Sequential beamforming for synthetic aperture imaging

Abstract

a b s t r a c tSynthetic aperture sequential beamforming (SASB) is a novel technique which allows to implement synthetic aperture beamforming on a system with a restricted complexity, and without storing RF-data. The objective is to improve lateral resolution and obtain a more depth independent resolution compared to conventional ultrasound imaging. SASB is a two-stage procedure using two separate beamformers. The initial step is to construct and store a set of B-mode image lines using a single focal point in both transmit and receive. The focal points are considered virtual sources and virtual receivers making up a virtual array. The second stage applies the focused image lines from the first stage as input data, and take advantage of the virtual array in the delay and sum beamforming. The size of the virtual array is dynamically expanded and the image is dynamically focused in both transmit and receive and a range independent lateral resolution is obtained. The SASB method has been investigated using simulations in Field II and by off-line processing of data acquired with a commercial scanner. The lateral resolution increases with a decreasing F#. Grating lobes appear if F# 6 2 for a linear array with k-pitch. The performance of SASB with the virtual source at 20 mm and F# = 1.5 is compared with conventional dynamic receive focusing (DRF). The axial resolution is the same for the two methods. For the lateral resolution there is improvement in FWHM of at least a factor of 2 and the improvement at À40 dB is at least a factor of 3. With SASB the resolution is almost constant throughout the range. For DRF the FWHM increases almost linearly with range and the resolution at À40 dB is fluctuating with range. The theoretical potential improvement in SNR of SASB over DRF has been estimated. An improvement is attained at the entire range, and at a depth of 80 mm the improvement is 8 dB.

Analog gradient beamformer for a wireless ultrasound scanner

“…10 The method has been clinically demonstrated to be equally good compared to conventional dynamic receive focusing, 11 with the advantages of reduced system requirements and effective reduction of the data transfer rate between the probe and the processing unit. A virtual source (VS) is emulated in front of the transducer by means of a focused emission.…”

“…The system is based on Synthetic Aperture Sequential Beamforming (SASB). 10 The approach has been demonstrated in the clinic to provide images equally good compared to conventional dynamic receive focusing, 11 while reducing the system requirements due to the implementation of a static-focus beamformer in the transducer handle. Only a single beamformed line per emission needs to be transmitted to the central unit, and the transfer rate is reduced by a factor M .…”

Clinical Evaluation of Synthetic Aperture Harmonic Imaging for Scanning Focal Malignant Liver Lesions

“…The first beamformer reduces the data throughput requirement to that of a single output signal, that is, a factor of 64 for a 64-channel receive system. The second beamformer recombines a set of emissions to create the final high-resolution image (Hemmsen et al 2012a;Kortbek et al 2013). Previous studies have evaluated the image quality of SASB against conventional dynamic receive focusing (DRF) and reported equally good image quality, indicating that SASB is applicable to medical imaging , 2012b, Hansen et al 2014.…”

Ultrasonic Synthetic Apertures: Review

“…The algorithm allowing considerable reduction of the data acquisition for SA image reconstruction was proposed by Karwat et al (2010). Kortbek et al (2013) proposed a novel approach to SA using virtual sources and virtual receivers dynamically expanded the array size and allowing dynamic focusing in both transmit and receive. The SAFT technique was considerably improved applying focusing beam before image (Mosey et al, 2013).…”