We investigated the impact of laser coherence length on reconstructed flow contrast images with our innovative speckle contrast diffuse correlation tomography (scDCT) device. We tested three lasers with varied coherence lengths: >10 meters, ~3.3 millimeters, and ~390 micrometers. Lasers with coherence lengths larger than millimeters yielded good-quality flow images with higher signal-to-noise ratios (SNR) and less image distortion. We concluded that scDCT measurements do not require excessively long coherence lasers with high costs.
We developed and evaluated a low-cost, miniaturized, and user-friendly speckle contrast diffuse correlation tomography (scDCT) device for noncontact, fast, high-density, and depth-sensitive imaging of CBF distribution in the brain. The new low-cost portable scDCT device was evaluated against an established large scDCT system using head-simulating phantoms with known optical properties and the mouse with transient ligations of common carotid arteries. Results taken from the two scDCT systems were highly consistent. The low-cost miniaturized scDCT has the potential to be commercialized as an affordable, portable, and ergonomic brain monitoring tool for neuroscience research in numerous academic and industrial laboratories.
KEYWORDS: Speckle, Laser speckle contrast imaging, Windows, Brain mapping, Simulation of CCA and DLA aggregates, Brain, 3D modeling, Spatial resolution, Tissues, Neurophotonics
SignificanceFrequent assessment of cerebral blood flow (CBF) is crucial for the diagnosis and management of cerebral vascular diseases. In contrast to large and expensive imaging modalities, such as nuclear medicine and magnetic resonance imaging, optical imaging techniques are portable and inexpensive tools for continuous measurements of cerebral hemodynamics. The recent development of an innovative noncontact speckle contrast diffuse correlation tomography (scDCT) enables three-dimensional (3D) imaging of CBF distributions. However, scDCT requires complex and time-consuming 3D reconstruction, which limits its ability to achieve high spatial resolution without sacrificing temporal resolution and computational efficiency.AimWe investigate a new diffuse speckle contrast topography (DSCT) method with parallel computation for analyzing scDCT data to achieve fast and high-density two-dimensional (2D) mapping of CBF distributions at different depths without the need for 3D reconstruction.ApproachA new moving window method was adapted to improve the sampling rate of DSCT. A fast computation method utilizing MATLAB functions in the Image Processing Toolbox™ and Parallel Computing Toolbox™ was developed to rapidly generate high-density CBF maps. The new DSCT method was tested for spatial resolution and depth sensitivity in head-simulating layered phantoms and in-vivo rodent models.ResultsDSCT enables 2D mapping of the particle flow in the phantom at different depths through the top layer with varied thicknesses. Both DSCT and scDCT enable the detection of global and regional CBF changes in deep brains of adult rats. However, DSCT achieves fast and high-density 2D mapping of CBF distributions at different depths without the need for complex and time-consuming 3D reconstruction.ConclusionsThe depth-sensitive DSCT method has the potential to be used as a noninvasive, noncontact, fast, high resolution, portable, and inexpensive brain imager for basic neuroscience research in small animal models and for translational studies in human neonates.
KEYWORDS: Brain, Ischemia, Simulation of CCA and DLA aggregates, Windows, Speckle, 3D image reconstruction, Sampling rates, Tissues, Reconstruction algorithms, Neuroimaging
SignificanceLow-frequency oscillations (LFOs) (<0.1 Hz) with respect to cerebral blood flow (CBF) have shown promise as an indicator of altered neurologic activity in the abnormal brain. Portable optical instruments have evolved to offer a noninvasive alternative for continuous CBF monitoring at the bedside compared with many large neuroimaging modalities. However, their utilization for acquiring LFOs of CBF has only been studied to a limited extent.AimWe aim to optimize an innovative speckle contrast diffuse correlation tomography (scDCT) system for the detection of LFOs within CBF variations.ApproachThe scDCT was optimized to achieve a higher sampling rate and a faster image reconstruction using a moving window 3D reconstruction algorithm with parallel computation. Power spectral density (PSD) analysis was performed to investigate altered LFOs during transient global cerebral ischemia in neonatal piglets.ResultsTransient global cerebral ischemia resulted in reductions in both CBF and PSD compared with their baseline values.ConclusionsSpontaneous LFOs, combined with CBF, provide a more comprehensive assay with the potential to clarify pathological mechanisms involved in brain injury. These results support scDCT’s inclusion and application in the growing area of LFO analysis and demonstrate its inherent advantage for neurological studies in preclinical and clinical settings, such as neonatal intensive care units.
Laser speckle contrast imaging (LSCI) illuminates continuous-wave (CW) laser light on tissue surface. We assembled an integrated LSCI system combining a CW laser at 785 nm and a picosecond pulsed laser at 775 nm. A CMOS camera collected images from mouse head with intact skull. The pulsed laser with engineered diffuser captured more details of brain vessels compared to the CW laser with glass diffusers. The consecutive ligations of left and right common carotid arteries resulted in significant CBF reductions. This research lays the ground to develop multimodal imaging systems integrating LSCI and other imaging techniques with shared pulse illuminations.
An innovative camera-based speckle contrast diffuse correlation tomography (scDCT) technology has been developed recently, which enables noncontact, noninvasive, high-density, 3D imaging of cerebral blood flow (CBF) distributions. This study demonstrated the capability and safety of scDCT technique for imaging of CBF distributions in a neonatal piglet model of transient ischemic stroke. Moreover, power spectral density analyses of low-frequency oscillations (LFOs) and the network connections over the brain were assessed before and after the induction of acute ischemic stroke. The stroke resulted in a substantial decrease in CBF, attenuations in resting-state LFOs, and functional connectivity disruptions in motor and somatosensory cortices.
KEYWORDS: Ischemia, Optical sensors, Simulation of CCA and DLA aggregates, Semiconductor lasers, Detector arrays, Spectroscopy, Speckle, Neuroscience, Laser tissue interaction, Head
We report an innovative, wearable, multiscale diffuse speckle contrast flowmetry (DSCF) probe for continuous transcranial imaging of cerebral blood flow (CBF) in animal s. Significant reductions in CBF during transient ligation of bilateral common carotid arteries were detected by DSCF (-35±13% in two mice and -59% in a piglet), meeting clinical expectations. Results from DSCF and an established CBF measurement device, diffuse correlation spectroscopy, were consistent and significantly correlated. With further optimization and validation in animals and humans, we expect to ultimately offer a unique, noninvasive, low-cost, and fast brain imaging tool for basic neuroscience research and clinical applications.
Intraventricular hemorrhage (IVH) is the most common neurological complication of prematurity. IVH is a bleeding inside or around ventricles, spaces in the brain containing the cerebrospinal fluid, which occurs as a result of the fragility and immaturity of blood vessels in premature brains. Severe IVH disrupts development of structural and functional connectivity networks, leading to impairments of cerebral development and neurologic deficits. Preterm infants with IVH are prone to alterations in cerebral blood flow (CBF) and associated spontaneous low-frequency fluctuations. However, there are no established noninvasive imaging methods for continuous monitoring of CBF alterations at the bedside in neonatal intensive care units. An innovative CCD/CMOS based speckle contrast diffuse correlation tomography (scDCT) technology has been recently developed in our laboratory, which enables noncontact, noninvasive, and high-density 3D imaging of CBF distributions in deep brain cortex. In the present study, the capability of scDCT technique for noncontact 3D imaging of CBF distributions in a neonatal piglet model of IVH was demonstrated. Moreover, power spectral density analyses of scDCT data were performed to assess alterations in spontaneous low frequency fluctuations in the resting brain, before and after inducing IVH. IVH resulted in a CBF decrease in deep brain cortex. Resting-state spontaneous low-frequency fluctuations after IVH showed attenuations in all frequencies (0.009– 0.08 Hz) compared to the baseline before IVH. In conclusion, scDCT is capable of detecting brain hemodynamic disruptions (reduction in CBF and attenuation in spontaneous low-frequency fluctuations) after IVH, which might be useful for instant management of IVH and associated complications.
We present an innovative, wearable, fiber-free, near-infrared diffuse speckle contrast flowmetry (DSCF) probe that is fixed on the skull for continuous monitoring of cerebral blood flow (CBF) variations in mice during anesthesia, awake, and freely behaving. Results show a small surge when the animal waked up, a mild decrease after the isoflurane washed off, a 37 ± 9% increase during 10%CO2 inhalation (n = 3), and mild elevations during grooming and walking. These CBF variations are consistent with clinical observations when recovery from anesthesia and impacts by isoflurane, hypercapnia (CO2), and activity-induced cortical excitations.
Significance: There is an essential need to develop wearable multimodality technologies that can continuously measure both blood flow and oxygenation in deep tissues to investigate and manage various vascular/cellular diseases.
Aim: To develop a wearable dual-wavelength diffuse speckle contrast flow oximetry (DSCFO) for simultaneous measurements of blood flow and oxygenation variations in deep tissues.
Approach: A wearable fiber-free DSCFO probe was fabricated using 3D printing to confine two small near-infrared laser diodes and a tiny CMOS camera in positions for DSCFO measurements. The spatial diffuse speckle contrast and light intensity measurements at the two different wavelengths enable quantification of tissue blood flow and oxygenation, respectively. The DSCFO was first calibrated using tissue phantoms and then tested in adult forearms during artery cuff occlusion.
Results: Phantom tests determined the largest effective source–detector distance (15 mm) and optimal camera exposure time (10 ms) and verified the accuracy of DSCFO in measuring absorption coefficient variations. The DSCFO detected substantial changes in forearm blood flow and oxygenation resulting from the artery occlusion, which meet physiological expectations and are consistent with previous study results.
Conclusions: The wearable DSCFO may be used for continuous and simultaneous monitoring of blood flow and oxygenation variations in freely behaving subjects.
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