High Frame Rate Volumetric Imaging of Microbubbles Using a Sparse Array and Spatial Coherence Beamforming

Abstract

Volumetric ultrasound imaging of blood flow with microbubbles enables more complete visualization of the microvasculature. Sparse arrays are ideal candidates to perform volumetric imaging at reduced manufacturing complexity and cable count. However, due to the small number of transducer elements, sparse arrays often come with high clutter levels, especially when wide beams are transmitted to increase the frame rate. In this study, we demonstrate with a prototype sparse array probe and a diverging wave transmission strategy, that a uniform transmission field can be achieved. With the implementation of a spatial coherence beamformer, background clutter signal can be effectively suppressed, leading to a signal to background ratio improvement of 25 dB. With this approach, we demonstrate the volumetric visualization of single microbubbles in a tissue-mimicking phantom as well as vasculature mapping in a live chicken embryo chorioallantoic membrane.

Full-visibility 3D imaging of oxygenation and blood flow by simultaneous multispectral photoacoustic fluctuation imaging (MS-PAFI) and ultrasound Doppler

“…The very good sensitivity of our transducer, that allowed working with a small number of channels, comes from the relatively large size of the individual elements and their distribution over a spherical surface, at the cost of a limited field-of-view. A recent study implemented Power Doppler imaging in chicken embryos 45 with a similar transducer geometry (although with a different technology and with 256 elements distributed over a plane), however ultrasound contrast agents were injected in the embryo to perform imaging, presumably because of sensitivity limitations. Ultrasound contrast agents were also used in the only prior publication reporting combined 3D ultrasound and 3D photoacoustic imaging 30 but the authors chose the transcranial mouse brain model that probably led to a limited sensitivity and to the need for contrast agents.…”

Four-dimensional computational ultrasound imaging of brain hemodynamics

“…However, these required the use and synchronization of multiple data acquisition systems which are both extremely costly and technically complex, making it infeasible for most clinical applications. To reduce the number of necessary independent data channels, two approaches are conventionally considered: (i) retaining a fully sampled array but using more complex readout schemes using application-specific integrated circuits (ASICs) to combine and prebeamform signals (16)(17)(18) and (ii) sparse arrays that strategically subsample an aperture with an element distribution designed to minimize side lobes (19,20). However, both methods impose compromises on the image formation process and such arrays are technically complex to realize.…”

Transcranial 3D ultrasound localization microscopy using a large element matrix array with a multi-lens diffracting layer: an in vitro study

“…However, increasing the number of channels to drive large matrix arrays is a technical challenge associated with tremendous cost and cumbersomeness. Different types of ultrasonic probes: multiple linear probes (Christensen-Jeffries et al 2016), multiplexed 2D matrix arrays (Heiles et al 2019, Chavignon et al 2021, rowcolum addressed arrays (Jensen et al 2020), sparse 2D arrays (Wei et al 2021) and hemi-spherical array (O′Reilly M A and Hynynen 2013) were developed and used in vitro and in vivo demonstrating promising results while reducing the number of elements and channels. However, these approaches could have a limited impact for transcranial ULM, mainly due to a limited sensitivity or a small field of view.…”