JP2000189409A - Radiation image signal detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sectional image and a three-dimensional image not influenced with a scatterd radiation in a cone beam CT device. SOLUTION: Only a relatively high energy level of a radiation (over 60 KeV) is radiated to an object 9 through a copper sheet filter 21. The radiation which penetrates the object 9 is detected with a quantum counting-type radiation detector 3 with an energy discriminating function. A detecting part 30 of the detector 3 generates voltage which corresponds to an energy level of a radiation particle. A signal processing part 40 calculates the number of the radiation particles and has an energy level over 60 KeV which is transmitted in the detecting part 30 in a fixed time, then a result of the calculation is used as a pixel data. The energy level of a primary radiation which goes almost straight on the object 9 is higher than that of scatterd radiation which is dispersed from the object 9 and energy discrimination is conducted by setting 60 KeV as a threshold, then an image data is formed based on only a primary radiation component thereby influence of scattered radiation can be decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation image signal detecting apparatus for obtaining a radiation image signal of a subject by detecting radiation transmitted through the subject with a radiation detector, and more particularly to improvement of image quality deterioration due to scattered radiation. It is about.

[0002]

2. Description of the Related Art Conventionally, in the field of medical images,
X-ray CT, MRI, and the like have been proposed as devices for obtaining morphological two-dimensional information (tomographic images) of a subject.

[0003] In "X-ray CT", a radiation source that emits radiation such as X-rays is arranged on one side of a subject, and a line sensor (one-dimensional solid-state radiation detector) is arranged on the other side of the subject. The radiation obtained is converted into a fan beam using a slit to remove scattered radiation, and the radiation source and the line sensor are relatively positioned around a virtual axis (hereinafter referred to as “body axis”) around the object with the object interposed therebetween. The transmitted radiation image signal of the subject is obtained by detecting the radiation transmitted through the subject by the line sensor while rotating the image in a predetermined direction, and based on a large number of transmitted radiation image information (one-dimensional image information) acquired at each rotation position, that is, at each projection direction. To obtain a tomographic image of the subject.

[0004] "MRI" is to obtain a tomographic image using nuclear magnetic resonance by a method substantially similar to the above-mentioned X-ray CT.

[0005] At present, researches on technologies for detecting morphological three-dimensional information (stereoscopic image) of a subject have been made, and for example, helical CT and cone beam CT have been proposed (see "Development of cone beam CT"). Current Status and Its Future "Image Information (M); January 1988, pp. 122-127.

"Helical CT" is one of the multi-layer X-ray CT techniques. Here, the “multi-layer X-ray CT method”
A radiation source that emits radiation is arranged on one side of the subject, a line sensor is arranged on the other side of the subject, and the radiation emitted from the radiation source is turned into a fan beam by a slit similarly to X-ray CT, and the radiation source and the line sensor are connected to the subject. The radiation transmitted through the subject is detected by a line sensor while relatively rotating around the body axis around the subject across the subject to obtain a transmitted radiation image signal of the subject, and acquired at each rotational position, that is, at each projection direction. The tomographic image data of the subject is calculated based on a large number of transmitted radiographic image information (one-dimensional image information) (up to this point, the operation is the same as that of the X-ray CT), and the radiation source and the line sensor are moved in the body axis direction. After the movement, the tomographic image data is calculated again in the same manner as described above, and the tomographic image data is calculated from the tomographic image data at a number of moving positions in the body axis direction. Image data by interpolation calculation is intended to determine the volume data (3-dimensional radiation image information) of the subject.

[0007] In obtaining tomographic image data continuous in the body axis direction, a technique in which a radiation source and a line sensor are moved in a spiral shape with the body axis of a subject as a center axis of rotation is particularly referred to as "helical CT." (Spiral C
T) ".

In this helical CT, a helical (scan) CT method using an area sensor (two-dimensional solid-state radiation detector) and a cone beam (cone beam) has also been proposed. 3D helical scan CT "IEICE Transactions D-
II vol.J74-D-II No.8 August 1991). Hereinafter, in order to distinguish the helical CT according to this method from the helical CT using the line sensor, the helical CT using the line sensor is referred to as a “normal helical CT”.
T ".

[0009] The "cone beam CT" means that a radiation source emitting cone-shaped radiation is arranged on one side of an object, an area sensor is arranged on the other side of the object, and the radiation source and the area sensor are sandwiched by the object. The transmitted radiation image signal of the subject is obtained by detecting the radiation transmitted through the subject while rotating relatively around the subject with the area sensor, and a plurality of transmitted radiation image information acquired at each rotational position, that is, at each projection direction. Based on this, volume data and tomographic image data relating to the subject are obtained.

[0010]

When a subject is irradiated with radiation, a part of the radiation is scattered at each part of the subject and becomes scattered radiation. Therefore, the scattered radiation component is included in the radiation transmitted through the subject, in addition to the primary radiation component emitted from the radiation source and traveling straight through the subject and transmitting.

Here, in the CT of the type using a line sensor as a radiation detector like X-ray CT or ordinary helical CT, the radiation emitted from the radiation source is converted into a fan beam by a slit as described above. Since only the radiation that passes through the subject and goes straight in is detected by the line sensor, the component of the scattered radiation is rarely detected, and the influence of the scattered radiation is relatively small.

On the other hand, in the helical CT or cone beam CT using the cone beam, since radiation is incident on the entire subject by irradiation of cone-shaped radiation, a large amount of scattered radiation is generated, and the scattered radiation passes through the subject. Light enters the area sensor. Accordingly, the area sensor detects not only the primary radiation that is applied to the subject and travels straight through the subject and passes through the subject, but also a large amount of scattered radiation scattered from each part of the subject. (A component due to primary radiation), which causes a problem that an image with degraded image quality is output, such as a decrease in contrast or an inability to obtain a sufficient S / N.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a radiation image signal detecting device capable of improving the problem of image quality deterioration due to scattered radiation.

[0014]

As described above, when a subject is irradiated with radiation, a part of the radiation is scattered at each part of the subject to become scattered rays, and some of the radiation transmitted through the subject goes straight in the subject. In addition to the primary radiation components that pass through,
This scattered ray component is included.

When the radiation penetrates the subject, the energy level of the transmitted radiation transmitted through the subject is slightly lower than that at the time of incidence on the subject (before transmission) due to radiation absorption by living body components such as bones and internal organs. I do.
However, the energy level of the scattered radiation is lower compared to the primary radiation.

The present invention has been made by paying attention to the difference between the energy levels of the primary radiation and the scattered radiation, and distinguishes the primary radiation and the scattered radiation by energy discrimination.
A radiation image signal is obtained based on only the next radiation.

That is, a first radiation image signal detecting apparatus according to the present invention has a radiation source for emitting radiation on one side of an object, a radiation detector on the other side of the object, and detects radiation transmitted through the object. A radiation image signal detection device that obtains a radiation image signal of a subject by detecting the radiation image signal by a detector, wherein the radiation detector outputs a signal of a level corresponding to the energy level of the radiation, and a detection unit that outputs the signal. A signal processing unit that obtains a radiation image signal based on only a signal having an energy component equal to or higher than a specific threshold, that is, a signal excluding a signal having an energy component equal to or lower than the threshold. Is what you do.

A second radiation image signal detecting apparatus according to the present invention has a radiation source emitting cone-shaped radiation on one side of an object, a radiation detector on the other side of the object, and a radiation source and a radiation detector. Is a radiation image signal detection device that obtains a radiation image signal of a subject by detecting radiation transmitted through the subject with a radiation detector while relatively rotating the subject around the subject with the radiation detector interposed therebetween. A detection unit that outputs a signal having a level corresponding to the energy level of radiation, and a signal output from the detection unit,
A signal processing unit for obtaining a radiation image signal based on only a signal having an energy component equal to or higher than a specific threshold, that is, a signal excluding a signal having an energy component equal to or lower than the threshold.

When "the radiation source and the radiation detector are relatively rotated about the subject with the subject interposed therebetween", at least the detection unit and the radiation source are relatively rotated about the subject with the subject interposed therebetween. The signal processing unit of the detector need not necessarily be rotated.

In the above, the "specific threshold value" means a value suitable for discriminating a relatively high energy component from a relatively low energy component (it does not need to be completely discriminated). It is desirable that a component having a relatively high energy be a primary radiation component which enters the subject and travels substantially straight, and a component having a relatively low energy be a scattered ray component scattered by the subject, and has a value suitable for distinguishing both components. desirable. It is desirable that the “specific threshold value” is determined in consideration of the radiation source, the age and gender of the subject, and various requirements of human internal and external organs.

The radiation detector used in the first and second radiation image signal detection devices is a solid-state detector having a detection part and a signal processing part and having an energy discriminating function, which is mainly composed of a semiconductor. If it is a detector,
Any material may be used, and its shape does not matter. It is preferable that a quantum counting type detector be used as the radiation detector.

The "energy discriminating function" means that the radiation incident on the detector is distinguished into a relatively low energy component and a relatively high energy component based on the difference in the energy level of the radiation. .

The "quantum counting type detector" uses a sensor (detection crystal) that outputs a signal of a level corresponding to the energy level of radiation photons (particles) as the detection unit,
When one radiation photon enters the sensor, a voltage pulse output from the sensor is compared with a threshold value by a comparator to discriminate energy, and a digital pulse obtained by this is counted by a counter for a certain period of time. The number of radiation photons incident on the sensor at the time is counted, and the counting result is input to the signal processing unit to obtain a radiation image signal ("INNERVISION (10/7) 1995"; pp. 47-4).
8, “Medical Electronics and Biotechnology, Volume 32 Special Issue (199
4) "; P311, Shimadzu Review Vol. 49, No3 (1992.10); P185-18
9 etc.).

As the radiation detector used in the second radiation image signal detecting device, it is particularly preferable to use an area sensor for detecting radiation two-dimensionally. In addition, a two-dimensional radiation image signal may be obtained by using a line sensor and arranging or moving a large number of the line sensors and combining their outputs.

In the second radiation image signal detecting device, the radiation source emitting cone-shaped radiation is limited to that used in a conventional cone beam CT using a point-shaped radiation source. Is not
It has a scanning type radiation source used in the document “SPIE VOL.2708 P140 to P149” and the apparatus proposed by the present applicant in Japanese Patent Application No. 10-238737, that is, a large number of radiation sources arranged on a plane, The radiation source may be of a type in which the subject is irradiated with radiation while sequentially switching each of the radiation sources. As the radiation detector used in this case, the radiation source has a detection area having an area smaller than the area of the surface on which a large number of radiation sources are arranged, and radiation emitted from each radiation source by scanning and transmitted through a subject. It is desirable to use a detector that sequentially detects The detector may be composed of one detection sensor, or may be composed of a plurality of detection sensors.

Further, the first and second embodiments according to the present invention
It is desirable that the radiation source of the radiation image signal detecting device of (1) is provided with irradiation energy control means for irradiating only radiation having an energy level equal to or higher than the threshold to the subject.

The irradiation energy control means may be any means that allows only radiation having an energy level equal to or higher than the threshold to enter the subject. At the time when the radiation is emitted, radiation having an energy level equal to or lower than the threshold is emitted. Even if included, for example, a filter such as a copper plate may be arranged between the source and the subject to remove radiation having an energy level equal to or lower than the threshold before the radiation enters the subject. . In this case, a filter such as a copper plate corresponds to irradiation energy control means.

It is needless to say that the radiation source is preferably a monochromatic radiation source that emits radiation of a single energy level. In this case, means for emitting radiation of a single energy level corresponds to irradiation energy control means.

[0029]

As described above, the radiation image signal detecting apparatus according to the present invention focuses on the difference between the energy levels of primary radiation and scattered radiation, and has a level corresponding to the energy level of radiation. Using a detection unit that outputs a signal, and a radiation detector including a signal processing unit that obtains a radiation image signal based only on a signal with an energy component equal to or greater than a specific threshold among the signals output from the detection unit, As a “specific threshold”, an appropriate value for discriminating the primary radiation component and the scattered radiation component is used, and a component containing a large amount of scattered radiation less than the threshold is not used as an image signal, and an energy component higher than the threshold is used. Since the image signal is obtained based only on the signal, the radiation image signal output from the signal processing unit is output as a result of detecting more components due to primary radiation. Come to be, it is possible to reduce the influence of scattered radiation. Therefore, if a tomographic image or a three-dimensional image is formed based on this image signal, an image with high image quality and high S / N and high contrast can be obtained.

In particular, in a CT apparatus using a cone beam and an area sensor, it is difficult to perform slit imaging for removing scattered radiation. However, the radiation image signal detecting apparatus according to the present invention is applied to a CT apparatus of the type. Then, the effect of the scattered radiation can be reduced without performing slit imaging, and thus the effect of the present invention on the CT apparatus of this type is very large.

Further, if a quantum counting type detector is used as the radiation detector, the energy level of radiation photons can be discriminated for each photon, and primary radiation and scattered radiation can be accurately and stably distinguished. Become. In addition, a radiation image signal of higher quality can be obtained by utilizing the excellent property of the quantum counting type detector, that is, the property of high sensitivity and wide dynamic range.

Further, the radiation source is provided with irradiation energy control means for irradiating only radiation having an energy level equal to or higher than the threshold to the subject. Among them, at least the radiation below the threshold is considered to contain many components of the scattered radiation, so that it is possible to accurately distinguish the scattered radiation from the primary radiation. In addition, all transmitted radiation having the same energy as the radiation emitted from the radiation source is regarded as primary radiation and detected, so that the radiation emitted from the radiation source can be used without waste. Further, as a secondary effect, the subject is not irradiated with radiation below the threshold value that does not contribute to the generation of a radiation image signal, so that exposure to the subject can be reduced.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a radiation image signal detecting apparatus according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a cone beam CT apparatus 1 to which a radiation image signal detecting apparatus according to an embodiment of the present invention is applied, and FIG. 2 is a diagram illustrating one pixel of a radiation detector 3 used in the CT apparatus 1. FIG. 3 is a block diagram (A) and a waveform diagram (B) showing details, and FIG. 3 is an energy spectrum diagram of radiation emitted from the radiation source 2.

As shown in FIG. 1, the CT apparatus 1 includes a radiation source 2 that emits a cone-shaped radiation R toward a subject 9.
A detection unit 30 disposed at a position facing the radiation source 2 with the subject 9 interposed therebetween and detecting radiation transmitted through the subject 9
And a radiation detector 3 comprising a signal processing unit 40 for obtaining transmitted radiation image data D based on the signal S output from the detection unit 30 and a subject related to the transmitted radiation image data D output from the radiation detector 3. An image data generator 5 for generating volume data and tomographic image data.

The radiation source 2 and the detection unit 30 of the radiation detector 3 are provided with a rotation unit (not shown) for relatively rotating the radiation source 2 and the radiation detector 3 around the object 9 with the object 9 interposed therebetween. The rotation means includes the radiation source 2 for the subject 9 and the detection unit 30.
Z while passing through the subject 9 while maintaining the above positional relationship with Z
The radiation source 2 and the detection unit 30 may be rotated with the body axis indicated by −Z ′ as a rotation axis, or the radiation source 2 and the detection unit 30 may be fixed and indicated by ZZ ′ in the figure. The object 9 may be rotated around the body axis as a rotation axis.

The radiation source 2 comprises a generator 20 for emitting X-rays as radiation and a filter 21. A source having a tube voltage of 140 KV is used for the generator 20. A copper plate having a thickness of 5 mm is used as the filter 21. The radiation emitted from the generator 20 is applied to the subject 9 after passing through the copper plate filter 21. After passing through the copper plate filter 21,
That is, as shown in FIG. 3, the energy level of the radiation particles incident on the subject 9 is about 60 KeV or more and about 140 KeV.
A peak of approximately 110 KeV within the range of KeV or less;
The components of approximately 60 KeV or less are removed. As a result, only radiation having a relatively high energy level with a threshold value of approximately 60 KeV is applied to the subject 9.

The thickness of the filter 21 depends on the energy level of the scattered radiation generated in the subject 9 of the radiation emitted from the generator 20 and transmitted through the subject 9 and incident on the detector 3. It is desirable to use a value that is convenient for distinguishing the energy level of the primary radiation that travels substantially straight, and the peak value of the energy level of the radiation applied to the subject 9 and the energy absorption characteristics of the primary radiation by the constituent elements of the subject In consideration of various requirements such as the degree of generation of scattered radiation and the like, it is desirable to set the thickness to be suitable for discriminating the energy between primary radiation and scattered radiation.

The radiation detector 3 includes a detection unit 30 that two-dimensionally detects radiation transmitted through the subject 9,
This is a quantum counting type detector provided with a signal processing unit 40 for obtaining transmitted radiation image data D based on the signal S output from the detection unit 30 (see “Medical Electronics and Biotechnology, 32nd above”).
Special Issue (1994) "). Hereinafter, referring to the detailed view of one pixel shown in FIG.
0 will be described.

The detection section 30 outputs a signal (detection crystal) 31 having a level corresponding to the individual energy level of the radiation particles of the radiation R transmitted through the subject 9, and amplifies the output signal of the sensor 31 to output a signal. An amplifier 32 for input to the processing unit 40 is provided.

As the sensor 31, any sensor may be used as long as it generates a signal corresponding to the energy of the incident radiation particles. In the present embodiment, a CdTe (cadmium telluride) crystal that generates a charge amount according to the energy of the radiation particles is used.

The amplifier 32 outputs a voltage pulse signal corresponding to the amount of charge generated by the sensor 31. At that time, the signal level is amplified to a level that can be used in the signal processing unit 40 in the subsequent stage.

The signal processing section 4 includes a comparator 41 and a counter 42. The comparator 41 compares the voltage pulse signal S input from the detection unit 30 with the reference voltage Vth as a threshold. As the reference voltage Vth,
In order to distinguish the scattered ray component and the primary radiation component from each other, the above-mentioned component of 60 KeV or less is removed, and the radiation particles of 60 KeV or less enter the sensor 31 in accordance with the radiation incident on the subject 9. When the output becomes L (low) and the radiation particles having a higher energy level enter the sensor 31, the output of the comparator 41 is set to H (high) (see the waveform diagram shown in FIG. 2B). ). Thereby, 60 Ke
It is possible to discriminate between a radiation component of V or more and a radiation component of less than V.

The counter 42 counts the number of times that the output of the comparator 41 becomes H in a certain time. Thereby, of the radiation incident on the sensor 31 within the unit time,
The number of radiation particles having an energy level of 60 KeV or more is counted.

That is, in the radiation detector 3 including the above-described detection unit 30 and signal processing unit 40, the sensor 3
The voltage pulse signal S is generated by one radiation particle that has entered 1 and the comparator 41 determines whether the voltage pulse signal S is equal to or higher than the reference voltage Vth. If the voltage pulse signal S output from the amplifier 32 is equal to the reference voltage V
If not less than th, the count value of the counter 42 at the subsequent stage is counted up. That is, a certain level (an energy level of radiation corresponding to the reference voltage Vth, which is 60 Ke in this example)
V) Radiation particles having energy equal to or more than one are counted one by one, and this count value D is input to the image data generation unit 5.

As described above, the details of the method of obtaining a radiation image by capturing the radiation particles one by one by the sensor 31 and counting the number of the radiation particles as described above are described in “Medical Electronics and Biotechnology”, Vol. 32; P311, “INNERVISION (10 ・
7) "1995 P47-P48 and others.

The image data generator 5 generates the transmitted radiation image data D using the count value input from the counter 42 as the data value of one pixel. That is, the radiation detector 3
Since the detecting unit 30 detects radiation two-dimensionally, the sensors 31 constituting the detecting unit 30 are sequentially switched, that is, each sensor 31 constituting the detecting unit 30 is electrically scanned, and The transmitted radiation image data D of the subject 9 is generated based on a count value based on the voltage pulse signal S output from the sensor 31.

As described above, since the count value input from the counter 42 is a result of counting radiation particles having an energy level of 60 KeV or more, the transmitted radiation image data D having an energy level of 60
Based on only radiation particles of KeV or higher.

The image data generating unit 5 further performs various signal processing such as γ correction and image distortion correction on the transmitted radiation image data D to generate projection image data of the subject 9, Using the projection image data (corresponding to the position), volume data and tomographic image data of the subject are generated.

As an algorithm for generating volume data, a Feldkamp algorithm (Feldkamp L
A, Davis LC, Kress JW, Practical cone-beam algoritm.
J Opt Soc Am A 1984; 1: P612-P619), filtered back projection (Image Analysis Handbook (The University of Tokyo Press) p3)
56 to p371) and other well-known calculation methods for reconstructing three-dimensional data can be used. Here, a detailed description of how to obtain the volume data D4 is omitted.

Hereinafter, the operation of the cone beam CT apparatus 1 to which the radiation image signal detecting apparatus according to the present invention is applied will be described.

Radiation is emitted from the generator 20 of the radiation source 2 and passed through the copper plate filter 21 to reduce the energy level to 6.
By removing components below 0 KeV, the energy level becomes 60
The subject 9 is irradiated with only the radiation R of KeV or more.

Each of the sensors 31 constituting the detection unit 30 of the radiation detector 3 detects a radiation transmitted through the subject 9 and obtains a voltage pulse signal S corresponding to the energy level of radiation particles forming the radiation. Input to the processing unit 40.

The comparator 41 of the signal processing unit 40 determines whether or not the voltage pulse signal S of one radiation particle incident on the sensor 31 is equal to or higher than the reference voltage Vth corresponding to the energy level of 60 KeV. The output is set to H. The counter 42 at the subsequent stage counts up the count value when the output of the comparator 41 becomes H. This is continued for a certain time, and a certain level (60 in this example) incident on the sensor 31 during the certain time.
Radiation particles having an energy of not less than KeV) are counted one by one, and the count value D is input to the image data generation unit 5.

The image data generating section 5 sets the count value of each sensor 31 input from the counter 42, that is, the count value of each pixel, as the data value of the pixel, and based on the data value (count value), transmits the transmitted radiation image. Generate data D.

Here, the count value input to the image data generation unit 5 is a result of counting the radiation particles having an energy level of 60 KeV or more in the counter 42, so that the transmitted radiation image data obtained has an energy level of 60 KeV. It is generated based only on the above radiation particles.

The energy level of the scattered radiation generated in the subject 9 is lower than the energy level of the primary radiation that travels straight through the subject 9 and is transmitted. It contains a lot, and the one with a relatively lower energy level contains a lot of scattered radiation. Also, as described above, the relatively high energy level 60
Radiation above KeV (Energy level peak is about 1
10 KeV) is radiated to the subject 9, and therefore, among radiation incident on the subject and transmitted therethrough, a relatively low energy level of 6 which is not included in the radiation incident on the subject.
0 KeV or less contains a lot of scattered radiation, and 60 KeV or more contains a lot of primary radiation. If energy discrimination is performed using the 60 KeV as a threshold, it can be considered that scattered radiation and primary radiation are accurately distinguished. it can. That is, when energy discrimination is performed using the energy level of 60 KeV as a threshold, the signals output from the counter 42 and the image data generation unit 5 contain a large amount of primary radiation.
This means that radiation of KeV or more has been detected, and as a result,
As the image data of each pixel, it is possible to obtain the image data in which the component due to the scattered radiation is reduced, and it is possible to obtain the transmitted radiation image data in which the influence of the scattered radiation is reduced.

Further, since a quantum counting type detector is used as the radiation detector and the energy level of each radiation particle is discriminated, primary radiation and scattered radiation can be distinguished with high accuracy. In addition, the high sensitivity and wide dynamic range of the excellent properties of the quantum counting type detector can be enjoyed, and higher quality image data can be obtained.

When the transmitted radiation image data at a predetermined rotation position with respect to the subject 9 of the radiation source 2 and the radiation detector 3 (specifically, the detection unit 30 thereof) is obtained in this manner, the radiation source 2 (the generation unit 20 and the The filter 21 is integrated) and the detection unit 30 of the radiation detector 3 is set to the body axis Z.
By rotating the subject 9 relatively around the subject 9 by a predetermined angle around −Z ′, the transmitted radiation image data in the rotational position, that is, the projection direction is obtained in the same manner as described above. Such processing is repeated until transmitted radiation image data for each projection direction over the entire circumference of the subject 9 is obtained.

The image data generation unit 5 performs various signal processing such as γ correction and image distortion correction on the transmitted radiation image data for each projection direction to generate projection image data of the subject 9, The volume data and the tomographic image data of the subject 9 are generated using the projection image data.

As described above, the transmitted radiation image data is
Since the influence of the scattered radiation is reduced, the influence of the scattered radiation is also reduced in the volume data and the tomographic image data. As an image based on the volume data and the tomographic image data, a high S / N having good image quality is obtained. -A high-contrast image can be obtained.

In the above embodiment, only relatively high-energy radiation is applied to the subject as a radiation source. However, the present invention is not necessarily limited to this, and the subject is applied to the subject. The energy level of the radiation may have a certain range from relatively low energy to relatively high energy. This is because even if the radiation at an energy level lower than the threshold is determined to be scattered radiation, even if the radiation is irradiated onto the subject from the radiation source, the radiation is simply invalid radiation that is not used as image data. In other words, according to the present invention, a radiation detector having an energy discrimination function is used, and among radiation transmitted through a subject,
It is considered that the relatively high energy component contains a large amount of primary radiation and the relatively low energy component contains a large amount of scattered radiation, and thus, the scattered radiation generated in the subject goes substantially straight.
Since the secondary radiation is distinguished from the secondary radiation (energy discrimination), the distribution of the energy level of the radiation incident on the subject is not an essential problem, although a difference occurs in the energy discrimination performance.

From such a viewpoint, in the above embodiment, the filter 21 is used so as not to irradiate the subject with unnecessary radiation which does not contribute to the generation of the radiation image data. By irradiating the subject with only radiation having a relatively high energy level that contributes to generating radiation image data, the radiation emitted from the radiation source can be used without waste, and it is efficient Of course.

Further, in the above-described embodiment, the radiation detector using the quantum counting type radiation detector capable of counting the energy level of radiation particles individually has been described. The present invention is not limited to this, and any material that can discriminate energy between scattered radiation having a relatively low energy level and primary radiation having a relatively high energy level may be used, For example, a device that distinguishes between the scattered radiation and the primary radiation based on the difference between the average energy levels thereof can also be used.

Further, in the above-described embodiment, the radiation image signal detecting apparatus according to the present invention is applied to the cone beam CT, but the present invention is not limited to this. That is, any device may be used as long as it detects radiation with a radiation detector and obtains a radiation image signal. The radiation image signal detection device according to the present invention, which distinguishes generated scattered radiation from primary radiation that travels substantially straight, can be applied.

The radiation detector used here may have any shape, regardless of its shape, and may have a shape conforming to the configuration of the apparatus. A dot sensor for detecting radiation in a zero-dimensional (dot-like) manner, a one-dimensional radiation sensor Any of a so-called line sensor for detecting the radiation in a second direction and a so-called area sensor for detecting the radiation in a two-dimensional manner may be used.

For example, in a conventional X-ray CT or a normal helical CT, slit imaging is sometimes performed to remove scattered radiation.
When applied to a line CT or the like, the effect of scattered radiation can be reduced without using a slit, so that slit imaging is not required.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a cone beam CT apparatus to which a radiation image signal detecting apparatus according to the present invention is applied.

FIG. 2 is a block diagram (A) and a waveform diagram (B) showing details of one pixel of the radiation detector.

FIG. 3 is an energy spectrum diagram of radiation emitted from a radiation source.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Cone beam CT apparatus which applied the radiation image signal detection apparatus 2 Radiation source 3 Radiation detector 5 Image data generation part 9 Subject 20 Generation part 21 Filter 30 Detection part 31 Sensor 32 Amplifier 40 Signal processing part 41 Comparator 42 Counter

Claims (4)

[Claims] 1. A radiation source for emitting radiation is arranged on one of the objects, a radiation detector is arranged on the other of the objects, and the radiation transmitted through the object is detected by the radiation detector, whereby the radiation of the object is detected. In a radiation image signal detection device that obtains an image signal, wherein the radiation detector outputs a signal having a level corresponding to the energy level of radiation, and among signals output from the detection unit, A signal processing unit for obtaining the radiation image signal based only on a signal based on an energy component. 2. A radiation source that emits cone-shaped radiation is arranged on one of the objects, a radiation detector is arranged on the other of the objects, and the radiation source and the radiation detector are sandwiched between the objects. A radiation image signal detection device that obtains a radiation image signal of the subject by detecting radiation transmitted through the subject with the radiation detector while relatively rotating around the radiation source, wherein the radiation detector has an energy level of radiation. And a signal processing unit that obtains the radiation image signal based only on a signal having an energy component equal to or greater than a specific threshold among the signals output from the detection unit. A radiation image signal detection device, characterized in that: 3. The radiation image signal detection device according to claim 1, wherein the radiation detector is a quantum counting type detector. 4. The radiation according to claim 1, wherein the radiation source includes irradiation energy control means for irradiating the subject with only radiation having an energy level equal to or higher than the threshold. Image signal detection device.