Abstract:We have developed an instrument for non-invasive optical imaging of the human brain that produces on-line images with a temporal resolution of 160 ms. The imaged quantities are the temporal changes in cerebral oxy-hemoglobin and deoxy-hemoglobin concentrations. We report real-time videos of the arterial pulsation and motor activation recorded on a 4 × 9 cm 2 area of the cerebral cortex in a healthy human subject. This approach to optical brain imaging is a powerful tool for the investigation of the spatial and temporal features of the optical signals collected on the brain. 2.Y. Hoshi, S. Mizukami, M. Tamura, "Dynamic features of hemodynamic and metabolic changes in the human brain during all-night sleep revealed by near-infrared spectroscopy," Brain Research 652, 257-262 (1994
We have noninvasively studied the motor cortex hemodynamics in human subjects under rest and motor stimulation conditions using a multichannel near‐infrared tissue spectrometer. Our instrument measures optical maps of the cerebral cortex at two wavelengths (758 and 830 nm), with an acquisition time of 160 ms per map. We obtained optical maps of oxy‐ and deoxy‐hemoglobin concentration changes in terms of amplitudes of folding average, power spectrum and coherence at the stimulation repetition frequency, and the phase synchronization index. Under periodic motor stimulation conditions, we observed coherence and frequency or phase synchronization of the local hemodynamic changes with stimulation. Our main findings are the following: (1) The amplitude of the hemodynamic response to the motor stimulation is comparable to the amplitude of the fluctuations at rest. (2) The spatial patterns of the oxy‐ and deoxy‐hemoglobin responses to the stimulation are different. (3) The hemodynamic response to stimulation shows a spatial localization and a level of phase synchronization with the motor stimulation that depends on the stimulation period.
Type 1 copper sites bind nitric oxide (NO) in a photolabile complex. We have studied the NO binding properties of the type 1 copper sites in two cupredoxins, azurin and halocyanin, by measuring the temperature dependence of the ligand binding equilibria and the kinetics of the association reaction after photodissociation over a wide range of temperature (80-280 K) and time (10(-6)-10(2) s). In both proteins, we find nonexponential kinetics below 200 K that do not depend on the NO concentration. Consequently, this process is interpreted as geminate recombination. In azurin, the rebinding can be modeled with the Arrhenius law using a single pre-exponential factor of 10(8.3) s-1 and a Gaussian distribution of enthalpy barriers centered at 22 kJ/mol with a width [full width at half-maximum (FWHM)] of 11 kJ/mol. In halocyanin, a more complex behavior is observed. About 97% of the rebinding population can also be characterized by a Gaussian distribution of enthalpy barriers at 12 kJ/mol with a width of 6.0 kJ/mol (FWHM). The pre-exponential of this population is 1.6 x 10(12) s-1 at 100 K. After the majority population has rebound, a power-law phase that can be modeled with a gamma-distribution of enthalpy barriers is observed. Between 120 and 180 K, an additional feature that can be interpreted as a relaxation of the barrier distribution toward higher barriers shows up in the kinetics. Above 200 K, a slower, exponential rebinding appears in both cupredoxins. Since the kinetics depend on the NO concentration, this process is identified as bimolecular rebinding.(ABSTRACT TRUNCATED AT 250 WORDS)
We have used Photon Density Wave Fluctuation Correlation Spectroscopy (PDW-FCS) to study spatial and temporal correlations of large-scale (~1 mm) optical fluctuations in turbid media such as tissues. Our method uses high frequency (110 MHz) intensity modulated near-infrared light traveling in multiply scattering media. We measure the power spectra of the average value (DC), modulation amplitude (AC) and phase (Φ) of the photon density wave launched in the turbid medium. We have designed an optical probe, consisting of two source-detector pairs, which in conjunction with a correlation algorithm restricts the region probed by the photon density wave.
Near-infrared spectroscopy and imaging are powerful tools to detect and continuously monitor the cerebral hemodynamic and oxygenation changes induced by brain activity. However, in addition to the focal neuronal-activation-induced hemodynamic signals, near-infrared methods are also sensitive to the cerebral hemodynamic fluctuations of systemic origin associated, for instance, with the arterial pulse, respiration, and heart rate fluctuations. We have used near-infrared spectroscopy to non-invasively measure the cerebral hemodynamics in a human subject at rest. We have observed hemoglobin oscillations at the heart rate (~1 Hz), respiratory rate (~0.2 Hz), and at lower frequencies that are associated with heart rate fluctuations and vasomotion activity. With near-infrared imaging, we have measured the spatial maps of temporal changes in the cerebral oxy- and deoxy- hemoglobin concentrations during motor activity (hand tapping). We have found a more localized activation-induced response in the deoxy-hemoglobin map with respect to the oxy-hemoglobin map. This result can be explained by the observed synchronization between the sequence of tapping/rest periods and several systemic physiological oscillation such as the arterial pulse, respiration, and heart rate fluctuations.
Using stopped-flow rapid mixing and flash photolysis techniques, the dissociation rate coefficients of horse carbonmonoxy myoglobin (hMbCO) and oxygenated myoglobin (hMbO2) in aqueous solution have been determined as a function of temperature between 274 and 342 K. From the Arrhenius plot, an activation enthalpy for dissociation of 74 kJ/mol was obtained for both ligands. The pronounced kinetic differences arise from markedly different pre-exponentials. We compare the Arrhenius parameters with those of the association reaction, as measured at cryogenic temperatures. In our analysis we conclude that the entropy loss upon binding of O2 is twice as large as that for CO. Taking reasonable estimates for the frequency factor, the transition state entropy in hMbO2 is located roughly half way in between the entropies of the bound and unbound states. By contrast, the entropy of the transition state in hMbCO appears to be identical to that of the bound state. Possible structural reasons for the different behavior are discussed.
We study the fluctuations in the photon-density wave parameters ͓average intensity ͑dc͒, modulation amplitude, and phase͔ caused by macroscopic fluctuations in the optical properties of turbid media. We present both a theoretical analysis based on diffusion theory and its experimental verification on a strongly scattering suspension containing absorbing particles ͑1-1.6 mm effective diameter͒ in turbulent motion. The photondensity waves are induced by the laser diode output ͑750 nm͒, which is intensity-modulated at 110 MHz. The dc, amplitude, and phase are acquired with an acquisition time per data point of 8 ms, which corresponds to a frequency bandwidth of 62.5 Hz. We have found that in the presence of the absorbing particles, the dc and phase average values and power spectra are in good agreement with our theoretical predictions. We have verified that our instrument can extend the measured frequency band up to the kHz region, which is appropriate for the study of fluctuations of optical parameters in biological tissues. ͓S1063-651X͑98͒01708-5͔
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