ABSTRACT
Implanted microelectrode arrays sense local neuronal activity, signals which are used as control commands for brain computer interface (BCI) technology. Patients with tetraplegia have used BCI technology to achieve an extraordinary degree of interaction with their local environment. However, current microelectrode arrays for BCIs lose the ability to record high-quality neural signals in the months-to-years following implantation. Very little is known regarding the dynamic response of neurons and vasculature in the months following electrode array implantation, but loss of structural integrity near the electrode may contribute to the degradation of recording signals. Here, we use in-vivo dual-modality imaging to characterize neuronal and vasculature structures in the same animal for 3 months following electrode insertion. We find ongoing neuronal atrophy, but relative vascular stability, in close proximity to the electrode, along with evidence suggesting links between rare, abrupt hypoxic events and neuronal process atrophy.
Subject(s)
Neurons , Animals , Electrodes, Implanted , Humans , MicroelectrodesABSTRACT
In this paper, we demonstrate the fabrication of contour-mode resonators (CMRs) with Al0.83Sc0.17N as a piezoelectric layer. Moreover, we assess the electromechanical coupling and the maximum achieved quality factor from 150 to 500 MHz. In comparison to pure aluminum nitride (AlN) CMRs, our results show electromechanical coupling coefficients of more than a 2× factor higher at around 200 MHz. The highest quality factor is measured on a CMR operating at 388 MHz and is in excess of 1600. From the characterization of devices operating at different frequencies, material parameters of the Al0.83Sc0.17N are extracted such as the stiffness constant, the relative permittivity, and the piezoelectric constant. In particular, the reported d31 piezoelectric constant is equal to -3.9 pm/V. This represents a 2.25× improvement when compared to pure AlN. Finally, we report the first temperature compensation experimental results for Al0.83Sc0.17N CMRs. Our results show that about 1.5 [Formula: see text] of sputtered oxide, deposited on top of a released resonator, allows near zero temperature coefficient of frequency variation for CMRs operating up to 500 MHz.
ABSTRACT
The vascular response during cortical microelectrode insertion was measured with amplitude decorrelation-based quantitative optical coherence angiography (OCA). Four different shank-style microelectrode configurations were inserted in murine motor cortex beneath a surgically implanted window in discrete steps while OCA images were collected and processed for angiography and flowmetry. Quantitative measurements included tissue displacement (measured by optical flow), perfused capillary density, and capillary flow velocity. The primary effect of insertion was mechanical perturbation, the effects of which included tissue displacement, arteriolar rupture, and compression of a branch of the anterior cerebral artery causing a global decrease in flow. Other effects observed included local flow drop-out in the region immediately surrounding the microelectrode. The mean basal capillary network velocity for all animals was 0.23 ( ± 0.05 SD ) and 0.18 ( ± 0.07 SD ) mm / s for capillaries from 100 to 300 µ m and 300 to 500 µ m , respectively. Upon insertion, the 2-shank electrode arrays caused a decrease in capillary flow density and velocity, while the results from other configurations were not different from controls. The proximity to large vessels appears to play a larger role than the array configuration. These results can guide neurosurgeons and electrode designers to minimize trauma and ischemia during microelectrode insertion.
ABSTRACT
We characterized image quality in optical coherence angiography (OCA) en face planes of mouse cortical capillary network in terms of signal-to-noise ratio (SNR) and Weber contrast (Wc) through a novel mask-based segmentation method. The method was used to compare two adjacent B-scan processing algorithms, (1) average absolute difference (AAD) and (2) standard deviation (SD), while varying the number of lateral cross-sections acquired (also known as the gate length, N). AAD and SD are identical at N = 2 and exhibited similar image quality for N<10. However, AAD is relatively less susceptible to bulk tissue motion artifact than SD. SNR and Wc were 15% and 35% higher for AAD from N = 25 to 100. In addition data sets were acquired with two objective lenses with different magnifications to quantify the effect of lateral resolution on fine capillary detection. The lower power objective yielded a significant mean broadening of 17% in Full Width Half Maximum (FWHM) diameter. These results may guide study and device designs for OCA capillary and blood flow quantification.
ABSTRACT
Speckle variance optical coherence angiography (OCA) was used to characterize the vascular tissue response from craniotomy, window implantation, and electrode insertion in mouse motor cortex. We observed initial vasodilation ~40% greater than original diameter 2-3 days post-surgery (dps). After 4 weeks, dilation subsided in large vessels (>50 µm diameter) but persisted in smaller vessels (25-50 µm diameter). Neovascularization began 8-12 dps and vessel migration continued throughout the study. Vasodilation and neovascularization were primarily associated with craniotomy and window implantation rather than electrode insertion. Initial evidence of capillary re-mapping in the region surrounding the implanted electrode was manifest in OCA image dissimilarity. Further investigation, including higher resolution imaging, is required to validate the finding. Spontaneous lesions also occurred in many electrode animals, though the inception point appeared random and not directly associated with electrode insertion. OCA allows high resolution, label-free in vivo visualization of neurovascular tissue, which may help determine any biological contribution to chronic electrode signal degradation. Vascular and flow-based biomarkers can aid development of novel neural prostheses.
