(19)
(11)EP 3 367 905 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
11.12.2019 Bulletin 2019/50

(21)Application number: 16859281.4

(22)Date of filing:  24.10.2016
(51)International Patent Classification (IPC): 
A61B 6/00(2006.01)
A61B 6/12(2006.01)
G01T 7/00(2006.01)
(86)International application number:
PCT/JP2016/004671
(87)International publication number:
WO 2017/073043 (04.05.2017 Gazette  2017/18)

(54)

RADIATION IMAGING SYSTEM, INFORMATION PROCESSING APPARATUS FOR IRRADIATION IMAGE, IMAGE PROCESSING METHOD FOR RADIATION IMAGE, AND PROGRAM

STRAHLUNGSBILDGEBUNGSSYSTEM, INFORMATIONSVERARBEITUNGSVORRICHTUNG ZUR STRAHLUNGSBILDGEBUNG, BILDVERARBEITUNGSVERFAHREN FÜR STRAHLUNGSBILD UND PROGRAMM

SYSTÈME D'IMAGERIE À RAYONNEMENT, APPAREIL DE TRAITEMENT D'INFORMATIONS POUR IMAGE D'IRRADIATION, PROCÉDÉ DE TRAITEMENT D'IMAGE POUR IMAGE DE RAYONNEMENT ET PROGRAMME


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 30.10.2015 JP 2015215209

(43)Date of publication of application:
05.09.2018 Bulletin 2018/36

(73)Proprietor: Canon Kabushiki Kaisha
Tokyo 146-8501 (JP)

(72)Inventors:
  • MACHIDA, Yoshihito
    Tokyo 146-8501 (JP)
  • IWASHITA, Atsushi
    Tokyo 146-8501 (JP)

(74)Representative: Saunders, Mark 
Canon Europe Limited 3 The Square Stockley Park
Uxbridge, Middlesex UB11 1ET
Uxbridge, Middlesex UB11 1ET (GB)


(56)References cited: : 
WO-A1-03/103495
JP-A- 2014 230 584
US-A1- 2009 296 884
US-B1- 6 233 473
JP-A- 2011 024 773
US-A1- 2008 232 668
US-A1- 2013 170 614
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    Technical Field



    [0001] The present invention relates to a radiation imaging system, an information processing apparatus which processes a radiation image, an information processing method for processing a radiation image, and a program.

    Background Art



    [0002] As an imaging apparatus used for a medical image diagnosis and a non-destructive inspection using radiation (X-rays), a radiation imaging apparatus using a flat panel detector (FPD) formed of semiconductor material has been used. Such a radiation imaging apparatus may be used as a digital imaging apparatus which captures still images and moving images in the medical image diagnosis, for example.

    [0003] Examples of the FPD include an integral sensor and a photon counting sensor. The integral sensor measures a total amount of charge generated by incident radiation. The photon counting sensor discriminates energy (wavelengths) of incident radiation and counts the numbers of times the radiation is detected for individual energy levels. Specifically, since the photon counting sensor has energy resolution capability, the photon counting sensor is expected to be applied to discrimination of substances and generation of an image and measurement of bone density in a case where imaging is virtually performed with monoenergetic radiation. However, since the number of incident radiation quanta is large, a high operation speed is required for individually counting the radiation quanta. Accordingly, it is difficult to realize the photon counting sensor in an FPD having a large area.

    [0004] Therefore, PTL 1 proposes a radiation imaging apparatus which realizes energy resolution capability by estimating the number of radiation quanta and an average value of energy using average image density information and distribution information of image density for each predetermined region. Specifically, PTL 1 discloses an information processing method for estimating the number of radiation quanta and an average value of the energy using average image density information and distribution information of image density for each predetermined region and obtaining two types of image information, that is, the number of radiation quanta and the average value of the energy of the radiation quanta. When the method disclosed in PTL 1 is employed, a sensor having energy resolution capability may be realized even in a case of a low operation speed when compared with the photon counting sensor.

    [0005] On the other hand, PTL 2 discloses a technique of an energy subtraction method. When the energy subtraction method is employed, two images are obtained by irradiation of respective two types of energy and a difference process is performed on the two images which have been subjected to a desired calculation so that the images of two substances having different attenuation coefficients are generated in a discrimination manner. The energy subtraction method utilizes a phenomenon in which different substances have different attenuation coefficients indicating degrees of attenuation of radiation at times when the radiation passes through the substances and the attenuation coefficients depend on energy of the radiation. Furthermore, PTL 2 further discloses a technique of dual-energy X-ray absorptiometry method (a DEXA method) which is a technique of measuring bone density utilizing the same phenomenon. However, radiation imaging is performed twice using two types of energy in the energy subtraction method and the DEXA method disclosed in PTL 2. Therefore, there arise problems in that artifact is generated due to a movement of a subject while energy is switched and in that high speed switching of radiation energy is required. In terms of these problems, the processing method disclosed in PTL 1 is more advantageous since substances may be discriminated from each other by one radiation imaging using one type of energy.

    [Citation List]


    [Patent Literature]



    [0006] 

    [PTL 1]
    Japanese Patent Laid-Open No. 2009-285356

    [PTL 2]
    Japanese Patent Laid-Open No. 2013-236962



    [0007] JP 2014-230584 describes an X-ray diagnostic apparatus which can generate quantitative X-ray image data of an analyte in which the influence of characteristics of the device is reduced. The X-ray diagnostic apparatus includes an X-ray irradiation unit, an X-ray detector, and a data processing system. The X-ray irradiation unit irradiates an analyte with an X-ray. The X-ray detector collects X-ray detection data by counting photons of the X-ray transmitted through the analyte with respect to a plurality of pixel positions for each of a plurality of energy bandwidths. The data processing system generates X-ray image data representing information unique to the analyte on the basis of the X-ray detection data.

    [0008] JP 2011-024773 describes an X-ray component measuring apparatus capable of measuring the components of a measurement object using the X-rays of a plurality of energy bands and easily changing the energy band to be identified corresponding to the measurement object. The X-rays irradiated from an X-ray generator are transmitted through the measurement object and made incident on an X-ray detector. The X-ray detector is a detector of a quantum counting system, and counts the number of X-ray quanta of the energy band sectioned by at least two thresholds set beforehand. On the basis of the number of the X-ray quanta counted by the X-ray detector, at least three kinds of component ratios are calculated. The threshold can be changed corresponding to the measurement object, and when three or more thresholds are adopted, at least four kinds of the component ratios are calculated.

    [0009] US 2009/296884 describes a technique capable of objectively discriminating the constituent of a subject also in an image in which density difference is not easily discriminated on a gray image obtained by image capturing for medical use using X-rays. An image capturing system for medical use includes: a detecting unit for detecting an X-ray dose by absorbing X-rays passed through a subject in image capturing for medical use and outputting absorbed X-ray dose information; an obtaining unit for obtaining image information of the subject from the absorbed X-ray dose information; an image processing unit for calculating average detection energy in each first predetermined region in the image information; and an output unit for outputting the average detection energy.

    [0010] US 2008/232668 describes a technique for appropriately separating three components contained in radiographic images. A component image generating unit separates an image component, which represents any one of a soft part component, a bone component and a heavy element component including an element having an atomic number higher than that of the bone component in a subject, from inputted three radiographic images, which represents degrees of transmission of three patterns of radiations having different energy distributions through the subject, by calculating a weighted sum for each combination of corresponding pixels between the three radiographic images using predetermined weighting factors.

    [0011] WO 03/103495 describes a method for detection of ionizing radiation comprises the steps of (i) directing ionizing radiation towards an object to be examined; (ii) preventing Compton scattered radiation, preferably at least 99% of the radiation Compton scattered in said object, from being detected; and (iii) detecting ionizing radiation spatially resolved as transmitted through said object to reveal a spatially resolved density of said object, wherein said ionizing radiation is provided within a spectral range such that more, preferably much more, photons of said ionizing radiation are Compton scattered than absorbed through the photoelectric effect in said object to thereby reduce the radiation dose to said object.

    [0012] US 6233473 describes determining body composition using fan beam dual-energy x-ray absorptiometry. True body composition is estimated using a dual-energy, fan-shaped distribution of x-rays and signal processing that corrects for mass magnification and other effects due to the geometry of the measurement system. To avoid inaccuracies due to beam hardening and certain other effects, the thickness of attenuating material along respective raypaths is obtained through using a four-dimensional look-up table derived experimentally from step-wedge measurements. To correct for mass magnification effects due to using a fan-shaped distribution of x-rays, another look-up table and interpolation between table entries are used to convert projected mass to true mass.

    [Summary of Invention]


    [Technical Problem]



    [0013] However, PTL 1 does not disclose a method for obtaining information for discriminating two substances constituting a radiation image using two types of image information, that is, the obtained number of radiation quanta and the obtained average value of the energy the radiation quanta.

    [Solution to Problem]



    [0014] Accordingly, the present invention provides a technique of obtaining information for discriminating two substances included in a radiation image of a subject without performing imaging by changing radiation energy. Aspects of the present invention are set out by the independent claims.

    Advantageous Effects of Invention



    [0015] The invention is defined in the appended claims. Aspects, embodiments and examples disclosed herein which do not fall within the scope of the appended claims do not form part of the invention, and are merely provided for illustrative purposes.

    [0016] According to the present invention, information for discriminating two substances included in a subject may be obtained without performing imaging by changing radiation energy.

    [0017] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

    Brief Description of Drawings



    [0018] 

    [fig.1] Fig. 1 is a diagram schematically illustrating a functional configuration of a radiation imaging system.

    [fig.2]Fig. 2 is a flowchart illustrating a processing flow.

    [fig.3]Fig. 3 is a graph illustrating linear attenuation coefficients of a bone and fat.

    [fig.4A]Fig. 4A is a table used by an estimation unit.

    [fig.4B]Fig. 4B is a table used by the estimation unit.

    [fig.5]Fig. 5 is a diagram schematically illustrating a functional configuration of a radiation imaging system.

    [fig.6]Fig. 6 is a flowchart illustrating a processing flow.

    [fig.7]Fig. 7 is a block diagram schematically illustrating the radiation imaging system.


    Description of Embodiments



    [0019] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that, in this specification, examples of radiation include, in addition to an α-ray, a β-ray, a γ-ray, and so on which are beams formed by particles (including photons) emitted due to radioactive decay, beams having energy substantially the same as that of the beams formed by particles, such as an X-ray, a particle ray, and a cosmic ray.

    First Embodiment



    [0020] A configuration and a processing flow of a radiation imaging system according to a first embodiment will now be described with reference to Figs. 1 and 2, respectively. Fig. 1 is a diagram schematically illustrating a functional configuration of the radiation imaging system according to the first embodiment. Fig. 2 is a flowchart illustrating a processing flow according to the first embodiment.

    [0021] The radiation imaging system may include a radiation imaging apparatus 10, a computer 13, a radiation control apparatus 12, and a radiation generation apparatus 11. The radiation generation apparatus 11 emits radiation to a subject. The radiation imaging apparatus 10 includes a detector having a plurality of pixels which obtain pixel values corresponding to the radiation which enters through the subject. The detector obtains pixel values corresponding to the radiation which enters through the subject. The computer 13 serving as an image processing unit and/or an image processing apparatus of the present invention estimates an average value of energy of radiation quanta which reach the detector using the pixel values and further estimates information on thicknesses of substances constituting the subject. The estimation will be described in detail hereinafter. Furthermore, the computer 13 supplies control signals to the radiation imaging apparatus 10 and the radiation control apparatus 12 based on imaging information input by a photographer (not illustrated) through a control table (not illustrated) included in the computer 13. When receiving the control signal from the computer 13, the radiation control apparatus 12 controls an operation of emitting radiation from a radiation source (not illustrated) included in the radiation generation apparatus 11 and an operation of a irradiation field diaphragm mechanism (not illustrated). The detector of the radiation imaging apparatus 10 outputs an image signal corresponding to the radiation emitted from the radiation generation apparatus 11 controlled by the radiation control apparatus 12. The output image signal is transmitted to the computer 13 after being subjected to image processing, such as offset correction, performed by a signal processor. Here, a general wireless communication or a general wired communication is used in the transmission. The transmitted image signal is subjected to required image processing performed by the computer 13 before being displayed in a display unit (not illustrated) of the computer 13. Note that a pixel value constitutes a pixel signal.

    [0022] The computer 13 includes, as a functional configuration thereof, a first calculation unit 131, a second calculation unit 132, and an estimation unit 133.

    [0023] In step S201, radiation is emitted to the radiation imaging apparatus 10 through the subject for a predetermined period of time so that the computer 13 obtains a plurality of digital image signals.

    [0024] Next, principle of calculations performed in step S202 and step S203 will be described. It is assumed here that the radiation emitted for the predetermined period of time is fixed and the subject does not move. An arbitrary one pixel is selected from among the obtained digital image signals. Although a digital signal (hereinafter referred to as a "pixel value") obtained from the selected pixel is ideally fixed, the pixel value varies in time series in practice. The variation includes quantum noise. The quantum noise is generated due to variation of the number of radiation quanta (the number of X-ray photons, for example) per unit time. If the variation of the number of radiation quanta is considered as occurrence probability of a discrete event per unit time, the variation of the number of radiation quanta is based on Poisson distribution which is discrete probability distribution having a specific random variable for counting discrete events generated at a given time interval. As for the Poisson distribution, when a random variable which has a value of a natural number satisfies a desired condition in a condition in which a constant λ is larger than 0, the random variable is based on the Poisson distribution of the parameter λ. Specifically, even in a case where images have the same average value of pixel values, distribution of the pixel values of one of the images formed by radiation quanta having larger energy is larger than that of the other image. By utilizing this, the energy of the radiation quanta, such as X-ray photons, may be estimated.

    [0025] Hereinafter, a method for estimating energy of radiation quanta will be described using expressions. First, it is assumed that radiation is emitted to the radiation imaging apparatus 10 T times (T is a natural number equal to or larger than 2) so that T digital image signals are obtained by the radiation imaging apparatus 10. Here, assuming that a pixel value of a pixel of a t-th digital image signal (t is a natural number equal to or larger than 2 and equal to or smaller than T) is denoted by "I(t)", the total number of radiation quanta which have reached the pixel and absorbed by the pixel is denoted by "N", and an average value of the energy of the radiation quanta is denoted by "EAve", Expression (1) below is obtained.



    [0026] According to Expression (1), assuming that an arithmetic average of the numbers of radiation quanta which have reached and which have absorbed by the pixel of a single digital image signal is denoted by "nAve", Expression (2) below is obtained.



    [0027] Furthermore, according to Expression (1), assuming that sample variance of the numbers of radiation quanta which have reached and which have absorbed by the pixel of the single digital image signal is denoted by "nVar", Expression (3) below is obtained.



    [0028] Here, in the Poisson distribution, an expected value and variance are equal to the parameter λ. Furthermore, as the number of samples is increased, the arithmetic average becomes close to the expected value and the sample variance becomes close to the variance. Therefore, assuming that the number of samples is sufficiently large (preferably infinite) and the arithmetic average nAve of the numbers of radiation quanta and the sample variance nVar of the numbers of radiation quanta are approximated so as to be equal to each other, Expression (4) is obtained since Expressions (2) and (3) are equal to each other.



    [0029] In this way, an average value EAve of the energy of the radiation quanta which have reached the pixel and which have been absorbed by the pixel is estimated and calculated using the pixel value I(t) of the pixel of the arbitrary t-th digital image signal.

    [0030] Furthermore, assuming that the arithmetic average of the pixel values I(t) is denoted by "IAve", an arithmetic average IAve is represented by Expression (5) below using the arithmetic average nAve of the number of radiation quanta.



    [0031] Furthermore, assuming that sample variance of the pixel values is denoted by "IVar", the sample variance IVar of the pixel values is represented by Expression (6) below using the sample variance nVar of the numbers of radiation quanta.



    [0032] Accordingly, an average value E of the energy of the radiation quanta which have reached the pixel and which have absorbed by the pixel is also represented by Expression (7) below.



    [0033] In step S202, the first calculation unit 131 calculates the sample variance IVar of the pixel values of the arbitrary pixel using the pixel values I(t) of the arbitrary pixel in accordance with Expression (8) below. Although the sample variance is used as variance in this embodiment, unbiased variance may be used. Furthermore, although an arithmetic average IAve of the pixel values I(t) is used as an average of pixel values, the present invention is not limited to this.
    [Math.1]



    [0034] In step S203, the second calculation unit 132 calculates the average value EAve of the energy of the radiation quanta of the arbitrary pixel using the sample variance IVar of the pixel values of the arbitrary pixel in accordance with Expression (9) below calculated using Expression (7). Here, α is an arbitrary constant used to perform conversion between a pixel value and a unit of energy. Although the sample variance is used as variance in this embodiment, unbiased variance may be used.
    [Math.2]



    [0035] In the following steps, information on thicknesses of the substances which constitute the subject are estimated using the average value of the energy of the radiation quanta of the arbitrary pixel calculated in step S202 and step S203 and the pixel values of the arbitrary pixel. Note that, for simplicity of description, it is assumed that a substance (a second constitutive substance) other than a bone (a first constitutive substance) in the substances included in a human body serving as an example of the subject is fat. Note that the first and second constitutive substances are different from each other. Although the substances other than a bone include fat, muscle, internal organs, and water, these substances have linear attenuation coefficients similar to one another when compared with that of the bone. Fig. 3 is a graph illustrating linear attenuation coefficients of a bone and fat. Although description will be made using the linear attenuation coefficients of a bone and fat hereinafter, two arbitrary linear attenuation coefficients are used depending on diagnosis usage or constitutive substances of the subject.

    [0036] In step S204, the estimation unit 133 estimates a thickness of the subject and a mix ratio of the substances included in the subject using the average value EAve of the energy of the radiation quanta of the arbitrary pixel and the arithmetic average IAve of the pixel values of the arbitrary pixel calculated using the pixel values of the arbitrary pixel. Here, the estimation unit 133 may estimate the thickness of the subject and the mix ratio of the substances included in the subject using a table illustrated in Fig. 4A. Fig. 4A is a first table indicating the relationship among a thickness d of the subject, a mix ratio γ of the substances included in the subject, and the arithmetic average IAve of the pixel values of the arbitrary pixel. Note that, in a case where the mix ratio γ is 1, the subject is constituted only by bones (the first constitutive substance), whereas in a case where the mix ratio γ is 0, the subject is constituted only by fat (the second constitutive substance). The first table is preferably obtained by experiment in advance. The first table may be calculated in advance in accordance with Expression (10) below. It is assumed here that a mass attenuation coefficient of a bone at a time when the radiation energy is E[kev] is denoted by "µ1(E)", a linear attenuation coefficient of fat at a time when the radiation energy is E[kev] is denoted by "µ2(E)", a thickness of the subject is denoted by "d", and the mix ratio of the substances included in the subject is denoted by "γ". Furthermore, rates (energy spectra) of the numbers of radiation quanta of energy of radial rays before the radial rays pass the subject are denoted by "n(E)". In step S204, the estimation unit 133 performs a calculation using Expression (10) below so as to obtain the thickness d of the subject and the mix ratio γ. Here, "β" denotes an arbitrary coefficient used to convert energy into a pixel value.
    [Math.3]



    [0037] Note that "n(E)" is preferably measured in advance using a commercially available spectrometer. Since a simple expression for obtaining an energy spectrum is publicly available, the energy spectrum may be calculated using the simple expression in accordance with conditions of a tube voltage, an additional filter, and the like at a time when radiation is emitted. Furthermore, "β" is determined based on characteristics of a scintillator used in the radiation imaging apparatus 10 and characteristics of a system gain.

    [0038] The estimation unit 133 may estimate the thickness of the subject and the mix ratio of the substances included in the subject in accordance with a table illustrated in Fig. 4B. Fig. 4B is a second table indicating the relationship among the thickness d of the subject, the mix ratio γ of the substances included in the subject, and the average value EAve of the energy of the radiation quanta of the arbitrary pixel. The second table is also preferably obtained by experiment in advance. The second table may be calculated in advance in accordance with Expression (11) below.
    [Math.4]



    [0039] The estimation unit 133 estimates thicknesses of the substances and the mix ratio of the substances included in the subject which satisfy the calculated average value EAve of the energy of the radiation quanta of the arbitrary pixel and the calculated arithmetic average IAve of the pixel values of the arbitrary pixel using the tables illustrated in Figs. 4A and 4B.

    [0040] Hereinafter, the estimation performed in a case where the arithmetic average IAve of the pixel values of the arbitrary pixel calculated from the pixel values of the arbitrary pixel is i3 of Fig. 4A and the calculated average value EAve of the energy of the radiation quanta of the arbitrary pixel is e4 of Fig. 4B will be described as an example. First, a combination of a thickness d of the subject and a mix ratio γ which satisfies i3 is retrieved from the first table in Fig. 4A. In this case, such combinations which satisfy i3 are included in a region 401. Thereafter, a combination of a thickness d of the subject and a mix ratio γ which satisfies e4 is retrieved from the second table in Fig. 4B. In this case, such combinations which satisfy e4 are included in a region 402. Finally, a combination of a thickness d of the subject and a mix ratio γ which satisfies both of the regions 401 and 402 is retrieved. In this case, a combination of a thickness d4 of the subject and a mix ratio γ4 satisfies both of the regions 401 and 402. As described above, since the two tables are used, the thickness of the subject and the mix ratio of the two substances included in the subject may be estimated. Although the tables have six rows and six columns as an example in this embodiment, larger tables are preferably used in practice. Furthermore, in a case where a plurality of results which satisfy both of the regions 401 and 402 are obtained in adjacent numerical values, a combination of the smallest thickness d and the smallest mix ratio γ is obtained taking influence of scattered radiation into consideration. In actual imaging, a pixel value may be larger than a normal value due to the influence of scattered radiation. Therefore, in the case where a plurality of results which satisfy both of the regions 401 and 402 are obtained in adjacent numerical values, a thickness d and a mix ratio γ which attain the largest calculated average value EAve of the energy of the radiation quanta of the arbitrary pixel and the largest calculated arithmetic average IAve of the pixel values of the arbitrary pixel are selected.

    [0041] By performing the process from step S201 to step S204 described above, information on the thicknesses of the substances included in the subject and information on a component ratio may be estimated. According to this embodiment, the information on the thicknesses of the two different substances included in the subject and the information on the component ratio of the substances may be estimated without changing radiation energy in imaging. Accordingly, information for discriminating two substances included in a radiation image which may be applied to a complicated radiographic system in general imaging and fluorography may be obtained.

    [0042] Although information on a bone and fat in a human body are estimated using the human body as the subject as an example in this embodiment, the present invention is not limited to this. For example, information on a contrast agent and a human body may be estimated so that visibility of distribution of the contrast agent is improved and an amount of the contrast agent to be used is reduced. Furthermore, information on a guide wire and a human body may be estimated so that visibility of the guide wire is improved, and accordingly, security of a patient during an operation may be ensured and a burden of a doctor during an operation may be reduced. In this way, information on a thickness and information on density of at least one of arbitrary different types of two substances may be obtained irrespective of a type of substance in the present invention.

    [0043] Furthermore, a value BMD [g/cm2] corresponding to bone density may be estimated by using density ρ1 [g/cm3] and a thickness d [cm] of the bone and a mix ratio γ, for example.

    [0044] Furthermore, although information on the thicknesses and the mix ratio of the substances included in the subject are estimated in this embodiment, the present invention is not limited to this. For example, if bone density and fat density may not be obtained or are unknown, the thicknesses d of the substances included in the subject may be multiplied by the density ρ so as to obtain a value pd. For example, first information on a thickness and density of the first constitutive substance is represented by "ρ1d1" and second information on a thickness and density of the second constitutive substance is represented by "ρ2d2". Here, it is assumed that a mass attenuation coefficient of a bone obtained when radiation energy is denoted by "E[kev]" is denoted by "µ(E)1", a thickness of the bone is denoted by "d1", and density of the bone is denoted by "ρ1". In addition, it is assumed that a mass attenuation coefficient of fat obtained when radiation energy is denoted by "E[kev]" is denoted by "µ(E)2", a thickness of the fat is denoted by "d2", and density of the fat is denoted by "ρ2". The estimation unit 133 estimates an arithmetic average iAve of the pixel values of the arbitrary pixel by performing calculation using Expression (12) below. Note that, although the arithmetic average iAve of the pixel values I(t) is estimated as an average of the pixel values, the present invention is not limited to this.
    [Math.5]



    [0045] Furthermore, the estimation unit 133 estimates an average value eAve of the energy of the radiation quanta of the arbitrary pixel by performing calculation using Expression (13) below. Note that, although the arithmetic average iAve of the pixel values I(t) is estimated as an average of pixel values, the present invention is not limited to this.
    [Math.6]



    [0046] Then the estimation unit 133 uses "ρ1" and "iAve" instead of "γ" and "IAve" of Fig. 4A and uses "ρ2" and "eAve" instead of "γ" and "EAve" of Fig. 4B so as to estimate information on thicknesses and densities of the substances included in the subject. Specifically, in the present invention, the estimation unit 133 may use the first table indicating the relationship between the arithmetic average IAve of the pixel values of the arbitrary pixel and the thicknesses d of the substances included in the subject for the estimation process. Furthermore, the estimation unit 133 may use the second table indicating the relationship between the calculated average value EAve of the energy of the radiation quanta of the arbitrary pixel and the thicknesses d of the substances included in the subject for the estimation process. Then the estimation unit 133 estimates information on the thicknesses of the substances included in the subject using the arithmetic average IAve of the pixel values of the arbitrary pixel, the arithmetic average IAve of the pixel values of the arbitrary pixel, the first table, and the second table.

    [0047] Furthermore, although the sample variance and the arithmetic average are calculated using a plurality of pixel values obtained in time series and an average value of the energy of the radiation quanta is estimated in this embodiment, the present invention is not limited to this. For example, a case of pixel values of an arbitrary one of a plurality of pixels arranged in two-dimensional space arrangement positions in a matrix having an X axis indicating columns and a Y axis indicating rows will be considered. In this case, the average value of the energy of the radiation quanta may be estimated after sample variance and an arithmetic average of the pixel values of the arbitrary pixel are calculated using pixel values of a plurality of surrounding pixels. By this, an energy image may be calculated from a single still image.

    [0048] Furthermore, although the arithmetic average and the sample variance calculated using the pixel values of the arbitrary pixel are used to obtain the average value EAve of the energy of the radiation quanta of this embodiment, the present invention is not limited to this. As described below, the average value of the energy of the radiation quanta is calculated based on the pixel values of the arbitrary pixel, and therefore, an amount of temporal and/or spatial change of a pixel value of the arbitrary pixel may be used for the calculation, for example.

    [0049] In actual radiation imaging, the subject may move while a plurality of images are captured (or a plurality of digital image signals are obtained by a radiation imaging apparatus 10). This happens in a case where imaging of an organ having a motion, such as a heart, is performed, a case where fluoroscopic radiography is performed during an operation, and the like. If a subject has a motion, the number of X-ray photons which is an example of the number of radiation quanta which reach a certain pixel is changed while the radiation imaging apparatus 10 outputs a plurality of image data. Specifically, the parameter λ of the Poisson distribution is changed. Accordingly, artifact is generated in an image generated using the average value of the energy, and therefore, diagnosis performance is degraded.

    [0050] Therefore, it is preferable that the energy of the radiation quanta in the arbitrary pixel is estimated using an amount of temporal and/or spatial change of a pixel value of the arbitrary pixel when the average value of the energy of the radiation quanta in the arbitrary pixel is estimated. Here, the amount of temporal change of a pixel value means a difference between a pixel value of a pixel corresponding to (a pixel in a position the same as or in the vicinity of) the arbitrary pixel in a frame different from a frame in which the arbitrary pixel is specified and the pixel value of the arbitrary pixel. Furthermore, the amount of spatial change of a pixel value means a difference between a pixel value of a pixel positioned adjacent to or in the vicinity of the arbitrary pixel in the frame in which the arbitrary pixel is specified and the pixel value of the arbitrary pixel. The amount of temporal and spatial change means mix of the means described above. Note that the number of pixel values of the arbitrary pixel and the number of pixel values of a pixel which is compared with the arbitrary pixel may be single or plural. In a case of a plurality of pixels, a representative value of the pixels (for example, a value obtained by performing a recursive filter process or an averaging process on the values of the arbitrary pixel) is determined as the pixel value. Note that, although the different frame described above used when the amount of temporal change is to be obtained is preferably adjacent to the specific frame in a time axis, the different frame may be separated from the specific frame to a degree in which the effect is not degraded. Furthermore, although the arbitrary pixel and the different pixel are preferably adjacent to each other when the amount of spatial change is to be obtained, the pixels may be separated from each other to a degree in which the effect is not degraded. A range in which the effect is not degraded in despite of the separation is referred to as an arbitrary range which includes some of all pixel values used in signal processing. By using the change amount, error of the estimation of the average value of the energy of the arbitrary pixel may be suppressed.

    [0051] More specifically, the present invention is based on a concept in which the sample variance of the pixel values is seen to be a half of square of the amount of temporal and/or spatial change of the pixel value of the arbitrary pixel and the energy of the radiation quantum in the arbitrary pixel is approximated. In particular, the present invention is based on a concept in which the sample variance of the pixel values is seen to be a half of square of a difference between the pixel value of the arbitrary pixel and the pixel value of the pixel in the position the same as the position of the arbitrary pixel in the different frame and the energy of the radiation quantum in the arbitrary pixel is approximated. Then averaging is performed using the approximated energy of the radiation quantum of the arbitrary pixel so that the average value of the energy of the radiation quantum of the arbitrary pixel is obtained. The energy of the radiation quantum in the arbitrary pixel has large error only when an expected value which is equal to the parameter λ of the Poisson distribution is changed. Accordingly, the generation of artifact may be suppressed.

    [0052] Furthermore, the average value of the energy of the radiation quanta may be estimated using the energy of the radiation quanta obtained by counting the numbers of detection in a plurality of energy levels for each arbitrary pixel using a photon counting sensor as a detector, for example. In this case, the pixel value of the arbitrary pixel in the present invention may include a pixel value of an arbitrary pixel in the photon counting sensor.

    Second Embodiment



    [0053] In a second embodiment, a method for generating pixel values of individual substances using information on thicknesses of the substances included in a subject obtained in the first embodiment will be described. Hereinafter, a method for generating an image of a human bone (a first constitutive substance) and an image of portions other than a bone in a discrimination manner will be described as an example with reference to Figs. 5 and 6. Fig. 5 is a diagram schematically illustrating a functional configuration of a radiation imaging system according to the second embodiment. Fig. 6 is a flowchart illustrating a processing flow according to the second embodiment. Note that functional configurations and processing steps which are the same as those of the first embodiment are denoted by reference numerals the same as those of the first embodiment, and detailed descriptions thereof are omitted.

    [0054] A pixel value generation unit 14 of Fig. 5 generates substance pixel values of the individual substances based on information on the thicknesses of the substances included in the subject and a mix ratio. The pixel value generation unit 14 includes a first pixel value generation unit 141 and a second pixel value generation unit 142. The first pixel value generation unit 141 generates a pixel value of a bone (a first pixel value) based on information on a thickness of the bone (the first constitutive substance) and a mix ratio (first information). The second pixel value generation unit 142 generates a pixel value of fat (a second pixel value) based on information on a thickness of the fat (the second constitutive substance) and a mix ratio (second information). Note that, for simplicity of description, as with the first embodiment, it is assumed that an image obtained by visualizing the substance other than the bone in the substances included in the substance is determined as a fat image. Although the substance other than the bone includes fat, muscle, internal organs, and water, these substances have linear attenuation coefficients similar to one another when compared with that of a bone.

    [0055] In step S205 of Fig. 6, a pixel value (a first pixel value) I1 of the bone is obtained using a calculation in accordance with Expression (14) below based on the first information obtained in the process from step S201 to step S204.
    [Math.7]



    [0056] In step S206, a pixel value (a second pixel value) I2 of the fat is calculated using a calculation in accordance with Expression (15) below based on the second information obtained in the process from step S201 to step S204.
    [Math. 8]



    [0057] By performing the process described above, substance pixel values of the individual two substances included in the subject may be generated.

    [0058] Although the method for generating pixel values of the bone and the fat in the human body serving as the subject is described as an example in this embodiment, the present invention is not limited to this. For example, information on a contrast agent and a human body may be estimated so that visibility of distribution of the contrast agent is improved and an amount of the contrast agent to be used is reduced. Furthermore, if a pixel value of the contrast agent is generated, an image equivalent to a digital subtraction angiography image may be generated without capturing an image before the contrast agent is injected, and therefore, a relative positional change between a subject and a radiation imaging apparatus during photographing may be coped with. Furthermore, information on a guide wire and a human body may be estimated so that visibility of the guide wire is improved, and accordingly, security of a patient during an operation is ensured and a burden of a doctor during an operation is reduced. In this way, the pixel values of the two arbitrary types of substance may be generated irrespective of types of substance in the present invention. Furthermore, in a case where pixel values of all the two types of substance are not required, that is, in a case where only a pixel value of the bone is required or a case where only a pixel value of the contrast agent is required, a corresponding one of the processes in step S205 and step S206 may be omitted. Note that the pixel values obtained in Expressions (14) and (15) correspond to a pixel value obtained when only a bone is virtually captured and a pixel value obtained when only fat is virtually captured, respectively, by the radiation imaging apparatus.

    [0059] Furthermore, the pixel values may be generated by performing calculations in accordance with Expression (16) and (17) below using an average (effective energy) Eeff of energy spectra of emitted radiation.
    [Math.9]

    [Math. 10]



    [0060] In this way, the calculation may be simplified using the effective energy of the emitted radiation.

    [0061] Furthermore, when arbitrary monochromatic radiation energy Emono is set, a pixel value of energy virtually having an arbitrary spectrum may be generated in accordance with a calculation of Expression (18) below.
    [Math. 11]



    [0062] It is assumed that a linear attenuation coefficient of an iodinated contrast agent is denoted by "µ1", a linear attenuation coefficient of the human body is denoted by "µ2", a thickness of the iodinated contrast agent is denoted by "d1", a thickness of the human body is denoted by "d2", and a mix ratio between the iodinated contrast agent and the human body is denoted by "γ", and contrast between the iodinated contrast agent and other substances is to be improved. In this case, since the iodinated contrast agent has a K absorption edge at 33.2 keV, the calculation is performed while arbitrary monochromatic radiation energy Emono of 33.2 keV is set.

    [0063] Furthermore, the various pixel values may be generated by performing calculations in accordance with Expressions (19) and (20) below using an arithmetic average IAve of pixel values based on obtained pixel values I(t).
    [Math. 12]

    [Math. 13]



    [0064] Furthermore, obtained information µ1dγ may be set as a pixel value (a first pixel value) of a bone and obtained information µ2d(1-γ) may be set as a pixel value (a second pixel value) of fat. By displaying the value µdγ, degrees of attenuation of radiation in the individual substances may be visualized. For example, if bone density and fat density may not be obtained or are unknown, the thicknesses d of the substances included in the subject may be multiplied by the density ρ so as to obtain a value pd instead of dγ. It is assumed that first information on a thickness and density of the first constitutive substance is represented by "ρ1d1" and second information on a thickness and density of the second constitutive substance is represented by "ρ2d2". By displaying the value pd, area densities of the individual substances may be visualized. For example, "ρ1d1" may visualize distribution of bone density. Furthermore, in a case where the bone density and fat density may be obtained or estimated by different methods, the individual thicknesses dy and d(1-γ) may be determined as a pixel value of the bone (the first pixel value) and a pixel value of the fat (the second pixel value). In this way, two-dimensional distributions of the thicknesses of the individual substances may be visualized.

    [0065] Hereinafter, a radiation imaging apparatus and a radiation imaging system which are suitable for obtaining pixel values to be used in the present invention will be described.

    [0066] First, the radiation imaging system will be described with reference to Fig. 7. Fig. 7 is a block diagram schematically illustrating the radiation imaging system. Note that configurations the same as those illustrated in Figs. 1 and 5 are denoted by reference numerals the same as those illustrated in Figs. 1 and 5 in this embodiment, and detailed descriptions thereof are omitted.

    [0067] A detector 101 may include a pixel array 102 including pixels in a matrix which convert radiation or light into electric signals, a driving circuit 103 which drives the pixel array 102, and an output circuit 104 which outputs the electric signals supplied from the driven pixel array 102 as image signals. The pixel array 102 includes the plurality of pixels which output electric signals corresponding to incident radiation so as to obtain pixel values corresponding to the radiation, and the plurality of pixels are preferably arranged in a matrix. Each of the plurality of pixels may include a photoelectric conversion element and a pixel circuit unit. The photoelectric conversion element converts light which has been converted from the radiation by a scintillator into charge, and a photodiode disposed on a semiconductor substrate, such as a silicon substrate, is used as the photoelectric conversion element. However, the present invention is not limited to this. A photoelectric conversion element of amorphous silicon disposed on an insulated substrate, such as a glass substrate, or a conversion element which directly converts radiation into charge without using a scintillator may be used, for example. A controller 107 of a radiation imaging apparatus 10 controls various units included in the radiation imaging apparatus 10 in response to control signals supplied from the computer 13. The detector 101 of the radiation imaging apparatus 10 outputs an image signal corresponding to the radiation emitted from the radiation generation apparatus 11 controlled by the radiation control apparatus 12. The output image signal is transmitted to the computer 13 after being subjected to image processing, such as offset correction, performed by a signal processor 105. Here, a general wireless communication or a general wired communication is used in the transmission. The transmitted image signal is subjected to required image processing performed by the computer 13 before being displayed in a display unit (not illustrated) of the computer 13.

    [0068] Note that embodiments of a system, an apparatus, a method, a program or a storage medium, and the like may be employed in the present invention, for example. Specifically, the present invention may be applied to a system including a plurality of devices or an apparatus including a single device. Furthermore, although the processes described above are preferably performed in accordance with programs, all or some of the processes may be performed by a circuit. Alternatively, the processes may be performed by the signal processor 105 instead of the computer 13 or may be performed utilizing both of the signal processor 105 and the computer 13. That is, the information processing unit and/or the information processing apparatus according to the present invention corresponds to at least one of the signal processor 105, the computer 13, and a combination of the signal processor 105 and the computer 13.

    [0069] The present invention is also realized by executing processing below. That is, software (programs) which realizes the functions of the foregoing embodiments is supplied to a system or an apparatus through a network or various storage media. Then a computer (or a CPU, an MPU, a GPU, or the like) included in the system or the apparatus reads and executes the programs.

    Other Embodiments



    [0070] Embodiments of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a 'non-transitory computer-readable storage medium') to perform the functions of one or more of the above-described embodiments and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiments, and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiments and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiments. The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like.


    Claims

    1. An information processing apparatus that performs a process of estimating information on thicknesses of substances included in a subject using pixel values of an arbitrary one of a plurality of pixels which obtain pixel values corresponding to incident radiation transmitted through the subject, an average value of energy of radiation quanta of the arbitrary pixel calculated in accordance with the pixel values of the arbitrary pixel, a first table indicating the relationship between the pixel values of the arbitrary pixel and the thicknesses of the substances included in the subject, and a second table indicating the relationship between the average value of the energy of the radiation quanta of the arbitrary pixel and the thicknesses of the substances included in the subject.
     
    2. A radiation imaging system comprising:

    a detector including a plurality of pixels which obtain pixel values corresponding to incident radiation transmitted through a subject; and

    an information processing apparatus according to claim 1.


     
    3. The radiation imaging system according to claim 2,
    wherein the information processing apparatus includes

    a first calculation unit configured to calculate an average of the pixel values of the arbitrary one of the plurality of pixels based on the pixel values of the arbitrary pixel,

    a second calculation unit configured to calculate an average value of the energy of the radiation quanta of the arbitrary pixel in accordance with variance of the pixel values of the arbitrary pixel calculated using the pixel values of the arbitrary pixel and an average of the pixel values of the arbitrary pixel calculated by the first calculation unit, and

    an estimation unit configured to estimate information on the thicknesses of the substances included in the subject using the average of the pixel values of the arbitrary pixel calculated by the first calculation unit, the average value of the energy of the radiation quanta of the arbitrary pixel calculated by the second calculation unit, the first table, and the second table.


     
    4. The radiation imaging system according to claim 3, wherein

    the first table indicates the relationship among the average of the pixel values of the arbitrary pixel, the thicknesses of the substances included in the subject, and a mix ratio between the substances included in the subject,

    the second table indicates the relationship among the average value of the energy of the radiation quanta of the arbitrary pixel, the thicknesses of the substances included in the subject, and the mix ratio between the substances included in the subject, and

    the estimation unit estimates information on the thicknesses of the substances included in the subject and the mix ratio.


     
    5. The radiation imaging system according to claim 4, wherein the image processing apparatus further includes a pixel value generation unit configured to generate pixel values of the substances in accordance with the estimated information on the thicknesses of the substances and the mix ratio.
     
    6.  The radiation imaging system according to claim 5, wherein the pixel value generation unit includes a first pixel value generation unit configured to generate a first pixel value which is a pixel value of a first constitutive substance based on first information on a thickness of the first constitutive substance and the mix ratio and includes a second pixel value generation unit configured to generate a second pixel value which is a pixel value of a second constitutive substance based on second information on a thickness of the second constitutive substance and the mix ratio.
     
    7. The radiation imaging system according to claim 6, wherein, when a linear attenuation coefficient obtained when radiation energy of the first constitutive substance in the two different substances included in the subject is represented by "E[kev]" is denoted by "µ1(E)", a linear attenuation coefficient obtained when radiation energy of the second constitutive substance in the two substances is represented by "E[kev]" is denoted by "µ2(E)", a thickness of the subject is denoted by "d", a mix ratio of the first constitutive substance is denoted by "γ", an arbitrary coefficient for conversion of the energy into a pixel value is denoted by "β", the first pixel value is denoted by "I1", and the second pixel value is denoted by "I2", the pixel value generation unit generates a pixel value of at least one of the substances by performing at least one of the following calculations:

    and


     
    8. The radiation imaging system according to claim 6, wherein, when effective energy of the radiation is denoted by "Eeff", a linear attenuation coefficient obtained when effective energy of the radiation of the first constitutive substance in the two different substances included in the subject is represented by "Eeff [kev] " is denoted by "µ1(Eeff)", a linear attenuation coefficient obtained when effective energy of the radiation of the second constitutive substance in the two substances is represented by "Eeff[kev]" is denoted by "µ2(Eeff)", a thickness of the first constitutive substance is denoted by "d1", a thickness of the second constitutive substance is denoted by "d2", a mix ratio of the first substance is denoted by "γ", an arbitrary coefficient for conversion of the energy into a pixel value is denoted by "β", the first pixel value is denoted by "I1", and the second pixel value is denoted by "I2", the pixel value generation unit generates a pixel value of at least one of the substances by performing at least one of the following calculations:

    and


     
    9. The radiation imaging system according to claim 6, wherein, when effective energy of the radiation is denoted by "Eeff", a linear attenuation coefficient obtained when effective energy of the radiation of the first constitutive substance in the two different substances included in the subject is represented by "Eeff[kev] " is denoted by "µ1(Eeff)", a linear attenuation coefficient obtained when effective energy of the radiation of the second constitutive substance in the two substances is represented by "Eeff[kev]" is denoted by "µ2(Eeff)", a thickness of the subject is denoted by "d", a mix ratio of the first substance is denoted by "γ", an arbitrary coefficient for conversion of the energy into a pixel value is denoted by "β", a calculated arithmetic average of the pixel values of the arbitrary pixel is denoted by "IAve", the first pixel value is denoted by "I1", and the second pixel value is denoted by "I2", the pixel value generation unit generates a pixel value of at least one of the substances by performing at least one of the following calculations:

    and


     
    10. The radiation imaging system according to claim 5, wherein, when a linear attenuation coefficient obtained when radiation energy of the first constitutive substance in the two different substances included in the subject is represented by "E[kev]" is denoted by "µ1(E)", a linear attenuation coefficient obtained when radiation energy of the second constitutive substance in the two substances is represented by "E[kev]" is denoted by "µ2(E)", a thickness of the subject is denoted by "d", a mix ratio of the first constitutive substance is denoted by "γ", an arbitrary coefficient for conversion of the energy into a pixel value is denoted by "β", arbitrary monochromatic radiation energy is denoted by "Emono", and a pixel value of energy having an arbitrary spectrum is denoted by "I(Emono)", the pixel value generation unit generates the pixel value of the energy having the arbitrary spectrum by performing the following calculation:


     
    11. The radiation imaging system according to claim 2, wherein the information processing apparatus includes

    a first calculation unit configured to calculate an average of the pixel values of the arbitrary one of the plurality of pixels based on the pixel values of the arbitrary pixel,

    a second calculation unit configured to calculate an average value of the energy of the radiation quanta of the arbitrary pixel in accordance with variance of the pixel values of the arbitrary pixel calculated using the pixel values of the arbitrary pixel and an average of the pixel values of the arbitrary pixel calculated by the first calculation unit, and

    an estimation unit configured to estimate information on the thicknesses of the substances included in the subject using the average of the pixel values of the arbitrary pixel estimated by performing a calculation using attenuation coefficients of the substances included in the subject, the average value of the energy of the radiation quanta of the arbitrary pixel estimated by performing a calculation using the attenuation coefficients of the substances included in the subject, the first table, and the second table.


     
    12. The radiation imaging system according to claim 11, wherein

    the first table indicates the relationship among the estimated average of the pixel values of the arbitrary pixel, the thicknesses of the substances included in the subject, and densities of the substances included in the subject,

    the second table indicates the relationship among the estimated average value of the energy of the radiation quanta of the arbitrary pixel, the thicknesses of the substances included in the subject, and a the densities of the substances included in the subject, and

    the estimation unit estimates information on the thicknesses and the densities of the substances included in the subject.


     
    13. The radiation imaging system according to claim 12, wherein the image processing apparatus further includes a pixel value generation unit configured to generate pixel values of the substances in accordance with the estimated information on the thicknesses and the densities of the substances.
     
    14. The radiation imaging system according to any one of claims 2 to 13, wherein the average value of the energy of the radiation quanta is calculated using an amount of temporal and/or spatial change of a pixel value of the arbitrary pixel.
     
    15.  An information processing method comprising performing a process of estimating information on thicknesses of substances included in a subject using pixel values of an arbitrary one of a plurality of pixels which obtain pixel values corresponding to incident radiation transmitted through the subject, an average value of energy of radiation quanta of the arbitrary pixel calculated in accordance with the pixel values of the arbitrary pixel, a first table indicating the relationship between the pixel values of the arbitrary pixel and the thicknesses of the substances included in the subject, and a second table indicating the relationship between the average value of the energy of the radiation quanta of the arbitrary pixel and the thicknesses of the substances included in the subject.
     
    16. A program that, when executed by an information processing apparatus according to claim 1 causes the information processing apparatus to perform an information processing method according to claim 15.
     


    Ansprüche

    1. Informationsverarbeitungsvorrichtung,
    die einen Prozess zum Schätzen von Information über Dicken von in einem Subjekt enthaltenen Substanzen durchführt unter Verwendung von Pixelwerten eines beliebigen von mehreren Pixeln, die Pixelwerte entsprechend einfallender Transmissionsstrahlung durch das Subjekt erhalten, sowie von einem Mittelwert einer Energie von Strahlungsquanten des beliebigen Pixels, der gemäß den Pixelwerten des beliebigen Pixels berechnet wurde, von einer ersten Tabelle, die die Beziehung zwischen den Pixelwerten des beliebigen Pixels und den Dicken der im Subjekt enthaltenen Substanzen angibt, und von einer zweiten Tabelle, die die Beziehung zwischen dem Mittelwert der Energie der Strahlungsquanten des beliebigen Pixels und den Dicken der im Subjekt enthaltenen Substanzen angibt.
     
    2. Strahlungsbildgebungssystem, umfassend:

    einen Detektor, der mehrere Pixel beinhaltet, die Pixelwerte entsprechend einfallender Transmissionsstrahlung durch das Subjekt erhalten, sowie

    eine Informationsverarbeitungsvorrichtung nach Anspruch 1.


     
    3. Strahlungsbildgebungssystem nach Anspruch 2, wobei die Informationsverarbeitungsvorrichtung beinhaltet:

    eine erste Berechnungseinheit, die konfiguriert ist, ein Mittel der Pixelwerte des beliebigen der mehreren Pixel basierend auf den Pixelwerten des beliebigen Pixels zu berechnen,

    eine zweite Berechnungseinheit, die konfiguriert ist zum Berechnen eines Mittelwerts der Energie der Strahlungsquanten des beliebigen Pixels gemäß einer Varianz der Pixelwerte des beliebigen Pixels, die unter Verwendung der Pixelwerte des beliebigen Pixels berechnet wurde, und eines Mittels der Pixelwerte des beliebigen Pixels, das durch die erste Berechnungseinheit berechnet wurde, sowie

    eine Schätzungseinheit, die konfiguriert ist zum Schätzen von Information über die Dicken der im Subjekt enthaltenen Substanzen unter Verwendung des Mittels der Pixelwerte des beliebigen Pixels, das durch die erste Berechnungseinheit berechnet wurde, des Mittelwerts der Energie der Strahlungsquanten des beliebigen Pixels, der durch die zweite Berechnungseinheit berechnet wurde, der ersten Tabelle, und der zweiten Tabelle.


     
    4. Strahlungsbildgebungssystem nach Anspruch 3, wobei:

    die erste Tabelle die Beziehung zwischen dem Mittel der Pixelwerte des beliebigen Pixels, den Dicken der im Subjekt enthaltenen Substanzen, und einem Mischungsverhältnis zwischen den im Subjekt enthaltenen Substanzen angibt,

    die zweite Tabelle die Beziehung zwischen dem Mittelwert der Energie der Strahlungsquanten des beliebigen Pixels, den Dicken der im Subjekt enthaltenen Substanzen, und dem Mischungsverhältnis zwischen den im Subjekt enthaltenen Substanzen angibt, und

    die Schätzungseinheit Information über die Dicken der im Subjekt enthaltenen Substanzen und das Mischungsverhältnis schätzt.


     
    5. Strahlungsbildgebungssystem nach Anspruch 4,
    wobei die Bildverarbeitungsvorrichtung weiterhin eine Pixelwerterzeugungseinheit beinhaltet, die konfiguriert ist, Pixelwerte der Substanzen gemäß der geschätzten Information über die Dicken der Substanzen und das Mischungsverhältnis zu erzeugen.
     
    6. Strahlungsbildgebungssystem nach Anspruch 5,
    wobei die Pixelwerterzeugungseinheit eine erste Pixelwerterzeugungseinheit beinhaltet, die konfiguriert ist, basierend auf erster Information über eine Dicke der ersten konstitutiven Substanz und das Mischungsverhältnis einen ersten Pixelwert zu erzeugen, der ein Pixelwert einer ersten konstitutiven Substanz ist, sowie eine zweite Pixelwerterzeugungseinheit beinhaltet, die konfiguriert ist, basierend auf zweiter Information über eine Dicke der zweiten konstitutiven Substanz und das Mischungsverhältnis einen zweiten Pixelwert zu erzeugen, der ein Pixelwert einer zweiten konstitutiven Substanz ist.
     
    7. Strahlungsbildgebungssystem nach Anspruch 6,
    wobei, wenn ein linearer Dämpfungskoeffizient, der erhalten wird, wenn eine Strahlungsenergie der ersten konstitutiven Substanz in den im Subjekt enthaltenen zwei verschiedenen Substanzen durch "E[kev]" dargestellt wird, mit "µ1(E)" bezeichnet wird, ein linearer Dämpfungskoeffizient, der erhalten wird, wenn eine Strahlungsenergie der zweiten konstitutiven Substanz in den zwei Substanzen durch "E[kev]" dargestellt wird, mit "µ2(E)" bezeichnet wird, eine Dicke des Subjekts mit "d" bezeichnet wird, ein Mischungsverhältnis der ersten konstitutiven Substanz mit "γ" bezeichnet wird, ein beliebiger Koeffizient zur Umwandlung der Energie in einen Pixelwert mit "β" bezeichnet wird, der erste Pixelwert mit "I1" bezeichnet wird, und der zweite Pixelwert mit "I2" bezeichnet wird, die Pixelwerterzeugungseinheit einen Pixelwert von wenigstens einer der Substanzen durch Durchführen von wenigstens einer der folgenden Berechnungen erzeugt:

    und


     
    8. Strahlungsbildgebungssystem nach Anspruch 6,
    wobei, wenn eine effektive Energie der Strahlung mit "Eeff" bezeichnet wird, ein linearer Dämpfungskoeffizient, der erhalten wird, wenn eine effektive Energie der Strahlung der ersten konstitutiven Substanz in den im Subjekt enthaltenen zwei verschiedenen Substanzen durch "Eeff[kev]" dargestellt wird, mit "µ1(Eeff)" bezeichnet wird, ein linearer Dämpfungskoeffizient, der erhalten wird, wenn eine effektive Energie der Strahlung der zweiten konstitutiven Substanz in den zwei Substanzen durch "Eeff[kev]" dargestellt wird, mit "µ2(Eeff)" bezeichnet wird, eine Dicke der ersten konstitutiven Substanz mit "d1" bezeichnet wird, eine Dicke der zweiten konstitutiven Substanz mit "d2" bezeichnet wird, ein Mischungsverhältnis der ersten Substanz mit "γ" bezeichnet wird, ein beliebiger Koeffizient zur Umwandlung der Energie in einen Pixelwert mit "β" bezeichnet wird, der erste Pixelwert mit "I1" bezeichnet wird, und der zweite Pixelwert mit "I2" bezeichnet wird, die Pixelwerterzeugungseinheit einen Pixelwert von wenigstens einer der Substanzen durch Durchführen von wenigstens einer der folgenden Berechnungen erzeugt:

    und


     
    9. Strahlungsbildgebungssystem nach Anspruch 6,
    wobei, wenn eine effektive Energie der Strahlung mit "Eeff" bezeichnet wird, ein linearer Dämpfungskoeffizient, der erhalten wird, wenn eine effektive Energie der Strahlung der ersten konstitutiven Substanz in den im Subjekt enthaltenen zwei verschiedenen Substanzen durch "Eeff[kev]" dargestellt wird, mit "µ1(Eeff)" bezeichnet wird, ein linearer Dämpfungskoeffizient, der erhalten wird, wenn eine effektive Energie der Strahlung der zweiten konstitutiven Substanz in den zwei Substanzen durch "Eeff[kev]" dargestellt wird, mit "µ2(Eeff)" bezeichnet wird, eine Dicke des Subjekts mit "d" bezeichnet wird, ein Mischungsverhältnis der ersten Substanz mit "γ" bezeichnet wird, ein beliebiger Koeffizient zur Umwandlung der Energie in einen Pixelwert mit "β" bezeichnet wird, ein berechnetes arithmetisches Mittel der Pixelwerte des beliebigen Pixels mit "IAve" bezeichnet wird, der erste Pixelwert mit "I1" bezeichnet wird, und der zweite Pixelwert mit "I2" bezeichnet wird, die Pixelwerterzeugungseinheit einen Pixelwert von wenigstens einer der Substanzen durch Durchführen von wenigstens einer der folgenden Berechnungen erzeugt:

    und


     
    10. Strahlungsbildgebungssystem nach Anspruch 5,
    wobei, wenn ein linearer Dämpfungskoeffizient, der erhalten wird, wenn eine Strahlungsenergie der ersten konstitutiven Substanz in den im Subjekt enthaltenen zwei verschiedenen Substanzen durch "E[kev]" dargestellt wird, mit "µ1(E)" bezeichnet wird, ein linearer Dämpfungskoeffizient, der erhalten wird, wenn eine Strahlungsenergie der zweiten konstitutiven Substanz in den zwei Substanzen durch "E[kev]" dargestellt wird, mit "µ2(E)" bezeichnet wird, eine Dicke des Subjekts mit "d" bezeichnet wird, ein Mischungsverhältnis der ersten konstitutiven Substanz mit "γ" bezeichnet wird, ein beliebiger Koeffizient zur Umwandlung der Energie in einen Pixelwert mit "β" bezeichnet wird, eine beliebige monochromatische Strahlungsenergie mit "Emono" bezeichnet wird, und ein Pixelwert von Energie mit einem beliebigen Spektrum mit "I(Emono)" bezeichnet wird, die Pixelwerterzeugungseinheit den Pixelwert der Energie mit dem beliebigen Spektrum durch Durchführen der folgenden Berechnung erzeugt:


     
    11. Strahlungsbildgebungssystem nach Anspruch 2, wobei die Informationsverarbeitungsvorrichtung beinhaltet:

    eine erste Berechnungseinheit, die konfiguriert ist, ein Mittel der Pixelwerte des beliebigen der mehreren Pixel basierend auf den Pixelwerten des beliebigen Pixels zu berechnen,

    eine zweite Berechnungseinheit, die konfiguriert ist zum Berechnen eines Mittelwerts der Energie der Strahlungsquanten des beliebigen Pixels gemäß einer Varianz der Pixelwerte des beliebigen Pixels, die unter Verwendung der Pixelwerte des beliebigen Pixels berechnet wurde, und eines Mittels der Pixelwerte des beliebigen Pixels, das durch die erste Berechnungseinheit berechnet wurde, sowie

    eine Schätzungseinheit, die konfiguriert ist zum Schätzen von Information über die Dicken der im Subjekt enthaltenen Substanzen unter Verwendung des Mittels der Pixelwerte des beliebigen Pixels, das durch Durchführen einer Berechnung unter Verwendung von Dämpfungskoeffizienten der im Subjekt enthaltenen Substanzen geschätzt wurde, des Mittelwerts der Energie der Strahlungsquanten des beliebigen Pixels, der durch Durchführen einer Berechnung unter Verwendung der Dämpfungskoeffizienten der im Subjekt enthaltenen Substanzen geschätzt wurde, der ersten Tabelle, und der zweiten Tabelle.


     
    12. Strahlungsbildgebungssystem nach Anspruch 11, wobei:

    die erste Tabelle die Beziehung zwischen dem geschätzten Mittel der Pixelwerte des beliebigen Pixels, den Dicken der im Subjekt enthaltenen Substanzen, und Dichten der im Subjekt enthaltenen Substanzen angibt,

    die zweite Tabelle die Beziehung zwischen dem geschätzten Mittelwert der Energie der Strahlungsquanten des beliebigen Pixels, den Dicken der im Subjekt enthaltenen Substanzen, und den Dichten der im Subjekt enthaltenen Substanzen angibt, und

    die Schätzungseinheit Information über die Dicken und die Dichten der im Subjekt enthaltenen Substanzen schätzt.


     
    13. Strahlungsbildgebungssystem nach Anspruch 12,
    wobei die Bildverarbeitungsvorrichtung weiterhin eine Pixelwerterzeugungseinheit beinhaltet, die konfiguriert ist, Pixelwerte der Substanzen gemäß der geschätzten Information über die Dicken und die Dichten der Substanzen zu erzeugen.
     
    14. Strahlungsbildgebungssystem nach einem der Ansprüche 2 bis 13,
    wobei der Mittelwert der Energie der Strahlungsquanten unter Verwendung eines Betrags einer zeitlichen und/oder räumlichen Änderung eines Pixelwerts des beliebigen Pixels berechnet wird.
     
    15. Informationsverarbeitungsverfahren,
    das ein Durchführen eines Prozesses umfasst zum Schätzen von Information über Dicken von in einem Subjekt enthaltenen Substanzen unter Verwendung von Pixelwerten eines beliebigen von mehreren Pixeln, die Pixelwerte entsprechend einfallender Transmissionsstrahlung durch das Subjekt erhalten, sowie von einem Mittelwert einer Energie von Strahlungsquanten des beliebigen Pixels, der nach Maßgabe der Pixelwerte des beliebigen Pixels berechnet wurde, von einer ersten Tabelle, die die Beziehung zwischen den Pixelwerte des beliebigen Pixels und den Dicken der im Subjekt enthaltenen Substanzen angibt, und von einer zweiten Tabelle, die die Beziehung zwischen dem Mittelwert der Energie der Strahlungsquanten des beliebigen Pixels und den Dicken der im Subjekt enthaltenen Substanzen angibt.
     
    16. Programm, das bei Ausführung durch eine
    Informationsverarbeitungsvorrichtung nach Anspruch 1 diese veranlasst, ein Informationsverarbeitungsverfahren nach Anspruch 15 durchzuführen.
     


    Revendications

    1. Appareil de traitement d'informations qui exécute un traitement d'estimation d'informations concernant des épaisseurs de substances comprises dans un sujet à l'aide de valeurs de pixel d'un pixel arbitraire d'une pluralité de pixels qui obtiennent des valeurs de pixel correspondant à un rayonnement incident transmis à travers le sujet, d'une valeur moyenne d'énergie de quanta de rayonnement du pixel arbitraire calculée conformément aux valeurs de pixel du pixel arbitraire, d'une première table indiquant la relation entre les valeurs de pixel du pixel arbitraire et les épaisseurs des substances comprises dans le sujet, et d'une seconde table indiquant la relation entre la valeur moyenne de l'énergie des quanta de rayonnement du pixel arbitraire et les épaisseurs des substances comprises dans le sujet.
     
    2. Système d'imagerie radiologique, comprenant :

    un détecteur comprenant une pluralité de pixels qui obtiennent des valeurs de pixel correspondant à un rayonnement incident transmis à travers un sujet ; et

    un appareil de traitement d'informations selon la revendication 1.


     
    3. Système d'imagerie radiologique selon la revendication 2, dans lequel l'appareil de traitement d'informations comprend
    une première unité de calcul configurée pour calculer une moyenne des valeurs de pixel du pixel arbitraire de la pluralité de pixels sur la base des valeurs de pixel du pixel arbitraire,
    une seconde unité de calcul configurée pour calculer une valeur moyenne de l'énergie des quanta de rayonnement du pixel arbitraire conformément à une variance des valeurs de pixel du pixel arbitraire calculée à l'aide des valeurs de pixel du pixel arbitraire et à une moyenne des valeurs de pixel du pixel arbitraire calculée par la première unité de calcul, et
    une unité d'estimation configurée pour estimer des informations concernant les épaisseurs des substances comprises dans le sujet à l'aide de la moyenne des valeurs de pixel du pixel arbitraire calculée par la première unité de calcul, de la valeur moyenne de l'énergie des quanta de rayonnement du pixel arbitraire calculée par la seconde unité de calcul, de la première table et de la seconde table.
     
    4. Système d'imagerie radiologique selon la revendication 3, dans lequel
    la première table indique la relation entre la moyenne des valeurs de pixel du pixel arbitraire, les épaisseurs des substances comprises dans le sujet et un taux de mélange entre les substances comprises dans le sujet,
    la seconde table indique la relation entre la valeur moyenne de l'énergie des quanta de rayonnement du pixel arbitraire, les épaisseurs des substances comprises dans le sujet et le taux de mélange entre les substances comprises dans le sujet, et
    l'unité d'estimation estime des informations concernant les épaisseurs des substances comprises dans le sujet et le taux de mélange.
     
    5. Système d'imagerie radiologique selon la revendication 4, dans lequel l'appareil de traitement d'image comprend en outre une unité de génération de valeurs de pixel configurée pour générer des valeurs de pixel des substances conformément aux informations estimées concernant les épaisseurs des substances et le taux de mélange.
     
    6. Système d'imagerie radiologique selon la revendication 5, dans lequel l'unité de génération de valeurs de pixel comprend une première unité de génération de valeur de pixel configurée pour générer une première valeur de pixel qui est une valeur de pixel d'une première substance constitutive sur la base de premières informations concernant une épaisseur de la première substance constitutive et le taux de mélange et comprend une seconde unité de génération de valeur de pixel configurée pour générer une seconde valeur de pixel qui est une valeur de pixel d'une seconde substance constitutive sur la base de secondes informations concernant une épaisseur de la seconde substance constitutive et le taux de mélange.
     
    7. Système d'imagerie radiologique selon la revendication 6, dans lequel, lorsqu'un coefficient d'atténuation linéaire, obtenu lorsqu'une énergie de rayonnement de la première substance constitutive des deux substances différentes comprises dans le sujet est représentée par « E[kev] », est désigné par « µ1(E) », qu'un coefficient d'atténuation linéaire, obtenu lorsqu'une énergie de rayonnement de la seconde substance constitutive des deux substances est représentée par « E[kev] », est désigné par « µ2(E) », qu'une épaisseur du sujet est désignée par « d », qu'un taux de mélange de la première substance constitutive est désigné par « γ », qu'un coefficient arbitraire de conversion de l'énergie en une valeur de pixel est désigné par « β », que la première valeur de pixel est désignée par « I1 » et que la seconde valeur de pixel est désignée par « I2 », l'unité de génération de valeurs de pixel génère une valeur de pixel d'au moins l'une des substances par une exécution d'au moins l'un des calculs suivants :

    et


     
    8. Système d'imagerie radiologique selon la revendication 6, dans lequel, lorsque l'énergie efficace du rayonnement est désignée par « Eeff », qu'un coefficient d'atténuation linéaire, obtenu lorsqu'une énergie efficace du rayonnement de la première substance constitutive des deux substances différentes comprises dans le sujet est représentée par « Eeff[kev] », est désigné par « µ1(Eeff) », qu'un coefficient d'atténuation linéaire, obtenu lorsqu'une énergie efficace du rayonnement de la seconde substance constitutive des deux substances est représentée par « Eeff[kev] », est désigné par « µ2(Eeff) », qu'une épaisseur de la première substance constitutive est désignée par « d1 », qu'une épaisseur de la seconde substance constitutive est désignée par « d2 », qu'un taux de mélange de la première substance est désigné par « γ », qu'un coefficient arbitraire de conversion de l'énergie en une valeur de pixel est désigné par « β », que la première valeur de pixel est désignée par « I1 » et que la seconde valeur de pixel est désignée par « I2 », l'unité de génération de valeurs de pixel génère une valeur de pixel d'au moins l'une des substances par une exécution d'au moins l'un des calculs suivants :

    et


     
    9. Système d'imagerie radiologique selon la revendication 6, dans lequel, lorsqu'une énergie efficace du rayonnement est désignée par « Eeff », qu'un coefficient d'atténuation linéaire, obtenu lorsqu'une énergie efficace du rayonnement de la première substance constitutive des deux substances différentes comprises dans le sujet est représentée par « Eeff[kev] », est désigné par « µ1(Eeff) », qu'un coefficient d'atténuation linéaire, obtenu lorsqu'une énergie efficace du rayonnement de la seconde substance constitutive des deux substances est représentée par « Eeff[kev] », est désigné par « µ2(Eeff) », qu'une épaisseur du sujet est désignée par « d », qu'un taux de mélange de la première substance constitutive est désigné par « γ », qu'un coefficient arbitraire de conversion de l'énergie en une valeur de pixel est désigné par « β », qu'une moyenne arithmétique calculée des valeurs de pixel du pixel arbitraire est désignée par « IAve », que la première valeur de pixel est désignée par « I1 » et que la seconde valeur de pixel est désignée par « I2 », l'unité de génération de valeurs de pixel génère une valeur de pixel d'au moins l'une des substances par une exécution d'au moins l'un des calculs suivants :

    et


     
    10. Système d'imagerie radiologique selon la revendication 5, dans lequel, lorsqu'un coefficient d'atténuation linéaire, obtenu lorsqu'une énergie de rayonnement de la première substance constitutive des deux substances différentes comprises dans le sujet est représentée par « E[kev] », est désigné par « µ1(E) », qu'un coefficient d'atténuation linéaire, obtenu lorsqu'une énergie de rayonnement de la seconde substance constitutive des deux substances est représentée par « E[kev] », est désigné par « µ2(E) », qu'une épaisseur du sujet est désignée par « d », qu'un taux de mélange de la première substance constitutive est désigné par « γ », qu'un coefficient arbitraire de conversion de l'énergie en une valeur de pixel est désigné par « β », qu'une énergie de rayonnement monochromatique arbitraire est désignée par « Emono », et qu'une valeur de pixel d'énergie ayant un spectre arbitraire est désignée par « I(Emono) », l'unité de génération de valeurs de pixel génère la valeur de pixel de l'énergie ayant le spectre arbitraire par une exécution du calcul suivant :


     
    11. Système d'imagerie radiologique selon la revendication 2, dans lequel l'appareil de traitement d'informations comprend
    une première unité de calcul configurée pour calculer une moyenne des valeurs de pixel du pixel arbitraire de la pluralité de pixels sur la base des valeurs de pixel du pixel arbitraire,
    une seconde unité de calcul configurée pour calculer une valeur moyenne de l'énergie des quanta de rayonnement du pixel arbitraire conformément à une variance des valeurs de pixel du pixel arbitraire calculée à l'aide des valeurs de pixel du pixel arbitraire et à une moyenne des valeurs de pixel du pixel arbitraire calculée par la première unité de calcul, et
    une unité d'estimation configurée pour estimer des informations concernant les épaisseurs des substances comprises dans le sujet à l'aide de la moyenne des valeurs de pixel du pixel arbitraire estimée par une exécution d'un calcul à l'aide de coefficients d'atténuation des substances comprises dans le sujet, de la valeur moyenne de l'énergie des quanta de rayonnement du pixel arbitraire estimée par une exécution d'un calcul à l'aide des coefficients d'atténuation des substances comprises dans le sujet, de la première table et de la seconde table.
     
    12. Système d'imagerie radiologique selon la revendication 11, dans lequel
    la première table indique la relation entre la moyenne estimée des valeurs de pixel du pixel arbitraire, les épaisseurs des substances comprises dans le sujet et des densités des substances comprises dans le sujet,
    la seconde table indique la relation entre la valeur moyenne estimée de l'énergie des quanta de rayonnement du pixel arbitraire, les épaisseurs des substances comprises dans le sujet et les densités des substances comprises dans le sujet, et
    l'unité d'estimation estime des informations concernant les épaisseurs et les densités des substances comprises dans le sujet.
     
    13. Système d'imagerie radiologique selon la revendication 12, dans lequel l'appareil de traitement d'image comprend en outre une unité de génération de valeurs de pixel configurée pour générer des valeurs de pixel des substances conformément aux informations estimées concernant les épaisseurs et les densités des substances.
     
    14. Appareil d'imagerie radiologique selon l'une quelconque des revendications 2 à 13, dans lequel la valeur moyenne de l'énergie des quanta de rayonnement est calculée à l'aide d'une quantité de variation temporelle et/ou spatiale d'une valeur de pixel du pixel arbitraire.
     
    15. Procédé de traitement d'informations comprenant l'étape consistant à exécuter un traitement d'estimation d'informations concernant des épaisseurs de substances comprises dans un sujet à l'aide de valeurs de pixel d'un pixel arbitraire d'une pluralité de pixels qui obtiennent des valeurs de pixel correspondant à un rayonnement incident transmis à travers le sujet, d'une valeur moyenne d'énergie des quanta de rayonnement du pixel arbitraire calculée conformément aux valeurs de pixel du pixel arbitraire, d'une première table indiquant la relation entre les valeurs de pixel du pixel arbitraire et les épaisseurs des substances comprises dans le sujet, et d'une seconde table indiquant la relation entre la valeur moyenne de l'énergie des quanta de rayonnement du pixel arbitraire et les épaisseurs des substances comprises dans le sujet.
     
    16. Programme qui, lorsqu'il est exécuté par un appareil de traitement d'informations selon la revendication 1, amène l'appareil de traitement d'informations à mettre en œuvre un procédé de traitement d'informations selon la revendication 15.
     




    Drawing























    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description