1. A method of quantifying a medical image, comprising: acquiring, by a processor in a computing system, regions of interest based on a medical image; filtering, by the processor, sizes of the acquired regions of interest using length scale analysis; classifying, by the processor, the regions of interest whose sizes have been filtered, according to the sizes of the regions of interest; and visualizing, by the processor, the regions of interest whose sizes have been filtered, so that the regions of interest whose sizes have been filtered are distinguished from each other in the medical image according to the sizes of the regions of interest, wherein the classifying comprises: acquiring a first size region from the regions of interest by filtering the sizes of the regions of interest using length scale analysis; eliminating the first size region from the regions of interest; and acquiring a second size region by filtering the regions of interest, from which the first size region has been eliminated, using length scale analysis on a size basis, and wherein the acquiring of the first size region comprises: blurring the regions of interest using a Gaussian LPF; extracting a set of pixels, whose intensity is equal to or higher than a reference value, based on the blurred regions of interest; generating a dilated region based on the set of pixels using a dilation method; and generating the first size region by mapping the dilated region to a region of interest including the set of pixels.