JPS63230151A - Measuring phantom for radiation image pickup apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to a radiographic imaging apparatus capable of reconstructing a tomographic image of an arbitrary tomographic plane by one-time imaging, in which each projection data necessary for reconstructing the tomographic image is The present invention relates to a measurement phantom for a radiographic imaging apparatus that can extract a shift amount with high precision.

[Conventional technology]

In a conventional radiation imaging apparatus of this type, the amount of shift given to each projection data in order to reconstruct a tomographic image of an arbitrary tomographic plane is determined by the position of the radiation source 1 and the radiation detector 2, as shown in FIG. I was looking for it by relationship. That is, the radiation source 1 and the radiation detector 2 are placed opposite to each other with a subject (not shown) in between, and they move relative to each other in a plane parallel to each other to digitize the projected image at each position. However, the position of the imaging point O' of the movement center ○ of the radiation 'g1 and the radiation detector 2 with respect to the incident projection plane of the radiation detector 2 remains constant. Here, a plane that includes the movement center ◯ and is parallel to the incident projection plane of the radiation detector 2 is called a loading plane 3. On the other hand, the position of the imaging point P' with respect to the incident projection plane of the radiation detector 2 at a point P, which is separated upward by Δ2 from the above-mentioned cross section 3, is in the direction of the six arrows of the radiation source 1 and in the direction of the arrow of the radiation detector 2. It is known that projection data at each position differs due to relative movement in the B direction. Note that reference numeral 4 is an arbitrary tomographic plane that includes the point P and is parallel to the incident projection plane of the radiation detector 2.

In this state, the angle between the straight line connecting the imaging point O' of the movement center 0 and the radiation source 1 and the center line 5 of relative motion is θ (this is called the exposure angle), and the radiation source 1 If the distance from the mounting surface 3 to the mounting surface 3 is a, and the distance from the mounting surface 3 to the incident projection plane of the radiation detector 2 is b, then the mounting surface 3
The amount of deviation d from the imaging point O' of point 0 above to the imaging point P' of point P on the arbitrary tomographic plane 4 is as follows. Therefore, by shifting the position of the imaging point P' toward the imaging point 0' by the amount of shift d, the imaging point P' of the point P on the arbitrary tomographic plane 4 can be shifted to any position of the relative movement. Its position remains unchanged even with respect to projection data. Therefore, in this case, it can be seen that the above deviation amount d is the shift amount for the projection data of the exposure angle θ. From this, it can be seen that the exposure angle θ at the time of measuring the projection image at each position is necessary in order to reconstruct the tomographic image of an arbitrary tomographic plane.

Conventionally, when measuring the projected image of the subject at each position, each exposure angle θ is directly measured, and the
Each shift amount d was calculated using equation 1). Alternatively, the speed of relative movement between the radiation source 1 and the radiation detector 2 and each of the specifications a and b may be determined according to the fixed device specifications of the radiographic imaging device.

The amount of shift at each position was calculated from Δ2 etc. as a time function.

[Problem that the invention seeks to solve]

However, when extracting the shift amount in such conventional radiographic imaging devices, first of all, it is difficult to directly measure each exposure angle θ when measuring the projected image at each position of the subject. It was difficult to measure the angle θ with high precision. Furthermore, if the time function is calculated as a function of time based on the moving speed or the like according to the device specifications, the radiographic imaging device does not necessarily move accurately according to the device specifications. Therefore, the shift amount of projection data at each position may not be extracted with high precision.

For this reason, image blurring may occur in the obtained tomographic image of an arbitrary tomographic plane, making it impossible to obtain good diagnostic information.

Therefore, an object of the present invention is to provide a measurement phantom for a radiographic imaging apparatus that can solve such problems.

[Means for solving problems]

The means of the present invention for solving the above-mentioned problems is to replace a large number of imaging point measuring members formed on a small object made of a material with a high radiation absorption coefficient with a flat plate made of a material with a low radiation absorption coefficient and high rigidity. The phantom members are arranged and fixed in a straight line with the required spacing between adjacent ones on the surface or inside of the support member of the phantom member. This is done using a measurement phantom for a radiographic imaging device that is fixed so that the arrangement direction of the members is upright or tilted.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a perspective view showing an embodiment of a measurement phantom for a radiographic imaging apparatus according to the present invention. This measurement phantom is used to extract the shift amount of each projection data necessary for reconstructing a tomographic image in a radiographic imaging apparatus capable of reconstructing a tomographic image of an arbitrary tomographic plane. It consists of a combination of 7.

The mounting base 6 supports and fixes a phantom member 7, which will be described later, and is made of a material with a low radiation absorption coefficient, such as synthetic resin or acrylic resin, and has a horizontal piece 8 and a vertical piece 9 formed into a flat plate at approximately right angles. are combined so that they intersect. The reason why the mounting base 6 is made of a material with a low radiation absorption coefficient is to allow the radiation from the radiation source to pass through it well and to prevent shadow images from remaining due to the radiation. .

A phantom member 7 is fixed to the upper surface of the mounting base 6. This fan 1-mem member 7 is for measuring the actual image formation point on the incident projection plane of the radiation detector due to radiation irradiation from the radiation source, and includes a support member 10,
A large number of imaging point measuring members 11.11. It consists of a combination of... The support member 10 is for arranging and fixing the image forming dot meter, 11, 11°, etc., which will be described later, and is made of a thin material with a low radiation absorption coefficient and high rigidity, such as synthetic resin or acrylic resin. It is formed into an elongated flat plate. The reason why this support member 10 is made of a material with a low radiation absorption coefficient is to allow the radiation to pass through well when irradiated from a radiation source, and to prevent shadow images caused by the radiation from remaining. .

The imaging point measuring members 11, 11. are made of a highly rigid material while maintaining flatness. . . is held at a constant position with respect to the irradiation radiation.

On the surface or inside the support member 10, there are a number of imaging point measuring members 11, 11. ...is fixed. This image forming point measuring member 11 is for measuring an image forming point due to radiation irradiation from a radiation source, and is made of a material 1 having a high radiation absorption coefficient, such as steel, and is formed into a spherical shape with a small diameter, and is made of a material 1 having a high radiation absorption coefficient, such as steel, and is formed into a spherical shape with a small diameter. The members 10 are arranged and fixed in a straight line along the longitudinal direction with equal intervals C between adjacent members by a required amount. The size of the image-forming point measuring member 11 is such that the image formed by radiation irradiation is approximately several pixels 2, for example, a diameter of 0.1~
It is about 5 ml. This is because a peak of the imaging point as an image is likely to appear when the size is around this level. Further, the distance C between the adjacent image forming point measuring members 11° 11 is such that the image forming position of the image forming point measuring member 11 at an arbitrary position where no image forming point measuring member 11 exists therebetween is determined by the distance C between the adjacent image forming point measuring members 11. The interval is determined by interpolation from the image point, for example, 5 to 50
It is about nm. Note that the image point measuring member 11 is made of a material with a high radiation absorption coefficient because it absorbs radiation well when irradiated from a radiation source, and the image point can be sufficiently recognized as an image. This is to ensure that. In addition, the reason why the imaging point measuring member 11 is made spherical is because a sphere has the same shape and the same center no matter which direction it is viewed from, so that it can be easily irradiated with radiation from each direction of the radiation source. This is because the size of the image forming point of the image forming point measuring member 11 is always in the opposite direction, and the center position thereof is also the same at each image forming point. Note that the imaging point measuring member 11 does not necessarily have to be spherical; for example, the length of the − side is O01 to 1.0 m.
As long as it is a small object, it may have a shape other than spherical.

The phantom member 7 formed as described above is
As shown in FIG. 1, the image forming point measuring members 11, 11.・・・
・The supporting member 10 is arranged so that the arrangement direction of the supporting member 10 is appropriately inclined.
is leaning against the horizontal piece 8 at an angle α, and is fixed with an adhesive or the like. Incidentally, the inclination angle α may be set to an appropriate angle within the range of 0″<α<90° depending on the purpose of measurement.

Next, extraction of the shift amount of each projection data necessary for reconstructing a tomographic image of an arbitrary tomographic plane using the measurement phantom 12 configured as described above will be explained.

First, if the relative movement between the radiation source and the radiation detector is in a linear trajectory, the measurement phantom 12 shown in FIG. and the radiation detector, the imaging point measuring members 11, 11 . Set the arrangement directions of ... to be orthogonal. At this time, the image forming point measuring members 1F, 11. The distance in the height direction along the center line 13 regarding the relative movement of... is, for example, 10 nv.
They are arranged with a determined interval C so that the distance is n. In this state, as shown in FIG. 2, the radiation source 1 is moved in the direction of arrow A to irradiate the phantom member 7 with radiation, and the radiation detector 2 is relatively moved in the direction of arrow B, and each Photographs are taken sequentially for each projection position. The projected images of the phantom member 7 photographed in this manner are generally as shown in FIGS. 3(a), (b), and (C). That is, Figures (a) and (c) are projection images Ia and Ic at the maximum exposure angle when radiation is irradiated from the direction 1a of the radiation source 1 and the IC shown in Figure 2, respectively. In Figure (b), the radiation source 1 irradiates radiation from the direction 1b located directly above the phantom member 7.
This is a projection image Ib at the minimum exposure angle. Then, in FIG. 2, an imaging point measuring member 11a located on the mounting surface 3
The image point on the incident projection plane of the radiation detector 2 is a□l
821 a3, and the image formation position on the incident projection plane remains unchanged in each projection image a to Ic. On the other hand, the image forming point of the other image forming point measuring member 11b located on the arbitrary tomographic plane 4 other than the above-mentioned cross section 3 with respect to the incident projection plane of the radiation detector 2 is b 1 b21 b, and the incident projection plane The upper imaging position differs for each projection image Ia to Ic.

Here, the imaging point measuring members 11a, 1lb.

. . . Imaging points a□ to a in each projected image Ia=Ic
, i+l)t~b 3 t... can be accurately detected with sub-pixel accuracy by the following procedure. First, a threshold is set for the density of each pixel of the projection image data,
Threshold processing is performed in which a value below or above this threshold is used as the overall threshold. By doing so, it is possible to clearly separate the imaging point measuring members 11a, llb, . . . from the background. Next, an imaging point area is set for each of the imaging parts of the imaging point measuring members 11a, 11b, . . . separated from the background part, and all pixels (IIj ), by calculating ΣTij ΣTij for the density Tij of
Find x+y). And the coordinates (x, y) of this center of gravity
The imaging point measuring members 11a, 1lb.

... is the position of the imaging point on the projected image. In this way, all the imaging point measuring members 11a, llb.

By determining the coordinates (xt y) of the center of gravity for the imaging point regions of..., each imaging point measuring member 11a, 11b,
It is possible to accurately detect the positions of the imaging points a1 to a3t, b1 to b31, and so on with an accuracy of less than a pixel.

In this way, each imaging point measuring member 11a, 11b, .
Although the position of the imaging point of ... can be detected accurately,
The above-mentioned image forming point measuring members 11a, llb.

The image forming point measuring member 11 at an arbitrary position where ... does not exist.
The imaging position may be determined in units of height 1+n+n by interpolation processing from the imaging points of existing imaging point measuring members in the vicinity, for example, point a and point b4.

At this time, as is clear from FIG. 2, for the imaging point measuring member 11 located above, the interval at which the image is formed on the incident projection plane of the radiation detector 2 increases as it goes upward. It is necessary to correct this magnification factor using a required arithmetic expression.

As described above, the image forming point measuring member 11a of the phantom member 7 in each of the projection images Ia to Ic.

11b,... imaging points a1 to a31 b□ to b31・
When the position of ... has been accurately detected, for example, in order to reconstruct a tomographic image of an arbitrary tomographic plane 4 that passes through the imaging point measuring member 11b in FIG. 1
)) Based on the position of the imaging point b2 in the projection image Ib of (a), for example, in the projection image Ia of FIG.
In the projected image Ic of the same figure (c), b
It is only necessary to shift by 3b2. As a result, the amount of shift when reconstructing a tomographic image of a tomographic plane at an arbitrary height is determined.

Note that the above-mentioned equation (1) is a function of the distance in FIG. That is, the value of the deviation id of the imaging point also changes depending on the position of the mounting surface 3. Therefore, it is insufficient to place the phantom member 7 on only one mounting surface 3 and measure it.

Therefore, the loading surface 3 is moved and set by appropriate values, and the deviation amount d is determined by the above equation (1), and the deviation ff1d is determined by interpolation for the loading surface between the jumps. In this way, for all the loaded planes corresponding to ΔZ in FIG. 6, the amount of shift for reconstructing the tomographic image of the tomographic plane separated by an arbitrary height can be determined. Then, a shift table is created by tabulating the shift amount data obtained in this way, and this is stored in a memory, and the required shift amount data is read out and shifted as necessary.

FIG. 4 is a perspective view showing a second embodiment of the present invention. In this embodiment, the phantom member 7 is brought into close contact with one side of the vertical piece 9 of the mounting base 6 and fixed with an adhesive or the like. In this case, the arrangement direction of the imaging point measuring members 11, 11°, . The measurement phantom 12' configured in this manner is used in a curved trajectory type radiation imaging apparatus in which the relative motion between the radiation source and the radiation detector draws a circular trajectory or the like as shown by the arrow. Then, the measurement phantom 12' shown in FIG. 4 is placed on the top surface of the top plate on which the subject is placed, with respect to the center line 14 regarding the relative movement between the radiation source and the radiation detector, which is indicated by the arrow.
Image forming point measuring members 11, 11 of the phantom member 7.・
The phantom member 7 may be set with its arrangement direction set at -M, and the radiation source may be irradiated and photographed while rotating the radiation source in the direction of the arrow. As a result, each imaging point measuring member 11, 11. The positions of the imaging points of . . . do not overlap, and a projection image similar to that shown in FIG. 3 can be obtained. Therefore, after that, the shift amount can be determined by performing the same processing as in the first embodiment shown in FIG.

FIG. 5 is a perspective view showing a modification of the second embodiment. This modification includes a large number of imaging point measuring members 11.11.・
... are directly arranged and fixed in a straight line on the surface or thick inside of the vertical piece 9 of the mounting base 6, and this is used as the phantom member 7'. In this case, the support member 1 shown in FIG.
o can be omitted.

〔Effect of the invention〕

Since the present invention is configured as described above, in a radiographic imaging apparatus capable of reconstructing a tomographic image of an arbitrary tomographic plane by one-time imaging, the exact relative movement between the radiation source 1 and the radiation detector 2 is not known. Even if one measurement phantom of the invention 12.12'.

By taking projection images of the phantom members 7, 7' using 12' as a subject, it is possible to directly extract the amount of shift required to reconstruct a tomographic image of an arbitrary tomographic plane. Therefore, there is no need to measure the exposure angle θ every time as in the past, and there is no need to calculate the amount of deviation of the imaging point between the cut plane and the arbitrary tomographic plane by calculating using the above formula (1). , it is possible to easily and quickly extract the shift amount of each projection data. In addition, since the imaging point measuring member 11 of the phantom members 7, 7' is formed into a small object made of a material with a high radiation absorption coefficient, the position of the imaging point can be detected accurately, and as a result, each of the above-mentioned The shift amount of projection data can be extracted with high precision.

Therefore, image blur does not occur in the obtained tomographic image of an arbitrary tomographic plane, and good diagnostic information can be obtained.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an embodiment of a measurement phantom for a radiographic imaging device according to the present invention, FIG. 2 is an explanatory diagram showing a state in which the measurement phantom is photographed as a subject by the radiographic imaging device, and FIG. An explanatory diagram showing a projection image obtained by the above photographing, FIG. 4 is a perspective view showing a second embodiment of the present invention, and FIG. 5 is a perspective view showing a modification of the second embodiment.
FIG. 6 is an explanatory diagram showing a state in which a shift amount for reconstructing a tomographic image of an arbitrary tomographic plane is determined in a conventional radiographic imaging apparatus. 1... Radiation source, 2... Radiation detector, 3...
・Cut section, 4...Arbitrary fault plane, 6...Mounting stand,
7゜7′...Phantom member, 8...Horizontal piece,
9... Vertical piece, 10... Supporting member, 11...
・Image point measurement member, 12.12', 12'...
Measurement phantom, C...interval, α...angle of inclination,
Ia~Ia...Projected image, a~a,...Image formation point, b□~b3...Image formation point.

Claims (1)

[Claims] A large number of imaging point measuring members made of a small object made of a material with a high radiation absorption coefficient are mounted on or inside a flat support member made of a material with a low radiation absorption coefficient and high rigidity.
Phantom members arranged and fixed in a straight line with a required distance between adjacent ones are placed on the upper surface of a mounting base made of a material with a low radiation absorption coefficient, and the arrangement direction of the imaging point measuring member is upright or inclined. A measurement phantom for a radiographic imaging device, characterized in that it is fixed as shown in FIG.