Mild cognitive disorders in patients is often not accompanied by focal changes in brain regions, which significantly complicates the objective assessment of pathology. Therefore, a new approach of quantitative analysis of brain single-photon emission computed tomography is developed. The analysis is based on calculating the average gradient of radioactivity distribution in a brain cross-section along a predetermined direction, as well as on Fourier spectra analysis, which are characterized by "1/f" (flicker noise) type behavior. Pilot clinical study of six patients shows promising prospects of the developed method.