X-ray CT apparatus and method of controlling thereof

1. An X-ray Computed Tomography (CT) apparatus, comprising:

a rotational-movement control unit that continuously rotates an X-ray radiation unit and an X-ray detecting unit in a circular orbit that is formed substantially about a subject placed on a top plate, and continuously reciprocates the top plate in a body axis direction of the subject;

an angle determining unit that determines an angle indicating a position of the X-ray radiation unit in the circular orbit at a moment to start radiation after a return of reciprocation, based on a time from a moment of completion of radiation in a movement to a certain direction until a moment to start radiation in a movement after the return, the time being calculated from scanning conditions; and

a radiation control unit that controls radiation by the X-ray radiation unit so as to start in accordance with the angle determined by the angle determining unit.

2. The X-ray CT apparatus according to claim 1 , wherein

the rotational-movement control unit reciprocates the top plate continuously in a first direction and in a second direction that is opposite to the first direction; and

the angle determining unit determines a first angle indicating a position of the X-ray radiation unit in the circular orbit at a moment to start radiation in a movement to the first direction, and a second angle indicating a position of the X-ray radiation unit in the circular orbit at a moment to start radiation in a movement to the second direction, so as to minimize a sum of a differential angle in a rotational direction between an angle at completion of radiation in a movement to the first direction and the second angle, and a differential angle in a rotational direction between an angle at completion of radiation in a movement to the second direction and the first angle, the sum being a value calculated from the scanning conditions.

3. The X-ray CT apparatus according to claim 1 , wherein the angle determining unit further uses a preparation time for starting radiation in a movement after a return, for determination of the angle.

4. A method of controlling an X-ray CT apparatus comprising:

rotating continuously an X-ray radiation unit and an X-ray detecting unit in a circular orbit that is formed substantially about a subject placed on a top plate, and continuously reciprocating the top plate in a body axis direction of the subject;

determining an angle indicating a position of the X-ray radiation unit in the circular orbit at a moment to start radiation after a return of reciprocation, based on a time from a moment of completion of radiation in a movement to a certain direction until a moment to start radiation in a movement after the return, which is a time calculated from scanning conditions; and

controlling radiation by the X-ray radiation unit so as to start in accordance with the angle determined.

5. The method according to claim 4 , further comprising:

reciprocating the top plate continuously in a first direction and in a second direction that is opposite to the first direction; and

determining a first angle indicating a position of the X-ray radiation unit in the circular orbit at a moment to start radiation in a movement to the first direction, and a second angle indicating a position of the X-ray radiation unit in the circular orbit at a moment to start radiation in a movement to the second direction, so as to minimize a sum of a differential angle in a rotational direction between an angle at completion of radiation in a movement to the first direction and the second angle, and a differential angle in a rotational direction between an angle at completion of radiation in a movement to the second direction and the first angle, the sum being a value calculated from the scanning conditions.

6. The method according to claim 4 , wherein a preparation time for starting radiation in a movement after a return is further used for the determining the angle.