JP7459593B2 - Ceramic fluorescent material, scintillator array, radiation detector and radiation computed tomography apparatus - Google Patents

Description

The present application relates to ceramic fluorescent materials, scintillator arrays, radiation detectors, and radiation computed tomography devices.

A radiation imaging system irradiates a subject with radiation such as alpha rays, beta rays, gamma rays, and X-rays, and images the radiation that has passed through the subject. Radiographic imaging systems are used in a variety of applied fields, including medical fields such as tomography, industrial fields such as non-destructive testing, security fields such as baggage inspection, and academic fields such as high-energy physics. In particular, radiation imaging systems used in the medical field are called radiation computed tomography devices, and are capable of acquiring tomographic images at any position of a subject and forming three-dimensional images from the acquired tomographic images. It is.

Currently, radiographic imaging systems that are primarily used commercially use radiation detectors that convert the intensity of radiation into electrical signals. The radiation detector includes a scintillator for converting the intensity of radiation into light, and a photodetector such as a CCD for converting the light into an electrical signal.

Conventionally, monocrystalline fluorescent materials such as Ce-doped Gd ₂ SiO ₅ (GSO) have been used as fluorescent materials for scintillators, but in recent years, polycrystalline fluorescent materials made of ceramic have come to be used. Polycrystalline fluorescent materials have advantages such as the ease of adjusting the material composition and the ability to manufacture large scintillators with high yield. For example, Patent Document 1 discloses a garnet phosphor doped with Ce.

Special Publication No. 2010-507008

There is a demand for radiation imaging systems capable of displaying higher-resolution images. For this reason, there is a demand for scintillators that can detect radiation more stably and with higher sensitivity. This disclosure provides a ceramic fluorescent material with stable sensitivity, a scintillator array, and a radiation detector and a radiation computed tomography apparatus using these.

A ceramic fluorescent material according to an embodiment of the present disclosure includes Ce as a light-emitting element, at least one member selected from the group consisting of Y, Gd, and Lu, at least one member selected from the group consisting of Al and Ga, and O. , a main component having a garnet crystal structure, and S,
The main component has the following general formula:
(Y, Gd, Lu, Ce) _3+a (Al, Ga) _5-a O ₁₂ (0≦a≦0.1)
has a composition represented by
The content of S is greater than 0 and less than 40 ppm by mass relative to the main component.

The emission drift of the ceramic fluorescent material after irradiation with 1 Gy of X-rays may be greater than 0% and less than 1%.

The S content may be greater than 0 and less than or equal to 15 ppm by mass relative to the main component.

The luminescence drift of the ceramic fluorescent material after irradiation with 1 Gy of X-rays may be greater than 0% and less than or equal to 0.3%.

The main component has the following general formula:
(L1 _{-x- zGdxCeZ ) 3+a} (Al1 _{-uGau ) 5- aO12}
(wherein L is at least one selected from the group consisting of Y and Lu, and 0≦a≦0.1, 0.15≦x≦0.3, 0.002≦z≦0.015, and 0.35≦u≦0.55).
The composition may be represented by the formula:

A scintillator array according to an embodiment of the present disclosure includes a plurality of scintillator elements arranged one-dimensionally or two-dimensionally, and each scintillator element includes the ceramic fluorescent material described above.

A radiation detector according to an embodiment of the present disclosure includes the scintillator array described above and a plurality of photodetecting elements arranged opposite to the plurality of scintillator elements of the scintillator array.

A radiation computed tomography apparatus according to an embodiment of the present disclosure includes a radiation source, the radiation detector, the radiation source, and a control unit that processes a detection signal output from the radiation detector.

The present disclosure provides a ceramic fluorescent material with stable sensitivity, a scintillator array, and a radiation detector and a radiation computed tomography apparatus using these.

FIG. 1 is a plan view showing an embodiment of a radiation detector. FIG. 1 is a cross-sectional view showing an embodiment of a radiation detector. 1 is a graph showing the relationship between the S content and luminescence drift in the fluorescent materials of Examples 1 to 19 and a comparative example. 1 is a graph showing the relationship between the S content in the fluorescent materials of Examples 1 to 19 and the luminescence drift.

The inventors of the present application have studied the stability of detection sensitivity of ceramic fluorescent materials used in scintillators from various viewpoints. As a result, it was found that in a radiation detector equipped with a scintillator made of a garnet-based ceramic fluorescent material, sensitivity changes occur when the scintillator is irradiated with a large amount of radiation. For example, if a medical CT device includes a scintillator made of a garnet-based ceramic fluorescent material, if images are taken continuously at short intervals, the sensitivity may increase and white areas may appear as noise unrelated to the subject. It turns out that there is. This increase in sensitivity is temporary, and if the scintillator is left unirradiated with X-rays, the sensitivity will return to its original level. For this reason, for example, if the number of times a CT apparatus takes images per day is low, the influence of sensitivity changes will be small.

However, when the number of scans taken per day increases, sensitivity changes cannot be ignored. In this case, for example, gain (sensitivity) correction can be performed to reduce the sensitivity change, but gain correction takes time. Furthermore, if the sensitivity change occurs in only a portion of the many scintillators arranged in the CT device, gain correction can result in a decrease in contrast.

This temporary change in the sensitivity of the scintillator is called luminescence drift, bright burn, positive hysteresis, etc., and is a known phenomenon in single crystal fluorescent materials. For example, JP 2003-107163 A and JP 2015-094736 A disclose a method for reducing bright burn in CsI single crystal scintillators by heating or irradiating them with visible light.

However, there have been no reports of such sensitivity changes occurring in polycrystalline scintillators. In addition, the heating or visible light irradiation disclosed in the above-mentioned patent documents is a method for erasing bright burns, and is not a method for providing a fluorescent material that is less likely to cause bright burns. Furthermore, in order to erase bright burns, a heating device or a visible light irradiation device must be installed in the CT scanner. In light of these issues, the inventors of the present application have come up with a new garnet-based ceramic fluorescent material that is less likely to cause sensitivity changes even when exposed to a large amount of radiation.

The ceramic fluorescent material of the present disclosure includes a main component and S. The main component contains Ce as a luminescent element, at least one element selected from the group consisting of Y, Gd, and Lu, at least one element selected from the group consisting of Al and Ga, and O, and has a garnet crystal structure. The main component is represented by the following general formula (1):
(Y, Gd, Lu, Ce) _{3 + a} (Al, Ga) _{5 - a} O ₁₂ (0≦a≦0.1) (1)
The content of S is more than 0 and 40 ppm by mass or less with respect to the main component.

As will be described in detail below, the inventors of the present application have discovered that in garnet-based ceramic fluorescent materials, temporary sensitivity changes due to exposure to large amounts of radiation are related to the amount of S contained in the ceramic fluorescent material, and that the sensitivity change can be suppressed by controlling the amount of S to a predetermined value or less. Therefore, the ceramic fluorescent material of this embodiment may have various compositions as long as it satisfies the above general formula (1). Y, Gd, Lu, and Ce are located at the divalent metal sites of the garnet crystal structure, and Al and Ga are located at the trivalent metal sites.

The main component of the ceramic fluorescent material preferably has a composition expressed by the following formula (2) in order to have better fluorescent properties as a scintillator.
(L _1-x-z Gd _{x Cez} ) _3+a (Al _1-u Ga _u ) _5-a O ₁₂ ...(2)
Here, L is at least one selected from the group consisting of Y and Lu, and 0≦a≦0.1, 0.15≦x≦0.3, 0.002≦z≦0.015, and 0. 35≦u≦0.55 is satisfied.

z indicates the content ratio of Ce, which is a luminescent element. When z is less than 0.002, the amount of Ce in the main component is too small, and the energy of incident X-rays cannot be efficiently converted into optical energy. Furthermore, when z exceeds 0.015, the amount of Ce in the garnet crystal structure increases, and the distance between Ce atoms decreases, causing energy migration (so-called concentration quenching). Therefore, from the viewpoint of light emission output, z is preferably within the above range.

x indicates the content ratio of Gd. Gd has a large atomic number and can adjust the X-ray absorption coefficient. In particular, when a ceramic fluorescent material is used in a medical CT device, depending on the amount of Gd added, hard X-rays (for example, the representative energy is 100 eV) and soft X-rays (for example, the representative energy is 50 eV) can be suitably adjusted. In general, parts of a subject such as blood vessels and muscles tend to absorb soft X-rays with relatively low energy and transmit hard X-rays with relatively high energy compared to parts such as bones. On the other hand, parts such as bones tend to absorb hard X-rays, which have relatively higher energy than parts such as blood vessels and muscles. Therefore, by appropriately adjusting the absorption ratio of soft X-rays and hard X-rays in the scintillator, it is possible to obtain an image in which tissues with different densities in the subject can be clearly distinguished. From this point of view, x is preferably in the range of 0.15≦x≦0.3.

L is at least one member selected from the group consisting of Y and Lu. Y has a smaller atomic number than Gd, and Lu has a larger atomic number than Gd. Therefore, the effective atomic number and X-ray absorption coefficient of the ceramic fluorescent material can be adjusted depending on the type of element included as the L element. The L element can also contribute to adjusting the fluorescence intensity, sintering temperature, and density of the resulting ceramic fluorescent material.

u determines the composition ratio of Al and Ga and can affect the luminescence output of the ceramic fluorescent material. When u satisfies 0.35≦u≦0.55, high light emission output can be achieved.

a affects the light output and afterglow, and afterglow can be reduced by making a a non-negative value. High light output can be achieved by making a satisfy the range of 0≦a≦0.1.

Next, the content of S will be explained. In general, the light emission of a ceramic fluorescent material is mainly related to the orbit of a metal element, so it is not common to replace O, which is an anion site, with another element. For example, Patent Document 1 discloses replacing O in a garnet-based phosphor with F, Cl, N, and S, but does not explain what effect S has. In other words, ceramic fluorescent materials having a garnet structure and containing S are not common. On the other hand, since S is lighter than the metal elements in the fluorescent material, even if S is included as an impurity, it is not considered to have a large effect on the fluorescent properties. For this reason, in conventional ceramic fluorescent materials, S is almost never intentionally added, and even if a small amount of S is contained as an impurity, it has not been considered a problem.

However, according to the inventor's study, the impurity level of S contained in general ceramic fluorescent materials is one of the causes of temporary sensitivity changes due to irradiation with large amounts of radiation. Do you get it.

A detailed study revealed that conventional ceramic fluorescent materials are manufactured using raw materials with a purity of about 3N. In this case, the ceramic fluorescent material produced contains several hundred ppm of S. It was found that this level of S causes a temporary change in the sensitivity of the ceramic fluorescent material.

In the ceramic fluorescent material of this embodiment, the content of S is greater than 0 and equal to or less than 40 mass ppm relative to the main component. This makes it possible to suppress temporary changes in the sensitivity of the ceramic fluorescent material. Specifically, the emission drift of the ceramic fluorescent material can be made greater than 0% and equal to or less than 1%.

Here, the emission drift is expressed as a percentage of the emission output measured before and after 1 Gy of X-rays is irradiated onto a plate made of a ceramic fluorescent material with a thickness of 1.5 mm, and the emission output after exposure is divided by the emission output before exposure. To measure the emission output, a separate measurement X-ray is irradiated and the emission output is measured with a photodetector such as a photodiode. The measurement before exposure and the exposure of X-rays, and the exposure of X-rays and the measurement after exposure are performed consecutively (for example, without an interval of 10 minutes or more). In the ceramic fluorescent material of this embodiment, the emission drift is a positive value. In other words, when a large amount of X-rays is irradiated, the sensitivity of the ceramic fluorescent material increases, and even if the ceramic fluorescent material is irradiated with X-rays at the same intensity as before the large amount of X-ray irradiation, the ceramic fluorescent material emits more intense light after the large amount of X-ray irradiation.

In the ceramic fluorescent material, the smaller the S content, the better. More preferably, the content of S is greater than 0 and less than 15 ppm by mass based on the main components. In this case, the emission drift after irradiation with 1 Gy of X-rays is greater than 0% and less than 0.3%.

Ideally, the S content in the ceramic fluorescent material is zero. However, it requires a large cost to reduce the content of S contained as an impurity to a certain value or less. According to the studies of the present inventors, from the viewpoint of manufacturing a commercial ceramic fluorescent material, the lower limit of the content of S contained as an impurity is about 4 ppm by mass. That is, the more preferable content of S is 4 ppm or more and 15 ppm or less by mass, based on 1 mass of the main component.

At this stage, the detailed reasons why temporary sensitivity changes in ceramic fluorescent materials can be suppressed by reducing the S content within the above range are not clear. However, it is thought that the mechanism by which temporary sensitivity changes occur in CsI single crystal scintillators is different from the mechanism by which temporary sensitivity changes occur in ceramic fluorescent materials. This is because CsI single crystals have a single crystal structure, which means that they contain extremely low amounts of impurities, and the level of S content is different to begin with.

The ceramic fluorescent material of this embodiment can be manufactured, for example, by using a high-purity raw material with a low S content. For example, it is possible to produce a ceramic fluorescent material having the above characteristics by using, as a raw material, a material that has a purity of 4N or more and does not contain S as a constituent element. In this case, it is preferable that contamination of S from vessels, equipment, etc. used during the manufacturing process is suppressed. As long as these conditions are met, the ceramic fluorescent material of this embodiment can be manufactured using, for example, a general manufacturing method. However, the purity of the raw material indicates the purity relative to the total amount of impurities, and the purity may not be proportional to the S content in the raw material. In other words, S is not included in the raw material as an impurity in excess of the impurity amount specified by the grade such as 4N, 5N, etc., but the proportion of S included in the total impurities may vary depending on, for example, the manufacturer and lot of the raw material. .

For example, a 5N grade raw material of an oxide containing a metal element represented by the general formula (1) is prepared, the raw material is crushed and mixed using a ball mill, and a molded body is obtained by press molding. Thereafter, a ceramic fluorescent material can be obtained by firing the molded body in an oxygen atmosphere.

As described above, according to the ceramic fluorescent material of this embodiment, the S content is greater than 0 and equal to or less than 40 mass ppm relative to the main component, making it possible to suppress temporary sensitivity changes caused by exposure to a large amount of radiation. Therefore, if a medical CT device is realized using a scintillator made of the ceramic fluorescent material of this embodiment, it will be possible to take images with stable sensitivity even when taking images continuously at a high frequency.

(other forms)
The ceramic fluorescent material of this embodiment can be implemented in various forms. First, as described in the above embodiment, when manufacturing a ceramic fluorescent material, a scintillator having a molded shape can be obtained by press-molding it into a desired shape. Further, for example, the ceramic fluorescent material of this embodiment can be suitably implemented in the form of a scintillator array, a radiation detector, and a radiation computed tomography device.

1 and 2 are a plan view and a cross-sectional view showing an example of a scintillator array 101 and a radiation detector 103 of this embodiment.

The radiation detector 103 includes a scintillator array 101 and a detector element array 102. The scintillator array 101 includes a plurality of scintillator elements 11 arranged one-dimensionally or two-dimensionally. In the embodiment shown in Figures 1 and 2, the plurality of scintillator elements 11 are arranged two-dimensionally along the x-axis and y-axis.

Each of the plurality of scintillator elements 11 includes the ceramic fluorescent material of the above embodiment. Therefore, the content of S in the ceramic fluorescent material of each scintillator element 11 is greater than 0 and less than 40 mass ppm relative to the main component, and temporary sensitivity changes due to irradiation with a large amount of radiation are suppressed. has been done. Further, such variations in sensitivity changes among the plurality of scintillator elements 11 are also suppressed. The plurality of scintillator elements 11 can be produced, for example, by dividing a scintillator made of the ceramic fluorescent material of the above embodiment, which is produced by press-molding into a plate shape and firing.

In this embodiment, the scintillator array 101 further includes a reflective member 12. The reflective member 12 is located between the plurality of scintillator elements 11 and on the first surface 11a of each scintillator element 11. The reflective member 31 has a characteristic of reflecting the light emitted by the scintillator element 11. For example, the reflective member 12 includes white titanium oxide powder and a resin such as epoxy. The reflection member 12 suppresses light generated by radiation incident on each scintillator element 11 from entering an adjacent scintillator element 11 and being detected by a photodetecting element provided in an adjacent scintillator element 11. In other words, crosstalk in the scintillator array 101 is suppressed.

The detection element array 102 includes a plurality of photodetection elements 13. The photodetector element 13 is a photoelectric conversion element that converts incident light into an electrical signal, and may be, for example, a photodiode such as a silicon photodiode, or a photon counter.

The plurality of photodetecting elements 13 are arranged facing the second surface 11b of the scintillator elements 11 of the scintillator array 101. For example, the plurality of photodetecting elements 13 are connected to the scintillator element 11 in the x-direction and the y-axis of the Arranged at the same pitch on the axis. In this embodiment, the detection element array 102 further includes a reflective member 12. The reflective member 12 covers the space between the plurality of photodetecting elements 13 and the bottom surface 13b of each photodetecting element 13, and suppresses crosstalk in the detecting element array 102 similarly to the scintillator array 101.

In the radiation detector 103, radiation such as X-rays incident from the first surface 11a of the plurality of scintillator elements 11 excites the ceramic fluorescent material in each of the plurality of scintillator elements 11, and the scintillator elements 11 emit light. The light emission is detected by a photodetection element 13 arranged corresponding to each scintillator element 11. Therefore, the radiation that is absorbed and attenuated according to the difference in the internal tissue by passing through the subject is detected in two dimensions, and a detection signal corresponding to the intensity of the radiation is output from each photodetecting element 13.

According to the radiation detector 103, the ceramic fluorescent material suppresses temporary sensitivity changes even when exposed to a large amount of radiation. Therefore, even if radiation is detected in short cycles, it is possible to detect radiation with stable sensitivity. Further, since the above-mentioned temporary sensitivity change is small, deterioration in in-plane uniformity of detection sensitivity is also suppressed.

The radiation computed tomography apparatus of this embodiment also includes a plurality of radiation detectors 103, a radiation source, and a control unit that processes detection signals output from the radiation detectors 103. According to the radiation computed tomography apparatus of this embodiment, bright burn is unlikely to occur even when imaging is performed continuously at short intervals, and images can be acquired with stable sensitivity. This can increase the daily operating rate of the radiation computed tomography apparatus, for example, and contribute to reducing imaging costs and medical costs.

In addition, a large radiation imaging system such as a computed tomography apparatus is equipped with a large number of radiation detectors 103. Therefore, according to the conventional technology, the degree of sensitivity change may vary among the multiple radiation detectors 103. In this case, if gain (sensitivity) correction is performed to cancel the sensitivity change, a larger contrast reduction occurs in the radiation detectors 103 with a large sensitivity change, and the reduction in contrast in the tomographic image becomes non-uniform, which may make it difficult to accurately distinguish tissues. In contrast, according to the radiation computed tomography apparatus of this embodiment, even if a large number of radiation detectors 103 are provided, the sensitivity change is uniformly small, so that the reduction in contrast is small and can occur uniformly in the image even if gain correction is performed.

(Example)
The ceramic fluorescent material of this embodiment was produced, and the S content and luminescence drift were measured. The results will be described below.

Example 1
As raw materials, 73.79 g of _{Y2O3 powder} , 29.80 g of _Gd2O3 powder, 0.77 g of _CeO2 powder, 38.16 g of _Al2O3 powder and 57.48 g of _{Ga2O3 powder} were weighed, and the weighed raw materials, ₁₃₀₀ g of high-purity _alumina balls with a diameter of 5 mm, and 200 cc of ethanol were placed in a resin pot with a capacity of 1 liter. The total amount of raw materials was 200 g, and the amount of raw materials took into account the contamination _{of Al2O3 from} the alumina balls. 5N grade raw materials were used.

The raw materials were pulverized using a pulverizer, and the pulverized powder obtained was uniaxially pressed at a pressure of 500 kg/ ^cm2 , and then cold isostatically pressed at a pressure of 3 ton/ ^cm2 to obtain a molded body with a relative density of 54%. This molded body was placed in an alumina sagger and sintered in oxygen at 1700°C for 12 hours to obtain a sintered body with a relative density of 99.9%.

The sintered body was polished to a thickness of 1.5 mm to prepare a sample for Example 1, and the emission drift was measured. The emission drift was defined as (emission output after X-ray exposure/emission output before X-ray exposure) x 100 (%).

The light output was measured in the following manner.
(1) Irradiate the sample with X-rays and measure the emission output (= emission output before exposure)
(2) The sample is continuously irradiated with X-rays at a dose of 1 Gy. (3) Immediately after the continuous irradiation is completed, the light emission output of the sample is measured again (=light emission output after exposure).
(4) Calculation of the emission drift from the emission output before and after exposure For the measurement of the emission output, a pulsed X-ray tube was used to generate X-rays at a tube voltage of 30 kV, and after the sample was irradiated with the X-rays, the emission output was measured using a silicon photodiode (S2281 manufactured by Hamamatsu Photonics). The same pulsed X-ray tube was also used for the exposure of 1 Gy.

The composition and S amount of the sample were determined by glow discharge mass spectrometry (GDMS).

<Examples 2 to 18>
A sample was prepared in the same manner as in Example 1 using a 5N grade raw material from a different lot or from a different manufacturer than in Example 1, and the amount of S was measured and the emission drift was calculated.

<Example 19>
Using 4N grade raw material as the raw material, a sample was prepared in the same manner as in Example 1, and the amount of S was measured and the emission drift was calculated.

Comparative Example
A sample was prepared in the same manner as in Example 1 using 3N grade raw materials, and the S content was measured and the emission drift was calculated.

<Results and Discussion>
The composition formula of the prepared sample was ( _{Y0.797Gd0.198Ce0.005} ) _3.01 ( _{Al0.581Ga0.419} ) _4.99O12 . Table 1 _{shows the} S content and emission drift value of Examples 1 to 18 _, 19 and Comparative Example. Also, Figs. 3 and ₄ show graphs in which the S content and emission drift value of Examples 1 to 18, 19 and Comparative Example are plotted on the horizontal and vertical axes, respectively. The graph shown in Fig. 4 is an enlarged view of a portion of the graph shown in Fig. 3. As shown in Fig. 3, according to the examples, it is considered that the S content in the ceramic fluorescent material and the emission drift value are proportional to each other, as shown by the dashed line.

As shown in Figures 3 and 4, when a large amount of radiation is irradiated, the ceramic fluorescent material having the garnet structure of composition formula (1) experiences a change in sensitivity in the direction of increasing sensitivity, and the light emission output after X-ray exposure is greater than before exposure. When 3N grade raw materials are used, the ceramic fluorescent material contains approximately 200 ppm of S, and the light emission drift value is approximately 3.4%. Furthermore, when 5N grade raw materials are used, the ceramic fluorescent material contains approximately 4 to 14 ppm of S, and the light emission drift value is approximately 0.1 to 0.3%.

If the emission drift value is about 1% or less, it is judged that the sensitivity change is sufficiently suppressed, and if the amount of S contained in the ceramic fluorescent material is 40 ppm or less, the temporary sensitivity change is suppressed. A well suppressed ceramic fluorescent material can be realized. Furthermore, it can be seen that by setting the S content in the ceramic fluorescent material to 15 ppm or less, it is possible to suppress the value of light emission drift to 0.3% or less.

11 Scintillator element 11a First surface 11b Second surface 12 Reflecting member 13 Light detection element 13a Light receiving surface 13b Bottom surface 101 Scintillator array 102 Detection element array 103 Radiation detector

Claims (7)

A ceramic fluorescent material containing Ce as a luminescent element, at least one element selected from the group consisting of Y, Gd, and Lu, at least one element selected from the group consisting of Al and Ga, and O, a main component having a garnet crystal structure, and S,
The main component has the following general formula:
(L1 - _x- zGdxCeZ ₎ 3 _{+ a} ( _{Al1 -} uGau ) _{5 -} aO12
(wherein L is at least one selected from the group consisting of Y and Lu, and 0<a≦0.1, 0.15≦x≦0.3, 0.002≦z≦0.015, and 0.35≦u≦0.55).
having a composition represented by
The ceramic fluorescent material has a content of S of more than 0 and not more than 40 ppm by mass relative to the main component. The ceramic fluorescent material according to claim 1, in which the luminescence drift after irradiation with 1 Gy of X-rays is greater than 0% and less than or equal to 1%. The ceramic fluorescent material according to claim 1, wherein the content of S is greater than 0 and less than or equal to 15 ppm by mass relative to the main component. The ceramic fluorescent material according to claim 3, wherein the luminescence drift after irradiation with 1 Gy of X-rays is greater than 0% and 0.3% or less. comprising a plurality of scintillator elements arranged in one or two dimensions,
A scintillator array, each scintillator element comprising a ceramic fluorescent material according to any of claims 1 to 4 . A scintillator array according to claim 5 ;
a plurality of photodetector elements disposed opposite the plurality of scintillator elements of the scintillator array;
A radiation detector comprising: a radiation source;
A radiation detector according to claim 6 ;
A radiation computed tomography apparatus comprising the radiation source and a control unit that processes a detection signal output from the radiation detector.

Images