JP2006312027A - Radiation diagnostic equipment - Google Patents

Abstract

In a PET-CT apparatus, a highly accurate body contour is detected only from a transmission CT apparatus, and the accuracy of truncation correction is improved.
First projection data acquired at a projection angle within a projection angle range in which the entire body part of the subject P is within the effective field of view, and within a projection angle range in which a part of the body part is outside the effective field of view. The second projection data acquired at the projection angle is collected, a plurality of primary extrapolation-type candidates are calculated based on the difference between the sum values, and a plurality of third projection data candidates are formed with the second projection data. And obtaining the third projection data from the plurality of third projection data candidates based on the difference between the centroid of the third projection data estimated from the centroid of the first projection data and the centroids of the plurality of third projection data candidates, Based on the third projection data, the position information of the body contour in the second projection data is detected to obtain a secondary extrapolation formula for correcting the second projection data, and formed by the second projection data and the secondary extrapolation formula. Obtain fourth projection data.
[Selection] Figure 1

Description

  The present invention relates to a radiation diagnostic apparatus that performs body contour detection of a subject only from a CT image acquired by a transmission CT apparatus.

  Among the radiation diagnostic apparatuses, transmission tomography (TCT) is a radiation source (X-ray or gamma ray) and a detector installed outside the subject, and the body axis of the subject. The radiation transmitted through the subject is measured as a pair, and a tomographic distribution of the radiation transmittance of the subject is obtained. A typical transmission CT is an X-ray CT (Computerized Tomography) apparatus, and a transmission combined with a SPECT (Single Photon Emission Computed Tomography) apparatus or a PET (Positron Emission Tomography) apparatus which is a nuclear medicine apparatus. There is a CT mechanism.

  For example, a PET device detects gamma rays (photons) emitted from RI (RadioIsotope) administered to a subject and measures the distribution of the RI in the body. The irradiated gamma rays are attenuated in the body of the subject. Therefore, in order to perform quantitative measurement with the PET apparatus, it is necessary to measure the attenuation distribution in the body using a transmission CT mechanism that uses an external gamma ray source, and to perform correction according to the measurement amount.

  Among the transmission CTs that use an external gamma ray source, the transmission CT using a fan beam collimator collimates the gamma rays at the two locations of the source and collimator, so there is little scattered radiation and the attenuation coefficient distribution in the body is accurately measured. There are advantages that can be done. On the other hand, the range limited by the collimator is the effective field of view of the detector, but if the fan beam collimator is used, the effective field of view of the detector is narrowed. An area outside the field of view cannot be photographed. Therefore, truncation (artifact) due to incomplete reconstruction of the image occurs. Even within the effective field of view, images cannot be accurately captured due to truncation.

  In order to eliminate truncation, an apparatus having a sufficiently large field of view may be used, but the apparatus becomes unnecessarily large and the apparatus cost increases. Therefore, there has been proposed a method for eliminating the truncation phenomenon in software without changing the hardware mechanism of the apparatus.

  As a technique for eliminating the truncation phenomenon, a method of approximating a body contour with an ellipse by a SPECT image acquired from a SPECT apparatus which is an emission CT apparatus, a technique using a Snake function by a SPECT image (IEEE Trans. Nucl Sci., Vol. 47). , No.3, pp 989-993).

As a technique for eliminating the truncation phenomenon, the body contour of the subject is detected from the SPECT image, and the sum of the projection data and the center of gravity of the CT image are calculated by elliptic approximation using the data indicating the body contour, and then projected. There is a technique that estimates a truncation part from the total value of data and the center of gravity of a CT image and extrapolates a quadratic expression to projection data (see, for example, Patent Document 1).
JP 2000-28728 A

  However, according to the conventional technique, it is necessary to detect the body contour of the subject from other than the truncation CT apparatus, that is, from the emission CT apparatus. Furthermore, the method of estimating the body contour from the CT image data acquired by the emission CT apparatus has a problem that the detection accuracy of the body contour is low.

  The present invention has been made in consideration of the above-described circumstances, and an object of the present invention is to provide a radiation diagnostic apparatus capable of accurately measuring the attenuation distribution in the body and performing truncation correction accurately and accurately.

  Another object of the present invention is to provide a radiation diagnostic apparatus capable of detecting a body contour with high accuracy only from a transmission CT apparatus.

  In order to solve the above-described problem, the radiation diagnostic apparatus according to the present invention uses a range limited by a collimator as an effective field of view of the detector, and the entire body part of the subject is within the effective field of view of the detector. Data for collecting first projection data acquired at a projection angle within an angle range and second projection data acquired at a projection angle within a projection angle range in which a part of the body part is outside the effective field of view of the detector A second extrapolation-type candidate for correcting the second projection data based on a difference between a collection unit and a total value of the first projection data and a total value of the second projection data; A plurality of third projection data candidates formed from the projection data and the plurality of primary extrapolation-type candidates are obtained, and the center of the third projection data estimated from the center of gravity of the first projection data and the plurality of third projection data Based on the difference from the centroid of the candidate, A primary correction unit that obtains the third projection data from projection data candidates; a body contour detection unit that detects position information of a body contour in the second projection data based on the third projection data; and a position of the body contour Based on the information, a secondary extrapolation equation for correcting the second projection data is obtained, and a second correction unit for obtaining the second projection data and the fourth projection data formed by the secondary extrapolation equation; An image reconstruction unit that reconstructs an image for each slice based on one projection data and the fourth projection data is provided.

  Further, in order to solve the above-described problem, the radiological diagnostic apparatus according to the present invention uses the range limited by the collimator as an effective field of view of the detector, and the whole body part of the subject is within the effective field of view of the detector. First projection data acquired at a projection angle within the projection angle range and second projection data acquired at a projection angle within a projection angle range where a part of the body part is outside the effective field of view of the detector. And a plurality of primary extrapolation formula candidates for correcting the second projection data based on a difference between a sum value of the first projection data and a sum value of the second projection data, and A plurality of third projection data candidates formed from the second projection data and the plurality of primary extrapolation-type candidates are obtained, and the center of gravity of the third projection data estimated from the first projection data and the plurality of third projection data Based on the difference from the centroid of the candidate, A primary correction unit that obtains the third projection data from projection data candidates; a body contour detection unit that detects position information of a body contour in the second projection data based on the third projection data; and a position of the body contour Based on the information, a secondary extrapolation equation for correcting the second projection data is obtained, and a second correction unit for obtaining the second projection data and the fourth projection data formed by the secondary extrapolation equation; An attenuation distribution correction unit that measures the attenuation distribution based on the four projection data and attenuates and corrects an image obtained based on the emission data based on the attenuation distribution is provided.

  Further, in order to solve the above-described problem, the radiological diagnostic apparatus according to the present invention uses the range limited by the collimator as an effective field of view of the detector, and the whole body part of the subject is within the effective field of view of the detector. First projection data acquired at a projection angle within the projection angle range and second projection data acquired at a projection angle within a projection angle range where a part of the body part is outside the effective field of view of the detector. A data collection unit, an addition processing unit for obtaining an addition value of the first projection data, an estimation processing unit for estimating a centroid position at a projection angle of the second projection data based on the first projection data, A body contour estimation unit that estimates the position information of the body contour in the second projection data based on the addition value and the position of the center of gravity, and the truncation portion of the second projection data is based on the position information of the body contour. Providing a projection data estimating unit which estimates the data.

  According to the radiation diagnostic apparatus of the present invention, it is possible to accurately measure the attenuation distribution in the body and to perform truncation correction accurately and accurately.

  Moreover, according to the radiation diagnostic apparatus which concerns on this invention, a highly accurate body outline can be detected only from a transmission CT apparatus.

  An embodiment of a radiation diagnostic apparatus according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram showing an embodiment of a radiation diagnostic apparatus according to the present invention.

  FIG. 1 shows a radiation diagnostic apparatus 10 having at least one transmission CT (Transmission Computerized Tomography) apparatus having an external radiation source. In the present embodiment, as an example of the radiation diagnostic apparatus 10, a combined machine of a PET (Positron Emission Tomography) apparatus 11 as an emission CT apparatus having no external radiation source and a transmission CT apparatus 12 having a gamma ray source. A description will be given using the PET-CT apparatus 10A. The emission CT apparatus is not limited to a PET apparatus, and may be a SPECT (Single Photon Emission Computed Tomography) apparatus, for example. The transmission CT apparatus may be a transmission CT apparatus having an X-ray source.

  The PET apparatus 11 of the PET-CT apparatus 10A detects gamma rays (photons) emitted from RI (Radiosotope) administered to the subject M, and collects PET data (emission data).

  On the other hand, the transmission CT apparatus 12 receives a gamma ray source 21 that irradiates gamma rays as radiation toward the subject M, and a signal indicating the position and the energy of the incident radiation when gamma rays that have passed through the subject M are incident. And a detector 22 for outputting an energy signal corresponding to. On the radiation incident side of the detector 22, there is provided a collimator 23 having a number of, for example, honeycomb-shaped openings arranged in a two-dimensional manner by a partition made of a radiation shielding material such as lead in the incident direction. Reference numeral 22 detects information on the radiation position within the subject M.

  The detector (not shown), the gamma ray source 21 and the detector 22 of the PET apparatus 11 are integrally supported by a gantry (not shown) so as to be rotatable around the body axis of the subject M. The detector and the detector 22 of the PET apparatus 11 are configured such that gamma rays are incident at each projection angle while being rotated by a minute angle around the body axis of the subject M.

  Further, the transmission CT apparatus 12 includes a CT data collection unit 41, a primary correction unit 42, a body contour detection unit 43, a secondary correction unit 44, and an image reconstruction unit 45.

  The CT data collection unit 41 receives 360-degree electrical signals from the detector 22 at a plurality of projection angles (view angles) while rotating the gamma ray source 21 and the detector 22 around the subject M, and projects them. Collected as projection data for each angle (transmission projection data).

  Here, the collimator 23 is roughly classified into a parallel (parallel) collimator or a fan beam collimator depending on the form of the opening. When the collimator 23 is a parallel collimator, the projection data collected by the CT data collection unit 41 is parallel beam data. On the other hand, when the opening of the collimator 23 is a fan beam collimator, the projection data collected by the CT data collection unit 41 becomes fan beam data. In this case, the CT data collection unit 41 or the CT data collection unit 41 is separate from the projection data. A conversion device (not shown) provided performs processing for converting fan beam data into parallel beam data.

  Further, when a fan beam collimator is used as the collimator 23, gamma rays are collimated at two locations of the gamma ray source 21 and the collimator 23, so that there is little scattered radiation and the attenuation distribution in the subject M is accurately measured. There is an advantage that can be. On the other hand, the range limited by the collimator is the effective field of view of the detector 22, but when the fan beam collimator is used, the effective field of view of the detector 22 is narrowed, so the body part of the subject M is measured. Depending on the projection angle, a part of the body part protrudes from the effective visual field, and truncation occurs in the CT image due to incomplete reconstruction. Therefore, when a fan beam collimator is used as the collimator 23 for the purpose of accurately measuring the attenuation distribution in the subject M, truncation correction of the CT image is indispensable.

  That is, for a plurality of projection data constituting a CT image of one slice, projections collected for each projection angle within a projection angle range in which the entire body part of the subject M is within the effective field of view of the detector 22 are collected. Data (hereinafter referred to as “first projection data”) and projection data (hereinafter referred to as “first projection data”) that is collected for each projection angle within a projection angle range in which a part of the body part is outside the effective visual field of the detector 22 (hereinafter referred to as truncation). "Second projection data").

  FIG. 2 is a diagram for explaining the outline of truncation occurrence.

FIG. 2 shows the gamma ray source 21 and detector 22 shown in FIG. Projection angle of the projection angle range overall physique of the subject M is within the field of view of the detector 22, for example, in the position of the projection angle theta _A, first projection data truncation is not generated is collected. On the other hand, the projection angle of the projection angle range some stature of the subject M is effective outside the field of view detector 22, for example, in the position of the projection angle theta _B, second projection data truncation occurs is collected .

  3 and 4 are diagrams showing examples of profile curves of projection data collected by the CT data collection unit 41. FIG.

3 shows the count value of the gamma rays incident on the detector 22 at the projection angle θ _A shown in FIG. 2 as the measurement position direction X (one end x _{0 of the} detector 22 <X <the other end x of the detector 22). It is a profile curve of the first projection data P [X, θ _A ] taken for each _matrix ). On the other hand, FIG. 4 shows the second projection data P [X, θ _B ] obtained by taking the count value of the gamma rays incident on the detector 22 at the position of the projection angle θ _B shown in FIG. It is a profile curve. In FIG. 4, in the range of X <x ₁ , x ₂ <X, gamma rays are not counted and truncation occurs.

  The primary correction unit 42 of the PET-CT apparatus 10A illustrated in FIG. 1 estimates a truncation portion of the second projection data, sequentially obtains a primary extrapolation formula for correcting (extrapolating) the truncation portion, The projection data is corrected by primary extrapolation. If the truncation does not occur, the primary correction unit 42, if truncation does not occur, “the projection data has a total sum that is constant at all projection angles” and “total integration weighted in the measurement image direction of the CT image”. The value (center of gravity) is fixed as seen from all projection angles ”.

  That is, the primary correction unit 42 uses the property of CT data to measure the body part of the subject M, and the projection angle at which a part of the body part protrudes outside the effective field of view of the detector 22. Is obtained as substitute data for the second projection data, the second projection data and the third projection data formed by the primary extrapolation formula.

  The primary correction unit 42 includes a total value calculation unit 51, a primary extrapolation candidate calculation unit 52, a third projection data candidate acquisition unit 53, a centroid calculation unit 54, a fitting processing unit 55, and a third projection data extraction unit 56. Is done.

  The total value calculation unit 51 calculates the total value (0th-order moment) for each projection data collected by the CT data collection unit 41. That is, the total value calculation unit 51 calculates the zeroth moment of the first projection data and the zeroth moment of the second projection data.

  The primary extrapolation candidate calculation unit 52 calculates a truncation portion of the second projection data based on the difference between the zeroth moment of the first projection data and the zeroth moment of the second projection data calculated by the summation value calculation unit 51. A plurality of primary extrapolation-type candidates to be corrected are calculated. For example, the primary extrapolation equation candidate calculation unit 52 obtains an average value from the zeroth-order moments for each of the plurality of first projection data, and calculates a plurality of values based on the difference between the average value and the zeroth-order moment of the second projection data. A candidate for the extrapolation formula is calculated.

  The third projection data candidate acquisition unit 53 corrects the second projection data for each primary extrapolation candidate, and determines a plurality of third projection data candidates formed by the second projection data and the primary extrapolation candidate. get.

  The center-of-gravity calculation unit 54 calculates the center of gravity (primary moment) for each of the plurality of first projection data collected by the CT data collection unit 41 and the plurality of third projection data candidates acquired by the third projection data candidate acquisition unit 53. First moments are calculated respectively.

  The fitting processing unit 55 performs a fitting process on the relationship between the primary moment and the projection angle for each first projection data calculated by the centroid calculating unit 54 into a trigonometric function (sin curve).

  The third projection data extraction unit 56 includes a first moment of the third projection data estimated from the first moments of the plurality of first projection data calculated by the center-of-gravity calculation unit 54, and a primary of a plurality of third projection data candidates. Based on the difference from the moment, third projection data is obtained from a plurality of third projection data candidates. Specifically, the third projection data extraction unit 56 includes the first moment of the third projection data estimated from the sin curve processed by the fitting processing unit 55 and a plurality of third projections calculated by the centroid calculation unit 54. A third projection data candidate having a first moment that minimizes the difference from the first moment for each data candidate is extracted as third projection data.

  The body contour detection unit 43 detects the body contour based on the third projection data extracted by the third projection data extraction unit 56, thereby detecting the position information of the body contour in the second projection data.

  Based on the position information of the body contour detected by the body contour detection unit 43, the secondary correction unit 44 corrects the second projection data by a multi-dimensional quadratic extrapolation method by a general method, and performs the second projection. Data and fourth projection data formed by secondary extrapolation are obtained.

  The image reconstruction unit 45 reconstructs a CT image for each slice based on the first projection data collected by the CT data collection unit 41 and the fourth projection data obtained by the secondary correction unit 44.

  The PET-CT apparatus 10A measures an attenuation distribution based on the first projection data and the fourth projection data, and an attenuation distribution correction unit 61 that corrects the attenuation of the PET data obtained by the PET apparatus 11 based on the measurement amount; An output unit 62 that externally outputs the CT image reconstructed by the image reconstruction unit 45 and the PET data output from the attenuation distribution correction unit 61 is provided.

  Each unit provided in the PET-CT apparatus 10A may be configured as hardware, or may function as software when a CPU (Central Processing Unit) (not shown) executes a program.

  Next, the operation of the PET-CT apparatus 10A as the radiation diagnostic apparatus 10 will be described.

  The PET apparatus 11 of the PET-CT apparatus 10A shown in FIG. 1 detects gamma rays emitted from the RI administered to the subject M, and collects PET data.

  On the other hand, the transmission CT apparatus 12 irradiates gamma rays from the gamma ray source 21 toward the subject M, and causes the gamma rays transmitted through the subject M to enter the detector 22 from the collimator 23. The CT data collection unit 41 receives 360-degree electrical signals from the detector 22 at a plurality of projection angles while rotating the gamma ray source 21 and the detector 22 around the subject M, and projects them for each projection angle. Collect as data.

  The primary correction unit 42 obtains second projection data in which a part of the body part of the subject M is outside the effective visual field of the detector 22 and generates truncation from the projection data collected for each projection angle, and estimates the truncation part. To do. Subsequently, the primary correction unit 42 corrects the truncation part of the second projection data by the primary extrapolation formula, and obtains the second projection data and the third projection data formed by the primary extrapolation formula.

Specifically, first, the total value calculation unit 51 provided in the primary correction unit 42 is set for each projection angle within a projection angle range in which the entire body part of the subject M is within the effective visual field of the detector 22 and no truncation occurs. In addition, the 0th-order moment of the first projection data taken for every measurement position direction is calculated. Similarly, the 0th-order moment of the second projection data is calculated for each projection angle within the projection angle range where truncation occurs. The primary correction unit 42 generates a projection angle within a projection angle range in which no truncation occurs, for example, the 0th-order moment M ₀ [θ _A ] of the projection data P [X, θ _A ] collected at the projection angle θ _A shown in FIG. , A projection angle within the projection angle range where truncation occurs, for example, the 0th-order moment I ₀ [θ _B ] of the projection data P [X, θ _B ] collected at the projection angle θ _B shown in FIG.
[Equation 1]
M ₀ [θ _A ] = ΣP [X, θ _A ] (x ₀ <X <x _matrix ) (1)
I ₀ [θ _B ] = ΣP [X, θ _B ] (x ₀ <X <x _matrix ) (2)
Respectively.

  FIG. 5 is a graph showing an example of the relationship between the projection angle and the 0th-order moment of the projection data collected for each projection angle.

Due to the nature of the projection data, in the ideal case where no truncation occurs in the projection data at all projection angles θ, the relationship between the projection angle θ in the ideal case and the zero-order moment of the projection data corresponding to the projection angle θ depends on the projection angle θ. Instead, the zero-order moment is a constant value (M ₀ [θ _A ]). However, in the relationship between the projection angle θ and the zero-order moment when truncation occurs in the projection data in the specific projection angle range B, the zero-order moment of the second projection data collected at the projection angle within the projection angle range B is This becomes smaller than the 0th-order moment of the first projection data collected at the projection angle within the projection angle range A where truncation does not occur. Further, the waveform of the 0th-order moment of the second projection data collected at the projection angle within the projection angle range B draws a substantially trigonometric function curve as the projection angle within the projection angle range B changes. In the case of the projection angle within the projection angle range B, data cannot be obtained in the range of X <x ₁ , x ₂ <X shown in FIG. This is because the next moment is reduced.

The primary extrapolation equation candidate calculation unit 52 of the primary correction unit 42 illustrated in FIG. 1 averages a plurality of 0th-order moments M ₀ [θ _A ] calculated by Equation (1). The primary outer interpolation equation candidate calculation unit 52 compares the zero-order moment _{M 0} [theta _A] 0th moment average value _{M 0} obtained by averaging, equation (2) 0th moment _{I 0} [theta _B] calculated in the To do. Specifically, a plurality of candidates for a first-order extrapolation equation that satisfies the condition that the difference between the zero-order moment average value M ₀ and the zero-order moment I ₀ [θ _B ] is minimized is calculated.

  FIG. 6 is a diagram for explaining a method of calculating a plurality of primary extrapolation-type candidates.

6 shows the second projection data P [X, θ _B ] shown in FIG. 4, the moving point a that moves in the range of x ₀ <a <x ₁ on the X axis, and x ₂ <b <x _matrix. The moving point b which moves in the range is shown. Here, the 0th-order moment average value M ₀ , which is the average value of the 0th-order moments collected for each projection angle θ _A where no truncation occurs, and the second projection data P [X, θ _B ] calculated by the equation (2). the difference between the 0th moment I _{0 [theta B]} of equal to the area formed by the primary outer interpolation equation and the X-axis. For example, if the primary extrapolation equation is a linear equation, the difference between the zero-order moment average value M ₀ and the zero-order moment I ₀ [θ _B ] is equal to the area indicated by the hatched portion in the figure.

Is established. From this equation (3), the relationship between the moving point a and the moving point b is determined, and a plurality of moving points a moving in the range of x ₀ <a <x1 and a point b determined by the position of the moving point a A primary extrapolation candidate H, that is, a plurality of candidates for the body contour (between ab) is calculated. The primary extrapolation candidate H is a primary extrapolation candidate that passes through the scan rotation coordinate system (a, 0) and (x ₁ , P [x ₁ , θ _B ]) in the range of a ≦ X ≦ x _1. From HL, and in the range of x ₂ ≦ X ≦ b, the scan rotation coordinate system (x ₂ , P [x ₂ , θ _B ]) and primary extrapolation candidate HR passing through (b, 0) are included.

  Here, a case where the primary extrapolation equation is a linear equation will be described, but the primary extrapolation equation is not limited to the linear equation, and may be, for example, a trigonometric function or a multi-order equation.

The third projection data candidate acquisition unit 53 illustrated in FIG. 1 corrects the truncation portion of the second projection data with a plurality of primary extrapolation candidates. Then, the second projection data P [X, θ _B ] in the range of x ₁ <X <x ₂ shown in FIG. 6 and a plurality of primary outliers in the ranges of a ≦ X ≦ x ₁ and x ₂ ≦ X ≦ b A plurality of third projection data candidates formed with the insertion candidate H are obtained.

  The center-of-gravity calculation unit 54 calculates a primary moment for each third projection data candidate. In addition, the center-of-gravity calculation unit 54 calculates the first moment of the first projection data for each projection angle within the projection angle range where truncation does not occur.

  The fitting processing unit 55 performs a fitting process on the first moment calculated for each projection angle within the projection angle range where truncation does not occur in the centroid calculating unit 54 into a sin curve.

  The third projection data extraction unit 56 uses the first moment of the third projection data estimated from the sin curve processed by the fitting processing unit 55 and one for each of a plurality of third projection data candidates calculated by the centroid calculation unit 54. A third projection data candidate having a first moment that minimizes the difference from the second moment is extracted as third projection data.

  FIG. 7 is a graph showing an example of the relationship between the projection angle within the projection angle range where truncation does not occur and the first moment of the projection data collected for each projection angle.

Due to the property that the total integral value weighted in the measurement position direction of the CT image is fixed as seen from the total projection angle, the first moment calculated by the centroid calculation unit 54 for each projection angle θ _A within the projection angle range where truncation does not occur. M ₁ [θ _A ] is fitted to a sin curve M ₁ f [θ].

Subsequently, the first moment T ₁ [θ _B ] (for example, x in FIG. 7) for each of the plurality of third projection data candidates calculated by the center-of-gravity calculation unit 54 and the sin curve M obtained by the fitting processing unit 55. _{A first} moment T ₁ [θ _B ] is specified such that the difference from the point M ₁ f [θ _B ] on ₁ f [θ] is minimized. Then, the third projection data candidate having the first moment T ₁ [θ _B ] when the difference is minimized is extracted as the third projection data.

  As described above, according to the primary correction unit 42 shown in FIG. 1, the truncation portion of the second projection data is corrected by an appropriate primary expression for each projection angle within the projection angle range where truncation occurs. It is possible to obtain the projection data and the third projection data formed by primary extrapolation.

  Subsequently, the body contour detection unit 43 detects the body contour based on the third projection data extracted by the third projection data extraction unit 56, thereby detecting the position information of the body contour in the second projection data. Therefore, the body contour detection unit 43 detects the position information of the body contour of the second projection data at every projection angle within the projection angle range where truncation occurs, and is necessary for the reconstruction of the CT image. It is possible to detect the position information of the body contour regarding the projection data of all projection angles. In addition, the body contour detection unit 43 binarizes the third projection data obtained by the primary correction unit 42 by setting a threshold value for each slice, backprojects the binarized data, and the body in the second projection data The position information of the contour may be detected. It is desirable that the body contour is smoothly smoothed by fitting processing using a seventh-order Fourier transform. Note that the order of the Fourier transform in this fitting process is not limited to the seventh order.

  The secondary correction unit 44 corrects the second projection data by a multi-dimensional quadratic extrapolation method using a general method using data indicating the body contour detected by the body contour detection unit 43, The projection data and the fourth projection data formed by secondary extrapolation are obtained.

  The image reconstruction unit 45 reconstructs a CT image for each slice based on the first projection data collected by the CT data collection unit 41 and the fourth projection data obtained by the secondary correction unit 44.

  The attenuation distribution correction unit 61 measures the attenuation distribution based on the first projection data collected by the CT data collection unit 41 and the fourth projection data obtained by the secondary correction unit 44, and the PET apparatus 11 uses this measurement amount. Attenuation correction is performed on the collected PET data.

  The output unit 62 externally outputs the CT image reconstructed by the image reconstruction unit 45 and the PET data output from the attenuation distribution correction unit 61.

  FIG. 8 is a diagram showing a CT image output from the output unit 62 on the screen.

  On the screen shown in FIG. 8, 3 × 3 CT images of the chest actually measured by lowering the arm of the subject M are displayed. The upper screen shows the case where the virtual visual field size of the collimator 23 shown in FIG. 1 is 400 mm, the middle screen shows the case where the virtual visual field size of the collimator 23 is 350 mm, and the lower screen shows the case where the virtual visual field size of the collimator 23 is 300 mm. The left column of the screen shows the case where truncation does not occur in all projection data. The column in the screen shows the body contour detected by the conventional method from the CT data acquired by the emission CT device when truncation occurs in a part of the projection data. The secondary correction is based on the body contour detected by the present invention from the CT data acquired by the emission CT device when truncation occurs in a part of the projection data and the right column of the screen shows the case where the secondary correction is performed based on the body contour. Each of the cases is shown.

  According to the screen shown in FIG. 8, the shape of the truncation portion can be recovered even when the virtual visual field size is 400, 350, and 300 mm. In particular, when the virtual visual field size is 400 mm, the shape of the truncation portion can be recovered well. . Further, when the virtual visual field size is 300 mm, an error of nearly 20% due to truncation can be reduced to about 3%.

  Note that the case where the PET-CT apparatus 10A as an example of the radiation diagnostic apparatus 10 shown in FIG. 1 is a complex machine of the emission CT apparatus 11 and the transmission CT apparatus 12 has been described. However, the radiation diagnostic apparatus 10 may be configured only by the transmission CT apparatus 12, in which case the CT image reconstructed by the image reconstruction unit 45 is sent to the output unit 62, and the CT image is externally transmitted from the output unit 62. Output.

  According to the PET-CT apparatus 10A as the radiation diagnostic apparatus 10 shown in FIG. 1, it is possible to accurately measure the attenuation distribution in the body and to perform truncation correction accurately and accurately.

  Further, according to the PET-CT apparatus 10A as the radiation diagnostic apparatus 10, a highly accurate body contour can be detected only from the transmission CT apparatus.

1 is a schematic diagram showing an embodiment of a radiation diagnostic apparatus according to the present invention. The figure explaining the outline | summary of truncation generation | occurrence | production. The figure which shows an example of the profile curve of 1st projection data. The figure which shows an example of the profile curve of 2nd projection data. The figure which shows an example of the relationship between a projection angle and the 0th-order moment of the projection data respectively corresponding to these projection angles. The figure explaining the method of calculating the candidate of a some primary extrapolation type | formula. The figure which shows an example of the relationship between the projection angle within the projection angle range where truncation does not occur, and the first moment of the projection data collected for each projection angle. The figure which shows CT image output on the screen from an output part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Radiation diagnostic apparatus 10A PET-CT apparatus 11 PET apparatus 12 Transmission CT apparatus 23 Collimator 41 CT data collection part 42 Primary correction part 43 Body outline detection part 44 Secondary correction part 45 Image reconstruction part 51 Sum total value calculation part 52 Primary outside Insertion candidate calculation unit 53 Third projection data candidate acquisition unit 54 Center of gravity calculation unit 55 Fitting processing unit 56 Third projection data extraction unit 61 Attenuation distribution correction unit 62 Output unit

Claims (10)

First projection data acquired at a projection angle within a projection angle range in which the range limited by the collimator is an effective field of view of the detector, and the entire body part of the subject is within the effective field of view of the detector, and the body part A data collection unit for collecting second projection data acquired at a projection angle within a projection angle range in which a part of the detector is outside the effective field of view of the detector;
Based on the difference between the total value of the first projection data and the total value of the second projection data, a plurality of primary extrapolation formula candidates for correcting the second projection data are calculated, and the second projection data and the second projection data A plurality of third projection data candidates formed by a plurality of primary extrapolation-type candidates are obtained, a center of gravity of the third projection data estimated from a center of gravity of the first projection data, and a center of gravity of the plurality of third projection data candidates A primary correction unit for obtaining the third projection data from the plurality of third projection data candidates based on the difference between
A body contour detector for detecting position information of a body contour in the second projection data based on the third projection data;
Based on the position information of the body contour, a secondary extrapolation formula for correcting the second projection data is obtained, and a secondary correction for obtaining the second projection data and the fourth projection data formed by the secondary extrapolation formula is obtained. And
A radiological diagnosis apparatus, comprising: an image reconstruction unit configured to reconstruct an image for each slice based on the first projection data and the fourth projection data. First projection data acquired at a projection angle within a projection angle range in which the range limited by the collimator is an effective field of view of the detector and the entire body part of the subject is within the effective field of view of the detector, and the body part A data collection unit for collecting second projection data acquired at a projection angle within a projection angle range in which a part of the detector is outside the effective field of view of the detector;
Based on the difference between the total value of the first projection data and the total value of the second projection data, a plurality of primary extrapolation formula candidates for correcting the second projection data are calculated to calculate the second projection data and the second projection data A plurality of third projection data candidates formed by a plurality of primary extrapolation-type candidates are obtained, and a difference between the center of gravity of the third projection data estimated from the first projection data and the center of gravity of the plurality of third projection data candidates A primary correction unit for obtaining the third projection data from the plurality of third projection data candidates based on
A body contour detector for detecting position information of a body contour in the second projection data based on the third projection data;
Based on the position information of the body contour, a secondary extrapolation formula for correcting the second projection data is obtained, and a secondary correction for obtaining the second projection data and the fourth projection data formed by the secondary extrapolation formula is obtained. And
A radiation diagnostic apparatus, comprising: an attenuation distribution correction unit that measures an attenuation distribution based on the fourth projection data and attenuates and corrects an image obtained based on the emission data based on the attenuation distribution. The radiation diagnostic apparatus according to claim 1, wherein the primary extrapolation formula is a primary formula. The radiation diagnostic apparatus according to claim 1, wherein the first-order extrapolation formula is a trigonometric function or a multi-order formula. The said data collection part performs the process which converts the fan beam data collected as said 1st projection data and said 2nd projection data into parallel beam data, when the said collimator is a fan beam collimator. And the radiation diagnostic apparatus according to any one of 2 above. 3. When the collimator is a fan beam collimator, a conversion device is provided that performs processing for converting fan beam data collected as the first projection data and the second projection data into parallel beam data. The radiation diagnostic apparatus as described in any one of these. The primary correction unit has a total value calculation unit for calculating the total value of the first projection data and the second projection data, and the total value of the first projection data and the total value of the third projection data are equal. A primary extrapolation equation candidate calculation unit that calculates the plurality of primary extrapolation equation candidates, a third projection data candidate acquisition unit that acquires the plurality of third projection data candidates, and a plurality of the first projections. A center-of-gravity calculation unit that calculates a center of gravity for each data and a center of gravity for each of the plurality of third projection data candidates; a fitting processing unit that performs a fitting process on the center of gravity for each of the plurality of first projection data into a trigonometric function; A third projection data extraction unit for extracting the third projection data candidate having the center of gravity that minimizes the difference between the center of gravity of each third projection data candidate and the trigonometric function as the third projection data. Radiodiagnostic apparatus as claimed in any one of claims 1 and 2, characterized. The radiation diagnostic apparatus according to claim 2, further comprising an image reconstruction unit configured to reconstruct an image for each slice based on the first projection data and the fourth projection data. The radiation diagnosis according to claim 1, further comprising an output unit that outputs an image reconstructed by the image reconstruction unit or an output from the attenuation distribution correction unit. apparatus. First projection data acquired at a projection angle within a projection angle range in which the range limited by the collimator is an effective field of view of the detector, and the entire body part of the subject is within the effective field of view of the detector, and the body part A data collection unit for collecting second projection data acquired at a projection angle within a projection angle range in which a part of the detector is outside the effective field of view of the detector;
An addition processing unit for obtaining an addition value of the first projection data;
An estimation processing unit that estimates a centroid position at a projection angle of the second projection data based on the first projection data;
A body contour estimation unit that estimates the position information of the body contour in the second projection data based on the added value and the gravity center position;
A radiation diagnostic apparatus, comprising: a projection data estimation unit that estimates data corresponding to a truncation part of the second projection data based on position information of the body contour.

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