An X-ray CT apparatus includes: a base; a main frame including a pair of tilt shafts, the main frame being supported in a tiltable manner by the base with a pair of bearings interposed in between, the bearings configured to rotatably support the respective tilt shafts; an X-ray tube and an X-ray detector positioned to face each other; an annular rotor configured to hold the X-ray tube and the X-ray detector, the rotor rotatably supported by the main frame with a bearing interposed in between; and a pair of reinforcement members extended from the main frame. One end of each of the pair of tilt shafts is fixed to the main frame, and the other end of each of the pair of tilt shafts is fixed to the respective reinforcement members.

CROSS REFERENCE OF THE RELATED APPLICATION

This application is based on and claims the benefit of priority from Japanese Patent Application No. 2008-235027, filed on Sep. 12, 2008; the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an X-ray CT apparatus, and particularly to an X-ray CT apparatus configured to take an X-ray CT scan while rotating an annular rotor holding an X-ray tube and an X-ray detector.

2. Description of the Related Art

As described in JP-A No. 2002-172112 (KOKAI), for instance, there has been known an X-ray CT apparatus including an annular rotor which holds an X-ray tube and an X-ray detector, and which is rotatably supported by a stator with a bearing interposed therebetween. The diameter of the bearing rotatably supporting the rotor is set almost equal to the diameter of a diagnosis opening portion which is formed inside the rotor. This X-ray CT apparatus takes an X-ray CT scan of a subject by: positioning the subject inside the diagnosis opening portion; subsequently emitting X-rays onto the subject from the X-ray tube while rotating the rotor around the subject; and detecting the X-rays transmitted through the subject by the X-ray detector.

Furthermore, as described in JP-A No. Hei 02-200251 (KOKAI), there has been known an X-ray CT apparatus which includes a tilt mechanism configured to tilt its rotor at a desired tilt angle. The X-ray CT apparatus including the tilt mechanism is capable of taking X-ray CT scans of a subject at various angles by tilting the rotor at desired tilt angles by use of the tilt mechanism.

In the foregoing X-ray CT apparatuses, however, no considerations have been given to the following points.

In these years, a rotational speed of a rotor tends to be increased because of a demand to shorten a time required to take an X-ray CT scan of a subject. When a rotor is rotated at a higher rotational speed, the rotor is distorted due to a slight displacement between the rotation center and the gravity center of the rotor, and thus the rotor vibrates in rotation. The vibration of the rotor in rotation puts an X-ray CT scan plane out of position, and thus deteriorates the quality of an image obtained by taking an X-ray CT scan.

Other causes of the vibration of the rotor in rotation include such phenomena that: a base portion of the cantilevered tilt shaft supporting the rotor in a tiltable manner is deformed; the rotor is unevenly supported between its two sides because a drive cylinder configured to tilt the rotor is provided at only one side of the rotor; a base fixed to the floor to support the rotor resonates with the rotation of the rotor.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an X-ray CT apparatus capable of suppressing vibration of a rotor even while rotating the rotor at high speed, and thus enhancing the quality of an image obtained by taking an X-ray CT scan.

A first aspect of the present invention is an X-ray CT apparatus includes: a base; a main frame including a pair of tilt shafts, the main frame being supported in a tiltable manner by the base with a pair of bearings interposed in between, the bearings configured to rotatably support the respective tilt shafts; an X-ray tube and an X-ray detector positioned to face each other; an annular rotor configured to hold the X-ray tube and the X-ray detector, the rotor rotatably supported by the main frame with a bearing interposed in between; and a pair of reinforcement members extended from the main frame. One ends of the pair of tilt shafts are fixed to the main frame, and the other ends of the pair of tilt shafts are fixed to the respective reinforcement members.

A second aspect of the present invention is an X-ray CT apparatus includes: a base; a main frame including a pair of tilt shafts, the main frame being supported in a tiltable manner by the base with a pair of bearings interposed in between, the bearings configured to rotatably support the respective tilt shafts; an X-ray tube and an X-ray detector positioned to face each other; an annular rotor configured to hold the X-ray tube and the X-ray detector, the rotor rotatably supported by the main frame with a bearing interposed in between; an expandable and contractible drive cylinder placed at a side of one of the pair of tilt shafts, the drive cylinder having one end connected to the base, and the other end connected to the main frame, the drive cylinder including an expansion/contraction driver which is a drive source for expansion and contraction; and an expandable and contractible cylinder placed at a side of the other one of the pair of tilt shafts, the cylinder having one end connected to the base, and the other end connected to the main frame, the cylinder including a brake configured to restrain expansion and contraction.

A third aspect of the present invention is an X-ray CT apparatus includes: a base; a main frame including a pair of tilt shafts, the main frame being supported in a tiltable manner by the base with a pair of bearings interposed in between, the bearings configured to rotatably support the respective tilt shafts; an X-ray tube and an X-ray detector positioned to face each other; an annular rotor configured to hold the X-ray tube and the X-ray detector, the rotor rotatably supported by the main frame with a bearing interposed in between; and supporters located across the rotor, the supporters configured to connect the base and the main frame. The base is fixed in intimate contact with a floor surface at positions where any node of a secondary vibration and any node of a tertiary vibration do not overlap each other, the secondary and tertiary vibrations occurring in the base between two endmost fixation positions where the base is fixed to the floor surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, descriptions will be hereinbelow provided for an embodiment of the present invention.

FIG. 1is a block diagram showing a schematic configuration of an X-ray CT apparatus according to the embodiment of the present invention. The X-ray CT apparatus includes a stage device1, a bed device2and an operation console device3.

The stage device1includes a stage controller4, a high voltage generator5, a rotation driver6, a tilt driver7, an X-ray tube8, an X-ray detector9and a data collector10.

The bed device2includes a bed base11, a bed driver12and a bed top board13.

The operation console device3includes a console controller14, an input operation unit15, a pre-processor16, an X-ray projection data storage17, a reconstruction processor18, an image data storage19, an image processor20and a display21.

The stage controller4controls all the component parts in the stage device1in response to inputs from the input operation unit15of the operation console device3.

The high voltage generator5supplies the X-ray tube8with a high voltage needed for the X-ray tube8to emit X-rays in accordance with a control signal transmitted from the stage controller4.

The X-ray tube8emits X-rays by using the high voltage supplied from the high voltage generator5. The X-rays emitted from the X-ray tube8is shaped like a fan or a cone.

The X-ray detector9detects the X-rays which are emitted from the X-ray tube8and subsequently transmit through a subject P. In a case of a single-slice CT apparatus, the X-ray detector9includes, for instance, 1000 channels of X-ray detecting elements which are arrayed in a line forming a fan or a straight line. In a case of a multiple-slice CT apparatus, the X-ray detector9is constructed as a two-dimensional X-ray detector including X-ray detecting elements which are aligned in an array in two directions (a slice direction and a channel direction) orthogonal to each other.

The data collector10includes data collecting elements which are aligned in an array as similar to the X-ray detecting elements of the X-ray detector9. The data collector10collects the X-rays (actually, detection signals) detected by the X-ray detector9in accordance with a data collection control signal outputted from the stage controller4. The data thus collected constitutes X-ray projection data.

The rotation driver6drives a motor (not illustrated) in accordance with a control signal outputted from the stage controller4, and rotationally drives a rotor described later.

The tilt driver7expands and contracts a drive cylinder and a following cylinder described later, in accordance with a control signal outputted from the stage controller4, and tilts the rotor together with a main frame described later, at a desired angle.

In accordance with an input received from the input operation unit15of the operation console device3, the bed driver12moves the bed base11upward and downward, and moves the bed top board13in longitudinal directions (directions indicated by an arrow X). The subject P who undergoes an X-ray CT scan is placed on the bed top board13in such a direction that the body axis of the subject P and the movement directions (the directions indicated by the arrow X) of the bed top board13coincide with each other.

The input operation unit15includes a keyboard, a touch panel, a mouse, and the like. Various input operations for driving the X-ray CT apparatus are carried out through the input operation unit15.

The console controller14generates a control signal in accordance with an input received from the input operation unit15. The console controller14transmits this control signal to the stage controller4, the bed driver12and the component parts in the operation console device3.

The pre-processor16applies preprocessing, such as a sensitivity correction and an X-ray strength correction, to the X-ray projection data outputted from the data collector10. The X-ray projection data to which the preprocessing such as the sensitivity correction are applied by the pre-processor16is temporarily stored in the X-ray projection data storage17.

The reconstruction processor18applies a back projection processing to the X-ray projection data which is stored in the X-ray projection data storage17, and thereby reconstructs the image data. A method adopted for this back projection is the same as publicly-known methods, thereby description thereof is omitted. In addition, in a case where the reconstruction processor18applies an interpolation processing to the X-ray projection data, the reconstruction processor18acquires X-ray projection data of an object slice position by use of any one of publicly known interpolation methods such as the 360-degree interpolation method, the 180-degree interpolation method (the opposed data interpolation method), and the like.

The image data thus reconstructed is temporarily stored in the image data storage19, and is thereafter sent to the image processor20. In accordance with an input received from the input operation unit15, the image processor20converts, by using a publicly-known method, the image data to image data such as: a cross-sectional image of a desired cross-section: a projection image made in a desired direction; or a three-dimensional image formed by use of a rendering process. Subsequently, the image processor20sends the image data to the display21. The display21displays an image on the basis of the image data.

FIG. 2is a front view showing an external configuration of the stage device1.FIG. 3is a side view showing the external configuration of the stage device1.

The stage device1includes: a base22; a pair of support bars23a,23bwhich are supporting members; a main frame24; a rotor25; a drive cylinder26; and a following cylinder27.

The base22is shaped like a rectangular frame. The support bars23a,23bare installed upright on the base22, i.e., at positions that are in both end portions in a longitudinal direction of the base22, and are in substantially central portions in a shorter side direction of the base22. A pillow block28is fixed to the top end portion of each of the support bars23a,23b. The pillow block28is a shaft box which contains a bearing28ain its inside. A portion of the pillow block28supporting an outer ring of the bearing28ais formed into a shape curving concavely. The bearing28ais supported inside the pillow block so as to be capable of being eccentric.

The rotor25has a diagnosis opening portion29formed in the center portion. The X-ray tube8and the X-ray detector9are held in their respective positions so as to face each other with this diagnosis opening portion29interposed in between. The diagnosis opening portion29is a part which the subject P undergoing the X-ray CT scan is put into or taken out of. By sliding the bed top board13in the horizontal directions, the subject P placed on the bed top board13is put into or taken out of the diagnosis opening portion29.

The rotor25is rotatably supported by the main frame24with a bearing30interposed in between, and is rotatable about the diagnosis opening portion29. The bearing30is located on a circle having radius equal to a rotation locus of the X-ray tube8that rotates with the rotation of the rotor25, and is located behind the X-ray tube8and the X-ray detector9, that is, on the opposite side of the X-ray tube8and the X-ray detector9from the bed device2.

The main frame24is attached onto the base22with the pair of support bars23a,23binterposed in between. The rotor25is rotatably supported by the main frame24with the bearing30interposed in between. Arms31a,31bare fixed to the two sides of the main frame24with the rotor25interposed therebetween. These arms31a,31bextend toward the sides of the rotor25. One end of one tilt shaft32ais fixed to the one arm31a, whereas one end of the other tilt shaft32bis fixed to the other arm31b. The tilt shafts32a,32bextend in the respective horizontal directions which are orthogonal to the rotation center of the rotor25. The tilt shafts32a,32bare rotatably supported by the bearings28aaccommodated in the pillow blocks28, respectively.

In addition, one end of an L-shaped reinforcement bracket33abeing a reinforcement member is fixed to the arm31a, whereas one end of an L-shaped reinforcement bracket33bbeing a reinforcement member is fixed to the arm31b. The other end of the reinforcement bracket33ais fixed to the other end of the tilt shaft32a, whereas the other end of the reinforcement bracket33bis fixed to the other end of the tilt shaft32b. Because these reinforcement brackets33a,33bare provided, the two ends of the tilt shaft32aare supported by the arm31aand the reinforcement bracket33a, respectively, whereas the two ends of the tilt shaft32bare supported by the arm31band the reinforcement bracket33b, respectively.

In addition, in the center portion of the main frame24, an opening portion34whose diameter is almost equal to the diameter of the diagnosis opening portion29of the rotor25is formed right behind the diagnosis opening portion29.

The drive cylinder26is placed on a side corresponding to the one tilt shaft32a. One end of the drive cylinder26is swingably connected to the base22, whereas the other end is swingably connected to the arm31a. The drive cylinder26includes an electric motor26awhich is an expansion/contraction driver. When this electric motor26ais driven by the tilt driver7, the drive cylinder26expands and contracts.

The following cylinder27is placed on a side corresponding to the other tilt shaft32b. One end of the following cylinder27is swingably connected to the base22, whereas the other end is swingably connected to the arm31b. As shown inFIG. 4, the following cylinder27includes a first pipe35and a second pipe36. The first pipe35is slidably fitted into the second pipe36. The first pipe35is connected to the arm31b, whereas the second pipe36is connected to the base22. A nut37is fixed inside the first pipe35, and an end of a screw stock38is rotatably held inside the second pipe36. The screw stock38is screwed into the nut37. This following cylinder27is configured to expand or contract in a way that the screw stock38having screwed in the nut37rotates on its axis when an external force acts on the first pipe35or the second pipe36in an expanding or contracting direction. Furthermore, a solenoid brake39configured to restrain the rotation of the screw stock38when the electricity is cut off is provided inside the second pipe36. The restraint of the rotation of the screw stock38by the brake39restrains the expansion and contraction of the following cylinder27. The ON and OFF control of the solenoid brake39is carried out in linkage with the control of the tilt driver7for causing the drive cylinder26to expand and contract.

The base22is fixed to the floor surface on which the stage device1is placed by use of anchor bolts. InFIG. 2, a wave line indicated by a broken line represents a primary vibration of the base22which is generated between the two endmost fixation positions X, Y where the base22is fixed to the floor surface; a wave line indicated by a long dashed short dashed line represents a secondary vibration of the base22which is generated between the fixation positions X, Y; and a wave line indicated by a long dashed double-short dashed line represents a tertiary vibration of the base22which is generated between the fixation positions X, Y. Between the fixation positions X, Y, the base22is fixed to the floor surface at four fixation positions A, B, C, D. These fixation positions A, B, C, D are determined so that the secondary and tertiary vibrations which occur in the base22between the fixation positions X, Y do not overlap each other at any node. Specifically, the position A is a position which is away from the position X by a quarter of the distance between the positions X, Y; the position B is a position which is away from the position X by five-twelfths of the distance between the positions X, Y; the position C is a position which is away from the position X by seven-twelfths of the distance between the positions X, Y; and the position D is a position which is away from the position X by three-fourths of the distance between the positions X, Y.

When an X-ray CT scan is taken of the subject P by use of the X-ray CT apparatus having such configuration, the subject P placed on the bed top board13is positioned inside the diagnosis opening portion29, and X-rays are emitted from the X-ray tube8while the rotor25is rotated. In addition, the drive cylinder26is expanded or contracted depending on the necessity, and the rotor25together with the main frame24is thus tilted about the tilt shafts32a,32b.

The rotor25is rotatably supported by the main frame24with the bearing30interposed in between. As the rotational speed of the rotor25increases, the rotor25is easier to vibrate. However, in this X-ray CT apparatus, the bearing30is located on the circle having radius equal to the rotation locus of the X-ray tube8that rotates with the rotation of the rotor25, and is larger in diameter than a bearing according to a conventional example whose diameter is a dimension almost equal to the diameter of the diagnosis opening portion29. The larger diameter of the bearing30makes it possible to restrain the distortion of the rotor25in rotation, and accordingly to restrain the vibration of the rotor25which occurs due to this distortion.

Thereby, in the X-ray CT scan taken while rotating the rotor25, the X-ray CT scan plane is less likely to be out of position. Accordingly, the quality of the image obtained by taking the X-ray CT scan can be enhanced.

When changing the direction in which the X-ray CT scan is applied to the subject P, the rotor25together with the main frame24is tilted about the axes of the respective tilt shafts32a,32b. The tilt shafts32a,32bare supported by their two ends, respectively, in a way that the one end of each of the tilt shafts32a,32bare fixed to the corresponding one of arms31a,31bwhereas the other end of each of the tilt shafts32a,32bare fixed to the corresponding one of reinforcement brackets33a,33b. For this reason, it is possible to enhance the rigidities of the respective tilt shafts32a,32bwithout making the tilt shaft32a,32bthicker. As a result, the deformations of the base portions of the tilt shafts32a,32bconnected to the arms31a,31bare prevented, and concurrently the tilt shafts32a,32bis prevented from tilting with respect to the arms31a,31b, respectively. Accordingly, it is possible to prevent the rotor25and the main frame24from vibrating due to the tilts of the tilt shafts32a,32bwith respect to the arms31a,31b.

Thereby, in the X-ray CT scan taken while rotating the rotor25, the X-ray CT scan plane is less likely to be out of position. Accordingly, the quality of the image obtained by taking the X-ray CT scan can be enhanced.

In the present embodiment, the pillow blocks28are used to rotatably support the respective tilt shafts32a,32b. Here, a portion of each pillow block28configured to support the outer ring of the corresponding bearing28ais formed into a concave curved shape. By using these pillow blocks28, the main frame24can be supported in a tiltable manner, even in a case where the two pillow blocks28are attached to their respective positions with poor accuracy, or where the two tilt shafts32a,32bare attached to their respective positions with poor accuracy.

Instead of these pillow blocks28, shaft boxes including deep grooves may be attached to the upper portions of the support bars23a,23bso that the outer ring of the bearings28aconfigured to rotatably support the respective tilt shafts32a,32bare fitted into the deep grooves, respectively. When the bearings28aconfigured to rotatably support the tilt shafts32a,32bare installed in the shaft boxes including such deep grooves, it is possible to prevent the tilt shafts32a,32bfrom tilting with respect to the arms31a,31b, respectively. Accordingly, it is possible to prevent the rotor25and the main frame24from vibrating due to the tilts of the tilt shafts32a,32bwith respect to the arms31a,31b.

When the rotor25is tilted together with the main frame24, the drive cylinder26provided near the tilt shaft32aon one side is expanded or contracted. Thereby, the rotor25together with the main frame24is tilted about the tilt shafts32a,32b. In a case where the drive cylinder26is expanded or contracted, the brake39of the following cylinder27near the tilt shaft32bon the other side is turned off, and the following cylinder27is expanded or contracted in conjunction with the expansion or contraction of the drive cylinder26. Once the expansion or contraction of the drive cylinder26is completed, the brake39of the following cylinder27is turned on, and the expansion and contraction of the following cylinder27is restrained.

Because the drive cylinder26is provided near the tilt shaft32aon the one side and the following shaft27is provided near the tilt shaft32bon the other side in this manner, the rotor25and the main frame24are evenly supported at the two sides of the rotor25. This makes it possible to prevent the vibrations of the rotor25and the main frame24during the rotation of the rotor25, although the vibrations would otherwise occur due to uneven support of the rotor25and the main frame24between the two sides of the rotor25.

Thereby, in the X-ray CT scan taken while rotating the rotor25, the X-ray CT scan plane is less likely to be out of position. Accordingly, the quality of the image obtained by taking the X-ray CT scan can be enhanced.

The base22is fixed to the floor surface on which the stage device1is placed by use of the anchor bolts. The base22is fixed to the floor surface at such positions that the secondary and tertiary vibrations of the base22which occur between the fixation positions X, Y do not overlap each other at any node, the fixation positions X, Y being two endmost positions where the base22is fixed to the floor surface. Thus, the vibration of the base22during the rotation of the rotor25can be restrained. Accordingly, the rotor25and the main frame24can be prevented from vibrating due to the vibration of the base22.

Thereby, in the X-ray CT scan taken while rotating the rotor25, the X-ray CT scan plane is less likely to be out of position. Accordingly, the quality of the image obtained by taking the X-ray CT scan can be enhanced.

Note that, in the foregoing embodiment, the drive cylinder26and the following cylinder27are used together. However, the present invention is not limited to this. For instance, instead of the following cylinder27, a different drive cylinder may be used. Here, the different drive cylinder and the drive cylinder26expand and contract in synchronism with each other.

The embodiment of the present invention has been described above. However the descriptions only exemplify the concrete example, and do not limit the invention. The concrete configurations and the like of each component parts can be modified whenever deemed necessary. In addition, the operations/working-effects described in the embodiment are only those enumerated as most preferable operations/working-effects brought about by the present invention. The operations/working-effects of the present invention are not limited to those described in the embodiment of the present invention.