1. A diagnosis assisting apparatus, comprising: one or more processors configured to: obtain a plurality of sets of volume data imaged by one or more imaging modalities, each of which represent the state of a beating heart of a single patient in different phases in one cardiac cycle; extract a plurality of coronary artery regions from at least two sets of volume data from among the obtained sets of volume data; set a plurality of analysis points at the same anatomical positions in each of the extracted coronary artery regions, which have been extracted from the at least two sets of volume data representing the state of the heart of the single patient at different phases, and establish correlations among the plurality of analysis points, which are set at the same anatomical positions among each of the coronary artery regions; calculate index values that indicate a character of plaque at each of the plurality of analysis points that have been set within each of the plurality of coronary artery regions; evaluate the index values, by integrating the index values, which are calculated at the plurality of analysis points that have been set in each of the coronary artery regions, by performing weighted calculations on the index values; and output the evaluated index values correlated with information regarding the anatomical positions.