Benefits of minimum-variance beamforming in medical ultrasound imaging

Abstract

Recently, significant improvement in image resolution has been demonstrated by applying adaptive beamforming to medical ultrasound imaging. In this paper, we have used the minimum-variance beamformer to show how the low sidelobe levels and narrow beamwidth of adaptive methods can be used, not only to increase resolution, but also to enhance imaging in several ways. By using a minimum-variance beamformer instead of delay-and-sum on reception, reduced aperture, higher frame rates, or increased depth of penetration can be achieved without sacrificing image quality. We demonstrate comparable resolution on images of wire targets and a cyst phantom obtained with a 96-element, 18.5-mm transducer using delay-and-sum, and a 48-element, 9.25-mm transducer using minimum variance. To increase frame rate, fewer and wider transmit beams in combination with several parallel receive beams may be used. We show comparable resolution to delay-and-sum using minimum variance, 1/4th of the number of transmit beams and 4 parallel receive beams, potentially increasing the frame rate by 4. Finally, we show that by lowering the frequency of the transmitted beam and beamforming the received data with the minimum variance beamformer, increased depth of penetration is achieved without sacrificing lateral resolution.

Forward-backward generalized sidelobe canceler beamforming applied to medical ultrasound imaging

“…8 In order to describe more conveniently, some variables will be redefined. For a linear array of M elements, the output of beamformer is given by 17…”

“…For medical ultrasound imaging, adaptive beamforming was first introduced by Capon. 5 Nowadays, most common adaptive beamforming is minimum variance (MV), [6][7][8][9] In order to improve the stability of adaptive beamforming, Johan-Fredrik Synnevåg 10 put forward diagonal loading (DL) to ultrasound imaging, and J. E Evans 11 proposed subaperture averaging algorithm to solve the coherence of ultrasound echo.…”

Capon Beamforming for Active Ultrasound Imaging Systems

“…This may also enable new imaging applications. Other examples can be found in [13] which also gives examples of how high spatial resolution can be traded for higher frame rates, which may be important for imaging fast-moving structures like the cardiac valves.…”

“…Right now there is a large interest in the field of medical ultrasound imaging [2][3][4][5], but also in synthetic aperture radar [6] and sonar [7]. Our group has applied high resolution methods to active sonar [8] and medical ultrasound [9][10][11][12][13][14] with significant improvement in image resolution.…”

“…In medical ultrasound, images must be formed at a frequency of up to [10][11][12][13][14][15] MHz from hundreds of elements at frame rates up to several hundred per second, and with several hundred lines per image. Since the early 90's there has been a transition from analog to digital beamforming, and more recently also to 3-D systems that acquire data from 2-D arrays with thousands of elements.…”