Temporal and spatial orchestration of neurovascular coupling in brain neuronal activity is crucial for comprehending the mechanism of functional cerebral metabolism and pathophysiology. Laser speckle contrast imaging (LSCI) through a thinned skull over the somatosensory cortex is utilized to map the spatiotemporal characteristics of local cerebral blood flow (CBF) in anesthetized rats during sciatic nerve stimulation. The time course of signals from all spatial loci among the massive dataset is hard to analyze, especially for the thousands of images, each of which composes millions of pixels. We introduce a temporal clustering analysis (TCA) method, which is proven as an efficient method to analyze functional magnetic resonance imaging (fMRI) data in the temporal domain. The timing and location of CBF activation shows that contralateral hindlimb sensory cortical microflow is activated to increase promptly in less than 1 s after the onset of 2-s electrical stimulation and is evolved in different discrete regions. This pattern is similar but slightly elaborated from the results obtained from laser Doppler flowmetry (LDF) and fMRI. We present this combination to investigate interacting brain regions, which might lead to a better understanding of the nature of brain parcellation and effective connectivity.
Temporal and spatial orchestration of neurovascular coupling in the brain neuronal activity is crucial for us to comprehend mechanism of functional cerebral metabolism and pathophysiology. Laser speckle contrast imaging (LSCI) through a thinned skull over the somatosensory cortex was utilized to map the spatiotemporal characteristics of local cerebral blood flow (CBF) in anesthetized rats during sciatic nerve stimulation. Since the time course of signals from all spatial loci among the massive dataset is hard to analyze, especially for the thousands of images each of which composes of millions of pixels, we introduced a temporal clustering analysis (TCA) method, which was proved as an efficient method to analyze functional magnetic resonance imaging (fMRI) data in the temporal domain. The timing and location of CBF activation showed that contralateral hindlimb sensory cortical microflow was activated to increase promptly in less than 1 s after the onset of 2 s electrical stimulation then evolved in different discrete regions. This pattern is similar but slightly elaborated to the results obtained from laser Doppler flowmetry (LDF) and fMRI. We presented this combination to investigate interacting brain regions and provided network-level analyses, which might possibly lead to a better understanding of the nature of brain parcellation and effective connectivity.
Laser speckle imaging (LSI) through a thinned skull over the somatosensory cortex was utilized to map the spatiotemporal characteristics of local cerebral flood flow (CBF) in anesthetized rats during sciatic nerve stimulation. Region-of-interest selection and Temporal clustering analysis (TCA) method was illustrated on the dataset from high-resolution optical imaging to detect the timing and location of CBF activation. Contralateral hindlimb sensory cortical microflow was activated to increase promptly in less than 1 s after the onset of 2 s electrical stimulation then evolved in different discrete regions. Individual arteries, veins and capillaries in different diameters were activated with the time going. This pattern is similar but slightly elaborated to the results obtained from laser Doppler flowmetry (LDF), functional magnetic resonance imaging (fMRI). We presented this combination to characterize the behaviors of CBF response to neuronal activity, which might possibly lead to a better understanding of neurovascular coupling and fMRI signals.
KEYWORDS: Nerve, Brain, Cerebral blood flow, Functional magnetic resonance imaging, Neuroimaging, Optical imaging, Signal to noise ratio, Speckle, In vivo imaging, Blood
In many studies on functional neuroimaging, change in local cerebral blood flow (CBF) induced by sensory stimulation is used as a substitutive marker for change in cortical neuronal activity by Roy and Sherrington’s postulation. The purpose of this study is to evaluate the close temporal relationship between evoked local CBF and neuronal activity through utilizing temporal clustering analysis (TCA) method to analyze the dataset obtained by high-resolution laser speckle imaging (LSI). We mapped a relatively large somatosensory area of cerebral cortex in successively and followed variations of cerebral blood flow under sciatic nerve stimulation in anesthetized rats using LSI technique. Then we illustrated TCA method on the optical imaging signals and investigated the temporal characteristics of CBF activation. Contralateral somatosensory cortical microflow was activated to increase promptly in less than 1 second after the onset of 2 seconds electrical stimulation (pulse parameters: 0.5ms, 5Hz, 350mV). The data of the present study may possibly shed light on the development question of functional magnetic resonance imaging (fMRI) whether the ultimate spatial resolution attainable by fMRI is limited by the physiology of the cerebral blood flow response to activation or by the hardware and signal-to-noise ratio.
Monitoring the spatio-temporal characteristics of blood flow (BF) is crucial for physiological studies. At present, most optical techniques used for monitoring the BF utilize either the Doppler effect or the temporal statistics of time-varying speckle to measure the blood velocity at a point. If a map of blood velocity distribution is required, some form of scanning must be introduced, thus limiting the temporal and spatial resolution. Laser speckle imaging (LSI) technique could provide real-time spatially resolved BF images without the need for scanning by utilizing the spatial statistics of time-integrated speckle. In present paper, the regional blood flows in the rat mesentery under the effect of phentolamine with incremental concentration were monitored using LSI method. Our results showed that for arterioles, the vessels expanded and BF increased under the treatment with phentolamine of 1μg/ml. However, as the concentration increased, the BF decreased and dilation only happened at the concentration of 100μg/ml; For venules, no dilation was observed except for the case of 100μg/ml while BF decreased. These suggested that compared with the conventional methods, LSI could obtain the spatio-temporal dynamic of BF in the mesentery with high resolution without scan, providing a new approach in studying the microcirculation in the mesentery.
This paper applied the zero-crossings of laser speckle (ZCLS) method, utilizing the diffraction of a focused Gaussian beam, to obtain the dynamics of lymph flow on the rat mesentery in vivo. Two experiments were designed in this study: one was the intralipid model experiment; and the other was the lymph flow under the influence of isoprenaline. In the former, the temporal dynamics of intralipid flow were acquired indicating the validity of the ZCLS method. In the latter, the speckle interferometry results manifested no significant changes in the average velocities of lymph flow, which was consistent with the result obtained by the conventional physiological method of frame by frame analysis. However, the speckle results also manifested that the lymph flow dynamics changed under the drug's influence, which could not be gained by the conventional physiological methods. These indicated that the speckle interferometry technique was promising to determine lymph-flow diagnostics.
At present, the easiest and most effective strategy of imaging functional architecture is based on the slow intrinsic changes in the optical properties of active brain tissue, permitting visualization of active cortical regions at a spatial resolution better than 50 micrometers . This can be accomplished without some of the problems associated with the use of extrinsic probes. Monitoring the spatio-temporal characteristics of cerebral blood flow (CBF) is crucial for studying the normal and pathological conditions of brain metabolism. Laser dynamic speckle imaging technique achieves this goal without the need for scanning by utilizing the spatial statistics of time-integrated speckle, which was first proposed by Fercher and Briers in the early eighties. Considering similarity of these two experimental systems, we are trying to integrate them into one system in order to acquire much more neurophysiological information simultaneously.
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