1. A method for determining a characteristic value for the perfusion of modified tissue regions in organs of living beings, having the following steps: a) determining a first volumetric flow rate of the blood by means of laser flowmetry at a first measurement point within the modified tissue region as a first measurement profile of a volumetric flow rate signal as a function of time; b) determining a second volumetric flow rate of the blood by means of laser flowmetry at a second measurement point within an unmodified tissue region as a second measurement profile of a volumetric flow rate signal as a function of time; c) carrying out a wavelet analysis of each of the measurement profiles as a three-dimensional representation of the signal intensity over a frequency or scaling axis and time; d) determining the profile of a vasomotion energy over the frequency or scaling axis for each of the measurement profiles subjected to the wavelet analysis, the vasomotion energy being the integral of the signal intensity with respect to time for a particular frequency or scaling value; e) subtracting the profile of the vasomotion energy of the second measurement profile from the profile of the vasomotion energy of the first measurement profile, so as to form a first difference profile; f) integrating the difference profile in order to obtain the characteristic value.