X-ray or gamma ray systems or devices – Electronic circuit – With display or signaling
Reexamination Certificate
1999-10-28
2001-12-11
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Electronic circuit
With display or signaling
C250S370090
Reexamination Certificate
active
06330303
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an X-ray imaging apparatus for converting an X-ray image of a specimen into electrical image signals according to the quantity of X-rays passed through the specimen, and more particularly to an X-ray imaging apparatus capable of performing real-time imaging and operating at high speed.
BACKGROUND OF THE INVENTION
Conventionally, in the field of medical diagnosis, an imaging apparatus using a film, an image-intensifier type imaging apparatus, etc. have been used as means for visualizing an X-ray image. In resent years, development of a flat-panel type X-ray imaging apparatus as a new imaging apparatus substituting the above apparatuses is active, and clinical experiments have been partly started.
This flat-panel type X-ray imaging apparatus uses, as a key device, a flat-panel type X-ray detector which is produced by combining a large-area thin-film transistor array technique used in an active matrix type liquid crystal display device and an X-ray conversion film technique for converting X-rays into electrical signals, and has various advantages over conventional X-ray imaging apparatuses. More specifically, the flat-panel type X-ray imaging apparatus achieves an improvement of the image quality and diagnosis support by digital image processing as well as instantaneous conversion of a result of imaging into image signals and display of the result on a display or output of the result to a printer, and easily stores and transfers the result of imaging as digital image information, compared with a conventional film-type imaging apparatus. Moreover, compared with the conventional image-intensifier type imaging apparatus, the flat-panel type X-ray imaging apparatus achieves a significant reduction in its thickness, and provides a large-area, high-resolution X-ray image.
The following description will explain the structure and operational principle of the flat-panel type X-ray imaging apparatus. The specific structure and properties of the flat-panel type X-ray detector are described in detail in documents, for example:
Denny L. Lee, et al., “A new digital detector for projection radiography”, SPIE, Vol.2432, pp237-249, 1995; and
Wei Zhao, et al., “A flat panel detector for digital radiology using active matrix readout of amorphous selenium”, SPIE, vol. 2708, pp523-531, 1996.
FIG. 18
shows an example of a conventional X-ray imaging apparatus using a flat-panel type X-ray detector. The X-ray imaging apparatus includes an X-ray generator
51
, a flat-panel type X-ray detector
52
, a control device
53
, an operator console
54
, an image processing device
55
, a display device
56
, and a printer device
57
.
X-rays emitted from the X-ray generator
51
pass through a specimen
58
, and are incident on the flat-panel type X-ray detector
52
. The incident X-rays are converted into a two-dimensional charge distribution according to the quantity of the incident X-rays, further converted into digital image signals and sequentially output. The digital image signals are subjected to image processing, such as a gray-scale correction, in the image processing device
55
, and sent as display signals to the display device
56
where the signals are visualized (displayed). Moreover, the digital image signals are sent to the printer device
57
and output as a print, if necessary. Although not shown in
FIG. 18
, it is possible to store digital image data in an image storage device or transmit the digital image data to a remote place.
The operator console
54
is provided with a switch for allowing an operator to instruct an irradiation start timing of X-rays, and X-ray imaging is started upon the operation of the switch. Besides, the control device
53
controls the entire sequence and timing.
By the way, the conversion method of the flat-panel type X-ray detector
52
is roughly classified into two types: a direct conversion method of directly converting X-rays into charge by a conversion layer; and an indirect conversion method of converting X-rays into light temporarily using a scintillator and then converting the light signals into electrical signals by a photodiode. The indirect conversion method is disclosed in, for example, Japanese laid-open patent application No. (Tokukaisho) 62-2933 (published Jan. 8, 1987). Here, for the sake of convenience of explanation, the following description will illustrate the direct conversion method.
FIG. 19
shows a schematic structure of essential sections of the flat-panel type X-ray detector
52
. A number of pixels
61
are arranged in a matrix form, and each pixel
61
is connected to a scanning line SLj (j=1 to m: m is an integer of not less than 2) and a signal line DLi (i=1 to n: n is an integer of not less than 2) through a TFT
72
(see
FIG. 21
) as a later-described switching element. Each scanning signal SLj is connected to a scanning line drive circuit
62
, while each signal line DLi is connected to a signal readout circuit
63
. The scanning line drive circuit
62
and signal readout circuit
63
are controlled by a timing control circuit
64
.
As the scanning line drive circuit
62
, a gate driver IC (Integrated Circuit) used in a general liquid crystal display device can be used. Besides, as shown in
FIG. 20
, for example, the signal readout circuit
63
includes: pre-amplifiers
65
which are provided in association with the signal lines DLi, respectively, and perform voltage conversion and amplification of input signals; a multiplexer
66
for switching the outputs from the pre-amplifiers
65
consecutively to an A/D converter
67
in a later stage; and the A/D converter
67
for converting analog image signals from the multiplexer
66
into digital image signals.
FIG. 21
depicts an example of a cross sectional structure of the pixel
61
of the flat-panel type X-ray detector
52
(see FIG.
18
).
FIG. 22
shows an equivalent circuit of the pixel
61
. As illustrated in
FIG. 21
, the pixel
61
includes a TFT (thin film transistor)
72
formed on a glass substrate
71
, a storage capacitor (Cs)
73
, etc.
The TFT
72
includes a gate electrode
74
connected to the scanning line SLj, a gate insulating film
75
formed to cover the gate electrode
74
, a source electrode
76
and a drain electrode
77
formed on the gate insulating film
75
. The source electrode
76
is connected to the signal line DLi, while the drain electrode
77
is connected to a pixel electrode
78
.
The storage capacitor
73
is configured such that the pixel electrode
78
and a lower common electrode
80
connected to the negative terminal of a bias power supply
79
face each other with an insulating film
81
therebetween. Additionally, a charge preventing layer
82
is formed to cover the source electrode
76
, drain electrode
77
and pixel electrode
78
.
As a TFT matrix formed by the TFT
72
and storage capacitor
73
, it is possible to use a TFT substrate which is produced in the process of manufacturing an active matrix type liquid crystal display device. For instance, a TFT substrate for use in an amorphous silicone (a-Si) TFT liquid crystal display device has scanning lines, signal lines, storage capacitors, etc., and can be used as the TFT matrix of a flat-panel type X-ray detector
52
by making slight changes.
Further, in each pixel
61
, a photoconductive film
83
, a dielectric layer
84
, and an upper common electrode
85
connected to the positive terminal of the bias power supply
79
are formed successively to cover the TFT
72
and storage capacitor
73
, and a pixel capacitor Cp (see
FIG. 22
) is produced. As a material for the photoconductive film
83
, a semiconductor material which absorbs X-rays and converts the X-rays into charge with high efficiency is used. For example, in the above documents, an amorphous selenium (a-Se) film formed in a thickness of 300 to 600 &mgr;m by vacuum evaporation is used.
Next, the following description will explain the operation of the flat-panel type X-ray detector
52
of the above-mentioned structure.
X-rays incident on the p
Oikawa Shiro
Yamane Yasukuni
Church Craig E.
Nixon & Vanderhye PC
Sharp Kabushiki Kaisha
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