Intracardiac ultrasound scanner using a micromachine (MEMS) actuator

Abstract

Catheter-based intracardiac ultrasound offers the potential for improved guidance of interventional cardiac procedures. The objective of this research is the development of catheter-based mechanical sector scanners incorporating high frequency ultrasound transducers operating at frequencies up to 20 MHz. The authors' current transducer assembly consists of a single 1.75 mm by 1.75 mm, 20 MHz, PZT element mounted on a 2 mm by 2 mm square, 75 mum thick polyimide table that pivots on 3-mum thick gold plated polyimide hinges. The hinges also serve as the electrical connections to the transducer. This table-mounted transducer is tilted using a miniature linear actuator to produce a sector scan. This linear actuator is an integrated force array (IFA), which is an example of a micromachine, i.e., a microelectromechanical system (MEMS). The IFA is a thin (2.2 mum) polyimide membrane, which consists of a network of hundreds of thousands of micron scale deformable capacitors made from pairs of metallized polyimide plates. IFAs contract with an applied voltage of 30-120 V and have been shown to produce strains as large as 20% and forces of up to 8 dynes. The prototype transducer and actuator assembly was fabricated and interfaced with a GagePCI analog to digital conversion board digitizing 12 bit samples at a rate of 100 MSamples/second housed in a personal computer to create a single channel ultrasound scanner. The deflection of the table transducer in a low viscosity insulating fluid (HFE 7100, 3M) is up to +/-10 degrees at scan rates of 10-60 Hz. Software has been developed to produce real-time sector scans on the PC monitor.

A micromachine high frequency ultrasound scanner using photolithographic fabrication

“…These results then were used to determine the thickness of an equivalent polyimide beam. The hinges then were evalu- ated in a manner similar to that derived in [13]. Once an approximate thickness, d, 4.86 pm, was determined, thc flexural stiffness, B I , of a single material beam was detcrmined by (1); and (2) was used to determine the spring constant, k , of the beam:…”

“…The 20 MHz and 30 MHz dcvices were used to image wire phantoms in a tank of fluid. The devices were interfaced with the single channel high frequency ultrasound system designed on a personal computer (PC) platform previously described in [13]. The geometry of the imaging setup, in addition to the spacing of the wires, allowed us to measure the sector angle.…”

“…We have previously described the development of a handcrafted prototype single-channel scanncr that used a micromachine (MEMS) actuator to steer a high frequency PZT piston transducer [13]. These prototype devices produced real-timc iniages of wire phantoms with sector scan angles up to 10" but were difficult to fabricate.…”

Synthetic muscle actuators: applications in ultrasonic imaging and optical beam steering

“…We have previously described a prototype high frequency ultrasound scanner that utilizes the IFA in order to tilt an ultrasound transducer to produce a sector scan [7]. The device consists of a 20 MHz PZT piston mounted on a 75 µm thick polyimide table that pivots on 3 µm gold plated polyimide hinges which also serve as the electrical connections for the transducer.…”

Microfabricated Instruments for Fetal Cardiac Surgery: Experiments on Haptic Tissue Recognition

“…In other interventions the surgeon, assisted by ultrasound imaging, could reach the right ventricle by means of a commercial radiofrequency (RF) catheter. Afterward, when the information provided by ultrasound images show the correctness of catheter positioning with respect to the obstructed valve, the surgeon perforates it by activating the RF device [20,18]. Not all the interventions performed by the above stated procedure have been completed successfully because the surgeon has great difficulties in correctly identifying the position of the obstructed valve inside the fetus heart.…”