Width-modulated square-wave pulses for ultrasound applications

Abstract

Abstract-A method of output pressure control for ultrasound transducers using switched excitation is described. The method generates width-modulated, square-wave pulse sequences that are suitable for driving ultrasound transducers using MOSFET devices or similar. Sequences are encoded using an optimized level-shifted, carrier-comparison, pulse-width modulation (PWM) strategy derived from existing PWM theory, and modified specifically for ultrasound applications. These modifications are: a reduction in carrier frequency so that the least amount of pulses are generated and minimal switching is necessary; alteration of a linear carrier form to follow a trigonometric relationship in accordance with the expected fundamental output; and application of frequency modulation to the carrier when generating frequency modulated, amplitude tapered signals.The PWM method permits control of output pressure for arbitrary waveform sequences at diagnostic frequencies (approximately 5 MHz) when sampled at 100 MHz, and is applicable to pulse shaping and array apodization. Arbitrary waveform generation capability is demonstrated in simulation using convolution with a transducer's impulse response, and experimentally with hydrophone measurement. Benefits in coded imaging are demonstrated when compared with fixed-width square-wave (pseudo-chirp) excitation in coded imaging, including reduction in image artifacts and peak sidelobe levels for two cases, showing 10 dB and 8 dB reduction in peak sidelobe level experimentally, compared to 11 dB and 7 dB reduction in simulation with the Field II package. In all cases the experimental observations correlate strongly with simulated data.

Increasing the sonoporation efficiency of targeted polydisperse microbubble populations using chirp excitation

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“…This component operates in a switched-mode, generating square-wave 'pseudo-chirps'. A novel pulse width-modulation technique has been developed to provide output amplitude pressure control from the switched-mode system [58]. This technique allows arbitrary waveforms to be generated from the transducer, whilst maintaining the simplicity of switched-mode circuits.…”

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“…Ultrasound array research platform II (UARPII), developed by Ultrasound Group, University of Leeds was used for the RF data acquisition [11], [12]. The 128 element L3-8/40EP (Prosonic Co., Ltd, Korea) medical probe with centre frequency of 4.79 MHz was used for shear wave generation and tracking.…”

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“…Arbitrary excitation can be emulated using switched mode excitation in conjunction with harmonic reduction pulse width modulation (HRPWM) [12][13][14][15][16] allowing excitation parameters to be tailored to the measurement, for example frequency modulation, amplitude control and temporal windowing.…”