Figure 3.

If the US beam passes through a low-attenuating structure, the signals reflected from the deep structure increase in relation to the surrounding tissues (A). The areas deep to a Baker’s cyst (B) and a complete tear of the supraspinatus tendon (C) become hyperechoic because of the posterior acoustic enhancement (and discrepancy of the acoustic impedance between two different tissues). White arrow: artifact due to posterior acoustic enhancement; white arrowhead: cartilage interface sign. MG: medial gastrocnemius muscle. Blue arrows: the projected and reflected US beams. Black circle: the low-attenuation structure.