Measurement and simulation of steered acoustic fields generated by a multielement array for therapeutic ultrasound

Abstract

Modelling of fields generated by therapeutic ultrasound arrays can be prone to errors arising from differences from nominal transducer parameters, and variations in relative outputs of array elements when driven under different conditions, especially when simulating steered fields. Here, the effect of element size, element positions, relative source pressure variations, and electrical crosstalk on the accuracy of modelling pressure fields generated by a 555 kHz 32-element ultrasonic array were investigated. For this transducer, errors in pressure amplitude and focal position were respectively reduced from 20% to 4% and 3.3 mm to 1.5 mm using crosstalk prediction, and experimentally determined positions.

Fig. 1

Axial-lateral plane through the measured and simulated geometrically focussed fields. Here, the measured field is the angular spectrum projection of the measured lateral plane (the dashed white line shows the position of the measured plane), and simulation is the simulated field using optimised element size, measured element positions, and crosstalk prediction.

Fig. 2

Lateral (left, middle) and axial (right) line scans passing through the focus of the measured (black line) and simulated fields with four different parameter combinations steered to (a) 0, 0, 100 mm, (b) 20, 0, 80 mm, and (c) 40, 0, 80 mm. (1) Nominal element size and positions, uniform source pressure; (2) optimised size, nominal positions, crosstalk prediction; (3) nominal size, measured positions, uniform source pressure; (4) optimised size, measured positions, crosstalk prediction.