X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
1999-11-05
2001-08-21
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S016000, C378S098110
Reexamination Certificate
active
06278760
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a radiation image forming method and apparatus. This invention particularly relates to a radiation image forming method and apparatus, wherein at least either one of a three-dimensional image and a tomographic image is formed from projection images having been obtained by irradiating radiation from different directions of projection to an object.
2. Description of the Prior Art
In the fields of medical images, research has heretofore been conducted to detect three-dimensional radiation image signals. As one of techniques for detecting three-dimensional radiation image signals, for example, cone-beam computed tomography (cone-beam CT) have been proposed. (The cone-beam CT is described in, for example, “Cone Beam CT—Present Status and Future Prospects,” Image Information (M), pp. 122-127, January 1988; and Japanese Unexamined Patent Publication No. 9(1997)-253079.)
With the cone-beam CT, a radiation source and a two-dimensional radiation detector are rotated around an object, cone-like radiation is irradiated from the radiation source to the object, and a three-dimensional radiation image signal (i.e., a volume signal) representing the object image is acquired from radiation image signals (specifically, projection image signals), which have been detected at respective positions of rotation by the radiation detector.
In Japanese Patent Application No. 10(1998)-238737, the applicant proposed a novel radiation image detecting apparatus, which enables a volume signal free from adverse effects of scattered radiation to be obtained. With the proposed radiation image detecting apparatus, a plurality of radiation sources, which are located on a surface, are changed over successively, and radiation image signals representing radiation images of an object are detected with a radiation detector having a detection area smaller than the area of the surface, on which the radiation sources are located. Also, two-dimensional radiation image signals at predetermined positions of rotation of the radiation sources are obtained from the output signals obtained from the radiation detector. The volume signal representing the image of the object is then obtained from the two-dimensional radiation image signals.
The apparatuses for acquiring the three-dimensional radiation image signals, such as the cone-beam CT scanners and the radiation image detecting apparatus proposed in Japanese Patent Application No. 10(1998)-238737, will hereinbelow be referred to as the radiation image forming apparatuses. In the radiation image forming apparatuses, a three-dimensional image (a 3D image) of the object is formed from the acquired volume signal and displayed on an image display device, such as a cathode ray tube (CRT) display device. Also, a tomographic image is formed from the volume signal and displayed on the image display device.
However, with the radiation image forming apparatuses described above, problems are encountered in that a specific structure pattern having high contrast, such as a bone pattern, becomes perceptible, and a pattern of a diseased part of the object having low contrast cannot be detected easily.
SUMMARY OF THE INVENTION
The primary object of the present invention is to provide a radiation image forming method, wherein a radiation image of an object is formed such that a pattern of a specific structure having low contrast, such as a pattern of a diseased part in the object, may be capable of being detected easily, and the radiation image may have good image quality and can serve as an effective tool in, particularly, an efficient and accurate diagnosis of an illness.
Another object of the present invention is to provide an apparatus for carrying out the radiation image forming method.
The present invention provides a first radiation image forming method, wherein at least either one of a three-dimensional image and a tomographic image of an object is formed from projection image signals, which represent projection images of the object and which have been obtained by irradiating cone-like radiation from different directions of projection to the object, the method comprising the steps of:
i) acquiring a plurality of projection image signals of different energy bands with respect to a single object and with respect to each direction of projection,
ii) performing energy subtraction processing on the plurality of the projection image signals of the different energy bands, which projection image signals have been acquired with respect to the same direction of projection, an energy subtraction-processed projection image signal being thereby formed with respect to each direction of projection, and
iii) forming at least either one of the three-dimensional image and the tomographic image of the object from the energy subtraction-processed projection image signals, which have been formed with respect to the different directions of projection.
The present invention also provides a second radiation image forming method, wherein a volume signal representing an image of an object is formed from projection image signals, which represent projection images of the object and which have been obtained by irradiating cone-like radiation from different directions of projection to the object, and at least either one of a three-dimensional image and a tomographic image of the object is formed from the volume signal, the method comprising the steps of:
i) acquiring a plurality of projection image signals of different energy bands with respect to a single object and with respect to each direction of projection,
ii) forming a volume signal from the projection image signals of an identical energy band having been acquired with respect to the different directions of projection, which projection image signals are among the plurality of the projection image signals of the different energy bands having been acquired with respect to the different directions of projection, a plurality of volume signals of the different energy bands being thereby formed,
iii) performing energy subtraction processing on the plurality of the volume signals of the different energy bands, an energy subtraction-processed volume signal being thereby formed, and
iv) forming at least either one of the three-dimensional image and the tomographic image of the object from the energy subtraction-processed volume signal.
In the first and second radiation image forming methods in accordance with the present invention, the cone-like radiation is irradiated from the different directions of projection to the object, and the projection image signals with respect to the different directions of projection are obtained. For such purposes, for example, as in the cone-beam CT, cone-like radiation may be irradiated from a radiation source and may be detected with a two-dimensional radiation detector. Alternatively, as described in Japanese Patent Application No. 10(1998)-238737, a plurality of radiation sources, which are located on a surface, may be changed over successively, and cone-like radiation as a whole may thus be irradiated to the object and may be detected with a radiation detector having a small area. (In such cases, the beam shape of the cone-like radiation is reverse to the beam shape of the cone-like radiation in the cone-beam CT). The radiation detector may be constituted of a single detection device or an array of a plurality of detection devices.
With the energy subtraction processing, a plurality of radiation images of a single object are formed with radiation having different energy levels by utilizing the characteristics such that a specific structure of the object has different levels of radiation absorptivity with respect to the radiation having different energy levels. Thereafter, a plurality of radiation image signals, which represent the radiation images of the object, are weighted, and the weighted image signals are subtracted from each other. A subtraction image signal is thus obtained, and an image, in which only the pattern of the specific structure of t
Arakawa Satoshi
Ogawa Eiji
Fuji Photo Film Co. , Ltd.
Ho Allen C.
Kim Robert H.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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