A system of medical imaging including a marking module, a classifying module, a region-of-interest determining module, a curve acquiring module and a delay calculating module. The marking module is used for marking one or more feature regions from pre-scanned images the classifying module is used for classifying the feature regions by using a classification algorithm model the region-of-interest determining module is used for selecting a feature region of the same type as a specific diagnostic tissue as a region of interest the curve acquiring module is used for acquiring a curve of CT values of the region of interest in function of time, based on a relationship between the CT values and scanning time points the delay calculating module is used for detecting a peak value of the curve and calculating a scan delay time based on a time point corresponding to the peak value.
