JP5239585B2 - X-ray imaging device - Google Patents

Description

  The present invention relates to a two-dimensional X-ray detector such as an FPD (flat panel X-ray detector) and a general X-ray imaging apparatus or a C-arm type X-ray apparatus having a grid for removing scattered X-rays. Regarding removal of grid shadows.

  In an X-ray imaging apparatus equipped with a detector capable of detecting X-rays in two dimensions, such as FPD, detection is performed in order to remove scattered X-rays generated when X-rays pass through the subject and obtain a high-contrast image. A grid is disposed over the entire front surface of the vessel. The grid is configured by arranging X-ray absorbing members at a predetermined pitch.

  An X-ray imaging apparatus provided with a grid that removes scattered X-rays has a drawback that X-rays are absorbed by an X-ray absorbing member constituting the grid, and striped shadows appear in an image at a predetermined pitch. Various methods for removing striped shadows by the grid have been proposed, and a method of removing the striped shadows by a frequency filter is the most common method.

  On the other hand, in an apparatus that can change the distance between the X-ray source and the two-dimensional X-ray detector (hereinafter referred to as SID), the position and shape of the striped shadow change according to the SID. . The change in the shape appears in such a manner that the striped shadow becomes thicker as the distance from the irradiation center increases. That is, the spatial frequency of the striped shadow differs between the center and the peripheral part. Therefore, it is difficult to simply remove the fringes with a frequency filter. A grid image that is captured by only the grid without passing through the subject under a plurality of imaging conditions that should correspond to such an apparatus is stored, and an image that is actually captured of the subject is stored in the stored grid image In Japanese Patent Application No. 2008-014603, a method of removing a grid image from the image by dividing by a grid image that matches the imaging condition is proposed (Japanese Patent Application No. 2008-014603).

In addition, the arrangement pitch of the X-ray absorbing members constituting the grid is the same as or an integer multiple of the pixel pitch of the X-ray flat panel detector, and is integrated with the X-ray flat panel detector so that a moire image (X-ray flat panel detection) is obtained. Occurrence of a long period of waviness that occurs when the pitch of the pixel of the unit is different from the pitch of the grid (see, for example, Patent Document 1). In the related art, if the technology for removing the striped shadow is applied, the device can reduce the adverse effect on the image due to the shadow of the X-ray absorbing member while physically removing the scattered radiation by the grid. Has been.
JP 2005-283360 A

  However, in order to remove the striped shadow of the grid by the above-described method, it is necessary to accurately specify the position of the striped shadow on the image. In this regard, the position of the striped shadow changes depending on the positional relationship between the X-ray source and the two-dimensional X-ray detector even if the grid is fixed to the two-dimensional X-ray detector. Even when the X-ray source and the two-dimensional X-ray detector are supported in an opposed state, the position of the striped shadow may change due to the deflection of the support mechanism or the like.

  Therefore, a grid image captured by only the grid without passing through the subject under a plurality of imaging conditions is stored, and an image actually captured by the subject is stored in the stored grid image as the imaging condition. Even by the method of removing the grid image from the image by dividing by the matching grid image, the grid image cannot be accurately removed.

The present invention adopts the following configuration in order to solve the above problems.
That is, an X-ray source that irradiates X-rays, a two-dimensional X-ray detector that detects the X-rays, and a plurality of X-ray absorptions disposed between the X-ray source and the two-dimensional X-ray detector. A scattered radiation removing grid having a member, a plurality of markers arranged on the scattered radiation removing grid, an image collecting means for collecting an image from the two-dimensional X-ray detector, and a marker from the collected image A marker projection position detecting means for extracting the projection position of the first marker, a first marker projection position previously extracted from the first image collected without passing through the subject, and a second image collected via the subject Grid shadow removal that obtains an image from which the projected image of the X-ray absorbing member is removed by correcting the second image based on an image obtained by deforming the first image based on the projected second marker position Having means The features.

  The present invention has SID detection means for detecting an SID that is the distance between the X-ray source and the two-dimensional X-ray detector, and the grid shadow removal means collects a plurality of SIDs in advance without passing through the subject. And an X-ray imaging apparatus using an image collected with an SID closest to the SID when the second image is collected among the stored images.

  The present invention further includes an X-ray imaging apparatus further comprising marker projection image correcting means for correcting a projected image of the marker in the image from which the projected image of the X-ray absorbing member has been removed.

  Scattered X-rays generated from the subject are removed by the grid, and an X-ray fluoroscopic image with good contrast and less noise such as striped shadows by the grid is obtained.

  An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of an X-ray imaging apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing a schematic configuration of the grid 4 according to the embodiment of the present invention. 3 and 4 are diagrams showing marker projection positions and irradiation fields calculated from two images. FIG. 5 is a diagram illustrating the operation of the X-ray imaging apparatus according to the embodiment of the present invention.

  As shown in FIG. 1, an X-ray imaging apparatus according to an embodiment of the present invention includes an X-ray source 3 that generates X-rays, and a grid 4 that removes scattered X-rays generated when the X-rays pass through a subject P. A two-dimensional X-ray detector 6 composed of, for example, an FPD, an image processor 7 that performs image processing of the output of the two-dimensional X-ray detector 6, a storage device 8 that stores image data, and an image A high voltage is supplied to the display 9 for displaying the operation screen, the moving unit 10 including the grid 4 and the two-dimensional X-ray detector 6, the movement controller 11 for driving the moving unit 10, and the X-ray source 3. The high voltage generator 2, the high voltage generator 2, the movement controller 11, the control device 1 that controls the entire device, and the like are included.

  As shown in FIG. 2, X-ray absorbing members 41 for removing scattered radiation are arranged on the grid 4 at a predetermined pitch. In addition, markers M1 to M4 made of members having an X-ray transmittance of, for example, about 20% to 40% are arranged at the four corners. Hereinafter, when a plurality of markers are collectively referred to, they are appropriately referred to as markers M. The nth marker M is referred to as a marker Mn.

  As the marker M, two-dimensional X-ray detection is performed on the transmitted X-ray of the marker M at the X-ray intensity (tube voltage, tube current, time applied to the X-ray source 3) in a range that may be irradiated for imaging. Any material can be used as long as it has an X-ray transmittance that can be detected by the device 6. For example, an aluminum plate having a thickness of about 2 mm satisfies the conditions.

The operation of the X-ray imaging apparatus according to the embodiment of the present invention will be described with reference to FIG.
(Step S1)
In a state where the subject P is excluded from the configuration of FIG. 1, imaging is performed while changing the SID by ΔSID, and an image Gp is obtained. Hereinafter, the image Gp picked up at the i-th time is set as an image Gp _i, and the SID detected by the SID detection unit at that time is set as SID _i .
By the marker projection position detecting means 12, the projection position _{P ni = (x pni, y} pni) marker Mn in each image Gp _i is calculated. The image Gp _i , SID _i and P _ni are set and stored in the storage device 8. ΔSID is 50 mm.

The image Gp _i photographed in step S1 and the storage device 8 are examples of the first image and the first image storage device of the present invention, respectively.

(Step S2)
Next, as shown in FIG. 1, the subject P is imaged to obtain an image Go. The image Go corresponds to the second image in the present invention. The SID at this time is SID _o .

(Step S3)
From the image Go, an edge is extracted by scanning the projected image of the marker M, and calculates an average center position thereof, a projection position _{Po ni = (x Poni, y} Poni) is calculated. In this case, among the four markers M, the image has selected three distinct, may calculate the projection position Po _ni. However, the selection process is not essential, and the positions of the projection images of all the markers M may be used. Two markers M may be used. As long as a plurality of projection positions _Poni are calculated, the number can be variously changed.

ただし、ＳＩＤ_ｉ−１＜ＳＩＤ_ｏ ≦ＳＩＤ_ｉである。 (Step S4)
The position Pr _n = (x _Prn , y _Prn ) of the standard marker Mn in the current SID _o is calculated. The position Pr _n uses P _ni corresponding to the one closest to SID _o among the SID _i stored in the storage device 8 in step S1. Furthermore, it is more preferable that the interpolation process is performed according to the following equation (1).

However, SID _i-1 <SID _o ≤SID _i .

ここで、未知数の数は、ｘ_Ｔ，ｙ_Ｔ，ｘ_Ｓ，ｙ_Ｓの４つであり、各変数がそれぞれｘ、ｙ成分を持つことから、ｎ＝２であれば４元の連立方程式となる。よって、左辺が０となるＴ，Ｓの組み合わせが存在する。また、ｎ＞２の場合は、右辺が最小になるように解を算出することができる。 (Step S5)
3 and 4 show the projection position Po _n (Po ₁ , Po ₂ , Po ₃ , Po ₄ ) calculated in step S3 and the position Pr _n (Pr ₁ , Pr ₂ , Pr ₃ , Pr ₄ ) calculated in step S4. ) Is displayed in two-dimensional coordinates of the overlapping axes x and y. For reference, the irradiation fields corresponding to each are overlapped as irradiation fields Vo and Vr. Here, in order to match the projection position of each marker Mn on the image Gp _i and image Go stored in the storage unit 8, calculates the amount of deforming the image Gp _i. In this embodiment, the amount of deformation is calculated as the expansion / contraction ratio S = (Sx, Sy) and the parallel movement amount T = (Tx, Ty).
That is, T and S satisfying the following equation 2 are calculated.

Here, the number of unknowns is four of x _T , y _T , x _S , and y _S , and each variable has x and y components. Therefore, if n = 2, Become. Therefore, there is a combination of T and S whose left side is 0. If n> 2, the solution can be calculated so that the right side is minimized.

(Step S6)
Based on the expansion / contraction rate S and the parallel movement amount T calculated in step S5, the image Gp _i stored in the storage device 8 that is closest to the SID _o is deformed, and the correction image Gr (x, y ). As the image Gp _i to be deformed, the image closest to SID _o is selected. However, in order to improve accuracy, an intermediate image between the image Gp _i-1 and the image Gp _i is associated with SID _o. May be used. The intermediate image can be obtained by a known morphing technique.

(Step S7)
Correction processing is performed to divide each pixel value of the image Go obtained in step S2 by each pixel value of the image Gr obtained in step S6. By the correction process, the pixel density of the projected image portion of the grid 4 and the marker M is reverted, and the shadow portion image of the marker M is also restored.
In this embodiment, the calculation is division, but subtraction may be used. Further, it is not a simple division, but may be a non-linear calculation or may be associated with a table. In addition, as long as the stretched image Gr is applied to the image Go, the calculation method can be variously changed.

(Step S8)
The original image of the projected portion of the marker M should also be restored by the calculation in step S7, but it is assumed that the projected shape of the marker M is slightly deformed due to the positional deviation of the X-ray source 3 or the like. In that case, there is a possibility that an artifact may occur in the periphery of the marker M. Therefore, the shadow edge portion of the marker M is corrected by the peripheral pixels. The correction process corresponds to the marker projection image correction unit in the present invention.
This process is not an essential configuration in the present invention.

  Since the present invention has the above-described configuration, the projection image of the grid 4 is enlarged / reduced in step S6, the position change of the grid shadow is corrected, and precise position information of the grid shadow is obtained. Therefore, it is possible to apply a grid shadow removal method that uses particularly precise grid shadow position information as a map. Scattered X-rays generated from the subject P are removed by the grid 4 so that the contrast is good. X-ray fluoroscopic images with little noise such as shadows can be obtained.

In the above embodiment, the expansion / contraction rate S and the parallel movement amount T are obtained by using Equation 2 as the evaluation function, but the present invention is not limited to such a method.
For example, the difference between the y coordinate position y _Pr1 of the standard marker M1 and the position y _Pr3 of the marker M3 is defined as Dy _Pr3 . Similarly, the y coordinate position y _Po1 of the marker M1 in actual photographing and the marker M3 when the difference between the position _{y Po3} was _{Dy Po3,} the axis y-direction scaling factor Sy near x-coordinate of the marker _M1, may be that the _Dy Pr3 _/ Dy _Po3. In this case, it is possible to calculate the expansion / contraction rate S by performing the same processing for a plurality of combinations in each of the axes x and y directions.
Furthermore, it is not limited to the point which calculates | requires the expansion-contraction rate S and the parallel displacement amount T. As long as the image Go is corrected based on the projection positions Po _ni and P _{ni of the} marker Mn and the image Gp, the correction method can be variously changed.

  In this embodiment, the difference in the imaging conditions is only the difference in the SID. However, when the apparatus is affected by distortion due to its own weight due to expansion / contraction / rotation of the apparatus, such as a C-arm X-ray apparatus or cone beam CT apparatus. The present invention can also be applied to the case where the imaging conditions other than the SID are determined for each apparatus state and captured and stored. In the embodiment shown in FIG. 2, the markers M are arranged at the four corners of the grid 4, but the number of markers M may be two or three. In addition, although the aluminum material was mentioned as an example as the marker M, a beryllium material or a thin metal may be sufficient and it is not limited to an aluminum material. As described above, the apparatus can have various configurations, and the present invention includes these modifications.

  The present invention relates to a two-dimensional X-ray detector such as an FPD and a general X-ray imaging apparatus or C-arm X-ray apparatus including a grid for removing scattered X-rays, and more particularly to removal of grid shadows.

It is a figure which shows schematic structure of the X-ray imaging device by the Example of this invention. It is a figure which shows schematic structure of the grid by the Example of this invention. It is a figure which shows the marker projection position and irradiation field which were calculated with two images. It is a figure which shows the marker projection position and irradiation field which were calculated with two images. It is a figure which shows operation | movement of the X-ray imaging device by the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control apparatus 2 High voltage generator 3 X-ray source 4 Grid 6 Two-dimensional X-ray detector 7 Image processor 8 Memory | storage device 9 Display 10 Moving part 11 Movement controller 12 Marker projection position detection means 41 X-ray absorption member M Marker M1 Marker M2 Marker M3 Marker M4 Marker P Subject Po ₁ Projection position Po ₂ Projection position Po ₃ Projection position Po ₄ Projection position Pr ₁ Position Pr ₂ Position Pr ₃ Position Pr ₄ Position Vo Irradiation field Vr Irradiation field x axis y axis

Claims (3)

An X-ray source for irradiating X-rays, a two-dimensional X-ray detector for detecting the X-rays, and a plurality of X-ray absorbing members disposed between the X-ray source and the two-dimensional X-ray detector. A grid for removing scattered radiation, a plurality of markers arranged on the grid for removing scattered radiation, an image collecting means for collecting an image from the two-dimensional X-ray detector, and a projection of the marker from the collected image Marker projection position detecting means for extracting the position, the first marker projection position extracted from the first image collected without going through the subject in advance, and the second image collected through the subject Grid shadow removing means for obtaining an image from which the projection image of the X-ray absorbing member is removed by correcting the second image based on an image obtained by deforming the first image based on a second marker projection position. It is characterized by having X-ray imaging apparatus.   SID detection means for detecting an SID that is the distance between the X-ray source and the two-dimensional X-ray detector, and the grid shadow removal means stores the first image in a plurality of different SIDs in advance. 2. An image collected by an SID closest to the SID at the time of collecting the second image is selected and used from the one image storage device and the stored first image. X-ray imaging apparatus.   3. The X-ray imaging apparatus according to claim 1, further comprising marker projection image correcting means for correcting a projected image of a marker in an image from which the projected image of the X-ray absorbing member has been removed.

Images