Functional near-infrared spectroscopy.

The purpose of the this article is to describe an emerging neuroimaging technology, functional near-infrared spectroscopy (fNIRs), which has several attributes that make it possible to conduct neuroimaging studies of the cortex in clinical offices and under more realistic, ecologically valid parameters. fNIRs use near-infrared light to measure changes in the concentration of oxygenated and deoxygenated hemoglobin in the cortex. Although fNIR imaging is limited to the outer cortex, it provides neuroimaging that is safe, portable, and very affordable relative to other neuroimaging technologies. It is also relatively robust to movement artifacts and can readily be integrated with other technologies such as EEG.     

Magnetic resonance functional imaging of the brain at 4 t

Blood Oxygenation Level Dependent (BOLD) contrast imaging of human brain function using echo-planar imaging at 4 T gives good freedom from motion artifact, high signal-to-noise ratio/unit time, and adequate spatial resolution. Studies were made of brain activation associated with perceptual and cognitive tasks of several minutes duration.Several cortical areas show task-dependent activity consistent across subjects, in images with a spatial resolution of 2.5 mm×2.5 mm×5 mm and a temporal resolution of up to 1 s. Multislice data were obtained at a rate of up to five slices per second. At 4 T, fractional changes of magnetic resonance (MR) image intensity up to 25% were observed.Novel cross-correlation methods, including the effect of the temporal point-spread function associated with the relatively slow hemodynamic response of the brain, allow activation maps of the brain to be generated with statistically meaningful thresholds.With appropriate data analysis, it is clear that oxygenation changes in large draining veins distant from active neural tissue do not dominate the changes observed, especially when brain tasks activating only a limited volume of gray matter are chosen. This is consistent with downstream dilution of blood oxygenation changes and direct optical observations of functional brain activity in animals.     

MRS studies of cancer

Cancer was an obvious disease to study by magnetic resonance spectroscopy (MRS); it produces large lesions that give clearly abnormal spectra, all treatment methods leave much to be desired, and radiotherapy, in particular, is limited by tissue hypoxia, a process that can be investigated by MRS.³¹P MRS has shown that tumor cells are not acidic, as had been thought; instead, the pH gradient across the tumor cell membrane is the reverse of that in a normal cell. This change in hydrogen-ion gradient is accompanied by changes in gradients of many other ions. Tumor oxygenation can be monitored in animal tumor models using the techniques employed for functional magnetic resonance imaging (MRI) of the brain. Large changes in signal are observed when drugs that reduce tumor blood flow are administered. ¹H NMR spectra of acid extracts of tumor or normal tissue biopsies contain sufficient information to permit classification (and thus, perhaps, diagnosis) if computer-based pattern recognition techniques are employed. Surprisingly, the same technique gives quite good classification of³¹P spectra takenin vivo. Can MRS beappliedin cancer therapy? Studies on tumor ion balance will help in the design of anticancer drugs and other therapies. Tumor blood flow studies using MRI could be applied to individual patients to predict the usefulness of radiotherapy and to assist in radiotherapy planning. Pattern recognition methods could automate the screening of biopsies and could also assist in interpretation of human spectra takenin vivo.     

Intraoperative application of optical spectroscopy in the presenceof blood

A simple but effective method of spectral processing was developed to minimize or remove the effects of the presence of superficial blood on tissue optical spectra and, hence, enhance the performance of optical-spectroscopic-based in vivo tissue diagnosis and surgical guidance. This spectral-processing algorithm was developed using the principles of absorption-induced light attenuation wherein the ratio of fluorescence intensity (F) and the hth power of diffuse reflectance intensity (Rd) at a given emission wavelength λ_m is immune to spectral distortions induced by the presence of blood on the tissue surface. Here, the exponent h is determined by the absorption coefficients of whole blood at the excitation and emission wavelengths. The theoretical basis of this spectral processing was verified using simulations and was experimentally validated. Furthermore, the optical spectra of brain tissues collected in vivo was processed using this algorithm to evaluate its impact on brain tissue differentiation using combined fluorescence and diffuse reflectance spectroscopy. Based on the simulation, as well as experimental results, it was observed that using F/Rd^h h can effectively reduce or remove spectral distortions induced by superficial blood contamination on tissue optical spectra. Thus, optical spectroscopy can also be used intraoperatively for applications such as surgical guidance of tumor resection     

Functional brain imaging using EPI at 3 T

Functional magnetic resonance imaging (fMRI) is becoming an important tool in the mapping of brain activation. However there are two main concerns that need to be answered before functional imaging can be considered truly useful as a neurophysiological tool. The first is that the detected activation may be derived from large veins and, thus, be spatially separate from the underlying brain activity. The second is the incomplete understanding of the brain transfer function and its relation to brain activity, blood flow, and metabolism. This work contains initial results that will help address these points. Models of the brain vasculature predict that signal changes on SE (spin-echo) images are expected to be much smaller in magnitude but very accurate in localizing true areas of activation than on GE (gradient-echo) images which are susceptable to large veins. By comparing activation from SE and GE EPI at 3 T, we have shown that the regions of activation are spatially very similar, suggesting that GE activation is closely linked to the underlying brain activity. We have identified an experimental impulse response of the brain following 8-s visual stimulation. This impulse response can be used to successfully predict the frequency response obtained experimentally and its shape suggests a resonance phenomenon. This suggests the brain transfer function can be modeled from linear response theory corresponding to the inherent feedback control mechanisms of the brain homeostasis. Continuation of this early work will help to identify the links between fMRI signal change and underlying brain physiology.     

Toward mapping spatiotemporal characteristics of muscle oxygenation in different motor modalities by multichannel near‐infrared spectroscopy

Commonly, the near‐infrared spectroscopy (NIRS) devices are used to measure muscle oxygenated hemoglobin (HBO) concentration and total hemoglobin (HBT) concentration with a single channel, which can obtain the temporal HBO and HBT signals. Lacking of the spatial information of muscle oxygenation will limit the exploration of the heterogeneity of muscle activities. In this study, a multichannel NIRS recording system was used to measure the muscle oxygenation with an attempt to simultaneously provide the temporal and spatial HBO and HBT concentration. In the experiment, the influences of four motor tasks, including active, passive, imaginary movement, and the control task (no movement), on muscle oxygenation were investigated in eight normal subjects. Our results showed that both amplitude and spatial heterogeneity associated with variation in muscle oxygenation during active and passive motor tasks were significantly different between the motor time and rest time (P < 0.05). Furthermore, the region where HBO concentration decreased during the active motor task was in accordance with the anatomical position of contracted muscle, which cannot be observed from the results of the passive task. Considering the imaginary and control tasks in which the muscle was in a fixed/stationary state, the amplitude and spatial heterogeneity associated with variations in muscle oxygenation only exhibited slight changes (P > 0.05). This pilot study suggested that the spatiotemporal information obtained from multichannel NIRS devices might be potential for accurate measurement of the variation in muscle oxygenation during motor tasks, which would be useful for different clinical applications.     

A multimodal imaging approach to the evaluation of post-traumatic epilepsy

Object

Electroencephalography-functional magnetic resonance imaging (EEG-fMRI) coregistration and high-density EEG (hdEEG) can be combined to map noninvasively abnormal brain activation elicited by epileptic processes. By combining noninvasive imaging techniques in a multimodal approach, we sought to investigate pathophysiological mechanisms underlying epileptic activity in seven patients with severe traumatic brain injury.

Materials and methods

Standard EEG and fMRI data were acquired during a single scanning session. The EEG-fMRI data were analyzed using the general linear model and independent component analysis. Source localization of interictal epileptiform discharges (IEDs) was performed using 256-channel hdEEG. Blood oxygenation level dependent (BOLD) localizations were then compared to EEG source reconstruction.

Results

On hdEEG, focal source localization was detected in all seven patients; in six out of seven it was concordant with the expected epileptic activity as defined by EEG data and clinical evaluation; and in four out of seven in whom IEDs were recorded, BOLD signal changes were observed. These activities were partially concordant with the source localization.

Conclusion

Multimodal integration of EEG-fMRI and hdEEG combining two different methods to localize the same epileptic foci appears to be a promising tool to noninvasively map abnormal brain activation in patients with post-traumatic brain injury.     

A pharmacokinetic model to study administration of intravenousanaesthetic agents

The compartmental model is widely used in pharmacokinetic studies. Its simulated results can be used in computer assisted drug infusion, particularly for intravenous anesthetic agents. The authors consider the three compartment mammillary model. To ensure optimum pharmacodynamic effects of the anesthetic agents, one must pay attention to compartment two (well-perfused tissues such as muscle and brain) rather than compartment one (blood vessels and organs abundant with vessels such as liver and kidneys) of the model (i.e. a compartment other than the blood plasma). The pharmacodynamic effects in the human body usually correlate with concentration in compartment two, which includes the targets of the anesthetic agents. The concentration in compartment two is easily monitored by noninvasive indices, and is suitable for the control of continuous computer-assisted infusions. One should also attend to physiological changes of the patient which may occur during a surgical procedure. Such changes may dramatically alter the pharmacokinetic parameters and thus affect the activity of intravenous anesthetic agents     

Calcite microcrystals in the pineal gland of the human brain: second harmonic generators and possible piezoelectric transducers

A new form of biomineralization in the pineal gland of the human brain has been studied. It consists of small crystals that are less than 20 /spl mu/m in length and that are completely distinct from the often-observed mulberry-type hydroxyapatite concretions. Cubic, hexagonal and cylindrical morphologies have been identified using scanning electron microscopy. Energy dispersive spectroscopy, selected-area electron diffraction and near infrared Raman spectroscopy established that the crystals were calcite. Experiments at the European Synchrotron Radiation Facility (ESRF) to study the biomineralization showed the presence of sulfur originating from both heteropolysaccharides and amino acids. Other studies at the ESRF furnished information on the complex texture crystallization of the calcite. With the exception of the otoconia structure of the inner ear, this is the only known non-pathological occurrence of calcite in the human body. The calcite microcrystals are believed to be responsible for the previously observed second harmonic generation in pineal tissue sections. There is a strong possibility that the complex twinned structure of the crystals may lower their symmetry and permit the existence of a piezoelectric effect.     

Quantifying venous flow dynamics by flow-dephased and flow-rephased functional magnetic resonance imaging

By combining flow-dephased and flow-rephased diffusion weighting with blood oxygenation level dependent functional magnetic resonance imaging, it is possible to study flow dynamics in the venous network of the human brain. Thereby, ballistic flow, which conserves direction and velocity during echo time, is separated from diffusive flow with many changes in direction and velocity. By using this technique with very low diffusion/flow weighting, the mean velocity of ballistic flow was quantified in this study. The result of 10.9±3.2 cm/s strongly indicates that large venous vessels are the source of ballistic flow     

Heritage of the tissue-bed oximeter

The pulse oximeter is well established in clinical medicine as a monitor of the efficacy of the cardiorespiratory system. The principle of this device represents the end of a long evolutionary line of noninvasive instruments designed to measure the redness of blood i.e. oxygen saturation. This historical note describes the many ingenious devices that are the heritage of the pulse oximeter, which was described by Nakajima et al. (1979) and Yoshiya et al. (1980)     

Optimized EPI for fMRI using a slice-dependent template-based gradient compensation method to recover local susceptibility-induced signal loss

Object  

Most functional magnetic resonance imaging (fMRI) experiments use gradient-echo echo planar imaging (GE EPI) to detect the blood oxygenation level-dependent (BOLD) effect. This technique may fail in the presence of anatomy-related susceptibility-induced field gradients in the human head. In this work, we present a novel 3D compensation method in combination with a template-based correction that can be optimized over particular regions of interest to recover susceptibility-induced signal loss without acquisition time penalty.     

The EMF to BBB connection

The author considers the effects of electromagnetic energy on the blood-brain barrier (BBB). The integrity of the BBB is necessary for proper function of the brain in mammals. Minor leakage of the BBB can lead to neural dysfunction and major leakage is associated with brain swelling, which can lead to death. Thus, any change in the BBB of humans by EM fields could cause significant adverse effects. It is well established that RF heating of the brain by several degrees will cause gross and easily detectable disruption of the BBB. Such exposure is far above recommended safety limits and would be clearly hazardous to a person for other reasons as well. This level of exposure is unlikely to occur from environmental or occupational exposures to microwaves, low frequency fields, or from MRI scanners. It may be a factor in hyperthermia treatment of brain cancer. It is far less clear that EM fields have any effect on the BBB, apart from those resulting from gross brain heating. Roughly an equal number of studies using low-level (nonheating) exposures to either RF or low frequency fields have reported effects as have found no effects. In retrospect, it is clear that any effect from such exposure is small. To measure reliably a small breakdown of the BBB in the face of biological and experimental variability requires quantitative techniques tailored for measurement of small changes in transcapillary transport. Such a study has never been carried out     

Work toward real-time control of a cortical neural prothesis.

Implantable devices that interact directly with the human nervous system have been gaining acceptance in the field of medicine since the 1960's. More recently, as is noted by the FDA approval of a deep brain stimulator for movement disorders, interest has shifted toward direct communication with the central nervous system (CNS). Deep brain stimulation (DBS) can have a remarkable effect on the lives of those with certain types of disabilities such as Parkinson's disease, Essential Tremor, and dystonia. To correct for many of the motor impairments not treatable by DBS (e.g. quadriplegia), it would be desirable to extract from the CNS a control signal for movement. A direct interface with motor cortical neurons could provide an optimal signal for restoring movement. In order to accomplish this, a real-time conversion of simultaneously recorded neural activity to an online command for movement is required. A system has been established to isolate the cellular activity of a group of motor neurons and interpret their movement-related information with a minimal delay. The real-time interpretation of cortical activity on a millisecond time scale provides an integral first step in the development of a direct brain-computer interface (BCI).     

Oxygen saturation-dependent effects on blood transverse relaxation at low fields

Objective

Blood oxygenation can be measured using magnetic resonance using the paramagnetic effect of deoxy-haemoglobin, which decreases the \(\textit{T}_{2}\) relaxation time of blood. This \(\textit{T}_{2}\) contrast has been well characterised at the \(\textit{B}_{{0}}\) fields used in MRI (1.5 T and above). However, few studies have characterised this effect at lower magnetic fields. Here, the feasibility of blood oximetry at low field based on \(\textit{T}_{2}\) changes that are within a physiological relevant range is explored. This study could be used for specifying requirements for construction of a monitoring device based on low field permanent magnet systems.

Methods

A continuous flow circuit was used to control parameters such as oxygen saturation and temperature in a sample of blood. It flowed through a variable field magnet, where CPMG experiments were performed to measure its \(\textit{T}_{2}\). In addition, the oxygen saturation was monitored by an optical sensor for comparison with the \(\textit{T}_{2}\) changes.

Results

These results show that at low \(\textit{B}_{{0}}\) fields, the change in blood \(\textit{T}_{2}\) due to oxygenation is small, but still detectable. The data measured at low fields are also in agreement with theoretical models for the oxy-deoxy \(\textit{T}_{2}\) effect.

Conclusion

\(\textit{T}_{2}\) changes in blood due to oxygenation were observed at fields as low as 0.1 T. These results suggest that low field NMR relaxometry devices around 0.3 T could be designed to detect changes in blood oxygenation.

     

Use of spin echo T2 BOLD in assessment of cerebral misery perfusion at 1.5 T

Inadequate blood supply relative to metabolic demand, a haemodynamic condition termed as misery perfusion, often occurs in conjunction with acute ischaemic stroke. Misery perfusion results in adaptive changes in cerebral physiology including increased cerebral blood volume (CBV) and oxygen extraction ratio (OER) to secure substrate supply for the brain. It has been suggested that the presence of misery perfusion may be an indication of reversible ischaemia, thus detection of this condition may have clinical impact in acute stroke imaging. The ability of single spin echo T₂ to detect misery perfusion in the rat brain at 1.5 T owing to its sensitivity to blood oxygenation level dependent (BOLD) contrast was studied both theoretically and experimentally. Based on the known physiology of misery perfusion, tissue morphometry and blood relaxation data, T₂ behaviour in misery perfusion was simulated. The interpretation of these computations was experimentally assessed by quantifying T₂ in a rat model for cerebral misery perfusion. CBF was quantified with the H₂ clearance method. A drop of CBF from 58 ± 8 to 17 ± 3 ml/100 g min in the parieto-frontal cortex caused shortening of T₂. from 66.9 ± 0.4 to 64.6 ± 0.5 ms. Under these conditions, no change in diffusion MRI was detected. In contrast, the cortex with CBF of 42 ± 7 ml/100 g min showed no change in T₂. Computer simulations accurately predicted these T₂, responses. The present study shows that the acute drop of CBF by 70% causes a negative BOLD that is readily detectable by T₂ MRI at 1.5 T. Thus BOLD may serve as an index of misery perfusion thus revealing viable tissue with increased OER.     

基于近红外光谱的脑血氧无创监测系统研究

目前临床使用的脑血氧无创监测设备大多为双波长,由于黑色素的吸收会导致测量结果出现偏差,因此需要对测量结果进行修正。为此本文基于近红外光谱无创监测脑血氧的基本原理,针对现有脑血氧无创监测设备的不足,考虑前额叶的光学特性,研制了一种四波长探测光源(700、760、805、850 nm)以及双路光电检测器的脑血氧无创监测传感装置,并建立了光谱吸光度的数学模型,在此基础上构建了新型的脑血氧无创监测系统,实现了可抑制皮肤黑色素成分干扰的脑血氧信息无创测量。最后通过对Valsalva运动以及空载的对照实验进行秩和分析,初步验证了本系统的有效性。     

Optical trapping and coherent anti-Stokes Raman scattering (CARS) spectroscopy of submicron-size particles

Optical trapping combined with coherent anti-Stokes Raman scattering (CARS) spectroscopy is demonstrated for the first time as a new technique for the chemical analysis of individual particles over an extended period of time with high temporal resolution. Single submicron-size particles suspended in aqueous media are optically trapped and immobilized using two tightly focused collinear laser beams from two pulsed Ti:Sapphire laser sources. The particles can remain stably trapped at the focus for many tens of minutes. The same lasers generate a CARS vibrational signal from the molecular bonds in the trapped particle when the laser frequencies are tuned to a vibrational mode of interest, providing chemical information about the sample. The technique is characterized using single polystyrene beads and unilamellar phospholipid vesicles as test samples and can be extended to the study of living biological samples. This novel method could potentially be used to monitor rapid dynamics of biological processes in single particles on short time scales that cannot be achieved by using other vibrational spectroscopy techniques.     

给水氧化性处理在直接空冷汽包炉机组的工业应用研究

给水加氧处理是一个新的电厂锅炉给水处理技术。在综述了机组炉水的磷酸盐处理和给水采用加联氨和氨的全挥发处理运行方式工况存在的问题的基础上,分析了给水加氧处理技术的基本原理和技术特点,通过工业性试验将此技术应用到直接空冷汽包炉机组,讨论了具体加氧方式、试验过程,热工系统含铁量和导电率的变化,并采用工业在线氧化还原电位仪进行炉内水工况的监测与控制优化了直接空冷机组炉内水处理工况,取得节能降耗及有利于安全与环保的目的。