Influence of a skull cranial window on the measurement of haemoglobin concentration in cortical tissue by multi-spectral imaging analysis

The simplified cranial window, which is transparent thinned skull, has been used for the optical imaging of cortical tissue of small animals to measure the concentration change in haemoglobin as an intrinsic signal of brain activation. The multi-spectral images of the cortical tissue of guinea pigs through the skull cranial window were compared with those of the exposed cortex to evaluate the influence of the scattering and absorption properties of the skull on the measurement of the concentration change in haemoglobin. Although skull thickness affects the sensitivity of the optical signal due to a decrease in mean optical path length in the cortical tissue, the influence of the skull cranial window on the wavelength dependence of optical path length can be ignored when the skull thickness is less than approximately 100 mm. Accurate concentration changes in oxygenated and deoxygenated haemoglobins can be calculated from the optical signal measured through a skull cranial window and the wavelength dependence of optical path length for the exposed cortex.     

Functional optical coherence tomography for detecting neural activity through scattering changes

We have demonstrated functional optical coherence tomography (fOCT) for neural imaging by detecting scattering changes during the propagation of action potentials through neural tissue. OCT images of nerve fibers from the abdominal ganglion of the sea slug Aplysia californica were taken before, during, and after electrical stimulation. Images acquired during stimulation showed localized reversible increases in scattering compared with those acquired before stimulation. Motion-mode OCT images of nerve fibers showed transient scattering changes from spontaneous action potentials. These results demonstrate that OCT is sensitive to the optical changes in electrically active nerve fibers.     

Differentiation of speech and nonspeech processing within primary auditory cortex

Primary auditory cortex (PAC), located in Heschl's gyrus (HG), is the earliest cortical level at which sounds are processed. Standard theories of speech perception assume that signal components are given a representation in PAC which are then matched to speech templates in auditory association cortex. An alternative holds that speech activates a specialized system in cortex that does not use the primitives of PAC. Functional magnetic resonance imaging revealed different brain activation patterns in listening to speech and nonspeech sounds across different levels of complexity. Sensitivity to speech was observed in association cortex, as expected. Further, activation in HG increased with increasing levels of complexity with added fundamentals for both nonspeech and speech stimuli, but only for nonspeech when separate sources (release bursts/fricative noises or their nonspeech analogs) were added. These results are consistent with the existence of a specialized speech system which bypasses more typical processes at the earliest cortical level.     

Imaging cortical electrical stimulation in vivo: fast intrinsic optical signal versus voltage-sensitive dyes

We applied high-temporal-resolution optical imaging utilizing both the fast intrinsic optical signal (fIOS) and voltage-sensitive dyes (VSDs) to observe the spatiotemporal characteristics of rat somatosensory cortex during electrical stimulation. We find that changes in both the fIOS and VSD signals occur rapidly (<30 ms) after the stimulus is applied, suggesting that both membrane depolarization and transmembrane ion movement occur shortly after the stimulus, preceding the more gradual physiological changes in oxygen consumption revealed by the slower component of the intrinsic optical signal. We find that the VSD signal spreads through a much larger area of cortex than the fIOS.     

Characterization of BOLD-fMRI signal during a verbal fluency paradigm in patients with intracerebral tumors affecting the frontal lobe

Previous studies have indicated that the BOLD-fMRI signal can be modified by tumor processes in close vicinity to functional brain areas. This effect has been investigated primarily for the perirolandic area but there is only a limited number of studies concerning frontal cortical regions. Therefore, the aim of the current study was to characterize BOLD-fMRI signal and activation patterns in patients with frontal brain tumors while performing a verbal fluency task. Six patients (ages 31-56 years) suffering from frontal (5 left sided and 1 right sided) intracerebral tumors were examined with fMRI while performing a verbal fluency task in a blocked paradigm design. Eight healthy volunteers served as the control group. The patients (5 right and 1 left handed) demonstrated left frontal activation which could be clearly located outside the tumor area and adjacent edema with varying degrees of additional right frontal activation. In the predominant left frontal activation cluster, the mean voxel based z-score and cluster size were not statistically different between patients and controls. The present fMRI study is indicating that language related BOLD signal changes in the frontal cortex of patients with tumors close to functional areas were comparable to the signal in normal controls. Additionally, the temporal hemodynamic response characteristic was comparable in both groups. This is an important finding consistent with PET results and corroborates the feasibility of functional mapping approaches in patients with tumors affecting the frontal lobe. Additional studies investigating alterations of the hemodynamic response depending on tumor location and histology are required in order to further elucidate the association between pathophysiology and BOLD fMRI signal.     

Activation of SC during electrical stimulation of LGN: retinal antidromic stimulation or corticocollicular activation?

We have recently used combined electrostimulation, neurophysiology, microinjection and functional magnetic resonance imaging (fMRI) to study the cortical activity patterns elicited during stimulation of cortical afferents in monkeys. We found that stimulation of a site in lateral geniculate nucleus (LGN) increases the fMRI signal in the regions of primary visual cortex receiving input from that site, but suppresses it in the retinotopically matched regions of extrastriate cortex. Intracortical injection experiments showed that such suppression is due to synaptic inhibition. During these experiments, we have consistently observed activation of superior colliculus (SC) following LGN stimulation. Since LGN does not directly project to SC, the current study investigated the origin of SC activation. By examining experimental manipulations inactivating the primary visual cortex, we present here evidence that the robust SC activation, which follows the stimulation of LGN, is due to the activation of corticocollicular pathway.     

Thermally induced defect photoluminescence in hydrogenated amorphous silicon

The intrinsic defect photoluminescence of hydrogenated amorphous silicon (a-Si:H) films has been investigated at high intensities of optical pumping that lead to heating of the film. It has been revealed that, for short heating times, the intensity of the defect photoluminescence increases exponentially with an increase in the temperature with an activation energy of 0.85 eV, which is considerably higher than the activation energy (∼0.2 eV) determined from experiments on classical annealing. This and other experimental results on the temperature dependence of the intensity and kinetics of the defect photoluminescence have been explained in terms of the “hydrogen glass” model by thermally induced generation of intrinsic defects in amorphous silicon. The results of the calculations are in good agreement with the experimental data on the defect photoluminescence that reflects the formation and annihilation of defects for short heating times under optical excitation.     

Quantification of venous blood signal contribution to BOLD functional activation in the auditory cortex at 3 T

Most modern techniques for functional magnetic resonance imaging (fMRI) rely on blood-oxygen-level-dependent (BOLD) contrast as the basic principle for detecting neuronal activation. However, the measured BOLD effect depends on a transfer function related to neurophysiological changes accompanying electrical neural activation. The spatial accuracy and extension of the region of interest are determined by vascular effect, which introduces incertitude on real neuronal activation maps. Our efforts have been directed towards the development of a new methodology that is capable of combining morphological, vascular and functional information; obtaining new insight regarding foci of activation; and distinguishing the nature of activation on a pixel-by-pixel basis. Six healthy volunteers were studied in a parametric auditory functional experiment at 3 T; activation maps were overlaid on a high-resolution brain venography obtained through a novel technique. The BOLD signal intensities of vascular and nonvascular activated voxels were analyzed and compared: it was shown that nonvascular active voxels have lower values for signal peak (P<10(-7)) and area (P<10(-8)) with respect to vascular voxels. The analysis showed how venous blood influenced the measured BOLD signals, supplying a technique to filter possible venous artifacts that potentially can lead to misinterpretation of fMRI results. This methodology, although validated in the auditory cortex activation, maintains a general applicability to any cortical fMRI study, as the basic concepts on which it relies on are not limited to this cortical region. The results obtained in this study can represent the basis for new methodologies and tools that are capable of adding further characterization to the BOLD signal properties.     

Laminar specificity in monkey V1 using high-resolution SE-fMRI

The lamination of mammalian neocortex is widely used as reference for describing a wide range of anatomical and physiological data. Its value lies in the observation that in all examined species, cortical afferents, intrinsic cells and projection neurons organize themselves with respect to the laminae. The comprehension of the computations, carried out by the neocortical microcircuits, critically relies on the study of the interlaminar connectivity patterns and the intralaminar physiological processes in vivo. High-resolution functional neuroimaging, enabling the visualization of activity in individual cortical laminae or columns, may greatly contribute in such studies. Yet, the BOLD effect, as measured with the commonly used GE-EPI, contains contributions from both macroscopic venous blood vessels and capillaries. The low density of the cortical veins limits the effective spatial specificity of the fMRI signal and yields maps that are weighted toward the macrovasculature, which thus can be significantly different from the actual site of increased neuronal activity. Spin-echo (SE) sequences yielding apparent T2-weighted BOLD images have been shown to improve spatial specificity by increasing the sensitivity of the signal to spins of the parenchyma, particularly at high magnetic fields. Here we used SE-fMRI at 4.7 T to examine the specificity and resolution of functional maps obtained by stimulating the primary visual cortex of monkeys. Cortical layers could be clearly visualized, and functional activity was predominantly localized in cortical layer IV/Duvernoy layer 3. The choice of sequence parameters influences the fMRI signal, as the SE-EPI is by nature sensitive to T2* in addition to its T2 dependency. Using parameters that limit T2* effects yielded higher specificity and better visualization of the cortical laminae. Because the demands of high-spatial resolution using SE severely decreases temporal resolution, we used a stimulus protocol that allows sampling at higher effective temporal resolution. This way, it was possible to acquire high-spatial and high-temporal resolution SE-fMRI data.     

Quantitative analysis of asymmetrical cortical activity in motor areas during sequential finger movement

Brain asymmetry is a phenomenon well known for handedness and has been studied in motor cortices. However, few quantitative studies on asymmetrical cortical activity in motor areas have been conducted. In this study, we systematically investigated asymmetrical cortical activity in motor areas during sequential finger movement by quantitatively analyzing functional magnetic resonance imaging (fMRI) blood oxygenation level-dependent (BOLD) responses. The norm of BOLD signal percentage of change was introduced to quantitatively measure the BOLD signal intensity change difference between the left and right motor areas. The results of the data collected from six subjects show that the norm of BOLD signal percentage of change in the right motor area is higher than that in the left motor area for two-hand movement (P=.0059) and single-hand movement (P=.0279) with right-handedness. These results from fMRI show the asymmetry of motor areas and may suggest that the left hemisphere motor area comes into being as an adaptation system that needs few neuron cells only to finish any movement task for right-handedness. The activation intensity in the left motor area is reduced with normal right finger movement. The activation intensity in the right motor area is obviously higher than that in the left motor area.     

Circular polarization intrinsic optical signal recording of stimulus-evoked neural activity

Linear polarization intrinsic optical signal (LP-IOS) measurement can provide sensitive detection of neural activities in stimulus-activated neural tissues. However, the LP-IOS magnitude and signal-to-noise ratio (SNR) are highly correlated with the nerve orientation relative to the polarization plane of the incident light. Because of the complexity of orientation dependency, LP-IOS optimization and outcome interpretation are time consuming and complicated. In this study, we demonstrate the feasibility of circular polarization intrinsic optical signal (CP-IOS) measurement. Our theoretical modeling and experimental investigation indicate that CP-IOS magnitude and SNR are independent from the nerve orientation. Therefore, CP-IOS promises a practical method for polarization IOS imaging of complex neural systems.     

Investigations of touchscreen glasses from mobile phones for retrospective and accident dosimetry

Touchscreen glasses of mobile phones are sensitive to ionizing radiation and have the potential of usage as an emergency dosimeter for retrospective dosimetry for the purpose of triage after a radiological accident or attack. In this study the TL glow curves and dosimetric properties of touchscreen glasses were studied in detail, such as intrinsic background dose, dose response, reproducibility, optical stability and long-term stability of the TL signal.Preliminary results are additionally presented to minimize the intrinsic background dose by mechanically removing the surface layer of the glass samples. Additionally chemical element analyses of the touchscreen glass samples were carried out to investigate the difference between glass samples which show a TL signal and samples which show neither an intrinsic zero dose signal nor a radiation induced TL signal.An irradiation trial using glass samples stored in the dark demonstrated a successful dose recovery. However, when applying a realistic, external light exposure scenario, dose underestimation was observed, even though samples were pre-bleached prior to measurement. More investigations have to be carried out in the future to solve the challenge of the low optical stability of the TL signal, if touchscreen glasses are to be used as a reliable emergency dosimeter.     

基于光学测棒的立体视觉坐标测量系统的研究

提出了一种基丁测量与校准功能合一的光学测棒的立体视觉坐标测最系统.采用光学测棒作为成像目标,通过任意放置的两台摄像机获取测棒上的发光特征点的图像实现被测物体三维坐标的测量,同时利用测量数据定期对两台摄像机外部方位参数进行校准.深入研究了两台摄像机内部参数和外部方位参数校准过程中的校准件和校准算法的设计,以及系统测量建模等关键技术,提出了相应的解决方案,减小了摄像机内外参数校准及测量模型对测量结果的影响,提高系统的测量精度.实验结果表明.该系统的最大测量误差为0.11 mm.     

Dependence of BOLD signal change on tactile stimulus intensity in SI of primates

Recently, we have demonstrated that the fine-digit topography (millimeter sized) previously identified in the primary somatosensory cortex (SI), using electrophysiology and intrinsic signal optical imaging, can also be mapped with submillimeter resolution using blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging at high field. In the present study, we have examined the dependence of BOLD signal response on stimulus intensity in two subregions of SI, Areas 3b and 1. In a region(s)-of-interest (ROI) analysis of Area 3b, BOLD signal amplitude increased linearly with increasing amplitude of an 8-Hz vibrotactile stimulus, and BOLD signal was sustained throughout the stimulation period. In contrast, in Area 1, a significant BOLD signal response was only observed with more intense stimuli, and ROI analysis of the dependence of BOLD response showed no significant dependence on stimulus intensity. In addition, activation was not sustained throughout the period of stimulation. Differing responses of Areas 3b and 1 suggest potentially divergent roles for subregions of SI cortices in vibrotactile intensity encoding. Moreover, this study underscores the importance of imaging at small spatial scales. In this case, such high-resolution imaging allows differentiation between area-specific roles in intensity encoding and identifies anatomic targets for detailed electrophysiological studies of somatosensory neuronal populations with different coding properties. These experiments illustrate the value of nonhuman primates for characterizing the dependence of the BOLD signal response on stimulus parameters and on underlying neural response properties.     

Glass‐embedded silver nanoparticle patterns by masked ion‐exchange process for surface‐enhanced Raman scattering

Glass‐embedded silver nanoparticle patterns were fabricated by masked silver–sodium ion‐exchange process followed by etching to reveal the particles for surface‐enhanced Raman scattering (SERS). The intensity of the enhanced Raman signal is comparable to that of the fluorescence, and the detection limit of 1 nM for Rhodamine 6G has been achieved. Raman images at different etching depths and corresponding morphological images are compared to find optimal SERS signal. Our results demonstrate that silver nanoparticle patterns embedded in glass can be used as SERS‐active substrates. Nanoparticles can be formed in a glass of high optical quality and have potential to be integrated with optical waveguides for a sensor chip. Copyright © 2010 John Wiley & Sons, Ltd.     

Parallel Detection of Multiple Transitional Spectral Patterns Using Optical Spectrogram Scope

In measurement of ultrafast phenomena caused by several photochemical reactions, multiple transitional spectral patterns contained in a signal pulse are directly associated with different interactions, allowing us to identify individual interactions from these patterns. We propose a new method by which we can detect multiple transitional spectral patterns contained in a signal pulse in parallel using optical spectrogram scope (OSS). In the experimental demonstration, we used an arrayed filter composed of matched filters recording three kinds of transitional spectral patterns in the OSS system, and we directly detected two different patterns contained in a signal pulse in parallel.     

Modulational instability effects in PSK modulated coherent fiber systems and their reduction by optical loss

We show using the propagating beam technique that if optical loss is neglected, the efficiency of PSK modulation in a coherent fiber system is severely compromised by modulational instability effects at sufficiently high signal powers. We note, however, that the intrinsic optical loss of a single mode fiber will to a large degree counteract the modulational instability and preserve the initial PSK pulse shape.     

Resolving dynamics of acoustic phonons by surface plasmons

We show that the dynamics of acoustic phonons generated by femtosecond impulsive optical excitation can be clearly resolved by a surface plasmon technique, with enhanced sensitivity orders of magnitude higher than regular optical probe measurements. Our calculations confirm that the enhanced sensitivity is an intrinsic property of the surface plasmon probe. Therefore, the surface plasmon technique is a promising tool to detect small signal changes in optical and mechanical properties on a microscopic scale.     

一种新的基于空间图案信号的多进制无线光通信技术

提出了一种新的多进制无线光通信技术,其基本原理是用一组相互易区分的空间图案代替传统无线通信中的会聚光斑传递信息.分析了该通信方案的信道容量,结果表明无线光通信系统存在未被利用的空间自由度,其大小与系统收发孔径和光波波长有关,与光场空间分布无关.通过合理设置系统的结构参数和设计信号图案,可以利用无线光通信系统的空间自由度增加信道容量.提出了一种实现该技术的光电系统方案,其关键组成部分为空间光调制器和图象相关器.详细描述了信号处理过程,具体包括二维相关处理、比较判决和进制转换三部分.分析了该方案的误码性能,得到了平均误码率的估算公式,分析得到了可降低误码率的信号设计基本规则.最后用一个透镜阵列处理器通过实验验证了该通信方案.     

The laminar pattern of resting state in human cerebral cortex

Resting state functional Magnetic Resonance Imaging (RS-fMRI) provides the means to measure neuronal activity. One of the most commonly used methods to explore the RS-fMRI signal is the Probabilistic Independent Component Analysis (PICA). PICA allows to depict brain functional connectivity (FC) networks. Yet most of the IC maps obtained with this method do not represent any particular FC network. Consequently, those IC maps are classified as artifacts or noise of an unknown source. We hypothesized that the unexplained RS-fMRI signal patterns that are picked up by the PICA can be related to the differences in oxygen metabolism and blood flow in cortical layers. This study aimed at (1) providing preliminary evidence to the effects of laminar organization of neocortex on the RS-fMRI signal, and (2) evaluating the application of laminar maps to aid the classification of IC maps. We created laminar maps 1–4 that depict relative cortical thickness of layers IV and VI. Our data show that the RS-fMRI signal is significantly related to the relative thickness of the cortical layer VI but not layer IV. Importantly, the laminar maps 1–4 overlap with four separate IC maps. Thus, the laminar maps 1–4 improve classification and interpretation of the IC maps. Moreover, the laminar maps 1–4 may be considered as FC networks that are the bridging piece between particular cognitive functions. Together, these data provide preliminary evidence to the fundamental questions about the role of cortical layering in the RS-fMRI signal and brain FC networks.