Methodology previously used to quantitatively analyze HIFU was adopted to assess therapeutic ultrasound devices.10,11 A useful metric is the fractional beamwidth, which measures the width of a cross section of the beam, counting all points in that cross section which are above a percentage of the peak LII. Consider, for example, the beam width at 80% of the peak of LII, measured at a depth of 3cm, which is 1.3cm, as shown in figure 1. One can therefore state that at z equals 3cm, a 1.3-cm wide cross section contains the points that are within the highest 80% of the peak LII of the entire beam. Similarly, 40% LII refers to the beam width that contains the intensities within the highest 40% of the peak LII field. Seven beam-width measurements were performed at 1-cm increments along the z axis