1. A method of training a detector for detecting spatial and temporal locations of a contrast injection in fluoroscopic image sequences, comprising: receiving a plurality of training volumes, each training volume formed by stacking a sequence of 2D fluoroscopic images, and each training volume annotated with a ground truth contrast injection location; estimating a heart rate for each training volume; estimating local frequency and phase in a neighborhood of the ground truth contrast injection location for each training volume; extracting features from each training volume that are frequency and phase invariant based on the estimated heart rate and the estimated local frequency and phase; and training a detector for detecting spatial and temporal locations of a contrast injection in fluoroscopic image sequences based on the training volumes and the extracted features for the training volumes.