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 208µm 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 1.6×10 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 µm, was reduced to 50µm 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 1885µm error for the uncorrected emission, to a 284µm error for the corrected counterpart. These findings suggest that super-resolution may be used more generally as a clinical imaging modality in the brain.

Early Ultrafast Ultrasound Imaging of Cerebral Perfusion correlates with Ischemic Stroke outcomes and responses to treatment in Mice

“…Specifically, ultrafast Doppler allows the monitoring of subtle Cerebral Blood Volume (CBV) changes without contrast agents and led to the development of the ultrasound analog of functional MRI (fMRI): functional Ultrasound (fUS) 11 - 16 . Ultrafast ultrasound also allows the detection of injected intravascular microbubbles, a clinical ultrasound contrast agent, and led to the development of Ultrasound Localization Microscopy (ULM) 17 - 20 which, unlike ultrafast Doppler, may allow transcranial imaging in adults patients 21 , 22 . In this study, we demonstrate that both modalities are adapted to the study of stroke in a mouse model, with ultrafast Doppler producing longitudinal monitoring and ULM proving an increased sensitivity and definition, two criteria which are mandatory for clinical applicability.…”

Super-resolution Ultrasound Imaging

“…In fact, multiple matrix arrays imaging simultaneously through the two temporal bones have been used by Lindsey et al (2011Lindsey et al ( , 2014 to produce 3-D images of the circle of Willis in human volunteers at normal resolution. Additionally, Soulioti et al (2020) recently performed transcranial super-resolution imaging of a tube phantom through human temporal bone with a 2.5-MHz diagnostic transducer, achieving an accuracy to that of O'Reilly and Hynynen (2013) and further supporting the feasibility of this approach. The implementation of super-resolution methods on such a system could create a powerful tool for imaging stroke.…”

Ray Theory-Based Transcranial Phase Correction for Intracranial Imaging: A Phantom Study

“…The ray-theory-based phase correction method has a wider imaging area than the limited beacon points with the timereversal method. It is also more universal and accurate than the auto-correlation method, in which the thickness compensation of cranial bones is necessary for accurate imaging [13]. The ray-theory-based phase correction has higher efficiency than full-wave simulation-based phase correction, while acoustic parameters are essential for those two methods.…”

“…A spatial-temporal inverse filter matrix was established between the dual-array probes to estimate the phase correction. Those methods, however, are unrealistic in practice, as they require the presence of transducers inside the cranial bones [13]. Vignon et al [14] then made further improvements by placing a pair of phase arrays on each side of the head and fabricating a virtual array between them.…”