| High intensity focused ultrasound (HIFU) is a noninvasive treatment technique developing rapidly nowadays. The focusing performance and dosage of HIFU are closely related to safety, effectiveness, and stability of treatment. The project is aimed to explore the feasibility in transducer performance evaluation, and HIFU treatment dosage measurements, with adoption of a temperature sensitive smart hydrogel as a smart ultrasound phantom to control its volume phase-transition temperature, test its acoustic and thermodynamic parameters, and preliminarily inspect the HIFU performance .P(NIPA-co-AA)[Poly(N-isopropylacrylamide-co-acrylamide)] hydro- gel is a kind of copolymer hydrogel which is sensitive to temperature variability. As the Molar ratio of Acrylamide(AAm) and N-isopropylacry- lamide (NIPA) within is directly interrelated with lower critical solution temperature (LCST), as mentioned above volume phase-transition temperature. An optimal method for the making of tissue-mimicking phantoms has been found through the test of LCST synthesized of different ratio of AAm and NIPA. By comparing with water ,the Density of this intelligent phantom is detected; by inserting pulse propagation,the Speed of sound is oberserved , then the acoustic impedance can be calculated;and by radiation pressuring, the sound attenuation coefficient is obtained . During the test of thermal properties, the measurement of specific heat (Differential Scanning Calorimetry, DSC) and thermal conductivity (tempering wire)can help to determine the level of similarity between this smart phantom and human tissue. In the subsequent observation of the performance of focused ultrasound, formation of visible focal region in intelligent phantom and the point irradiance from HIFU,the change rules of long axis and minor axis ratio, as well as the rule of vanishment of focal region with time are detected. Furthermore, the relationship between power increasement and volume of visible focal region can be analyzed through the point irradiance from focused ultrasound.Through the experiment mentioned above, we've discovered the regulation of AAm/NIPA(M/M) and smart phantoms. When AAm/NIPA(M/M) is 0.41, the phase-transition temperature of smatr phantom is 61℃,and the appearance is colorless, smooth and elastic. And the internal is slim without foam. Various parameters of smart phantom are shown as follows: density is 1.03±0.02 g/cm3, acoustic velocity is 1559±9 m/s, sound attenuation coefficien is 12±3 dB/m (1MHz) . Also, the specific heat and thermal conductivity is very close to water. All this measured acoustical and thermal properties suggest smart phantom suitable as a tissue mimicing materials. When smart phantom is radiated by HIFU , the elliptical focal region can be exhibited clearly in the phantom. The contrast spot is not transparent but white and ellipsoideus, the visual focal region's volume and shape are related to radiation dose as well.Results of this research showed that this kind of smart phantom can be applied in the evaluation of focusing performance of the focused ultrasound transducer. We can adopt the parameters of shape and volume of visible focal region generated in the smart phantom as the mode of calculating of focused ultrasound doses, such as HIFU. In the subsequent research, we will further explore the combination of biological tissue of multi -phase and multi-layer as the medium. Smart phantoms will play an important role in various aspects, such as the observation of efficiency of focused ultrasound, research of focused ultrasound treatment dose and focal region, as well as standard establishment and clinical application, etc.
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