JP2000070252A - X-ray image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the burden on an examiner such as a medical doctor by providing a phase means estimating a phase angle and an intersection means estimating an intersection angle so as to correct the direction and inclination of a displayed image reconstituted from the respective X-ray images based on the phase angle and the intersection angle. SOLUTION: Two X-ray images are first read out from a storing means to be inputted to a pre-processing part 10 and a first adding means 14. The part 10 executes preprocessing to the read X-ray image of each projection angle to output preprocessed image data to a reconstitution arithmetic means 11 to reconstitute a three-dimensional X-ray absorption distribution image in the visual field area of an examinee 6 from image data of each projection angle after correction and to output it to an imaging means 12. Then imaging processing is executed and a three-dimensional image is converted to a two-dimensional image to display a display means. At this time, based on the projection angle and the intersection angle of the two X-ray images inputted from first/second error arithmetic means 16 and 19, the means 12 corrects and aligns the reference positions of two two-dimensional images.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray imaging apparatus, and more particularly to a technique which is effective when applied to the positioning of an X-ray image picked up at a later time.

[0002]

2. Description of the Related Art As shown in FIG. 7, a cone beam X-ray tomographic imaging apparatus, which is a conventional X-ray imaging apparatus, measures a measurement, that is, an X-ray image, and processes the measured data. And a data processing unit 2. The measuring unit 1 includes an X-ray source 4 and a detector 5 arranged at positions facing each other across a subject 6, and the X-ray source 4 and a detector 5.
And the scanning drive unit 3 that rotates the object around the subject 6. The X-ray source 4 is an X-ray source that irradiates a cone beam (pyramid or cone) X-ray 8 from an X-ray focal point 7 to a subject 6. The detector 5 was a two-dimensional detector having an X-ray image intensifier-TV camera system, a TFT matrix or the like, and having a two-dimensionally spread detection capability. The scanning drive unit 3 is a rotation drive unit that rotates an imaging system including the X-ray source 4 and the detector 5 around the rotation center axis 9 and moves the imaging system along the rotation center axis 9. Therefore, in the conventional X-ray imaging apparatus,
Each time the scan driver 3 rotates the X-ray source 4 and the detector 5 by a small angle, the projection of X-rays from the X-ray source 4 and the measurement of the transmitted X-ray intensity by the detector 5 are performed over the entire circumference of the subject. One hundred to several hundred sets of transmitted X-ray intensity data (X-ray images) were repeatedly collected. Note that the rotation angle (imaging angle) at which the scanning drive unit 3 is positioned in a predetermined projection is called a projection angle.

On the other hand, a data processing unit 2 includes a pre-processing unit 10 for performing pre-processing such as gamma correction, image distortion correction, logarithmic conversion and sensitivity unevenness correction of a captured X-ray image,
Reconstruction calculating means 11 for reconstructing a three-dimensional X-ray absorption coefficient distribution image in the field of view of the subject 6 from the line image, and a two-dimensional image obtained by performing an imaging process such as a volume rendering process or a maximum intensity projection process. Imaging means 12 for displaying as
And an instruction device 13 for inputting measurement instructions and display instructions by the operator. Therefore, in the image processing unit 2, based on the display instruction of the operator,
The pre-processing unit 10 corrects the image quality deterioration factor of the collected X-ray image, and the reconstruction calculation unit 11 reconstructs a three-dimensional X-ray absorption count distribution image from the corrected X-ray image. The image has been converted into a two-dimensional image that can be displayed on a display device (not shown) by the imaging means and displayed. However, for the display position and display conditions, the operator inputs parameters such as a viewpoint and a part to be observed from the pointing device 13 via a keyboard, a mouse, a track ball, or the like, and the imaging unit 12 displays a desired image. I was letting it. In addition, as a reconstruction calculation method, (LA Feldkamp et al. Practical cone beam algor
ithm, J.Opt.Soc.Am.A, Vol.1, No.6, pp612-619, 1984)
(Hereinafter referred to as “Reference 1”) Feldkamp
There is known a cone beam reconstruction calculation method based on the above method.

[0004]

SUMMARY OF THE INVENTION As a result of studying the above prior art, the present inventor has found the following problems. In the diagnosis using the conventional X-ray imaging apparatus, the examiner of the doctor makes a diagnosis using the captured three-dimensional reconstructed image, but when making a treatment plan or performing follow-up of the treatment. It has been common to compare a plurality of three-dimensional reconstructed images of the same subject imaged at different times.

[0005] For example, when comparing the subject 6 before and after surgery, or when observing the progress of treatment,
Also, there is a case where a projection image or a three-dimensional reconstructed image acquired in real time during an operation is compared with a three-dimensional reconstructed image used for an operation plan. In this case, it is necessary to align the three-dimensional reconstructed images captured at different times. In general, when performing imaging at different times in imaging using a cone-beam X-ray tomography apparatus, the subject 6 It is difficult to exactly reproduce the positional relationship between the measurement unit 1 and the measurement unit 1. For this reason, conventionally, an examiner such as a doctor has to align the three-dimensional reconstructed images in the head, and this operation requires skill and is a burden in performing an accurate diagnosis. Had become.

As a method for solving this problem, the subject 6
There is a method in which a marker serving as a reference for positioning is fixed, and the subject 6 is positioned on the measuring unit 1 based on the marker. However, this method has a problem that the subject 6 must keep the marker on during the period in which imaging is likely to be performed, which places a heavy burden on the subject 6.

As another method, there has been a method of performing registration between three-dimensional reconstructed images using an image recognition technique. In this method, there has been a method of comparing three-dimensional reconstructed images or comparing a positional relationship between characteristic portions thereof to determine a positional relationship between the two. However, in this method,
An enormous amount of calculation is required, and for this reason, for example, a three-dimensional reconstructed image acquired prior to surgery and used for surgical planning, and a projection image acquired in real time during surgery,
Alternatively, it has been difficult to perform registration with a three-dimensional reconstructed image and compare the two.

[0008] An object of the present invention is to provide an X-ray imaging apparatus capable of reducing the burden on the examiner such as a doctor.

Another object of the present invention is to provide an X-ray imaging apparatus capable of improving the diagnostic efficiency of an examiner such as a doctor.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0011]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

(1) An X-ray imaging apparatus for rotating an imaging system including an X-ray source and an X-ray detector at predetermined imaging angles around a subject to reconstruct and display an X-ray image captured, When displaying X-ray images captured at different times, for each X-ray image, the projection value for each imaging angle is integrated in parallel with the rotation center axis of the imaging system, and the distribution curve of the integrated value is compared. Phase means for estimating a phase angle, and intersection means for integrating the projection values for each projection angle on a straight line passing through the center of the X-ray image, comparing distribution curves of the integrated values, and estimating an intersection angle. Then, based on the phase angle and the intersection angle, the direction and the inclination of the display image reconstructed from the respective X-ray images were corrected.

(2) In the X-ray imaging apparatus according to (1), the X-ray source is means for irradiating a cone or pyramid-shaped X-ray beam, and the detector is a projection image of the subject. Are means having a viewing angle that falls within the viewing range.

(3) In the X-ray imaging apparatus according to the above (1) or (2), the phase means integrates the projection value for each X-ray image in parallel with the rotation center axis of the imaging system. One adding means, first comparing means for comparing the integrated value of each X-ray image and selecting a phase angle candidate, and first error calculation for calculating an error between the phase angle candidates and estimating the phase angle And a second integrating means for integrating projection values on a straight line passing through the center of the projection image, and a second integrating means for comparing integrated values for each X-ray image and selecting a candidate for an intersection angle. The comparison means includes a second error calculation means for calculating an error between the candidates for the intersection angle and estimating the intersection angle.

(4) In the X-ray imaging apparatus according to the above (3), the X-ray absorption coefficient distribution of the subject is represented by f (x,
y, z), the rotation tangent direction on the projection plane is u, the rotation center axis direction is v, the imaging angle is A, and the projection is P (A, u,
In the case of v), the first addition means comprises means for calculating the value P0 (A, u) according to the equation 1 for the imaging angle A and the position u.

(5) In the X-ray imaging apparatus according to the above (4), the first comparing means compares the value P0 (A, u) obtained from the first X-ray image with the second X-ray image. Value P0 'obtained from
(A ', u) and P0 within a predetermined error range.
(A, u) means for selecting a combination of the first imaging angle A and the second imaging angle A 'that satisfies (A, u) ≒ P0' (A ', u).

(6) In the X-ray imaging apparatus according to the above (5), the first comparing means compares the value P0 (A, 0) obtained from the first X-ray image with the second X-ray image. Value P0 'obtained from
(A ′, 0), and within a predetermined error range, P
There is provided a means for determining one or more combinations of the first imaging angle A and the second imaging angle A ', where 0 (A, 0) ≒ P0' (A ', 0).

(7) In the X-ray imaging apparatus described in the above (5) or (6), the predetermined weight function is W
(U), the miscalculation of the value P0 (A, u) obtained from the first X-ray image and the value P0 ′ (A ′, u) obtained from the second X-ray image is expressed by E
When (A, A ′) is satisfied, the first error calculating means:
A, A ′ at which the error E (A, A ′) is minimized according to Equation 2.
Is used as a phase angle.

(8) In the X-ray imaging apparatus according to any one of (3) to (7), the X-ray absorption coefficient distribution of the subject is represented by f (x, y, z), The rotation tangent direction on the projection plane is u, the rotation center axis direction is v, the distance from the rotation center axis of an arbitrarily set point on the projection plane is r, and the arbitrarily set point and the rotation center axis are connected. Assuming that the angle between the straight line and u is b and the projection at the imaging angle A is Pp (A, b, r), the second adding means calculates the projection Pp0 according to Equation 3.
(B) calculating means.

(9) In the X-ray imaging apparatus according to any one of the above (3) to (8), the second comparing means may use the value Pp0 ( 0) and a value Pp0 ′ (b ′) obtained from the second X-ray image, and selects an angle b ′ such that Pp0 (0) ≒ Pp0 ′ (b ′) within a predetermined error range. Consists of

(10) In the X-ray imaging apparatus according to any one of (3) to (9), the value Pp0 (b) obtained from the first X-ray image and the second X-ray Value P obtained from line image
When the miscalculation with p0 '(b') is Eb (b '),
The second error calculating means calculates the error Eb according to Equation 4.
(B ') is a means for setting the intersection angle to be the minimum b.

(11) In the X-ray imaging apparatus according to any one of the above (1) to (10), a reconstructed image whose inclination and direction have been corrected is displayed on the same display screen.

According to the above-mentioned means (1) to (11), when displaying X-ray images taken at different times, the phase means uses the imaging system to project the projection value for each imaging angle for each X-ray image. By integrating the distribution curve of the integrated value and estimating the phase angle, as shown in the section of the principle described later, that is, the direction of the display image after reconstruction, that is, each X-ray It is possible to estimate the displacement amount (first displacement amount) of the subject with respect to the rotation direction of the imaging system when capturing an image. Also, the intersection means integrates the projection values for each projection angle on a straight line passing through the center of the X-ray image, compares the distribution curve of the integrated values and estimates the intersection angle. As described above, the inclination of the display image after the reconstruction, that is, the displacement amount (second displacement amount) of the subject with respect to the rotation axis direction of the imaging system at the time of capturing each X-ray image can be estimated. Based on the shift amount and the second shift amount, it is possible to perform display in which the direction and the inclination of the subject in each reconstructed image are aligned.

Therefore, it is not necessary for the examiner such as a doctor to correct the direction and the inclination of each reconstructed image, so that the burden upon drafting a treatment plan can be reduced. As a result, the diagnostic efficiency of the examiner such as a doctor can be improved.

(Principle) FIG. 2 shows two or more Xs according to the present invention.
FIG. 2 is a diagram for explaining the principle of alignment between a line image and a reconstructed image. The principle of alignment will be described below with reference to FIG. Here, a three-dimensional X-ray absorption coefficient distribution based on a subject (not shown) is defined as f (x, y, z). At this time, x, y, and z are coordinate systems fixed to the subject in order to simplify the discussion.

In FIG. 2, a first circular trajectory C is a trajectory of the detector (X-ray detector) at the time of the first imaging, and the scanning drive unit (X-ray source and detector) rotates the z-axis about the rotation axis. A circular orbit with axis 9 is shown, and the projection angle of the source with respect to the x-axis is A. Such assumptions do not detract from the generality of the following discussion. The projection on the detection surface imagined on the detector is indicated by P (A, u, v), the axis u is taken in the tangential direction of the circular orbit C, and the axis v is taken in parallel with the rotation center axis 9, that is, the z axis. FIG. 3 shows the positional relationship between the circular trajectory C and the subject at this time, and the circular trajectory indicated by a dotted line is the second circular trajectory C ′ at the time of capturing the second projection image.

The second circular trajectory C 'is the circular trajectory of the detector at the time of the second imaging, and the rotation center O of the scanning drive unit coincides with the first circular trajectory C. The projection on the detection plane imagined on the detector is denoted by P ′ (A ′, u ′, v ′), the axis u ′ is the tangential direction of the second circular orbit C ′, and the axis v ′ is z ′. Take parallel to the axis. FIG. 4 shows the positional relationship between the second circular orbit C ′ and the subject at this time, and the circular orbit indicated by the dotted line is the first circular orbit C.

However, it is assumed that the projection of the subject falls within the field of view of the detector at any projection angle on the first circular orbit C and the second circular orbit C '. The first circular orbit C and the second circular orbit C ′ intersect at points Q and Q ′, and the intersection angle is represented by B
Indicated by However, in the following description, the intersection angle B is in the range of -90 degrees to +90 degrees. This assumption is realistic enough within the expected usage.

In FIG. 3, a position R is a position (OR⊥Q) rotated 90 degrees from the point Q along the first circular orbit C.
Q ′), and a position R ′ indicates a position (OR′⊥QQ ′) rotated by 90 degrees from the point Q along the second circular orbit C ′, and by using the positions R and R ′, Intersection angle B
Can be represented as the angle ROR '. The intersection S is the intersection between the first circular orbit C and the x-axis, the intersection S 'is the intersection between the second circular orbit C' and the x'-axis, and the projection angle A 'is the source at the time of the second photographing. Are respectively shown. The angle Ar between the x-axis and the straight line OR indicates the projection angle when the source is at the position R,
An angle Ar 'formed between the x' axis and the straight line OR 'indicates a projection angle when the source is at the position R'.

Next, the principle of registration of two or more X-ray images according to the present invention will be described with reference to FIGS. 2 to 5. The reconstructed image obtained by the first radiography and the reconstructed image obtained by the second radiography are obtained. It can be seen that the registration with the obtained reconstructed image results in obtaining the intersection angle B, the angle Ar, and the angle Ar ′ in FIG.

First, the X-ray absorption coefficient distribution f in the subject
As is well known, between the (x, y, z) and the projection P (A, u, v) on the first imaging, that is, on the first circular orbit C, a point on the X-ray source and the detection surface By the line integral on the X-ray beam connecting (u, v) (referred to as path S), the following equation 5 is obtained.
Holds. Similarly, the same relationship holds during the second shooting, that is, in the case of the projection P ′ (A ′, u ′, v ′) on the second circular orbit C ′.

[0032]

(Equation 5)

Here, as shown in FIG. 5, P0 (A, u) is obtained for each projection angle on the first circular orbit C. At this time, P0 (A, u) is given by the following equation (6).

[0034]

(Equation 6)

The projection P 'on the second circular orbit C'
Similarly, with respect to (A ', u', v '), P0'
(A ', u') is obtained. At this time, P0 ′ (A ′,
u ′) is given by the following equation (7).

[0036]

(Equation 7)

Here, on each of the circular orbits C and C ′,
Assuming that the projection angles when the X-ray source reaches the position R and the position R ′ are Ar and Ar ′, respectively, P0 (A
(r, 0) = P0 ′ (Ar ′, 0). This indicates that it is equal to the area of the X-ray absorption coefficient on the plane ROR 'of the subject. On the other hand, even if the same Ar and Ar ', if u ≠ 0, P0 (Ar, u) ≠ P
0 ′ (Ar ′, u). However, if the width of the field of view of the detector is sufficiently small as compared with the distance between the X-ray source and the detector, that is, if the opening angle of the cone beam X-ray is sufficiently small, the predetermined error And P0 (Ar,
u) ≒ P0 ′ (Ar ′, u).

Therefore, at the projection angles A and A ′ (where 0 ≦ A, A ′ <2π), P0 (A, 0) and P0 ′ (A ′, 0) are obtained, and P0 (A1,0) = P
Projection angles A1 and A1 'satisfying 0' (A1 ', 0)
To obtain the projection angles A1 and A1 '.
Is equal to the projection angles Ar and Ar ′, respectively. However, the X-ray absorption coefficient distribution f (x, y,
z) and the positional relationship between the circular orbits C and C ′,
It is possible that there are a plurality of sets of projection angles A1 and A1 'that satisfy P0 (A1,0) = P0' (A1 ', 0).

In such a case, the plural sets of projection angles A1 and A1 'are set as candidates for Ar and Ar', respectively, and the projection angles A1 and A1 'are set within the effective range of the detector (umin ≦ u).
≤ umax) and P0 (A1,
u) A1 and A1 'satisfying {P0' (A1 ', u)
By narrowing down, the projection angles Ar and Ar ′ can be obtained. Within the effective range of the detector (umin ≦
For u of u ≦ max), P within a predetermined error range
A method for obtaining A1 and A1 'that satisfies 0 (A1, u) ≒ P0' (A1 ', u) is a method for minimizing an error E (A, A') between both curves obtained by the following equation (8). The angles A1 and A1 'may be obtained. Where w in Equation 8 is
(U) is a predetermined weight function. As mentioned above, u =
When 0, P0 (A1, u) is equal to P0 ′ (A1 ′, u), and the difference between the two increases as u departs from zero. Therefore, when calculating the error E (A, A ′), u By applying a weighting function w (u) so that the weight is increased as the value is closer to zero, it is possible to make a more accurate determination that reflects this property.

[0040]

(Equation 8)

Next, a procedure for obtaining the intersection angle B will be described. By the procedure described above, the projection angles Ar and Ar ′
Are determined, the positions of the points Q and Q 'on the respective circular orbits C and C' are also determined. Therefore, the first imaging, that is, the projection angle of the point Q on the circular orbit C is Aq,
Assuming that the projection angle of the point Q on the second imaging, that is, the circular orbit C ', is Aq', the projections in the first imaging and the second imaging when the X-ray source is at Q are P coordinates in polar coordinates, respectively.
p (Aq, b, r) and Pp '(Aq', b ', r)
It can be expressed as. Here, b and b ′ represent angles from the u and u ′ axes on the respective projection planes, and r represents a distance from the origin on the projection plane. By its definition, Pp '(Aq', b ', r) is Pp (Aq, b,
r) rotated by the intersection angle B, and Pp (A
q, b, r) = Pp ′ (Aq ′, b−B, r). Therefore, to determine the intersection angle B, the projection Pp '
It is clear that it is sufficient to check how much angle (Aq ′, b ′, r) is rotated to match the projection Pp (Aq, b, r).

The simplest method for checking the coincidence is to rotate the projection Pp '(Aq', b ', r) little by little and to determine the angle at which the error between the projection Pp (Aq, b, r) and the projection Pp (Aq, b, r) becomes minimum. It is a method to ask. However, in this method, a large number of image rotation processes must be performed, and the process requires a great deal of time.

As another method, a method for more easily obtaining the rotation angle will be described below. Here, Pp0 (b) and Pp0 ′ (b ′) are defined as shown in FIG. 6 and Equations 9 and 10 below.

[0044]

(Equation 9)

[0045]

(Equation 10)

First, Pp0 (0) is obtained, and -π / 2 ≦
In the range of b ′ <π / 2, Pp0 ′ (b1 ′) = Pp0
B1 ′ that becomes (0) is obtained. Then, -b1 'is equal to the intersection angle B to be obtained. However, in general, Pp0 ′ (b′i)
= B'i satisfying Pp0 (0) (where i = 0,
1, 2,... M) are plural. Therefore, the plurality of b ′
i (where i = 0, 1, 2,... m) as candidates,
The curve Pp0 (b) according to the following equation 11 in i
Ebi = Eb between the curve and the curve Pp0 ′ (b′i + b)
(B'i) is obtained, and with b'i minimizing it,
The intersection angle is B.

[0047]

[Equation 11]

According to the procedure described above, the projection angle A
r, Ar ′ and the intersection angle B are calculated, and the coordinates of the projection image (X-ray image) obtained by the first or second imaging are moved based on the calculated values, whereby the two X-ray images are obtained. The displacement can be corrected.

In the above description, for simplicity, the projection angle and the measurement data are all treated as if they were continuous quantities. However, in actual measurement, the X-ray image output from the detector is Since the image is converted into a digital image, the projection angle, the measurement data, and the like change discretely.

[0050]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings together with embodiments (examples) of the invention. In all the drawings for describing the embodiments of the present invention, components having the same functions are denoted by the same reference numerals, and their repeated description will be omitted.

FIG. 1 is a view for explaining a schematic configuration of a cone beam X-ray tomography apparatus which is an X-ray imaging apparatus according to an embodiment of the present invention, wherein 1 is a measuring section, 2 is an image processing section,
3 is a scanning drive unit, 4 is an X-ray source, 5 is a detector (X-ray detector), 6 is an object, 7 is an X-ray focal point, 8 is an X-ray, 9 is a rotation center axis, and 10 is a preprocessing unit. , 11 are reconstruction operation means, 12
Is an imaging unit, 13 is a pointing device, 14 is a first adding unit,
Reference numeral 15 denotes first comparing means, 16 denotes first error calculating means, 17 denotes second adding means, 18 denotes second comparing means, and 19 denotes second error calculating means. The measuring unit 1 according to the present embodiment
Has the same configuration as that of the measuring unit 1 in the conventional X-ray imaging apparatus, and a detailed description thereof will be omitted. However, the measurement unit 1 according to the present embodiment scans the X-ray source 4, the detector 5, and the imaging system including the X-ray source 4 and the detector 5, which are opposed to each other, around the subject 6. It is composed of a drive unit 3.

In FIG. 1, an image processing unit 2 according to the present embodiment includes, for example, a pre-processing unit 10, a reconfiguration operation unit 11, an image forming unit 12, First adding means 14, first comparing means 15, first error calculating means 16, second adding means 17,
The pointing device 1 realized by the second comparing means 18 and the second error calculating means 19 and the input device of the information processing device
And 3.

The pre-processing unit 10 controls the X
This is a well-known preprocessing unit that performs preprocessing such as gamma correction of a line image, image distortion correction, logarithmic conversion, and sensitivity unevenness correction.

The reconstruction calculating means 11 is a well-known reconstruction means for reconstructing a three-dimensional X-ray absorption coefficient distribution image in the field of view of the subject 6 from the X-ray images at each projection angle.

The imaging means 12 converts the three-dimensional image into a two-dimensional image by performing an imaging process such as a volume rendering process or a maximum intensity projection process on the three-dimensional X-ray absorption count distribution image. It is a means to do. Further, the imaging unit 12 moves the display angle of the two-dimensional image to the display (direction and tilt) from the instructed direction based on the display instruction input by the operator (not shown) from the instructing device 13. By moving the display reference position of one of the two-dimensional images, that is, the direction and the inclination of the reconstructed image, based on the intersection angle B and the phase angles Ar and Ar ′ input from the two-error calculating means 19, two X-rays are obtained. Align the images.

The first adding means 14 is means for calculating the sum of the projection values on the projection image in a direction parallel to the rotation center axis 9 of the imaging system for each projection angle, and can be realized by a well-known adding means. is there.

The first comparing means 15 is a well-known means for finding a set of projection angles at which the sum of the two projection values calculated by the first adding means 14 becomes equal within a preset error range.

The first error calculating means 16 includes the first comparing means 1
5 is a means for obtaining a projection angle within the range of the effective width of the detector 5 from the set of projection angles obtained. For example, the effective width of the detector 5 is substituted for all the sets of projection angles. This is a means for calculating the sum of the projection values obtained and selecting the projection angle having the closest sum among the sums of the projection values at this time.

The second addition means 17 is means for calculating the sum of the projection values on a straight line passing through the center of the projection image and in any direction on the projection image at a predetermined projection angle. It can be realized by:

The second comparing means 18 is a means for obtaining a set of projection angles at which the sum of the two projection values calculated by the second adding means 17 becomes equal within a predetermined error range. It can be realized by means.

The second error calculating means 19 is provided with the second comparing means 1
8 is a means for obtaining a projection angle within the range of the effective width of the detector 5 from the set of projection angles obtained. For example, the effective width of the detector 5 is substituted for all the sets of projection angles. The sum of the calculated projection values is calculated, and the projection angle with the closest sum is selected from the sum of the projection values at this time, and the projection angle is set as the intersection angle B.

Next, the operation of the X-ray imaging apparatus of the present embodiment will be described based on FIG. 1 and the principle section. However,
In the following description, a case will be described in which X-ray images of the same subject captured at different times are displayed on the same screen.

Two X-ray images (image data) are read out from a storage unit (not shown) based on an image display instruction from an operator (not shown), and input to the preprocessing unit 10 and the first adding unit 14.

The preprocessing unit 10 performs preprocessing such as gamma correction, image distortion correction, logarithmic conversion, and sensitivity unevenness correction on the read X-ray image for each projection angle, and reconstructs the image data after the preprocessing. Output to the calculating means 11. The reconstruction calculating means 11 calculates the object 6 from the corrected image data for each projection angle.
Reconstructs a three-dimensional X-ray absorption distribution image in the field of view of
Output to the imaging means 12. The imaging unit 12 converts the input three-dimensional X-ray absorption distribution image into a two-dimensional image by performing an imaging process such as a well-known volume rendering process or a maximum intensity projection process. The data is output and displayed on display means (not shown). At this time, the imaging unit 12 sets the projection angles Ar and A of the two X-ray images input from the first error calculation unit 16 and the second error calculation unit 19.
Based on r ′ and the intersection angle B, the reference positions of the two two-dimensional images are corrected and aligned.

<< Explanation of Correction Operation >> Next, in accordance with the processing procedure shown in FIG.
4, first comparing means 15, first error calculating means 16, second adding means 17, second comparing means and second error calculating means 19
The calculation procedure of the intersection angle B and the projection angles Ar and Ar ′ in will be described.

First, the procedure for calculating the projection angles Ar and Ar 'will be described. In the following description, P0 (Ar, 0) is not necessarily used due to the measurement and calculation errors shown in the above-described principle.
= P0 '(Ar', 0). Therefore,
In the present embodiment, the following procedures (1) to (4) are calculated by the first adding means 14, the first comparing means 15, and the first error calculating means 16 to obtain Ar and Ar '.

(1) Projection angles A and A ′ on the first circular orbit C and the second circular orbit C ′ (where 0 ≦ A,
P0 (A, 0) and P0 ′ at A ′ <2π)
(A ′, 0) is obtained.

(2) P0 (Ai,
0) ≒ P0 ′ (A′i, 0) (where i = 1, 2,...)
A set of projection angles (Ai, A′i) that is n) is obtained and set as a candidate for a target set of projection angles (Ar, Ar ′).

(3) For each candidate of the set of projection angles, an error Ei = E (Ai, A'i) (where i = 1, 2,... N) is obtained according to Equation 8.

(4) The set (Ai,
A′i) is Ar and Ar ′, respectively.

First, the first adding means 14 determines whether or not 2
For each of the X-ray images, the sum of the projection values in the direction parallel to the rotation center axis 9 of the scanner (imaging system), that is, P0 (A, u) and P0 ′ (A ′,
u ′) is calculated. Here, P0 (A, u) indicates the sum of the projection values of the X-ray image (first X-ray image) on one side, and P0 ′
(A ′, u ′) indicates the sum of the projection values of the X-ray image (second X-ray image) on the other side.

Next, the first comparing means 15 performs projection so that P0 (Ai, 0) ≒ P0 ′ (A′i, 0) (where i = 1, 2,... N) within a predetermined error range. Set of corners (Ai, A '
i) is obtained and set as candidates for Ar and Ar ′, respectively. However, the range of the error in the first comparing means 15 is
Indicates the degree of margin when the imaging target region does not entirely fall within the imaging range of the detector 5 as in the case where the imaging of the head of the human body is performed. The setting is made based on the result.

Next, the first error calculating means 16 calculates the error Ei = E (Ai, A'i) (where i =
1, 2,... N), a set of projection angles (Ai, A′i) that minimizes the error Ei is obtained, and the set of projection angles (Ai, A′i) at that time is input. (Ar, Ar ′) for one of the X-ray images is output to the imaging unit 12 and the second addition unit 17.

Next, the procedure for calculating the intersection angle B will be described.
As in the case of the above set of projection angles (Ar, Ar ′), Pp0 ′ (b1 ′) = Pp due to measurement and calculation errors and the like.
B1 ′ that becomes 0 (0) does not always exist. Therefore, in the present embodiment, the following procedures (5) to (5)
The intersection angle B is obtained by (8).

(5) According to the definition of Expression 9, Pp0
Find (0).

(6) P obtained according to the definition of Expression 10
From p0 ′ (b ′), within a predetermined error range, Pp0 ′
(B′i) ≒ Pp0 (0) (where 0 ≦ b′i <π)
B′i (where i = 0, 1, 2,... M) that satisfies is satisfied as a candidate for the intersection angle B.

(7) Each candidate b′i (where i = 0,
1, 2,... M), according to Equation 11, the curve Pp0
The error Ebi = (b) between the curve Pp0 ′ (b′i + b) and the curve Pp0 ′ (b′i + b)
Eb (b'i) is obtained.

(8) Error Ebi (where i = 1, 2, 2)
.. M) are minimized, and -b'i is changed to the intersection angle B.
And

First, the sums Pp0 (b), Pp0 of the projection values passing through the center of the projected image and on a straight line in an arbitrary direction on the projected image when the second adding means 17 has the projection angles Aq and Aq '.
Find 0 '(b'). Here, Pp0 (b) indicates the sum of the projection values of the X-ray image (first X-ray image) on one side, and Pp0 (b)
0 ′ (b ′) indicates the sum of the projection values of the X-ray image on the other side (second X-ray image).

Next, the second comparing means 18 determines that Pp0 '(b'i) ≒ Pp0 (0) (where i
= 1, 2,... M), and the intersection angle B
As a candidate. However, the range of the error in the second comparing means 18 is also the same as the range of the error in the first comparing means 15 described above, and the region to be imaged is detected as in the case where the subject 6 images the head or the like of a human body. Since the margin when not completely within the imaging range of the device 5 is shown,
An experiment or the like is performed in advance for each imaging target portion, and the setting is made based on the result.

Next, the second error calculating means 19 calculates the error Ebi = Eb (b'i) (where i =
1, 2,... M). Next, the second error calculating means 19
Calculates b′i that minimizes the error Ebi, sets the angle −b′i at that time as the intersection angle B between the two input X-ray images, and outputs the intersection angle B to the imaging unit 12.

As described above, in the X-ray imaging apparatus of the present embodiment, first, when displaying X-ray images taken at different times read from the storage means (not shown), the first adding means 14 The projection value for each imaging angle is integrated for each X-ray image in parallel with the rotation center axis of the imaging system, and based on the distribution curve of the integration value, the first comparing means 15 compares the X-ray image with the subject for each X-ray image. A set of phase angles (Ar, Ar ′) indicating the amount of deviation from the reference coordinates set in (1) is obtained, and the first error calculating means 16 calculates the set of projection angles (Ai, A ′) that minimizes the error Ei according to Equation 8. i) is obtained, and a set of projection angles at that time is defined as (Ar, Ar ′) with respect to the input X-ray image.

Next, the second adding means 17 integrates the projection value for each projection angle for each X-ray image on a straight line passing through the center of the X-ray image, and based on the distribution curve of the integrated value, The second comparison means 18 obtains a plurality of candidates for the angle of a straight line connecting the points R and R 'provided on the rotation trajectory drawn by the imaging system when each X-ray image is taken and the rotation center, and obtains a second error. The calculating means 19 calculates b′i at which the error Ebi is minimized according to Equation 11.
And the angle −b′i at that time is defined as the intersection angle B of the input X-ray image.

Next, the imaging means 12 sets the set of projection angles (A
r, Ar ′) and the angle of intersection B, after correcting the orientation and inclination of the display image after reconstruction, and displaying the corrected image on a display unit (not shown), so that the subject and the X-ray imaging apparatus at the time of imaging can be displayed. It is possible to correct the orientation and the angle at the time of displaying the reconstructed image that differs depending on the positional relationship with the measurement unit 1.

Therefore, it is not necessary for the examiner such as a doctor to correct the direction and the inclination of each reconstructed image, so that the burden at the time of drafting a treatment plan can be reduced. As a result, the diagnostic efficiency of the examiner such as a doctor can be improved.

In the X-ray imaging apparatus of the present embodiment, the X-ray image picked up by the detector 5 is directly
And input to the first adding means 14, but the present invention is not limited to this, and it goes without saying that the X-ray image may be temporarily stored in a storage means (not shown) and read out. .

In the X-ray imaging apparatus according to the present embodiment,
The case where two X-ray images read from the storage unit are displayed has been described. However, the present invention is not limited to this. For example, when comparing reconstructed images before and after surgery, one X-ray image is displayed. It is needless to say that the line image is an X-ray image read from the storage means, and the other X-ray image may be an X-ray imaged by real-time measurement.

As described above, the invention made by the present inventor is:
Although specifically described based on the embodiments of the present invention, the present invention is not limited to the embodiments of the present invention, and it is needless to say that various modifications can be made without departing from the gist of the present invention. .

[0089]

The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described as follows. (1) The burden on the examiner such as a doctor can be reduced. (2) The diagnostic efficiency of the examiner such as a doctor can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a schematic configuration of a cone beam X-ray tomography apparatus which is an X-ray imaging apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the principle of registration of two or more X-ray images and reconstructed images according to the present invention.

FIG. 3 is a diagram for explaining a positional relationship between a circular orbit of an imaging system and a subject.

FIG. 4 is a diagram for explaining a positional relationship between a circular orbit and a subject when capturing a second X-ray image.

FIG. 5 is a diagram for explaining a relationship between an X-ray image at each projection angle and a distribution curve of projection values in a u-axis direction.

FIG. 6 is a diagram for explaining a relationship between an X-ray image for each projection angle and a distribution curve of projection values on a straight line passing through a rotation center axis.

FIG. 7 is a diagram for explaining a schematic configuration of a cone beam X-ray tomographic imaging apparatus which is a conventional X-ray imaging apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Measurement part, 2 ... Image processing part, 3 ... Scan drive part, 4 ... X
Source: 5, detector: 6, subject: 7, X-ray focus, 8: X
Line 9, rotation center axis 10, preprocessing unit 11, reconstruction calculation means 12, imaging means 13, indicating device 14, first addition means 15, first comparison means 16, first Error calculation means, 17 second addition means, 18 second comparison means, 19
... Second error calculation means.

Claims (11)

[Claims] An X-ray imaging apparatus configured to rotate an imaging system including an X-ray source and an X-ray detector at predetermined imaging angles around a subject to reconstruct and display an X-ray image captured, and to display the X-ray image. When displaying X-ray images captured at the same time, the projection values for each of the imaging angles are integrated in parallel with the rotation center axis of the imaging system, and the distribution curve of the integrated values is compared for each X-ray image. Phase means for estimating an angle, and intersection means for integrating projection values for each projection angle on a straight line passing through the center of the X-ray image, comparing distribution curves of the integrated values, and estimating an intersection angle. , Based on the phase angle and the intersection angle,
An X-ray imaging apparatus wherein the direction and inclination of a display image reconstructed from a line image are corrected. 2. The X-ray imaging apparatus according to claim 1, wherein the X-ray source is means for irradiating a cone or pyramid-shaped X-ray beam, and the detector is configured to display a projected image of the subject in a field of view. An X-ray imaging apparatus, characterized in that the X-ray imaging apparatus has a viewing angle within a range. 3. The X-ray imaging apparatus according to claim 1, wherein the phase unit integrates a projection value for each X-ray image in parallel with a rotation center axis of the imaging system, First comparing means for comparing the integrated value for each X-ray image and selecting a candidate for the phase angle;
A first error calculating means for calculating an error between the candidates of the phase angle and estimating the phase angle, wherein the crossing means is a second integrating means for integrating projection values on a straight line passing through the center of the projected image; A second comparing means for comparing the integrated value of each X-ray image to select a candidate for the intersection angle, and a second error calculating means for calculating an error between the candidates for the intersection angle and estimating the intersection angle. An X-ray imaging apparatus characterized by the above-mentioned. 4. The X-ray imaging apparatus according to claim 3, wherein an X-ray absorption coefficient distribution of the subject is f (x, y, z), a rotation tangent direction on a projection plane is u, and a rotation center axis. Assuming that the direction is v, the imaging angle is A, and the projection at this time is P (a, u, v), the first addition means calculates the value P0 (A, u) for the imaging angle A and the position u according to Equation 1. An X-ray imaging apparatus characterized by comprising means for calculating (1). (Equation 1) 5. The X-ray imaging apparatus according to claim 4, wherein said first comparing means includes a value P0 obtained from a first X-ray image.
(A, u) and the value P0 ′ (A ′,
u) and P0 (A, u) Ｐ within a predetermined error range.
An X-ray imaging apparatus, comprising: means for selecting a combination of a first imaging angle A and a second imaging angle A 'to be P0' (A ', u). 6. The X-ray imaging apparatus according to claim 5, wherein said first comparing means is configured to output a value P0 obtained from a first X-ray image.
(A, 0) and the value P0 ′ (A ′,
0) and P0 (A, A,
0) An X-ray imaging apparatus comprising means for determining one or more combinations of a first imaging angle A and a second imaging angle A 'that satisfies ≒ P0' (A ', 0). 7. The X-ray imaging apparatus according to claim 5, wherein W (u) is a predetermined weighting function, and P is a value obtained from the first X-ray image.
0 (A, u) and the value P0 ′ (A ′,
u), the first error calculating means calculates an error E (A, A ′) according to the following equation (2).
An X-ray imaging apparatus comprising: means for setting a combination of A and A 'that minimizes A') to a phase angle. (Equation 2) 8. The X-ray imaging apparatus according to claim 3, wherein an X-ray absorption coefficient distribution of the subject is represented by f (x, y, z), U is the rotation tangent direction, v is the direction of the rotation center axis, r is the distance of the point arbitrarily set on the projection plane from the rotation center axis, and u is a straight line connecting the arbitrarily set point and the rotation center axis.
B and the projection at the imaging angle A is Pp (A,
b, r), wherein the second addition means comprises means for calculating the projection Pp0 (b) according to equation (3). (Equation 3) 9. The X-ray imaging apparatus according to claim 3, wherein the second comparing unit obtains a value Pp0 obtained from a first X-ray image.
(0) is compared with a value Pp0 ′ (b ′) obtained from the second X-ray image, and Pp0 (0) ≒ Pp0 ′ within a predetermined error range.
An X-ray imaging apparatus comprising means for selecting an angle b 'to be (b'). 10. The X-ray imaging apparatus according to claim 3, wherein the value Pp0 (b) obtained from the first X-ray image and the value Pp0 (b) obtained from the second X-ray image are obtained. When erroneous calculation with the value Pp0 '(b') is Eb (b '), the second error calculating means sets b' in which the error Eb (b ') is the minimum according to the following equation 4 as an intersection angle. An X-ray imaging apparatus comprising: (Equation 4) 11. The X-ray imaging apparatus according to claim 1, wherein a reconstructed image whose inclination and direction are corrected is displayed on the same display screen. Line imaging device.