration.

In the X-ray CT apparatus according to the fifth aspect,
Among the many channels of the detector, a plurality of channels near the end in the width direction are set as the monitor channels. By arranging the monitor channels in the vicinity of the ends in the width direction in this way, the transmission X-ray data can be acquired in the channels near the center of the width direction, which simplifies the processing.

[0018]

The present invention will be described in more detail with reference to the embodiments shown in the drawings. The present invention is not limited to this. —First Embodiment— FIG. 1 is a block diagram of a first embodiment of an X-ray CT apparatus according to the present invention. The X-ray CT apparatus 100 includes an operation console 1, an imaging table 8 and a scanning gantry 9. The operation console 1 outputs an input device 2 that receives an operator's instructions and information, a central processing unit 3 that executes a scanning process and an image reconstruction process, and a control signal to a scanning table 8 and a scanning gantry 9. Control interface 4, a data acquisition buffer 5 that collects data acquired by the scanning gantry 9, and a CRT 6 that displays a tomographic image, a scout image, and the like. On the imaging table 8, the subject is placed and moved in the body axis direction.
The scanning gantry 9 includes an X-ray controller 10, an X-ray tube T, a collimator K, a detector D, and a data acquisition unit 1.
4 and a rotation controller 15 for rotating the X-ray tube T and the like around the body axis of the subject. The central processing unit 3 functions as a scattered component amount calculation means and a scattered component correction means according to the present invention.

FIG. 2 is an explanatory diagram of a situation in which the X-ray CT apparatus 100 scans a subject. The X-ray emitted from the X-ray tube T is fan-shaped by the collimator K and has a thickness w.
The beam is focused on the line beam Xr, passes through the subject H, and the transmitted component X
It becomes p and is incident on the region of the width w of the central portion of the detector D in the thickness direction. Further, the X-ray beam Xr is scattered by the subject H, becomes a scattered component Xs, and enters the entire surface of the detector D. Lead blocks L1 and L2 that partially shield the scattered component Xs are provided in the vicinity of the widthwise end portion Zr of the detector D.
Is attached.

FIG. 3 is a schematic perspective view of the detector D.
The detector D has a large number of channels Ci arranged in the width direction. The number of channels is 800, for example. The width t of one channel is, for example, 0.5 mm, and the thickness d is, for example, 25 mm. The transmission component Xp and the scattering component Xs are incident on the central portion P of the detector D in the thickness direction. Further, the scattered component Xs is incident on the vicinity S1 and S2 of the end portion of the detector D in the thickness direction. The lead blocks L1 and L2 partially shield the vicinity S1 and S2 of the detection surfaces of the plurality of channels in the thickness direction, and by combining a plurality of lead plates having different widths, the shielding area between the channels ( Or between channel groups). The thickness τ of the lead plate is, for example, 0.2 mm, and the height y is, for example, 10 mm.

FIG. 4 is a schematic plan view of the detector D.
Channel C1 not shielded by lead blocks L1 and L2, channel C2 shielded by lead block L2 by thickness τ, channel C3 shielded by lead blocks L1 and L2 by thickness 2τ, lead blocks L1 and L2
Channels C4, ..., Which are blocked by a thickness of 3τ, are monitor channels.

FIG. 5 shows each monitor channel C1, C2, ...
Is a graph in which the horizontal axis represents the thickness x of the shielding area and the vertical axis represents the count value α, and the count values α1, α2, ... Of the monitor channels C1, C2, ... When the subject H is scanned are plotted. As the thickness x of the shielding region increases, the scattered component Xs is shielded, so that the count value decreases.
If a relational expression q between the thickness x of the shielding region and the count value is obtained and the thickness x = d of the shielding region is substituted into the relational expression q, the virtual count value αd when all the scattering components Xs are shielded Can be estimated. Further, by substituting the thickness x = 0 of the shielding region into the relational expression q, the virtual count value α0 when the scattering component Xs is not shielded can be obtained. This virtual count value α
By subtracting the virtual count value αd from 0, the scattered component amount β per channel can be calculated. When the thickness x of the shielding region is actually increased to shield the central portion P in the thickness direction of the detector D, the transmission component Xp is shielded, and the count value α rapidly decreases. Then, the thickness of the shielding area x = d
Then, the count value becomes 0. That is, the virtual count value αd is a value that cannot be measured and is obtained only by calculation from the relational expression q.

FIG. 6 is a flowchart of the scattered component correction processing in the X-ray CT apparatus 100. Step V
In 1, the subject H is scanned and the count value α in each channel Ci of the detector D is acquired. In step V2,
Count values α1, α of monitor channels C1, C2, ...
A linear expression q is obtained from 2, ... By the method of least squares. In step V3, the thickness of the shielding region x = 0 and d
By substituting for the virtual count value α0 when the scattered component Xs is not blocked and the virtual count value αd when all the scattered component Xs is blocked. In step V4, the virtual count value αd is subtracted from the virtual count value α0 to calculate the scattered component amount β. In step V5, each channel C
The scattered component amount β is subtracted from the count value α at i, and the subtraction result is transmission X-ray data γ. In addition, the amount of scattered components in the monitor channels C1, C2, ... Is obtained from the linear expression q, and the count value α in the monitor channels C1, C2 ,.
If subtracted from 1, α2, ..., Monitor channels C1, C
It is also possible to obtain transmitted X-ray data γ for 2, ...

According to the X-ray CT apparatus 100 of the first embodiment described above, the scattered component amount β is calculated from the count value α obtained by scanning the subject H, and at the same time, the linear expression q is calculated to obtain the scattered component amount. Calculate β. Therefore, the correction accuracy can be sufficiently improved. In addition, it does not take time and effort to operate.

Second Embodiment The second embodiment is different from the first embodiment in that the detector D shown in FIG. 7 is used. In the detector D shown in FIG. 7, the lead block Lw shields the vicinity S1 in the thickness direction and the vicinity P in the center of the detection surfaces of the plurality of channels, and partially shields the vicinity S2 in the thickness direction. The shielding area is changed between channels (or between channel groups) by combining a plurality of lead plates having different widths. The thickness τ of the lead plate is, for example, 0.2 mm, and the height y is, for example, 10 mm.

FIG. 8 is a schematic plan view of the detector D.
Channel C not completely shielded by lead block Lw
1, channel C2 not shielded by thickness τ2, thickness 2
Channels C3 not shielded by τ3 and channels C4, ... Not shielded by the thickness 3τ are respectively monitor channels.

FIG. 9 shows each monitor channel C1, C2, ...
Is a graph in which the horizontal axis represents the thickness x of the shielding area and the vertical axis represents the count value α, and the count values α1, α2, ... Of the monitor channels C1, C2, ... When the subject H is scanned are plotted. As the thickness x of the shielded region decreases, the scattered component Xs enters, so the count value increases. If a relational expression q between the thickness x of the shielding region and the count value is obtained and the thickness x = 0 of the shielding region is substituted into the relational expression q, the virtual count value α0 when the scattering component Xs is not shielded is estimated. it can. This virtual count value α0 is the amount β of scattered components per channel. If the thickness x of the shielding region is actually reduced so as not to shield the central portion P in the thickness direction of the detector D, the transmission component Xp is incident, and the count value α rapidly increases. Then, the thickness of the shielding area x = 0
Then, count value = transmitted component amount + scattered component amount. That is, the virtual count value α0 is a value that cannot be measured and is obtained only by calculation from the relational expression q.

FIG. 10 is a flowchart of the scattered component correction processing in the second embodiment. In step U1, the subject H is scanned and the count value α in each channel Ci of the detector D is acquired. At step U2, a linear expression q is obtained from the count values α1, α2, ... Of the monitor channels C1, C2 ,. In step U3, 1
Substituting the thickness x = 0 of the shielding area into the following equation q, the scattered component X
A virtual count value α0 when s is not cut off is obtained and is set as a scattered component amount β. In step U4, the scattered component amount β is subtracted from the count value α in each channel Ci, and the subtraction result is used as transmission X-ray data γ.

According to the second embodiment described above, the scattered component amount β is calculated from the count value α obtained by scanning the subject H, and at the time of scanning, the linear expression q is obtained to calculate the scattered component amount. Therefore, the correction accuracy can be sufficiently improved. In addition, it does not take time and effort to operate.

-Third Embodiment- The third embodiment is secondly in that the detector D shown in FIG. 11 is used.
Different from the embodiment. In the detector D shown in FIG. 11, the lead block Lw ′ is obtained by deforming the stepped end surface of the lead block Lw of the second embodiment into a flat shape. FIG. 12 is a schematic plan view of the detector D. Since the edges of the shield region are oblique, an average thickness may be used as the thickness x of the shield region of each monitor channel C1, C2, .... Except for the above, the same as the second embodiment, and the same effect as the second embodiment can be obtained. Similarly, the stepped end faces of the lead blocks L1 and L2 in the first embodiment may be deformed into a flat shape.

[0031]

According to the X-ray scattering component correcting method and the X-ray CT apparatus of the present invention, the amount of the scattering component is calculated from the count value obtained by scanning the subject, so that the correction accuracy can be sufficiently improved. In addition, the troublesome operation of measuring the phantom becomes unnecessary.

[Brief description of drawings]

FIG. 1 is a block diagram showing an X-ray CT apparatus according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a situation in which a subject is scanned by the X-ray CT apparatus in FIG.

FIG. 3 is a perspective view of a main part of a detector in the X-ray CT apparatus in FIG.

FIG. 4 is a plan view of a main part of the detector shown in FIG.

FIG. 5 is a relationship diagram between a length of a shielding area and a count value in a monitor channel.

6 is a flowchart of a scattered component correction process in the X-ray CT apparatus of FIG.

FIG. 7 is a perspective view of a main part of a detector according to a second embodiment of the present invention.

8 is a plan view of relevant parts of the detector shown in FIG. 7. FIG.

FIG. 9 is a relationship diagram between the length of a shielded area and a count value in a monitor channel.

FIG. 10 is a flowchart of scattered component correction processing according to the second embodiment of the present invention.

FIG. 11 is a perspective view of essential parts of a detector according to a third embodiment of the present invention.

12 is a plan view of relevant parts of the detector shown in FIG. 11. FIG.

FIG. 13 is an explanatory diagram of a situation in which a subject is scanned by a conventional X-ray CT apparatus.

FIG. 14 is a perspective view of a main part of a detector in a conventional X-ray CT apparatus.

FIG. 15 is an explanatory diagram showing a conventional method for measuring the amount of scattered components.

FIG. 16 is an explanatory diagram showing a projected image of a phantom.

FIG. 17 is a relationship diagram between the area of a projected image and the amount of scattered components.

FIG. 18 is a flowchart of a conventional scattered component correction process.

[Explanation of symbols]

100 X-ray CT system 1 Operation console 2 input devices 3 Central processing unit 8 shooting table 9 Operation gantry Ci channel D, D'detector L1, L2, Lw Lead block T X-ray tube β, βh Scattered component amount

Continuation of the front page (56) Reference JP-A-5-56962 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) A61B 6/00-6/14

Claims (5)

(57) [Claims] 1. An X-ray CT apparatus having a detector in which a large number of channels are arranged in the width direction, wherein a plurality of channels among the plurality of channels have different detection areas for X-ray scattering components between channels or between channel groups. A detector which is defined as a monitor channel, a scattering component amount calculating means for calculating the amount of scattering component per channel based on a detection value acquired by the monitor channel by scanning the subject, and the detection by scanning the subject X-ray CT apparatus, comprising: a scattering component correcting unit that subtracts the amount of the scattering component from the detection value acquired in each channel of the detector to acquire the transmitted X-ray data of each channel. 2. An X-ray CT apparatus having a detector in which a large number of channels are arranged in the width direction, wherein a plurality of the plurality of channels have a detection surface at least in the vicinity of an end portion in the thickness direction of the detector. Also, a detector that is a monitor channel having a different detection area between channels or channel groups, and a scatter component that calculates the amount of scatter component per channel based on the detection value obtained in the monitor channel by scanning the subject. And a scattering component correcting unit that subtracts the amount of the scattered component from the detection value acquired by each channel of the detector by scanning the subject and acquires the transmitted X-ray data of each channel. Characteristic X-ray CT device. 3. The X-ray CT apparatus according to claim 2, wherein the vicinity of the ends in the thickness direction of the detection surfaces of the plurality of channels is shielded by a lead block and the shielded area is changed between channels or between channel groups. The X-ray CT apparatus is characterized in that the monitor channel is configured thereby. 4. The X-ray CT apparatus according to claim 1, wherein a plurality of channels near a width direction end of a large number of channels arranged in the width direction of the detector are the monitor. An X-ray CT apparatus characterized by being used as a channel. 5. The X-ray CT apparatus according to claim 3, wherein the horizontal axis represents the thickness of the shielding area of the lead blocks in the thickness direction of the detection surfaces of the plurality of channels, and the detection acquired by the monitor channel. It is characterized in that the detected counter value is plotted on a graph whose vertical axis is the counter value, and the scattered component amount per channel is calculated by obtaining a linear expression using the least square method. X-ray CT
apparatus.