Step-FMCW signaling and target detection for ultrasound imaging systems with conformal transducer arrays

Abstract

This paper presents the use and evaluation of stepped frequency modulated continuous waves (FMCW) in a conformal ultrasound array-based medical imaging system currently in development. Conventional medical ultrasound systems featuring rigid transducer arrays are highly user-dependent and require manual rotation and translation to identify and image landmarks. Conformal ultrasound arrays have a larger aperture that can follow the surface curvature of the body, thereby enabling increased data capture without mechanical scanning. The complexity of image reconstruction in conformal ultrasound necessitates the use of step-FMCW, since it directly captures the frequency space thereby enabling image reconstruction techniques to operate directly on the data, greatly simplifying and allowing for real-time performance. Further, FMCW is advantageous in general since it requires lower peak power and produces better receiver noise characteristics than conventional pulse-echo signaling. In the proposed stepped FMCW signaling, packets of acoustic waves at stepped frequencies are emitted from transducers sequentially. Phase and magnitude information from each transmitter-receiver pair of the array are captured producing the frequency space representation of the conventional A-scan data. The results comprise of simulations and bistatic experimental data produced by the step-FMCW signaling method, and obtained using a multistatic transducer array with a stationary metal target. In experimental verification using, the step- FMCW signaling and processing method gave accurate target detection, thereby demonstrating its viability in a conformal ultrasound array and imaging system.