Adaptive receive and transmit apodization for synthetic aperture ultrasound imaging

Abstract

Abstract-This paper suggests a framework for utilizing adaptive, data-dependent apodization weights on both the receiving and transmitting aperture for Synthetic Aperture (SA) ultrasound imaging. The suggested approach is based on the Minimum Variance (MV) beamformer and consists of two steps. A set of uniquely designed receive apodization weights are applied to pre-summed element data forming a set of adaptively weighted images; these are in SA literature conventionally referred to as low-resolution images. The adaptive transmit apodization is obtained by applying MV across the full set of single emission images before summation. The method is investigated using simulated SA ultrasound data obtained using Field II. Data of 13 point targets distributed at depths from 40 mm to 70 mm, and a 5.5 MHz, 64-element linear array transducer have been used. The investigation has shown that the introduction of adaptive apodization weights on the transmitting aperture provides a main-lobe reduction (estimated at −30 dB) by a factor of 1.8 compared to the method using adaptive apodization weights on the receiving aperture only.

A comparison between temporal and subband minimum variance adaptive beamforming

“…Holfort et al 18,19 that implemented the frequency domain MV beamformer, have applied it to different imaging sequences such as synthetic aperture and plane wave imaging. They have proposed the application of minimum variance apodization weights both in the transmitting and receiving apertures 20 and have investigated the influence of sound speed errors on the adaptive beamformer.…”

Towards a Reduced-Wire Interface for CMUT-Based Intravascular Ultrasound Imaging Systems

“…The dynamic range is lower than desired because of the non-ideal operation of the CMUT array and the mechanical and electrical noise in the experimental setup, limiting the SNR of the individual pulse-echo signals to only 15 dB. Beamforming, on the other hand, improved the dynamic range by ~15 dB [16]. In the images in Fig.…”

“…To reduce power consumption and system complexity, we utilized synthetic-aperture imaging method, in which only one U-Rx CMUT and its associated TIA are activated at any time. A control circuit that is run by a signal derived from the power carrier, selects each U-Tx-Rx pair at 25.6 μ s intervals based on the anticipated round-trip pulse-echo travel time from a target at 1 cm imaging depth [16]. To achieve better noise performance in the following stages, a single-to-differential converter was implemented to follow the TIA.…”

“…To reduce the SoC power consumption and system complexity, we adopted the synthetic-aperture imaging method that uses only one pair of transmitting (U-Tx) and receiving (U-Rx) CMUT elements for each ultrasound firing event [16]. The following section described the CMUTs used in this IVUS imaging system.…”

Toward a reduced-wire readout system for ultrasound imaging

“…Therefore, TIAs can operate at low voltage and there is no need to implement high voltage protection switches. In addition, because our target is synthetic aperture ultrasound imaging [11], only one CMUT is used at a given time. A 2-bit counter is used as a channel selector, and it chooses which of the 4 TIAs is connected to the rest of the system.…”