Different methods of speckle-metrology, which may be used in biomedical diagnostics, are considered in this paper.
Cross-correlation technique, digital speckle-photography, LASCA are compared. Advantages and disadvantages of
these methods are demonstrated; the limits for minimal resolution are studied.
Effects of laser at the wavelength of 650 nm on the isolated vessels of white rat mesentery have been analyzed. Influence of laser irradiation on the statement of blood microcirculation in mucous membrane of human oral cavity has been investigated. Temporal changes of hemodynamics have been studied by methods of laser photoplethysmography, Doppler diagnostics and laser speckle imaging technique. Influence of coherent light (at the wavelength 630 nm) on the intensity of microcirculation in the capillary net of mucous membrane has been demonstrated directly during the short-time session of laser therapy.
In this paper different methods of processing of speckle pattern are compared. Two configuration of illumination perfusion by speckle-modulated coherent irradiation and Gaussian beam are analyzed. Optimal optical scheme of digital speckle-microscopy is found for monitoring of blood microcirculation.
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.
Intrinsic optical signals imaging (IOSI) and laser speckle imaging (LSI) are both novel techniques for functional neuroimaging in vivo. Combining them to study cortical spreading depression (CSD) which is an important disease model for migraine and other neurological disorders. CSD were induced by pinprick in Sprague-Dawley rats. Intrinsic optical signals (IOS) at 540 nm showed CSD evolution happened in one hemisphere cortex at speeds of 3.7±0.4 mm/min, and the vasodilation closely correlated a four-phasic response. By LSI, we observed a transient and significant increase cerebral blood flow (CBF). In this paper, optical imaging would be showed as a powerful tool for describing the hemodynamic character during CSD in rat.
The spatio-temporal characteristics of changes in cerebral blood volume associated with neuronal activity were investigated in the hindlimb somatosensory cortex of α-chloralose/urethan anesthetized rats (n=10) with optical imaging at 570nm through a thinned skull. Activation of cortex was carried out by electrical stimulation of the contralateral sciatic nerve with 5Hz, 0.3V pulses (0.5ms) for duration of 2s. The stimulation evoked a monophasic optical reflectance decrease at cortical parenchyma and arteries sites rapidly after the onset of stimulation, whereas no similar response was observed at vein compartments. The optical signal changes reached 10% of the peak response 0.70±0.32s after stimulation onset and no significant time lag in this 10% start latency time was observed between the response at cortical parenchyma and arteries compartments. The evoked optical reflectance decrease reached the peak (0.25%±0.047%)2.66±0.61s after the stimulus onset at parenchyma site, 0.40±0.20s earlier (P<0.05) than that at arteries site (0.50%±0.068% 3.06±0.70s). Variable location within the cortical parenchyma and arteries compartment themselves didn’t affect the temporal characteristics of the evoked signal significantly. These results suggest that the sciatic nerve stimulation evokes a local blood volume increase at both capillaries (cortical parenchyma) and arterioles rapidly after the stimulus onset but the evoked blood volume increase in capillaries could not be entirely accounted for by the dilation of arterioles.
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.
The spatio-temporal characteristics of changes in cerebral blood volume associated with neuronal activity were investigated in the hindlimb somatosensory cortex of α-chloralose/urethan anesthetized rats (n=10) with optical imaging at 570nm through a thinned skull. Activation of cortex was carried out by electrical stimulation of the contralateral sciatic nerve with 5Hz, 0.3V pulses (0.5ms) for duration of 2s. The stimulation evoked a monophasic optical reflectance decrease at cortical parenchyma and arteries sites rapidly after the onset of stimulation, whereas no similar response was observed at vein compartments. The optical signal changes reached 10% of the peak response 0.70±0.32s after stimulation onset and no significant time lag in this 10% start latency time was observed between the response at cortical parenchyma and arteries compartments. The evoked optical reflectance decrease reached the peak (0.25%±0.047%) 2.66±0.61s after the stimulus onset at parenchyma site, 0.40±0.20s earlier (P<0.05) than that at arteries site (0.50±0.068% 3.06±0.70s). Variable location within the cortical parenchyma and arteries compartment themselves didn’t affect the temporal characteristics of the evoked signal significantly. These results suggest that the sciatic nerve stimulation evokes a local blood volume increase at both capillaries (cortical parenchyma) and arterioles rapidly after the stimulus onset but the evoked blood volume increase in capillaries could not be entirely accounted for by the dilation of arterioles.
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.
In this study the action of different doses of glucose solution on scattering properties of skin in vivo have been investigated. The application of glucose as hyperosmotic agent leads to the significant increasing of the tissue optical transmittance. There are dose dependent and time dependent effects of glucose on the skin reflectance. The good clearing of tissue is given after undercutaneous administration of 40 percent and 35 percent glucose solutions. The application of such doses of glucose allows one to visualize the small blood vessels in rat skin. The optimal interval of time for the clearing of rat skin is 15 minutes after injection. The method of clearing tissue is conventient, cheap and simple for The diagnostic of microcirculation of skin in vivo.
Laser speckle system was used to measure thermally induced change in velocity of blood flow inside micrangium of rat's mesentery. Meanwhile, the diameter of blood vessels was measured with pickup camera. Based on these measurements, changes in blood perfusion by heat were deduced. The results indicated that velocity of blood flow depended on temperature when tissue was heated, as well as time.
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.
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.
An experimental monitoring of tissue modification of in vitro and in vivo rabbit dura mater with administration of osmotical agents, 40% glucose solution and glycerol, using optical coherence tomography was presented. The preliminary results of experimental study of influence of osmotical liquids (glucose solutions, glycerol) of rabbit dura mater were reported. The significant decreasing of the light from surface and increasing of the light from the deep of dura mater under action of osmotical solutions and the increasing of OCT imaging depth were demonstrated. Experiments showed that administration of osmolytes to dura mater allowed for effective and temporary control of its optical characteristics, which made dura mater more transparent, increased the ability of light penetrating the tissue, and consequently improved the optical imaging depth. It is a significant study, which can improve penetration of optical imaging of cerebral function and acquire more information of the deep brain tissue.
An experimental study of controlling the optical properties of in vitro and in vivo rabbit dura mater with administration of osmotical agents, 40% glucose solution and glycerol, using video camera and spectrometer was presented. The preliminary results of experimental study of influence of osmotical liquids (glucose solutions, glycerol) on transmittance (in vitro) and reflectance (in vivo) spectra of rabbit dura mater were reported. The significant decreasing of the reflectance and increasing of the transmittance of dura mater under action of osmotical solutions were demonstrated. Experiments showed that administration of osmolytes to dura mater allowed for effective and temporary control of its optical characteristics, which made dura mater more transparent, increased the ability of light penetrating the tissue, and consequently improved the optical imaging depth. It is a significant study, which can improve penetration of optical imaging of cerebral function and acquire more information of the deep brain tissue.
The lymph flow diagnostics in microvessels of rat mesentery were performed using light biomicroscopy, speckle- interferometry and spectroscopy. By light microscopy method we have got the dynamic of microvessels images in real time and registered phasic contractions and valve function of lymphatics, lymph and blood flow. The mean velocity of lymph flow was the highest at the moderate number of lymphocytes in flow. We had found the close links between phasic contractions, valve activity and lymph flow intensity. The high-resolution speckle-microscopy quickly gives much information about average lymph flow velocity, but only the relative value of velocity can be estimated. The phasic contractions cause the changes of the speckle signals and led to the modification of lymph flow in microvessels. The reflectance spectra characterize functional state of lymphatics and lymph flow in microvessels.
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