Characterizing the steering performance of a diagnostic-therapeutic ultrasound array using measured and synthesized holograms

Acoustic holography is frequently used for the characterization of fields generated by ultrasound transducers. For arrays with electronic focusing and beam steering, separate holograms are needed to represent the 3D field for each combination of array parameters. In this paper, we show that holograms for the field generated by each individual element in an ultrasound array can be recorded in a single hydrophone scan, by interleaving a series of excitations at each measurement location in which each element is driven separately. Such holograms were recorded for a 64-element diagnostic-therapeutic linear array with a nominal focal length of 50 mm and pitch of 0.8 mm, which is smaller than the wavelength at the operating frequency of 1.05 MHz. The resulting holograms reveal aspects of crosstalk and variations between array elements. By summing the elemental holograms with the appropriate phase shifts, holograms are synthesized representing source conditions for cases where the entire array is used to generate different beam configurations, with focal lengths between 35 mm and 60 mm, and steering angles of up to 20°. These synthetic holograms are shown to accurately characterize non-ideal steering behavior of the transducer, confirmed through direct hydrophone measurements. [Work supported by NIH grants R01EB023910 and R01EB025187.]