Super resolution imaging through the human skull

Abstract

High resolution transcranial ultrasound imaging in humans has been a persistent challenge for ultrasound due to the imaging degradation effects from aberration and reverberation. These mechanisms depend strongly on skull morphology and they have high variability across individuals. Here we demonstrate the feasibility of human transcranial super-resolution imaging using a geometrical focusing approach to concentrate energy at the region of interest, and a phase correction focusing approach that takes the skull morphology into account. It is shown that using the proposed focused method, we can image a 208$\mu$m microtube behind a human skull phantom in both an out-of-plane and an in-plane configuration. Individual phase correction profiles for the temporal region of the human skull were calculated and applied to transmit-receive a custom-focused super-resolution imaging sequence through a human skull phantom, targeting the microtube, at 68.5mm in depth, at 2.5 MHz. Microbubble contrast agents were diluted to a concentration of 1.6$\times$10$^6$ bubbles/mL and perfused through the microtube. It is shown that by correcting for the skull aberration, the RF signal amplitude from the tube improved by a factor of 1.6 in the out-of-plane focused emission case. The lateral registration error of the tube's position, which in the uncorrected case was 990 $\mu$m, was reduced to 50$\mu$m in the corrected case as measured in the B-mode images. Sensitivity in microbubble detection for the phase corrected case increased by a factor of 1.5 in the out-of-plane imaging case, while in the in-plane case it improved by a factor of 1.3 while achieving an axial registration correction from an initial 1885$\mu$m error for the uncorrected emission, to a 284$\mu$m error for the corrected counterpart. These findings suggest that super-resolution may be used more generally as a clinical imaging modality in the brain.