Radiant energy – Invisible radiant energy responsive electric signalling – With or including a luminophor
Reexamination Certificate
2001-03-27
2003-05-06
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
With or including a luminophor
C250S370090, C250S370110
Reexamination Certificate
active
06559449
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a flat panel X-ray detector.
In recent years, preparation of data base on the medical data on a patient is being promoted in a medical field in order to perform the medical treatment promptly and appropriately. It should be noted in this connection that the patient utilizes in general a plurality of medical organizations. Therefore, if there is no data prepared in another medical organization, there is possibility that an appropriate medical treatment is not performed.
The data base preparation is also required in respect of the image data of the X-ray photography, and it is hoped from this point that a digital system be developed in respect of the X-ray photograph. It was customary in the past to use a silver halide film in the medical X-ray diagnostic apparatus. For employing a digital system in the medical X-ray diagnostic apparatus, it was necessary to develop the photograph film image and scan again the developed film image with a scanner, which was laborious and time-consuming.
In recent years, a system of directly converting the image into digital data has been realized by using the CCD camera sized about one inch. However, in photographing, for example, a lung, a region of about 40 cm×40 cm is photographed, making it necessary to use an optical apparatus for collecting light, leading to the problem that the apparatus is rendered bulky.
As a system for overcoming the above-noted problems inherent in the two systems described above, proposed is a flat panel X-ray detector of an indirect conversion system using an amorphous silicon thin film transistor (a-Si TFT).
FIG. 1
shows the circuit construction of the flat panel X-ray detector. The operation of the flat panel X-ray detector will now be described with reference to FIG.
1
.
The flat panel X-ray detector shown in
FIG. 1
is a flat panel X-ray detector of an indirect conversion type, in which an incident X-ray is converted into a visible light by, for example, a phosphor, and the converted visible light is further converted into an electric charge for each pixel by a photo-conduction film.
As shown in
FIG. 1
, the flat panel X-ray detector comprises pixels e (i, j) (i=1 to 2000, j=1 to 2000). Each pixel e comprises a switching TFT
401
formed of a-Si, a photo-conduction film
402
and a Cst
403
. These pixels e are arranged to form an array, the row of the array consisting of hundreds of to thousands of pixels e and the column of the array also consisting of hundreds of to thousands of pixels. A negative bias voltage is applied from a power source
404
to the photo-conduction film
402
. The switching TFT
401
is connected to a signal line
405
and to a scanning line
406
and is subjected to an on-off control by a scanning line driving circuit
407
. The terminal of the signal line
405
is connected to an amplifier
410
for the signal detection via a change-over switch
409
that is controlled by a signal line control circuit
408
.
If an X-ray is incident, the phosphor (not shown) irradiated with the X-ray emits a fluorescent light. The fluorescent light is then converted into an electric charge by the photo-conduction film
402
, and the electric charge is accumulated in the Cst
403
. If a scanning line
406
is driven by the scanning line driving circuit
407
so as to turn on a column of switching TFTs
401
connected to one of the scanning lines
406
, the accumulated charge is transferred through the signal line
405
toward the amplifier
410
. By the change-over switch
409
, the charge is supplied to the amplifier
410
for each pixel so as to be converted into a dot sequential signal.
The amount of the electric charge differs depending on the amount of light incident on the pixels (i, j) so as to change the output amplitude of the amplifier
410
. By subjecting the output signal of the amplifier
410
to an A/D conversion, the electric charge can be converted directly into a digital image. Further, the pixel region can be made thin and large by utilizing the array of the switching TFTs
401
.
FIG. 2
is a plan view showing the construction of the pixel
501
included in the flat panel X-ray detector. As shown in the drawing, the pixel
501
comprises a switching TFT
401
for the reading, a Cst
403
, a Cst line
502
connected to the Cst
403
, an auxiliary electrode
503
facing the Cst
403
, a pixel electrode
504
, a signal line
405
, and a scanning line
406
. A contact portion
505
is formed in each of the switching TFT
401
and the auxiliary electrode
503
.
It should be noted that the layers above the pixel electrode
504
and the region outside the pixel
501
are omitted from the drawing of FIG.
2
. Incidentally, it is possible to utilize the floating capacitance of the other elements and the wiring in place of arranging the Cst
403
.
FIG. 3
is a cross sectional view along the line II—II shown in
FIG. 2
, which shows the constructions of the layers formed above the pixel electrode
504
.
As shown in
FIG. 3
, a pixel electrode
504
, a p-type contact film
601
, a photo-conduction film
402
, an n-type contact film
602
, a common electrode
603
, a phosphor layer
604
and a reflective layer
605
are laminated in the order mentioned on the structure including the switching TFT
401
, the Cst
403
, the auxiliary electrode
503
, the signal line
405
and the scanning line (not shown).
If an X-ray is incident on the phosphor layer
604
through the reflective layer
605
, a fluorescent light is emitted from the phosphor layer
604
irradiated with the X-ray, and the fluorescent light thus emitted is scattered. The fluorescent light then enters the photo-conduction film
402
directly or is reflected from the reflective layer
605
and, then, the reflected fluorescent light enters the photo-conduction film
402
. In the photo-conduction film
402
, the fluorescent light is converted into an electric charge. It should be noted that, since voltage is applied across the photo-conduction film
402
, the generated electric charge is attracted by the pixel electrode
504
for each pixel
501
so as to be accumulated in the Cst
403
through the pixel electrode
504
.
In the flat panel X-ray detector of the construction described above, a fluorescent light is emitted in every direction from the phosphor layer
604
upon irradiation with the X-ray. The fluorescent light thus emitted is scattered and reflected from the reflective layer
605
. It follows that it is highly possible for the fluorescent light emitted from the phosphor layer
604
in a certain pixel to arrive at the photo-conduction film
402
of the adjacent pixel. It should be noted that voltage is applied to the photo-conduction film
402
and, thus, the electric charge converted from the fluorescent light is scarcely scattered so as to arrive at the pixel electrode
504
corresponding to the particular region. Also, there is a problem that the light emitted from the phosphor is attenuated by the absorption within the phosphor film and by the reflection from the upper surface and the bottom surface of the film so as to lower the efficiency.
As a result, the fluorescent light emitted from the phosphor layer
604
is scattered so as to arrive at the adjacent pixel. The fluorescent light is converted into an electric charge in the photo-conduction film
402
of the adjacent pixel, and the electric charge thus generated is accumulated in the pixel electrode
504
of the adjacent pixel. It follows that a problem is generated that the resolution is deteriorated.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a flat panel X-ray detector, which has a high resolution and permits manufacturing a large apparatus with a low cost.
According to the present invention, there is provided a flat panel X-ray detector, comprising an X-ray-electric charge conversion film converting an incident X-ray into an electric charge, a pixel electrode contiguous to the X-ray-electric charge conversion film and arranged for every pixel, a s
Atsuta Masaki
Ikeda Mitsushi
Kinno Akira
Naito Katsuyuki
Tanaka Manabu
Hannaher Constantine
Kabushiki Kaisha Toshiba
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