A method of estimating the viscoelasticity of a material using ultrasound, the method comprising: - receiving a plurality of time-amplitude curves measured at a plurality of space points, wherein said time-amplitude curves reflect time evolutions of a propagating mechanical wave, the propagating mechanical wave being a shear wave generated by application of ultrasound; - estimating the viscoelasticity of a material between any set of space points using the time-amplitude curves measured at those space points, - wherein the step of estimating the viscoelasticity comprises: ∘ determining a model to describe the response of the material between said space points to a mechanical wave, and ∘ obtaining model parameters of the model using system identification, wherein the system identification is based on maximum likelihood or least-squares impulse response fitting; and - estimating an impulse response for the system identification by: o defining a time-amplitude curve measured at a space point as an input time-amplitude curve; o defining a time-amplitude curve measured at another space point as an output time-amplitude curve; o defining the impulse response that describes the relation between the input time-amplitude curve and the output time-amplitude curve; and o estimating the impulse response from the input time-amplitude curve and the output time-amplitude curve. - receiving a plurality of time-amplitude curves measured at a plurality of space points, wherein said time-amplitude curves reflect time evolutions of a propagating mechanical wave, the propagating mechanical wave being a shear wave generated by application of ultrasound; - estimating the viscoelasticity of a material between any set of space points using the time-amplitude curves measured at those space points, - wherein the step of estimating the viscoelasticity comprises: ∘ determining a model to describe the response of the material between said space points to a mechanical wave, and ∘ obtaining model parameters of the model using system identification, wherein the system identification is based on maximum likelihood or least-squares impulse response fitting; and ∘ determining a model to describe the response of the material between said space points to a mechanical wave, and ∘ obtaining model parameters of the model using system identification, wherein the system identification is based on maximum likelihood or least-squares impulse response fitting; and - estimating an impulse response for the system identification by: o defining a time-amplitude curve measured at a space point as an input time-amplitude curve; o defining a time-amplitude curve measured at another space point as an output time-amplitude curve; o defining the impulse response that describes the relation between the input time-amplitude curve and the output time-amplitude curve; and o estimating the impulse response from the input time-amplitude curve and the output time-amplitude curve. o defining a time-amplitude curve measured at a space point as an input time-amplitude curve; o defining a time-amplitude curve measured at another space point as an output time-amplitude curve; o defining the impulse response that describes the relation between the input time-amplitude curve and the output time-amplitude curve; and o estimating the impulse response from the input time-amplitude curve and the output time-amplitude curve. <EOS>