Abstract: The method of the disclosure comprises the stages of injecting an alternating AC signal into at least one electrode positioned on the skin of the patient in a region of interest, measuring the signal induced into at least one electrode, extracting at least an envelope of the signal measured and determining the difference between the envelope and a reference signal. The envelope may be extracted by demodulating the signal measured, and this demodulation may be carried out by way of an associated rectifier diode, in a preferred embodiment, and an RC filter. The reference signal may be an envelope corresponding to the demodulated signal of another electrode, the injected signal, ground or a fixed voltage value.