Patent Number: 
Section: claims

1. A radiation imaging apparatus comprising:a radiation source for performing multiple radiation emissions to a subject;a filter having at least one filter area for changing energy distribution of radiation in at least one of the multiple radiation emissions, the filter periodically shifting between an inserted state in which the at least one filter area is inserted in a path of radiation and a retracted state in which the at least one filter area is retracted from the path;a cycle determining section for determining a shift cycle of the filter for shifting the at least one filter area between the inserted state and the retracted state before a start of the first radiation emission based on subject information;a driver for driving the filter to shift at the determined shift cycle, the driver driving the filter to start shifting before a start of the first radiation emission and to shift until an end of the last radiation emission after the first radiation emission; andan emission controller for outputting a signal for starting a radiation emission to the radiation source to control emission timing of radiation,wherein the subject information includes cardiac cycle information and respiration information of the subject, and the radiation imaging apparatus further includes a signal detector for detecting a cardiac signal indicating a state of the cardiac cycle information and a respiratory signal indicating a state of the respiration information, andwherein the cycle determining section determines the shift cycle so as to be in synchronization with the cardiac cycle information, and the emission controller synchronizes the emission timing with a phase of the respiration based on the respiratory signal. 2. The radiation imaging apparatus of claim 1, further including a filter phase detector for detecting a phase of the filter, and the emission controller synchronizes the emission timing with the phase of the filter. 3. The radiation imaging apparatus of claim 1, wherein the filter includes multiple filter areas and the multiple filter areas are selectively inserted in sequence into the path. 4. The radiation imaging apparatus of claim 1, wherein the filter includes multiple filters each having at least one filter area, and the multiple filters are selectably used. 5. The radiation imaging apparatus of claim 4, wherein each of the multiple filters is individually rotatable, and arranged to be insertable into the path, and has a transmission area for retracting the at least one filter area of the filter from the path when the at least one filter area of another filter is inserted in the path. 6. A radiation imaging apparatus comprising:a radiation source for performing multiple radiation emissions to a subject;a filter having at least one filter area for changing energy distribution of radiation in at least one of the multiple radiation emissions, the filter periodically shifting between an inserted state in which the at least one filter area is inserted in a path of radiation and a retracted state in which the at least one filter area is retracted from the path;a cycle determining section for determining a shift cycle of the filter for shifting the at least one filter area between the inserted state and the retracted state based on subject information; anda driver for driving the filter to shift at the determined shift cycle, the driver driving the filter to start shifting before a start of the first radiation emission and to shift until an end of the last radiation emission after the first radiation emission, wherein the subject information is body thickness of the subject, and the cycle determining section determines the shift cycle in accordance with a maximum exposure time determined based on the body thickness. 7. An imaging control device for controlling a radiation source for performing multiple radiation emissions to a subject, and a filter having at least one filter area for changing energy distribution of radiation in at least one of the multiple radiation emissions, the filter periodically shifting between an inserted state in which the at least one filter area is inserted in a path of radiation and a retracted state in which the at least one filter area is retracted from the path, the imaging control device comprising:a cycle determining section for determining a shift cycle of the filter for shifting the at least one filter area between the inserted state and the retracted state before a start of the first radiation emission based on subject information;a controller for controlling a driver for driving the filter, the controller controlling the driver to shift the filter at the determined shift cycle by starting before a start of the first radiation emission and until an end of the last radiation emission after the first radiation emission; andan emission controller for outputting a signal for starting a radiation emission to the radiation source to control emission timing of radiation,wherein the subject information includes cardiac cycle information and respiration information of the subject, and the radiation imaging apparatus further includes a signal detector for detecting a cardiac signal indicating a state of the cardiac cycle information and a respiratory signal indicating a state of the respiration information, andwherein the cycle determining section determines the shift cycle so as to be in synchronization with the cardiac cycle information, and the emission controller synchronizes the emission timing with a phase of the respiration based on the respiratory signal.