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Image reconfiguration device, image reconfiguration method, image reconfiguration program, ct device

外国特許コード F120007034
掲載日 2012年11月19日
出願国 欧州特許庁(EPO)
出願番号 07832069
公報番号 2092891
公報番号 2092891
出願日 平成19年11月13日(2007.11.13)
公報発行日 平成21年8月26日(2009.8.26)
公報発行日 平成26年9月17日(2014.9.17)
国際出願番号 JP2007072339
国際公開番号 WO2008059982
国際出願日 平成19年11月13日(2007.11.13)
国際公開日 平成20年5月22日(2008.5.22)
優先権データ
  • 2007JP072339 (2007.11.13) WO
  • 特願2006-307058 (2006.11.13) JP
発明の名称 (英語) Image reconfiguration device, image reconfiguration method, image reconfiguration program, ct device
発明の概要(英語) A computerized tomography apparatus and program for obtaining a cross-sectional image corresponding to projections are provided in which, for a temporary cross-sectional image f(x, y) obtained in some manner, an evaluation function E is defined which includes differences between projections calculated from f(x, y) and measured projections, and f(x, y) is changed in a manner which substantially decreases E.
The computerized tomography apparatus and program are characterized in which a back projection operation, which is required by conventional computerized tomography, is not essentially required.
The computerized tomography apparatus and program are particularly effective in removal or reduction of metal artifacts, aliasing artifacts and the like.(see diagramm)
特許請求の範囲(英語) [claim1]
1. An image reconstructing device for obtaining a cross-sectional image of an object from radiographic projections obtained by irradiating the object with a beam of radiation, comprising: means (a) for obtaining an energy E 0 including differences between projections calculated from a current estimated cross-sectional image of the object and the radiographic projections, wherein the energy E 0 is given by (Equation image 18 not included in text)
where H 0: differences between projections calculated from the current estimated cross-sectional image and the radiographic projections, c 0: a coefficient which represents a strength of a smoothing term, sigma 0: a standard deviation of a local region of the current estimated cross-sectional image, T: a virtual temperature parameter, and S 0: an entropy, calculated based on a number of pixels having the same pixel value, of a local region of the current estimated cross-sectional image;means (b) for modifying a portion of the current estimated cross-sectional image; means (c) for obtaining an energy E 1 including differences between projections calculated from the modified estimated cross-sectional image and the radiographic projections, wherein the energy E 1is given by (Equation image 19 not included in text)
where H: differences between projections calculated from the modified estimated cross-sectional image and the radiographic projections, c: a coefficient which represents a strength of a smoothing term, sigma : a standard deviation of a local region of the modified estimated cross-sectional image, T: the virtual temperature parameter, and S: an entropy, calculated based on a number of pixels having the same pixel value, of a local region of the modified estimated cross-sectional image;means (d) for obtaining a differential DELTA E between the energy E 0 and the energy E 1; means (e) for determining whether or not the modification is to be accepted, based on an acceptance function using the differential DELTA E and the temperature parameter T for controlling an acceptance probability, and reflecting a result of the determination on the current estimated cross-sectional image; and means (f) for changing a value of the temperature parameter T every time the number of iterations of a series of processes of the means (a) to (e) reaches a predetermined value.
[claim2]
2. The image reconstructing device of claim 1, comprising: instead of the means (a) and (c) for obtaining E 0 and E 1, means (h) for calculating DELTA H using (Equation image 20 not included in text)
and obtaining DELTA E in means (d) including the calculated DELTA H as a component,
where, when the current estimated cross-sectional image of the object is represented by f(x, y) and the portion modified by the means (b) is represented by DELTA f(x, y), DELTA f(x, y) is a cross-sectional image having a value of DELTA micron only at a coordinate point (x 0, y 0) and zero elsewhere, and p(r, theta ) represents a projection calculated from the current estimated cross-sectional image of the object, p 0(r, theta ) represents a radiographic projection of the object, r represents a channel position of a one-dimensional detector taking the projection, theta represents a projection angle, and r(theta )=x 0costheta +y 0sintheta .
[claim3]
3. The image reconstructing device of claim 1, comprising: instead of the means (a) and (c) for obtaining E 0 and E 1, means (h) for calculating DELTA H using (Equation image 21 not included in text)
and obtaining DELTA E in means (d) including the calculated DELTA H as a component,
where, when the current estimated cross-sectional image of the object is represented by f(x, y) and the portion modified by the means (b) is represented by DELTA f(x, y), DELTA f(x, y) is a cross-sectional image having a value of DELTA micron only at a coordinate point (x 0, y 0) and zero elsewhere, and p(r, theta ) represents a projection calculated from the current estimated cross-sectional image of the object, p 0(r, theta ) represents a radiographic projection of the object, r represents a channel position of a one-dimensional detector taking the projection, theta represents a projection angle, r(theta )=x 0costheta +y 0sintheta , and M represents the number of projection angles.
[claim4]
4. The image reconstructing device of claim 2 or 3, wherein
the means (h) calculates DELTA sigma using , (Equation image 22 not included in text)
and obtains DELTA E including as a component a sum of a product cDELTA sigma of the calculated DELTA sigma and a coefficient c, and the DELTA H,
where sigma represents a standard deviation of luminance values of dxd pixels around the coordinate point (x 0, y 0) and is calculated by (Equation image 23 not included in text)
and f i and f j represent values of f(x 0, y 0) before and after the modification by the means (b),
where (Equation image 24 not included in text) (Equation image 25 not included in text)
[claim5]
5. The image reconstructing device of claim 2 or 3, wherein
the means (h) calculates DELTA S using (Equation image 26 not included in text)
and obtains DELTA E including as a component a sum of a product -TDELTA S of the calculated DELTA S and the temperature parameter T, and the DELTA H,
where S represents an entropy of a local region image of dxd pixels around the coordinate point (x 0, y 0) and is calculated by (Equation image 27 not included in text)
where N: a total number of pixels in the local region image, N i: a total number of pixels whose pixel value is a digital value of i, N j: a total number of pixels whose pixel value is a digital value of j , k: a constant, a pixel value is changed from the digital value i to the digital value j by the modification by the means (b).
[claim6]
6. The image reconstructing device of claim 1, comprising: instead of the means (e) and (f), means (e1) for determining whether or not the modification is to be accepted, based on an acceptance function using the differential DELTA E and the temperature parameter T for controlling an acceptance probability, and reserving reflection of a result of determination on the current estimated cross-sectional image; and means (f1) for reflecting the reservation(s) in the means (e1) on the current estimated cross-sectional image and changing a value of the temperature parameter T every time the number of iterations of a series of processes of the means (a) to (d) and (e1) reaches a predetermined value.
[claim7]
7. An image reconstructing device for obtaining a cross-sectional image of an object from projections obtained by irradiating the object with a beam of radiation, comprising: means (m1) for calculating a back projection g 0(x, y) of a radiographic projection p 0(r, theta ) of the object by a back projection operation without filtering; means (m2) for calculating a projection p(r, theta ) from a current estimated cross-sectional image f(x, y) of the object, and calculating a back projection g(x, y) of the projection p(r, theta ) by a back projection operation without filtering; means (m3) for generating an image DELTA micron (x, y) whose pixel value is a change value
of the current estimated cross-sectional image f(x, y) of the object; means (m4) for generating an image DELTA H(x, y) by applying(Equation image 28 not included in text)
to each pixel value,
where M: the number of projection angles;means (m5) for calculating DELTA E(x, y) using the DELTA H(x, y),
where DELTA E(x, y) represents a differential between evaluation functions E 0(x, y) and E 1(x, y), E 0(x, y) represents an evaluation function including a difference between the projection p(r, theta ) calculated from the estimated cross-sectional image f(x, y) and the radiographic projection p 0(r, theta ), and E 1(x, y) represents an evaluation function including a difference between a projection p(r, theta )+DELTA p(r, theta ), calculated from a sum f(x, y)+DELTA micron (x, y) of the estimated cross-sectional image f(x, y) and the image DELTA micron (x, y) obtained by the means (m3), and the radiographic projection p 0(r, theta );means (m6) for setting the DELTA micron (x, y) to 0 at a coordinate point (x, y) where the DELTA E is positive; and means (m7) for setting a sum of the estimated cross-sectional image f(x, y) and the image DELTA micron (x, y) obtained by the means (m6) as a new estimated cross-sectional image f(x, y) and repeating processes of the means (m2) to (m6) with respect to the new estimated cross-sectional image f(x, y).
[claim8]
8. An image reconstructing device for obtaining a cross-sectional image of an object from projections obtained by irradiating the object with a beam of radiation, comprising: means (m1) for calculating a back projection g 0(x, y) of a radiographic projection p 0(r, theta ) of the object using (Equation image 29 not included in text) r: a channel position of a one-dimensional detector taking the projection, theta : a projection angle,means (m2) for calculating a projection p(r, theta ) from a current estimated cross-sectional image f(x, y) of the object, and calculating a back projection g(x, y) of the projection p(r, theta ) using (Equation image 30 not included in text) means (m3) for generating an image DELTA micron (x, y) whose pixel value is a change value of the current estimated cross-sectional image f(x, y) of the object; means (m4) for generating an image DELTA H(x, y) by applying (Equation image 31 not included in text)
to each pixel value,
where M: the number of projection angles;means (m5) for generating DELTA sigma (x, y) by applying (Equation image 32 not included in text)
to each pixel value,
where sigma represents a standard deviation of luminance values of dxd pixels around a coordinate point (x 0, y 0) and is calculated by (Equation image 33 not included in text)
and f i and f j represent values of f(x 0, y 0) before and after a change,
where (Equation image 34 not included in text) (Equation image 35 not included in text) means (m6) for generating an image DELTA S by applying (Equation image 36 not included in text)
to each value,
where S represents an entropy of a local region image of dxd pixels around the coordinate point (x 0, y 0) and is calculated by (Equation image 37 not included in text)
where N: a total number of pixels in the local region image, N i: a total number of pixels whose pixel value is a digital value of i, N j: a total number of pixels whose pixel value is a digital value of j , k: a constant, a pixel value is changed from the digital value i to the digital value j by the modification by the means (b);means (m7) for calculating DELTA E(x, y) based on (Equation image 38 not included in text)
where c: a coefficient, T: a virtual temperature parameter,means (m8) for setting the DELTA micron (x, y) to 0 at a coordinate point (x, y) where the DELTA E is positive; means (m9) for setting a sum of the estimated cross-sectional image f(x, y) and the image DELTA micron (x, y) obtained by the means (m8) as a new estimated cross-sectional image f(x, y); and means (m10) for multiplying the T by alpha , alpha <1, and repeating processes of the means (m2) to (m9).
[claim9]
9. A method for obtaining a cross-sectional image of an object from radiographic projections obtained by irradiating the object with a beam of radiation, comprising the steps of: (a) obtaining an energy E 0 including differences between projections calculated from a current estimated cross-sectional image of the object and the radiographic projections, wherein the energy E 0 is given by (Equation image 39 not included in text)
where H 0: differences between projections calculated from the current estimated cross-sectional image and the radiographic projections, c 0: a coefficient which represents a strength of a smoothing term, sigma 0: a standard deviation of a local region of the current estimated cross-sectional image, T: a virtual temperature parameter, and S 0: an entropy, calculated based on a number of pixels having the same pixel value, of a local region of the current estimated cross-sectional image;(b) modifying a portion of the current estimated cross-sectional image; (c) obtaining an energy E 1 including differences between projections calculated from the modified estimated cross-sectional image and the radiographic projections, wherein the energy E 1 is given by (Equation image 40 not included in text)
where H: differences between projections calculated from the modified estimated cross-sectional image and the radiographic projections, c: a coefficient which represents a strength of a smoothing term, sigma : a standard deviation of a local region of the modified estimated cross-sectional image, T: the virtual temperature parameter, and S: an entropy, calculated based on a number of pixels having the same pixel value, of a local region of the modified estimated cross-sectional image;(d) obtaining a differential DELTA E between the energy E 0 and the energy E 1; (e) determining whether or not the modification is to be accepted, based on an acceptance function using the differential DELTA E and the temperature parameter T for controlling an acceptance probability; (f) reflecting a result of the determination on the current estimated cross-sectional image, and returning to the step (a); (g) changing a value of the temperature parameter T every time the number of iterations of the steps (a) to (f) reaches a predetermined value; and (h) determining whether or not the result of the determination in the step (e) satisfies predetermined stop conditions, and if the result of the determination in the step (e) satisfies predetermined stop conditions, ending the process.
[claim10]
10. An image reconstructing program for obtaining a cross-sectional image of an object from radiographic projections obtained by irradiating the object with a beam of radiation, wherein
the program causes a computer to execute the steps of: (a) obtaining an Energy E 0
including differences between projections calculated from a current estimated cross-sectional image of the object and the radiographic projections, wherein the energy E 0 is given by (Equation image 41 not included in text)
where H 0: differences between projections calculated from the current estimated cross-sectional image and the radiographic projections, c 0: a coefficient which represents a strength of a smoothing term, sigma 0: a standard deviation of a local region of the current estimated cross-sectional image, T: a virtual temperature parameter, and S 0: an entropy, calculated based on a number of pixels having the same pixel value, of a local region of the current estimated cross-sectional image;(b) modifying a portion of the current estimated cross-sectional image; (c) obtaining an energy E 1 including differences between projections calculated from the modified estimated cross-sectional image and the radiographic projections, wherein the energy E 1 is given by (Equation image 42 not included in text)
where H: differences between projections calculated from the modified estimated cross-sectional image and the radiographic projections, c: a coefficient which represents a strength of a smoothing term, sigma : a standard deviation of a local region of the modified estimated cross-sectional image, T: the virtual temperature parameter, and S: an entropy, calculated based on a number of pixels having the same pixel value, of a local region of the modified estimated cross-sectional image;(d) obtaining a differential DELTA E between the energy E 0 and the energy E 1; (e) determining whether or not the modification is to be accepted, based on an acceptance function using the differential DELTA E and the temperature parameter T for controlling an acceptance probability; (f) reflecting a result of the determination on the current estimated cross-sectional image, and returning to the step (a); and (g) changing a value of the temperature parameter T every time the number of iterations of the steps (a) to (f) reaches a predetermined value.
[claim11]
11. A CT apparatus comprising: means (A) for obtaining radiographic projections by irradiating an object with a beam of radiation; and means (B) for obtaining a cross-sectional image of the object from the projections,
wherein the means (B) includes: means (b1) for obtaining an energy E 0 including differences between projections calculated from a current estimated cross-sectional image of the object and the projections by irradiating the object with the beam of radiation (hereinafter referred to as "radiographic projections"), wherein the energy E 0 is given by (Equation image 43 not included in text)
where H 0: differences between projections calculated from the current estimated cross-sectional image and the radiographic projections, c 0: a coefficient which represents a strength of a smoothing term, sigma 0: a standard deviation of a local region of the current estimated cross-sectional image, T: a virtual temperature parameter, and S 0: an entropy, calculated based on a number of pixels having the same pixel value, of a local region of the current estimated cross-sectional image;means (b2) for modifying a portion of the current estimated cross-sectional image; means (b3) for obtaining an energy E 1 including differences between projections calculated from the modified estimated cross-sectional image and the radiographic projections, wherein the energy E 1 is given by (Equation image 44 not included in text)
where H: differences between projections calculated from the modified estimated cross-sectional image and the radiographic projections, c: a coefficient which represents a strength of a smoothing term, sigma : a standard deviation of a local region of the modified estimated cross-sectional image, T: the virtual temperature parameter, and S: an entropy, calculated based on a number of pixels having the same pixel value, of a local region of the modified estimated cross-sectional image;means (b4) for obtaining a differential DELTA E between the energy E 0 and the energy E1: means (b5) for determining whether or not the modification is to be accepted, based on an acceptance function using the differential DELTA E and the temperature parameter T for controlling an acceptance probability, and reflecting a result of the determination on the current estimated cross-sectional image; and means (b6) for changing a value of the temperature parameter T every time the number of iterations of a series of processes of the means (b1) to (b5) reaches a predetermined value.
  • 出願人(英語)
  • KYOTO INSTITUTE OF TECHNOLOGY
  • 発明者(英語)
  • NISHIKAWA YUKIHIRO
国際特許分類(IPC)
指定国 Contracting States: AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IS IT LI LT LU LV MC MT NL PL PT RO SE SI SK TR
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