WO2018066570A1 - Radiography device, radiography system, radiography method, and program - Google Patents

Radiography device, radiography system, radiography method, and program Download PDF

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WO2018066570A1
WO2018066570A1 PCT/JP2017/036019 JP2017036019W WO2018066570A1 WO 2018066570 A1 WO2018066570 A1 WO 2018066570A1 JP 2017036019 W JP2017036019 W JP 2017036019W WO 2018066570 A1 WO2018066570 A1 WO 2018066570A1
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energy
radiation
feature amount
average
value
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野田　剛司
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キヤノン株式会社
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment

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  • the present invention relates to a radiation imaging apparatus, a radiation imaging system, a radiation imaging method, and a program.
  • FPD flat panel detectors
  • Such a radiographic apparatus is used, for example, as a digital imaging apparatus for moving image shooting such as still image shooting such as general shooting or fluoroscopic shooting in medical image diagnosis. Since FPD can process radiographic imaging information as a digital image, various applications have been put to practical use.
  • the attenuation coefficient representing the degree to which radiation is attenuated when passing through the substance varies depending on the substance.
  • the attenuation coefficient depends on the energy of radiation. Therefore, it is possible to generate an image in which two substances having different attenuation coefficients are separated by taking two images of radiation with two types of energy, obtaining two images, calculating an appropriate coefficient after logarithmic conversion, and performing a difference. it can.
  • the pixel value of FPD is proportional to the product of the energy of incident radiation and the number of photons.
  • the number of incident photons decreases for radiation with high energy, so photon noise (Poisson noise).
  • Poisson noise has the property of increasing.
  • Patent Document 1 describes a method of estimating average energy from the distribution of photon noise of radiation. However, when actually measuring the energy of incident radiation, it may not match the estimated value.
  • the radiation imaging apparatus of the present invention is a calculation means for calculating an energy feature amount of radiation from a dispersion value and an average value of pixel values of a radiographic image, and correcting fluctuations of the energy feature amount based on the average value. Correction means for calculating an average energy of the radiation.
  • FIG. 1 is a diagram illustrating a functional configuration example of the first embodiment.
  • the radiation imaging system 100 of the present invention includes a radiation tube 101, a radiation generation device 102, an FPD (radiation detection unit) 104, an FPD control unit 105, a monitor 106, an operation unit 107, an image storage unit 108, and an image processing unit 109. .
  • the radiation tube 101 irradiates the subject 103 with radiation.
  • the radiation generator 102 applies a high voltage pulse to the radiation tube 101 by pressing the exposure switch to generate radiation.
  • the FPD 104 detects radiation and outputs image data of a radiation image.
  • the FPD 104 is controlled by the FPD control unit 105 to convert the radiation that has passed through the subject 103 into visible light using a fluorescent material, and detects it with a photodiode.
  • the detected electrical signal is AD-converted and transmitted to the FPD control unit 105 as a digital image (radiation image).
  • the FPD control unit 105 includes an image storage unit 108 and an image processing unit 109 and is built in one or a plurality of computers.
  • the computer includes, for example, main control means such as a CPU and storage means such as ROM (Read Only Memory) and RAM (Random Access Memory). Further, the computer may be provided with graphic control means such as GPU (Graphics Processing Unit), communication means such as a network card, input / output means such as a keyboard, display or touch panel.
  • main control means such as a CPU and storage means such as ROM (Read Only Memory) and RAM (Random Access Memory).
  • graphic control means such as GPU (Graphics Processing Unit)
  • communication means such as a network card
  • input / output means such as a keyboard, display or touch panel.
  • these constituent units are connected by a bus or the like, and are controlled by the main control unit executing a program stored in the storage unit.
  • the monitor 106 displays the digital image received by the FPD control unit 105 and the digital image processed by the image processing unit 109, and provides the digital image for confirmation of radiography by the radiographer and diagnosis by the doctor.
  • the operation unit 107 can input an instruction to the FPD 104 or the image processing unit 109, and may include a user interface.
  • the image storage unit 108 stores the digital image output from the FPD control unit 105 and the digital image processed by the image processing unit 109.
  • the image processing unit 109 generates an average energy image from the radiation digital image captured by the FPD 104.
  • the image processing unit 109 includes a variance calculation unit (dispersion calculation unit) 110, an average value calculation unit (average value calculation unit) 111, an energy feature amount calculation unit (calculation unit) 112, a calibration table holding unit 113, and An average energy calculation unit (correction unit) 114 is provided.
  • a plurality of radiographic images captured by the FPD 104 are stored in the image storage unit 108 and transferred to the image processing unit 109 by the FPD control unit 105 (step S201).
  • step S201 the average value calculation unit 111 generates an average value image A (x, y) from the plurality of input radiation images M (x, y, t) according to the equation (1).
  • x and y are the coordinates of the pixels of the radiation image.
  • t is an integer and represents the frame number of the radiographic image taken in time series. Brackets ⁇ > t represent time averages. In this way, the average value calculation unit 111 calculates the average value of the pixel values of the radiation image.
  • step S ⁇ b> 202 the variance calculation unit 110 calculates the variance image V (x, y) from the plurality of input radiation images M (x, y, t) and the average value image A (x, y) according to Equation (2). Is generated. In this way, the variance calculation unit 110 calculates the variance of the pixel values of the radiation image.
  • step S203 the energy feature amount calculation unit 112 generates an energy feature amount image E s (x, y) according to Equation (3).
  • the energy feature amount calculation unit (calculation unit) 112 calculates the radiation energy feature amount from the variance value V (x, y) and the average value A (x, y) of the pixel values of the radiation image.
  • E s (x, y) is calculated.
  • the energy feature amount calculation unit 112 calculates the energy feature amount from the variance and the average value.
  • Equation (3) represents the average energy of radiation that has reached the FPD 104. That is, since the output is proportional to the product of the number of photons of radiation that has reached the FPD 104 and the energy of each photon, Equation (3) becomes Equation (4).
  • the fluctuation of the number of photons of radiation reaching the FPD 104 follows the Poisson distribution, and the Poisson distribution has the property that the variance is equal to the expected value. Therefore, the following relationship holds for the number N of photons of radiation that reaches the FPD 104.
  • Equation (3) is found to be an amount corresponding to the average energy E. Since the unit is different from the energy feature value E s and the energy E, by multiplying a predetermined coefficient to the energy characteristic quantity E s, the energy feature value E s may be matched with the average energy E.
  • the energy feature value E s was found to vary according to the average value of the pixel values of the radiographic image.
  • the energy feature value E s is should be constant regardless of the average value of the pixel values of the radiographic image, actual energy feature value E s It turned out that it changes according to the average value of the pixel value of a radiographic image.
  • Energy feature value E s in accordance with equation (7) is corrected by the average value A of the pixel values, the mean energy E is corrected.
  • the average energy calculation unit 114 uses the calibration table LUT2D to calculate the average energy E from the average value image based on the average value A (x, y) and the feature amount image based on the energy feature amount E s (x, y). An average energy image by (x, y) is generated.
  • the average energy calculation unit (correction unit) 114 corrects the energy feature value E s based on the calibration table LUT2D.
  • the mean energy calculation unit (correction unit) 114 by correcting on the basis of the variation of the energy feature value E s to the average value A, and calculates an average energy E of the radiation.
  • the average energy E from the energy feature value E s is not estimated uniquely, even if the energy feature value E s is changed according to the average value A of the pixel values of the radiographic image the energy feature value E s can be appropriately corrected.
  • the average energy E can be specified with high accuracy, and a high-precision average energy image can be provided.
  • average the energy E is calculated, as shown in FIG. 3, such as the approximate function relation between the average value A of the energy feature value E s and the pixel value
  • the average energy E may be calculated by using a function. (Create calibration table)
  • the calibration table LUT2D is generated based on radiographic images acquired by photographing phantoms having different thicknesses.
  • FIG. 4 is a radiation energy spectrum showing the relationship between the radiation energy and the normalized photon number when the acrylic plate as a phantom is radiographed for each thickness of the acrylic plate.
  • the peak of the radiation spectrum shifts to the higher energy side as the material through which the radiation passes becomes thicker (as the material penetration distance of the radiation becomes longer) .
  • the peak P2 is shifted to the higher energy side than the peak P1. This is called beam hardening.
  • the thicker the material through which radiation is transmitted the higher the average energy of radiation by shifting the peak of the radiation spectrum to the higher energy side by beam hardening.
  • the average energy is measured by beam hardening by changing the thickness of the acrylic plate.
  • the average energy is measured by simply changing the radiation tube voltage and changing the radiation energy. May be performed.
  • the calibration table LUT2D is generated based on the radiation image acquired by changing the tube voltage.
  • the average energy is changed by changing the acrylic thickness. ing. This is because measuring the change in the average energy by changing the thickness of the substance is closer to the change in the average energy of the radiation actually transmitted through the subject.
  • the energy feature value E s is changed according to the average value A, needs to be corrected in an amount corresponding to the energy feature value E s to the actual average energy E There is.
  • the average energy calculation unit (correction unit) 114 based on a first function representing the relationship between the energy feature value E s and the average value A, to correct for variations in energy feature value E s.
  • the first function is a higher-order function of the average value A.
  • Equation (8) a function of energy feature value E s is expressed by Equation (8).
  • Coefficients C 1 , C 2 , C 3 , and C 4 are calculated for each average energy E (43.7 keV, 48.7 keV, 51.7 keV, 53.9 keV).
  • the coefficients C 1 , C 2 , C 3 , and C 4 of the predetermined average energy E may be calculated, and the coefficients C 1 , C 2 , and C 3 may be commonly used for the other average energy E. In this case, it can be applied to various average energy E by changing C 4 according to the average energy E. Further, a coefficient commonly used for other average energy E may be calculated from coefficients C 1 , C 2 , and C 3 of a plurality of predetermined average energy E.
  • Equation (9) The relationship between the energy feature amount E s , the average value A, and the average energy E is expressed.
  • FIG. 5 shows the result of approximation with a cubic function using equation (9).
  • FIG. 6 is a graph showing the relationship between the average energy E and D (E). As shown in FIG. 6, it can be seen that D (E) changes linearly according to the average energy E. In this case, D (E) can be expressed by a linear function of average energy E as shown in Expression (10).
  • the coefficient C 4 of the zero-order term of the average value A in the cubic function (first function) of the equation (8) is a linear function (second Function).
  • Expression (11) is derived from Expression (9) and Expression (10).
  • the cubic function (first function) in equation (8) or the linear function (second function) in equation (10) is derived from the measured energy value of the radiation measured while changing the phantom or tube voltage. It is burned. As described above, the cubic function (first function) of the equation (8) or the linear function (second function) of the equation (10) is based on the energy measurement value of the radiation, and the energy feature amount E s. , The average value A, and the average energy E.
  • the average energy calculation unit (correction unit) 114 uses the coefficient C 1 of the cubic function (first function) of Expression (8) and the linear function (second function) of Expression (10). , C 2 , C 3 , L 1 , and L 2 , refer to the calibration table LUT2D. Thereby, the fluctuation
  • the average energy calculation unit (correction unit) 114 corrects the fluctuation of the energy feature amount E s by referring to a calibration table that holds the relationship between the energy feature amount E s , the average value A, and the average energy E.
  • the average energy calculation unit (correction unit) 114 has coefficients C 1 , C 2 , and C 3 of the cubic function (first function) in Expression (8) and the linear function (second function) in Expression (10). , by common L 1, L 2, on the basis of the coefficients, calculates the average energy E from the energy feature value E s and the average value a.
  • the average energy calculation unit (correction unit) 114 generates an average energy image based on the corrected energy feature value E s.
  • the average energy calculation unit 114 uses the calibration table LUT2D to calculate the average energy E (x, y) from the average value image based on the average value A (x, y) and the feature amount image based on the energy feature amount E s (x, y). ) To generate an average energy image.
  • the average energy E can be specified with high accuracy, and a high-precision average energy image can be provided.
  • an average energy image based on average energy E (x, y) is generated from an average value image based on average value A (x, y) and a feature amount image based on energy feature amount E s (x, y). Is done.
  • the average energy calculation unit (correction unit) 114 corrects the in-plane distribution of the energy feature value E s in the radiation image.
  • the in-plane distribution correction of the frame is performed on the energy feature amount E s (x, y), and the corrected energy feature amount E gs (x, y) is calculated.
  • the average energy calculation unit 114 calculates the average energy based on the average energy E (x, y) from the average value image based on the average value A (x, y) and the feature amount image based on the corrected energy feature amount E gs (x, y). Generate an image.
  • FIG. 7 is a diagram illustrating a functional configuration example of the second embodiment.
  • FIG. 8 is a flowchart showing the processing of the second embodiment. Note that a description of the same configuration, function, and operation as in the first embodiment will be omitted, and differences from the present embodiment will be mainly described.
  • the image processing unit 109 includes an in-plane distribution correction unit 115.
  • step S204 prior to applying the calibration table LUT2D in step S205, the in-plane distribution of the energy feature value E s is corrected.
  • the in-plane distribution correction unit 115 performs the in-plane distribution (spatial distribution) of the energy feature quantity E s according to the equation (12) based on the reference energy feature quantity E s0 calculated from the radiographic image taken without the subject. ) And a corrected energy feature amount E gs is calculated.
  • the energy feature amount calculation unit 112 generates an energy feature amount E s0 (x, y) from the radiographic image captured in the absence of the subject according to the equation (3).
  • the overline of E s0 is the in-plane average value (spatial average value) of the reference energy feature quantity E s0 (x, y).
  • the energy feature amount calculation unit (calculation unit) 112 calculates a reference energy feature amount E s0 (x, y) of radiation from a dispersion value and an average value of pixel values of a radiographic image captured in the absence of a subject.
  • the in-plane distribution correction unit (correction unit) 115 corrects the in-plane distribution of the energy feature amount E s based on the in-plane average value in the radiographic image of the reference energy feature amount E s0 (x, y). Accordingly, the average energy E can be calculated by applying the same calibration table LUT2D regardless of the pixel position (x, y).
  • step S205 the average energy calculation unit 114 uses the calibration table LUT2D to calculate the average energy from the average value image based on the average value A (x, y) and the feature amount image based on the corrected energy feature amount E gs (x, y). An average energy image with E (x, y) is generated.
  • the energy feature amount E gs is corrected by the average value A of the pixel values according to the equation (13) instead of the equation (7), and the average energy E is calculated.
  • the present invention can take an embodiment as a system, apparatus, method, program, storage medium, or the like. Specifically, the present invention may be applied to a system composed of a plurality of devices, or may be applied to an apparatus composed of one device.
  • the present invention supplies software (programs) for realizing the functions of the above-described embodiments to a system or apparatus via a network or various storage media, and a computer (CPU, MPU, etc.) of the system or apparatus reads the program. May be executed.
  • the present invention can also be realized by a process in which one or more processors in a computer of a system or apparatus read and execute a program, and can also be realized by a circuit (for example, an ASIC) that realizes one or more functions.

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Abstract

Provided is a radiography device with which, by correcting an energy feature value which is computed from a variance value and a mean value of pixel values of a radiographic image, it is possible to acquire a high-precision mean energy image. This radiography device comprises: a computation means which computes an energy feature value of radiation from a variance value and a mean value of pixel values of a radiographic image; and a correction means which, by correcting variations of the energy feature value on the basis of the mean value, computes the mean energy of the radiation.

Description

放射線撮影装置、放射線撮影システム、放射線撮影方法、及びプログラムRadiation imaging apparatus, radiation imaging system, radiation imaging method, and program
　本発明は、放射線撮影装置、放射線撮影システム、放射線撮影方法、及びプログラムに関するものである。 The present invention relates to a radiation imaging apparatus, a radiation imaging system, a radiation imaging method, and a program.
　現在、医療画像診断や非破壊検査に用いる放射線撮影装置として、半導体材料によって形成された平面検出器（Ｆｌａｔ　Ｐａｎｅｌ　Ｄｅｔｅｃｔｏｒ：以下「ＦＰＤ」と略す）が普及している。このような放射線撮影装置は、例えば医療画像診断においては、一般撮影のような静止画撮影や透視撮影のような動画撮影のデジタル撮影装置として用いられている。ＦＰＤは、放射線による撮影情報をデジタル画像として処理可能なため、様々なアプリケーションが実用化されている。 Currently, flat panel detectors (hereinafter referred to as “FPD”) made of semiconductor materials are widely used as radiation imaging apparatuses used for medical image diagnosis and nondestructive inspection. Such a radiographic apparatus is used, for example, as a digital imaging apparatus for moving image shooting such as still image shooting such as general shooting or fluoroscopic shooting in medical image diagnosis. Since FPD can process radiographic imaging information as a digital image, various applications have been put to practical use.
　そのうちの１つの技術として、エネルギーサブトラクションがある。一般的に、放射線が物質中を透過するときに減衰する程度を表す減弱係数は、物質によって異なる。そして、減弱係数は、放射線のエネルギーに依存する。したがって、２種類のエネルギーの放射線で撮影し２つの画像を取得し、対数変換した後に適切な係数を演算して差分することで、減弱係数の異なる２つの物質を分離した画像を生成することができる。 One of these technologies is energy subtraction. In general, the attenuation coefficient representing the degree to which radiation is attenuated when passing through the substance varies depending on the substance. The attenuation coefficient depends on the energy of radiation. Therefore, it is possible to generate an image in which two substances having different attenuation coefficients are separated by taking two images of radiation with two types of energy, obtaining two images, calculating an appropriate coefficient after logarithmic conversion, and performing a difference. it can.
　一方で、ＦＰＤの画素値は、入射放射線のエネルギーとフォトン数の積に比例するが、同じ画素値でも、エネルギーが高い放射線の場合は、入射フォトン数が少なくなるため、フォトンノイズ（ポアソンノイズ）が増大する性質がある。これを利用することで、放射線フォトン数や平均エネルギーを推定する方法が提案されている（特許文献１参照）。 On the other hand, the pixel value of FPD is proportional to the product of the energy of incident radiation and the number of photons. However, even with the same pixel value, the number of incident photons decreases for radiation with high energy, so photon noise (Poisson noise). Has the property of increasing. By utilizing this, a method for estimating the number of radiation photons and the average energy has been proposed (see Patent Document 1).
特開２０１３－２３６９６２号公報JP 2013-236862 A
　特許文献１には、放射線のフォトンノイズの分散から平均エネルギーを推定する方法が記載されている。しかしながら、実際に入射放射線のエネルギーの測定を行ってみると、推定値と一致しない場合がある。 Patent Document 1 describes a method of estimating average energy from the distribution of photon noise of radiation. However, when actually measuring the energy of incident radiation, it may not match the estimated value.
　この結果、特許文献１に記載された発明により特定の撮影条件で推定された平均エネルギーを用いて較正を行っても、正確な平均エネルギー画像を取得することができない。 As a result, an accurate average energy image cannot be acquired even if calibration is performed using the average energy estimated under specific imaging conditions according to the invention described in Patent Document 1.
　本発明の放射線撮影装置は、放射線画像の画素値の分散値と平均値から放射線のエネルギー特徴量を算出する算出手段と、前記エネルギー特徴量の変動を前記平均値に基づいて補正することにより、前記放射線の平均エネルギーを算出する補正手段と、を備える。 The radiation imaging apparatus of the present invention is a calculation means for calculating an energy feature amount of radiation from a dispersion value and an average value of pixel values of a radiographic image, and correcting fluctuations of the energy feature amount based on the average value. Correction means for calculating an average energy of the radiation.
第１の実施形態の機能構成例を示す図である。It is a figure which shows the function structural example of 1st Embodiment. 第１の実施形態の手順を示すフローチャートである。It is a flowchart which shows the procedure of 1st Embodiment. 平均値とエネルギー特徴量との関係を示す図である。It is a figure which shows the relationship between an average value and an energy feature-value. 放射線エネルギースペクトルの変化を示す図である。It is a figure which shows the change of a radiation energy spectrum. 平均値とエネルギー特徴量との関係を関数で近似した図である。It is the figure which approximated the relationship between an average value and energy feature-value with a function. 平均エネルギーと係数との関係を示す図である。It is a figure which shows the relationship between average energy and a coefficient. 第２の実施形態の機能構成例を示す図である。It is a figure which shows the function structural example of 2nd Embodiment. 第２の実施形態の手順を示すフローチャートである。It is a flowchart which shows the procedure of 2nd Embodiment.
　（第１の実施形態）
　以下、本発明の第１の実施形態について図面を参照して説明する。図１は、第１の実施形態の機能構成例を示す図である。 (First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a functional configuration example of the first embodiment.
　本発明の放射線撮影システム１００は、放射線管１０１、放射線発生装置１０２、ＦＰＤ（放射線検出部）１０４、ＦＰＤ制御部１０５、モニタ１０６、操作部１０７、画像保存部１０８、及び画像処理部１０９を備える。 The radiation imaging system 100 of the present invention includes a radiation tube 101, a radiation generation device 102, an FPD (radiation detection unit) 104, an FPD control unit 105, a monitor 106, an operation unit 107, an image storage unit 108, and an image processing unit 109. .
　放射線管１０１は、被写体１０３に放射線を照射する。放射線発生装置１０２は、曝射スイッチの押下により、放射線管１０１に高電圧パルスを与え、放射線を発生させる。ＦＰＤ１０４は、放射線を検出し、放射線画像の画像データを出力する。ＦＰＤ１０４は、ＦＰＤ制御部１０５に制御されて、被写体１０３を通過した放射線を蛍光体により可視光に変換し、フォトダイオードで検出する。検出された電気信号は、ＡＤ変換されてデジタル画像（放射線画像）として、ＦＰＤ制御部１０５に送信される。 The radiation tube 101 irradiates the subject 103 with radiation. The radiation generator 102 applies a high voltage pulse to the radiation tube 101 by pressing the exposure switch to generate radiation. The FPD 104 detects radiation and outputs image data of a radiation image. The FPD 104 is controlled by the FPD control unit 105 to convert the radiation that has passed through the subject 103 into visible light using a fluorescent material, and detects it with a photodiode. The detected electrical signal is AD-converted and transmitted to the FPD control unit 105 as a digital image (radiation image).
　ＦＰＤ制御部１０５は、画像保存部１０８及び画像処理部１０９を備え、１つ又は複数のコンピュータに内蔵される。コンピュータには、例えば、ＣＰＵなどの主制御手段、ＲＯＭ（Ｒｅａｄ　Ｏｎｌｙ　Ｍｅｍｏｒｙ）、ＲＡＭ（Ｒａｎｄｏｍ　Ａｃｃｅｓｓ　Ｍｅｍｏｒｙ）などの記憶手段が具備される。また、コンピュータには、ＧＰＵ（Ｇｒａｐｈｉｃｓ　Ｐｒｏｃｅｓｓｉｎｇ　Ｕｎｉｔ）などのグラフィック制御手段、ネットワークカード等の通信手段、キーボード、ディスプレイ又はタッチパネルなどの入出力手段などが具備されていてもよい。 The FPD control unit 105 includes an image storage unit 108 and an image processing unit 109 and is built in one or a plurality of computers. The computer includes, for example, main control means such as a CPU and storage means such as ROM (Read Only Memory) and RAM (Random Access Memory). Further, the computer may be provided with graphic control means such as GPU (Graphics Processing Unit), communication means such as a network card, input / output means such as a keyboard, display or touch panel.
　なお、これら各構成手段は、バスなどにより接続され、記憶手段に記憶されたプログラムを主制御手段が実行することで制御される。 Note that these constituent units are connected by a bus or the like, and are controlled by the main control unit executing a program stored in the storage unit.
　モニタ１０６は、ＦＰＤ制御部１０５で受信されたデジタル画像や画像処理部１０９で画像処理されたデジタル画像を表示し、放射線撮影技師の撮影確認や医師の診断用にデジタル画像を供する。 The monitor 106 displays the digital image received by the FPD control unit 105 and the digital image processed by the image processing unit 109, and provides the digital image for confirmation of radiography by the radiographer and diagnosis by the doctor.
　操作部１０７は、ＦＰＤ１０４や画像処理部１０９に指示を入力することができ、ユーザーインターフェイスを具備してもよい。画像保存部１０８は、ＦＰＤ制御部１０５から出力されたデジタル画像や画像処理部１０９で画像処理されたデジタル画像を保存する。 The operation unit 107 can input an instruction to the FPD 104 or the image processing unit 109, and may include a user interface. The image storage unit 108 stores the digital image output from the FPD control unit 105 and the digital image processed by the image processing unit 109.
　画像処理部１０９は、ＦＰＤ１０４で撮影された放射線デジタル画像から平均エネルギー画像を生成する。その構成として、画像処理部１０９は、分散計算部（分散算出部）１１０、平均値計算部（平均値算出部）１１１、エネルギー特徴量計算部（算出部）１１２、較正テーブル保持部１１３、及び平均エネルギー計算部（補正部）１１４を具備する。 The image processing unit 109 generates an average energy image from the radiation digital image captured by the FPD 104. As its configuration, the image processing unit 109 includes a variance calculation unit (dispersion calculation unit) 110, an average value calculation unit (average value calculation unit) 111, an energy feature amount calculation unit (calculation unit) 112, a calibration table holding unit 113, and An average energy calculation unit (correction unit) 114 is provided.
　次に、本実施形態の処理について、図２に示すフローチャートを用いて詳細に説明する。 Next, the processing of this embodiment will be described in detail using the flowchart shown in FIG.
　＜平均エネルギーＥの推定＞
　ＦＰＤ制御部１０５によって、ＦＰＤ１０４で撮影された複数の放射線画像は画像保存部１０８に保存されるとともに画像処理部１０９に転送される（ステップＳ２０１）。 <Estimation of average energy E>
A plurality of radiographic images captured by the FPD 104 are stored in the image storage unit 108 and transferred to the image processing unit 109 by the FPD control unit 105 (step S201).
　ステップＳ２０１では、平均値計算部１１１は、入力された複数の放射線画像Ｍ（ｘ，ｙ，ｔ）から、式（１）に従い、平均値画像Ａ（ｘ，ｙ）を生成する。ここで、ｘとｙは放射線画像の画素の座標である。ｔは、整数であり、時系列に撮影された放射線画像のフレーム番号を表す。ブラケット＜＞ｔは、時間平均を表す。このように、平均値計算部１１１は、放射線画像の画素値の平均値を算出する。 In step S201, the average value calculation unit 111 generates an average value image A (x, y) from the plurality of input radiation images M (x, y, t) according to the equation (1). Here, x and y are the coordinates of the pixels of the radiation image. t is an integer and represents the frame number of the radiographic image taken in time series. Brackets <> t represent time averages. In this way, the average value calculation unit 111 calculates the average value of the pixel values of the radiation image.
Figure JPOXMLDOC01-appb-M000001
Figure JPOXMLDOC01-appb-M000001
　ステップＳ２０２では、分散計算部１１０は、入力された複数の放射線画像Ｍ（ｘ，ｙ，ｔ）と平均値画像Ａ（ｘ，ｙ）から式（２）に従い、分散画像Ｖ（ｘ，ｙ）を生成する。このように、分散計算部１１０は、放射線画像の画素値の分散を算出する。 In step S <b> 202, the variance calculation unit 110 calculates the variance image V (x, y) from the plurality of input radiation images M (x, y, t) and the average value image A (x, y) according to Equation (2). Is generated. In this way, the variance calculation unit 110 calculates the variance of the pixel values of the radiation image.
Figure JPOXMLDOC01-appb-M000002
Figure JPOXMLDOC01-appb-M000002
　ステップＳ２０３では、エネルギー特徴量計算部１１２は、式（３）に従い、エネルギー特徴量画像Ｅｓ（ｘ，ｙ）を生成する。式（３）に示すように、エネルギー特徴量計算部（算出部）１１２は、放射線画像の画素値の分散値Ｖ（ｘ，ｙ）と平均値Ａ（ｘ，ｙ）から放射線のエネルギー特徴量Ｅｓ（ｘ，ｙ）を算出する。このように、エネルギー特徴量計算部１１２は、分散と平均値からエネルギー特徴量を算出する。 In step S203, the energy feature amount calculation unit 112 generates an energy feature amount image E s (x, y) according to Equation (3). As shown in Expression (3), the energy feature amount calculation unit (calculation unit) 112 calculates the radiation energy feature amount from the variance value V (x, y) and the average value A (x, y) of the pixel values of the radiation image. E s (x, y) is calculated. As described above, the energy feature amount calculation unit 112 calculates the energy feature amount from the variance and the average value.
Figure JPOXMLDOC01-appb-M000003
Figure JPOXMLDOC01-appb-M000003
　特許文献１にも開示されているように、式（３）は、ＦＰＤ１０４に到達した放射線の平均エネルギーを表す。つまり、ＦＰＤ１０４に到達した放射線のフォトン数と各フォトンが持っているエネルギーの積に比例した出力をするため、式（３）は式（４）となる。 As disclosed in Patent Document 1, Equation (3) represents the average energy of radiation that has reached the FPD 104. That is, since the output is proportional to the product of the number of photons of radiation that has reached the FPD 104 and the energy of each photon, Equation (3) becomes Equation (4).
Figure JPOXMLDOC01-appb-M000004
Figure JPOXMLDOC01-appb-M000004
　また、ＦＰＤ１０４に到達する放射線のフォトン数のゆらぎは、ポアソン分布に従い、ポアソン分布は、期待値と分散が等しい性質がある。したがって、ＦＰＤ１０４に到達した放射線のフォトン数Ｎには、以下の関係が成り立つ。 Further, the fluctuation of the number of photons of radiation reaching the FPD 104 follows the Poisson distribution, and the Poisson distribution has the property that the variance is equal to the expected value. Therefore, the following relationship holds for the number N of photons of radiation that reaches the FPD 104.
Figure JPOXMLDOC01-appb-M000005
Figure JPOXMLDOC01-appb-M000005
　ここで、式（４）の分母を式（５）で置き換えると、式（６）となり、式（３）のエネルギー特徴量Ｅｓは、平均エネルギーＥに相当する量であることがわかる。なお、エネルギー特徴量ＥｓとエネルギーＥとは単位が異なるため、エネルギー特徴量Ｅｓに所定の係数を乗算することにより、エネルギー特徴量Ｅｓを平均エネルギーＥに一致させてもよい。 Here, by replacing the denominator of Equation (4) in equation (5), equation (6), and the energy feature value E s of Equation (3) is found to be an amount corresponding to the average energy E. Since the unit is different from the energy feature value E s and the energy E, by multiplying a predetermined coefficient to the energy characteristic quantity E s, the energy feature value E s may be matched with the average energy E.
Figure JPOXMLDOC01-appb-M000006
Figure JPOXMLDOC01-appb-M000006
　しかしながら、実際にＦＰＤ１０４がエネルギー特徴量Ｅｓを計算すると、図３に示すように、エネルギー特徴量Ｅｓは、放射線画像の画素値の平均値に応じて変化することがわかった。 However, when actually FPD104 calculates the energy feature value E s, as shown in FIG. 3, the energy feature value E s was found to vary according to the average value of the pixel values of the radiographic image.
　＜エネルギー特徴量Ｅｓの補正＞
　図３は、放射線画像の画素値の平均値ＬＳＢとエネルギー特徴量Ｅｓとの関係を、実際の放射線の平均エネルギーＥ（４３．７ｋｅＶ，４８．７ｋｅＶ，５１．７ｋｅＶ，５３．９ｋｅＶ）ごとにプロットしたグラフである。それぞれの平均エネルギーＥは、エネルギースペクトロメーターを用いて測定した値である。 <Correction of energy feature value E s>
3, the relationship between the average value LSB and energy feature value E s of pixel values of the radiographic image, the actual radiation mean energy E (43.7keV, 48.7keV, 51.7keV, 53.9keV) per the This is a plotted graph. Each average energy E is a value measured using an energy spectrometer.
　式（６）によれば、平均エネルギーＥが一定である場合、エネルギー特徴量Ｅｓは、放射線画像の画素値の平均値にかかわらず一定となるはずであるが、実際のエネルギー特徴量Ｅｓは、放射線画像の画素値の平均値に応じて変化することがわかった。 According to equation (6), if the average energy E is constant, the energy feature value E s is should be constant regardless of the average value of the pixel values of the radiographic image, actual energy feature value E s It turned out that it changes according to the average value of the pixel value of a radiographic image.
　すなわち、平均エネルギーＥを特定するためには、エネルギー特徴量Ｅｓを補正する必要がある。一般に、ＦＰＤ１０４の内部では、放射線フォトンを蛍光体により可視光に変換してから、フォトダイオードで受光し、電子へ変換する複雑な物理過程を経るため、式（６）では、正確な平均エネルギーＥが算出されないと考えられる。 That is, in order to identify the average energy E, it is necessary to correct the energy feature value E s. In general, in the FPD 104, a complicated physical process of converting radiation photons into visible light by a phosphor, receiving light by a photodiode, and converting it into electrons is performed. Is not calculated.
　そこで、本発明では、この課題を解決して、平均エネルギーＥを高い精度で推定するため、図３のような放射線画像の画素値の平均値とエネルギー特徴量Ｅｓとの関係を較正テーブル（２軸エネルギー較正テーブル）ＬＵＴ２Ｄで表す。較正テーブルＬＵＴ２Ｄを参照して、エネルギー特徴量Ｅｓは画素値の平均値Ａにより補正される。較正テーブルＬＵＴ２Ｄは、較正テーブル保持部１１３に保存される。較正テーブル保持部１１３は、算出されたエネルギー特徴量Ｅｓの変動を補正するための較正テーブルＬＵＴ２Ｄを保持する。 Therefore, in the present invention, to solve this problem, in order to estimate the average energy E with high accuracy, calibrate the relationship between the average value and the energy feature value E s of pixel values of the radiographic image, such as the table of FIG. 3 ( Biaxial energy calibration table) LUT2D. With reference to the calibration table LUT2D, energy feature value E s is corrected by the average value A of the pixel values. The calibration table LUT2D is stored in the calibration table holding unit 113. Calibration table holding unit 113 holds the calibration table LUT2D for correcting the variation of the calculated energy feature value E s.
　エネルギー特徴量Ｅｓは、式（７）に従い、画素値の平均値Ａにより補正され、平均エネルギーＥが補正される。 Energy feature value E s in accordance with equation (7), is corrected by the average value A of the pixel values, the mean energy E is corrected.
Figure JPOXMLDOC01-appb-M000007
Figure JPOXMLDOC01-appb-M000007
　ステップＳ２０５では、平均エネルギー計算部１１４は、較正テーブルＬＵＴ２Ｄを用いて、平均値Ａ（ｘ，ｙ）による平均値画像とエネルギー特徴量Ｅｓ（ｘ，ｙ）による特徴量画像から、平均エネルギーＥ（ｘ，ｙ）による平均エネルギー画像を生成する。平均エネルギー計算部（補正部）１１４は、較正テーブルＬＵＴ２Ｄに基づいてエネルギー特徴量Ｅｓを補正する。このように、平均エネルギー計算部（補正部）１１４は、エネルギー特徴量Ｅｓの変動を平均値Ａに基づいて補正することにより、放射線の平均エネルギーＥを算出する。 In step S205, the average energy calculation unit 114 uses the calibration table LUT2D to calculate the average energy E from the average value image based on the average value A (x, y) and the feature amount image based on the energy feature amount E s (x, y). An average energy image by (x, y) is generated. The average energy calculation unit (correction unit) 114 corrects the energy feature value E s based on the calibration table LUT2D. Thus, the mean energy calculation unit (correction unit) 114, by correcting on the basis of the variation of the energy feature value E s to the average value A, and calculates an average energy E of the radiation.
　これにより、図３のように、エネルギー特徴量Ｅｓから平均エネルギーＥが一意に推定されず、エネルギー特徴量Ｅｓが放射線画像の画素値の平均値Ａに応じて変化する場合であっても、エネルギー特徴量Ｅｓを適切に補正することができる。この結果、高精度で平均エネルギーＥを特定し、高精度の平均エネルギー画像を提供することができる。 Thus, as shown in FIG. 3, the average energy E from the energy feature value E s is not estimated uniquely, even if the energy feature value E s is changed according to the average value A of the pixel values of the radiographic image the energy feature value E s can be appropriately corrected. As a result, the average energy E can be specified with high accuracy, and a high-precision average energy image can be provided.
　なお、本実施形態では、較正テーブルＬＵＴ２Ｄを参照して、平均エネルギーＥが算出されるが、図３のような、エネルギー特徴量Ｅｓと画素値の平均値Ａとの関係を近似関数などの関数で表し、関数を用いることで、平均エネルギーＥが算出されてもよい。
　（較正テーブルの作成） In the present embodiment, with reference to the calibration table LUT2D, average the energy E is calculated, as shown in FIG. 3, such as the approximate function relation between the average value A of the energy feature value E s and the pixel value The average energy E may be calculated by using a function.
(Create calibration table)
　次に、ステップＳ２０５で用いられる較正テーブルＬＵＴ２Ｄの作成について詳細に説明する。較正テーブルＬＵＴ２Ｄは、厚さが異なるファントムを撮影して取得された放射線画像に基づいて生成される。図４は、ファントムであるアクリル板を放射線撮影した際の放射線エネルギーと正規化フォトン数の関係をアクリル板の厚さごとに表した放射線エネルギースペクトルである。 Next, the creation of the calibration table LUT2D used in step S205 will be described in detail. The calibration table LUT2D is generated based on radiographic images acquired by photographing phantoms having different thicknesses. FIG. 4 is a radiation energy spectrum showing the relationship between the radiation energy and the normalized photon number when the acrylic plate as a phantom is radiographed for each thickness of the acrylic plate.
　図４に示すように、放射線スペクトルは、アクリル板が厚くなるにつれて、放射線エネルギーが低いほど、正規化フォトン数が少なくなり、放射線を減弱する。放射線エネルギーが低い放射線ほど物質中を透過するときに減衰するため、放射線スペクトルのピークは、放射線が透過する物質が厚くなるにつれて（放射線の物質透過距離が長くなるにつれて）、高エネルギー側にシフトする。図４では、ピークＰ１よりもピークＰ２のほうが、高エネルギー側にシフトしている。これをビームハードニング（線質硬化）と呼ぶ。 As shown in FIG. 4, in the radiation spectrum, as the acrylic plate becomes thicker, the lower the radiation energy, the smaller the number of normalized photons and the less the radiation. Since the radiation with lower radiation energy attenuates when passing through the material, the peak of the radiation spectrum shifts to the higher energy side as the material through which the radiation passes becomes thicker (as the material penetration distance of the radiation becomes longer) . In FIG. 4, the peak P2 is shifted to the higher energy side than the peak P1. This is called beam hardening.
　したがって、放射線が透過する物質が厚くなるほど、ビームハードニングにより放射線スペクトルのピークが高エネルギー側にシフトすることで、放射線の平均エネルギーが高くなる。 Therefore, the thicker the material through which radiation is transmitted, the higher the average energy of radiation by shifting the peak of the radiation spectrum to the higher energy side by beam hardening.
　なお、本実施形態ではアクリル板の厚さを変化させて、ビームハードニングにより平均エネルギーの測定を行っているが、単純に放射線管電圧を変化させて放射線エネルギーを変化させることにより平均エネルギーの測定を行ってもよい。較正テーブルＬＵＴ２Ｄは、管電圧を変化させて取得された放射線画像に基づいて生成される。 In this embodiment, the average energy is measured by beam hardening by changing the thickness of the acrylic plate. However, the average energy is measured by simply changing the radiation tube voltage and changing the radiation energy. May be performed. The calibration table LUT2D is generated based on the radiation image acquired by changing the tube voltage.
　ただし、放射線管電圧の変化による平均エネルギーの変化とビームハードングによる平均エネルギーの変化では、放射線スペクトル形状の変化が異なるため、本実施形態では、アクリルの厚さを変化させて平均エネルギーを変化させている。物質の厚さを変化させて平均エネルギーの変化を測定するほうが、実際に被写体を透過した放射線の平均エネルギーの変化に近いからである。 However, since the change in the shape of the radiation spectrum differs between the change in average energy due to the change in radiation tube voltage and the change in average energy due to beam hardening, in this embodiment, the average energy is changed by changing the acrylic thickness. ing. This is because measuring the change in the average energy by changing the thickness of the substance is closer to the change in the average energy of the radiation actually transmitted through the subject.
　前述したように、平均エネルギーＥが一定であっても、エネルギー特徴量Ｅｓが平均値Ａに応じて変化するため、エネルギー特徴量Ｅｓを実際の平均エネルギーＥに相当する量に補正する必要がある。 As described above, it is an average energy E is constant, the energy feature value E s is changed according to the average value A, needs to be corrected in an amount corresponding to the energy feature value E s to the actual average energy E There is.
　そこで、図５に示すように、平均値Ａに対するエネルギー特徴量Ｅｓの挙動を関数で近似する。平均エネルギー計算部（補正部）１１４は、エネルギー特徴量Ｅｓと平均値Ａとの関係を表す第１の関数に基づいて、エネルギー特徴量Ｅｓの変動を補正する。第１の関数は、平均値Ａの高次関数である。 Therefore, as shown in FIG. 5, to approximate the behavior of the energy feature value E s to the average value A in the function. The average energy calculation unit (correction unit) 114, based on a first function representing the relationship between the energy feature value E s and the average value A, to correct for variations in energy feature value E s. The first function is a higher-order function of the average value A.
本実施形態では、図５に示すように、図３でプロットされた点を平均値Ａの３次関数（第１の関数）でそれぞれ近似する。この場合、エネルギー特徴量Ｅｓの関数は式（８）で表される。 In this embodiment, as shown in FIG. 5, the points plotted in FIG. 3 are approximated by a cubic function (first function) of average value A, respectively. In this case, a function of energy feature value E s is expressed by Equation (8).
Figure JPOXMLDOC01-appb-M000008
Figure JPOXMLDOC01-appb-M000008
　平均エネルギーＥ（４３．７ｋｅＶ，４８．７ｋｅＶ，５１．７ｋｅＶ，５３．９ｋｅＶ）ごとにそれぞれの係数Ｃ１，Ｃ２，Ｃ３，Ｃ４を算出する。 Coefficients C 1 , C 2 , C 3 , and C 4 are calculated for each average energy E (43.7 keV, 48.7 keV, 51.7 keV, 53.9 keV).
　また、所定の平均エネルギーＥの係数Ｃ１，Ｃ２，Ｃ３，Ｃ４を算出し、係数Ｃ１，Ｃ２，Ｃ３を他の平均エネルギーＥに共通に用いてもよい。この場合、平均エネルギーＥに応じてＣ４を変化させることで様々な平均エネルギーＥに適用することができる。また、所定の複数の平均エネルギーＥの係数Ｃ１，Ｃ２，Ｃ３から、他の平均エネルギーＥに共通に用いられる係数を算出してもよい。 Further, the coefficients C 1 , C 2 , C 3 , and C 4 of the predetermined average energy E may be calculated, and the coefficients C 1 , C 2 , and C 3 may be commonly used for the other average energy E. In this case, it can be applied to various average energy E by changing C 4 according to the average energy E. Further, a coefficient commonly used for other average energy E may be calculated from coefficients C 1 , C 2 , and C 3 of a plurality of predetermined average energy E.
　本実施形態では、平均エネルギーＥに共通に用いられる係数Ｃ１，Ｃ２，Ｃ３を算出し、平均エネルギーＥに依存する係数Ｃ４をＤとして、式（９）によりエネルギー特徴量Ｅｓが表され、エネルギー特徴量Ｅｓ、平均値Ａ、及び平均エネルギーＥの関係が表される。 In the present embodiment, to calculate the average coefficients C 1 commonly used for energy E, C 2, C 3, the coefficient C 4 which depends on the average energy E as D, the energy feature value E s by Equation (9) The relationship between the energy feature amount E s , the average value A, and the average energy E is expressed.
Figure JPOXMLDOC01-appb-M000009
Figure JPOXMLDOC01-appb-M000009
　図５は、式（９）用いて３次関数で近似した結果である。図６は、平均エネルギーＥとＤ（Ｅ）との関係を示すグラフである。図６に示すように、Ｄ（Ｅ）は、平均エネルギーＥに応じて線形に変化することがわかる。この場合、式（１０）に示すように、Ｄ（Ｅ）は、平均エネルギーＥの１次関数で表すことができる。 FIG. 5 shows the result of approximation with a cubic function using equation (9). FIG. 6 is a graph showing the relationship between the average energy E and D (E). As shown in FIG. 6, it can be seen that D (E) changes linearly according to the average energy E. In this case, D (E) can be expressed by a linear function of average energy E as shown in Expression (10).
Figure JPOXMLDOC01-appb-M000010
Figure JPOXMLDOC01-appb-M000010
　式（１０）に示すように、式（８）の３次関数（第１の関数）における平均値Ａの０次項の係数Ｃ４は、平均エネルギーＥを変数とする１次関数（第２の関数）である。式（９）及び式（１０）から式（１１）が導かれる。 As shown in the equation (10), the coefficient C 4 of the zero-order term of the average value A in the cubic function (first function) of the equation (8) is a linear function (second Function). Expression (11) is derived from Expression (9) and Expression (10).
Figure JPOXMLDOC01-appb-M000011
Figure JPOXMLDOC01-appb-M000011
　式（８）の３次関数（第１の関数）又は式（１０）の１次関数（第２の関数）は、ファントムや管電圧などを変化させながら測定された放射線のエネルギー測定値から導かれる。前述のように、式（８）の３次関数（第１の関数）又は式（１０）の１次関数（第２の関数）は、放射線のエネルギー測定値に基づいて、エネルギー特徴量Ｅｓ、平均値Ａ、及び平均エネルギーＥの関係を近似する関数である。 The cubic function (first function) in equation (8) or the linear function (second function) in equation (10) is derived from the measured energy value of the radiation measured while changing the phantom or tube voltage. It is burned. As described above, the cubic function (first function) of the equation (8) or the linear function (second function) of the equation (10) is based on the energy measurement value of the radiation, and the energy feature amount E s. , The average value A, and the average energy E.
　予め算出された係数、Ｃ１，Ｃ２，Ｃ３，Ｌ１，Ｌ２に基づいて、較正テーブルＬＵＴ２Ｄが作成される。較正テーブル保持部１１３に保存された較正テーブルＬＵＴ２Ｄを参照し、式（１１）にエネルギー特徴量Ｅｓ及び平均値Ａを入力すると、較正された平均エネルギーＥが算出され、高精度のエネルギー較正が可能になる。 Previously calculated coefficients, based on C 1, C 2, C 3 , L 1, L 2, calibration table LUT2D is created. Referring to a calibration table LUT2D stored in a calibration table holding unit 113, entering the energy feature value E s and the average value A in the equation (11), calibrated average energy E is calculated, the energy calibration of high-precision It becomes possible.
　前述のステップＳ２０５で、平均エネルギー計算部（補正部）１１４は、式（８）の３次関数（第１の関数）及び式（１０）の１次関数（第２の関数）の係数Ｃ１，Ｃ２，Ｃ３，Ｌ１，Ｌ２を保持する較正テーブルＬＵＴ２Ｄを参照する。これにより、エネルギー特徴量の変動が補正される。 In step S205 described above, the average energy calculation unit (correction unit) 114 uses the coefficient C 1 of the cubic function (first function) of Expression (8) and the linear function (second function) of Expression (10). , C 2 , C 3 , L 1 , and L 2 , refer to the calibration table LUT2D. Thereby, the fluctuation | variation of an energy feature-value is correct | amended.
　平均エネルギー計算部（補正部）１１４は、エネルギー特徴量Ｅｓ、平均値Ａ、及び平均エネルギーＥの関係を保持する較正テーブルを参照することにより、エネルギー特徴量Ｅｓの変動を補正する。 The average energy calculation unit (correction unit) 114 corrects the fluctuation of the energy feature amount E s by referring to a calibration table that holds the relationship between the energy feature amount E s , the average value A, and the average energy E.
　平均エネルギー計算部（補正部）１１４は、式（８）の３次関数（第１の関数）及び式（１０）の１次関数（第２の関数）の係数Ｃ１，Ｃ２，Ｃ３，Ｌ１，Ｌ２を共通させて、係数に基づいて、エネルギー特徴量Ｅｓ及び平均値Ａから平均エネルギーＥを算出する。 The average energy calculation unit (correction unit) 114 has coefficients C 1 , C 2 , and C 3 of the cubic function (first function) in Expression (8) and the linear function (second function) in Expression (10). , by common L 1, L 2, on the basis of the coefficients, calculates the average energy E from the energy feature value E s and the average value a.
　平均エネルギー計算部（補正部）１１４は、補正されたエネルギー特徴量Ｅｓに基づいて平均エネルギー画像を生成する。平均エネルギー計算部１１４は、較正テーブルＬＵＴ２Ｄを用いて、平均値Ａ（ｘ，ｙ）による平均値画像とエネルギー特徴量Ｅｓ（ｘ，ｙ）による特徴量画像から、平均エネルギーＥ（ｘ，ｙ）による平均エネルギー画像を生成する。この結果、高精度で平均エネルギーＥを特定し、高精度の平均エネルギー画像を提供することができる。 The average energy calculation unit (correction unit) 114 generates an average energy image based on the corrected energy feature value E s. The average energy calculation unit 114 uses the calibration table LUT2D to calculate the average energy E (x, y) from the average value image based on the average value A (x, y) and the feature amount image based on the energy feature amount E s (x, y). ) To generate an average energy image. As a result, the average energy E can be specified with high accuracy, and a high-precision average energy image can be provided.
　（第２の実施形態）
　第１の実施形態では、平均値Ａ（ｘ，ｙ）による平均値画像とエネルギー特徴量Ｅｓ（ｘ，ｙ）による特徴量画像から、平均エネルギーＥ（ｘ，ｙ）による平均エネルギー画像が生成される。 (Second Embodiment)
In the first embodiment, an average energy image based on average energy E (x, y) is generated from an average value image based on average value A (x, y) and a feature amount image based on energy feature amount E s (x, y). Is done.
　第２の実施形態では、平均エネルギー計算部（補正部）１１４は、放射線画像におけるエネルギー特徴量Ｅｓの面内分布を補正する。エネルギー特徴量Ｅｓ（ｘ，ｙ）にフレームの面内分布補正を施し、補正エネルギー特徴量Ｅｇｓ（ｘ，ｙ）が算出される。そして、平均エネルギー計算部１１４は、平均値Ａ（ｘ，ｙ）による平均値画像と補正エネルギー特徴量Ｅｇｓ（ｘ，ｙ）による特徴量画像から、平均エネルギーＥ（ｘ，ｙ）による平均エネルギー画像を生成する。 In the second embodiment, the average energy calculation unit (correction unit) 114 corrects the in-plane distribution of the energy feature value E s in the radiation image. The in-plane distribution correction of the frame is performed on the energy feature amount E s (x, y), and the corrected energy feature amount E gs (x, y) is calculated. Then, the average energy calculation unit 114 calculates the average energy based on the average energy E (x, y) from the average value image based on the average value A (x, y) and the feature amount image based on the corrected energy feature amount E gs (x, y). Generate an image.
　＜エネルギー特徴量Ｅｓの面内分布補正＞
　図７は、第２の実施形態の機能構成例を示す図である。図８は、第２の実施形態の処理を示すフローチャートである。なお、第１の実施形態と同様の構成、機能、及び動作についての説明は省略し、主に本実施形態との差異について説明する。 <Plane distribution correcting the energy feature value E s>
FIG. 7 is a diagram illustrating a functional configuration example of the second embodiment. FIG. 8 is a flowchart showing the processing of the second embodiment. Note that a description of the same configuration, function, and operation as in the first embodiment will be omitted, and differences from the present embodiment will be mainly described.
　画像処理部１０９は、面内分布補正部１１５を具備する。ステップＳ２０４では、ステップＳ２０５で較正テーブルＬＵＴ２Ｄを適用する前に、エネルギー特徴量Ｅｓの面内分布が補正される。面内分布補正部１１５が、被写体がない状態で撮影された放射線画像から算出された基準エネルギー特徴量Ｅｓ０に基づいて、式（１２）に従い、エネルギー特徴量Ｅｓの面内分布（空間分布）を補正し、補正エネルギー特徴量Ｅｇｓを算出する。 The image processing unit 109 includes an in-plane distribution correction unit 115. In step S204, prior to applying the calibration table LUT2D in step S205, the in-plane distribution of the energy feature value E s is corrected. The in-plane distribution correction unit 115 performs the in-plane distribution (spatial distribution) of the energy feature quantity E s according to the equation (12) based on the reference energy feature quantity E s0 calculated from the radiographic image taken without the subject. ) And a corrected energy feature amount E gs is calculated.
Figure JPOXMLDOC01-appb-M000012
Figure JPOXMLDOC01-appb-M000012
　エネルギー特徴量計算部１１２は、式（３）に従い、被写体がない状態で撮影された放射線画像からエネルギー特徴量Ｅｓ０（ｘ，ｙ）を生成する。ここで、Ｅｓ０のオーバーラインは、基準エネルギー特徴量Ｅｓ０（ｘ，ｙ）の面内平均値（空間平均値）である。 The energy feature amount calculation unit 112 generates an energy feature amount E s0 (x, y) from the radiographic image captured in the absence of the subject according to the equation (3). Here, the overline of E s0 is the in-plane average value (spatial average value) of the reference energy feature quantity E s0 (x, y).
　エネルギー特徴量計算部（算出部）１１２は、被写体がない状態で撮影された放射線画像の画素値の分散値と平均値から放射線の基準エネルギー特徴量Ｅｓ０（ｘ，ｙ）を算出する。面内分布補正部（補正部）１１５は、基準エネルギー特徴量Ｅｓ０（ｘ，ｙ）の放射線画像における面内平均値に基づいて、エネルギー特徴量Ｅｓの面内分布を補正する。これにより、画素の位置（ｘ，ｙ）にかかわらず、同じ較正テーブルＬＵＴ２Ｄを適用することで、平均エネルギーＥの算出が可能になる。 The energy feature amount calculation unit (calculation unit) 112 calculates a reference energy feature amount E s0 (x, y) of radiation from a dispersion value and an average value of pixel values of a radiographic image captured in the absence of a subject. The in-plane distribution correction unit (correction unit) 115 corrects the in-plane distribution of the energy feature amount E s based on the in-plane average value in the radiographic image of the reference energy feature amount E s0 (x, y). Accordingly, the average energy E can be calculated by applying the same calibration table LUT2D regardless of the pixel position (x, y).
　ステップＳ２０５では、平均エネルギー計算部１１４は、較正テーブルＬＵＴ２Ｄを用いて、平均値Ａ（ｘ，ｙ）による平均値画像と補正エネルギー特徴量Ｅｇｓ（ｘ，ｙ）による特徴量画像から、平均エネルギーＥ（ｘ，ｙ）による平均エネルギー画像を生成する。 In step S205, the average energy calculation unit 114 uses the calibration table LUT2D to calculate the average energy from the average value image based on the average value A (x, y) and the feature amount image based on the corrected energy feature amount E gs (x, y). An average energy image with E (x, y) is generated.
　つまり、本実施形態では、エネルギー特徴量Ｅｇｓが、式（７）の代わりに式（１３）に従い、画素値の平均値Ａにより補正され、平均エネルギーＥが算出される。 That is, in the present embodiment, the energy feature amount E gs is corrected by the average value A of the pixel values according to the equation (13) instead of the equation (7), and the average energy E is calculated.
Figure JPOXMLDOC01-appb-M000013
Figure JPOXMLDOC01-appb-M000013
　以上が本発明の代表的な実施形態の例であるが、本発明は、上記及び図面に示す実施形態に限定することなく、その要旨を変更しない範囲内で適宜変形して実施できるものである。 The above is an example of a typical embodiment of the present invention, but the present invention is not limited to the embodiment described above and shown in the drawings, and can be appropriately modified and implemented within the scope not changing the gist thereof. .
　また、本発明は、例えば、システム、装置、方法、プログラム、若しくは記憶媒体などとしての実施態様を採ることもできる。具体的には、複数の機器から構成されるシステムに適用してもよいし、また、１つの機器からなる装置に適用してもよい。 Also, the present invention can take an embodiment as a system, apparatus, method, program, storage medium, or the like. Specifically, the present invention may be applied to a system composed of a plurality of devices, or may be applied to an apparatus composed of one device.
　本発明は、上記の実施形態の機能を実現するソフトウェア（プログラム）をネットワーク又は各種記憶媒体を介してシステム又は装置に供給し、システム又は装置のコンピュータ（ＣＰＵやＭＰＵなど）がプログラムを読み出すことにより実行されてもよい。また、本発明は、システム又は装置のコンピュータにおける１つ以上のプロセッサーがプログラムを読出し実行する処理でも実現可能であり、１以上の機能を実現する回路（例えば、ＡＳＩＣ）によっても実現可能である。 The present invention supplies software (programs) for realizing the functions of the above-described embodiments to a system or apparatus via a network or various storage media, and a computer (CPU, MPU, etc.) of the system or apparatus reads the program. May be executed. The present invention can also be realized by a process in which one or more processors in a computer of a system or apparatus read and execute a program, and can also be realized by a circuit (for example, an ASIC) that realizes one or more functions.
　本発明は上記実施の形態に制限されるものではなく、本発明の精神及び範囲から離脱することなく、様々な変更及び変形が可能である。従って、本発明の範囲を公にするために以下の請求項を添付する。 The present invention is not limited to the above embodiment, and various changes and modifications can be made without departing from the spirit and scope of the present invention. Therefore, in order to make the scope of the present invention public, the following claims are attached.
　この出願は２０１６年１０月６日に出願された日本国特許出願第２０１６－１９８４６８からの優先権を主張するものであり、その内容を引用してこの出願の一部とするものである。 This application claims priority from Japanese Patent Application No. 2016-198468 filed on Oct. 6, 2016, the contents of which are incorporated herein by reference.

Claims (18)

  1. 　放射線画像の画素値の分散値と平均値から放射線のエネルギー特徴量を算出する算出手段と、
    　前記エネルギー特徴量の変動を前記平均値に基づいて補正することにより、前記放射線の平均エネルギーを算出する補正手段と、
    　を備えることを特徴とする放射線撮影装置。     A calculation means for calculating an energy feature amount of radiation from a dispersion value and an average value of pixel values of the radiation image;
    Correction means for calculating the average energy of the radiation by correcting the fluctuation of the energy feature amount based on the average value;
    A radiation imaging apparatus comprising:
  2. 　前記補正手段は、前記エネルギー特徴量と前記平均値との関係を表す第１の関数に基づいて、前記エネルギー特徴量の変動を補正する請求項１に記載の放射線撮影装置。 2. The radiation imaging apparatus according to claim 1, wherein the correction unit corrects a variation in the energy feature amount based on a first function representing a relationship between the energy feature amount and the average value.
  3. 　前記第１の関数は、前記平均値の高次関数であることを特徴とする請求項２に記載の放射線撮影装置。 The radiation imaging apparatus according to claim 2, wherein the first function is a higher-order function of the average value.
  4. 　前記第１の関数における前記平均値の０次項の係数は、前記平均エネルギーを変数とする第２の関数であることを特徴とする請求項２又は３に記載の放射線撮影装置。 The radiation imaging apparatus according to claim 2 or 3, wherein the coefficient of the zero-order term of the average value in the first function is a second function having the average energy as a variable.
  5. 　前記第２の関数は、前記平均エネルギーの１次関数であることを特徴とする請求項４に記載の放射線撮影装置。 The radiation imaging apparatus according to claim 4, wherein the second function is a linear function of the average energy.
  6. 　前記第１の関数又は前記第２の関数は、前記放射線のエネルギー測定値から導かれることを特徴とする請求項２乃至５の何れか１項に記載の放射線撮影装置。 6. The radiographic apparatus according to claim 2, wherein the first function or the second function is derived from an energy measurement value of the radiation.
  7. 　前記第１の関数又は前記第２の関数は、前記放射線のエネルギー測定値に基づいて、前記エネルギー特徴量、前記平均値、及び前記平均エネルギーの関係を近似する関数であることを特徴とする請求項２乃至６の何れか１項に記載の放射線撮影装置 The first function or the second function is a function that approximates a relationship between the energy feature amount, the average value, and the average energy based on an energy measurement value of the radiation. Item 7. The radiation imaging apparatus according to any one of Items 2 to 6.
  8. 　前記補正手段は、前記第１の関数及び前記第２の関数の係数を共通させて、前記係数に基づいて、前記エネルギー特徴量及び前記平均値から前記平均エネルギーを算出することを特徴とする請求項２乃至７の何れか１項に記載の放射線撮影装置。 The correction means uses the coefficients of the first function and the second function in common and calculates the average energy from the energy feature amount and the average value based on the coefficient. Item 8. The radiation imaging apparatus according to any one of Items 2 to 7.
  9. 　前記補正手段は、前記第１の関数及び前記第２の関数の係数を保持する前記較正テーブルを参照することにより、前記エネルギー特徴量の変動を補正する請求項２乃至８の何れか１項に記載の放射線撮影装置。 9. The correction unit according to claim 2, wherein the correction unit corrects the fluctuation of the energy feature amount by referring to the calibration table that holds the coefficients of the first function and the second function. The radiation imaging apparatus described.
  10. 　前記補正手段は、前記エネルギー特徴量、前記平均値、及び前記平均エネルギーの関係を保持する較正テーブルを参照することにより、前記エネルギー特徴量の変動を補正する請求項１乃至９の何れか１項に記載の放射線撮影装置。 The said correction | amendment means correct | amends the fluctuation | variation of the said energy feature-value by referring the calibration table holding the relationship of the said energy feature-value, the said average value, and the said average energy. The radiation imaging apparatus described in 1.
  11. 　前記補正手段は、前記放射線画像における前記エネルギー特徴量の面内分布を補正することを特徴とする請求項１乃至１０の何れか１項に記載の放射線撮影装置。 The radiographic apparatus according to claim 1, wherein the correction unit corrects an in-plane distribution of the energy feature amount in the radiographic image.
  12. 　前記算出手段は、被写体がない状態で撮影された放射線画像の画素値の分散値と平均値から放射線の基準エネルギー特徴量を算出し、
    　前記補正手段は、前記基準エネルギー特徴量の前記放射線画像における面内平均値に基づいて、前記エネルギー特徴量の面内分布を補正することを特徴とする請求項１１に記載の放射線撮影装置。     The calculation means calculates a reference energy feature amount of radiation from a variance value and an average value of pixel values of a radiographic image captured in a state where there is no subject,
    The radiographic apparatus according to claim 11, wherein the correction unit corrects an in-plane distribution of the energy feature amount based on an in-plane average value of the reference energy feature amount in the radiation image.
  13. 　前記補正手段は、補正された前記エネルギー特徴量に基づいて平均エネルギー画像を生成することを特徴とする請求項１乃至１２の何れか１項に記載の放射線撮影装置。 13. The radiation imaging apparatus according to claim 1, wherein the correction unit generates an average energy image based on the corrected energy feature amount.
  14. 　放射線画像の画素値の分散を算出する分散算出手段と、
    　放射線画像の画素値の平均値を算出する平均値算出手段と、
    　前記分散と平均値からエネルギー特徴量を算出する算出手段と、
    　該算出されたエネルギー特徴量の変動を補正するための較正テーブルを保持する保持手段と、
    　前記較正テーブルに基づいてエネルギー特徴量を補正する補正手段とを備えることを特徴とする放射線撮影装置。     Dispersion calculating means for calculating dispersion of pixel values of the radiation image;
    An average value calculating means for calculating an average value of the pixel values of the radiation image;
    Calculating means for calculating an energy feature amount from the variance and the average value;
    Holding means for holding a calibration table for correcting fluctuations in the calculated energy feature amount;
    A radiation imaging apparatus comprising: a correction unit that corrects an energy feature amount based on the calibration table.
  15. 　放射線を発生させる放射線発生手段と、
    　前記放射線を検出し、放射線画像の画像データを出力する放射線検出手段と、
    　前記放射線画像の画素値の分散値と平均値から放射線のエネルギー特徴量を算出する算出手段と、
    　前記エネルギー特徴量の変動を前記平均値に基づいて補正することにより、前記放射線の平均エネルギーを算出する補正手段と、
    　を備えることを特徴とする放射線撮影システム。     Radiation generating means for generating radiation;
    Radiation detecting means for detecting the radiation and outputting image data of a radiation image;
    Calculating means for calculating an energy feature amount of radiation from a variance value and an average value of pixel values of the radiation image;
    Correction means for calculating the average energy of the radiation by correcting the fluctuation of the energy feature amount based on the average value;
    A radiation imaging system comprising:
  16. 　放射線画像の画素値の分散値と平均値から放射線のエネルギー特徴量を算出する工程と、
    　前記エネルギー特徴量の変動を前記平均値に基づいて補正することにより、前記放射線の平均エネルギーを算出する工程と、
    　を備えることを特徴とする放射線撮影方法。     Calculating an energy feature amount of radiation from a dispersion value and an average value of pixel values of the radiation image;
    Calculating the average energy of the radiation by correcting the fluctuation of the energy feature amount based on the average value;
    A radiation imaging method comprising:
  17. 　放射線画像の画素値の分散を算出する工程と、
    　放射線画像の画素値の平均値を算出する工程と、
    　前記分散と平均値からエネルギー特徴量を算出する工程と、
    　該算出されたエネルギー特徴量の変動を補正するための較正テーブルを保持する工程と、
    　前記較正テーブルに基づいてエネルギー特徴量を補正する工程と、
    　を備えることを特徴とする放射線撮影方法。     Calculating a variance of pixel values of the radiation image;
    Calculating an average pixel value of the radiation image;
    Calculating an energy feature amount from the variance and the average value;
    Holding a calibration table for correcting variations in the calculated energy feature amount;
    Correcting the energy feature based on the calibration table;
    A radiation imaging method comprising:
  18. 　コンピュータを請求項１乃至１４の何れか１項に記載の放射線撮影装置の各手段として機能させるためのプログラム。 A program for causing a computer to function as each unit of the radiation imaging apparatus according to any one of claims 1 to 14.
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JP2013236962A (en) * 2007-08-15 2013-11-28 Fujifilm Corp Image component separating device, method and program
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