1. A method for evaluating medical image data comprising: providing a first medical image dataset of an organ system of an examination subject to a computer, said organ system having a first side and a second side that are characteristically bilaterally symmetrical with respect to each other, said first medical image dataset comprising first medical image data comprising first image components; providing said computer with a second medical image dataset of said organ system, said second medical image dataset comprising second medical image data comprising second image components; in said computer, processing said first medical image dataset and said second medical image dataset in a processing algorithm to obtain a result image by, in said processing algorithm, executing a global image data subtraction wherein said first image components of said first medical image data and said second image components of said second medical image data are subtracted from one another in order to obtain a global image data subtraction image dataset, and thereafter executing a symmetry subtraction, within said global image subtraction data set, in which symmetry subtraction image components of the first side and the second side of the organ system are subtracted from one another; and making said result image dataset available in electronic form from said computer as a data file.