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Beamforming is a signal processing technique used with arrays of transducers that control the directionality of -- or sensitivity to -- radiation patterns. While beamforming algorithms have been used in ultrasound scanners for nearly 50 years, they typically result in degraded images that are blurry or cluttered. Why? Because of off-axis signals -- the sound wave reflections coming from undesired locations within the organ or tissue.

Led by Associate Professor Wiliam F. Walker, biomedical engineers at the University of Virginia School of Engineering and Applied Science have come up with an improved beamforming algorithm -- called the Time-domain Optimized Near-field Estimator (TONE) -- which improves the contrast and resolution of ultrasound images.

"The potential applications for this algorithm are almost infinite," said James H. Aylor, dean of U.Va.'s School of Engineering and Applied Science. "Not only can it be used in the medical community to benefit patients nationwide, it will have applications in the fields of radio astronomy, seismology and more."

The TONE algorithm reduces undesired off-axis signals, resulting in higher definition images, but at the price of a much greater computational load. Developed on desktop PCs, the algorithm overwhelmed the PC's processing capability. The team addressed this problem by implementing the algorithms in MATLAB, then parallelizing them with Star-P (an interactive parallel computing platform from Interactive Supercomputing) to run interactively on a 32-processor Linux cluster with 64 gigabytes of memory.

"For almost four decades, beamforming algorithms have been refined for RADAR and SONAR," said Walker. "While these algorithms are tremendously powerful, they don't generally translate well to medical ultrasound imaging."

When screening for breast cancer or diagnosing other life threatening conditions using ultrasound technology, it is imperative that images are well-defined. Even so, clinical imaging specialists know that many patients simply "image poorly" -- that is, images of their organs and tissues remain unclear.

"Off-axis signals — reflections coming from undesired locations — degrade images produced by current ultrasound systems" said Research Associate Francesco Viola. "TONE reduces the contribution of these unwanted signals, thereby forming images with greatly increased contrast and resolution."

The team performed a series of simulations using sample ultrasound data to test the performance of this algorithm and compared it to conventional beamforming strategies (CBF) used by current ultrasound scanners. Imaging trials were conducted using wires suspended in water, a typical set up to test image resolution and contrast in medical ultrasound. The results show a significant improvement in spatial resolution over CBF.

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