In ultrasonic imaging, reduction of lateral sidelobes can result in an improved image with less distortion and fewer artifacts. In general, apodization is used to lower sidelobes in exchange for increasing the width of the mainlobe and thus decreasing lateral resolution. Null subtraction imaging (NSI) is a nonlinear image processing technique that uses different receive apodizations on copies of the same RF data to maintain low sidelobe levels while simultaneously improving lateral resolution. The images created with three different apodization functions are combined to form an image with low sidelobe levels and apparent improvements in lateral resolution compared to conventional rectangular apodization. To evaluate the performance of this technique for different imaging tasks, experiments were performed on an ATS539 phantom containing wire targets to assess lateral resolution and cylindrical anechoic and hyperechoic targets to assess contrast. NSI images were compared against rectangular apodized images and minimum variance (MV) beamformed images. In experiments, the apparent lateral resolution was observed to improve by a factor of more than 35 times when compared to rectangular apodization. Image quality was assessed by estimation of lateral resolution (−6-dB receive beamwidth), mainlobe to sidelobe ratio (MSR) and contrast-to-noise ratio (CNR). Imaging with NSI using a focal number of 2 (f/2), the −6-dB beamwidth on receive as measured from a small wire target in the ATS phantom was 0.03λ compared to 2.79λ for rectangular apodization. Sidelobes were observed to decrease by 32.9 dB with NSI compared to rectangular apodization. However, the ability to observe the contrast of anechoic and hyperechoic targets reduced when utilizing the NSI scheme, i.e., the CNR decreased from −3.05 to −1.01 for anechoic targets and 1.65 to 0.45 for the hyperechoic targets.
Methods for digital, phase-coherent acoustic communication date to at least the work of Stojanjovic, et al [20], and the added robustness afforded by improved phase tracking and compensation of Johnson, et al [21]. This work explores the use of such methods for communications through tissue for potential biomedical applications, using the tremendous bandwidth available in commercial medical ultrasound transducers. While long-range ocean acoustic experiments have been at rates of under 100kbps, typically on the order of 1-10kbps, data rates in excess of 120Mb/s have been achieved over cm-scale distances in ultrasonic testbeds [19]. This paper describes experimental transmission of digital communication signals through samples of real pork tissue and beef liver, achieving data rates of 20-30Mbps, demonstrating the possibility of real-time video-rate data transmission through tissue for inbody ultrasonic communications with implanted medical devices.
Pulse-echo reconstruction of sound speed has long been considered a difficult problem within the domain of quantitative biomedical ultrasound. However, recent results (Jaeger 2015 Ultrasound
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