  Imaging the human brain vasculature with high spatial and temporal resolution
remains challenging in the clinic today. Transcranial ultrasound is scarcely
used for cerebrovascular imaging, due to low sensitivity and strong phase
aberrations induced by the skull bone that only enable major brain vessel
imaging, even with ultrasound contrast agent injection (microbubbles). Here, we
propose an adaptive aberration correction technique for skull bone aberrations
based on the backscattered signals coming from intravenously injected
microbubbles. Our aberration correction technique was implemented to image
brain vasculature in adult humans through temporal and occipital bone windows.
For each patient, an effective speed of sound, as well as a phase aberration
profile, were determined in several isoplanatic patches spread across the
image. This information was then used in the beamforming process. It improved
image quality both for ultrafast Doppler imaging and Ultrasound Localization
Microscopy (ULM), especially in cases of thick bone windows. For ultrafast
Doppler images, the contrast was increased by 4dB on average, and for ULM, the
number of detected microbubble tracks was increased by 38%. This technique is
thus promising for better diagnosis and follow-up of brain pathologies such as
aneurysms or stroke and could make transcranial ultrasound imaging possible
even in particularly difficult-to-image patients.
