An all-fiber-optic confocal interference microscope using a broadband near-infrared light source is demonstrated. Detection of interference fringes increases sensitivity and usage of a broadband source reduces undesirable interference between optical components.
Quantification of brain function is a significant milestone towards understanding of the underlying workings of the brain. Photoacoustic (PA) imaging is the emerging brain sensing modality by which the molecular light absorptive contrast can be non-invasively quantified from deep-lying tissue (~several cm). In this BRAIN initiative effort, we propose high-speed transcranial PA imaging using a novel, compact pulsed LED illumination system (Prexion Inc., Japan) with 200-uJ pulse energy for 75-ns duration, and pulse repetition frequency (PRF) up to 4kHz at near-infrared (NIR) wavelengths of 690-nm and 850-nm switchable in real-time. To validate the efficacy of the proposed system, preliminary ex vivo experiments were conducted with mice skull and human temporal bone, which included vessel-mimicking tubes filled with 10% Indian Ink solution and light absorptive rubber material, respectively. The results indicated that significant PA contrast, 150% signal-to-noise ratio (SNR), can be achieved through the mice skull only with 64 subsequent frame averaging. The minimal number of frames for averaging required was only 16 to generate signal above background noise, leading to 250 Hz frame rate in the strictest temporal frame separation. Furthermore, distinguishable PA contrast was achieved with human temporal bone with 64-frame averaging. Overall, the preliminary results indicate that the LED illumination system can be a cost-effective solution for high-speed PA brain imaging in preclinical and clinical applications, compared to expansive and bulky Nd:YAG laser systems commonly used in PA imaging.
Fluorescence molecular tomography (FMT) is a promising tool for real time in vivo quantification of neurotransmission (NT) as we pursue in our BRAIN initiative effort. However, the acquired image data are noisy and the reconstruction problem is ill-posed. Further, while spatial sparsity of the NT effects could be exploited, traditional compressive-sensing methods cannot be directly applied as the system matrix in FMT is highly coherent. To overcome these issues, we propose and assess a three-step reconstruction method. First, truncated singular value decomposition is applied on the data to reduce matrix coherence. The resultant image data are input to a homotopy-based reconstruction strategy that exploits sparsity via ℓ1 regularization. The reconstructed image is then input to a maximum-likelihood expectation maximization (MLEM) algorithm that retains the sparseness of the input estimate and improves upon the quantitation by accurate Poisson noise modeling. The proposed reconstruction method was evaluated in a three-dimensional simulated setup with fluorescent sources in a cuboidal scattering medium with optical properties simulating human brain cortex (reduced scattering coefficient: 9.2 cm−1, absorption coefficient: 0.1 cm−1 and tomographic measurements made using pixelated detectors. In different experiments, fluorescent sources of varying size and intensity were simulated. The proposed reconstruction method provided accurate estimates of the fluorescent source intensity, with a 20% lower root mean square error on average compared to the pure-homotopy method for all considered source intensities and sizes. Further, compared with conventional ℓ2 regularized algorithm, overall, the proposed method reconstructed substantially more accurate fluorescence distribution. The proposed method shows considerable promise and will be tested using more realistic simulations and experimental setups.
Abstract Despite current progress achieved in the surgical technique of radical prostatectomy, post-operative complications such as erectile dysfunction and urinary incontinence persist at high incidence rates. In this paper, we present a functional intra-operative guidance of the cavernous nerve (CN) network for nerve-sparing radical prostatectomy using near-infrared cyanine voltage-sensitive dye (VSD) imaging, which visualizes membrane potential variations in the CN and its branches (CNB) in real time. As a proof-of-concept experiment, we demonstrated a functioning complex nerve network in response to electrical stimulation of the CN, which was clearly differentiated from surrounding tissues in an in vivo rat prostate model. Stimulation of erection was confirmed by correlative intracavernosal pressure (ICP) monitoring. Within 10 min we performed trans-fascial staining of the CN by direct VSD administration. Our findings suggest the applicability of VSD imaging for nerve-sparing radical prostatectomy.
Abstract Astrocytes are a direct target of neuromodulators and can influence neuronal activity on broad spatial and temporal scales through their close proximity to synapses. However, our knowledge about how astrocytes are functionally recruited during different animal behaviors and their diverse effects on the CNS remains limited. To enable measurement of astrocyte activity patterns in vivo during normative behaviors, we developed a high-resolution, long working distance, multi-core fiber optic imaging platform that allows visualization of cortical astrocyte calcium transients through a cranial window in freely moving mice. Using this platform, we defined the spatiotemporal dynamics of astrocytes during diverse behaviors, ranging from circadian fluctuations to novelty exploration, showing that astrocyte activity patterns are more variable and less synchronous than apparent in head-immobilized imaging conditions. Although the activity of astrocytes in visual cortex was highly synchronized during quiescence to arousal transitions, individual astrocytes often exhibited distinct thresholds and activity patterns during explorative behaviors, in accordance with their molecular diversity, allowing temporal sequencing across the astrocyte network. Imaging astrocyte activity during self-initiated behaviors revealed that noradrenergic and cholinergic systems act synergistically to recruit astrocytes during state transitions associated with arousal and attention, which was profoundly modulated by internal state. The distinct activity patterns exhibited by astrocytes in the cerebral cortex may provide a means to vary their neuromodulatory influence in response to different behaviors and internal states.
A novel approach for post-surgical volumetric evaluation of the quality of corneal incisions and wound healing is presented. It is based on high-resolution 3-D spectral-domain optical coherence tomography providing both multiple-cross-sectional and volumetric images.
We have demonstrated a polarization sensitive cartilage and muscle imaging based on common path optical coherence tomography (CP-OCT) using near infrared source. The axial and lateral resolutions of our PS-OCT system are 9μm and 6μm, respectively. The internal structural information has been extracted by the real-time signal analysis (Fourier Transform) from the modulated spectral intensity depending on the beam and tissue birefringence. Preliminary results using fresh beef and in vivo rat show that we can visualize the birefringence effect of the tissue collagen fibers in the samples for better image contrast and sensitivity for detection of hidden dermal structures. Compared to conventional CP-OCT, our proposed PS-OCT could provide depth-resolved images, which reflect tissue birefringence.
We demonstrate the subsurface imaging of an articular cartilage using Fourier-domain common-path optical coherence tomography.The bare fiber probe integrated with a hypodermic needle provides the rigidness required to perform lateral scanning with less microscale bending.By submerging both the probe and the specimen into saline solution, we not only reduce the beam divergence, but also increase the signal-to-noise ratio compared with the measurement in free space.Our system can differentiate the characteristic cartilage zones and identity various micro-structured defects in an ex vivo chicken knee cartilage, thus demonstrating that it could be used to conduct early arthritis diagnosis and intraoperative endo-microscopy.
Anastomosis is one of the most commonly performed procedure in the clinical environment that involves tubular structures, such as blood vessel, lymphatic vessel, seminal duct and ureter. Suture based anastomosis is still the foundation for most basic surgical training and clinical operation, although alternate techniques have been developed and under development. For those tubular-structure-anastomosis, immediate real-time post-operative evaluation of the surgical outcome is critical to the success of surgery. Previously evaluation is mostly based on surgeons' experience. Fourier-domain optical coherence tomography is high-speed, high-resolution noninvasive 3D imaging modality that has been widely used in the biomedical research and clinical study. In this study we used Fourier-domain optical coherence tomography as an evaluation tool for anastomosis of lymphatic vessels, ureter and seminal duct in rodent model. Immediate post-operative and long term surgical site data were collected and analyzed. Critical clinical parameters such as lumen patency, anastomosed site narrowing and suture error detection are provided to surgeons.
In this study, we demonstrate an automated data acquisition/analysis platform for both long-term motion tracking and functional brain imaging in freely moving mice. Our system utilizes a fiber-bundle based fluorescence microscope for 24 hours imaging of cellular activities within the brain while also monitoring corresponding animal behaviors using a NIR camera. Synchronized software and automation of analysis allow quantification of all animal behaviors and their brain activities over extended periods of time. Our platform can be used for interrogation of the brain activities in different behavioral states and is also well-suited for longitudinal studies of cellular activities in freely moving animals.
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