Beam width measurements in low acoustic velocity phantoms.

Analysis of focused ultrasound (US) beams in low acoustic velocity phantoms demonstrates that beam width measurements yield results much larger than comparable measurements in phantoms with the correct acoustic velocity, 1540 m/s. These erroneous beam width measurements are shown to be due to two factors: a refocusing of the beam due to the low acoustic velocity (as compared with the design focus at 1540 m/s) and the necessary repositioning of the wire targets in these phantoms to simulate target depths in US phantoms with the proper acoustic velocity.