Characterisation of ultrasonic transducers used in medical applications and investigation of their effects in phantom tissue

The overall goal of this thesis is to characterize the high intensity focused ultrasound (HIFU) transducers used in medical applications and to investigate the effect in phantom tissue. Two types of HIFU transducers have been characterized by electrical, acoustical and thermal methods. A new method has been presented for measurement of instantaneous input electrical power of HIFU transducers. The aim is to establish a relationship between ultrasonic powers produced due to applied electrical power and measure the effectiveness of HIFU transducers. New ultrasound pressure measurement system has been designed and constructed at TUBİTAK UME Ultrasound Laboratory. System consists of a water tank, positioning system, measurement devices and a controlling program. The ultrasound field radiated by HIFU has been investigated by measuring its pressure field and mapping in 2-D and 3-D. A temperature measurement set up in a phantom tissue has been constructed. Two temperature sensors that were produced at TÜBİTAK UME Temperature laboratories were used. Platinum resistance (Pt100) temperature sensors and thin wire thermocouples are embedded into a phantom tissue. Temperature change and temperature distribution have been investigated. Correlations between ultrasonic power, electrical power, ultrasonic pressure and temperature rise have been presented. Theoretical model found in literature and experimental results were compared and an agreement was shown. Theoretical model for ultrasound pressure field was realized by using a KZK (Khokhlov, Zabolotskaya and Kuznetsov) nonlinear parabolic equation and temperature rise in phantom tissue caused by absorption of HIFU energy is often described using Pennes' bioheat transfer equation.