Methodology on quantification of sonication duration for safe application of MR guided focused ultrasound for liver tumour ablation

Abstract Background and objective Magnetic Resonance Guided Focused Ultrasound (MRgFUS) for liver tumour ablation is a challenging task due to motion caused by breathing and occlusion due the ribcage between the transducer and the tumour. To overcome these challenges, a novel system for liver tumour ablation during free breathing has been designed. Methods The novel TRANS-FUSIMO Treatment System (TTS, EUFP7) interacts with a Magnetic Resonance (MR) scanner and a focused ultrasound transducer to sonicateto a moving target in liver. To meet the requirements of ISO 13485; a quality management systemfor medical device design, the system needs to be tested for certain process parameters. The duration of sonicationand, the delay after the sonicationbutton is activated, are among the parameters that need to be quantified for efficient and safe ablation of tumour tissue. A novel methodology is developed to quantify these process parameters. A computerised scope is programmed in LabVIEW to collect data via hydrophone; where the coordinates of fiber-optic sensorassembly was fed into the TRANS-FUSIMO treatment software via Magnetic Resonance Imaging (MRI) to sonicateto the tip of the sensor, which is synchronised with the clock of the scope, embedded in a degassed water tank via sensor assembly holder. The sonicationswere executed for 50 W, 100 W, 150 W for 10 s to quantify the actual sonicationduration and the delay after the emergency stop by two independent operators for thirty times. The deviation of the system from the predefined specs was calculated. Student's- T testwas used to investigate the user dependency. Results The duration of sonicationand the delay after the sonicationwere quantified successfully with the developed method. TTS can sonicatewith a maximum deviation of 0.16 s (Std 0.32) from the planned duration and with a delay of 14 ms (Std 0.14) for the emergency stop. Student's T testsindicate that the results do not depend on operators (p > .05). Conclusion The evidence obtained via this protocol is crucial for translation- of-research into the clinics for safe application of MRgFUS. The developed protocol could be used for system maintenance in compliance with quality systems in clinics for daily quality assurance routines.