X-ray computed tomography apparatus

1. An X-ray computed tomography apparatus comprising:

an X-ray tube configured to generate X-rays;

an X-ray detector configured to detect X-rays generated from the X-ray tube and transmitted through a subject;

a support mechanism configured to rotatably support the X-ray tube and the X-ray detector;

an input unit configured to repeatedly input, from an electrocardiograph, a trigger signal originating from a specific cardiac phase in a cardiac cycle of the heart of the subject;

an RR period determination unit configured to determine whether a period between an input time point of a latest trigger signal, of the repeatedly input trigger signals, and an input time point of a trigger signal immediately before the latest trigger signal is not less than a preset first threshold, for each input of the latest trigger signal;

a condition determination unit configured to determine whether projection data which is configured to be substantially used for image reconstruction at a reconstruction target phase have been acquired, if it is determined that the period is not less than the first threshold;

a control unit configured to terminate generation of X-rays from the X-ray tube, if it is determined that the projection data which is configured to be substantially used have been acquired.

2. The X-ray computed tomography apparatus of claim 1 , further comprising an elapsed time determination unit configured to determine whether an elapsed time from a start time point of a scan has exceeded a second threshold indicating a preset scheduled scan time,

wherein the condition determination unit is configured to determine whether projection data which is configured to be substantially used for image reconstruction at a reconstruction target phase have been acquired, if it is determined that the period is not less than the first threshold or the elapsed time has exceeded the second threshold, and

the control unit terminates generation of X-rays from the X-ray tube, if it is determined that the projection data which is configured to be substantially used have been acquired.

3. The X-ray computed tomography apparatus of claim 1 , further comprising an elapsed time determination unit configured to determine whether an elapsed time from a start time point of a scan has exceeded a second threshold indicating a preset scheduled scan time,

wherein the elapsed time determination unit determines whether the elapsed time has exceeded the second threshold, if it is determined that the period is less than the first threshold, and

the control unit terminates generation of X-rays from the X-ray tube, if it is determined that the projection data which is configured to be substantially used have been acquired or it is determined that the elapsed time has exceeded the second threshold.

4. The X-ray computed tomography apparatus of claim 1 , further comprising a tube current control unit configured to control a tube current flowing in the X-ray tube so as to alternately switch between a first current value and a second current value smaller than the first current value,

wherein the condition determination unit determines whether the reconstruction target phase is included in a first period in which the tube current has the first current value, if it is determined that the period is not less than the first threshold, and

the control unit terminates generation of X-rays from the X-ray tube, if it is determined that the reconstruction target phase is included in the first period.

5. The X-ray computed tomography apparatus of claim 3 , further comprising a tube current control unit configured to control a tube current so as to alternately generate the X-rays and stop generating the X-rays,

wherein the condition determination unit determines whether the reconstruction target phase is included in an irradiation period in which the X-rays are generated, if it is determined that the period is not less than the first threshold, and

the control unit terminates generation of the X-rays, if it is determined that the reconstruction target phase is included in the irradiation period.

6. The X-ray computed tomography apparatus of claim 3 , further comprising:

a counting unit configured to count a beat count when it is determined that the projection data which is configured to be substantially used have been acquired; and

a valid count determination unit configured to determine whether the beat count has reached a preset target count,

wherein the elapsed time determination unit determines whether the elapsed time has exceeded the second threshold, if it is determined that the beat count has not reached the target count, and

the control unit terminates generation of the X-rays from the X-ray tube, if it is determined that the beat count has reached the target count or it is determined that the beat count has not reached the target count and it is determined that the elapsed time has exceeded the second threshold.

7. The X-ray computed tomography apparatus of claim 2 , wherein the second threshold is set in accordance with an instruction from a user.

8. The X-ray computed tomography apparatus of claim 1 , further comprising an irradiation time determination unit configured to determine whether a total irradiation time of X-rays from the X-ray tube has exceeded a second threshold indicating a preset scheduled irradiation time,

wherein the control unit terminates generation of X-rays from the X-ray tube, if it is determined that the projection data which is configured to be substantially used have been acquired or it is determined that the total irradiation time has exceeded the second threshold.

9. The X-ray computed tomography apparatus of claim 1 , wherein the first threshold is set based on a period of one pulsation of the subject which is measured in advance.

10. The X-ray computed tomography apparatus of claim 2 , further comprising a tube current control unit configured to control a tube current so as to alternately generate the X-rays and stop generating the X-rays,

wherein the condition determination unit determines whether the reconstruction target phase is included in an irradiation period in which the X-rays are generated, if it is determined that the period is not less than the first threshold, and

the control unit terminates generation of the X-rays, if it is determined that the reconstruction target phase is included in the irradiation period.

11. The X-ray computed tomography apparatus of claim 3 , wherein the second threshold is set in accordance with an instruction from a user.