1. A medical imaging apparatus comprising: a scanner configured to acquire projection data of an object in a plurality of directions; a display configured to display a sectional image generated based on the projection data; a processor configured to, in response to receiving an input of selecting a region of interest in the displayed sectional image, generate a volume of interest corresponding to the region of interest, generate two-dimensional (2D) reprojection images by reprojecting the volume of interest through maximum value projection in two or more directions, and control the display to display at least one of the 2D reprojection images, wherein the processor is further configured to extract feature information from the 2D reprojection images in which a maximum value in each of the two or more directions is extracted from voxels of the volume of interest, and wherein the processor is further configured to generate a feature vector by fusing the feature information extracted from the 2D reprojection images reprojected in the two or more directions, and determine whether a certain substance exists in the volume of interest based on the generated feature vector.