Background: It has been demonstrated that agar-based gel phantoms can emulate the acoustic parameters of real tissues and are the most commonly used tissue-mimicking materials for high-intensity focused ultrasound applications. The following study presents ultrasonic attenuation measurements of agar-based phantoms with different concentrations of additives (percent of agar, silicon dioxide and evaporated milk) in an effort of matching the material's acoustic property as close as possible to human tissues. Methods: Nine different agar-based phantoms with various amounts of agar, silicon dioxide, and evaporated milk were prepared. Attenuation measurements of the samples were conducted using the through-transmission immersion techniques. Results: The ultrasonic attenuation coefficient of the agar-based phantoms varied in the range of 0.30–1.49 dB/cm-MHz. The attenuation was found to increase in proportion to the concentration of agar and evaporated milk. Silicon dioxide was found to significantly contribute to the attenuation coefficient up to 4% weight to volume (w/v) concentration. Conclusion: The acoustic attenuation coefficient of agar-based phantoms can be adjusted according to the tissue of interest in the range of animal and human tissues by the proper selection of agar, silicon dioxide, and evaporated milk.

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Background A magnetic resonance image (MRI) guided robotic device for focussed ultrasound therapy of prostate cancer (PC) was developed. The device offers movement in 5 degrees of freedom (DOF) and uses a single‐element transducer that operates at 3.2 MHz, has a diameter of 25 mm and focuses at 45 mm. Methods The MRI compatibility of the system was evaluated in a 1.5 T scanner. The ability of the transducer to create lesions was evaluated in laboratory and MRI settings, on ex vivo pork tissue and in vivo rabbit thigh tissue. Results Cavitational and thermal lesions were created on the excised pork tissue. In vivo experiments proved the efficacy of the system in ablating muscle tissue without damaging intervening areas. Conclusions The MRI compatible robotic system can be placed on the table of any commercial MRI scanner up to 7 T. The device has the ability of future use for transrectal focal therapy of PC with the patient in supine position.