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.

Background: A robotic system for Magnetic Resonance guided Focussed Ultrasound (MRgFUS) therapy of tumours in the breast, bone, thyroid, and abdomen was developed.Methods: A special C-shaped structure was designed to be attached to the table of conventional magnetic resonance imaging (MRI) systems carrying 4 computercontrolled motion stages dedicated to positioning a 2.75 MHz spherically focussed transducer relative to a patient placed in the supine position. The developed system was evaluated for its MRI compatibility and heating abilities in agar-based phantoms and freshly excised tissue.Results: Compatibility of the system with a clinical high-field MRI scanner was demonstrated. FUS heating in the phantom was successfully monitored by magnetic resonance thermometry without any evidence of magnetically induced phenomena.Cigar-shaped discrete lesions and well-defined areas of overlapping lesions were inflicted in excised tissue by robotic movement along grid patterns. Conclusions:The developed MRgFUS robotic system was proven safe and efficient by ex-vivo feasibility studies.

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.

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Background: A prototype robotic system that uses magnetic resonance guided focused ultrasound (MRgFUS) technology is presented. It features three degrees of freedom (DOF) and is intended for thermal ablation of abdominal cancer. Methods:The device is equipped with three identical transducers being offset between them, thus focussing at different depths in tissue. The efficacy and safety of the system in ablating rabbit liver and kidney was assessed, both in laboratory and magnetic resonance imaging (MRI) conditions.Results: Despite these organs' challenging location, in situ coagulative necrosis of a tissue area was achieved. Heating of abdominal organs in rabbit was successfully monitored with MR thermometry. Conclusions:The MRgFUS system was proven successful in creating lesions in the abdominal area of rabbits. The outcomes of the study are promising for future translation of the technology to the clinic.