Calibration of Field II using a convex ultrasound transducer

Abstract

Field II is an ultrasound simulation program capable of simulating the pressure scattering from inhomogeneous tissue. The simulations are based on a convolution between spatial impulse responses from the field in front of the transducer and the volt-to-surface acceleration impulse response of the transducer. For such simulations to reflect actual measured intensities and pressure levels, the transducer impulse response is to be known. This work presents results of combining a modified form of a 1D linear transducer model originally suggested by Willatzen together with the Field II program to calibrate the pressure and intensity simulations of a 128 element convex medical transducer with elevation focus at 70 mm. The simulations are compared to pressure measurements from a transducer driven at 4.0 MHz using a research scanner with a commercial transducer amplifier from BK Medical (Herlev, Denmark). As input waveform to the Field II model we measured the output voltage of the research amplifier. The peak voltage was limited to 31 V to avoid too high non-linear effects. We measured the hydrophone output from three transducer front elements by averaging 40 shoot sequences on each element using a remotely controlled Agilent MSO6014A oscilloscope. The pressure along the center line in a distance of 33 mm, 72 mm, and 112 mm from each element was measured as well as the intensity in the elevation plane in each depth.Results show that the 1D modeling of the linear transducer impulse response predicts the pulse waveforms satisfying. We show a root mean square error of approximately 26% on the pressure prediction and a root mean square error on the intensity prediction from 5.8–16.2% from 72 mm to 112 mm, and an average of 15.4% at 33 mm, when a 1.7 dB amplitude correction is made.