Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
2000-03-23
2002-06-11
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
C250S363020, C250S367000, C250S370110, C250S385100
Reexamination Certificate
active
06403965
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an X-ray image detector system. More specifically, the invention relates to an X-ray image detector system for use in an X-ray diagnosing system for medical use.
2. Description of the Related Art
In recent years, in the field of medical treatment, the database of medical data for patients makes progress in order to rapidly and precisely carry out medical treatment. Patients usually receive diagnostics of a plurality of medical treatment facilities. In such a case, if there are no data of other medical treatment facilities, there is some possibility that medical treatment can not be precisely carried out. As an example, there is a problem of medicines or drugs. It is required to take account of drugs administered in other medical treatment facilities to administer appropriate drugs to carry out medical treatment.
It is also required to make database for image data of radiography. In accordance with this database system, it is desired to digitize X-ray images. In an X-ray diagnosing system for medical use, a silver halide film is conventionally used to detect an image. In order to digitize this diagnostic data, it is required to scan the film by a scanner after developing the film, so that it takes a great deal of time. Recently, there is realized a system for directly digitizing an image using a CCD camera having a size of about one inch and an image intensifier tube. However, when an image of, such as a lung, is detected by this system, it is required to provide an optical system for condensing light to detect an image of a region of about 40 cm ×40 cm, so that there is a problem of increasing the system size. There is also a problem in that resolution decreases due to the distortion of an optical system.
In order to solve these problems, there is proposed a flat-panel X-ray detector of an indirect conversion system using a thin film transistor (which will be hereinafter referred to as a “TFT”) having an active layer of an amorphous silicon as a switching element (see, e.g., U.S. Pat. No. 4,689,487).
FIG. 8
shows a circuit construction of this flat-panel X-ray detector, and the operation thereof will be described below.
This flat-panel X-ray detector is a detector of an indirect conversion system for converting an incident X-ray into luminescent light by means of a phosphor or the like to change the converted light to an electric charge by means of a photoelectric transfer film of each pixel (picture element). This flat-panel X-ray detector has pixels e
1,1
, . . . , e
m,n
arranged in the form of an array wherein hundreds to thousands pixels are arranged on each side. Each element e
i,j
(i=1, . . . , m, j=1, . . . , n) has a TFT
701
, a photoelectric transfer film
702
and a pixel capacity
703
. The photoelectric transfer film
702
and the pixel capacity
703
are connected in parallel. To one end thereof, a negative bias voltage is applied by means of a power supply
704
, and the other end is connected to one of the source and drain of the TFT
701
. The other end of the source and drain of the TFT
701
is connected to a signal line
705
, and the gate of the TFT
701
is connected to a scanning line
706
. The on/off of the TFT
701
is controlled by a scanning line driving circuit
707
. The terminal of the signal line
705
is connected to an amplifier
710
for signal detection via a switch
709
controlled by a signal line control circuit
708
.
If X-rays are incident on the flat-panel X-ray detector, the phosphor irradiated with the X-rays emits light, and the emitted light is converted into an electric charge by means of the photoelectric transfer film
702
, so that the electric charge accumulates in the pixel capacity
703
. When one scanning line
706
is driven by the scanning line driving circuit
701
so that all of TFTs
701
connected to the scanning line
706
are turned on, the accumulating charge is transferred to the amplifier
710
via the signal line
705
. Then, the electric charge for each pixel is inputted to the amplifier
710
by means of the switch
709
to be converted to dot sequential signals capable of being displayed on a CRT or the like. The quantity of electric charge varies in accordance with the quantity of light being incident on each pixel e
i,j
(i=1, . . . , m, j=1, . . . , n), so that the amplitude of output of the amplifier
710
varies.
The flat-panel X-ray detector of the indirect conversion system shown in
FIG. 8
can directly form a digital image by the A/D conversion of the output signal of the amplifier
710
. Moreover, it is possible to produce a pixel region of a thin and large-screen by the array of the TFTs
701
.
There are other flat-panel X-ray detectors of a direct conversion system for directly converting X-rays being incident on pixels into an electric charge.
The flat-panel X-ray detector of this direct conversion system has no phosphor. At this point, the flat-panel X-ray detector of the direct conversion system is different from that of the above-described indirect conversion system. In addition, in the flat-panel X-ray detector of the direct conversion system, the magnitude of a bias applied to a photoelectric transfer film or an X-ray-to-charge converting film is different from that in the indirect conversion system.
In the case of the indirect conversion system, a bias of several volts to over ten volts is applied to the photoelectric transfer film. When fluorescence enters the photoelectric transfer film, the electric charge accumulates in the pixel capacity provided in parallel to the photoelectric transfer film in each pixel. In this case, the voltage applied to the pixel capacity is a bias of several volts to over ten volts applied to the photoelectric transfer film at the maximum.
On the other hand, in the direct conversion system, the X-ray-to-charge converting film, the pixel capacity and the TFT serving as a switch for each pixel are connected in series, and a high bias of several kV is applied thereto. Therefore, when X-rays are incident on the pixel, the electric charge produced by the X-ray-to-charge converting film accumulates in the pixel capacity. However, if the quantity of incident X-ray is excessive, the electric charge accumulating in the pixel capacity increases, so that it is afraid that a high voltage of more than 10 kV is applied to the insulator films of the pixel capacity and the TFT to cause electrical break-down. For that reason, the direct conversion system must take measures to prevent an excessive voltage from being applied to the pixel capacity and TFTS.
Therefore, a protecting TFT serving as a protecting non-linear element is provided in each of pixels. Thus, when excessive X-rays enter a pixel, a higher electric charge than that defined by a bias is. discharged to the outside of the pixel via the protecting TFT to prevent the dielectric breakdown of the TFT and pixel capacity.
FIG. 9
shows the construction of a pixel of a flat-panel X-ray detector of a direct conversion system using the protecting TFT, and the operation thereof will be described below.
Each pixel
801
of a flat-panel X-ray detector of a direct conversion system shown in
FIG. 9
comprises a TFT
701
used as a switching element, an X-ray-to-charge converting film
802
, and a pixel capacity
703
. Similar to the X-ray detector shown in
FIG. 8
, the pixels
801
are arranged in the form of an array. The pixel capacity
703
is connected to a pixel capacity bias
803
. To the X-ray-to-charge converting film
802
, a negative bias voltage is applied by a high-voltage power supply
804
. The gate of the TFT
701
is connected to a scanning line
706
, and one of the source and drain of the TFT
701
is connected to a signal line
705
, so that the on/off of the TFT
701
is controlled by means of a scanning line driving circuit
707
. The terminal of the signal line
705
is connected to an amplifier
710
for signal detection. A protecting TFT
805
is biased by a power supply
Atsuta Masaki
Ikeda Mitsushi
Kinno Akira
Suzuki Kouhei
Hannaher Constantine
Israel Andrew
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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