WO2014156611A1 - 画像処理装置、放射線撮影装置および画像処理方法 - Google Patents
画像処理装置、放射線撮影装置および画像処理方法 Download PDFInfo
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Definitions
- the present invention relates to an image processing apparatus and method for processing an image captured by a radiation imaging apparatus such as an X-ray CT apparatus.
- a radiation source and a detector in which a large number of detection elements for detecting radiation are arranged opposite to each other with the inspection object interposed therebetween, and the radiation transmitted through the inspection object is detected by the detector. Therefore, radiation imaging apparatuses that create images to be inspected are widely used.
- a radiation imaging apparatus is used in which a radiation source and a detector are rotated around an inspection object, and tomographic images of the inspection object are obtained using projection data captured at various angles of rotation.
- a typical example is an X-ray CT apparatus. In such a radiographic apparatus, the number of X-ray detectors in the rotation axis direction has been increased, so that a wide range can be imaged with one rotation, and the imaging time can be shortened.
- a defective detector element occurs due to a failure or manufacturing failure of a photodiode that changes light into an electric signal or a reading circuit, and may exist immediately after the device is manufactured or may be accompanied by use of the device. If a detector having a defective element is used as it is in a CT apparatus, artifacts are generated in the reconstructed image, which hinders diagnosis and causes a problem.
- the sure way to remove the influence of the defective element is to replace the defective element and the detector containing it with a new one.
- a large amount of cost, man-hours, and time are required for replacement work and preparation of a replacement detector before occurrence.
- the dead time of the apparatus occurs.
- Another method is image correction. This is, for example, as described in Patent Document 1, for the acquired image, it is a method such that the average value of the surrounding normal elements is the correction value of the defective element, can be quickly and easily coped with, It is valid. In particular, when a defective element occurs in a clinical field, the dead time of the apparatus can be minimized, which is effective.
- the accuracy of correction decreases as the focal spot size decreases.
- An object of the present invention is to make it difficult to see image degradation and artifacts caused by defective elements that cannot be solved by conventional methods.
- the present invention achieves the above-mentioned problem by correcting the output of the surrounding normal elements used for correcting the defective elements by blurring processing instead of correcting only the output of the defective elements.
- the image processing apparatus of the present invention includes an image creating unit that creates an image using projection data including output values of each detection element of a detector formed by arranging a plurality of detection elements, and the detection
- a data correction unit that corrects imperfections of the projection data due to defective elements included in the vessel, and the data correction unit is estimated for the defective elements and an estimation unit that estimates an output value of the defective elements
- a blur processing unit that performs blur processing on the output value of the detection element located around the defective element using the estimated output value, and for the defective element, the estimated output value is used as an output value, and the detection is performed.
- the element performs correction using the output value after the blurring process as an output value
- the image creation unit creates the image using the projection data corrected by the data correction unit.
- the present invention it is difficult to see the deviation of the output value of the defective element in the detector data composed of the output value of each detection element. Similarly, even in the reconstructed image, artifacts caused by the deviation of the output value of the defective element are blurred and can be made difficult to see.
- FIG. 1 Schematic diagram of X-ray CT apparatus to which the present invention is applied
- Figure showing a configuration example of an X-ray detector
- Flow chart showing the procedure of correction processing Diagram showing an example of a defective element map Diagram showing the relationship between defective elements and surrounding elements used for correction
- amendment The figure explaining other examples of defective element correction
- FIGS. 5A and 5B are diagrams illustrating the effect of blur amount limitation appearing in a reconstructed image, where FIG. 5A illustrates an image when the blur amount limitation is not performed, and FIG. 5B illustrates an image when the blur amount limitation is performed.
- FIG. 5A illustrates an image when the blur amount limitation is not performed
- FIG. 5B illustrates an image when the blur amount limitation is performed.
- the radiographic apparatus uses a radiation source, a detector that is arranged opposite to the radiation source and includes a plurality of detection elements, and projection data that includes output values of the detection elements of the detector.
- An image creation unit that creates an image to be inspected, and a data correction unit that corrects imperfections in the projection data due to defective elements included in the detector.
- the data correction unit is an estimation unit that estimates an output value of a defective element included in the detector, and a first adjacent element that is a detection element adjacent to the defective element using the estimated output value estimated for the defective element.
- a blur processing unit that performs a blur process on the output value of the element, and for the defective element and the first adjacent element, the estimated output value and the output value after the blur process are used as corrected output values, respectively.
- the image creation unit creates the image using the projection data corrected by the data correction unit.
- the radiographic apparatus further includes a rotating plate that rotates the radiation source and the detector around the inspection target, and projection data including output values of the detection elements is the detection A plurality of projection data having different positions in the rotation direction of the device are included.
- the image creation unit includes a data correction unit that corrects the loss of the projection data caused by a defective element included in the detector, and a reconstruction unit that reconstructs the image using the corrected projection data,
- the data correction unit includes the estimation unit and the blurring processing unit described above, and for the defective element and the first adjacent element, the estimated output value and the corrected output value after the blurring process are set as corrected output values, respectively.
- FIG. 1 is a schematic diagram of an X-ray CT apparatus to which the present invention is applied
- FIG. 2 is a diagram showing a configuration example of an X-ray detector.
- the outline of the X-ray CT apparatus 100 of the present embodiment will be described with reference to FIG.
- the X-ray CT apparatus of this embodiment mainly includes an X-ray source 107, an X-ray collimator 116, an X-ray detector 104, a signal collection unit 118, a central processing unit 105, a display unit 106, an input unit 119, a control unit 117,
- the storage unit 109, the gantry rotating unit 101, and the bed top plate 103 are configured.
- a plurality of X-ray detectors 104 are arranged in an arc shape with the X-ray source 107 as a substantial center, and are mounted on the gantry rotating unit 101 together with the X-ray source 107.
- an X-ray grid is installed in front of the X-ray detector 104, and among the X-rays emitted from the X-ray source 107, the X-rays scattered by the subject 102, etc. Is prevented from entering the X-ray detector 104.
- the X-ray detector 104 includes a scintillator that converts X-rays into light and a photodiode that converts light from the scintillator into electric charge in the channel direction and the slice direction.
- the structure is two-dimensionally arranged, and the amount of charge corresponding to the incident X-ray can be obtained.
- the X-ray detector 104 is configured such that the channel direction of the X-ray detector element coincides with the rotation direction of the X-ray detector 104 (arrow A in FIG. 1) and the slice direction coincides with the rotation axis direction (B in FIG. 2). Is arranged.
- FIG. 1 for simplicity of explanation, the case of eight X-ray elements in the channel direction is shown, and in FIG. 2, only three X-ray detectors 104 are shown. In this apparatus, for example, there are about 40 pieces.
- an imaging method for acquiring a reconstructed image (hereinafter referred to as actual imaging) and an image processing method using this X-ray CT apparatus will be described.
- actual imaging when the start of actual imaging is input from the input unit 119, X-rays are emitted from the focal point of the X-ray source 107.
- the X-ray is irradiated by the X-ray collimator 116 and the irradiation field is limited toward the subject 102 placed on the bed top plate 103, and the X-ray transmitted through the subject 102 is detected by the X-ray detector 104.
- This imaging is repeated by rotating the gantry rotating unit 101 in the rotation direction A while changing the X-ray irradiation angle with respect to the subject 102 to acquire projection data for 360 degrees.
- the irradiation angle for acquiring the projection data is referred to as a view angle.
- Shooting is performed during a plurality of views, for example, every 0.4 degrees.
- the charge amount obtained in this way is collected by the signal collecting unit 118 and converted into a digital signal to create raw data.
- correction processing is performed on the raw data by the central processing unit 105 to create projection data.
- reconstruction is performed to create a reconstructed image of the X-ray absorption coefficient distribution of the subject 102. The result is displayed on the display unit 106.
- correction processing for example, offset correction S300 for correcting the zero level of the X-ray detector 104, sensitivity correction of the X-ray detector 104, air correction S320 for correcting the X-ray irradiation distribution, and the output value of the defective element are estimated.
- Defective element correction S330 is performed.
- the correction processing of FIG. 3 is an example, and does not limit the present invention. For example, there are cases where these correction orders are different, when other corrections are applied, or when there is no correction other than the defective element correction S330.
- the central processing unit 105 first performs an offset correction S300 on the raw data 143 received from the signal collecting unit 118.
- This correction is realized by, for example, subtracting the offset data 140 that has been created in advance and saved in the storage unit 109 from the raw data.
- the offset data 140 is zero-level data. For example, raw data is acquired without irradiating X-rays, and is generated by performing an averaging process on the view.
- the LOG conversion is, for example, a conversion as shown in Expression (1) where the value X before conversion and the value Y after conversion are used.
- a and b are constant coefficients.
- air correction S320 is performed. This correction is realized, for example, by subtracting the sensitivity / X-ray distribution data 141 created in advance of the main imaging and stored in the storage unit 109 from the raw data after the LOG conversion S310. Sensitivity / X-ray distribution data 141 is obtained by, for example, irradiating X-rays from the focal point of the X-ray source 107 without providing the subject 102 to obtain raw data. Created by converting.
- defective element correction S330 is performed.
- This correction S330 is performed in order to prevent artifacts in the reconstructed image due to inclusion of defective elements in the detector, and defective element output estimation processing (hereinafter, estimation processing) for estimating the output value of the defective elements. (Also referred to as S331) and blurring processing S332 for changing the output of normal elements around defective elements.
- the corrections S300 to S330 may be realized by the central processing unit 105 being stored as a program in a hard disk or a medium of a computer, or may be realized by an electric circuit.
- the central processing unit 105 and the electric circuit that perform the correction process are referred to as a data correction unit, a defective element output estimation processing unit (estimation unit), and a blur processing unit.
- the reconstruction processing S340 is performed to create the reconstructed image 145. Finally, the reconstructed image 145 is displayed on the display unit 106.
- the X-ray CT apparatus of the present embodiment is characterized by defective element correction caused by defective elements included in the X-ray detector 104 among the above-described correction processes, and a defective element output estimation process technique and a blurring process technique There are various methods. Hereinafter, typical embodiments of defective element correction will be described in detail.
- the estimated output value of the defective element is calculated using the output value of the first adjacent element located around the defective element, and in the blurring process, the estimated value estimated for the defective element
- the blur value is calculated using at least one of the output value and the output value of the second adjacent element other than the defective element located around the first adjacent element, and the blur amount is calculated as the output value of the first adjacent element.
- Add and perform blurring More specifically, a value obtained by multiplying the estimated output value estimated for the defective element by a first blurring rate, the output value of the first adjacent element, and adjacent to the first adjacent element, the defective element
- a blurring process is performed using a value obtained by multiplying the second adjacent element other than the second blurring factor by the second blurring factor.
- FIG. 4 shows an example of the defective element map 142.
- 0 represents a normal element
- 1 represents a defective element.
- FIG. 4 shows a case where eight elements in the channel direction A and eight elements in the slice direction B exist two-dimensionally and there is a defective element at the position of the fourth slice in the fourth channel.
- the defect element map 142 is created in advance of photographing and stored in the storage unit 109.
- the creation for example, an image irradiated with X-rays without a subject and an image without irradiation are obtained, and the output change amount is significantly larger or smaller than the average change amount of all elements. Is a defective element.
- this method for determining a defective element is an example, and does not limit the present invention.
- an estimated output value of the defective element is calculated using, for example, output values of normal elements (elements other than the defective element) around the defective element.
- this defective element is mth in the channel direction and nth in the slice.
- m is an integer of 2 or more
- n is a natural number.
- FIG. 5 shows an array of 5 ⁇ 5 detection elements centered on the defective element S (m, n). There are eight elements around the defective element S (m, n), and the estimation process can be performed using at least one output value of any of these eight elements (normal elements). .
- the output value of the defective element S (m, n) is estimated using the output values of two normal elements S (m + 1, n) and S (m ⁇ 1, n) adjacent in the channel direction.
- Fig. 6 shows an overview of the processing.
- the defective element S (m, n) is represented as S3, and two elements S (m + 1, n) and S (m ⁇ 1, n) adjacent in the channel direction are represented as S2 and S4.
- the estimated output value Q (m, n) of the defective element S3 is given by the equation (2 ).
- Equation (2) calculates the estimated output value by linear interpolation, but the estimated output value is calculated not only by linear interpolation but also by various nonlinear interpolations such as polynomials and by function fitting using adjacent elements. You may calculate using a function.
- the output of one element adjacent in the channel direction It can also be calculated from the value or extrapolated from the element adjacent to the defective element and the output value of the element adjacent thereto.
- the output values of the elements S (M, n + 1) and S (M, n-1) adjacent in the slice direction may be used instead of the elements adjacent in the channel direction.
- the output value of an element adjacent in the slice direction may be used.
- the estimation process is performed using the output values of the surrounding normal elements alone or in combination, as in the case where the defective element is at the detector end. Can do.
- the blurring process S332 corrects image degradation due to a deviation between the estimated output value of the defective element estimated by the above-described estimation process S331 and its true output value (output value obtained if there is no defect). And is performed on an element adjacent to the estimated defect element (hereinafter referred to as a first adjacent element).
- the first adjacent element to be subjected to the blurring process is an element that forms the same reconstructed image as the defective element in the reconstruction process.
- the first adjacent element is adjacent to the defective element in the channel direction.
- the output value P2 of the first adjacent element S2, the output value P1 of the element S1 adjacent to the first adjacent element S2 (hereinafter referred to as the second adjacent element), and the defective element S3 after the estimation process S331 Is used to determine an output value (corrected output value) after the blurring process of the first adjacent element S2.
- the first output using the output value P4 of the first adjacent element S4, the output value P5 of the second adjacent element S5 adjacent to the first adjacent element S4, and the estimated output value Q3 of the defective element S3 after the estimation process S331 is used.
- An output value (corrected output value) Q4 after blurring processing of the adjacent element is determined.
- the defective element S3 that is the target of the estimation process S331 is adjacent to the first adjacent elements S2 and S4, but is not included in the “second adjacent element” because it is expressed separately from the second adjacent elements S1 and S5. To.
- the correction output values Q (m ⁇ 1, n) and Q (m + 1, n) of the two first adjacent elements S2 and S4 are expressed as follows. For example, it can be calculated by the calculation of equation (3).
- the blurring rate ⁇ can be determined in consideration of the deviation between the estimated output value of the defective element and the true value. As described above, in the blurring process, when the estimated output value of the defective element has a deviation (error), the artifact caused by the deviation is locally blurred around the defective element to make the artifact inconspicuous. It is. The visibility of the artifact can be reduced as the blurring rate ⁇ is increased. However, if the blurring rate ⁇ is excessively increased, a new artifact is generated by the blurring process S332.
- the defect element output estimation process S331 and the blur process S332 are applied by changing the blurring rate ⁇ , the artifact amount is evaluated, and the optimum blurring rate ⁇ is actually captured. Decide in advance.
- the corrected output value after blurring processing may be obtained from the output value of the first adjacent element and the estimated output value of the defective element .
- the corrected output value Q (m + j) of the first adjacent element of the end channel is expressed by Equation (4). , n).
- the defective element output estimation process S331 The estimated value Q (m + 2i, n) of the second adjacent element obtained in (1) may be used.
- the output value P4 of the first adjacent element S4 in order to calculate the corrected output value of the first adjacent element S4 adjacent to the defective element S3, the output value P4 of the first adjacent element S4, the estimated output value Q3 of the defective element S3, and the defect
- the estimated output value Q5 of the element S5 is used.
- the blurring process S332 is realized even if the second adjacent element is a defective element by performing the blurring process S332 after performing the defective element output estimation process S331 on all the defective elements. be able to.
- the corrected output value Q (m + I, n) of the first adjacent element is the estimated output value Q (m, n) of the defective element and the output value P (m + i, n) of the first adjacent element.
- the output value P (m + 2i, n) of the second adjacent element but this is an example.
- the estimated output value Q (m, n) of the defective element and the output value P (m + 2i of the second adjacent element) , n) may be used without performing the blurring process S332. It is also possible to perform blurring processing using the output of another element.
- the correction output value of the first adjacent element is calculated using the weighted addition of Expressions (3) and (4).
- the function used for the blurring process is not limited to this, and various functions are used. be able to. If the function is generalized as f at this time, the corrected output value Q (m + i, n) of the first adjacent element can be expressed by Expression (5).
- the estimated output value or the corrected output value is used as the pixel value for the element estimated and corrected in the defective element correction S330.
- the output value is a pixel value, and is stored as projection data 144 as shown in FIG. 3 (see FIG. 3). Since the X-ray CT apparatus can obtain a plurality of projection data having different view angles, the defect element correction S330 described above is performed on the plurality of projection data.
- a reconstruction operation S340 such as convolution is performed on the corrected projection data to create a reconstructed image 145 of the subject 102 and display it on the display unit 106.
- the blurring process S332 when the blurring process S332 is performed on the first adjacent element located around the defective element, the estimated output value of the defective element has a deviation (error), and an artifact is generated.
- the surrounding area can be slightly blurred locally to make the artifacts inconspicuous.
- the blurring process of Expression (3) is not performed (a) and the blurring process (blur rate ⁇ : 0.5) is performed (b)
- These images are images created by artificially generating defective elements and changing the presence or absence of the blurring process S332 with respect to the raw data 143 obtained by imaging with the X-ray detector 104 having no defective elements. It can be seen that the artifact indicated by the arrow in the image 146 is reduced in the image 147, and the effect of the blurring process S332 can be seen.
- the first embodiment has been described mainly with respect to the output estimation process of the defective element and the blurring process for the output of the surrounding normal elements, but various changes are made to the specific contents of the output estimation process and the blurring process. In addition, the order and the like can be changed as appropriate.
- a modified example of the first embodiment will be described.
- the estimated output value is obtained using the output value of the element adjacent to the channel direction, but not only the adjacent element but also the output of the element at the position where one or more elements are sandwiched from the defective element May be used.
- the selection of such an element is useful when the adjacent element is also a defective element or when two or more defective elements are adjacent to each other.
- the element to be used may be changed according to the position of the defective element or other factors, and the element used for the interpolation method or estimation.
- the case where the defective element that is the target of the estimation process and the output value of the adjacent element used for the estimation process are output values of the same view has been described.
- the estimation process is performed using the output values of different views. It is also possible to perform. For example, it is possible to use one or more output values of projection data acquired at different rotation periods or data with different view angles even at the same view angle.
- FIG. 9 shows an example using data with different angles. In FIG. 9, the element positions are shown in a format different from that in FIG. 5, S (channel, view).
- the estimated output value of the defective element S (m, v1) of the target view (view of angle v1) is the value of the first adjacent element of the past view (view of angle v0) acquired before that. It is obtained using the output value or the output value of the first neighboring element of the future view (view of angle v2) acquired after that.
- output values of the same slice are used, but output values of different slices may be used.
- output values of different views may be used.
- the view angle difference is preferably up to about 5 degrees.
- Example 2 of blurring process change Instead of adding signals with a constant blurring rate for each defective element, it may be changed according to the position of the defective element, the output value, or the like.
- the blurring rate is changed according to the distance from the rotation center. Specifically, an element close to the rotation center produces an artifact with a smaller error than a distant element, so that the blurring rate increases as the element is closer to the rotation center, and the blurring rate decreases as the element is farther from the rotation center.
- the blurring rate, the correction value of the defective element, the output value of the first adjacent element, the output value and correction value of the peripheral element of the first adjacent element, the amount of change in the view direction of those output values and correction values It may be changed depending on the amount of change in the channel or slice direction.
- examples of the amount of change are noise and SNR. Accordingly, it is possible to provide a blurring rate according to the visibility of artifacts that change according to the output level of the reconstructed image, the noise level, or the like, or according to the structure of the subject. By adjusting the blurring rate in this way, unnecessary blurring can be suppressed and sufficient artifacts can be reduced.
- the corrected output value of the first adjacent element is calculated from the estimated output value of the defective element, the output value of the first adjacent element, and the output value of the second adjacent element in the same view.
- the same defect that the correction output value of the first adjacent element in the projection data of a given view was calculated for the projection data of the view acquired before that view (past view) and the view acquired after that The estimated output value of the element, the output value of the first adjacent element, and the output value of the second adjacent element may be used.
- the angle difference between the views to be used is preferably within several degrees.
- the blurring process is performed on the value after the LOG conversion.
- the addition process may be performed after the inverse conversion of the LOG conversion, and the LOG conversion may be performed again.
- the defective element correction S330 was performed after the air correction S320, for example, before the offset correction S300, between the offset correction S300 and the LOG conversion S310, between the LOG conversion S311 and the air correction S320, You can do that. Further, in addition to the defective element correction S330, in the case where some of the processes in FIG. 3 are not present, or in the case where another process is added to FIG. 3, any process may be performed before the reconstruction process S340. It may be done in order.
- a blur processing control unit is provided. That is, in the present embodiment, the central processing unit 105 includes a correction control unit that controls the blurring amount or the blurring rate by the blurring processing unit.
- the correction control unit sets the blurring amount or blurring rate according to conditions such as the position of the defective element in the detector, the size of the radiation focus that irradiates the detector with radiation, and the output noise ratio (SNR) of the detector. Control.
- the first adjacent element adjacent to the defective element is not uniformly blurred, but the presence / absence of the blurring process and the degree of blurring are determined according to the conditions of the device and other factors. It is characteristic to change.
- the blurring process control according to the focus size which is a typical factor, will be described. Since the other processes are the same as those in the first embodiment described above and the modified examples thereof, the overlapping description will be omitted, and will be described in detail with reference to FIG. 10, focusing on the contents of the blurring process S332 shown in FIG. .
- FIG. 10 is a flow showing processing of the defective element correction S330 of the second embodiment.
- defective element output estimation processing S331 is performed. This process is the same as the estimation process of the first embodiment, and the output value of the position (pixel) of the defective element obtained from the defective element map is adjacent to the position in the channel direction, slice direction, or tanning direction.
- the estimation is performed using the output value of the normal element or a combination of the output values of these normal elements.
- the estimation method may be linear interpolation as shown in Equation (2), or may be estimation using other functions.
- first determination step S333 it is determined whether or not to perform blurring processing according to the focus size. If blurring processing is performed, the process proceeds to the second determination step S335. If blurring processing is not performed, the process proceeds to processing S337. move on. The determination of whether or not to perform the blurring process is based on the focus size (X-ray focus size) when X-rays are emitted from the X-ray source 100.
- a plurality of focus sizes can be switched and used, and the focus size is selected via the input unit 119.
- the central processing unit 105 performs determination S333 using information on the selected focus size.
- an X-ray range W is defined as a range in which X-rays 168 irradiated from the focal point 162 and transmitted through the object 163 to reach the X-ray detector 104 are incident on the X-ray detector 104. Therefore, since the output values of the adjacent elements 164 and 166 include information that should be included in the defective element 165, the output estimation of the defective element 165 using these can achieve high accuracy, and is blur correction unnecessary?
- the blur rate may be small.
- the focal size L0 that does not require such blurring processing is a focal size that does not cause artifacts without performing blurring correction, and can be obtained by pre-shooting.
- the focus size L is smaller than L0, the ratio of the X-rays incident on the adjacent elements 164 and 166 out of the X-rays transmitted through the object 163 decreases, and a defective element using the output of the adjacent element The accuracy of 165 output estimation is low. Therefore, it is preferable to perform the blurring process.
- the focus size of the X-ray is sufficiently small, the X-ray transmitted through the object 163 is not incident on the adjacent elements 164 and 166, and the output estimation is performed. The accuracy is low, and a large amount of blur correction is required.
- the process proceeds to blurring process S3321, and if the focus size L is greater than the lower limit value, the process proceeds to blurring process S3322.
- the lower limit L1 of the focus size is a sufficiently small value whose estimation accuracy does not depend on the focus size. Similarly to L0, the lower limit L1 can be obtained by pre-shooting. Alternatively, for example, a focus size at which the X-ray range W is the same as the size of the defective element may be L1.
- the output value of the first adjacent element that is the target of the blurring process, the estimated output value of the defective element, and the first adjacent element are adjacent to each other.
- the output value of the second adjacent element is corrected by Expression (3) or Expression (4).
- a predetermined blurring rate ⁇ 0 set in advance is used as the blurring rate ⁇ .
- the blurring rate ⁇ 0 can be obtained by preliminary shooting together with the lower limit value L1 of the focus size.
- Formula (3) or Formula (4) is applied with the blurring rate ⁇ varied depending on the focal spot size. That is, in the range where the focus size L is from L0 to L1, the irradiation range applied to the adjacent elements 164 and 166 decreases linearly with respect to the focus size. Change linearly as shown in (7).
- the blurring rate ⁇ may not be linearly changed with respect to the focus size, but may be various functions of the linear focus size, or a value determined in advance without using the function.
- Projection data is created using the corrected output value of the first adjacent element after the blurring processes S3321 and S3322 as the output value of the first adjacent element, and the estimated output value of the defective element as the output value (process S339).
- the output value of the first adjacent element is used as it is, and the estimated output value is determined for the defective element.
- Use projection data is created (process S337). Reconstructing an image from projection data is the same as in the first embodiment, and a description thereof will be omitted.
- the present embodiment by adjusting the presence / absence of the blurring process and the degree of the blurring process according to the focus size, it is possible to prevent occurrence of artifacts due to unnecessary blurring process, and to optimize blurring according to the accuracy of the estimation process. Processing can be performed.
- the above-described method for determining the blurring rate is an example, and does not limit the present invention.
- the case where two threshold values L0 and L1 are set and the focus size range is divided into three and different processes are performed has been described. Only the presence / absence may be adjusted, or the blurring rate may be changed within a predetermined range without determining the presence / absence of the blurring process.
- blurring processing may be performed with all focus sizes of a plurality of switchable focus sizes, or blur correction may be performed with only some focus sizes.
- the central processing unit 105 performs the blurring process S332 in the defect element correction S330, and when the large focus is selected, the defective element It is possible that the blurring process S332 is not performed in the correction S330. Further, the blurring rate may be changed depending on the focus size, and the blurring rate may be reduced in the case of a large focus.
- the photographed object 163 in FIG. 11 corresponds to a part or part of the subject 102, and the amount of X-rays that are incident on the adjacent elements 164 and 166 varies depending on the position and size of the object 102. It is.
- the amount of artifacts and the visibility are different depending on the image filter and reconstruction filter used for shooting, tube current, tube voltage, position of defective elements, the number of projection data used to generate the reconstructed image, etc.
- the presence / absence of blur correction and the blur ratio may be changed.
- the defect element correction includes the defect element output estimation process and the blurring process as in the first embodiment.
- This embodiment is different from the first embodiment in that the output estimation method in the defective element output estimation process S331 and the blurring process S332 are limited. That is, the central processing unit (blurring processing unit) of the third embodiment includes a row and / or a row adjacent to a row and / or a column including a defective element that is a target for estimating an estimated output value, among the plurality of detection elements. A deviation amount from the true value of the estimated output value estimated by the estimation unit is estimated using the output value of the detection element in the column, and the blur amount or blur ratio is adjusted according to the deviation amount.
- ⁇ Defective element output estimation processing S331 the deviation between the output value of the defective element obtained by interpolation and the original output value is estimated, and the output of the defective element is estimated by taking this deviation amount into consideration.
- the estimated output value that takes into account the estimated deviation (referred to as the estimated deviation amount) is, for example, when the position of the defective element is (m, n) and the estimated deviation amount for the defective element is ⁇ (m, n). It can be expressed by (8).
- Equation (8) The first term on the right side of Equation (8) is equal to the right side of Equation (2), and the output value of the defective element is set to the output value P (m, n ⁇ 1), P (m, It is the value interpolated from n + 1).
- the deviation amount ⁇ (m, n) is calculated using the output values of the corresponding normal elements in columns or rows different from the normal elements S1 and S3 used for estimation. Different columns or rows are typically adjacent slices or channels.
- FIGS. 12B and 12C show output values of corresponding detection elements in columns or rows different from the detection elements S1 to S3 shown in FIG.
- the first adjacent elements S1, S3 are elements adjacent in the channel direction in the same slice as the defective element S2, and the corresponding elements S11, S13, and S21 in the slices on both sides adjacent to this slice , 23, and a case where the deviation amount is estimated and used for output estimation of the defective element will be described.
- the estimated output value of the defective element S2 by the equations (2), (3) Is calculated.
- This estimated output value is set as a temporary estimated value.
- the same calculation is performed for two elements (S11 and S13 in FIG. 12B) corresponding to different slices (channel numbers are the same), and the two elements
- the output of the element sandwiched between (S12 in FIG. 12B) is estimated.
- the difference between the estimated output value Q (m, n-1) and the output value P (m, n-1) of the element S12 is defined as a deviation amount ⁇ (m, n-1).
- the estimated output value of the defective element S2 can be calculated from the deviation amount ⁇ (m, n) obtained by the equation (10) and the equation (8).
- the defective element S2 is not the end in the slice direction.
- the estimated deviation amount ⁇ (m, n + j) calculated from the slice adjacent to the slice. May be used as the estimated deviation amount ⁇ (m, n).
- the estimated deviation amount ⁇ (m, n) can be expressed as in equation (11) instead of equation (10).
- the estimated deviation amount ⁇ (m, n) may be regarded as zero.
- the output estimation process for example, if any of the output values of the elements adjacent in the slice direction used for calculating the deviation amount cannot be obtained because it is a defective element, the output of the next adjacent element is further obtained. It may be used, or one of the sets of elements in the slices on both sides may be used.
- the provisional estimated output value and the estimated output value are calculated using the output values of the first adjacent elements adjacent in the channel direction. However, the provisional estimated output value is calculated in the first implementation. As described in the embodiments and the modified examples, it is possible to use various combinations of normal elements.
- a temporary correction output value Q ′ (m + i, n) of the first adjacent element is calculated (S550).
- This calculation method is the same as the calculation method of the corrected output value Q (m + i, n) of the first embodiment, for example, and is calculated using the equation (3).
- the blurring amount D (m + i, n) is calculated (S551).
- the blur amount D (m + i, n) is the difference between the temporary corrected output value and the true output value, and can be expressed by Expression (12).
- the limited amount M (m, n) of the blur amount is calculated (S552).
- This amount limits the blurring amount performed in the blurring process S332 for each defective element, and is set as a function of the estimated deviation amount ⁇ (m, n) of the defective element calculated in the estimation process S331.
- the estimated deviation amount ⁇ (m, n) represents the deviation amount of the linear interpolation of the defective element, and when the deviation amount is large, the estimation accuracy by the linear interpolation decreases. I can say that.
- the limited amount is a function that decreases when the estimated deviation amount ⁇ (m, n) is large.
- the function shown in Equation (13) can be used.
- a and B are constants, and can be determined by image quality evaluation prior to actual shooting.
- the above-described function is a case where the limited amount M (m, n) changes linearly with respect to the estimated deviation amount ⁇ (m, n), but the function can take various functions. That is, the limited amount can be expressed by the generalized equation (14),
- the function g in the equation (14) various functions such as a polynomial function, a trigonometric function, an exponential function, and a logarithmic function can be adopted.
- Various step functions whose values are determined for each threshold may be used.
- the limited amount M (m, n) may be determined from the estimated deviation amount ⁇ (m, n) using a table prepared in advance.
- the limited amount M calculated in the above-described process S552 and the blur amount D calculated in S551 are compared, and the true correction output value Q (m + i, n) of the first adjacent element is determined (S553).
- the comparison result is divided into three conditions, and the corrected output value Q is determined for each condition.
- the limited amount M (m, n) is set to the output value P (m + i, n) of the first adjacent element.
- a corrected output value Q (m + i, n) is set (S554).
- the blur amount is limited to the limited amount M (m, n).
- the blurring amount D (m + i, n) is smaller than -M (m, n) (condition 2)
- -M (m, n) is added to the output value P (m + i, n) and the corrected output value Q (m + i, n) n) (S555). That is, the blurring amount is limited to ⁇ M (m, n).
- condition 3 the provisional corrected output value Q ′ (m + i, n) calculated from the expression (3) is used as the corrected output value as it is.
- the limiting amount M may be a common limiting amount for all the first adjacent elements adjacent to the defective element, but may be calculated and applied separately.
- the blurring amount D is in the range of ⁇ M to M by providing the first adjacent element with a limitation on the correction amount (blurring amount) of the output value based on the shift amount. Therefore, unnecessary blurring can be suppressed and artifacts in the reconstructed image can be prevented from occurring.
- the blurring amount D is determined using the limited amount M (m, n), but as a result, the blurring rate ⁇ (formula (3)) is determined using the limited amount, This can be regarded as an example of a method for changing the blurring rate ⁇ .
- FIG. 14 shows an image 148 when a limited amount is not provided for the blurring process and an image 149 when a limited amount is provided. Both show reconstructed images of the head phantom. These images are images created by generating a defective element in a pseudo manner with respect to the raw data 143 obtained by photographing with the X-ray detector 104 having no defective element, and performing defect element correction S330. For both images, the defect element output estimation processing S331 and the blurring processing S332 are performed. It can be seen that artifacts indicated by arrows in the image 148 are reduced in the image 149, and the effect of providing a limited amount can be seen.
- the provisional estimated output value of the defective element is calculated by interpolation using the output value of the element adjacent in the channel direction, and the estimated deviation amount is calculated using the output value of the adjacent slice.
- the defective element may be interpolated using the value in the slice direction, and the estimated deviation amount may be calculated using the output value of the adjacent channel.
- a temporary estimated output value and an estimated deviation amount are calculated from the output values and correction amounts of elements in different sets. At this time, these sets may include common elements. There may be a case where an element belonging to both the channel direction and the slice direction is used, or an element around a defective element is used.
- the provisional estimated output value and the deviation amount are obtained by linear interpolation, but this is an example and does not limit the present invention.
- various interpolations such as polynomial interpolation and nonlinear interpolation may be used.
- the first term of Equation (9) for calculating the estimated deviation amount ⁇ (m, n + i) is also the same interpolation.
- a method for calculating a temporary estimated output value it may be obtained by fitting using a linear or higher order function. At this time, the same term is also applied to the first term of Equation (9).
- the estimated deviation amount ⁇ (m, n) can be calculated from the estimated deviation amount ⁇ (M, N) (M and N are integers) in the element (position (M, N)) adjacent to the defective element.
- the deviation amount ⁇ (M, N) can be calculated from Equation (16) derived in the same manner as in Equation (9).
- P (M, N) represents the output value of the element at position (M, N)
- p k (M, N) represents the element at position (M, N) as the position of the defective element. When replaced, it represents the output value of the element set corresponding to the output value “p k (m, n)” of the element set used to calculate the provisional correction value.
- the estimated deviation amount ⁇ (m, n) is calculated as an average value of the estimated deviation amounts ⁇ (M, N) of elements adjacent in the slice direction.
- the present invention is not limited to this.
- elements adjacent in the channel direction are used, elements in both the channel and slice directions are used, and elements around the defective element may be used.
- the estimated deviation amount of these elements is averaged, but also a case where it is determined by fitting using a function.
- p k (m, n) is not limited to the output value of the same view as the view for which the estimated deviation amount ⁇ (M, N) is calculated, but for past and future views, that is, views with different view angles and cycles. It may be an output value, or may be output values of two or more views of the present, the past, and the future.
- the limited amount M for limiting the blurring amount in the blurring process is a function of the estimated deviation amount of the estimated output value of the defective element, but the limited amount M is the estimated output value Q of the defective element or the defect It may be a function of output values of pixels around the element. Further, it may be a function of the change amount of the estimated output value of the defective element or the change amount of the output value of other pixels.
- examples of the amount of change are noise and SNR.
- the amount of incident light on the detector can be calculated from the output of the reference detector and the amount of change.
- the reference detector is a detector arranged at a position where X-rays emitted from the X-ray source 107 are directly incident without passing through a normal subject, and even if it is a part of the X-ray detector 104 , May be provided separately.
- the limited amount M may be calculated using output values or estimated values of elements of various views including the past and the future.
- the estimated deviation amount ⁇ calculated in the defective element output estimation process S331 is used as the estimated deviation amount for calculating the limited amount in the blurring process S332, but the estimated deviation amount ⁇ for the blurring process S332 is used. May be obtained separately. This may be obtained from other elements, for example, an estimated deviation amount ⁇ calculated by various peripheral elements including the second adjacent element. Further, it may be obtained by an expression other than the expressions (9) and (10) shown above, for example, an element around the first adjacent element, an element around another defective element, the second used for the blurring process S332.
- a corrected output value is obtained by Equation (3), and blurring processing is performed from the amount of deviation from the output value of that element.
- An estimated deviation amount ⁇ for S332 may be calculated.
- the corrected output value (estimated value) is calculated using the output value of the peripheral element without using the output value of the element, and the estimated output value obtained in the defective element output estimating process S331
- an estimated deviation amount ⁇ for the blurring process S332 may be calculated. Note that the method of calculating the corrected output value is not limited to Equation (3).
- the estimated deviation amount ⁇ (m, n) calculated in the defective element output estimation process S331 is used as the estimated deviation amount for calculating the limited amount in the blurring process S332, separately There are advantages in that the time required for calculation is shorter than that required, and the memory used can be reduced.
- Example of changing blur process >>
- the method of limiting the blurring amount in the blurring process S332 by providing a limited amount has been described.
- the purpose of the third embodiment is to limit the blurring amount in consideration of various factors related to the occurrence of artifacts.
- the present invention is not limited to this method, and various methods can be adopted.
- the blurring rate ⁇ shown in Equation (3) may be changed directly.
- the blurring rate ⁇ may be, for example, a function of the estimated deviation amount ⁇ (m, n), and the estimated output value Q (m, n) of the defective element, It may be a function such as an output value of a pixel around the defective element, an estimated output value of the defective element, an output value or change amount of other pixels, or an output value or change amount of the reference detector.
- the present invention is not limited to this, and a large number of detection elements for detecting radiation are arranged.
- the present invention can be applied to any apparatus equipped with the above-described detector and a central processing unit that corrects an output value of a defective element included in the detector.
- Any detector can be used as long as it can detect radiation of various wavelengths such as visible light, infrared rays, ultraviolet rays, and gamma rays in addition to X-rays.
- the present invention also includes an image processing apparatus that does not include a detector and that processes output data of the detector to generate image data.
- the image processing apparatus includes a detector that includes a plurality of detection elements, an image generation unit that generates an image using projection data including output values of the detection elements, and a defect included in the detector.
- a data correction unit that corrects incompleteness of projection data by the element.
- the data correction unit estimates the output value of the defective element, and uses the estimated output value estimated for the defective element to perform the blurring process on the output value of the detection element located around the defective element.
- a correction unit that performs the correction using the estimated output value as the output value for the defective element and the output value after the blurring process as the output value for the detection element subjected to the blurring process.
- the image creation unit creates an image using the projection data corrected by the data correction unit.
- the image processing apparatus can be composed of, for example, a central processing unit and a user interface (UI) that also serves as a display and an input.
- the image processing apparatus outputs the output data collected by the detector of the image capturing apparatus directly from the image capturing apparatus or via communication or a portable medium, and information (defective element map) regarding the defective element of the detector. Input and perform defective element correction.
- the output data captured by the image processing apparatus may be raw data from a detector, or data that has been subjected to correction such as offset correction or air correction.
- the illustrated image processing apparatus 200 includes a central processing unit 210, a storage unit 250, and a UI device 260 (corresponding to the display unit 106 and the input unit 119 in FIG. 1) connected to the central processing unit 210 as necessary. ing.
- the central processing unit 210 includes a main control unit 220, a data correction unit 230, an image creation unit 240, and the like.
- a display control unit 270 is also included.
- the data correction unit 230 performs various corrections on the input data according to the properties of the data, and includes a defective element correction unit 330.
- the defective element correction unit 330 includes a defective element output estimation unit 331 and a blur processing unit 332.
- the defective element output estimation unit 331 uses the positional information and output data of the defective element map 142 to estimate the output of the defective element.
- the blurring processing unit 332 uses the estimated output value of the defective element estimated by the output estimation unit 331 and the output value (or estimated output value) of the surrounding element to blur the output value of the peripheral element of the defective element. Do. In the blurring process, whether or not the blurring process is performed is adjusted according to the degree of artifact that may occur. Conditions necessary for these processes are set or input through the UI 260.
- the processes in the output estimation unit 331 and the blurring processing unit 332 are as described in the first to third embodiments, and duplicate descriptions are omitted.
- the image creation unit 240 creates projection image data using the output data after the defect element correction unit 330 has corrected.
- the output data consists of multiple pieces of data with different rotation angles (views), such as an X-ray CT system, perform calculations such as convolution on multiple pieces of projection data (corrected projection data). Reconstruct a tomogram.
- the image processing apparatus includes the display unit 106, the reconstructed image data is converted into display data superimposed with other necessary display information by the display control unit 270 and displayed on the display unit 106. If necessary, it is transferred to another display device or photographing device or stored in a storage means.
- the image processing apparatus can process output data from a plurality of different radiation imaging apparatuses, and can obtain the effects of the present invention without changing an existing radiation imaging apparatus.
- various applications are possible, such as processing an image of a remote imaging device and returning it to a remote location.
- the blur processing unit 332 of the image processing apparatus may include a correction control unit that controls the blur amount or the blur ratio.
- the correction control unit may control the blurring amount or the blurring ratio using the estimated output value of the defective element, as in the second embodiment or the third embodiment, or the detection element located around the defective element.
- the blur amount or blur ratio may be controlled using the output value or the estimated output value.
- the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention at the stage of implementation. Is possible. Further, the above embodiment includes various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, some components may be deleted from all the components shown in the embodiment.
- the output value of the defective element is estimated to reduce the artifact, and the remaining artifact due to the estimated deviation of the defective element can be made inconspicuous.
- X-ray CT device imaging device
- 107 X-ray source 101 gantry rotating unit
- 102 subject 103 bed top plate
- 104 X-ray detector 105 central processing unit
- 106 display unit 109 storage unit
- 116 X-ray Collimator 117
- Control unit 118
- Signal collection unit 119
- 330 Defect element correction unit 331 Defect element output estimation unit, 332 Blur processing unit, 142 Defect element map, 143 Raw data, 144 Projection data, 145 Reconstructed image, 146 ⁇ 149 Reconstructed image
Abstract
Description
本実施形態では、推定処理では、前記欠陥素子の周囲に位置する第1隣接素子の出力値を用いて、当該欠陥素子の推定出力値を算出し、ぼかし処理では、欠陥素子について推定された推定出力値と、第1隣接素子の周囲に位置する、欠陥素子以外の第2隣接素子の出力値との少なくとも一方を用いてぼかし量を算出し、第1隣接素子の出力値に前記ぼかし量を加算してぼかし処理を行う。より具体的には、欠陥素子について推定された推定出力値に対し第1のぼかし率をかけた値と、前記第1隣接素子の出力値と、前記第1隣接素子に隣接し、前記欠陥素子以外の第2隣接素子に第2のぼかし率をかけた値と、を用いてぼかし処理を行う。
まず、欠陥素子出力推定処理S331では、図3に示すように、記憶部109に記憶された欠陥素子マップ142の欠陥素子情報を取得し、マップに登録された位置の素子に対し推定処理を行う。図4に欠陥素子マップ142の一例を示す。図中、0が正常素子を、1が欠陥素子を、それぞれ表す。図4では、チャネル方向Aに8個、スライス方向Bに8個の素子が2次元的に存在し、4チャネル3スライス目の位置に欠陥素子がある場合を示すが、この素子数、欠陥素子の位置、欠陥素子マップは一例であり、本発明を限定するものではない。
この欠陥素子がチャネル方向でm番目、スライスでn番目にあるとする。ここでmは2以上の整数、nは自然数である。図5に、欠陥素子S(m,n)を中心に置いた5×5の検出素子の配列を示す。この欠陥素子S(m,n)の周囲には、8個の素子が存在し、推定処理はこれら8個の素子(正常素子)のいずれか少なくも一つの出力値を用いて行うことができる。
次にぼかし処理S332は、上述した推定処理S331によって推定された欠陥素子の推定出力値とその真の出力値(欠陥がなければ得られた出力値)とのずれに起因する画像の劣化を補正するための処理であり、推定処理された欠陥素子に隣接する素子(以降、第1隣接素子と記す)に対して行う。ぼかし処理の対象となる第1隣接素子は、再構成処理にて、欠陥素子と同一の再構成像を形成する素子であり、例えば欠陥素子とチャネル方向に隣接する素子である。以下の説明では、一例として、推定処理と同様に図6に示すチャネル方向に隣接する素子S2とS4を対象とする場合を説明する。
例えば、第1隣接素子のある(m+j)チャネル(j=1または-1)が端部チャネルの場合、式(4)のように、端部チャネルの第1隣接素子の補正出力値Q(m+j,n)を求める。
<<欠陥素子出力推定処理の変更例>>
第一実施形態では、チャネル方向に対して隣接する素子の出力値を用いて、推定出力値を求めたが、隣接素子のみでなく、欠陥素子から1つ以上素子を挟んだ位置の素子の出力を用いても良い。特に隣接素子も欠陥素子である場合や2つ以上の欠陥素子が隣接して存在する場合などで、このような素子の選択が有用である。また、用いる素子は、欠陥素子の位置やその他の要因に応じて、補間の方法や推定に使用する素子を変更しても良い。
第一実施形態では、ぼかし処理S332として、式(3)に示したように、両側の隣接素子からのぼかし率αを同じにして、信号の加算を行う場合を示したが、ぼかし率を異ならせてもよい。例えば、第2隣接素子の出力値のぼかし率をα1、欠陥素子の出力値のぼかし率をα2(α1≠α2)として、式(6)により第1隣接素子の出力値を算出してもよい。
各欠陥素子について一定のぼかし率で信号の加算を行うのではなく、欠陥素子の位置や出力値等に応じて変更してもよい。ぼかし率を欠陥素子の位置によって変更する例として、回転中心からの距離に応じてぼかし率を変更する。具体的には、回転中心に近い素子では遠い素子よりも小さな誤差でアーチファクトを生じるので、素子が回転中心に近いほどぼかし率を大きくし、回転中心から遠いほどぼかし率を小さくする。
第一実施形態では、ぼかし処理S332にて、第1隣接素子の補正出力値を、同じビューにおける欠陥素子の推定出力値と第1隣接素子の出力値と第2隣接素子の出力値から算出したが、図9を用いた推定処理の変更例から類推できるように、ぼかし処理についても異なるビューの出力値や推定値を用いることも可能である。例えば、所定のビューの投影データにおける第1隣接素子の補正出力値を、そのビューより前に取得されたビュー(過去のビュー)やそれより後に取得されたビューの投影データについて算出した、同じ欠陥素子の推定出力値、第1隣接素子の出力値、第2隣接素子の出力値を用いても良い。
第一実施形態では、LOG変換後の値に対してぼかし処理を行っているが、LOG変換の逆変換を行った後に加算処理を行い、再度LOG変換を行っても良い。
本実施形態は、ぼかし処理の制御部を設けたことが特徴である。すなわち、本実施形態では中央処理装置105は、ぼかし処理部によるぼかし量またはぼかし率を制御する補正制御部を備える。補正制御部は、検出器における欠陥素子の位置、検出器に放射線を照射する放射線焦点の大きさ、及び、検出器の出力ノイズ比(SNR)等の条件に応じて、ぼかし量またはぼかし率を制御する。
或いは、例えば、X線範囲Wが、欠陥素子のサイズと同じになる焦点サイズをL1としてもよい。
本実施形態においても、欠陥素子補正が欠陥素子出力推定処理とぼかし処理を含むことは第一実施形態と同様である。本実施形態は、欠陥素子出力推定処理S331における出力推定手法と、ぼかし処理S332に制限を設ける点で、第一実施形態と異なる。すなわち第三実施形態の中央処理装置(ぼかし処理部)は、複数の検出素子の配列のうち、推定出力値を推定する対象である欠陥素子を含む行及び/又は列に隣接した行及び/又は列の検出素子の出力値を用いて、推定部が推定した推定出力値の、真の値からのずれ量を推定し、当該ずれ量に応じて、前記ぼかし量又はぼかし率を調整する。
まず欠陥素子出力推定処理S331では、補間によって求めた欠陥素子の出力値と本来の出力値とのずれを推定し、このずれ量を加味して欠陥素子の出力を推定する。推定したずれ(推定ずれ量という)を加味した推定出力値は、例えば、欠陥素子の位置を(m,n)とし、その欠陥素子についての推定ずれ量をΔ(m,n)とすると、式(8)で表すことができる。
ぼかし処理S332では、ぼかし量を所定の限定値で制限して、限定値で制限される範囲で第1隣接素子の補正出力値Q(m+i,n)を決定する。この処理の手順を、図13を参照して説明する。
<<出力推定処理の変更例>>
第三実施形態では、欠陥素子の仮の推定出力値を、チャネル方向に隣接する素子の出力値を用いて補間して算出し、推定ずれ量の算出を隣接スライスの出力値を用いて行ったが、これは一例であり、例えば欠陥素子の補間をスライス方向の値を用いて行い、推定ずれ量を隣接チャネルの出力値を用いて算出しても良い。更に、異なる集合の素子の出力値や補正量から、仮の推定出力値の算出と、推定ずれ量の算出を行うさまざまな場合が有り得る。このときこれらの集合が、共通の素子を含んでいても構わない。チャネル方向とスライス方向の両方向に属する素子を用いる場合や、欠陥素子の周辺の素子を用いる場合があっても良い。
ただし本発明はこれに限るものではなく、チャネル方向に隣接する素子を用いる場合、チャネルとスライス方向の両方の素子を用いる場合、欠陥素子の周辺の素子を用いる場合などもあり得る。更にこれらの素子の推定ずれ量を平均する場合だけでなく、関数によってフィッティングで決定する場合などもあり得る。更に「pk(m,n)」は、推定ずれ量Δ(M、N)を算出したビューと同じビューの出力値に限らず、過去や未来のビュー、つまりビュー角度や周期が異なるビューの出力値であってもよく、現在、過去、未来の2つ以上のビューの出力値であってもよい。
第三実施形態では、ぼかし処理におけるぼかし量を制限する限定量Mを、欠陥素子の推定出力値の推定ずれ量の関数としたが、限定量Mは、欠陥素子の推定出力値Qや、欠陥素子の周辺の画素の出力値の関数であってもよい。また欠陥素子の推定出力値の変化量や、それ以外の画素の出力値の変化量の関数であってもよい。ここで変化量の一例は、雑音やSNRである。このように関数を決定することで、適切な限定量Mを決定することができる。例えば検出器への入射線量が多くSNRが高いときには、より再構成像でのアーチファクトは見え易いため、小さな限定量Mを与えてぼかし量を減らすことでアーチファクトを抑制することができる。
第三実施形態では、ぼかし処理S332で限定量を算出するための推定ずれ量として、欠陥素子出力推定処理S331で算出した推定ずれ量Δを用いたが、ぼかし処理S332のための推定ずれ量Δを別途求めてもよい。これは他の素子から求めてもよく、例えば、第2隣接素子を含む様々な周辺素子で算出した推定ずれ量Δであってもよい。また、先に示した式(9)や式(10)以外の式で求めてもよく、例えば第1隣接素子の周辺の素子、その他の欠陥素子の周囲の素子、ぼかし処理S332に用いる第2隣接素子、第2隣接素子の周辺の素子などの1つ以上の素子(欠陥素子は除く)について、式(3)により補正出力値を求め、その素子の出力値とのずれ量から、ぼかし処理S332のための推定ずれ量Δを算出しても良い。
第三実施形態では、ぼかし処理S332におけるぼかし量を、限定量を設けて制限する手法を説明したが、第三実施形態の趣旨は、アーチファクト発生に関わる諸要因を考慮してぼかし量を制限するというものであり、この手法に限定されず、種々の手法が採り得る。
例えば式(3)に示したぼかし率αを、直接変化させてもよい。このときぼかし率αは、限定量M(m,n)の場合と同様に、例えば推定ずれ量Δ(m,n)の関数としても良く、欠陥素子の推定出力値Q(m,n)、欠陥素子の周辺の画素の出力値、欠陥素子の推定出力値やそれ以外の画素の出力値や変化量の関数、リファレンス検出器の出力値や変化量などの関数であってもよい。
上述した第一~第三実施形態では、医療用のX線CT装置に本発明を適用した実施形態を記したが、本発明はこれに限るものではなく、放射線を検出する検出素子を多数配列した検出器と、その検出器に含まれる欠陥素子の出力値補正を行う中央処理装置と、を搭載したあらゆる装置に適用できる。例えば、非破壊検査用のX線CT装置、X線コーンビームCT装置、デュアルエネルギーCT装置、X線画像診断装置、X線画像撮影装置、X線透視装置、マンモグラフィー、デジタルサブトラクション装置、核医学検診装置、放射線治療装置などに適用できる。検出器としては、X線のほか、可視光、赤外線、紫外線、ガンマ線など、さまざまな波長の放射線を検出するものであれば、いずれも採用することができる。
本発明は、検出器を含まず、検出器の出力データを処理し画像データを作成する画像処理装置も含まれる。以下、画像処理装置の実施形態を説明する。本実施形態の画像処理装置は、複数の検出素子を配列してなる検出器の、各検出素子の出力値からなる投影データを用いて画像を作成する画像作成部と、検出器に含まれる欠陥素子による投影データの不完全性を補正するデータ補正部と、を備える。
Claims (16)
- 複数の検出素子を配列してなる検出器の、各検出素子の出力値からなる投影データを用いて画像を作成する画像作成部と、前記検出器に含まれる欠陥素子による前記投影データの不完全性を補正するデータ補正部と、を備え、
前記データ補正部は、前記欠陥素子の出力値を推定する推定部と、前記欠陥素子について推定された推定出力値を用いて、当該欠陥素子の周囲に位置する検出素子の出力値にぼかし処理を行うぼかし処理部と、を備え、前記欠陥素子については前記推定出力値を出力値とし、前記検出素子についてはぼかし処理後の出力値を出力値とする補正を行い、
前記画像作成部は、前記データ補正部によって補正された投影データを用いて前記画像の作成を行うことを特徴とする画像処理装置。 - 請求項1に記載の画像処理装置であって、
前記ぼかし処理部によるぼかし量またはぼかし率を制御する補正制御部をさらに備えたことを特徴とする画像処理装置。 - 請求項2に記載の画像処理装置であって、
前記補正制御部は、前記欠陥素子の周囲に位置する第1隣接素子の出力値と、前記第1隣接素子の周囲に位置する第2隣接素子の出力値と、前記第1隣接素子の出力値を用いて算出される前記欠陥素子の推定出力値との中の少なくとも一つを用いてぼかし量またはぼかし率を制御することを特徴とする画像処理装置。 - 請求項3に記載の画像処理装置であって、
前記検出器は、第1の方向及び当該第1の方向と交差する第2の方向に配列した複数の検出素子を含み、
前記ぼかし処理部は、前記複数の検出素子の配列のうち、前記推定出力値を推定する対象である欠陥素子を含む行及び/又は列に隣接した行及び/又は列の検出素子の出力値を用いて、前記推定部が推定した推定出力値の、真の値からのずれ量を推定し、当該ずれ量に応じて、前記ぼかし量またはぼかし率を調整することを特徴とする画像処理装置。 - 請求項2に記載の画像処理装置であって、
前記補正制御部は、前記検出器における前記欠陥素子の位置、前記検出器に放射線を照射する放射線焦点の大きさ、及び、前記検出器の出力ノイズ比、のいずれかを含む条件に応じて、前記ぼかし量またはぼかし率を制御することを特徴とする画像処理装置。 - 請求項5に記載の画像処理装置であって、
前記補正制御部は、前記ぼかし量またはぼかし率、もしくは前記ぼかし量又はぼかし率を決定する条件を入力するための入力部を備えることを特徴とする画像処理装置。 - 請求項1に記載の画像処理装置であって、
前記推定部は、前記欠陥素子の周囲に位置する第1隣接素子の出力値を用いて、当該欠陥素子の推定出力値を算出し、
前記ぼかし処理部は、前記欠陥素子について推定された推定出力値と、前記第1隣接素子の周囲に位置し、前記欠陥素子以外の第2隣接素子の出力値との少なくとも一方を用いてぼかし量を算出し、前記第1隣接素子の出力値に前記ぼかし量を加算してぼかし処理を行うことを特徴とする画像処理装置。 - 請求項1に記載の画像処理装置であって、
前記推定部は、前記欠陥素子の周囲に位置する第1隣接素子の出力値を用いて、当該欠陥素子の推定出力値を算出し、
前記ぼかし処理部は、前記欠陥素子について推定された推定出力値に対し第1のぼかし率をかけた値と、前記第1隣接素子の出力値と、前記第1隣接素子の周囲に位置し、前記欠陥素子以外の第2隣接素子に第2のぼかし率をかけた値と、を用いてぼかし処理を行うことを特徴とする画像処理装置。 - 請求項1に記載の画像処理装置であって、
前記検出器は、第1の方向及び当該第1の方向と交差する第2の方向に配列した複数の検出素子を含み、
前記推定部は、前記第1の方向において前記欠陥素子に隣接する検出素子の出力値及び/又は前記第2の方向において前記欠陥素子に隣接する検出素子の出力値を用いて、前記欠陥素子の推定出力値を推定し、
前記ぼかし処理部は、前記推定部が前記推定出力値を推定するのに用いた検出素子に対しぼかし処理を行うことを特徴とする画像処理装置。 - 請求項9に記載の画像処理装置であって、
前記ぼかし処理部は、前記複数の検出素子の配列のうち、前記推定出力値を推定する対象である欠陥素子を含む行及び/又は列に隣接した行及び/又は列の検出素子の出力値を用いて、前記推定部が推定した推定出力値の、真の値からのずれ量を推定し、当該ずれ量に応じて、ぼかし量又はぼかし率を調整することを特徴とする画像処理装置。 - 放射線源と、当該放射線源に対向配置され、複数の検出素子を配列してなる検出器と、前記検出器の各検出素子の出力値をもとに検査対象の画像を作成する画像作成部とを備え、
前記画像作成部は、請求項1に記載の画像処理装置を備えたことを特徴とする放射線撮影装置。 - 請求項11に記載の放射線撮影装置であって、前記放射線撮影装置が、X線CT装置であることを特徴とする放射線撮影装置。
- 請求項12に記載の放射線撮影装置であって、
前記データ補正部は、前記検出器の回転方向の位置が異なる複数の投影データのうち、一部の投影データについて、前記推定部による推定出力値の推定と前記ぼかし処理部によるぼかし処理を行い、残りの投影データについては、前記一部の投影データについて推定された推定出力値とぼかし処理に用いたぼかし量を流用して、回転方向の位置が異なるすべての投影データを補正することを特徴とする放射線撮影装置。 - 複数の検出素子を配列してなる検出器の、各検出素子の出力値を用いて画像を作成する画像処理方法であって、
前記検出器に含まれる欠陥素子の出力値を、当該欠陥素子の周囲の、欠陥素子以外の検出素子の出力値を用いて推定するステップと、
前記欠陥素子について推定された推定出力値を用いて、当該欠陥素子の周囲の検出素子の出力値にぼかし処理を行うステップと、
当該ぼかし処理に用いるぼかし量又はぼかし率を設定するステップと、
前記欠陥素子及びぼかし処理の対象とである検出素子については推定出力値及びぼかし処理後の出力値をそれぞれ用いて前記画像の作成を行うステップと、を含む画像処理方法。 - 請求項14に記載の画像処理方法であって、
前記ぼかし処理を行うステップの前に、ぼかし処理の有無を判断するステップをさらに含むことを特徴とする画像処理方法。 - 請求項14に記載の画像処理方法であって、
前記ぼかし量又はぼかし率を設定するステップは、前記欠陥素子の推定出力値と真の出力値とのずれ量を推定するステップと、推定されたずれ量を用いて、前記ぼかし量又はぼかし率の制限値を設定するステップと、を含み、
前記ぼかし処理を行うステップは、前記制限値で制限されたぼかし量又はぼかし率を用いてぼかし処理を行うことを特徴とする画像処理方法。
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JP2019519900A (ja) * | 2016-06-28 | 2019-07-11 | ゼネラル・エレクトリック・カンパニイ | X線の生成に使用するためのカソードアセンブリ |
JP7005534B2 (ja) | 2016-06-28 | 2022-01-21 | ゼネラル・エレクトリック・カンパニイ | X線の生成に使用するためのカソードアセンブリ |
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Publication number | Publication date |
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CN105025795B (zh) | 2017-10-27 |
JP6348108B2 (ja) | 2018-06-27 |
JPWO2014156611A1 (ja) | 2017-02-16 |
CN105025795A (zh) | 2015-11-04 |
US20160015351A1 (en) | 2016-01-21 |
US10010303B2 (en) | 2018-07-03 |
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