X-ray or gamma ray systems or devices – Accessory – Alignment
Reexamination Certificate
1998-01-16
2003-01-07
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Accessory
Alignment
C378S063000
Reexamination Certificate
active
06502984
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radiographic apparatus for photographing a radiographic image of an object in the medical field or nondestructive inspection field.
2. Related Background Art
(1)
FIG. 1
is a diagram of a conventional radiographic apparatus. A radiographic image photographing means
302
for photographing a transmitted radiographic image of an object S is disposed in front of a radiation generating means
301
as a radiation source for generating radiation. The radiation generating means
301
and radiographic image photographing apparatus
302
irradiate radiation and photograph an image of the object S on the basis of the photographing conditions, e.g., the tube voltage or tube current for an X-ray tube as the radiation source, irradiation time, and the like, set by the operator using a photographing condition setting means
303
.
(2) In X-ray radiography, X-rays that have scattered inside an object largely influence the image. In order to efficiently remove scattered X-rays, a scattered X-ray removing grid (to be simply referred to as a grid hereinafter) is used to help improve the contrast and sharpness of an X-ray image. The grid used can be classified into a parallel grid and convergence grid depending on their structures.
FIG. 2
is a sectional view of the parallel grid, in which copper foils
391
and intermediate substances
390
are disposed to be parallel to each other and in a direction perpendicular to incoming X-rays.
FIG. 3
is a sectional view of the convergence grid, in which copper foils
391
and intermediate substances
390
are disposed to converge at a single point (in this case, a convergence point
401
). The intermediate substance consists of aluminum, wood, or the like.
(3) Conventional radiography uses a system as a combination of a film and intensifying paper. In recent years, along with the development of computers, various types of digital image photographing apparatuses have been developed and are used in clinical applications. A photographing apparatus using a photostimulable phosphor sheet as one of such apparatuses temporarily records a radiographic image of an object S on a photostimulable phosphor sheet, and then irradiates excitation light such as a laser beam onto that photostimulable phosphor sheet to cause stimulated emission. Based on an image signal obtained by photoelectrically reading the emitted light, a radiographic image of the object S is printed on a silver halide film or is displayed on a CRT display.
On the other hand, a photographing apparatus using a photodetection array converts a radiographic image of the object S into a visible image via a scintillator or image intensifier, converts that visible image into an image signal via the photodetection array, and prints or displays the radiographic image of the object on a silver halide film or CRT display.
(4) Furthermore, in radiography in the medical field, in order to obtain a high-quality image without re-photographing, the radiographic conditions must be set to match the state and characteristics of the object S. That is, the field of irradiation, quality, and exposure dose of radiation must be optimized, and appropriate image processes are required for a digital radiographic image to make it easier to see.
FIG. 4
shows the arrangement of a radiographic apparatus according to the third conventional art. When a radiation generating means
301
irradiates radiation onto an object S, the radiation is intensity-modulated and scattered in accordance with the internal structure of the object S owing to interactions such as absorption, scattering, and the like of the object S with respect to the radiation, and then reaches a radiographic image photographing means
302
to obtain a radiographic image. Note that a grid
304
disposed in front of the radiographic image photographing means
302
removes scattered radiation to improve the contrast of the radiographic image.
In general, the radiographic image photographing means
302
comprises a phosphor CaWO
4
or the like that produces luminescence at an intensity proportional to the exposure dose, and a silver halide film, and the image of the object S is recorded on the film as a latent image. After development, the recorded image is presented as a visible image that gives a density proportional to the logarithm of the luminescence amount, and is used in diagnosis, inspection, and the like.
Also, a computed radiography (CR) apparatus using an imaging plate applied with a BaFBr:Eu phosphor and BaF:Eu phosphor which produce photostimulated luminescence is also used. The CR apparatus temporarily records a radiographic image of the object S on the imaging plate, and then irradiates excitation light such as a laser beam onto the imaging plate to cause stimulated emission. The apparatus prints or displays the radiographic image of the object S on a silver halide film or CRT display on the basis of an image signal obtained by photoelectrically reading the emitted light.
Furthermore, recently, a technique for reading a digital image using, as the radiographic image photographing means
302
, a photoelectric conversion device on which pixels each consisting of a very small photoelectric conversion element, switching element, and the like are arranged in a lattice pattern, has been developed.
(5) It is important in radiography to obtain a high-quality image without re-photographing, and optimal radiographic conditions must be selected in correspondence with the state and characteristics of the object S and those of the radiographic apparatus. That is, the field of irradiation must be stopped down, and the dose and quality of radiation must be optimized. Furthermore, when a radiographic image is to be digitally processed, posture determination, edge extraction, and the like of the object S are required.
In order to stop down the field of irradiation, a lead aperture stop is conventionally inserted immediately after the radiation generation device, and is manually moved. In order to confirm the divergence of radiation, a visible light source is arranged at a position conjugate with the radiation generating means
301
, and the operator visually checks the degree of eclipse of the projected light by the aperture stop. In addition, in an X-ray radiography apparatus, the irradiation range is confirmed in advance using a television monitor.
Upon setting the dose and quality of radiation, the photographer sets them by determining proper conditions on the basis of the posture and photographing portion of the object S, or inputs information associated with the posture and the photographing portion of the object S to the apparatus, which automatically sets proper conditions.
(a) However, in conventional art (1) above, since the operator must set optimal photographing conditions to obtain a radiographic image which is easy to observe, he or she must change the positional relationship between the radiation generating means
301
and radiographic image photographing means
302
depending on the photographing method used, and must measure the distance between them using a scale in every change. Furthermore, before the operator gains experience in using the apparatus, e.g., immediately after installation of the photographing apparatus, he or she must create an irradiation condition table or the like and must photograph with reference to that table. Upon creating the irradiation condition table, the operator must make physical contact with a patient as the object S to directly measure the breast thickness using a tool such as a breast meter or the like.
(b) When the grid described in conventional art (2) is used, grid cutoff occurs.
FIG. 5
shows the case wherein grid cutoff has occurred due to the parallel grid, and illustrates an X-ray tube focal point F, and shadow images
414
a
and
414
b
on an image receiving surface
413
obtained when X-rays are transmitted through lead foils
412
a
and
412
b
of a grid
411
. The lead foils
412
a
is projected as a shadow image broade
Hirai Akira
Kawasaki Keiichi
Ogura Takashi
Canon Kabushiki Kaisha
Church Craig E.
Fitzpatrick ,Cella, Harper & Scinto
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