Method for a non-destructive, non-contacting and image forming examination of a sample by means of a heat flow thermography method where the examination consists of evaluating the presence of any gradients in heat flow velocity of heat flowing in the sample at respective depth distances from a surface of the sample, comprising: exciting the sample by means of periodic heat pulses (P i) from at least one excitation source, and capturing a plurality of thermal image sequences, each thermal image sequence comprising a plurality of images of a surface from which thermal flow originates caused by the heat pulses by at least one infrared camera, implementing different relative time delays Δt between a starting point of imaging of the respective image sequences and a starting point of the periodic excitation, combining all captured image sequences in a way that all images are arranged in a correct time sequence, and extracting from the rearranged image sequence an indication of the existence and depth distance of a heat flow transition from a surface of the sample, characterized in that the sample is excited by applying heat pulses to the sample with a lock-in frequency, an excitation period of the heat pulses is controlled during which the excitation of the sample by means of the heat pulses takes place, and in that the excitation periods of the excitation pulses extend across at least one period of the lock-in frequency, in that off-periods of the excitation pulses between excitation periods extend up to a point of time when an equilibrium condition is reached with respect to the dissipation of the heat applied during the excitation of the sample, and in that thermal image sequences are captured by capturing the plural image sequences during successive excitation periods of the heat pulses with the imaging frequency. exciting the sample by means of periodic heat pulses (P i) from at least one excitation source, and capturing a plurality of thermal image sequences, each thermal image sequence comprising a plurality of images of a surface from which thermal flow originates caused by the heat pulses by at least one infrared camera, implementing different relative time delays Δt between a starting point of imaging of the respective image sequences and a starting point of the periodic excitation, combining all captured image sequences in a way that all images are arranged in a correct time sequence, and extracting from the rearranged image sequence an indication of the existence and depth distance of a heat flow transition from a surface of the sample, characterized in that the sample is excited by applying heat pulses to the sample with a lock-in frequency, an excitation period of the heat pulses is controlled during which the excitation of the sample by means of the heat pulses takes place, and in that the excitation periods of the excitation pulses extend across at least one period of the lock-in frequency, in that off-periods of the excitation pulses between excitation periods extend up to a point of time when an equilibrium condition is reached with respect to the dissipation of the heat applied during the excitation of the sample, and in that thermal image sequences are captured by capturing the plural image sequences during successive excitation periods of the heat pulses with the imaging frequency.