1. Beckman Laser Institute, Department of Biomedical Engineering, University of California, Irvine, Irvine, California 92612, USA
2. Department of Cogno-Mechatronics Engineering, Pusan National University, Busan 609-735, South Korea
3. Department of Biomedical Engineering, NIH Ultrasonic Transducer Resource Center, University of Southern California, Los Angeles, California 90089, USA