Sung Soo Jung

Evaluation of Tissue Mimicking Quality of Tofu for Biomedical Ultrasound

The tissue mimicking quality of tofu has been evaluated in terms of acoustic properties and acousto/thermal conversion as functions of frequency and diffraction corrected intensity over the 2 MHz to 18 MHz range using three unfocussed transducers with center frequencies of 5 MHz, 10 MHz and 15 MHz. The density and acoustic velocity were close to the American Institute of Ultrasound in Medicine (AIUM) recommended values for the soft tissue, however, the attenuation increases nonlinearly with frequency as alpha = 0.56 x f(1.3). As a result, the temperature rise in tofu due to ultrasound absorption is expressed by the product of the acousto/thermal conversion factor and the attenuation/diffraction corrected acoustic intensity. The decrease of temperature rise with depth measured by embedded thermocouples agrees with the theoretical exponential decrease of the attenuation/diffraction corrected acoustic intensity. The heat capacity per unit mass of tofu is 0.76 cal/g degrees C (equivalent to 3.18 J/g degrees C) of which about 76% is water. The nonlinear frequency dependence of attenuation in tofu as f(1.3) correctly describes the frequency dependence of temperature rise. The present results suggest that tofu may only be used in a limited low MHz range in view of the estimation of temperature rise and penetration depth due to nonlinear frequency dependence of attenuation.

RESPONSE OF A 1-3 PIEZOELECTRIC COMPOSITE TRANSDUCER FOR ELASTIC WAVES GENERATED DURING GLASS CAPILLARY BREAKAGE

The 1-3 piezoelectric composite transducer with the 60% volume fraction of the PZT-5A was fabricated by the dicing-filling method. The electrical and acoustical characteristics of the 1-3 piezoelectric composite transducer were compared and analyzed by the electrical impedance measurements and the pulse-echo method. The mechanical quality coefficient (Q) and the resonant frequency were 18.5 and 1.6 MHz, respectively. The elastic waves generated during glass capillary breakage were observed by 1-3 piezoelectric composite transducer. The observed AE signals are well matched with the perpendicular component of the particle velocity calculated by computer. The observed AE signal and its frequency spectrum show that the pulse-type signals of AE observed by 1-3 piezoelectric composite transducer may be depend on the the vibration mode of thickness with the plate response of the wide band.