Radiation measuring apparatus and radiation measuring method

A radiation measuring apparatus (20) includes a scatterer detector (10A), an absorber detector (10B) and a processing unit (12). Pixel electrodes (2) of the scatterer detector (10A) and the absorber detector (10B) are arranged such that a distance between centers of two neighbor pixel electrodes (2) is smaller than a mean free path of a recoil electron generated in the Compton scattering of an electromagnetic radiation. The processing unit (12) specifies and incidence direction of the electromagnetic radiation based on a recoiling direction to which the recoil electron recoils. In this way, an electron tracking-type Compton camera is realized which confines the incidence direction of the electromagnetic radiation by using the recoiling direction of the recoil electron in a Compton camera using a semiconductor detector.

TECHNICAL FIELD

The present invention relates to a radiation measuring apparatus and a radiation measuring method, and especially, to a technique to detect an electromagnetic radiation such as X-ray and gamma ray by using a semiconductor detector.

BACKGROUND ART

A radiation measuring apparatus used to detect an electromagnetic radiation such as X-ray and gamma ray is sometimes configured to be able to specify an incidence direction of the electromagnetic radiation when an event has occurred in which the electromagnetic radiation is inputted to a detector of the radiation measuring apparatus. It becomes possible to specify a spatial distribution of radiation sources by specifying the incidence direction of the electromagnetic radiation. This is very useful in practical use.

One of the radiation measuring apparatuses that are configured to specify the incidence direction of the electromagnetic radiation is a Compton camera. The Compton camera is a radiation measuring apparatus that images a spatial distribution of radiation sources by using the Compton scattering. The Compton camera specifies the incidence direction of the electromagnetic radiation (e.g. X-ray, gamma ray) by using the Compton scattering, and generates the image showing the spatial distribution of radiation sources from the specified incidence directions.

FIG. 1is a diagram showing the overview of a Compton scattering of gamma ray. When the gamma ray is inputted to substance, a photon of the incident gamma ray collides with an electron in the substance to be scattered. At this time, the electron with which the photon has collided spatters (the spattered electron is called “a recoil electron”) and a part of energy of the photon of the incident gamma ray is given to the electron. Thus, the energy of the scattered photon of gamma ray becomes lower than that of the incident gamma ray. Supposing that the energy of the photon of incident gamma ray is E0, the energy acquired by the recoil electron is E1, and the energy of the scattered photon of gamma ray is E2, the following equation (1) is met:
E0=E1+E2(1)

FIG. 2is a diagram showing the principle of a Compton camera, especially, the principle of specifying the incidence direction of the electromagnetic radiation. Typically, the detecting section of Compton camera has a scatterer and an absorber. An event has occurred in which the photon of electromagnetic radiation inputted from a radiation source is scattered by the scatterer in the Compton scattering, and the photon to have been scattered in the Compton scattering is absorbed by the absorber in the photoelectric absorption, a scattering angle θ of the electromagnetic radiation (in other words, an angle between a line segment which links the radiation source and the position X1and a line passing through positions X1and X2) is given by the following equation (2):

cos⁢⁢θ=1-me⁢c2⁡(1E2-1E1+E2)(2)
where meis a rest mass of an electron, and c is a speed of light. Also, E1is the energy acquired by the recoil electron in the scatterer in the Compton scattering and E2is the energy of the photon absorbed by the absorber.

The Compton camera estimates a spatial distribution of radiation sources based on data of the scattering angle θ of the electromagnetic radiation obtained in this way and images the spatial distribution of radiation sources. More specifically, a Compton cone (a cone surface configured as a set of points where radiation sources can be located) in each event is reconstructed from data of a position X1where the Compton scattering has occurred in each event, a position X2where the photoelectric absorption has occurred, and the scattering angle θ of the electromagnetic radiation in the Compton scattering, and an image corresponding to the superposition of Compton cones of the respective events is generated as a radiation source distribution image showing the spatial distribution of radiation sources.

As would be understood from the above, the scattering angle θ of the electromagnetic radiation can be calculated only from the position X1where the Compton scattering has occurred in each event, the energy E1acquired by the recoil electron in the Compton scattering, and the energy E2of the photon absorbed by the absorber. The position of the radiation source is specified only as a point on a circle where the radiation source can exist. However, if a recoiling direction of the recoil electron (a direction to which the recoil electron recoils) can be specified, another circle (another cone surface) can be defined based on the recoiling direction of the recoil electron. Thus, theoretically, it is possible to specify the incidence direction of the electromagnetic radiation as a direction which passes intersecting points of two circles. However, actually, the incidence direction of the electromagnetic radiation is specified as an arc due to the fluctuation of energy of the recoil electron, as shown inFIG. 3. For example, such a technique is disclosed in the international publication WO 2007/145154 (Patent Literature 1). The Compton camera which confines the incidence direction of the electromagnetic radiation based on the recoiling direction of the recoil electron is sometimes called an electron tracking-type Compton camera.

As the techniques in relation to the present invention, the international publication WO 2011/001610 (Patent Literature 2) discloses a gamma ray direction detecting apparatus having a detector including a plurality of detection pixels which detect gamma ray.

CITATION LIST

Patent Literature

SUMMARY OF THE INVENTION

However, the Compton camera using a semiconductor detector is not realized because a technique of confining the incidence direction of the electromagnetic radiation by using the recoiling direction of a recoil electron is generally not established in a practical form. An examination result exists in which measures the recoiling direction of the recoil electron is measured fey using CCD (charge coupled device) as the semiconductor detector.

However, because a read time of data is very long in the CCD, the dead time becomes very large so that it is difficult to realize a practical Compton camera. In the international publication WO 2007/145154A (Patent Literature 1), a gas chamber-type detector is used as a detector in which the Compton scattering occurs. However, the gas chamber-type detector must be made large-sized to secure enough detection efficiency to gamma ray, and the detector of the absorption section needs to be made large-sized. Also, in order to get a high angle resolution, a high energy resolution is necessary. However, the gas chamber-type detector is low in the energy resolution, compared with the semiconductor detector.

Therefore, an object of the present invention is to realize an electron tracking-type Compton camera which confines an incidence direction of an electromagnetic radiation by using a recoiling direction of a recoil electron in a Compton camera using a semiconductor detector.

The other objects and new features of the present invention will be understood from the following disclosure.

According to an aspect of the present invention, the radiation measuring apparatus includes at least one scatterer detector, functioning as a scatterer that scatters an electromagnetic radiation of a measurement object; at least one absorber detector functioning as an absorber that absorbs the electromagnetic radiation; and a processing unit. Each of the scatterer detector and the absorber detector includes: a semiconductor substrate; and a plurality of pixel electrodes arranged in a matrix on a first main surface of the semiconductor substrate. The plurality of pixel electrodes are arranged such that a distance between centers of two neighbor pixel electrodes is smaller than a mean free path of a recoil electron generated in the Compton scattering of the electromagnetic radiation. The processing unit extracts events based on signals obtained from the scatterer detector and the absorber detector, and specifies an incidence direction of the electromagnetic radiation based on a recoiling direction to which a recoil electron recoils, to each of the extracted events, in each of which the Compton scattering has occurred in either of the scatterer detectors, the recoil electron generated in the Compton scattering in either of the scatterer detectors recoils to a direction having an in-plane component of the semiconductor substrate in an inside of the scatterer detector in which the Compton scattering has occurred, and photoelectric absorption has occurred in which the photon scattered in the Compton scattering is absorbed in either of the absorber detectors.

When energy of a photon of the electromagnetic radiation of the measurement object is 0.3 to 2.0 MeV, it is desirable that the plurality of pixel electrodes of the scatterer detector and the absorber detector are arranged such that the distance of the centers of the two neighbor pixel electrodes is in a range of 10 to 20 μm.

In the suitable embodiment, the scatterer detector further includes a plurality of back electrodes arranged on a second main surface which is opposite to the first main surface of the semiconductor substrate, and each of the plurality of back electrodes of the scatterer detector is arranged to be opposite to more than one of the plurality of pixel electrodes of the scatterer detector. Here, a number of the plurality of back electrodes is less than a number of the plurality of pixel electrodes in each of the scatterer detectors. In this case, the radiation measuring apparatus may further includes: a first signal processing section configured to generate first pixel electrode measurement data from a first analog signal read from the plurality of pixel electrodes of the scatterer detector; a temporary storing area provided to temporary store the first pixel electrode measurement data; a second signal processing section configured to generates back electrode measurement data from a second analog signal read from the plurality of back electrodes of the scatterer detector; and a data processing section. In this case, it is desirable that the data processing section reads from the temporary storing area, pixel electrode measurement data which are selected the first pixel electrode measurement data according to the back electrode measurement data, to transfer to the processing unit, and that the processing unit carries out extraction of the event and specification of the incidence direction of the electromagnetic radiation based on the selected pixel electrode measurement data.

In this case, the radiation measuring apparatus further includes; a third signal processing section configured to generate second pixel electrode measurement data from a third analog signal read from the plurality of pixel electrodes of the absorber detector. It is desirable that the data processing section, selects the selected pixel electrode measurement data according to the back electrode measurement data and the second pixel electrode measurement data.

In one embodiment, it is desirable that the data processing section transfers to the processing unit, the first pixel electrode measurement data obtained in a frame period, the second pixel electrode measurement data, and the back electrode measurement data, when the back electrode measurement data and the second pixel electrode measurement data obtained in the frame period meet a predetermined condition, and that the the processing unit carries out the extraction of the event and the specification of the incidence direction of the electromagnetic radiation based on the first pixel electrode measurement data, the second pixel electrode measurement data, and the back electrode measurement data obtained in the frame period.

It is desirable that when the first signal processing section is integrated into a signal processing IC, each of the plurality of pixel electrodes of the scatterer detector is connected with a pad prepared in the signal processing IC through a bump.

In a suitable embodiment, the plurality of pixel electrodes of the scatterer detector are arranged in first direction parallel to the first main surface and to a second direction parallel to the first main surface and perpendicular to the first direction, and each of the plurality of back electrodes is formed to extend to the first direction.

In one embodiment, each of the scatterer detector and the absorber detector comprises a plurality of back electrodes arranged on the second main surface which is opposite to the first main surface of the semi conductor substrate, and each or the plurality of back electrodes is arranged to be opposite to more than one of the plurality of pixel electrodes, and a number of the plurality of back electrodes is less than a number of the plurality of pixel electrodes is in each of the scatterer detector and the absorber detector. In this case, desirably, the radiation measuring apparatus further includes: a first signal processing section configured to generate pixel electrode measurement data from a first analog signal read from the plurality of pixel electrodes of the scatterer detector and the absorber detector; a temporary storing area provided to temporarily store the pixel electrode measurement data a second signal processing section configured to generate back electrode measurement data from a second analog signal read from the plurality of back electrode of the scatterer detector and the absorber detector; and a data processing section. The the processing unit carries out the extraction of the event and the specification of the incidence direction of the electromagnetic radiation based on the selected pixel electrode measurement data.

According to another aspect of the present invention, the semiconductor detector used to detect a radiation includes: a semiconductor substrate, a plurality of pixel electrodes arranged in a matrix on a first main surface of the semiconductor substrate, and a plurality of back electrodes arranged on a second main surface which is opposite to the first main surface of the semiconductor substrate. Each of the plurality of back electrodes is arranged to be opposite to more than one of the plurality of pixel electrodes, and a number of the plurality of back electrodes is less than a number of the plurality of pixel electrodes.

According to another aspect of the present invention, the radiation measuring apparatus includes: the above-mentioned semiconductor detectors; a first signal processing section configured to generate first pixel electrode measurement data from a first analog signal read from the plurality of pixel electrodes; a temporary storing area provided to temporary store the first pixel electrode measurement data; a second signal processing section configured to generates back electrode measurement data from a second analog signal read from the plurality of back electrodes; a data processing section configured to read from the temporary storing area, pixel electrode measurement data which are selected the first pixel electrode measurement data according to the back electrode measurement data, to transfer to the processing unit; and a processing unit configured to carry out extraction of the event and specification of the incidence direction of the electromagnetic radiation based on the selected pixel electrode measurement data.

It is desirable that the processing unit carries out an operation to measure the electromagnetic radiation based on the back electrode measurement data in addition to the pixel electrode measurement data read from the temporary storing area.

According to another aspect of the present invention, radiation measuring apparatus is provided to realize an electron tracking-type Compton camera using a radiation measuring apparatus which includes a scatterer detector functioning as a scatterer of scattering art electromagnetic radiation of a measurement object; and an absorber detector functioning as an absorber of absorbing the electromagnetic radiation, wherein each of the scatterer detector and the absorber detector includes a semiconductor substrate and a plurality of pixel electrodes arranged on a main surface of the semiconductor substrate, and wherein the plurality of pixel electrodes of each of the scatterer detector and the absorber detector are arranged such that a distance between centers of two neighbor pixel electrodes is smaller than a mean free path of a recoil electron generated in the Compton scattering of the electromagnetic radiation. The radiation measuring method includes: extracting based on a signal obtained from the scatterer detector and the absorber detector, an event, in which the Compton scattering has occurred in either of the scatterer detectors, the recoil electron generated in the Compton scattering in either of the scatterer detectors recoils to a direction having an in-plane component of the semiconductor substrate in an inside of the scatterer detector in which the Compton scattering has occurred, and photoelectric absorption has occurred in which the photon scattered in the Compton scattering is absorbed in either of the absorber detectors; and specifying the incidence direction of the electromagnetic radiation based on the recoiling direction to which the recoil electron recoils.

According to the present invention, in the Compton camera using the semiconductor detector, a technique of realizing an electron tracking-type Compton camera can be provided which confines the incidence direction of the electromagnetic radiation by using the recoiling direction of the recoil electron.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present invention will be described with reference to the attached drawings. Note that an identical or similar component is referred to by using an identical or corresponding reference numeral in the following description.

First Embodiment

FIG. 4is a block diagram showing an apparatus configuration of a Compton camera20in a first embodiment of the present invention. As shown inFIG. 4, the Compton camera20in the present embodiment includes a plurality of detector modules11A and11B, which are stacked, a processing unit12and a display device13.

The detector module11A is a module that includes a semiconductor detector functioning as a scatterer, and the detector module11B is a module that includes a semiconductor detector functioning as an absorber. In the following description, the semiconductor detector functioning as the scatterer is called a scatterer detector10A and the semiconductor detector functioning as the absorber is called an absorber detector10B. The scatterer detector10A and the absorber detector10B are sometimes collectively called semiconductor detectors10. The detector module11A is located on the incidence side of electromagnetic radiation (e.g. gamma ray and X ray) to be measured, and the detector module11B is located on a rear side of the detector modules11A.

The processing unit12carries out data processing to measurement data obtained from an analog signal read from the scatterer detector10A and the absorber detector10B, to calculate a spatial distribution of radiation sources. The processing unit12has a storage device12a, and stores measurement data and so on necessary for data processing in the storage device12a. The display device13is used as a user interface of the Compton camera20. For example, the display device13is used to display the spatial distribution of radiation sources calculated by the processing unit12.

FIG. 5is a block diagram showing the configuration of the detector module11A having the scatterer detector10A. Note that the detector module11B having the absorber detector10B has the configuration similar to the detector module11A except that the absorber detector10B is substituted for the scatterer detector10A. As shown inFIG. 5, the detector module11A includes a signal processing IC (integrated circuit)21and an interface22in addition to the scatterer detector10A.

FIG. 6toFIG. 8are diagrams conceptually showing the configurations of the scatterer detector10A and the absorber detector10B in one embodiment of the present invention. In this case,FIG. 6is a top view showing the configuration of the semiconductor detector10, andFIG. 7is a bottom view showing the configurations of the scatterer detector10A and the absorber detector10B. Also,FIG. 8is a sectional view showing the sectional configuration of the scatterer detector10A and the absorber detector10B in the A-A section (seeFIG. 6andFIG. 7). Note that the description is given below, by using the XYZ rectangular coordinates system, and a direction is sometimes shown as a direction of the coordinate axis of the XYZ rectangular coordinates system.

As shown inFIG. 6toFIG. 8, each of the scatterer detector10A and the absorber detector10B includes a semiconductor substrate1. For example, the semiconductor substrate1is formed of semiconductor such as CdTe and silicon. In this case, in the scatterer detector10A, the semiconductor substrate1is formed of material (e.g. silicon) with small atomic number so as to become easy for the Compton scattering to occur. On the other hand, in the absorber detector10B, the semiconductor substrate1is formed of material (e.g. CdTe) with large atomic number. Note that in the present embodiment, the configuration of the scatterer detector10A and the absorber detector10B is identical except for the point that the material of the semiconductor substrate1is different.

A plurality of pixel electrodes2are formed on a front main surface1aof the semiconductor substrate1, and a back electrode3is formed on a back main surface1b. Here, the front main surface1aand the back main surface1bare two surfaces having the largest area, of the surfaces of the semiconductor substrate1, and are opposite to each other. In the present embodiment, the front main surface1aand the back main surface1bare parallel to the XZ plane.

As shown inFIG. 6, the pixel electrodes2are arranged in a matrix to configure so-called “pixel-type” detector. In the present embodiment, each of the pixel electrodes2is rectangular, more specifically, has a square planar shape. The back electrode3is provided to oppose to the plurality of pixel electrodes2. Each of parts of the semiconductor substrate1that are sandwiched by each pixel electrode2and the back electrode3configures a pixel. An analog signal corresponding to a quantity of electric charges generated in each pixel is obtained from each the pixel electrode2. The configuration in which the single back electrode3is provided on the back main surface1bof the semiconductor substrate1is shown inFIG. 6toFIG. 8. However, the configuration in which a plurality of back electrodes3are formed is possible, and will be described later in detail.

Returning toFIG. 5again, the signal processing IC21operates as a signal processing section that processes the analog signal read from the pixel electrode2of the scatterer detector10A or the absorber detector10B. The signal processing IC21reads the analog signals at a same time from all the pixel electrodes2of the scatterer detector10A or the absorber detector10B in each frame period. The “frame period” is a period during which the analog signal is once read from each of the pixel electrodes2of the scatterer detector10A or the absorber detector10B. The each frame period is a period to read the analog signal from each pixel electrode2. The signal processing IC21carries out the analog-digital conversion to the analog signal read from the pixel electrode2to generate measurement data showing the signal level of the analog signal. The measurement data obtained from the analog signal read from each pixel electrode2of the scatterer detector10A or the absorber detector10B is hereinafter called “pixel electrode measurement data”. Each signal processing IC21transmits the pixel electrode measurement data generated from the scatterer detector10A or the absorber detector10B (more strictly, the pixel electrode measurement data generated from the analog signals read from the pixel electrodes2of the scatterer detector10A or the absorber detector10B) to the processing unit12through the interface22. Moreover, the signal processing IC21has a function of driving the back electrodes3of the scatterer detector10A or the absorber detector10B to a desired potential.

The interface22has a function of exchanging data between the signal processing IC21and the processing unit12. In detail, the interface22transfers the pixel electrode measurement data to the processing unit12from the signal processing IC21. Also, the interface22transfers control data for controlling the signal processing IC21to the signal processing IC21from the processing unit12.

The Compton camera20in the present embodiment is configured to specify the incidence direction of the electromagnetic radiation (e.g. gamma ray and X-ray) by using a recoiling direction of a recoil electron generated in the Compton scattering, that is, a direction to which the recoil electron recoils, and to calculate a spatial distribution of radiation sources. More specifically, in the Compton camera20of the present embodiment, from the pixel electrode measurement data obtained from the scatterer detector10A and the absorber detector10B, an event is extracted in which the Compton scattering has occurred in either of the scatterer detectors10A, the recoil electron generated in the Compton scattering recoils to a direction having a component in an in-plane direction of the semiconductor substrate1in the inside of the scatterer detector10A in which the Compton scattering has occurred, and the photoelectric absorption has occurred in which a photon scattered in the Compton scattering is absorbed in either of the absorber detectors10B. Regarding such an event, the incidence direction of the electromagnetic radiation is specified by using the recoiling direction of the recoil electron and the spatial distribution of radiation sources is calculated.

When a technique of confining the incidence direction of the electromagnetic radiation by using the recoiling direction of the recoil electron is adopted, it is required to improve a spatial resolution of each scatterer detector10A and each absorber detector10B. To realize the spatial resolution which is required to specify the recoiling direction of the recoil electron, in the present embodiment, a pitch between the pixel electrodes2in each scatterer detector10A and each absorber detector10B, i.e. a distance between the centers of neighbor pixel electrodes2is controlled according to a mean free path of the recoil electron generated in the Compton scattering of the electromagnetic radiation to be measured. InFIG. 6, the pitch between the pixel electrodes2is shown as a symbol dPIXEL. Here, “the center of the pixel electrode2” means a center of gravity in the plane shape, and is equal to an intersection point of the diagonal lines when the pixel electrode2is rectangular (or square).

In detail, the pixel electrodes2of each of the scatterer detector10A and the absorber detector10B are arranged so that the pitch between the pixel electrodes2becomes smaller than the mean free path of the recoil electron. It is desirable that the pitch between the pixel electrodes2is sufficiently smaller than the mean free path of the recoil electron. More specifically, the pitch is desirably equal to or smaller than ⅕ of the mean free path of the recoil electron, and more desirably, equal to or smaller than 1/10 thereof. Here, the mean free path of the recoil electron is a parameter that is determined based on the energy of the incident electromagnetic radiation (e.g. gamma ray or X-ray). When the gamma ray with the energy of 0.3 to 2.0 MeV is measured, the mean free path of the recoil electron is in a range of 100 μm to hundreds of μm. Therefore, it is desirable chat the pitch between the pixel electrodes2is equal to or less than 20 μm, and more desirable that the pitch is in a range of 10 μm to 20 μm.

Next, the operation of Compton camera20in the present embodiment will be described.FIG. 9is a flow chart showing a procedure of calculating the spatial distribution of radiation sources in the Compton camera20of the present embodiment.

The pixel electrode measurement data are sequentially acquired from each detector modules11A and11B in the frame period when the electromagnetic radiation is inputted, and is stored in the storage device12aof the processing unit12. In detail, the pixel electrode measurement data are acquired as follows.

The signal processing IC21of each detector module11A and11B reads an analog signal from each pixel electrode2of the scatterer detector10A or the absorber detector10B in each frame period, and carries out the analog-digital conversion to the read analog signal to generate the pixel electrode measurement data. The signal processing IC21transfers the generated pixel electrode measurement data to the processing unit12through the interface22. The pixel electrode measurement data sent from the signal processing IC21to the processing unit12are stored in the storage device12aof the processing unit12.

A track of the recoil electron generated in the Compton scattering is specified from the pixel electrode measurement data acquired from the detector module11A in which the scatterer detector10A is loaded. For example, as shown inFIG. 10, it can be detected from the pixel electrode measurement data that the recoil electron passed through pixels located continuously in the scatterer detector10A, e.g. pixels of the pixel electrodes2a,2b, and2cin a frame period. In this case, it is possible to specify when the track of the recoil electron inside the scatterer detector10A is a track that reaches the pixel electrode2cfrom the pixel electrode2a. Also, it is possible to detect that the track of the recoil electron inside the scatter detector10A has been stopped inside a single pixel from the pixel electrode measurement data in a frame period (for example, a case where the recoil electron recoils from the pixel outside the scatterer detector10A).

An event in which the reconstruction of a Compton cone should be carried out, i.e. the incidence direction of the electromagnetic radiation should be specified is extracted from the pixel electrode measurement data which has been stored in the storage device12aof the processing unit12. In more detail, at step S03, an event is extracted in which:

(1) the Compton scattering of a photon of an electromagnetic radiation has occurred in a scatterer detector10A, and then the photon scattered in the Compton scattering is absorbed through the photoelectric absorption by the absorber detector10B, and

(2) a recoiling direction of a recoil electron generated in the Compton scattering is a direction having an in-plane component of the semiconductor substrate1in the scatterer detector10A.

To extract such an event, the track of the recoil electron calculated at the step S02is referred to. For example, if the track of the recoil electron passes a plurality of continuously located pixels, it is possible to specify that the recoiling direction of the recoil electron is a direction having a component of an in-plane direction of the semiconductor substrate1.

It is desirable from the viewpoint of easily associating the event and the pixel electrode measurement data that the track of the recoil electron calculated at the step S02is referred to, in the extraction of the event at the step S03. At present, in a general measurement technique of the electromagnetic radiation (gamma ray, X ray and so on), there is a difficulty in associating the event and the measurement data. Especially, in the environment of electromagnetic radiations with very strong strength, because the situation occurs in which the plurality of electromagnetic radiations are incident at a same time, a problem of associating the event and the measurement data becomes serious. Therefore, in the general measurement technique of the electromagnetic radiation, the measurement of the electromagnetic radiation is stopped every time detecting the incidence of the electromagnetic radiation. That is, a trigger is generated when the incidence of the electromagnetic radiation is detected and the collection of the measurement data is temporarily stopped. After that, the measurement data are read to carry out data processing, and moreover, the collection of the measurement data is resumed after resetting a processing system of the data processing. In such a procedure, a dead time is generated (the time during which the electromagnetic radiation cannot be measured) to decline the efficiency of the measurement of the electromagnetic radiation.

On the other hand, in the present invention, it is possible to easily specify the pixel electrode measurement data corresponding to the identical event by using data of a track of the recoil electron. Therefore, the electromagnetic radiation can be measured while continuously acquiring the pixel electrode measurement data.

In addition, it is useful for the noise reduction when the Compton camera20is used in the environment where many neutrons are inputted, e.g. in cosmic space to refer to the track of the recoil electron. When the neutron is inputted to the scatterer detector10A or the absorber detector10B, no recoil electron is generated because the inputted neutron is elastically scattered with an atomic nucleus of material of the semiconductor substrate1. Therefore, noise can be reduced by excluding events in which the track of recoil electron do not exist.

The reconstruction of Compton cone, i.e. the specification of the incidence direction of the electromagnetic radiation is carried out to the event extracted at the step S03. The reconstruction of Compton cone is carried out based on the pixel electrode measurement data stored in the storage device12aof the processing unit12. First, a position X1of occurrence of the Compton scattering in the scatterer detector10A, energy E1acquired by the recoil electron in the Compton scattering, a position X2of occurrence of the photoelectric absorption in the absorber detector10B, and energy E2of the photon absorbed in the photoelectric absorption are calculated in each extracted event.

Moreover, the scattering angle θ of the electromagnetic radiation in the Compton scattering is calculated to each extracted event. The calculation of the scattering angle θ of the electromagnetic radiation is carried out based on the above-mentioned equations (1) and (2) or equations equivalent to the equations (1) and (2).

The first Compton cone can be reconstructed to each event from the position X1of occurrence of the Compton scattering, energy E1acquired by the recoil electron in the Compton scattering, a position X2of occurrence of the photoelectric absorption, energy E2of the photon absorbed in the photoelectric absorption, and the scattering angle θ of the electromagnetic radiation.

Moreover, regarding the extracted event, the second Compton cone is reconstructed based on the recoiling direction of the recoil electron inside the scatterer detector10A. Here, the recoiling direction of the recoil electron can be obtained from the track of the recoil electron calculated at the step S02. The processing unit12specifies the incidence direction of the electromagnetic radiation as an arc from the first Compton cone and the second Compton cone reconstructed for every event. The processing unit12generates incidence direction data that contains data of the incidence direction of the electromagnetic radiation specified in this way, and stores in the storage device12aof the processing unit12.

The processing unit12calculates a spatial distribution of radiation sources based on the incidence direction data obtained at the step S04, and moreover, generates a radiation source distribution image showing the spatial distribution of radiation sources. The processing unit12displays the generated radiation source distribution image on the display device13according to an operation by a user to a user interface of the processing unit12.

As described above, in the Compton camera20of the present embodiment, the track of the recoil electron generated in the Compton scattering is calculated, and the incidence direction of the electromagnetic radiation is specified by using the recoiling direction of the recoil electron. As mentioned above, by specifying the incidence direction of the electromagnetic radiation by using the recoiling direction of the recoil electron, a range of incidence direction of the electromagnetic radiation can be confined.

Here, in the Compton camera20of the present embodiment, the event is extracted in which the Compton scattering has occurred in either of the scatterer detectors10A, the recoil electron generated in the Compton scattering recoils in the inside of the scatterer detector10A to a direction having a component of an in-plane direction of the semiconductor substrate1, and the photoelectric absorption has occurred in which the photon scattered in the Compton scattering is absorbed by either of the absorber detectors10B. The incidence direction of the electromagnetic radiation can be specified by carrying out data processing of the pixel electrode measurement data corresponding to the event.

In addition, in the Compton camera20of the present embodiment, in order to make it possible to specify of the recoiling direction of the recoil electron, a pitch between the pixel electrodes2of each scatterer detector10A and each absorber detector10B, i.e. a distance between the centers of neighbor pixel electrodes2is selected according to the mean free path of the recoil electron generated in the Compton scattering of the electromagnetic radiation to be measured. Thus, the spatial resolution which is necessary to specify the recoiling direction of the recoil electron can be realized in each scatterer detector10A and each absorber detector10B.

Second Embodiment

In the Compton camera20of the first embodiment, a pixel-type detector is used that includes the pixel electrodes2arranged in a matrix as each scatterer detector10A and each absorber detector10B. One problem regarding the use of pixel-type detector is in that a quantity of data to be processed by the processing unit12increases when increasing the number of the pixel electrodes2. When detecting the electromagnetic radiation by using the pixel-type detector, the data obtained from each pixel electrode must be processed. However, when tire number of the pixel electrodes increases, a quantity of data to be processed increases.

Especially, in the Compton camera20of the first embodiment, in order to specify the track of the recoil electron (the recoiling direction of the recoil electron), the spatial resolution of each scatterer detector10A and each absorber detector10B must be made high. For this purpose, the number of pixel electrodes2must be increased. To deal with the increase of a quantity of data to be processed, the processing unit12with high ability must be used. However, this increases a cost. In the second embodiment, a configuration is shown that deals with the problem of increase of a quantity of data to be processed, following the increase of the number of the pixel electrodes2in each scatterer detector10A and/or each absorber detector10B.

More specifically, in the second embodiment, the configuration of each scatterer detector10A is changed.FIG. 11toFIG. 14are diagrams conceptually showing the configuration of each scatterer detector10A in the second embodiment. Here,FIG. 11is a perspective view showing the configuration of each scatterer detector10A in the second embodiment, andFIG. 12is a top view showing the configuration of each scatterer detector10A. Also,FIG. 13is a bottom view showing the configuration of each scatterer detector10A, andFIG. 14is a sectional view showing a section configuration in the B-B section ofFIGS. 12 and 13. Note that in the following description, a direction is sometimes shown as a direction of the coordinate axis of the XYZ rectangular coordinates system.

The configuration of the scatterer detector10A in the second embodiment is almost the same as that of the scatterer detector10A in the first embodiment, but is different from it in that a plurality of back electrodes3are formed on the back main surface1bof the semiconductor substrate1, as shown inFIG. 11toFIG. 13. Note that only the single back electrode3is provided on the back main surface1bin the scatterer detector10A or the first embodiment. Note that the pixel electrodes2are arranged in a matrix, as in the first embodiment.

More specifically, in the scatterer detector10A of the second embodiment, the back electrode3is configured as a stripe type of electrode extending in the X axis direction (the first direction), and the back electrodes3are arranged in the Y axis direction (the second direction perpendicular to the first direction) side-by-side. Each of the back electrodes3is provided to oppose to a plurality of pixel electrodes2. In the present embodiment, each of the back electrodes3is arranged to oppose to a plurality of pixel electrodes2that are arranged in a line in the X direction. Note that the number of back electrodes3is smaller than the number of pixel electrodes2because each of the back electrodes3is arranged to oppose to the plurality of pixel electrodes2. Also, in the configuration of the present embodiment shown inFIG. 11toFIG. 14, each of the pixel electrodes2is arranged to oppose to one of the plurality of back electrodes3but not to oppose to another back electrode3. A part of the semiconductor substrate1sandwiched by each pixel electrode2and the back electrode3configures a pixel. An analog signal corresponding to a quantity of electric charge generated in each pixel is obtained from the pixel electrode2.

In the scatterer detector10A of such a configuration, it can be detected from a signal obtained from the back electrode3that any radiation has been inputted into either pixel, and the pixel electrode measurement data at a time when the electromagnetic radiation has been inputted into the scatterer detector10A can be selected from the pixel electrode measurement data obtained from the pixel electrodes2. In detail, when the electromagnetic radiation has been inputted into the pixel, electric charges are generated in the pixel, and the signals are generated in the pixel electrode2of the pixel and the back electrode3opposing to the pixel electrode2. It can be detected from the signal generated in the back electrode3that any electromagnetic radiation has been inputted to either of the pixels of the plurality of pixel electrodes2opposing to the back electrode3. Here, because the number of back electrodes3is smaller than the number of pixel electrodes2, a calculation load to process the signal generated in the back electrode3can be made small, and it is easy to generate a trigger to obtain the signal from the back electrode3. By selecting the pixel electrode measurement data at a time when any electromagnetic radiation has been inputted, from or the pixel electrode measurement data which are obtained from the pixel electrodes2of the scatterer detector10A based on the signal obtained from the back electrode3, and by analyzing the selected pixel electrode measurement data to detect the radiation, a quantity of the pixel electrode measurement data to be processed can be reduced.

In the configuration shown inFIG. 11toFIG. 14, the configuration is shown that has the striped-type back electrodes3. However, if each of the back electrodes3is arranged to oppose to the plurality of pixel electrodes2and the number of back electrodes3is less than the number of pixel electrodes2, the arrangement of the back electrodes3may be variously changed.

FIG. 15andFIG. 16show the configuration of the scatterer detector10A in which the arrangement of back electrodes3is different. Here,FIG. 15is a bottom view showing the configuration of the scatterer detector10A, andFIG. 16is a sectional view of the scatterer detector10A in the C-C section shown inFIG. 15.

In the configuration shown inFIG. 15andFIG. 16, the back electrodes3are arranged in a matrix (3 rows 3 columns in an example ofFIG. 15). Here, each of the back electrodes3is arranged to oppose to the pixel electrodes2arranged in a 4×4 matrix. In this case, note that each of the pixel electrodes2opposes to one of the plurality of back electrodes3but does not oppose to another back electrode3.

Even in such a configuration, by using the signal obtained from the back electrode3, the pixel electrode measurement data obtained from the pixel electrode2in a position where the electromagnetic radiation has been inputted to the scatterer detector10A and the Pixel electrodes2in the neighborhood of the position can be selected from the pixel electrode measurement data obtained from all the pixel electrodes2. Here, as shown inFIG. 11toFIG. 14, it is easy to acquire the signal from the back electrode3in the configuration using the striped-type back electrodes3. Thus, it is desirable to use the striped-type back electrodes3.

FIG. 17is a block diagram showing an example of configuration of a Compton camera20A of the second embodiment using the above-mentioned scatterer detector10A. The configuration of the Compton camera20A in the second embodiment is similar to that of the Compton camera20in the first embodiment. The Compton camera20A of the second embodiment includes the plurality of detector modules11A and11B, the processing unit12and the display device13, like the Compton camera20in the first embodiment. Here, in the Compton camera20A of the second embodiment, the configuration of the detector module11A loaded with the scatterer detectors10A is changed following a change of the configuration of the scatterer detector10A, and moreover, a data transfer device14is provided. The data transfer device14has a function of temporarily storing the pixel electrode measurement data obtained from the pixel electrodes2of the scatterer detector10A, and selectively transferring the effective pixel electrode measurement data of the stored pixel electrode measurement data to the processing unit12(that is, the pixel electrode measurement data used to calculate the spatial distribution of radiation sources), as mentioned later.

FIG. 18is a block diagram showing the configuration of the detector modules11A having the scatterer detectors10A and the detector modules11B having the absorber detectors10B and the configuration of data transfer device14in the second embodiment.

The detector module11A in the second embodiment includes signal processing ICs21and23and interfaces22and24. The signal processing IC21functions as a signal processing section that processes the analog signal read from each pixel electrode2of the scatterer detector10A. In detail, the signal processing IC21reads the analog signals at the same time from all the pixel electrodes2of the scatterer detector10A in each frame period, carries out analog-digital conversion to the read analog signals and generates the pixel electrode measurement data showing the signal level of the analog signal. The signal processing IC21transmits the generated pixel electrode measurement data to the data transfer device14through the interface22.

On the other hand, the signal processing IC23functions as a signal processing section that processes the analog signal react from each back electrode3of the scatterer detector10A. In detail, the signal processing IC23carries oat analog-digital conversion to the analog signal read from each back electrode3, and generates the measurement data showing a signal level of the analog signal. The measurement data obtained from the analog signal read from each back electrode3are hereinafter called a “back electrode measurement data”. The signal processing IC23transmits the generated back electrode measurement data to the data transfer device14through the interface24. The back electrode measurement data obtained in each detector module11A are used in the data transfer device14to select the pixel electrode measurement data to be finally transferred to the processing unit12, as mentioned later.

Assuming that the configuration of the absorber detector10B and that of the detector module11B are same as those of the first embodiment (that is, the absorber detector10B has the single back electrode3), the description is given. However, the absorber detector10B is possible to have a plurality of back electrodes3in she same way as the scatterer detector10A (such a modification example will be described later).

The data transfer device14has a function of transferring the pixel electrode measurement data and the back electrode measurement data obtained from each scatterer detector10A, and the pixel electrode measurement data obtained from each absorber detector10B to the processing unit12. In this case, the data transfer device14is configured to select the pixel electrode measurement data necessary to measure an electromagnetic radiation (e.g. the pixel electrode measurement data corresponding to the time when the electromagnetic radiation is inputted) from the pixel electrode measurement data obtained from each scatterer detector10A to transfer to the processing unit12. This selection is carried out based on the back electrode measurement data obtained from each scatterer detector10A and the pixel electrode measurement data obtained from each absorber detector10B. Since only the selected pixel electrode measurement data are sent to the processing unit12, the quantity of pixel electrode measurement data to be processed by the processing unit12can be reduced.

In detail, the data transfer device14includes a data p routes sing section15, a memory16, a data processing section17and an interface18. The data processing section15, the memory16, the data processing section17, and the interface18may be implemented as the integrated circuits (IC), respectively. Also, some of the data processing section15, the memory16, the data processing section17, and the interface18may be realized by an integrated circuit that is monolithically integrated.

The data processing section15receives the pixel electrode measurement data obtained in each scatterer detector10A from a corresponding detector module11A to store in the memory16. At this time, the data processing section15generates time data in synchronization with generation of the pixel electrode measurement data (that is, the time data of the contents synchronizing with the time when the pixel electrode measurement data are generated), and the generated time data are stored in the memory16together with the pixel electrode measurement data. In the present embodiment, the time data showing the time when data processing section15receives the pixel electrode measurement data from the detector module11A is stored in the memory16together with the pixel electrode measurement data. The memory16provides tire temporary storing area16ato temporarily store the pixel electrode measurement data obtained from each scatterer detector10A and the time data corresponding to the pixel electrode measurement data.

The data processing section17processes the back electrode measurement data obtained from each scatterer detector10A and the pixel electrode measurement data obtained from each absorber detector10B. In detail, the data processing section17generates the time data in synchronization with the generation of the back electrode measurement data obtained from each scatterer detector10A (that is, the time data having the content which is synchronized with the time when the back electrode measurement data is generated), and generates the time data in synchronization with the generation of the pixel electrode measurement data obtained from each absorber detector10B (that is, the time data having the content which is synchronized with the time when the pixel electrode measurement data are generated). In the present embodiment, the time data corresponding to the back electrode measurement data obtained from the scatterer detector10A are generated to show the time when the data processing section17receives the back electrode measurement data from each scatterer detector10A, and the time data corresponding to the pixel electrode measurement data obtained from the absorber detector10B are generated to show the time when the data processing section17receives the pixel electrode measurement data from each absorber detector10B. Moreover, the data processing section17determines whether or not the pixel electrode measurement data and the back electrode measurement data obtained from each scatterer detector10A in each frame period and the pixel electrode measurement data obtained from each absorber detector10B in the frame period should foe transferred to the processing unit12. This determination is carried cat based on the back electrode measurement data obtained from each scatterer detector10A and the pixel electrode measurement data obtained from each absorber detector10B. When determining to be transmitted, the data processing section17transfers the pixel electrode measurement, data and the back electrode measurement data obtained from each scatterer detector10A and the pixel electrode measurement data obtained from each absorber detector10B to the processing unit12. In this transfer, the data processing section17transfers the pixel electrode measurement data and the back electrode measurement data obtained from each scatterer detector10A and the pixel electrode measurement data obtained from each absorber detector10B to the processing unit12along with the time data corresponding to these data. The pixel electrode measurement data, the back electrode measurement data and the time data corresponding to them which have been transferred to the processing unit12are stored in the storage device12aand are used to specify the incidence direction of electromagnetic radiation and to calculate the spatial distribution of radiation sources.

More specifically, when the back electrode measurement data obtained from each scatterer detector10A and the pixel electrode measurement data obtained from each absorber detector10B in a frame period meet a predetermined condition (to be sometimes referred to as a “data acquisition condition” below), the data processing section17transfers the pixel electrode measurement data and the back electrode measurement data obtained from each scatterer detector10A in the frame period, and the pixel electrode measurement data obtained from each absorber detector10B in the frame period, and the time data corresponding to them, to the processing unit12. Here, note that the pixel electrode measurement data obtained from each scatterer detector10A are stored in the temporary storing area16aof the memory16, together with the time data. The data processing section17refers to the time data to select the pixel electrode measurement data and the corresponding time data, corresponding to the frame period during which the data acquisition condition is met, from the pixel electrode measurement data obtained from each scatterer detector10A, and to read from the temporary storing area16a, and transmits the pixel electrode measurement data and the time data read from the temporary storing area, to the processing unit12. The transfer of the pixel electrode measurement data, the back electrode measurement data and the time data to the processing unit12is carried out through the interface18.

For example, when it is determined from the back electrode measurement data obtained from each scatterer detector10A and the pixel electrode measurement data obtained from each absorber detector10B in a frame period that an electromagnetic radiation has inputted to either of the scatterer detector10A or the absorber detector10B in the frame period, the pixel electrode measurement data and the back electrode measurement data obtained from each scatterer detector10A in the frame period and the pixel electrode measurement data obtained from each absorber detector10B in the frame period may be transferred to the processing unit12. At this time, regarding the pixel electrode measurement data obtained from each scatterer detector10A, the pixel electrode measurement data corresponding to the frame period which meets the data acquisition condition are selected while referring to the time data, and the selected pixel electrode measurement data are transferred to the processing unit12. As another example, when it is determined from the back electrode measurement data obtained from each scatterer detector10A and the pixel electrode measurement data obtained from each absorber detector10B in a frame period that an electromagnetic radiation has inputted to one scatterer detector10A and one absorber detector10B (it is supposed that the Compton scattering has occurred in the one scatterer detector10A and the photoelectric absorption has occurred in the one absorber detector10B), the pixel electrode measurement data and the back electrode measurement data obtained from each scatterer detector10A in the frame period and the pixel electrode measurement data obtained from each absorber detector10B in the frame period may be transferred to the processing unit12. In this case, the pixel electrode measurement data corresponding to the frame period which meets the data acquisition condition are selected from the pixel electrode measurement data obtained from each scatterer detector10A while referring to the time data, and the selected pixel electrode measurement data are read from the temporary storing area16aand are transferred to the processing unit12, in the same way as mentioned above.

The processing unit12carries out data processing to the pixel electrode measurement data and the back electrode measurement data which are transferred from the data transfer device14and calculates a spatial distribution of radiation sources. For example, the processing unit12calculates a position X1of occurrence of the Compton scattering, energy E1acquired by the recoil electron in the Compton scattering, a track of the recoil electron (i.e. a recoiling direction), a position X2of occurrence of the photoelectric absorption, energy E2of a photon absorbed in the photoelectric absorption, and a scattering angle θ of the electromagnetic radiation, from the pixel electrode measurement data obtained from the scatterer detector10A in a frame period and the pixel electrode measurement data obtained from the absorber detector10B in the frame period. The processing unit12further calculates the incidence direction of the electromagnetic radiation and the spatial distribution of radiation sources from these data. At this time, the processing unit12may improve calculation precision of the energy E1acquired by the recoil electron in the Compton scattering by referring to the back electrode measurement data obtained from the scatterer detector10A.

FIG. 19is a sectional view showing an example of implementation of the scatterer detector10A of the detector module11A. In one embodiment, the detector module11A includes a printed circuit board25. The scatterer detector10A and the signal processing IC23are connected to wiring pattern lines formed on the printed circuit board25. In detail, the scatterer detector10A is connected to a wiring pattern line26formed on the printed circuit board25. Here, the wiring pattern line26is a wiring line to electrically connect the back electrode3of the scatterer detector10A and the signal processing IC23. That is, the back electrode3of the scatterer detector10A is connected to the wiring pattern line26. On the other hand, the signal processing IC23is connected to wiring pattern lines26and27. Here, the wiring pattern line27is a wiring line to electrically connect the signal processing IC23and the interface22.

On the other hand, the pixel electrodes2of the scatterer detector10A and the signal processing IC21are connected by a flip chip connection. In detail, the signal processing IC21has pads21aand bumps28are connected to the pads21a. The bumps28are connected to the pixel electrodes2of the scatterer detector10. The analog signal generated by each pixel electrode2is read into the pad21aof the signal processing IC21through the bump28. In the Compton camera20A of the present embodiment, the plurality of pixel electrodes2are connected with the signal processing IC21in parallel by such a configuration. It is effective for the improvement of time resolution that the plurality of pixel electrodes2are connected with the signal processing IC21in parallel.

Note that inFIG. 19, the interfaces22and24are not shown but the interfaces22and24may be mounted on the printed circuit board25.

Next, the operation of the Compton camera20A in the present embodiment will be described. A procedure of calculating the spatial distribution of radiation sources in the Compton camera20A of the present embodiment is almost the same as in the Compton camera20in the first embodiment (seeFIG. 9). The measurement data (the pixel electrode measurement data and the back electrode measurement data) are acquired (Step S01), and a track of the recoil electron is calculated (Step S02). An event is extracted by using the track of recoil electron calculated at the step S02(Step S03), and the reconstruction of a Compton cone, i.e. the incidence direction of the electromagnetic radiation is specified for the extracted event (Step S04). Moreover, the spatial distribution of radiation sources is calculated by using the incidence direction of the specified electromagnetic radiation.

The generation and display of the radiation source distribution image showing the spatial distribution of radiation sources are carried out (Step S05).

Here, in the Compton camera20A of the second embodiment, when the back electrode measurement data obtained from each scatterer detector10A and the pixel electrode measurement data obtained from each absorber detector10B in each frame period in the acquisition of the measurement data (step S01) meet a predetermined data acquisition condition, the pixel electrode measurement data and the back electrode measurement data obtained from each scatterer detector10A in the frame period, the pixel electrode measurement data obtained from each absorber detector10B in each frame period, and the time data corresponding to them are transferred to the processing unit12. In this point, the Compton camera20A in the second embodiment differs from the Compton camera20in the first embodiment. By such an operation, in the second embodiment, necessary data of the pixel electrode measurement data obtained from each scatterer detector10A are selectively transferred to the processing unit12. Thus, the data quantity of the pixel electrode measurement data to be processed by the processing unit12can be reduced.

FIG. 20is a timing chart showing the operation of acquisition of the measurement data in the present embodiment. The operation in the (N−1)thto the (N+1)thframe periods is shown inFIG. 20.

The signal processing IC21of each detector module11A reads an analog signal from each pixel electrode2of the scatterer detector10A in each frame period, carries out the analog-digital conversion to the read analog signal to generate the pixel electrode measurement data. As mentioned above, the pixel electrode measurement data are data showing a signal level of the analog signal read from each pixel electrode2. The pixel electrode measurement data obtained from the scatterer detector10A in this way are transferred to the data processing section15of the data transfer device14, and are scored in the temporary storing area of the memory16. At this time, the time data corresponding to the pixel electrode measurement data (the time data synchronized with the generation of the pixel electrode measurement data) are stored in the temporary storing area16aof the memory16in addition to the pixel electrode measurement data obtained from the scatterer detector10A.

On the other hand, the signal processing IC23of each detector module11A reads an analog signal from each back electrode3of the absorber detector10B in each frame period, carries out the analog-digital conversion to the read analog signal and generates the back electrode measurement data. The back electrode measurement data obtained from the scatterer detector10A in this way, are transferred to the data processing section17of the data transfer device14.

Moreover, the signal processing IC21of each detector module11B reads the analog signal from each pixel electrode of the absorber detector10B in each frame period, and carries out the analog-digital conversion to the read analog signal to generate the pixel electrode measurement data. The pixel electrode measurement data obtained from the absorber detector10B in this way are transferred to the data processing section17of the data transfer device14.

InFIG. 20, the pixel electrode measurement data obtained in the frame period (more strictly, the pixel electrode measurement data generated from the analog signal read from each pixel electrode2of the scatterer detector10A and the absorber detector10B in the kthframe period) is shown by a symbol DPIXEL(k). Also, in the back electrode measurement data obtained in the kthframe period (more strictly, the back electrode measurement data generated from the analog signal read from each back electrode3of the scatterer detector10A in the kthframe period) is shown as a symbol DR(k).

When the back electrode measurement data obtained from each scatterer detector10A and the pixel electrode measurement data obtained from each absorber detector10B in each frame period meet a predetermined data acquisition condition, the data processing section17reads the pixel electrode measurement data obtained from each scatterer detector10A and the time data corresponding to them from the memory16in the frame period, and transfers the pixel electrode measurement data and the back electrode measurement data obtained from each scatterer detector10A in the frame period, the pixel electrode measurement data obtained from each absorber detector10B in the frame period, and the time data corresponding to them to the processing unit12.

For example, when it is determined from the back electrode measurement data obtained from each scatterer detector10A in a frame period, and the pixel electrode measurement data obtained from each absorber detector10B that an electromagnetic radiation is inputted to either of the scatterer detector10A or the absorber detector10B in the frame period, the pixel electrode measurement data and the back electrode measurement data obtained from each scatterer detector10A in the frame period, and the pixel electrode measurement data obtained from each absorber detector10B in the frame period may be transferred to the processing unit12. As another example, when it is determined from the back electrode measurement data obtained from each scatterer detector10A in a frame period and the pixel electrode measurement data obtained from each absorber detector10B that an electromagnetic radiation has been inputted to one scatterer detector and one absorber detector10B (the case where the Compton scattering occurred in the scatterer detector10A and the photoelectric absorption occurred in the absorber detector10B), the pixel electrode measurement data and the back electrode measurement data obtained from each scatterer detector10A in the frame period, and the pixel electrode measurement data obtained from each absorber detector10B in the frame period may be transferred to the processing unit12. The pixel electrode measurement data and the back electrode measurement data sent from data processing section17to the processing unit12are stored in the storage device12aof the processing unit12.

For example, as shown inFIG. 20, it is supposed to be determined that the back electrode measurement data obtained from each scatterer detector10A and the pixel electrode measurement data obtained from each absorber detector10B in the Nthframe period meet the predetermined data acquisition condition (for example, an electromagnetic radiation has been determined to be inputted to either of the scatterer detector10A or the absorber detector10B). In this case, the data processing section17transfers the pixel electrode measurement data DPIXEL(N) obtained from each scatterer detector10A and each absorber detector10B in the Nthframe period, the back electrode measurement data DR(N) obtained from each absorber detector10B, and the time data corresponding to them to the processing unit12. At this time, as for the pixel electrode measurement DPIXEL(N) obtained from each scatterer detector10A, the pixel electrode measurement data corresponding to the frame period which meets the data acquisition condition are selected while referring to the time data, and the selected pixel electrode measurement data and the corresponding time data are read from the temporary storing area16aand are transferred to the processing unit12.

In the operation shown inFIG. 20, the pixel electrode measurement data DPIXEL(N) obtained from each scatterer detector10A and each absorber detector10B and the back electrode measurement data DR(N) from each absorber detector10B in the Nthframe period are transferred to the processing unit12in the following frame period (the (N+1)thframe period). However, the timing of the transfer to the processing unit12of the pixel electrode measurement data and the back electrode measurement data obtained in the Nthframe period can be selected appropriately after detection of the incidence of the electromagnetic radiation.

The processing unit12carries out the calculation of a track of the above-mentioned recoil electron (Step S02), the extraction of the event (Step S03), the reconstruction of Compton cone (Step S04), and the generation and display of a radiation source distribution image (step S05) based on the pixel electrode measurement data, the back electrode measurement data, and the time data corresponding to them which are stored in the storage device12a. In this place, in the reconstruction of Compton cone at step S04, the processing unit12may improve calculation precision of the energy E1acquired by the recoil electron in the Compton scattering by using the back electrode measurement data obtained from the scatterer detector10A in addition to the pixel electrode measurement data obtained from each scatterer detector10A.

According to the operation described above, necessary data of the pixel electrode measurement data obtained from the scatterer detector10A can be selectively transferred to the processing unit12. Unnecessary pixel electrode measurement data are not transferred to the processing unit12. Therefore, it is possible to reduce a quantity of data to be processed by the processing unit12. Such an advantage is conspicuous, especially, when many pixel electrodes2are provided for the scatterer detector10A.

Third Embodiment

In the second embodiment, the scatterer detector10A is configured, to have the structure of the plurality of back electrodes3as shown inFIG. 11toFIG. 16. However, in the Compton camera20B of the third embodiment, the above-mentioned structure is adopted in which the plurality of back electrodes3are provided in the absorber detector10B.

FIG. 21is a block diagram of an example of configuration of the Compton camera20B in the third embodiment. The configuration of Compton camera20B in the third embodiment is similar to that of the Compton camera20A in the second embodiment. However, in the Compton camera20B of the third embodiment, the configuration of the detector module11B loaded with the absorber detector10B is changed to the configuration similar to the detector module11A loaded with the scatterer detector10A, following the change of the configuration of the absorber detector10B.

FIG. 22is a block diagram showing the configuration of detector modules11A and11B, and the configuration of the data transfer device14in the Compton camera20B of the third embodiment. The detector module11A includes the scatterer detector10A, the signal processing ICs21and23and the interfaces22and24in the third embodiment, like the second embodiment. In the same way, the detector module11B includes the absorber detector10B, and the signal processing ICs21and23and the interfaces22and24. The configuration of detector module11B is same as that of the detector module11A except for the point that the absorber detector10B is substituted for the scatterer detector10A.

Here, in the Compton camera20B of the third embodiment, all of the pixel electrode measurement data obtained from the scatterer detector10A and the absorber detector10B are transferred to the data processing section15, and stored in the temporary storing area16aof the memory16. On the other hand, all of the back electrode measurement data obtained from the scatterer detector10A and the absorber detector10B are transferred to the data processing section17. The data processing section17processes the back electrode measurement data obtained from each scatterer detector10A and each absorber detector10B.

In detail, the data processing section17determines whether or not the pixel electrode measurement data and the back electrode image data obtained from each scatterer detector10A and each absorber detector10B in each frame period and the time data corresponding to them should be transferred to the processing unit12. In the present embodiment, this determination is carried out based on the back electrode measurement data obtained from each scatterer detector10A and each absorber detector10B. The pixel elect rode measurement data, the back electrode measurement data and the time data corresponding to them transferred to the processing unit12are stored in the storage device12a, and are used for the specification of incidence direction of electromagnetic radiation and the calculation the spatial distribution of radiation sources.

More specifically, when the back electrode measurement data obtained from each scatterer detector10A and each absorber detector10B in a frame period meets a predetermined data acquisition condition, the data processing section17transfers the pixel electrode measurement data and the back electrode measurement data obtained from each scatterer detector10A in the frame period and the pixel electrode measurement data obtained from each absorber detector10B in the frame period to the processing unit12. Here, note that the pixel electrode measurement data obtained from each scatterer detector10A and each absorber detector10B have been stored in the temporary storing area16aof the memory16together with the time data referring to the time data, the data processing section17selects the pixel electrode measurement data corresponding to the frame period which meets the data acquisition condition, from the pixel electrode measurement data obtained from each scatterer detector10A and each absorber detector10B, to read from the temporary storing area16a, and transmits the pixel electrode measurement data read from the temporary storing area16ato the processing unit12. The transfer of pixel electrode measurement data and back electrode measurement data to the processing unit12is carried out through the interface18.

Next, the operation of Compton camera20B in the third embodiment will be described. A procedure of calculating the spatial distribution of radiation sources in the Compton camera20A of the present embodiment is almost similar to the operation of the Compton camera20and20A in the first and second embodiments (reference toFIG. 9). The measurement data (the pixel electrode measurement data and the back electrode measurement data) are acquired (Step S01), and a track of the recoil electron is calculated (Step S02). An event is extracted by using the track of the recoil electron calculated at the step S02(Step S03). About the extracted event, the reconstruction of Compton cones, i.e. the incidence direction of the electromagnetic radiation is specified (Step S04). Moreover, the spatial distribution of radiation sources is calculated by using the specified incidence directions of the electromagnetic radiations. The generation and display of the radiation source distribution image showing the spatial distribution of radiation sources are carried out (Step S05).

However, in the point that the pixel electrode measurement data and the back electrode measurement data obtained from each scatterer detector10A and each absorber detector10B are transferred to the processing unit12in the frame period, when the back electrode measurement data obtained from each scatterer detector10A and each absorber detector10B in each frame period meet a predetermined data acquisition condition in the acquisition of the measurement data (step S01), the third embodiment is different from the second embodiment in the Compton camera20. In such an operation, in the third embodiment, the necessary data of the pixel electrode measurement data obtained from each scatterer detector10A and each absorber detector10B are selectively transferred to the processing unit12, and a quantity of pixel electrode measurement data to be process by the processing unit12can be more reduced than in the second embodiment.

When the back electrode measurement data obtained from each scatterer detector10A and each absorber detector10B in each frame period meet the predetermined data acquisition condition, the data processing section17reads the pixel electrode measurement data obtained from each scatterer detector10A and each absorber detector10B in the frame period from the memory16, and transfers the pixel electrode measurement data and the back electrode measurement data obtained from each scatterer detector10A and each absorber detector10B in the frame period, and the time data corresponding to them to the processing unit12. Note that the pixel electrode measurement data obtained from each scatterer detector10A and each absorber detector10B have been stored in the temporary storing area16aof the memory16together with the time data. Referring to the time data, the data processing section17selects the pixel electrode measurement data corresponding to the frame period which meets the data acquisition condition, from the pixel electrode measurement data obtained from each scatterer detector10A and each absorber detector10B to read from the temporary storing area16a, and transmits the pixel electrode measurement data read from the temporary storing area16ato the processing unit12.

For example, when it is determined from the back electrode measurement data obtained from each scatterer detector10A and each absorber detector10B in a frame period that an electromagnetic radiation has been inputted to either of the scatterer detector10A or the absorber detector10B in the frame period, the pixel electrode measurement data and the back electrode measurement data obtained from each scatterer detector10A and each absorber detector10B in the frame period may be transferred to the processing unit12. At this time, the pixel electrode measurement data, corresponding to the frame period which meets the data acquisition condition, are selected from the pixel electrode measurement data obtained from each scatterer detector10A and each absorber detector10B while referring to the time data, and the selected pixel electrode measurement data are transferred to the processing unit12. As another example, when it is determined from the back electrode measurement data obtained from each scatterer detector10A and each absorber detector10B in a frame period that the electromagnetic radiation is inputted to one scatterer detector and one absorber detector10B (it is supposed that the Compton scattering occurs in the one scatterer detector10A and the photoelectric absorption occurs in the absorber detector10B), the pixel electrode measurement data and the back electrode measurement data obtained from each scatterer detector10A and each absorber detector10B in the frame period may be transferred to the processing unit12. The pixel electrode measurement data and the back electrode measurement data sent from the data processing section17to the processing unit12are stored in the storage device12aof the processing unit12. In this case, in the same way, the pixel electrode measurement data, corresponding to the frame period which meets the data acquisition condition, are selected from the pixel electrode measurement data obtained from each scatterer detector10A and each absorber detector10B, while referring to the time data, and the selected pixel electrode measurement data are transferred to the processing unit12.

The processing unit12carries out the calculation of a track of a recoil electron (Step S02), the extraction of an event (Step S03), the reconstruction of Compton cone (Step S04), and the generation and display of the radiation source distribution image (step S05) as mentioned above, based on the pixel electrode measurement data and the back electrode measurement data stored in the storage device12a. Here, in the reconstruction of Compton cone at step S04, the processing unit12may calculate the energy E1acquired by the recoil electron in the Compton scattering in an improved precision by using the pixel electrode measurement data obtained from each scatterer detector10A and the back electrode measurement data obtained from the scatterer detector10A. In addition, the processing unit12may calculate the energy E2of the photon absorbed in the photoelectric absorption in an improved precision based on the pixel electrode measurement data obtained from each absorber detector10B and the back electrode measurement data obtained from the absorber detector10B.

According to the operation described above, necessary data of the pixel electrode measurement data obtained from the scatterer detector10A and the absorber detector10B can be selectively transferred to the processing unit12. Unnecessary pixel electrode measurement data are not transferred to the processing unit12. Therefore, it is possible to reduce a quantity of data to be processed by the processing unit12. Such an advantage is conspicuous, especially, when the pixel electrodes2of a large number are provided for the scatterer detector10A and the absorber detector10B.

As described, the embodiments of the present invention are variously described but the present invention is not limited to the above-mentioned embodiments. It would be clear to the skilled person that the present inventions can be implemented with various changes.

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