X-ray or gamma ray systems or devices – Electronic circuit – X-ray source power supply
Reexamination Certificate
2001-01-17
2004-01-06
Oen, William (Department: 2855)
X-ray or gamma ray systems or devices
Electronic circuit
X-ray source power supply
Reexamination Certificate
active
06674836
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-007815, filed Jan. 17, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
This invention relates to an X-ray computer tomography apparatus, and more particularly to a thin-type X-ray computer tomography apparatus (hereinafter, referred to as an X-ray CT apparatus) provided with a small-sized high-voltage transformer capable of supplying power and stepping up the voltage by itself in a noncontacting manner.
In the field of X-ray CT apparatuses, high-speed tomographic techniques for turning the rotatable gantry section with respect to the static gantry section at high speed are being developed rapidly. With the high-speed tomographic techniques, not only a larger amount of image information can be obtained in a short time but also the time during which the subject is tied down. Thus, the techniques are very effective in a group medical examination as well as an ordinary physical examination. In recent years, a high-speed rotation of about 0.5 second has already been put to practical use and further an ultrahigh-speed rotation of less than 0.3 second is gradually gaining practicality.
Because of the problem of centrifugal force acting on the rotatable gantry section by high-speed rotation, the gantry of the X-ray CT apparatus have been required to be made smaller in size, particularly thinner along the axis of the body of the subject. Although various measures have been taken to improve the method of arranging the units in the rotatable gantry section, it is necessary to make each unit as small as possible to reduce the size of the rotatable gantry section itself. In the X-ray CT apparatus, the top on which the subject has been laid is inserted into a cylindrical space formed within the rotatable gantry section and then pictures are taken. In such an X-ray CT apparatus, it is necessary to improve the accessibility of the subject as in the magnetic resonance imaging apparatus. An improvement in the accessibility enables various medical procedures when the subject is inserted into the apparatus. Moreover, the subject has a less feeling of confinement in the cylindrical space.
The power supply from the static gantry section to the rotatable gantry section is carried out in a contacting manner or a noncontacting manner. One example of supplying power in a contacting manner is achieved by using a slip ring mechanism. As is well known, the slip ring mechanism has a brush provided on the rotatable gantry section and causes the brush to come into contact with the slip ring provided on the static gantry section, thereby supplying power from the static gantry section to the rotatable gantry section. The slip ring mechanism is considered to be unsuitable for high-speed rotation, because the friction between the brush and the slip ring produces heat and abrasion powder. In addition, since there is a possibility of electric discharges, the slip ring is regarded as unsuitable for power transmission of such a high voltage, for example, 10 kV or more as is applied across both ends of an X-ray tube. Under these conditions, several concepts of X-ray CT apparatuses that supply power from the static gantry section to the rotatable gantry section in a noncontacting manner have been proposed.
One known noncontacting-type X-ray CT apparatus is disclosed in U.S. Pat. No. 4,912,735. This X-ray CT apparatus supplies power in a noncontacting manner by electromagnetic induction.
FIG. 11
is a schematic circuit diagram of a conventional X-ray CT apparatus that supplies power from the static gantry section to the rotatable gantry section.
FIG. 12
shows the location of the individual component parts. In
FIG. 12
, an AC/DC converter
14
b
is connected to an alternating-current (a.c.) power source
11
provided on the side face of the lower part of the inside of the static gantry section
111
. The output terminal of the AC/DC converter
14
b
is connected to an inverter
15
. The output of the inverter
15
is connected to the primary coil
116
of the static gantry section
111
. The primary coil
116
is wound around the cylindrical static gantry section
111
in such a manner that it surrounds the outer surface of the static gantry section
111
. The rotatable gantry section
112
has a cylindrical shape as the static gantry section
111
does and is provided on the static gantry section
111
on the same central axis of the cylinder in such a manner that it can rotate. On the rotatable gantry section
112
, a secondary coil
119
is provided in a position facing the primary coil
116
of the static gantry section
111
. Like the primary coil
116
, the secondary coil
119
is wound around the rotatable gantry section
112
in such a manner that it surrounds the outer surface of the rotatable gantry section
112
. A high-voltage transformer
113
is connected to the secondary coil
119
. A rectifier
20
is connected to the output terminal of the high-voltage transformer
113
. An X-ray tube
21
is connected to the output terminal of the rectifier
20
. A magnetic field generated at the primary coil
116
induces power at the secondary
119
. The electromagnetic induction enables power to be supplied from the static gantry section
111
to the rotatable gantry section
112
.
The conventional X-ray CT apparatus with the above configuration that supplies power in a noncontacting manner has the following problem.
As compared with an ordinary transformer where the cores are integrally formed, the leakage inductance between the cores of the separate primary coil
116
and secondary coil
119
is greater, impeding a high-frequency operation, which makes it difficult to miniaturize the unit. The miniaturization is possible only when the operation of the unit is carried out at higher speed. For this reason, in general, to reduce the leakage inductance, the primary coil
116
is arranged as close to the secondary coil
119
as possible or the coil windings are wound even in the grooves of the cores, thereby improving the degree of coupling. In such a manner of improving the degree of coupling, there arises a problem that realizing the high frequency operation by overcoming the leakage inductance between the separated cores is limited. Moreover, it makes high-voltage insulation difficult from the viewpoint of manufacturing techniques. Thus, to obtain a high voltage of about 75 kV to 150 kV on the secondary side, it is necessary to provide an additional high-voltage transformer
113
. This puts significant restriction on the rotatable gantry section being made smaller and thinner. In the X-ray CT apparatus, the primary coil
116
is wound around the cylindrical static gantry section
111
in such a manner that it surrounds the outer surface of the static gantry section
111
and the secondary coil
119
is wound around the rotatable gantry section
112
in such a manner that it surrounds the outer surface of the rotatable gantry section
112
, with the result that the distance between the windings facing each other is relatively long. This makes the parasitic capacitance large, making a high-frequency operation difficult, which is one of the causes of the difficulty in making the unit smaller and thinner.
Another known noncontacting X-ray CT apparatus is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 7-204192 and Jpn. Pat. Appln. KOKAI Publication No. 8-336521. Each of these conventional X-ray CT apparatuses has the following configuration.
Each of the X-ray CT apparatuses comprises electromagnetic induction transmission means including a first winding provided on the fixed frame of a scanner and a second winding provided on the rotary section of the scanner in such a manner that it faces the first winding, and a high-voltage generator connected to the electromagnetic induction transmission means. Each of the X-ray CT apparatuses supplies specific power in a noncontacting manner by electromagnetic induct
Harada Sanae
Harada Toyoshige
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