Preliminary ex vivo feasibility study on targeted cell surgery by high intensity focused ultrasound (HIFU)

High intensity focused ultrasound (HIFU) has become a new noninvasive surgical modality in medicine. A portion of tissue seated inside a patient’s body may experience coagulative necrosis after a few seconds of insonification by high intensity focused ultrasound (US) generated by an extracorporeal focusing US transducer. The region of tissue affected by coagulative necrosis (CN) usually has an ellipsoidal shape when the thermal effect due to US absorption plays the dominant role. Its long and short axes are parallel and perpendicular to the US propagation direction respectively. It was shown by numerical computations using a nonlinear Gaussian beams model to describe the sound field in a focal zone and ex vivo experiments that the dimension of the short and long axes of the tissue which experiences CN can be as small as 50 μm and 250 μm respectively after one second exposure of US pulse (the spatial and pulse average acoustic power is on the order of tens of Watts and the local acoustic spatial and temporal pulse averaged intensity is on the order of 3×104Wcm2) generated by a 1.6 MHz HIFU transducer of 12 cm diameter and 11 cm geometric focal length (f-number = 0.92). The concept of thermal dose of cumulative equivalent minutes was used to describe the possible tissue coagulative necrosis generated by HIFU. The numbers of cells which suffered CN were estimated to be on the order of 40. This result suggests that HIFU is able to interact with tens of cells at/near its focal zone while keeping the neighboring cells minimally affected, and thus the targeted cell surgery may be achievable.

Research highlights
► Numerical computations using a nonlinear Gaussian beams model predicts temperature rise at focal zone of a high intensity focused ultrasound (HIFU).
► The cumulative equivalent minutes thermal dose was used to describe the possible tissue coagulative necrosis generated by HIFU.
► Ex vivo experimental results using fresh bovine livers demonstrate HIFU beam can interact with individual cells.