Imaging with concave large-aperture therapeutic ultrasound arrays using conventional synthetic-aperture beamforming

Yayun Wan, Emad S Ebbini

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


Several dual-mode ultrasound array (DMUA) systems are being investigated for potential use in image-guided surgery. In therapeutic mode, DMUAs generate pulsed or continuous-wave (CW) high-intensity focused ultrasound (HIFU) beams capable of generating localized therapeutic effects within the focal volume. In imaging mode, pulse-echo data can be collected from the DMUA elements to obtain B-mode images or other forms of feed-back on the state of the target tissue before, during, and after the application of the therapeutic HIFU beam. Therapeutic and technological constraints give rise to special characteristics of therapeutic arrays. Specifically, DMUAs have concave apertures with low f-number values and are typically coarsely sampled using directive elements. These characteristics necessitate pre- and post-beamforming signal processing of echo data to improve the spatial and contrast resolution and maximize the image uniformity within the imaging field of view (IxFOV). We have recently developed and experimentally validated beamforming algorithms for concave large-aperture DMUAs with directive elements. Experimental validation was performed using a 1 MHz, 64-element, concave spherical aperture with 100 mm radius of curvature. The aperture was sampled in the lateral direction using elongated elements 1 - λ × 33.3̄ - λ with 1.333̄ - λ center-to-center spacing (λ is the wavelength). This resulted in f-number values of 0.8 and 2 in the azimuth and elevation directions, respectively. In this paper, we present a new DMUA design approach based on different sampling of the shared concave aperture to improve image quality while maintaining therapeutic performance. A pulse-wave (PW) simulation model using a modified version of the Field II program is used in this study. The model is used in generating pulse-echo data for synthetic-aperture (SA) beamforming for forming images of a variety of targets, e.g., wire arrays and speckle-generating cyst phantoms. To provide validation for the simulation model and illustrate the improvements in image quality, we show SA images of similar targets using pulse-echo data acquired experimentally using our existing 64-element prototype. The PW simulation model is used to investigate the effect of transducer bandwidth as well as finer sampling of the concave DMUA aperture on the image quality. The results show that modest increases in the sampling density and transducer bandwidth result in significant improvement in spatial and contrast resolutions in addition to extending the DMUA IxFOV.

Original languageEnglish (US)
Article number4589185
Pages (from-to)1705-1718
Number of pages14
JournalIEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
Issue number8
StatePublished - Aug 2008

Bibliographical note

Funding Information:
Manuscript received March 15, 2007; accepted February 23, 2008. Funded in part by Grant EB8191 from the National Institutes of Health. Parts of this work were funded by Grant CA66602 from the National Institutes of Health and Grant DAMD 17-01-1-0330, U.S. Army Medical Research and Materiel Command. The authors are with the Department of Electrical and Computer Engineering, University of Minnesota–Twin Cities (e-mail: Digital Object Identifier 10.1109/TUFFC.2008.856


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