Figure 5b. Color Doppler images show the effects of the transmit focal zone location on acoustic emission in woodchuck liver. (a) With a 12-mm-deep focal zone, acoustic emission signals in the anterior portion of the normal liver parenchyma demarcate the anterior border of a hepatoma (arrowheads). (b) With the color box and focal zone placed deeper (ie, at 20 mm), acoustic emission signals occur in the posterior region of the liver. The posterior border of the tumor (arrowheads) is delineated.