Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
1998-01-13
2001-07-24
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
C250S363090, C250S252100, C250S374000
Reexamination Certificate
active
06265720
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radiographic apparatus which can present fine contrast of image information.
2. Related Background Art
In general, a radiographic apparatus is used in the fields of medical radiography, industrial nondestructive radiography, and the like. The use mode of the apparatus will be described below with reference to FIG.
1
. When radiation generated by a radiation source
1
is irradiated 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 enters a radiographic unit
2
. In the radiographic unit
2
, a housing
3
which has a window portion for transmitting the radiation and intercepts light from its interior, a grid
4
for removing unwanted scattered radiation produced by the object S, a phosphor
5
for converting the radiation into fluorescence, and an image receiving means
6
sequentially are arranged.
The radiation reaches the grid
4
via the radiation window portion of the housing
3
. The grid
4
is normally a plate obtained by cutting a multi-layered member obtained by alternately stacking lead plates and aluminum plates, and removes unwanted scattered radiation produced by the object S by matching the directions of the nearly parallel lead plates with the primary radiation traveling direction, thus improving the contrast of a radiographic image which is transmitted through the grid
4
.
In general, as the phosphor
5
, an intensifying screen obtained by applying CaWO
4
or Gd
2
O
2
S:Tb on a support material, or a fluorescent crystal such as CsI is used. Since the phosphor
5
has characteristics of emitting fluorescence at an intensity proportional to the dose of radiation, the radiographic image is converted into a visible light image by the phosphor
5
. The image receiving means
6
disposed behind the phosphor
5
generates an image corresponding to the received light amount, and the visible light image generated by the phosphor
5
is converted into an image corresponding to its light amount by the image receiving means
6
.
Normally, the image receiving means
6
comprises a film, and the radiographic image is recorded as a latent image that gives a photographic density nearly proportional to the logarithm of the amount of fluorescence on the film. After development, the recorded image is presented as a visible image, which 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 as photostimulable phosphors is also used. When the imaging plate that has been primarily excited upon irradiation of radiation is subjected to secondary excitation using visible light such as a red laser beam or the like, emission called photostimulated fluorescence is produced. The CR apparatus detects this emission using a photosensor such as a photomultiplier or the like, thereby acquiring a radiographic image.
Furthermore, recently, a technique for acquiring a digital image using, as the image receiving means, a photoelectric conversion apparatus in which pixels each made up of a very small photoelectric conversion element, switching element, and the like, are arranged in a matrix, has been developed.
FIG. 2
is an explanatory view of a conventional radiographic apparatus using a photoelectric conversion apparatus. A photoelectric conversion apparatus
7
serving as a light-receiving means and consisting of amorphous silicon is disposed behind a phosphor
5
. In the photoelectric conversion apparatus
7
, a plurality of pixels are formed in a matrix by stacking various semiconductor layers on the surface, at the side of the phosphor, of a transparent glass substrate having a thickness of several mm and both surfaces polished.
A radiation source
1
is connected to the output from a radiation generating apparatus
11
, and the output from a radiographic unit
2
is connected to an A/D converter
12
. The radiation generating apparatus
11
and A/D converter
12
are connected to a CPU
14
, temporary storing apparatus
15
, external storing apparatus
16
, and display apparatus
17
via a bus line
13
.
In general radiography, radiation generated by the radiation source
1
in response to a signal from the CPU
14
is transmitted through, absorbed, and scattered by the object S.
This radiation is converted into fluorescence by the phosphor
5
via the grid
4
, and is further converted into visible light by the phosphor
5
. The converted visible light illuminates the pixels on the photoelectric conversion apparatus
7
, which detects that light as a radiographic image analog signal having information of the object S. The radiographic image analog signal- is converted into a digital signal by the A/D converter
12
, and the digital signal is transferred to the temporary storing apparatus
15
. Also, the digital signal is transferred to and stored in the external storing apparatus
16
. Furthermore, the digital signal is subjected to an image process suited for diagnosis, and is indicated on the display apparatus
17
for the purpose of diagnosis.
On the other hand, a radiographic apparatus in which a phosphor is stacked on two-dimensional photoelectric conversion elements comprising CCDs, amorphous silicon or amorphous selenium is known.
An example of merits expected using an apparatus such as the CR apparatus, photoelectric conversion apparatus, and the like, which can directly acquire digital data, is as follows. An image process is facilitated, and correction of improper photographing condition, image emphasis of the region of interest, and the like can be easily achieved. Using an image communication means such as a facsimile apparatus or the like, expert doctors in urban hospitals can make diagnosis for patients in remote places without any expert doctors. Furthermore, when image digital data are stored in magnetooptical disks or the like, the storage space can be greatly reduced as compared to a case wherein films are stored. Also, since previous images can be easily searched, a reference image can be indicated more easily than a case wherein films are to be searched.
However, in the above-mentioned conventional arts, the output of the radiographic apparatus is unstable. In a screen film system using a film as the image receiving means, as shown in
FIG. 1
, the output becomes unstable due to the use of films. Films have sensitivity differences depending on their manufacturing lots and management conditions, and a sensitivity difference as large as about 10% is often observed. The film temperature upon photographing largely influences the sensitivity, and films photographed irrespective of these film sensitivity differences suffer large variations in photographic density. Furthermore, when photographed films are developed, the temperature of the developing solution, the developing time, and the fatigue of the developing solution often considerably change the photographic density. As described above, in the screen film system that uses films with unstable sensitivities and photographic densities as the image receiving means, it is very hard to obtain constant photographic densities. The system requires of a radiographic engineer much labor such as checking of the film sensitivity, maintenance of an automatic developing machine, and the like to stabilize the photographic density.
Even the CR apparatus that uses the imaging plate as the image receiving means suffers a problem called fading. Fading is a phenomenon in which the radiographic image information accumulated on the imaging plate upon irradiation of the radiation decreases over time until it is read. As is known, if one hour has elapsed at 32° C., the light emission amount decreases by about 20 to 40%. The imaging plate is normally sealed in a portable light-shielding member called a cassette, and is carried into a photographing s
Endo Yutaka
Yamazaki Tatsuya
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Hannaher Constantine
Israel Andrew
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