X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
2004-02-04
2004-11-09
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S004000, C250S551000
Reexamination Certificate
active
06816566
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a noncontact type signal transmission device which uses light to perform noncontact signal transmission between members whose relative positions change.
A noncontact type signal transmission device of this type is used, for example, in an X-ray computed tomography apparatus. A noncontact type signal transmission device called a slip ring made up of an annular conductive ring and a conductive brush that comes into contact with the ring is used in many conventional X-ray computed tomography apparatuses to perform continuous rotation (continuous scanning). This slip ring makes much noise and hence is not suitable for weak signals, although it is suitable for the supply of power to an X-ray tube.
Recently, X-ray computed tomography apparatuses using noncontact type signal transmission devices have become available on the market.
As shown in
FIG. 1
, for example, a noncontact type signal transmission device used in an X-ray computed tomography apparatus is comprised of a stationary portion
301
, a rotating ring
302
located inside the stationary portion
301
, a plurality of light-emitting diodes
101
discretely arranged on the outer surface of the rotating ring
302
, and a plurality of photodiodes
201
discretely arranged on the inner surface of the stationary portion
301
. An analog signal output from an X-ray detector is coded into a binary code, and the light-emitting diodes
101
are turned on/off in accordance with the code. This turn on/off operation is decoded through the photodiodes
201
.
For the sake of descriptive convenience, a rotating coordinate system X′Y′Z′ is defined, which rotates about the rotation axis of the rotating ring
302
at an angular velocity equal to the rotational movement of the rotating ring
302
. Assume that the X′-axis of this rotating coordinate system is the optical axis of light from the light-emitting diode
101
of interest, the Y′-axis is a tangent on the rotational orbit of the light-emitting diode
101
of interest, and the Z′-axis is an axis that is parallel to the rotation axis (orthogonal axis to the paper) and crosses the other axes at the light-emitting diode
101
of interest.
One of important parameters for the design of a noncontact type signal transmission device is the distance between each light-emitting diode
101
and a corresponding photodiode
201
. As shown in
FIG. 2
, each photodiode
201
must be spaced apart from a corresponding light-emitting diode
101
by a certain distance so that the irradiation area from a given light-emitting diode
101
to the stationary portion
301
is seamlessly connected to (in practice, overlaps) the irradiation area from an adjacent light-emitting diode
101
to the stationary portion
301
. If, however, each photodiode
201
is spaced apart from a corresponding light-emitting diode
101
too much, the amount of light received by the photodiode
201
decreases, resulting in a deterioration in sensitivity. The distance between each light-emitting diode
101
and a corresponding photodiode
201
must therefore be optimized.
In recent years, in the field of X-ray computed tomography apparatuses, techniques such as volume CT and digital rotational angiography have been put into practice. In some case, however, the amount of data handled in volume TC or the like becomes several ten or hundred times lager than the amount of data handled in single slice scanning.
To transmit such an enormous amount of data at high speed, the ON/OFF frequency of each light-emitting diode
101
must be increased to several MHz or several GHz in some cases.
If, however, the ON/OFF frequency of each light-emitting diode is increased, the amount of light emitted from the light-emitting diode decreases. Accordingly, the amount of light received by the photodiode decreases. As a consequence, a transmission error is likely to occur.
In general, the amount of light received is inversely proportional to the square of the distance between a light-emitting means and a light-receiving means. More specifically, as shown in
FIG. 2
, the amount of light received by the photodiode
201
decreases in inverse proportion to the square of a distance t
1
between the light-emitting diode
101
and the photodiode
201
. In contrast to this, the amount of light received increases as the distance t
1
decreases. That is, a decrease in the amount of light received can be suppressed by brining the photodiode
201
close to the light-emitting diode
101
.
If, however, each photodiode
201
is brought near a corresponding light-emitting diode
101
too much, an area appears, as shown in
FIG. 3
, in which the irradiation area from a given light-emitting diode
101
does not overlap that from the adjacent light-emitting diode
101
. When the photodiode
201
passes through this non-overlap region, a transmission error tends to occur. However, if setting density of LED
101
is higher to eliminate the non-overlap region, a new problem of cost-up generates.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a noncontact type signal transmission device which can transmit a large amount of data at high speed with high reliability.
A noncontact type signal transmission device includes light-emitting devices and light-receiving devices. The member mounting the light-emitting devices or the light-receiving devices moves along a predetermined orbit relative to the member mounting another. Beam condensing devices are disposed between the light-emitting devices and the light-receiving devices. Each beam condensing device has a function of condensing light from the light-emitting device in a direction substantially perpendicular to the orbit. The function of each beam condensing device is to increase the amount of light received by each light-receiving device and to improve light reception sensitivity.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
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patent: 4796183 (1989-01-01), Ermert et al.
patent: 4996435 (1991-02-01), Keller
patent: 5134639 (1992-07-01), Vekstein et al.
patent: 5229871 (1993-07-01), Czarnek et al.
patent: 5336897 (1994-08-01), Watanabe et al.
patent: 5354993 (1994-10-01), Kedmi et al.
patent: 5469488 (1995-11-01), Ono
patent: 5-274587 (1993-10-01), None
patent: 7-079963 (1995-03-01), None
Hamada Yuji
Nambu Kyojiro
Church Craig E.
Kiknadze Irakli
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