Evaluation of a transparent cranial implant as a permanent window for cerebral blood flow imaging

Abstract

Laser speckle imaging (LSI) of mouse cerebral blood flow was compared through a transparent nanocrystalline yttria-stabilized zirconia (nc-YSZ) cranial implant over time (at days 0, 14, and 28, n = 3 mice), and vs. LSI through native skull (at day 60, n = 1 mouse). The average sharpness of imaged vessels was found to remain stable, with relative change in sharpness under 7.69% ± 1.2% over 28 days. Through-implant images of vessels at day 60 appeared sharper and smaller on average, with microvessels clearly visible, compared to through-skull images where vessels appeared blurred and distorted. These results suggest that long-term imaging through this implant is feasible.

Theranostic cranial implant for hyperspectral light delivery and microcirculation imaging without scalp removal

“…Therefore, brain imaging has been predominantly demonstrated in rodent open-skull and thinned skull models. Likewise, in our own prior studies we have found that optical imaging through the intact skull of mice diminishes detection of the intrinsic optical signals [24][25][26][27] . Moreover, the optical properties of the inhomogeneous cranial bone overlap with those of brain tissue and jointly these factors decrease the accuracy and reliability of the data.…”

“…Glass and PDMS windows are powerful research techniques, but are not appropriate for human application as permanent cranial implants for patients. Like skull thinning and polishing techniques, glass-based windows compromise protection for the brain due to the extremely low fracture toughness of typical glasses (KIC = 0.7-0.9 MPa m1/2) 36 which increases potential for catastrophic failure by fracture, while the effect of skull optical clearing agents for long-term use on human skull is still unknown 24 . A number of biomedical considerations including biocompatibility, mechanical strength, and ageing should be examined in order to create an optical window for eventual clinical application 24 .…”

“…Like skull thinning and polishing techniques, glass-based windows compromise protection for the brain due to the extremely low fracture toughness of typical glasses (KIC = 0.7-0.9 MPa m1/2) 36 which increases potential for catastrophic failure by fracture, while the effect of skull optical clearing agents for long-term use on human skull is still unknown 24 . A number of biomedical considerations including biocompatibility, mechanical strength, and ageing should be examined in order to create an optical window for eventual clinical application 24 . Conventional cranial prosthesis including titanium, alumina, and acrylic 37 , have not provided the requisite combination of transparency and toughness required for clinically-viable transparent cranial implants.…”

“…Conventional cranial prosthesis including titanium, alumina, and acrylic 37 , have not provided the requisite combination of transparency and toughness required for clinically-viable transparent cranial implants. To address this challenge, our group has previously introduced a transparent nanocrystalline yttria-stabilized-zirconia cranial implant material, which possesses the mechanical strength and biocompatibility which are prerequisites for a clinically-viable permanent cranial implant for patients [24][25][26][27][38][39][40][41][42][43][44][45][46] . This implant has been referred to in the literature as the "Window to the Brain" (WttB) implant.…”

Optical Access to Arteriovenous Cerebral Microcirculation Through a Transparent Cranial Implant

“…When MSRI has been applied through the intact skull, only skull regions and not individual microvessels are visible . Likewise, in our own prior studies we have found that imaging through intact skull with LSI limits the size of vessels that can be detected, and precludes imaging of the microcirculation . Moreover, the absorption and reflectance features of the inhomogeneous cranial bone overlap with those of brain tissue, and the skull also has its own vessels.…”