GANTRY OF APPARATUS FOR PHOTOGRAPHING CROSS SECTION USING RADIOACTIVE RAYS

Abstract: A gantry of an apparatus for photographing a cross sec­ tion using radioactive rays of the present invention features in lowering cost of a mechanism for adjusting the inclination and improving the reliability and safety. Variable force of a drive cylinder (43) is acted upon one main arm (14) of two main arms (13, 14) that are coupled together, and constant force of a gas spring (42) is acted upon the other main arm (13). Motion of the inclination is carried out by cooperation of the two main arms (13, 14) without developing any twist therebetween.

Description: Technical Field The present invention relates to an improved mechanism for adjusting the tilt of the gantry of a CT (computerized tomography) scanner. Background Art As shown in Fig. 4, a well-known gantry for use in a CT (computerized tomography) scanner comprises a radiation-projecting portion 6, a detector portion 7 for detecting the radiation transmitted through an object 3 to be examined, a rotating means (not shown) for rotating the projecting portion 6 and the detector portion 7 around a cylindrical opening 5 to scan the object 3, and a tilt adjusting mechanism (not shown). The projecting portion 6 has a radiation source 1 and a collimator 2 that shapes the radiation emanating from the source 1 into a fan-shaped beam S, which is directed to the object 3. This object is inserted into the opening 5 by a cradle 4. The tilt adjusting mechanism serves to incline the gantry itself forward or rearward so that the plane of the fan-shaped beam S is tilted toward or away from the direction in which the object 3 is inserted, the direction being indicated by the arrow X. Main portions of the conventional tilt adjusting mechanism are shown in Fig. 5 (a) and (b). Fig. 5 (a) is a rear view of the gantry, i.e., a view taken from the direction opposite to the direction indicated by the arrow X. Fig. 5(b) is a side elevation of the gantry. The tilt adjusting mechanism consists primarily of a pair of main arms 13, 14, and a driving portion 17 that tilts the arms 13 and 14 simultaneously forward or rearward. The arm 13 has at its one end an arc-shaped peripheral portion riding on two rollers 11 which are rotatably mounted to a side plate 10. The other end is joined to a frame 12 to hold one side of the frame 12. The arm 14 holds the other side of the frame 12, and rides on two rollers 15 rotatably mounted to a side plate 16. A cylindrical shaft (not shown) is mounted to the frame 12 via a bearing (not shown). The frame 12 supports the radiation-projecting portion 6 and the detector portion 7 via the cylindrical shaft, as shown in Fig. 4. The driving portion 17 comprises an electric motor 18 that is controlled by a control portion (not shown), a pulley 19 directly coupled to the shaft of the motor, a worm gear 20, a pulley 21 directly coupled to the input shaft of the gear 20, a sprocket 22 directly coupled to the output shaft of the gear 20, a connecting shaft 28 held to bearings 26 and 27, a timing belt 29 wound on the pulleys 19 and 21, a chain 30 trained around the sprockets 22 and 23, another chain 32 trained around the sprocket 24, and a further chain 34 trained around the sprocket 25. The sprockets 23 and 24 are rigidly fixed to one end of the connecting shaft 28, while the sprocket 25 is rigidly secured to the other end. One end of the chain 32 is fastened to the main arm 13, the other end being secured to a drum 31 for winding up the chain. Similarly, one end of the chain 34 is fastened to the main arm 14, whereas the other end is affixed to a drum 33 for winding up the chain. A gantry mechanism composed of the frame 12, the main arms 13, 14, and other components is rotated by the motor 18 about the center O₁ of a scanned region in a direction indicated by the arrow A₁ or A₂. The center of gravity of the gantry mechanism lies at a location O₂ different from the center O₁. When no restriction is imposed on the gantry mechanism, it is free to rotate in the direction indicated by the arrow A₂. In the operation of the structure constructed as described above, when the control portion issues an instruction to drive the motor 18 so that the chain 32 may be wound on the drum 31, the chain 34 is also driven via the connecting shaft 28. Thus, the main arms 13 and 14 are rotated simultaneously in the direction indicated by the arrow A₁. When the motor 18 is driven in such a direction that the chain 32 is payed out, the chain 34 is also payed out. This allows the arms 13 and 14 to rotate together in the direction indicated by the arrow A₂ by their own weight. By controlling the operation of the motor 18 in this way under the instruction of the control portion, the gantry mechanism can be tilted toward or away from the direction X in which the object to be examined is inserted. In the conventional gantry for the CT scanner, the driving portion 17 is made up of a number of components, including the motor, the pulleys, the timing belt, the worm gear, the sprockets, the chains, the connecting shaft, and the drums for winding up the chains. Hence, the gantry is expensive to manufacture. Also, it is complex in structure. Further, it is difficult to secure high reliability or safety, because chains that wear quickly are used. US-PS 4 177 382 discloses a computerized tomographic apparatus for medical radiographic purposes comprising a gantry which is operated by the use of a cylinder at each of its both sides. US-PS 4 475 072 discloses an X-ray table having an elevator mounted on a base for vertical movement in which excessive loading of ball-and-screw drives is avoided by a pair of gas springs. Disclosure of the Invention It is the object of the present invention to provide a gantry for use in a CT scanner, the gantry having a tilt adjusting mechanism which is economical to manufacture and is highly reliable and safe. This object is solved by a gantry for a CT scanner comprising the features of claim 1. The gantry according to the invention has main arms 13 and 14 coupled together, a driving cylinder 43 having a driving shaft 47 that exerts a variable force on the arm 14, and a gas spring 42 that exerts a constant force on the other arm 13. The shaft 47 and the spring 42 cooperate to tilt the arms 13 and 14 without producing twisting motion between the arms 13 and 14. Brief Description of the Drawings Figures 1(a) and 1(b) are rear and side elevations of a gantry according to the invention; Figures 2(a), 2(b), 2(c) are diagrams for illustrating the manner in which the gantry shown in Figures 1(a) and 1(b) is tilted; Figures 3(a) and 3(b) are side elevations of another gantry according to the invention; Figure 4 is a perspective view of a CT scanner; Figures 5(a) and 5(b) are views similar to Figures 1(a) and 1(b), but showing a conventional gantry. Best Mode for Carrying Out the Invention The present invention is hereinafter described in detail by referring to the drawings. Figs. 1(a) and 1(b) show a gantry according to the invention. Fig. 1(a) is a rear view of main portions of the tilt adjusting mechanism of the gantry. Fig. 1(b) is a side elevation of main portions of the tilt adjusting mechanism. It is to be noted that like components are indicated by like reference numerals throughout Figs. 1(a), 1(b), 5(a), and 5(b). In this example, main arms 13 and 14 are mounted on rollers 11 and 15, respectively, and are connected together by a connecting rod 40. Thus, the arms 13 and 14 can rotate together in a direction indicated by the arrow A₁ or A₂. The arms 13 and 14 are coupled to a gas spring 42 and a cylinder 43, respectively, which are mounted on a base plate 41. The cylinder 43 has a casing whose one end 44 is rotatably held to a pin 46 that is firmly fixed to a block 45. This block 45 is securely fixed to the plate 41. The cylinder 43 further has a driving shaft 47 whose front end is rotatably held to a pin 49 fixed to a plate 48, which is firmly attached to the arm 14. The driving shaft 47 of the cylinder 43 is caused to make a rectilinear motion in a direction indicated by the arrow B₁ or B₂, by means of an electric motor 50 which operates on a control signal from a control portion (not shown). The spring 42 has a casing whose one end 51 is rotatably held to a pin 53 mounted to a plate 52, which is rigidly fixed to the arm 13. The spring 42 further includes a connecting rod 54 whose front end 55 is rotatably held to a pin 57. This pin 57 is mounted to a block 56 that is firmly fixed to the base plate 41. Pressurized nitrogen or other gas is sealed up hermetically within the casing of the spring 42. This spring 42 has a small spring constant, and is designed to deliver a given force in the direction in which the spring expands, irrespective of the stroke of the driving shaft 47. The spring 42 and the shaft 47 of cylinder 43 substantially equally share the force that resists the moment produced by the weight of the gantry itself, the moment acting in the direction indicated by the arrow A₂. When the control signal produces a control signal to drive the motor 50 so that the driving shaft 47 of the cylinder 43 may be moved in the direction indicated by the arrow B₁, the main arm 14 is rotated in the direction indicated by the arrow A₁. The arm 13 coupled to this arm 14 by the connecting rod 40 is also turned. Since the arm 13 receives substantially the same force from the spring 42 as the force applied to the arm 14, the arms 14 and 13 rotate without producing twisting motion between them. As a result, as shown in Fig. 2(b), the gantry can be tilted forward by a desired angle in the direction of the arrow X. This is same in the case where the motor 50 turns reversely to make the gantry tilt rearward as shown in Fig. 2 (c). The force is equally applied to the arms 13 and 14 to support the torque due to the self weight of the gantry so that the gantry can be tilted without producing twisting motion between the arms 13 and 14. Fig. 2(a) shows the condition in which the gantry is in its vertical position. Although the driving shaft for tilting the gantry mechanism is disposed only at one side of the gantry mechanism in this way, the gantry mechanism can be tilted without producing twisting motion between the main arms that are disposed on opposite sides of the mechanism. It should be understood that the main portions of the tilt adjusting mechanism are not limited to the example described above. For example, as shown in Fig. 3 (a) and (b), pins 58 and 59 may be provided on opposite sides of the frame 12 such that the frame 12 may be held to bearings 60 and 61. Note that like components are denoted by like reference numerals throughout Fig. 1 (a) and (b) and Fig. 3 (a) and (b). Also, the shaft of the cylinder may be actuated hydraulically, rather than by an electric motor. As described thus far, the invention provides a tilt adjusting mechanism having a simple driving portion. Therefore, a CT scanner gantry whose tilt adjusting mechanism is economical to fabricate and is highly reliable and safe can be achieved.

Claims: A gantry for a CT scanner comprising: a gantry mechanism (12, 13, 14) which is capable of rotating about a horizontal axis (O₁), so that the gantry mechanism is tilted forward or away from the direction (X) in which an object to be examined is inserted and the center of gravity (O₂) of which is eccentric with reference in to the axis of rotation, and a force-generating means (42, 43) for applying forces to the gantry mechanism at two positions (48, 52) which are spaced from each other in a direction parallel to the axis of rotation of the gantry mechanism, in order that the torque caused by the eccentricity of the center of gravity of the gantry mechanism is opposed by the applied forces and that the posture of the gantry mechanism is maintained, characterized in that the force-generating means comprise a cylinder (43) having a driving shaft (47) that applies a variable force at one of said two positions (48) and a gas spring (42) that applies a constant force at the other position (52). The gantry for a CT scanner of claim 1, wherein the shaft (47) is driven by an electric motor. The gantry for a CT scanner of claim 1, wherein the shaft (47) is driven hydraulically.

Inventors: TAKAHASHI, RYO
Applicants: YOKOGAWA MEDICAL SYSTEMS, LTD
Application year: 1986
Main classification: A61B6
IPC codes: A61B6, G01N23