Patent Number: 053596390
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to computerized tomography (CT) for obtaining sectional images of an examinee by emitting X-rays from radial directions to the examinee, and particularly to a method and apparatus for obtaining a plurality of sectional images of an examinee lying still. 2. Description of the Related Art This type of CT apparatus includes an X-ray emitter and an X-ray detector opposed to each other across an examinee lying still on a top board. X-rays are emitted from radial directions to scan the examinee and collect projection data relating to X-ray absorption in the examinee's body. The data is reversely projected to reconstruct a distribution image of X-ray absorption coefficients in a sectional plane across the examinee's body, thereby to obtain a sectional image of the body. After one slice is scanned, the top board is slid to adjust a next slice of concern of the examinee to a direction of X-ray emission from the X-ray emitter, and a sectional image of this slice is obtained as above. If a sectional plane has an excessive slice thickness, a virtual image called a partial volume artifact tends to appear in a reconstructed image of, for example, the osseous basal region of brains. In practice, as disclosed in Japanese Patent Publication (Unexamined) No. 61-109551, data of numerous thin slice planes are collected and put to data processing such as addition to obtain a clear image of a thick sectional plane. However, such a method of obtaining a sectional image has the following disadvantage. The top board on which an examinee lies is slid at a relatively low speed (about 2 seconds) in order to avoid a displacement between a sectional plane of a site of concern and the X-ray emitter or the like. 0n the other hand, scanning by the X-ray emitter or the like is carried out at high speed (about 1 second). To collect data of numerous sectional planes under such conditions, sliding of the top board supporting the examinee and scanning by the X-ray emitter or the like must alternately be repeated numerous times. A long time is required to collect data of all of desired sectional planes particularly because of the slow sliding movement of the top board. SUMMARY OF THE INVENTION This invention has been made having regard to the state of the art noted above, and its object is, in relation to collection of data of numerous sectional planes with a CT apparatus, to provide a method and apparatus for reducing the time required to collect data of all of required sectional planes. The above object is fulfilled, according to one aspect of this invention, by a method of obtaining a sectional image of an examinee based on projection data relating to X-ray absorption in sectional planes of the examinee, which data are collected radially of the sectional planes by causing X-ray emitting means and X-ray detecting means opposed to each other across the examinee to scan the sectional planes of the examinee lying still, the method comprising the steps of: (a) scanning a predetermined number of sectional planes starting with a sectional plane in an initial position by successively shifting a direction of X-ray emission from the X-ray emitting means along a body axis of the examinee; PA1 (b) effecting a reset operation, after scanning the predetermined number of sectional planes, to switch the direction of X-ray emission to scan a sectional plane in the initial position, and moving the examinee synchronously with the reset operation to set a new sectional plane adjacent the predetermined number of sectional planes to the initial position; and PA1 (c) repeating the steps (a) and (b) above until all sectional planes are scanned. PA1 X-ray emitting direction switching means for shifting a direction of X-ray emission from the X-ray emitting means along a body axis of the examinee; PA1 examinee moving means for moving the examinee along the body axis; and PA1 control means for effecting a switching control by driving the X-ray emitting direction switching means to shift the direction of X-ray emission from the X-ray emitting means to scan one sectional plane and then a next sectional plane adjacent thereto, thereby to scan successively a predetermined number of sectional planes starting with a sectional plane in an initial position, a reset control by driving the X-ray emitting direction switching means, after scanning the predetermined number of sectional planes, to switch the direction of X-ray emission to scan a sectional plane in the initial position, and a further control by driving the examinee moving means to move the examinee synchronously with the reset control to set a new sectional plane adjacent the predetermined number of sectional planes to the initial position. A predetermined number of sectional planes are scanned, starting with a sectional plane in the initial position, by successively shifting the direction of X-ray emission from the X-ray emitting means along the body axis of the examinee. A reset operation is effected, after scanning the predetermined number of sectional planes, to switch the direction of X-ray emission to scan a sectional plane in the initial position. The examinee is moved synchronously with the reset operation to set a new sectional plane adjacent the predetermined number of sectional planes to the initial position. Subsequently, a predetermined number of sectional planes are scanned, starting with the new sectional plane in the initial position, by successively shifting the direction of X-ray emission from the X-ray emitting means along the body axis of the examinee. After scanning the predetermined number of sectional planes, a reset operation is effected and the examinee is moved to set a new sectional plane adjacent the predetermined number of sectional planes to the initial position as above. These operations are repeated until all sectional planes are scanned. That is, a predetermined number of sectional planes are successively scanned, starting with a sectional plane in the initial position, by shifting the direction of X-ray emission from the X-ray emitting means without moving the examinee. Consequently, the slow movement of the examinee does not occur during scanning of the predetermined number of sectional planes, thereby to achieve a substantial reduction in the time taken in collecting data of all sectional planes. With an increase in the number of sectional planes from which data are collected, the examinee moving time is correspondingly reduced to promote the reduction in processing time. In a further aspect of this invention, an apparatus for executing the above method is provided, which comprises: For scanning a predetermined number of sectional planes, starting with a sectional plane in the initial position, the control means drives the X-ray emitting direction switching means to shift successively the direction of X-ray emission from the X-ray emitting means along the body axis of the examinee. The control means effects a reset control, after scanning the predetermined number of sectional planes, to drive the X-ray emitting direction switching means to switch the direction of X-ray emission to scan a sectional plane in the initial position. The examinee moving means is driven synchronously with the reset control to move the examinee to set a new sectional plane adjacent the predetermined number of sectional planes to the initial position. Subsequently, the control means drives the X-ray emitting direction switching means to scan a predetermined number of sectional planes, starting with the new sectional plane in the initial position, by successively shifting the direction of X-ray emission from the X-ray emitting means along the body axis of the examinee. After scanning the predetermined number of sectional planes, the control means effects a reset control and moves the examinee to set a new sectional plane adjacent the predetermined number of sectional planes to the initial position as above. These operations are repeated until all sectional planes are scanned. That is, a predetermined number of sectional planes are successively scanned, starting with a sectional plane in the initial position, by driving the X-ray emitting direction switching means which is relatively fast, without moving the examinee which is relatively slow. This achieves a substantial reduction in the time taken in collecting data of all sectional planes. With an increase in the number of sectional planes from which data are collected, the examinee moving time is correspondingly reduced to promote the reduction in processing time.