JP2000023965A - Radiation imaging instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance an image quality by imaging reconfiguration by use of projection data formed through the accurate detection of the number of photons in X-rays. SOLUTION: An electric charge created by an X-ray detector in accordance with the dose of X-rays is detected by a current detection system 2 as a current value and a pulse detection system 3 also detects it as the count of charge pulses corresponding to the charge. When the dose of X-rays is small, a computation selecting part 4 selects the count from the pulse detection system 3 for output as the present number of photons in the X-rays; when the dose of X-rays increases, the current value from the current detection system 2 is selected for output as the present number of photons in the X-rays. Thus when the dose of X-rays is small, image reconfiguration can be performed by use of the count value unaffected by circuit noises, whereas when the dose of X-rays is large, the image reconfiguration can be performed by use of the current value having no relation with the failure to count pulses, whereby picture quality can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation imaging apparatus suitable for use in an apparatus for capturing an image using radiation, such as an X-ray CT apparatus for capturing an image using X-rays. Both a current detection system that detects the number of photons of radiation transmitted through or scattered by the subject by a current value and a pulse detection system that detects the number of photons by the number of charge pulses are provided, and each detection output is provided at a predetermined timing. The present invention relates to a radiation imaging apparatus capable of accurately detecting the number of radiation photons without being affected by noise or the like by switching between the methods.

[0002]

2. Description of the Related Art Conventionally, X-rays are emitted to a subject, and X-rays transmitted through or scattered by the subject are detected by an X-ray detector. An X-ray CT apparatus that captures a fluoroscopic image, a tomographic image, or a three-dimensional image of a subject based on the number of photons) is known. Such X-ray C
The T device is a current detection system that indirectly detects a current value corresponding to the charge formed by detecting the X-ray by the X-ray detector as the number of photons of the X-ray, or counts a charge pulse of the charge, There is a pulse detection system that indirectly detects this count value as the number of X-ray photons.

[0003] The current detection system has a configuration shown in FIG. 7, in which a charge supplied from a radiation detector 100, which is an X-ray detector, is converted into a resistor R, a capacitor C, and an operational amplifier 101.
The integration process is performed by the integrator 102, which detects a current value corresponding to the charge. Then, this current value is referred to as AD
Digitized by the converter 103, the data processing unit 1
At 04, the data is subjected to predetermined data processing and supplied to the image reconstruction system. This makes it possible to perform image reconstruction processing based on the current value corresponding to the number of X-ray photons detected by the X-ray detector as shown in FIG. 8, and to form a tomographic image or the like of the subject. Can be.

The pulse detection system has the configuration shown in FIG. 9 and is supplied from the radiation detector 100 in FIG.
The charge as shown in FIG.
05 to the comparator 106, and FIG.
By performing binarization in comparison with the reference voltage from the reference voltage generator 107 at the level indicated by the middle dotted line, a charge pulse as shown in FIG. Then, the charge pulse is counted by the counter 108. The data processing unit 104
Based on the concept of "one photon = one charge pulse",
Predetermined data processing is performed on the count value from the counter 108, and this is supplied to an image reconstruction system. As a result, as shown in FIG. 10B, image reconstruction processing can be performed based on the charge pulse corresponding to the number of X-ray photons detected by the X-ray detector, and a tomographic image of the subject can be obtained. Can be formed.

[0005]

However, when the number of X-ray photons incident on the radiation detector is small, or when the energy of the incident photons is low, the amount of charges formed by the radiation detector decreases, The current value of the current formed by the integrator 102 is also small. For this reason, in the current detection system, when the current value becomes small, there is a problem that the number of photons of radiation cannot be accurately detected due to the influence of the noise of the current detection system at the level indicated by the dotted line in FIG.

On the other hand, in the pulse detection system, the radiation detector 1
When the number of photons of X-rays incident on 00 increases, FIG.
As shown in FIG. 7, the charge pulses overlap with each other in time, and a phenomenon called pile-up in which each charge pulse cannot be distinguished individually occurs. Further, there are restrictions on the time resolution of the comparator 106 and the counting rate of the counter 108, and the pulses may be counted down. For this reason, the pulse detection system has a problem in that when the number of X-ray photons increases, the number of radiation photons cannot be accurately detected.

[0007] X-ray CT having any detection system
Since the apparatus cannot accurately detect the number of photons of radiation, there is a problem that image quality is deteriorated in the reconstructed image.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and accurately detects a radiation dose of radiation without being affected by a radiation dose of radiation incident on a radiation detector, and generates a reconstructed image. An object of the present invention is to provide a radiation imaging apparatus capable of improving image quality.

[0009]

A radiation imaging apparatus according to the present invention irradiates an object with radiation from radiation irradiating means, captures a radiation image formed thereby by a radiation detecting means, and obtains a radiation image of the object. Assuming a radiation imaging apparatus that captures an image, current detection means for detecting a current value corresponding to a radiation output from the radiation detection means, and the radiation detection means as characteristic means for solving the above-described problems. Pulse detection means for detecting a pulse count value corresponding to a radiation output from the apparatus, and a current value from the current detection means or a pulse count value from the pulse detection means in accordance with the output value of the radiation detection output. Selection means for selecting and outputting.

In such a radiation imaging apparatus, the selection means selects and outputs a current value from the current detection means or a pulse count value from the pulse detection means according to the output value of the radiation detection output. I do. Thereby, while the current value from the current detection means is affected by the noise,
Using the count value of the pulse from the pulse detecting means, the current value from the current detecting means can be used when the current value from the current detecting means is no longer affected by noise. For this reason, it is possible to prevent noise that is problematic at a low dose at the time of current measurement, and to prevent counting of pulses at a high dose (high counting rate) that is problematic at the time of pulse measurement. Therefore, it is possible to accurately detect the radiation dose of the radiation and improve the image quality of the reconstructed image without being affected by the radiation dose of the radiation incident on the radiation detection unit.

Further, the radiation imaging apparatus according to the present invention irradiates the object with the radiation from the radiation irradiating means, and captures the radiation image formed thereby by the radiation detecting means.
Assuming a radiation imaging apparatus that captures a radiation image of an object, as a characteristic means for solving the above-described problems,
Current detection means for detecting a current value corresponding to the radiation output from the radiation detection means, pulse detection means for detecting a count value of a pulse corresponding to the radiation output from the radiation detection means, and the object is irradiated. Switching means for switching the radiation output from the radiation detecting means in accordance with the radiation dose of the radiation and supplying the radiation output to the current detecting means or the pulse detecting means.

In such a radiation imaging apparatus, the switching means switches the radiation output from the radiation detecting means in accordance with the radiation dose of the radiation radiated to the object, and switches the current detecting means or the pulse detecting means. To supply. As a result, while the current value from the current detection means is affected by the noise, the pulse count value from the pulse detection means is used, and when the current value from the current detection means is no longer affected by the noise, The current value from the detecting means can be used. For this reason, it is possible to prevent noise that is problematic at a low dose at the time of current measurement, and to prevent counting of pulses at a high dose (high counting rate) that is problematic at the time of pulse measurement. Therefore, it is possible to accurately detect the radiation dose of the radiation and improve the image quality of the reconstructed image without being affected by the radiation dose of the radiation incident on the radiation detection unit.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] "Configuration of First Embodiment" (Configuration of Data Detection Unit) The radiation imaging apparatus according to the present invention is, for example, a third-generation X-ray CT apparatus. Can be applied to The X-ray CT apparatus according to the first embodiment of the present invention has a data detecting unit 1 as shown in FIG.
have. The data detection unit 1 includes a current detection system 2 that detects the number of X-ray photons incident on the X-ray detector as a current value, a pulse detection system 3 that detects the number of photons as a count value of charge pulses, A calculation switching unit 4 for switching and outputting a current value or a count value from each of the detection systems 2 and 3 at a predetermined timing.

The current detection system 2 includes a resistor R and a capacitor C1.
And an integrator 14 comprising an operational amplifier 6 and the integrator 1
And an AD converter 7 for digitizing an integrated output from the X-ray detector 4 and supplying the digitized output to the operation switching unit 4. The charge supplied from the X-ray detector is integrated by an integrator 14 to reduce the charge amount. A current having a value corresponding to the current is formed.

The pulse detection system 3 includes a smoothing capacitor C2 for forming a DC signal corresponding to the electric charge from the X-ray detector, an amplifier 8 for amplifying the DC signal from the smoothing capacitor C2 with a predetermined gain, and a comparator for comparison. A reference voltage source 9 for generating a reference voltage, and a comparator 10 for forming a charge pulse corresponding to the charge amount by comparing a DC signal from the amplifier 8 with a reference voltage from the reference voltage source 9 for comparison. And an operation switching unit 4 that counts the charge pulses from the comparator 10 and supplies the count value to the operation switching unit 4.

(Configuration of the whole X-ray CT apparatus)
The configuration of the entire apparatus is as shown in FIG. 2, and the data detection unit 1 having the above-described configuration is provided at the subsequent stage of the X-ray detector 22. The X-ray detector 22 is provided in the gantry rotating unit so as to rotate while maintaining the positional relationship facing the X-ray tube 21 as shown in FIG. X-rays are emitted, and an X-ray image is captured by the X-ray detector 22 so that a desired part of the subject is imaged. In addition, the X-ray CT apparatus continuously moves the bed on which the subject is placed by a predetermined amount, and applies X-rays to the subject while rotating the X-ray tube 21 and the X-ray detector 22. It is also possible to perform imaging by so-called helical scan for performing imaging by irradiation.

The X-ray CT apparatus performs predetermined data processing for image reconstruction on the current value or the count value selected by the operation switching unit 4 of the data detecting unit 1 as shown in FIG. A data processing unit 23 that forms
A data storage unit 24 that temporarily stores the projection data formed by the data processing unit 23, and performs image reconstruction processing based on the projection data from the data processing unit 23 or the projection data read from the data storage unit 24 to perform tomography. And an image reconstruction unit 25 for forming an image.

The X-ray CT apparatus includes an X-ray control / high voltage generator 26 for controlling the X-ray tube 21 for irradiation at a predetermined tube voltage, a tube current, and a predetermined timing. A gantry rotating unit 27 provided with the X-ray detector 22, a bed 28 on which a subject is placed, and a gantry / bed driving control unit 2 for rotatingly driving the gantry rotating unit and controlling movement of the bed 28.
9 and an operation unit 30 for setting a tube voltage, a tube current, an irradiation timing, and the like for driving the X-ray tube 21.

Further, the X-ray CT apparatus has an image storage section 31 for storing the tomographic image formed by the image reconstruction section 25.
An image processing unit 32 for displaying and processing the tomographic image read from the image storage unit 31; an image display unit 33 for displaying the tomographic image displayed and processed by the image processing unit 32; And a central processing unit 34 (CPU) for performing control.

[Operation of First Embodiment] (Operation of Entire X-ray CT Apparatus) Next, the operation of the X-ray CT apparatus according to the first embodiment having such a configuration will be described. For example, when performing imaging by helical scan using this X-ray CT apparatus, the operator operates the operation unit 30 to set the helical pitch (bed moving amount) tube voltage, current sensitivity, exposure timing, and the like. . When this setting is made,
The CPU 34 controls the rotation of the X-ray tube 21 and the X-ray detector 22 of the gantry rotating unit 27 via the gantry / bed driving control unit 29, and sets the bed 28 through the gantry / bed driving control unit 29. The movement is controlled by the helical pitch. Then, the X-ray tube 21 is controlled to be irradiated with the set irradiation timing, tube voltage and current-sensitive current via the X-ray control / high voltage generator 26. As a result, X-rays are helically irradiated to the subject on the bed 28, and imaging by helical scan is performed.

The X-ray detector 22 captures an X-ray image formed by exposing the subject to X-rays, and forms an electric charge corresponding to the number of photons of the captured X-rays. Then, the charge is supplied to the data detection unit 1. The data detection unit 1 detects a current of a value corresponding to the charge amount or a count value of a charge pulse corresponding to the charge amount, as described later, and supplies the detection output to the data processing unit 23. The data processing unit 23 forms projection data based on the detection output supplied from the data detection unit 1, and supplies the projection data to the data storage unit 24 and the image reconstruction unit 25.

The image reconstruction unit 25 performs an image reconstruction process based on the projection data read from the data storage unit 24 or the projection data from the data processing unit 23 to form a tomographic image. Then, the tomographic image is supplied to the CPU 34. The CPU 34 controls the storage of the tomographic image in the image storage unit 31 or supplies the tomographic image to the image processing unit 32. The image processing unit 32 performs a display process on the supplied tomographic image, and supplies this to the image display unit 33. Thus, the tomographic image captured by the helical scan can be displayed on the image display unit 33.

(Operation of Data Detecting Unit) Here, the electric charge formed by the X-ray detector 22 according to the number of photons of the incident X-ray is supplied to the current detecting system 2 via the input terminal 12 shown in FIG.
And the pulse detection system 3. The current detection system 2 forms a current having a value corresponding to the charge by the integrator 14, digitizes the current by the AD converter 7, and supplies it to the operation switching unit 4. Further, the pulse detection system 3
The charge is binarized by a comparator 10 based on a reference voltage supplied from a reference voltage source 9 for comparison to form a charge pulse, and the number of pulses is counted by a counter 11, and the counted value is calculated by the operation switching unit 4. To supply.

FIG. 4 shows the relationship between the dose of X-rays detected by the X-ray detector 22 and the measured value of the number of photons detected as a current value or a count value of charge pulses by the data detection unit 1. The step-like graph shows the count value of the charge pulse, and the linear graph shows the current value. As can be seen from the graph of FIG.
The operation switching unit 4 keeps the calculation switching unit 4 until the measured value of the number of photons exceeds the level of the circuit noise of the data detection unit 1.
The count value of the charge pulse supplied from the pulse detection system 3 is selected and output (photon count mode), and when the measured value of the number of photons exceeds the level of the circuit noise of the data detection unit 1, the current detection system 2 is selected and output (current mode).

That is, in the current detection system 2, when the number of X-ray photons incident on the X-ray detector 22 is small or when the energy of the incident photons is low, the X-ray detector 22
, The amount of charge formed by the current detection system 2 decreases, and the current value detected by the current detection system 2 also decreases. Therefore, the current value is
At a circuit noise level lower than or equal to the circuit noise level of the data detector 1, the number of photons cannot be accurately detected. In contrast, the pulse detection system 3 has a configuration for counting the number of charge pulses.
Even when the number of X-ray photons incident on the X-ray detector 22 is small or the energy of the incident photons is low, the count value corresponding to the number of photons can be accurately detected. For this reason, the calculation switching unit 4 selects the count value of the charge pulse supplied from the pulse detection system 3 until the measured value of the number of photons exceeds the level of the circuit noise of the data detection unit 1. Output.

On the other hand, in the pulse detection system 3, the X-ray detector 2
When the number of photons of the X-ray incident on 2 increases, the charge pulses overlap with each other in time, making it difficult to accurately count each charge pulse. In contrast, the current detection system 2
In this case, if the number of X-ray photons increases and the current value to be detected becomes equal to or higher than the circuit noise level of the data detection unit 1, the number of photons can be accurately detected. For this reason,
After the measured value of the number of photons exceeds the level of the circuit noise of the data detection unit 1, the operation switching unit 4 selects and outputs the current value supplied from the current detection system 2.

In other words, the operation switching unit 4 selects and outputs the count value from the pulse detection system 3 when the current detection system 2 cannot accurately detect the number of photons,
When the number of photons cannot be accurately detected by the pulse detection system 3, the current value from the current detection system 2 is selected and output. As a result, it is possible to select and output a count value or a current value that exactly corresponds to the number of X-ray photons currently detected by the X-ray detector 22.

The count value or current value selected by the operation switching unit 4 is supplied to the data processing unit 23 shown in FIG. As described above, the count value or the current value supplied to the data processing unit 23 is:
At present, the value accurately corresponds to the number of X-ray photons detected by the X-ray detector 22. For this reason, the data processing unit 23 can form projection data accurately corresponding to the current number of X-ray photons, and based on the projection data, generate a tomographic image of the tomographic image formed by the subsequent image reconstructing unit 25. Image quality can be improved.

"Effects of the First Embodiment" As is clear from the above description, the X-ray CT apparatus of the first embodiment uses the number of X-ray photons detected by the X-ray detector 22. Are simultaneously detected by the current detection system 2 and the pulse detection system 3,
Until the measured value of the number of photons exceeds the circuit noise of the data detector 1, the count value from the pulse detection system 3 is used as the measured value of the photon. After the circuit noise is exceeded, the current value from the current detection system 2 is used as the measured value of the photons, so that the current value of the radiation is not affected by the number of photons of the radiation incident on the X-ray detector 22. The number of photons can be accurately detected. Therefore, the image quality of the reconstructed image can be improved.

In the above description of the first embodiment, when the measured value of the number of photons exceeds the level of the circuit noise of the data detection unit 1, the calculation switching unit 4 calculates the charge pulse count value. Although the output was switched to the current value from the above, the X-ray of a known dose was made incident on the X-ray detector 22 in advance, the charge pulse was counted, and the X-ray dose at which the count leakage occurred was obtained in advance. The switching from the count value to the current value may be performed when the count value approaches the X-ray dose at which the count omission occurs during actual imaging.

[Modification of First Embodiment] The first embodiment described above
In the description of the embodiment, the current detection system 2 and the pulse detection system 3 detect the current value or the count value of the charge pulse based on the electric charge formed by the X-ray detector 22. Is the X-ray detector 2 as shown in FIG.
The current detection system 2 may be connected to the second cation collection side electrode 22a (or the hole collection side electrode), and the pulse detection system 3 may be connected to the electron collection side electrode 22b. Even in this case, the current number of photons can be simultaneously detected as the current value or the count value of the charge pulse, and these can be appropriately selected and used by the operation switching unit 4 to achieve the above-described first embodiment. The same effect as in the embodiment can be obtained.

[Second Embodiment] Next, a second embodiment of the present invention will be described.
An X-ray CT apparatus according to the embodiment will be described. In the above-described first embodiment, the data detection unit 1 simultaneously detects the current value and the count value of the charge pulse, and appropriately selects and uses them. However, the second embodiment is different from the first embodiment. ,
The current detection system 2 and the pulse detection system 3 are switched and used according to the X-ray dose. Note that the first
This embodiment is different from the second embodiment only in this point. For this reason, in the following description of the second embodiment, only this difference will be described, and redundant description will be omitted.

"Configuration of the Second Embodiment" That is, the X-ray CT apparatus of the second embodiment converts the electric charge supplied from the X-ray detector 22 into the current detection system 2 as shown in FIG. Switch 51 for controlling the supply to the X-ray detector 22
And a second switch 52 for controlling the supply of the electric charge supplied from the second switch to the pulse detection system 3. The switches 51 and 52 are controlled to be switched by the CPU 34 in accordance with the X-ray dose.

[Operation of Second Embodiment] In the X-ray CT apparatus of the second embodiment, an X-ray of a known X-ray dose is made incident on the X-ray detector 22 in advance to generate a charge pulse. Counting is performed, and an X-ray dose that causes a count omission is detected. CP
U34 stores the X-ray dose that causes the count omission. The CPU 34 starts the X-ray tube 2
1 and the tube current (or tube voltage)
, The current X-ray dose is detected. Then, the second switch 52 is turned on until the current X-ray amount becomes the X-ray amount at which the count omission occurs, and the second switch 52 is turned on when the current X-ray amount becomes the X-ray amount at which the count omission occurs. The first switch 51 is turned on.

Accordingly, the X-ray detector 22 is not used until the current X-ray dose reaches the X-ray dose at which the count omission occurs.
Is supplied to the pulse detection system 3 via the second switch 52, and the count value of the charge pulse formed by the pulse detection system 3 is converted to the data processing unit 23 shown in FIG. Will be supplied. When the current X-ray amount becomes the X-ray amount at which the count omission occurs, the charge from the X-ray detector 22 is changed to the first switch 51.
, And the current value formed by the current detection system 2 is supplied to the data processing unit 23 shown in FIG. 2 as the number of X-ray photons.

"Effects of the Second Embodiment"
Immediately after the start of imaging with a small X-ray dose, the count value of the charge pulses formed by the pulse detection system 3 can be used, so that the number of photons can be accurately detected without being affected by the circuit noise of the data detection unit 1. Can also be X
When the dose increases and the X-ray dose causes a count leak in the pulse detection system 3, the current value formed by the current detection system 2 can be used, so that the number of photons can be accurately calculated without a count leak. Can be detected. Therefore, the same effects as those of the above-described first embodiment can be obtained, for example, the image quality of the reconstructed image can be improved.

The above-described embodiments are merely examples of the present invention. Therefore, the present invention is not limited to each of the embodiments. , The charge from the X-ray detector 22 is converted into a current by the integrator 14 and measured. However, this may be any circuit configuration that can measure the charge from the X-ray detector 22. Needless to say, various changes can be made according to the design and the like within a range not departing from the technical idea according to the present invention.

[0038]

The radiation imaging apparatus according to the present invention can accurately detect the number of radiation photons without being affected by the number of radiation photons incident on the radiation detection means. Therefore, the image quality of the reconstructed image can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a data detection unit provided in an X-ray CT apparatus according to a first embodiment to which a radiation imaging apparatus according to the present invention is applied.

FIG. 2 is a block diagram of the X-ray CT apparatus according to the first embodiment.

FIG. 3 is a diagram showing a positional relationship between an X-ray tube and an X-ray detector provided in a gantry rotating unit of the X-ray CT apparatus according to the first embodiment.

FIG. 4 is a diagram for explaining switching timing of each detection output of a current detection system and a pulse detection system provided in the data detection unit.

FIG. 5 is a block diagram of a main part of a modification of the X-ray CT apparatus according to the first embodiment.

FIG. 6 is a block diagram of a data detection unit provided in an X-ray CT apparatus according to a second embodiment to which the radiation imaging apparatus according to the present invention is applied.

FIG. 7 is a block diagram of a current detection system provided in a conventional X-ray CT apparatus.

FIG. 8 is a characteristic diagram showing a relationship between a current detection output of a current detection system provided in a conventional X-ray CT apparatus and an X-ray dose.

FIG. 9 is a block diagram of a pulse detection system provided in a conventional X-ray CT apparatus.

FIG. 10 is a characteristic diagram showing a relationship between a pulse detection output of a pulse detection system provided in a conventional X-ray CT apparatus and an X-ray dose.

FIG. 11 is a diagram for explaining pile-up that occurs in a pulse detection system provided in a conventional X-ray CT apparatus when an X-ray dose increases.

[Description of Signs] 1 ... Data detection unit, 2 ... Current detection system, 3 ... Pulse detection system, 4 ... Operation switching unit, 6 ... Op amp, 7 ... AD converter, 8 ... Amplifier, 9 ... Comparison reference voltage source, 10 ...
Comparator, 11 ... Counter, 12 ... Input terminal, 13
... output terminal, 14 ... integrator

Claims (8)

[Claims] 1. A radiation imaging apparatus that irradiates radiation from a radiation irradiating unit onto an object, captures a radiation image formed thereby by the radiation detecting unit, and captures a radiation image of the object, wherein the radiation detecting unit Current detection means for detecting a current value corresponding to a radiation output from the apparatus; a pulse detection means for detecting a count value of a pulse corresponding to the radiation output from the radiation detection means; and Selecting means for selecting and outputting a current value from the current detecting means or a count value of a pulse from the pulse detecting means. 2. The method according to claim 1, wherein the selecting unit counts a pulse from the pulse detecting unit when the output value of the radiation detection output is a value indicating that the current value from the current detecting unit is affected by noise. When the output value of the radiation detection output is a value indicating that the current value from the current detection means is not affected by noise, the current value from the current detection means is selected. The radiation imaging apparatus according to claim 1, wherein the radiation image is outputted. 3. The method according to claim 1, wherein the selecting unit is configured to, when the output value of the radiation detection output is a value indicating that no count omission occurs in the count value of the pulse from the pulse detecting unit, output the pulse from the pulse detecting unit. When the output value of the radiation detection output is a value indicating that the count value of the pulse from the pulse detecting means causes a count omission, the current value from the current detecting means is selected. The radiation imaging apparatus according to claim 1, wherein the radiation image is selected and output. 4. The radiation detecting means according to claim 1, wherein said current detecting means is connected to an anode side of said radiation detecting means, and said pulse detecting means is connected to a cathode side of said radiation detecting means. The radiation imaging apparatus according to claim 1. 5. A radiation imaging apparatus which irradiates radiation from a radiation irradiating unit onto an object, captures a radiation image formed thereby by the radiation detecting unit, and captures a radiation image of the object, wherein the radiation detecting unit Current detection means for detecting a current value corresponding to the radiation output from the apparatus; pulse detection means for detecting a count value of a pulse corresponding to the radiation output from the radiation detection means; radiation of the radiation applied to the object A radiation imaging apparatus, comprising: switching means for switching the radiation output from the radiation detecting means in accordance with the amount and supplying the radiation output to the current detecting means or the pulse detecting means. 6. The pulse counting means for counting pulses from the pulse detecting means when the output value of the radiation detection output is a value indicating that the current value from the current detecting means is affected by noise. And outputting a current value from the current detection means when the output value of the radiation detection output is a value indicating that the current value from the current detection means is not affected by noise. The radiation imaging apparatus according to claim 5, wherein 7. The pulse signal from the pulse detection means when the output value of the radiation detection output is a value indicating that no count omission occurs in the count value of the pulse from the pulse detection means. And outputting the current value from the current detection means when the output value of the radiation detection output is a value indicating that the count value of the pulse from the pulse detection means causes a count omission. The radiation imaging apparatus according to claim 5, wherein: 8. The radiation imaging apparatus according to claim 1, wherein the radiation detection output from the radiation detection unit is a charge corresponding to a radiation dose.