Method for measuring an ultrasound parameter of a viscoelastic medium to be characterized, the method being carried on with an ultrasound system including an ultrasound transducer configured to emit a sequence of ultrasound shots and to receive corresponding echo signals from a region of interest, and a processor programmed to generate, in a first mode of operation, a sequence of ultrasound shots to measure an attenuation of ultrasound signals in a tissue, the method comprising: generating the sequence of ultrasound shots to the region of interest and receiving corresponding first mode echo signals from the region of interest, wherein the sequence of ultrasound shots is generated for a period of time (200, 204) of at least 2 seconds; recording first mode ultrasound attenuation values (α) associated with the received first mode echo signals; and calculating a value (156, 166, 176, 224, 262) of the ultrasound parameter using the first mode ultrasound attenuation values (α); characterized in that the method further comprising processing the first mode ultrasound attenuation values using one or more quality criteria to determine, among the recorded first mode ultrasound attenuation values, ultrasound attenuation values that have a predetermined quality level, and wherein the value of the ultrasound parameter is calculated using first mode ultrasound attenuation values that have the predetermined quality level, wherein the one or more quality criteria include a correlation criterion and wherein the processing includes associating each one of the received first mode echo signals with a correlation coefficient and selecting each of the received first mode echo signal having the correlation coefficient past a predetermined threshold value to determine, among the received first mode echo signals, first mode echo signals that are sufficiently decorrelated. generating the sequence of ultrasound shots to the region of interest and receiving corresponding first mode echo signals from the region of interest, wherein the sequence of ultrasound shots is generated for a period of time (200, 204) of at least 2 seconds; recording first mode ultrasound attenuation values (α) associated with the received first mode echo signals; and calculating a value (156, 166, 176, 224, 262) of the ultrasound parameter using the first mode ultrasound attenuation values (α); characterized in that the method further comprising processing the first mode ultrasound attenuation values using one or more quality criteria to determine, among the recorded first mode ultrasound attenuation values, ultrasound attenuation values that have a predetermined quality level, and wherein the value of the ultrasound parameter is calculated using first mode ultrasound attenuation values that have the predetermined quality level, wherein the one or more quality criteria include a correlation criterion and wherein the processing includes associating each one of the received first mode echo signals with a correlation coefficient and selecting each of the received first mode echo signal having the correlation coefficient past a predetermined threshold value to determine, among the received first mode echo signals, first mode echo signals that are sufficiently decorrelated.