A Comparison of the Performance of Different Multiline Transmit Setups for Fast Volumetric Cardiac Ultrasound

Abstract

It was previously demonstrated in 2-D echocardiography that a proper multiline transmit (MLT) implementation can be used to increase frame rate while preserving image quality. Initial findings for extending MLT to 3-D showed that it might address the low spatiotemporal resolution of current volumetric ultrasound systems. However, to date, it remains unclear how much transmit/receive parallelization would be possible using a 3-D MLT system. Therefore, the aim of this paper was to contrast different MLT setups for 3-D imaging by computer simulation in order to determine an optimal tradeoff between the amount of parallelization of an MLT system and the corresponding signal-to-noise ratio of the resulting images. Hereto, the image quality of several MLT setups was estimated by quantifying their crosstalk energy level. The results showed that for the tested setups, 4MLT broad beams and 9MLT narrow beams with Tukey ( α = 0.5 ) apodization in transmit and receive give the highest frame rate gain while maintaining an acceptable interbeam interference level. Moreover, although 16MLT narrow beams with Tukey/Tukey ( α = 0.5 ) apodization did show more pronounced interbeam interference, its gain in frame rate might outweigh its predicted loss in image quality. As such both 9MLT and 16MLT narrow beams were tested experimentally. For both systems, four receive lines were reconstructed from each transmit beam. The contrast-to-noise ratio of these imaging strategies was quantified and compared with the image quality obtained with line-by-line scanning. Despite some expected loss in image quality, the resulting images of the parallelized systems were very competitive to the benchmark, while speeding up the acquisition process by a factor of 36 and 64, respectively.

Automatic Definition of an Anatomic Field of View for Volumetric Cardiac Motion Estimation at High Temporal Resolution

“…Such staggering was chosen to be half the thickness of the hollow cone at the focal depth. The cross-talk energy level of the MLT systems can be determined using the process described in [17]. As such, simulations of the two-way beam profiles were performed on a plane parallel to the transducer surface (i.e., C-plane) at a depth of 65 mm (i.e., around halfway the common imaging depth for cardiac applications).…”

“…As such, simulations of the two-way beam profiles were performed on a plane parallel to the transducer surface (i.e., C-plane) at a depth of 65 mm (i.e., around halfway the common imaging depth for cardiac applications). This depth was chosen based on our previous in silico findings [17] while using the exact same system configuration. It was shown that the best performing system at this depth was also the system of choice at other depths and steering angles.…”

“…To quantify how the energy of a beam spreads in the volume and potentially interferes with other MLT beams, the same procedure as in [17] was followed. In short, a beam was transmitted into one of the MLT directions (θ i ) and subsequently received along each of the MLT beam directions (including the same transmit direction: θ 1...i...j ).…”

“…Indeed, we recently demonstrated that by small modifications of the transmit beamforming (i.e., introducing small delays or phase shifts between different MLT beams), the near-field pressure can be adjusted to remain within safety regulations [15]. Finally, in order to test the feasibility of MLT for volumetric imaging, a qualitative [16] and a quantitative [17] study were recently performed where the 2D findings were extrapolated to 3D. It was shown, by in silico and in vitro experiments, that a 16MLT-4MLA with transmit and receive apodization (Tukey α = 0.5) generates volumetric images within a single heartbeat with an appropriate image quality for functional cardiac imaging [17].…”

“…Finally, in order to test the feasibility of MLT for volumetric imaging, a qualitative [16] and a quantitative [17] study were recently performed where the 2D findings were extrapolated to 3D. It was shown, by in silico and in vitro experiments, that a 16MLT-4MLA with transmit and receive apodization (Tukey α = 0.5) generates volumetric images within a single heartbeat with an appropriate image quality for functional cardiac imaging [17].…”