Optimized Bias Voltage Modulation Sequence for cMUT and Nonlinear Contrast Imaging

Abstract

Rationale and aim: In the field of ultrasonic contrast agent imaging, Capacitive Micromachined Ultrasonic Transducer (cMUT) are of great interest because of their wide frequency bandwidth. However, due to their intrinsic nonlinear behaviour, their use with classical nonlinear imaging techniques (pulse inversion, amplitude modulation, harmonic imaging..) is still limited. Different approaches have been proposed to suppress the nonlinear part of the emitting signal from a cMUT. Recently, a new imaging sequence called Bias Voltage Modulation (BVM) has shown very good potential but is limited to the conventional regime of the probe (well below the collapse voltage). Thus the probe's sensitivity is not optimized. Materials and methodsAn improved version of the BVM sequences is proposed to allow the use of bias voltages close to the collapse voltage. The principle is to change the coefficients associated with the successive pulses of the sequence. Experiments have been performed using a 128-element cMUT probe connected to an open scanner. For microbubbles measurements, Sonovue contrast agents have been imaged through a flow phantom. A contrast to tissue ratio (CTR) and a signal to noise ratio (SNR) were calculated to assess the efficacy of the new approach. ResultsThe application of BVM sequence with new coefficients show an increase of the CTR of 19dB at high bias voltage (90% of the collapse) compared to the classical BVM sequence. Due to the high sensitivity of the probe in this regime, the SNR is also increased by 9dB. These results reveal that the BVM sequence can be optimized further and applied at bias voltage close to the collapse and thus fully exploit the potential of the cMUT technology for contrast agent imaging.