Abstract
Medical ultrasonic arrays are typically characterized in controlled water baths using measurements by a hydrophone, which can be translated with a positioning stage. Characterization of 3D acoustic fields conventionally requires measurements at each spatial location, which is tedious and time-consuming, and may be prohibitive given limitations of experimental setup (e.g., the bath and stage) and measurement equipment (i.e., the hydrophone). Moreover, with the development of new ultrasound sequences and modalities, multiple measurements are often required to characterize each imaging mode to ensure performance and clinical safety. Acoustic holography allows efficient characterization of source transducer fields based on single plane measurements. In this work, we explore the applicability of a re-radiation method based on the Rayleigh–Sommerfeld integral to medical imaging array characterization. We show that source fields can be reconstructed at single crystal level at wavelength resolution, based on far-field measurements. This is herein presented for three practical application scenarios: for identifying faulty transducer elements; for characterizing acoustic safety parameters in focused ultrasound sequences from 2D planar measurements; and for estimating arbitrary focused fields based on calibration from an unfocused sound field and software beamforming. The results experimentally show that the acquired pressure fields closely match those estimated using our technique.
Highlights
Characterization of medical transducers and the acoustic fields they generate is a common need and standard process, during most development stages of ultrasound equipment and imaging sequences
The characterization of acoustic fields is a crucial step for certification of new ultrasound transducers
Mechanical index (MI) and thermal index (TI) are the two important parameters, where the former characterizes the possibility of cavitation and the latter any potential thermal damage to tissue [3]
Summary
Characterization of medical transducers and the acoustic fields they generate is a common need and standard process, during most development stages of ultrasound equipment and imaging sequences. Characterization of acoustic fields is typically performed with temperature-controlled water bath experiments, where an acoustic recording device (“hydrophone”) is used on a mechanical translation stage to record the time-varying output at many locations of interest in space, while repeating the acoustic transmit at each point Since this is a highly time-consuming process, often a single plane or a small focal area is scanned, and the testing of several transmission parameters becomes prohibitive, most development currently being performed on simulation software. Based on a single unfocused plane wave excitation, the re-radiation method allows (i) to detect faulty elements in the transducer array, (ii) to simulate a focused sound fields, and (iii) to estimate safety indices. We present the practical aspects of our experimental setup, e.g., to avoid fully immersing our ultrasound probe
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