Tissue characterisation.

Many attempts have been made in the past 20 years to derive more quantitative information relating to tissue structure from the returned ultrasound beam. The qualitative method of characterising tissue from visual inspection of the image with interpretation of artifacts remains the most successful one. Potential quantitative methods include estimation of: attenuation, speed of sound, acoustic impedance, scattering characteristics, non-linearity of propagation, tissue motion and the specific perfusion patterns detected by the Doppler shift. The authors conclude that only image inspection and Doppler techniques have shown progress toward the concept of telehistology expressed in the 1970s. Further advances in quantitation of the Doppler signals and development of contrast agents appear promising for the future.