This PDF file contains the front matter associated with SPIE Proceedings Volume 12828, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Optical imaging of the brain has expanded dramatically in the past two decades. New optics, indicators, and experimental paradigms are now enabling in-vivo imaging from the synaptic to the cortex-wide scales. To match the resulting flood of data across scales, computational methods are continuously being developed to meet the need of extracting biologically relevant information. In this pursuit challenges arise in some domains (e.g., SNR and resolution limits in micron-scale data) that require specialized algorithms. These algorithms can, for example, make use of state-of-the-art machine learning to maximally learn the details of a given scale to optimize the processing pipeline. In contrast, other methods, however, such as graph signal processing, seek to abstract away from some of the details that are scale-specific to provide solution to specific sub-problems common across scales of neuroimaging. Here we discuss limitations and tradeoffs in algorithmic design with the goal of identifying how data quality and variability can hamper algorithm use and dissemination.

While near-infrared spectroscopy has been shown to be a useful technique for the non-invasive monitoring of cerebral hemodynamics, sensitivity to superficial hemodynamic changes continues to be a challenge in the field. Here, we apply a previously designed hexagonal dual-slope module to human subjects during a visual stimulation protocol. The enrolled subjects have different scalp-to-cortex distances, as measured with ultrasound imaging. This work investigates the cerebral hemodynamic response to visual stimulation as measured non-invasively by optical intensity (I) collected with a single distance (SD) or dual-slope (DS) source-detector arrangement [SDI(25 mm), SDI(35 mm), DSI]. The observed results in relation to scalp-to-cortex distance are then validated through theoretical simulations in two-layered media, and these simulations confirm that as the cortical depth increases the sensitivity to the brain decreases faster for single-distance measurements than dual-slope measurements. This finding supports the value of dual-slope measurements for enhanced sensitivity to the brain.

The ischemic stroke animal model has gained increasing popularity to elucidate the pathophysiology and evaluate the efficacy of reperfusion and neuroprotective strategies for ischemic injuries. Various conventional methods to induce the ischemic models have been reported, however, it is difficult to control specific neurological deficits, mortality rates, and the extent of the infarction since the size of the affected region is precisely controlled, which limits the closeness of animal model to human stroke. In this study, we report a novel creation method of the target ischemic stroke model by simultaneous vessel monitoring and photothrombosis induction using localization photoacoustic microscopy (L-PAM), which minimizes infarct size at a precise location with high reproducibility. By utilizing the proposed L-PAM system, we resolve the occurred position error of the scanner for high-speed imaging caused by external resistance, which enables the precise localization up to a single micro-vasculature. The reproducibility and validity of the suggested target ischemic stroke model-inducing method have been successfully proven through repeated experiments and histological analyses. These results demonstrate that the proposed method is able to induce the closest ischemic stroke model to the clinical pathology for brain ischemia research from inducement dynamics, occurrence mechanisms to the recovery process.

5-aminolevulinic acid (5-ALA) mediated interstitial photodynamic therapy (iPDT) is undergoing clinical trials for the treatment of malignant gliomas. 5-ALA iPDT is based on the creation of reactive oxygen species (ROS) via excitation of 5-ALA mediated protoporphyrin IX (PpIX) in the tumor cells and causing a phototoxic reaction. After iPDT local chemo-radiation is performed as adjuvant therapy. 16 newly diagnosed glioblastomas and 44 malignant glioma recurrences treated with 5-ALA iPDT in Munich were retrospectively analyzed for treatment outcome, spectral online monitoring and changes in the MRI. iPDT for newly diagnosed glioblastomas showed a median overall survival (OS) of 28 months, 16.4 months progression free survival (PFS), respectively. 43.8% patients with newly diagnosed glioblastoma experienced a long term PFS > 24 months. In addition, the methylation of the MGMT promotor showed to be a prognostic factor for prolonged survival (p=0.04). In case of recurrent malignant gliomas PFS after iPDT was 7.1 months with 25% >24 months survival after iPDT (17.9% PFS > 24 months). Analysis of spectral online monitoring showed that a measured decrease of the laser light transmission between the cylindrical diffuser fibers, used for the irradiation, can be associated with silent hemorrhages visible in terms of T1-hyperintensity in the MRI after iPDT. Overall 5-ALA iPDT is a promising tool for the treatment of glioblastomas and other malignant gliomas with prolonged survival and minimally invasive surgery.

The presence of human hair in the area of sensing interest during functional near-infrared spectroscopy (fNIRS) procedures is a known factor that can prevent proper coupling with the scalp, resulting in signal loss and a reduction in signal-to-noise ratio (SNR). Researchers struggle to find a technique for hair clearance that is accessible, simple and time efficient to operate, and applicable to hair of many different characteristics – including length, shaft thickness, curl or coil, and density. Our group has developed a novel, mechanical attachment compatible with commercial fNIRS systems to facilitate rapid hair clearance and better through-hair SNR for a range of hair types and textures, promoting wider subject inclusivity. Our attachment, named the “Mini Comb,” comprises three parts: a twistable cover, a support piece and six sliding legs. The twistable cover allows the design to be operated by a simple twisting mechanism and has a versatile design that allows it to be deployed in multiple commercial systems. The support piece serves to keep the Mini Comb system connected and in place. The sliding legs move hair strands away from a central region of interest to clear a path for signal acquisition and proper electronics contact with the scalp. We have developed five unique designs for the sliding legs to achieve hair clearance in a wide variety of hair types and subject populations. Results obtained with wigged mannequins show the Mini Comb designs are able to create hair clearance across these variable hair types.

Previous studies have shown that the optical coherence tomography (OCT) signal in white matter (WM) is affected by the WM fiber bundles orientation with respect to the microscope’s optical axis. In this paper, we aim to exploit this contrast mechanism to generate a multi-orientation representation of WM microstructure in whole mouse brains. To achieve this, a serial blockface histology set-up has been developed combined with spectral domain OCT equipped with a long-range 10x magnification objective, achieving a near isotropic resolution of 3 micron laterally (xy) and 3.5 micron axially (z). With this imaging system, a map of WM structures can be generated for an entire agarose embedded mouse brain. To precisely control the mouse brain orientation within the agarose, we designed a multi-part 3D printed mold, which allows us to choose the vibratome’s slicing plane (e.g., coronal, axial, sagittal, etc.). After the serial OCT acquisition, every slice is reconstructed as 2D images and stacked to obtain a 2.5D volume. The reconstruction process uses a nextflow computational pipeline, allowing us to parallelize the calculations. Our proposed imaging method emphasizes different WM structures according to their orientation, which we illustrated in the mouse’s anterior commissure olfactory limb. This structure is very bright when observed in axial slices, whereas it has a darker appearance in the coronal slices. Using this method, we plan to acquire whole mouse brains oriented in multiple directions and to create a multi-orientation mouse brain template, which we believe will prove useful to get a better understanding of complex WM microstructure geometries, such as fiber crossing areas.

The hippocampus (HC) is a subcortical brain region that plays essential roles in learning and memory. It is strongly associated with Alzheimer’s disease (AD), an incurable and deadly neurodegenerative disease which is progressive and requires longitudinal observation. Two-photon microscopy (2PM) is applied here to investigate hippocampal alterations in living mouse models and better understand pathological changes during neurodegeneration. The common procedure is to surgically expose the rodent cortex and have it sealed with a coverslip to allow optical access. However, in some studies, repeated tissue injections are needed to deliver exogenous contrast agents or pharmacological agents, and current injection strategies are not compatible with subcortical imaging, which limits the ability to study subcortical lesions longitudinally. To tackle this issue, we developed a technique where both imaging and injection can be conducted. Our previous development enabled 2PM imaging in the HC using a gradient-index (GRIN) lens. We engineered a customized cannula using polyimide tubing and transparent acrylic, and implanted it into mouse brain. It allows removable insertion of a GRIN lens and enables longitudinal investigation. In this study, we improved our cannula design to enable imaging and injections. The acrylic window is replaced with an optically-transparent, biocompatible, oxygen impermeable plastic, which maintains seal after needle penetration. Here we report injection and imaging results in phantoms and animals. Our design opens opportunities for comprehensive longitudinal imaging of subcortical lesions.

The monitoring of partial pressure of oxygen in brain tissue (PbtO₂) holds paramount importance in both neuroscience research and the management of brain-related disorders. While imaging techniques offer avenues to directly or indirectly assess brain oxygenation, their applicability is limited in the study of certain disease models involving behaving animals. Here, we present an optoelectronic probe for real-time and continuous PbtO₂ monitoring, offering wireless capabilities and providing high temporal and spatial resolutions. This probe measures oxygen partial pressure (PO₂) through phosphorescence quenching, and the implantable probe integrates a micro-scale violet light-emitting diode (LED), a thin-film filter, a micro-scale photodetector, and an oxygen-sensing film. An implantable optoelectronic probe and a wireless control circuit miniaturized to centimeter scales form a system for monitoring PbtO₂. Implanted into the brain of rats, this battery-free system demonstrates efficacy in capturing PbtO₂ changes in response to alterations in the fraction of inspired oxygen (FiO₂).

Our understanding of hemodynamic signals, blood perfusion and oxygen saturation (sO₂), recorded through fiber-based instruments is limited. To address this, a potential method can be to simultaneously acquire hemodynamic signals with widely used fluorescence fiber photometry signals. We report a novel System for the Simultaneous Measurement of Fluorescence and Hemodynamics (SSMFH) from deep brain regions of freely moving rodents. SSMFH has been developed by modifying our previous white light reflectance single fiber system (SFS) that enabled measurement of blood perfusion and oxygen saturation from freely moving rodents. SSMFH has been designed to be easily integrated with a commercial fluorescence fiber photometry system for time-locked measurement of both hemodynamics and fluorescence signals. SSMFH can be additionally synchronized to behavioral monitoring cameras and other behavioral equipment during experiments. In contrast to previous work in the literature, SSMFH enables hemodynamic recordings from deep brain regions using a wide spectral range (∼ 545nm to 700nm) without the need for injection of an activity-independent fluorescent reporter. The details of the design will be presented along with data to illustrate proof-of-concept through an animal experiment. GCaMP-based fiber photometry and its relation to neuronal activity is well understood. Hemodynamic measurement with simultaneous and co-localized GCaMP based neuronal activity recording can help in understanding variations in in-vivo hemodynamic signals. SSMFH can be used to correct fluorescence measurements which are affected by blood absorption changes.

Noninvasive neuroimaging, though critical to both scientific research and clinical applications, has long lacked a technology that is both high resolution, robust to motion, and useable in naturalistic settings. While functional near infrared spectroscopy (fNIRS) and diffuse optical tomography (DOT) have made advances toward these goals, conventional systems still limit scanning environments and retain some motion susceptibility. Our new wearable, high-density (WHD) DOT system makes huge strides forward, offering the high spatial resolution of conventional DOT with added robustness to many types of motion. We validated our system on the benchtop and in vivo with a variety of well-characterized tasks, including visual, auditory, language processing, motor, and more, along with resting state functional connectivity. We also tested performance under different motion conditions, ranging from none at all to large amplitude motions, and even in situations impossible for most other neuroimaging modalities, such as freely walking. Our WHD system provided results comparable to conventional DOT systems, and outperformed them when compared under motion conditions; in WHD, large motions introduce minimal artifacts into recorded data, even without motion correction. WHD DOT has lower quantitative and qualitative motion metrics and artifacts than conventional, fiber-based DOT. Its lightweight, portable nature also enables neuroimaging in different settings, such as non-laboratory and naturalistic environments. These advancements will allow studies of brain function in previously intractable settings, high motion populations such as Parkinson’s patients, and tasks involving movement.

The Neurovascular Unit (NVU) dynamically regulates oxygen supply to satisfy neural metabolic demand. Amyloid-β (Aβ) accumulation and hyperphosphorylated Tau in Alzheimer’s disease (AD) disrupt the NVU. Empirical evidence strongly indicates that physical activity (PA) reduces the rate of cognitive impairment, but the physiological mechanism(s) PA’s neuroprotective benefits remain unclear. We propose PA improves the brain parenchymal oxygenation and reduces metabolic deficits. Using the novel oxygen sensitizer, Oxyphor 2P, and 2-photon phosphorescence lifetime imaging (2P-PLIM), our results indicate that the PA shows the potential to curtail AD progression by increasing microvascular oxygenation and preserving NVU function.