Performance optimization of ultrasonic needle actuating device for insertion operation into tissue mimics

Needle insertion with ultrasound actuation has been proven as an effective way to reduce the penetration force and needle deflection within soft tissue, facilitating operational manoeuverability and targeting accuracy in cancer biopsy and regional anaesthesia. In such percutaneous procedures, loading conditions from adjacent soft tissue alter the needle transducer's impedance and cause deterioration of its vibration performance. In this paper, we report the needle transducer's structure and working principle; we investigate the loading effects from tissue mimics on the transducer's resonant impedance and vibration performance; and we show how to enhance the needle transducer's vibration performance through optimization of geometrical dimensions and the electrical driving method. Structural optimization was carried out with different transversal dimensions of the needle. Electrical driving optimization was done by tracking the working resonant frequency and stabilizing the driving signal during operation. Experimental trials confirmed a force reduction of 70.2% with the structural optimization and 73.7% with the electrical driving optimization for the insertion operation into gelatin phantom, compared with a static needle.