X-ray or gamma ray systems or devices – Electronic circuit – X-ray source power supply
Reexamination Certificate
1999-07-20
2001-03-27
Porta, David P. (Department: 2876)
X-ray or gamma ray systems or devices
Electronic circuit
X-ray source power supply
C378S097000, C378S098700
Reexamination Certificate
active
06208710
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray diagnostic apparatus and radiation diagnostic apparatus for sensing an X-ray image (radiation image) of a subject.
Most of X-ray diagnostic apparatuses have an automatic exposure control function of automatically controlling the photographing time in order to keep the image density constant. The automatic exposure control is based on the following principle. An X-ray sensor is interposed between a subject and X-ray detector. An output from the X-ray sensor is temporally integrated by an integrator. The integrated value corresponds to an image density. The integrated value is compared with a reference value. When the integrated value reaches the reference value, irradiation of X-rays on the subject stops. Instead of the X-ray sensor, part of output light from an image intensifier is drawn in a photomultiplier to monitor the exposure time based on the output, or the exposure time is monitored based on part of an image signal photographed by a TV camera. Also, exposure is controlled based on an output from a planar detector prepared by arraying a plurality of semiconductor elements (Jpn. Pat. Appln. KOKAI Publication No. H7-201490). An X-ray diagnostic apparatus of this type can more appropriately control exposure, does not require any sensor other than the planar detector, and can realize cost reduction and high reliability.
In recent years, there is proposed a technique of forming a 1-frame image using not the entire detectable area of the planer detector but an arbitrary partial region (imaging region) in the detectable area (Japanese Patent Application No. H9-164249).
Since the imaging region can be arbitrarily set, as described above, the X-ray sensor for exposure-controlling may deviate from the imaging region to generate an exposure control error.
If the imaging region is set at particularly the periphery of the detectable area, X-rays are obliquely incident on the imaging region to distort an image.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to eliminate any exposure control error in an X-ray diagnostic apparatus and radiation diagnostic apparatus capable of forming an image using an arbitrary partial region in the detectable area.
It is another object of the present invention to eliminate any image distortion in an X-ray diagnostic apparatus and radiation diagnostic apparatus capable of forming an image using an arbitrary partial region in the detectable area.
The X-ray diagnostic apparatus according to the present invention forms image data using an arbitrary region in the detectable area of a planar detector having a plurality of X-ray detector elements arrayed in a matrix. An X-ray sensor array for exposure-controlling having a plurality of X-ray sensors arrayed in a matrix overlaps the planar detector. An X-ray controller controls an X-ray tube unit on the basis of an output from the X-ray sensor array in order to optimize the X-ray dose on a subject. A controller selects at least one X-ray sensor in accordance with the position of a partial region where an image is formed. The controller controls at least one of the X-ray sensor array and X-ray controller so as to control the X-ray dose on the basis of an output from the selected X-ray sensor. Since the X-ray dose is adjusted based on an output from an X-ray sensor corresponding to the position of a partial region where an image is formed, any exposure control error can be eliminated.
The X-ray diagnostic apparatus according to the present invention forms image data using an arbitrary region in the detectable area of a planar detector having a plurality of X-ray detector elements arrayed in a matrix. The relative positions of the planar detector and X-ray tube unit can be changed by a movement mechanism. The controller can change the relative positions in accordance with a region where an image is formed. Hence, even if the region where an image is formed is set at the periphery of the detectable area, X-rays can be substantially vertically incident on the region where an image is formed, thereby eliminating any image distortion.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
REFERENCES:
patent: 5937027 (1999-08-01), Thevenin et al.
patent: 5949848 (1999-09-01), Gilblom
patent: 6047042 (2000-04-01), Khutoryansky et al.
patent: 6106152 (2000-08-01), Thumberg
patent: 7-201490 (1995-08-01), None
patent: 2500895 (1996-03-01), None
patent: 11-9581 (1999-01-01), None
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Porta David P.
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