X-ray or gamma ray systems or devices – Specific application – Tomography
Reexamination Certificate
2000-06-05
2002-04-30
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Tomography
C378S017000
Reexamination Certificate
active
06381299
ABSTRACT:
TECHNICAL FIELD
The present invention is related to an X-ray examination apparatus and an imaging method of an X-ray image. More specifically, the present invention is a directed to a technique for reconstructing either a tomographic image (tomogram) or a three-dimensional image of a measuring object larger than a viewing field angle of an X-ray detector from such a X-ray image produced by imaging the measuring object while such a measuring object is rotated, and is arranged between an X-ray source and the X-ray detector.
BACKGROUND ART
As a conventional X-ray examination apparatus, there is such an X-ray CT apparatus (X-ray tomographic imaging apparatus) by which while both an X-ray source and an X-ray detector where detecting elements are arranged in one dimensional manner are rotated around an examination object by 1 rotation, a rotary imaging operation is carried out so as to acquire a distribution of X-ray absorption coefficients within the examination object as a tomographic image. Also, a s a method for acquiring a 3-dimensional image by an X-ray CT apparatus, there is a spiral scanning method in which while an examination object is continuously moved along a direction perpendicular to a rotation plane, rotary imaging operation is carried out plural times.
As a method for acquiring a distribution of X-ray absorption coefficients as a three-dimensional image, there is a cone-beam CT apparatus by which while both an X-ray source and a 2-dimensional X-ray image detector are rotated around an examination object by 1 rotation, imaging operation is carried out and a 3-dimensional image reconstruction is carried out from the acquired rotary imaging data. In such a cone-beam CT apparatus, it is generally known that a viewing angle of a cross-tomographic plane is limited by a viewing angle of a 2-dimensional X-ray image detector. Various research works about such cone-beam CT apparatuses have be potentially carried out. That is, these cone-beam CT apparatuses are capable of acquiring the 3-dimensional images having the larger viewing field angles than the viewing field of the 2-dimensional X-ray detector from the two-dimensional images which are imaged by the two-dimensional X-ray detector whose viewing field is limited.
The cone-beam CT apparatus capable of enlarging the viewing field is disclosed in, for example, JP-A-8-117220 (simply referred to as a “publication 1” hereinafter), and “SPIE Medical Imaging”, pages 349 to 357 in 1997 (will be simply referred to as a “publication 2” hereinafter). In the cone-beam CT apparatus described in the publication 2, while both the X-ray source and the X-ray image detector are rotated around the examination object by two rotations, namely the normal rotation and the reverse rotation. While the examination object is reciprocated along the direction parallel to the rotation plane in the same time period as the rotation time period, the rotary X-ray imaging operation is carried out 2 times so as to acquire the three-dimensional image having the larger viewing angle than the viewing field of the two-dimensional X-ray detector from the two-dimensional image.
There are various sorts of apparatuses in which while both X-ray sources and X-ray image detectors are fixed and also examination objects such as various sorts of materials and air line baggages are rotated, rotary imaging operations are carried out.
DISCLOSURE OF THE INVENTION
Generally speaking, in the spiral scanning method, very long measurement time is required so as to make the resolution along the direction perpendicular to the rotation plane equal to the resolution within the rotation plane. As a result, the resolution along the direction perpendicular to the rotation plane would be lowered, as compared with the resolution within the rotation plane. In the cone-beam CT apparatus, the 3-dimensional image data is obtained only by performing the rotary imaging operation for one rotation. Moreover, the 3-dimensional image having the voxel resolution is obtained, and the size of this voxel resolution is the same as that within the rotation plane along the direction perpendicular to the rotation plane. As a consequence, this spiral scanning method is featured by that the true 3-dimensional imaging operation can be carried out.
The inventors of the present invention could find out the below-mentioned problems after considering the conventional techniques. Nowadays, X-ray CT apparatuses and the like are utilized not only as specific-purpose apparatuses, but also as usual-purpose examination apparatuses. However, since the conventional X-ray CT apparatuses and the like are directed to examine seriously-injured objects under examination, these objects under examination generally lie down as body attitudes. On the other hand, while performing routine diagnoses with respect to respiratory system organs such as a lung, circulatory system organs such as a blood vessel, and skeleton such as a backbone and pelvis, it is very important to image 3-dimensional images having large viewing fields as well as high resolution under such a body attitude condition that objects under examination is diagnosed under standing position, or sitting condition, namely daily natural attitude conditions in order to diagnose patients conditions. A need is made of developing such an X-ray CT apparatus for realizing a rotary imaging operation in which a rotation axis is located perpendicular to the horizontal plane in order that the object under examination is imaged under standing position, or sitting position.
In the case that the conventional X-ray apparatus, or the conventional cone-beam CT apparatus is knocked over so as to realize the rotary imaging operation, there is a first problem that a very wide floor area is required so as to install the gantry. Furthermore, in order to achieve such a purpose capable of improving resolution of an imaged image, a distance between an X-ray source and a detector cannot be changed over a wide range, resulting in a second problem. As a method of solving this second problem, for instance, there is an X-ray baggage examination (checking) apparatus used to check a baggage and the like. This X-ray baggage examination apparatus is arranged by an X-ray source, a detector arranged opposite to this X-ray source, and a rotation apparatus arranged in such a manner that a rotation axis is located on a straight line for connecting the X-ray source and the detector. While an examination object is set on the rotation apparatus, X-ray images of the examination object are imaged along a plurality of directions.
However, the imaging method of the X-ray baggage examination apparatus owns similar problems to those disclosed in the publication 1 and the publication 2. In other words, there is a third problem. That is, since the viewing field of the 2-dimensional detector is narrow, the sufficiently wide imaging viewing field cannot be secured when such a large body portion as a lung is imaged. As a result, the organ such as the lung cannot be acquired as a single reconstructed image.
On the other hand, as the 2-dimensional X-ray image detector used in the cone-beam CT apparatus, the following combined detectors may be employed, for instance, a combination between a television camera and an X-ray image intensifier (simply referred to as an “X-ray I.I.” hereinafter) for converting an X-ray into an optical image, another combination between a fluorescent plate and a television camera, an another combination between a fluorescent plate and a plane sensor constructed of a 2-dimensional array made of amorphous silicon photodiodes and TFT elements. Generally speaking, these 2-dimensional X-ray image detectors own such a problem that an image quality of a reconstructed image is deteriorated, as compared with the 1-dimensional array detector used in the X-ray CT apparatus.
One of various reasons why the image quality of the reconstructed image is deteriorated is given as follows. That is to say, the sensitivities for the respective elements cannot be precisely corrected due to the sensitivity of the 2-dime
Baba Rika
Kasagima Nobuhisa
Kawai Hiroyuki
Koike Koichi
Kuba Akira
Antonelli Terry Stout & Kraus LLP
Church Craig E.
Hitachi Medical Corporation
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