Design And Development Of An Internal Motorized Intravascular Ultrasound (IVUS) Probe

Over the past decades,there has been a considerable progress in researching the cardiovascular disease,and many imaging techniques were developed for the diagnosis and treatment of the heart diseases.Catheter-based intravascular ultrasound(IVUS)imaging combines noninvasive ultrasonic diagnosis and minimally invasive catheter intervention,which uses a miniature high-frequency ultrasonic transducer disposed at the end of a coronary catheter to transmit and receive high-frequency ultrasound signal,achieving the real-time cross-sectional imaging of the coronary artery by mechanical rotating or electronic scanning.However,the current intravascular ultrasound catheter uses an outer motor and a flexible drive shaft transmitting rotational motion,and the image obtained is easy to distort due to non-uniform rotation through the bending vessel segment,which is mainly caused by the frictional force between the flexible drive shaft and catheter wall.A micro motor placed in the end of the catheter could be a feasible solution as an alternative to the flexible drive shaft.The micro motor rotates directly an ultrasonic transducer or a miniature reflecting mirror instead of transmitting rotational motion,reducing the image distortion.This study presents a design of rotational IVUS probe using a micro electromagnetic motor as the actuator for IVUS imaging,which rotates directly a miniature high-frequency ultrasonic transducer realizing ultrasound beam scanning.We present the design,fabrication and characterization of the ultrasonic transducer and the actuator of the rotational IVUS probe,respectively.We optimally designed the structure of the miniature high-frequency ultrasonic transducer based on PZT-5H ceramic material using the finite element simulation.The prototype of the 46 MHz miniature high-frequency ultrasonic transducer has the-6 dB fractional bandwidth of 47 % and the insertion loss of 15 dB,which shows the superior sensitivity.We present a micro electromagnetic motor as the actuator for IVUS imaging.The prototype micro electromagnetic motor with a size of 1.5 mm outer diameter and 6.0 mm length was fabricated.The micro motor consists of two single-strand flexible coils as the stator and a two-pole permanent magnet as the rotor.We measured the rotational speed of the micro electromagnetic motor by using a hall sensor.The micro motor can generate a largely uniform rotational speed needed for real-time IVUS imaging.A maximum stable speed of 16800 revolutions per minute was achieved with 1.1 V p-p driving voltage.We estimated the driving torque of the micro electromagnetic motor using static electromagnetic simulation of the micro motor model.The micro motor can generate a torque of 13 μNm approximately with 1.0A effective driving current,which shows the superior driving capability.Based on the ultrasonic transducer and the actuator,we perform the preliminary integrated packaging of the rotational IVUS probe.The ionic liquid is proposed as the electrical and acoustic coupling medium of the rotational IVUS probe.We evaluated the electrical and acoustic coupling properties of the ionic liquid.The result verified the feasibility of the rotational IVUS probe design.