for at least one operating frequency, measuring, with a plurality of pairs of non-colocalized elastic wave sensors comprising transmitting sensors and receiving sensors, a plurality of signals propagating in the structure, the measured signals being arranged in a measurement matrix having dimensions equal to a number of transmitting sensors by a number of receiving sensors,

determining a plurality of propagation modes guided by the structure, correcting the measured signals based on ultrasound signals measured or simulated for the same structure in the absence of any defect,

converting the measurement matrix into a wave field scattering matrix U,

determining, at each point of a sampling grid, a test vector F defining the structure without any defect, the components of the test vector F being the projections of a Green tensor from the defect-free domain onto the transverse functions of the guided propagation modes,

applying a numerical inversion method to determine a vector H of modal components such that U.H=F at each point of a sampling grid,

determining an image of the structure based on the vector H, and

displaying the image on a screen.