JPH0434705B2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field) The present invention relates to X-ray CT (computer tomography)
The present invention relates to an apparatus, and more particularly, to an improvement in a beam hardening correction method.

(Prior Art) In an X-ray CT apparatus, corrections such as beam hardening, identification of an object to be imaged, etc. have been conventionally performed. FIG. 1 shows an example of the essential parts of this type of device. In the figure, X-ray tube 1 that generates X-rays
Two types of tube voltage are available, E ₁ and E ₂ , and switch 2
It is now possible to select. X-rays generated from the X-ray tube 1 pass through the object to be imaged 3 and enter the X-ray detector array 4 . The X-ray detector array 4 is an airtight container filled with gas (Xe gas, etc.), and an electrode plate extending long in parallel to the X-ray incident direction is provided inside the container. The electrode plate has a large number of signal electrodes 41 and bias electrodes 42 arranged alternately, and one element of the detector consists of one signal electrode 4.
1 and bias electrodes 42 on both sides of which a high voltage E is applied. The transmitted X-rays enter the container through the entrance window 43 of the detector array 4 and ionize the gas filled therein. An ionizing current corresponding to the incident X-ray dose is obtained from the signal electrode 41, which is converted into a voltage by amplifiers 51 and 52 and then sent to the data processing device 6. The data processing device 6 converts the projection data acquired in this manner into digital signals and processes them as appropriate to reconstruct a tomographic image of the object to be imaged.

In this case, switch the tube voltage of the X-ray tube,
The detector output x ₁ (E ₁ ) when the tube voltage is E ₁ and the tube voltage
Obtain the detector output x ₂ (E ₂ ) at E ₂ and process this data to obtain information regarding the energy characteristics of the X-ray absorption rate of the object to be imaged 3, and perform corrections such as beam hardening and correction of the imaged object. The body is being identified.

However, this case has the following problems.

It is not easy to change the tube voltage in terms of hardware. For example, lowering the tube voltage lowers the energy, but also sharply reduces the X-ray output.

It takes time because the measurement is done in two parts. Errors occur when the subject is moving.

(Objective of the Invention) The present invention has been made in view of such problems, and its purpose is to perform beam hardening using a detector that can obtain information regarding the energy characteristics of the X-ray absorption rate of an imaged object. is corrected more accurately,
An object of the present invention is to provide an X-ray CT device that can obtain images suitable for diagnosis.

(Structure of the Invention) In the present invention that achieves this object, an X-ray source such as an X-ray tube is disposed facing the X-ray source, and the radiation emitted from the X-ray source passes through the object to be imaged and enters the object. It consists of an In an X-ray CT device that displays a spatial distribution of linear absorption as a tomographic image or a transmission image, the detector array has an X-ray entrance window.
It is an airtight container filled with Xe gas, and consists of a signal electrode plate and a bias electrode plate arranged parallel to the X-ray incident direction in the gas, and the signal electrode plate is placed on the side closer to the X-ray incidence window. The information is divided into two or more in the direction farther from the lower energy X
The present invention is characterized in that it is configured to operate to reconstruct an image by utilizing the high sensitivity distribution to line components.

(Example) Hereinafter, an example of the present invention will be described in detail using the drawings.

FIG. 2 is a block diagram of main parts showing an example of an embodiment of the present invention. In the figure, reference numeral 10 denotes an X-ray tube, which is driven by a certain predetermined constant voltage and generates X-rays. Reference numeral 40 denotes an X-ray detector array, which is an airtight container filled with Xe gas, similar to the conventional one, but differs from the conventional one in its electrode structure. That is, the signal electrodes 410 each arranged between a large number of bias electrodes 42 to which voltage E from a high voltage source is applied in parallel are arranged parallel to the X-ray incident direction, but the X-ray incident window 43 It is divided into three parts from the nearest to the farthest. The divided signal electrodes P ₁₁ , P ₁₂ , P ₁₃ , P ₂₁ , P ₂₂ , and P ₂₃ are respectively amplifiers (current-voltage converters) A ₁₁ , A ₁₂ ,
Connected to the input terminals of A ₁₃ , A ₂₁ , A ₂₂ , and A ₂₃ . The output of each amplifier is led to the arithmetic processing unit 60, where it is converted into a digital signal and then subjected to appropriate arithmetic processing to obtain the spatial distribution of the X-ray absorption rate of the object to be imaged as a tomographic image or a transmission image. , these images are displayed on a display device 70.

The operation in such a configuration will be explained next.
If the energy of the X-rays that have passed through the imaged object 3 and entered the X-ray detector array 40 is low, most of them are absorbed by the Xe gas near the window 43.
Generates ionized ions, which are mainly
It is collected by signal electrodes such as P ₁₁ and P ₂₁ . If the energy is high, the Xe gas near the window will not absorb all of it, and the rest will be absorbed by the part far from the window.
It also ionizes Xe gas and is sensitive to P ₁₁ and P ₂₁ as well as P ₁₃ and P ₂₃ . This situation is shown in FIG. Therefore, in the arithmetic processing unit 60, for example, A=x ₁₃ /(x ₁₁ +x ₁₂ +x ₁₃ ) (however, x ₁₁ ,
x ₁₂ and x ₁₃ are the respective outputs of the electrodes P ₁₁ , P ₁₂ , and P ₁₃ known via amplifiers A ₁₁ , A ₁₂ , and A ₁₃ ), in addition to the X-ray absorption value, A If is large, it means that the X-rays that entered the detector had a relatively high content of high energy, and the object to be imaged was a material with a relatively low absorption rate of high energy. .

In the case of X-ray CT equipment, in order to compensate for beam hardening based on energy characteristics, for example, y=
The nonlinearity of the detector output x is corrected as x + ax ² + bx ³ , but y = x ₁ + a ₁ x ₁ ² + b ₁ x ₁ ² + x ₂ +
_{A 2 x 2} ² ＋b ₂ x ₂ ² _{＋ x 3 ＋} a _{3 x} ³ _{＋ a 3} By optimizing , images more suitable for diagnosis can be obtained. Note that the number of divisions of the signal electrode is not limited to three, but may be two or more. Alternatively, such a correction method can be applied not only to CT, but also to other transmitted images such as so-called scout views.

(Effects of the Invention) As explained above, according to the present invention, since the electrode of the X-ray detector using Xe gas is divided in the X-ray incident direction, it has the ability to discriminate X-ray energy. Therefore, it is not necessary to switch the tube voltage of the X-ray tube as in the past, and it is also possible to perform beam hardening correction more accurately than with such a conventional correction method, making it possible to obtain a better image. can.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of the main configuration of a conventional X-ray CT device having a beam hardening correction function, and FIG. 2 is an example of an implementation of an X-ray CT device having a beam hardening correction function according to the present invention. FIG. 3 is an explanatory diagram showing the signal sensitivity of divided electrodes. 3... object to be imaged, 10... X-ray tube, 40... X-ray detector, 42... bias electrode, 43... X-ray entrance window,
P ₁₁ , P ₁₂ , P ₁₃ , P ₂₁ , P ₂₂ , P ₂₃ ... divided electrode, E...
High voltage source, _A11 to _A23 ...Amplifier, 60...Arithmetic processing unit, 70...Display device.

Claims (1)

[Claims] 1. An X-ray source such as an X-ray tube, and an X-ray detector that is placed opposite the X-ray source and converts the X-rays emitted from the X-ray source and transmitted through the imaged object into electrical signals. It consists of an array, a device that converts the output signal of the detector into a digital signal and performs calculation processing, and a device that displays the calculation results as an image. In an X-ray CT apparatus displaying as
It is an airtight container filled with Xe gas and has a ray entrance window. The information is divided into two or more from the side closer to the X-ray entrance window to the side farther from the X-ray entrance window, and each of them or a combination thereof supplies different information to the arithmetic processing unit, and this arithmetic processing unit is configured to detect signals from electrodes close to the X-ray entrance window far away. An X-ray CT device characterized in that it is configured to operate to reconstruct an image by utilizing a high sensitivity distribution to X-ray components with lower energy than signals from electrodes.