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

Abstract

Objective Early diagnosis and acute knowledge of cerebral disease require to map the microflows of the whole brain. Recently, ultrasound localization microscopy (ULM) was applied to map and quantify blood microflows in 2D in the brain of adult patients down to the micron scale. Whole brain 3D clinical ULM remains challenging due to the transcranial energy loss which reduces significantly the imaging sensitivity. Approach Large aperture probes with a large surface can increase both the field of view and sensitivity. However, a large active surface implies thousands of acoustic elements, which limits clinical translation. In a previous simulation study, we developed a new probe concept combining a limited number of elements and a large aperture. It is based on large elements, to increase sensitivity, and a multi-lens diffracting layer to improve the focusing quality. In this study, a 16 elements prototype, driven at 1MHz frequency, was made and in vitro experiments were performed to validate the imaging capabilities of this new probe concept. Main results First, pressure fields emitted from a large single transducer element without and with diverging lens were compared. Low directivity was measured for the large element with the diverging lens while maintaining high transmit pressure. The focusing quality of 4x3cm matrix arrays of 16 elements without/with lenses were compared. In vitro experiments in a water tank and through a human skull were achieved to localize and track microbubbles in tubes. Significance Ultrasound localization microscopy (ULM) was achieved demonstrating the strong potential of multi-lens diffracting layer to enable microcirculation assessment over a large field of view through the bones.

Four-dimensional computational ultrasound imaging of brain hemodynamics

“…By modifying the field in this way, we more evenly sample the k -space of our imaging aperture while avoiding any symmetries that would give rise to artifacts such as grating lobes ( Fig. 1B ) ( 21 ). This more uniform sampling of k -space increases the lateral resolution of the imaging system at the expense of increased clutter/side lobes, which can be seen in the imaging performance of the bare probe versus the probe with mask (cUSi) on a numerical phantom ( Fig.…”

The development of a 1.25 MHz 1024-channel sparse array for human transcranial imaging: in vitro characterization

“…The challenge of small element transducer designs is their lack of sensitivity. Instead of targeting low grating lobes in their transducer design, Favre et al demonstrated the potential for the development of a large aperture array with a large element size of 4λ in silico [36] and in vitro [37]. To combat the significantly high grating lobes caused by the use of large elements, Favre et al modeled a multi-lens diffracting layer that improved both the resolution and grating lobes of the received signal.…”