A medical image diagnostic system includes processing circuitry configured (to): (a) acquire a trained model generated by using, as learning data, images or signals corresponding to a first group of time-series images acquired by performing a first pre-scan on a first patient injected with a contrast agent in a first examination, as well as timing information about timing of a transition from a first pre-scan to a first main scan in a first examination, and information about appropriateness of the timing; and (b) determine appropriate timing of a transition from a second pre-scan to a second main scan by inputting, to the trained model, images or signals corresponding to a second group of time-series images acquired by performing the second pre-scan on a second patient injected with a contrast agent in the second examination different from the first examination.