Gantry for CT scanner

Details Gantry for CT scanner Gantry for CT scanner

1986-08-27

1988-06-07

Howell, Janice A.

X-ray or gamma ray systems or devices

Specific application

Computerized tomography

378 17, G01T 1166

Patent

active

047501952

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Technical Field
The present invention relates to an improved mechanism for adjusting the tilt of the gantry of a CT (computerized tomography) scanner.
2. 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 O.sub. 1 of a scanned region in a direction indicated by the arrow A.sub.1 or A.sub.2. The center of gravity of the gantry mechanism lies at a location O.sub.2 different from the center O.sub.1. When no restriction is imposed on the gantry mechanism, it is free to rotate in the direction indicated by the arrow A.sub.2.
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 A.sub.1. 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 A.sub.2 by their own weight. By

REFERENCES:
patent: 4115695 (1978-09-01), Kelman
patent: 4139775 (1979-02-01), Williams

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