X-ray tomograph and stereoradioscopic image construction equipment

An X-ray tomograph comprises an X-ray generator having a function of moving the focal position and radiating X-rays toward a subject, an X-ray image receiving element for receiving transmission images created by X-rays radiated from the X-ray generator, and an image processing section for creating a tomographic image by processing the transmission images of the subject received by the X-ray image receiving element. A stereoradioscopic image constructing equipment comprises the X-ray tomograph and a stereoradioscopic image constructing section for creating a stereoradioscopic image by subjecting the created tomographic images to image processing. By using the X-ray tomograph, a tomographic image can be created without providing any high-precision movable mechanism, and a tomographic image of even a soft subject can be correctly created.

This is the U.S. National Stage of International Patent Application No. PCT/JP2005/003199, filed on Feb. 25, 2005, which relies for priority upon Japanese Patent Application No. 2004-054625, filed on Feb. 27, 2004, the contents of both of which are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present invention relates to an X-ray tomograph for creating a tomographic image by processing plural transmission images received by radiating X-rays and to a stereoradioscopic image constructing equipment provided with the X-ray tomograph.

BACKGROUND ART

Conventionally, an X-ray tomograph is used to inspect, for example, the inside structure of a subject without destruction. The X-ray tomograph comprises an X-ray generator for radiating X-rays to a subject and an X-ray image receiving element for receiving transmission images formed by the X-rays radiated from the X-ray generator. The X-ray generator is configured to be rotatable around the subject on the same plane by a mechanical movable mechanism. The X-ray image receiving element can be rotated by a mechanical movable mechanism in correspondence with the movement of the X-ray generator. Besides, the X-ray image receiving element is connected to an image processing device which processes the transmission images received by the X-ray image receiving element to create a tomographic image. (See, for example, Patent Document 1)

But, a method using the above X-ray tomograph has a disadvantage that a high-precision movable mechanism must be used to rotate the X-ray generator and the X-ray image receiving element in order to keep a spatial resolution of several micrometers.

The subject may be rotated and translated instead of the rotations of the X-ray generator and the X-ray image receiving element, but such a method needs a high-precision movable mechanism for rotation of the subject and has a disadvantage that it cannot be used for examination of, for example, a soft subject which is deformed when rotated.

DISCLOSURE OF THE INVENTION

The present invention has been made to solve these problems, and an object thereof is to provide an X-ray tomograph that can provide a tomographic image without having a high-precision movable mechanism and also obtain a tomographic image of a soft subject, and a stereoradioscopic image constructing equipment having the X-ray tomograph.

The X-ray tomograph of the invention comprises an X-ray generator having a function of moving a focal position and radiating X-rays toward a subject, an X-ray image receiving element for receiving a plurality of transmission images of the subject formed by the X-rays radiated from the X-ray generator while the focal position is moved, and an image processing section for creating a tomographic image by processing the plurality of transmission images of the subject received by the X-ray image receiving element.

The stereoradioscopic image constructing equipment of the invention comprises the above-described X-ray tomograph of the invention, and a stereoradioscopic image constructing section for creating a stereoradioscopic image by processing the plurality of tomographic images created by the X-ray tomograph.

According to the present invention, the tomographic image of the subject can be obtained easily without provision of a movable mechanism for moving, for example, an X-ray generator, an X-ray image receiving element or a subject by radiating the X-rays to the subject while moving a focal position of the X-ray generator, receiving by the X-ray image receiving element the plural transmission images of the subject formed by the X-rays from the different focal positions, and processing the received transmission images by the image processing section to create the tomographic image. A tomographic image of, for example, a soft subject can also be obtained securely.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the invention will be described with reference to the drawings. It is to be understood that the present invention is not limited to the following embodiments.

FIG. 1shows the stereoradioscopic image constructing equipment of one embodiment of the invention. This stereoradioscopic image constructing equipment is provided with an X-ray CT (computed tomography) apparatus1as an X-ray tomograph and an image processing device2. The stereoradioscopic image constructing equipment is used for nondestructive inspection or the like of a subject3.

The X-ray CT apparatus1is provided with an X-ray tube4as an X-ray generator and an X-ray image receiving element5. The X-ray tube4and the X-ray image receiving element5are disposed to face each other, and the X-ray image receiving element5is connected to the image processing device2. The subject3is disposed between the X-ray tube4and the X-ray image receiving element5and fixed on a fixing stand such as an X-Y-Z table (not shown).

The X-ray tube4is formed to have a substantially cylindrical shape and disposed such that a central axis O agrees substantially with the center of the X-ray image receiving element5. The X-ray tube4has a radiation plane4awhich is parallel to the X-ray image receiving element5. The radiation plane4ahas an X-ray generating source4bas a focal point for generation of X-rays toward the subject3. The X-ray generating source4bis disposed to be rotatable on a circumference having a prescribed radius r with the central axis O of the X-ray tube4as the center on the radiation plane4a. In other words, the X-ray tube4has a function to move the positions of the X-ray generating source4b, and the X-ray generating source4bis configured to be rotatable, for example, one degree at a time with respect to the central axis O along the entire circumference, namely 360 degrees.

The X-ray image receiving element5is, for example, a square planar image intensifier or a planar X-ray detector, and receives an X-ray image, which has passed through the subject3after radiation from the X-ray generating source4bof the X-ray tube4, upon converting into a transmission image G which is an image signal. And, the transmission image G is sent to the image processing device2.

The image processing device2has a computer6as a processing arithmetic logic unit and a monitor7as an image display part connected to the computer6. The computer6processes the transmission image G transmitted from the X-ray image receiving element5and has an image processing section and a stereoradioscopic image constructing section.

The image processing section of the computer6cuts out square images from individual transmission images G0, G1, . . . , Gi, . . . , Gn corresponding to individual positions A0, A1, . . . , Ai, . . . , An of the X-ray generating source4bof the X-ray tube4as shown inFIG. 2throughFIG. 4and accumulates the cut-out images CG to create an accumulated image SG. The images are cut out into a square shape with a virtual center0B, which is positioned on a circumference having a radius R from a center0G of the transmission image, determined as the center. The cutout images CG correspond to arbitrary tomographic planes S which intersect in the axial direction of the X-ray tube4and are different from one another.

Laminographs, namely tomographic images T, of the subject3corresponding to the individual tomographic planes S are created by calculating a brightness value B of each pixel of the obtained accumulated image SG and extracting pixels having the brightness value B which is between a prescribed upper limit threshold value TH and a prescribed lower limit threshold value TL smaller than the upper limit threshold value TH.

Here, a ratio between the radius r and the radius R is indicated as a ratio between a distance fod and a distance Δf as shown inFIG. 2. Specifically, it is expressed as R=r×Δf/fod, where the distance fod indicates a distance from the radiation plane4aof the X-ray tube4to the tomographic plane S of the subject3, and the distance Δf indicates a difference between the distance fod and a distance fid from the radiation plane4aof the X-ray tube4to the X-ray image receiving element5. The upper limit threshold value TH and the lower limit threshold value TL are previously determined according to the brightness value B of the pixels of the accumulated image SG.

The stereoradioscopic image constructing section of the computer6creates a three-dimensional image, namely a stereoradioscopic image D, by composing upon correcting a geometrical enlargement ratio P of the tomographic images T created by the image processing section for each of the plural tomographic planes S which intersect in the axial direction of the X-ray tube4and are different from one another. Here, the geometrical enlargement ratio P is indicated as a ratio between the distance fid (a distance from the radiation plane4aof the X-ray tube4to the X-ray image receiving element5) and the distance fod (a distance from the radiation plane4aof the X-ray tube4to the tomographic plane S of the subject3) shown inFIG. 2. Specifically, it is expressed as P=fid/fod.

The monitor7displays the tomographic images T of the subject3and the stereoradioscopic image D created by the computer6.

An X-ray tomographic process and a stereoradioscopic image constructing process according to an embodiment of the invention will be described with reference toFIG. 2throughFIG. 4.

First, the subject3is fixed to the fixing stand, and the rotating radius r of the X-ray generating source4bof the X-ray tube4is determined such that an X-ray is radiated to a prescribed tomographic plane S1of the subject3.

Then, an X-ray is radiated from the X-ray generating source4blocated at A0to the subject3as shown inFIG. 2. And, the X-ray generating source4bis moved, for example, one degree at a time with respect to the central axis O along the circumference with the radius r on the radiation plane4a, to convert the X-ray image of the subject3corresponding to a position Ai into a transmission image Gi.

At this time, the X-ray image receiving element5has the center0B of the X-ray image of the subject3positioned on a virtual circumference C1with a radius R1corresponding to the position of the tomographic plane S1with a center0G of the transmission images G as the center, and the X-ray image of the subject3rotates along the circumference about the center0G of the transmission image G with the movement of the X-ray generating source4bof the X-ray tube4.

Creation of the accumulated image will be described more specifically assuming that the subject3has a shape as shown in, for example,FIG. 5or a shape that a spherical substance has three holes H1, H2, H3therein.

As shown inFIG. 6, the whole of the X-ray image of the subject3is moved such that its center is positioned on a circumference C with a radius R having the center0G of the transmission images G as the center. At the same time, the hole H2positioned outside of the tomographic plane S1which passes through the center of the subject3as shown inFIG. 7andFIG. 8AthroughFIG. 8Dchanges its positions within a circle with the center of the cutout images CG of the transmission images G0, G1, . . . , Gi, . . . , Gn determined as the center. As a result, the accumulated image SG has a small brightness value B of pixels at the position corresponding to the hole H2because the brightness value B of the pixels at the position corresponding to the hole H2cancel each other in the individual transmission images G0, G1, . . . , Gi, . . . , Gn as shown inFIG. 9AthroughFIG. 9C.

The computer6extracts pixels having the brightness value B between the upper limit threshold value TH and the lower limit threshold value TL from the individual pixels of the accumulated image SG1to create the tomographic image T1shown inFIG. 3. And, the tomographic image T1is sent to and shown on the monitor7.

Similarly, the computer6of the image processing device2creates square cutout images CGm0, CGm1, . . . , CGmi, . . . , CGmn with a center0B, which is positioned on a virtual circle Cm having a radius Rm with respect to the transmission images G0, G1, . . . , Gi, . . . , Gn determined as the center, and accumulates the cutout images CGm0, CGm1, . . . , CGmi, . . . , CGmn to create the accumulated image SGm. And, pixels with the brightness value B between the upper limit threshold value TH and the lower limit threshold value TL are extracted from the pixels of the individual accumulated images SGm to create a tomographic image Tm corresponding to individual tomographic plane Sm.

Thus, according to the above embodiment, an X-ray is radiated to the subject3while moving the position of the X-ray generating source4bof the X-ray tube4, and the transmission images G0, G1, . . . , Gi, . . . , Gn of the subject3by the X-rays with the different focal positions are received by the X-ray image receiving element5. And, the received transmission images G0, G1, . . . , Gi, . . . , Gn are processed by the image processing section of the computer6to obtain the tomographic image T.

Specifically, it is configured that the X-ray generating source4bof the X-ray tube4is moved along the circumference, the transmission images G0, G1, . . . , Gi, . . . , Gn of the subject3corresponding to the individual positions of the X-ray generating source4bare accumulated to create the accumulated image SG, and the pixels with the brightness value B of the accumulated image SG between the prescribed upper limit threshold value TH and the prescribed lower limit threshold value TL are extracted to create the tomographic images T.

Therefore, the X-ray CT apparatus1which is a conventional X-ray transmission inspection apparatus is provided with a function to rotate the positions of the X-ray generating source4bof the X-ray tube4along the circumference, so that the tomographic image T of the subject3can be obtained easily without disposing a movable mechanism for moving the X-ray tube4or the like. For example, a tomographic image of a soft subject3can also be obtained surely.

And, the stereoradioscopic image D can be obtained easily by synthesizing upon correcting the geometrical enlargement ratio P of the tomographic image T, so that the stereoradioscopic image constructing equipment can be made compact and inexpensive.

Besides, the tomographic images T corresponding to the individual tomographic planes S can be obtained by one rotation of the X-ray generating source4balong the circumference, so that a photographing speed of the tomographic image T can be enhanced, and a time required to obtain the tomographic image T can be decreased regardless of the size of the subject3in comparison with the method to rotate and translate the X-ray tube or the subject. Therefore, if the subject3is a human, a burden on the subject can be reduced when photographing.

In the above-described embodiment, if the tomographic image T of the subject3can be obtained without fail, the X-ray generating source4bcan be moved along a variety of orbits other than the circumference, such as a figure of8in a planar view.

INDUSTRIAL APPLICABILITY

According to the present invention, an tomographic image of a subject can be obtained easily without provision of a movable mechanism for moving, for example, an X-ray generator, an X-ray image receiving element or a subject, and an tomographic image of a soft subject or the like can also be obtained securely.