Mapping blood microflows of the whole brain is crucial for early diagnosis of
cerebral diseases. Ultrasound localization microscopy (ULM) was recently
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 significantly reduces the
imaging sensitivity. Large aperture probes with a large surface can increase
both resolution and sensitivity. However, a large active surface implies
thousands of acoustic elements, with limited clinical translation. In this
study, we investigate via simulations a new high-sensitive 3D imaging approach
based on large diverging elements, combined with an adapted beamforming with
corrected delay laws, to increase sensitivity. First, pressure fields from
single elements with different sizes and shapes were simulated. High
directivity was measured for curved element while maintaining high transmit
pressure. Matrix arrays of 256 elements with a dimension of 10x10 cm with small
( λ /2), large (4 λ ), and curved elements (4 λ ) were
compared through point spread functions analysis. A large synthetic microvessel
phantom filled with 100 microbubbles per frame was imaged using the matrix
arrays in a transcranial configuration. 93% of the bubbles were detected with
the proposed approach demonstrating that the multi-lens diffracting layer has a
strong potential to enable 3D ULM over a large field of view through the bones