1. An operating method for an imaging system for time-resolved mapping of an examination object moving periodically with various phases, comprising: generating a first set of projection recordings of the examination object by the imaging system at a first set of different angles using ECG gating; synchronously injecting a contrast agent at a start of the recording of the first set of projection recordings; simultaneously recording a first phase signal indicating a first set of phases of the periodically moving examination object at time of recording the first set of the projection recordings; reconstructing a first set of static three-dimensional image data sets in the first set of phases from the first set of the projection recordings; calculating three-dimensional motion fields corresponding to defined reference phases from the first set of the three-dimensional image data sets by which two of the first set of the three-dimensional image data sets are mapped onto one another; generating a second set of projection recordings of the examination object by the imaging system at a second set of different angles without using ECG gating during said generating the second set of projection recordings; simultaneously recording a second phase signal indicating a second set of phases of the periodically moving examination object at time of recording the second set of the projection recordings; injecting a contrast-agent bolus synchronized at a start of the recording of the second set of the project recordings after the contrast agent injected at the start of the recording of the first set of projection recordings presents homogeneously; generating a sequence of motion-compensated three-dimensional image data sets in the defined reference phases by reconstructing a second set of three-dimensional image data sets from the second set of the projection recordings using the three-dimensional motion fields, wherein the three-dimensional motion fields indicate a temporal motion of the periodically moving examination object, and wherein the second set of projection recordings are recorded from phases that do not correspond to the defined reference phases of the first set of the projection and the three-dimensional motion fields, and wherein the second set of projection recordings are converted into the first set of projection recordings for the defined reference phases to calculate the sequence of motion-compensated three-dimensional image data sets using the three-dimensional motion fields, and dynamically tracking an inflow of the contrast-agent bolus injected at the start of the recording of the second set of projection recordings over time on the sequence of motion-compensated three-dimensional image data sets.