Magnetic-resonance-imaging-coupled broadband near-infrared tomography system for small animal brain studies

A novel magnetic-resonance-coupled broadband near-infrared (NIR) tomography system for small animal brain studies is described. Several features of the image formation approach are new in NIR tomography and represent major advances in the path to recovering high-resolution hemoglobin and oxygen saturation images of tissue. The NIR data were broadband and continuous wave and were used along with a second-derivative-based estimation of the path length from water absorption. The path length estimation from water was then used along with the attenuation spectrum to recover absorption and reduced scattering coefficient images at multiple wavelengths and then to recover images of total hemoglobin and oxygen saturation. Going beyond these basics of NIR tomography, software has been developed to allow inclusion of structures derived from MR imaging (MRI) for the external and internal tissue boundaries, thereby improving the accuracy and spatial resolution of the properties in each tissue type. The system has been validated in both tissue-simulating phantoms, with 10% accuracy observed, and in a rat cranium imaging experiment. The latter experiment used variation in inspired oxygen (FiO2) to vary the observed hemoglobin and oxygen saturation images. Quantitative agreement was observed between the changes in deoxyhemoglobin values derived from NIR and the changes predicted with blood-oxygen-level-dependent (BOLD) MRI. This system represents the initial stage in what will likely be a larger role for NIR tomography, coupled to MRI, and illustrates that the technological challenges of using continuous-wave broadband data and inclusion of a priori structural information can be met with careful phantom studies.     

The Performance of a Noncoherent FSK Receiver Preceded by a Bandpass Limiter

Many applications of the bandpass limiter involve either coherent or noncoherent demodulation following the limiter. In this paper we study the performance of a noncoherent frequency-shift keying (FSK) receiver when it is preceded by a bandpass limiter. In particular, we obtain expressions for signal suppression- factor, output signal-to-noise ratio (SNR), and error probability from which one can assess the degradation in performance of the receiver due to the presence of the limiter. Both narrow-band and wide-band cases are treated thus covering situations where no frequency uncertainty exists (i.e., known carrier frequency) as well as large-frequency uncertainties. Also discussed is the first-order signal plus noise probability density function (pdf) following noncoherent demodulation.     

An analysis of social interaction between novice older adults when learning gesture-based skills through simple digital games

Universal Access in the Information Society - This paper reports three exploratory empirical studies with older adults that had little or no prior experience with interactive technologies. The...     

Measurement of cytochrome oxidase and mitochondrial energetics by near-infrared spectroscopy

Cytochrome oxidase is the terminal electron acceptor of the mitochondrial respiratory chain. It is responsible for the vast majority of oxygen consumption in the body and essential for the efficient generation of cellular ATP. The enzyme contains four redox active metal centres; one of these, the binuclear CuA centre, has a strong absorbance in the near-infrared that enables it to be detectable in vivo by near-infrared spectroscopy. However, the fact that the concentration of this centre is less than 10% of that of haemoglobin means that its detection is not a trivial matter. Unlike the case with deoxyhaemoglobin and oxyhaemoglobin, concentration changes of the total cytochrome oxidase protein occur very slowly (over days) and are therefore not easily detectable by near-infrared spectroscopy. However, the copper centre rapidly accepts and donates an electron, and can thus change its redox state quickly; this redox change is detectable by near-infrared spectroscopy. Many factors can affect the CuA redox state in vivo (Cooper et al. 1994), but most significant is likely to be the molecular oxygen concentration (at low oxygen tensions, electrons build up on CuA as reduction of oxygen by the enzyme starts to limit the steady-state rate of electron transfer). The factors underlying haemoglobin oxygenation, deoxygenation and blood volume changes are, in general, well understood by the clinicians and physiologists who perform near-infrared spectroscopy measurements. In contrast, the factors that control the steady-state redox level of CuA in cytochrome oxidase are still a matter of active debate, even amongst biochemists studying the isolated enzyme and mitochondria. Coupled with the difficulties of accurate in vivo measurements it is perhaps not surprising that the field of cytochrome oxidase near-infrared spectroscopy has a somewhat chequered past. Too often papers have been written with insufficient information to enable the measurements to be repeated and few attempts have been made to test the algorithms in vivo. In recent years a number of research groups and commercial spectrometer manufacturers have made a concerted attempt to not only say how they are attempting to measure cytochrome oxidase by near-infrared spectroscopy but also to demonstrate that they are really doing so. We applaud these attempts, which in general fall into three areas: first, modelling of data can be performed to determine what problems are likely to derail cytochrome oxidase detection algorithms (Matcher et al. 1995); secondly haemoglobin concentration changes can be made by haemodilution (using saline or artificial blood substitutes) in animals (Tamura 1993) or patients (Skov & Greisen 1994); and thirdly, the cytochrome oxidase redox state can be fixed by the use of mitochondrial inhibitors and then attempts make to cause spurious cytochrome changes by dramatically varying haemoglobin oxygenation, haemoglobin concentration and light scattering (Cooper et al. 1997). We have previously written reviews covering the difficulties of measuring the cytochrome near-infrared spectroscopy signal in vivo (Cooper et al. 1997) and the factors affecting the oxidation state of cytochrome oxidase CuA (Cooper et al. 1994). In this article we would like to strike a somewhat more optimistic note--we will stress the usefulness this measurement may have in the clinical environment, as well as describing conditions under which we can have confidence that we are measuring real changes in the CuA redox state.     

Mechanisms of Extraction of Aroma Compounds from Foods, Using Adsorbents. Effect of Various Parameters

Due to their high adsorbing capacity, different solids (carbonaceous adsorbents, zeolites, and polymers) are used to extract and concentrate aroma compounds from foods. Adsorption mechanisms are described in two phases, a kinetic stage that involves the diffusion of the analytes within the adsorbent pores and a thermodynamic stage that can be described by adsorption isotherms. These two phases determine the extraction time and the capacity of the adsorbent for a given aroma compound. Several applications involving adsorbents or sorbents have been developed, including purge and trap, solid-phase microextraction (SPME), and stir bar sorptive extractions (SBSE), headspace sorptive extraction (HSSE), which now are widely used for aroma extractions. Different extraction modes (in the headspace or by immersion in the sample) can be used to recover aroma compounds in foods. The same adsorption mechanisms take place in both cases. Various parameters affecting the extraction kinetics and the capacity of the adsorbent have to be optimized when developing an extraction method. They can be divided into three groups: physicochemical characteristics of the adsorbent, including its porosity and hydrophobia; physicochemical characteristics of the aroma compounds (among them, two parameters play an important role, the sample/adsorbent partition coefficient, which determines the affinity for the adsorbent and the volumetric mass, which influences the diffusion in the adsorbent pores); and the extrinsic parameters that depend on the sampling conditions such as pH, temperature, gas or solvent flows, time, and composition of the sample. Several models used to determine the diffusivity and partition coefficient of aroma between the food sample and the adsorbents have been developed. They are useful to understand the behavior of aroma compounds in regards to various adsorbents and in selecting the adsorbent material with the greatest affinity for the target aroma compounds. Quantitative studies based on adsorbent extraction of volatiles have been carried out. Nevertheless, competition between analytes and the saturation of these materials are limiting parameters. Thus, new strategies (SBSE, HSSE) are being developed to avoid these limiting aspects of adsorbents in order to use them in a quantitative way.     

A survey on managing users’ preferences in ambient intelligence

Universal Access in the Information Society - Understanding the importance of preference management in ambient intelligent environments is key to providing systems that are better prepared to meet...     

Magnetic resonance-coupled fluorescence tomography scanner for molecular imaging of tissue

A multichannel spectrally resolved optical tomography system to image molecular targets in small animals from within a clinical MRI is described. Long source/detector fibers operate in contact mode and couple light from the tissue surface in the magnet bore to 16 spectrometers, each containing two optical gratings optimized for the near infrared wavelength range. High sensitivity, cooled charge coupled devices connected to each spectrograph provide detection of the spectrally resolved signal, with exposure times that are automated for acquisition at each fiber. The design allows spectral fitting of the remission light, thereby separating the fluorescence signal from the nonspecific background, which improves the accuracy and sensitivity when imaging low fluorophore concentrations. Images of fluorescence yield are recovered using a nonlinear reconstruction approach based on the diffusion approximation of photon propagation in tissue. The tissue morphology derived from the MR images serves as an imaging template to guide the optical reconstruction algorithm. Sensitivity studies show that recovered values of indocyanine green fluorescence yield are linear to concentrations of 1 nM in a 70 mm diameter homogeneous phantom, and detection is feasible to near 10 pM. Phantom data also demonstrate imaging capabilities of imperfect fluorophore uptake in tissue volumes of clinically relevant sizes. A unique rodent MR coil provides optical fiber access for simultaneous optical and MR data acquisition of small animals. A pilot murine study using an orthotopic glioma tumor model demonstrates optical-MRI imaging of an epidermal growth factor receptor targeted fluorescent probe in vivo.     

Identification of 1-cyano-2,3-epithiopropane in volatiles of a model system from brussels sprouts (Brassica Oleraceae L var Bullata subvar Gemmifera DC)

Volatiles produced in model systems consisting of a crude enzyme preparation from Brussels sprouts (Brassica oleraceae L var bullata subvar gemmifera DC), sinigrin, ascorbic acid and 2-mercaptoethanol were investigated using gas chromatography-mass spectroscopy. 2-Propen-1-yl isothiocyanate was the only breakdown product of sinigrin in the absence of 2-mercaptoethanol but in its presence 1-cyano-2,3-epithiopropane and small amounts of 2-propen-1-yl cyanide also were formed. The identification of the 1-cyano-2,3-epithiopropane was confirmed by comparison with a standard produced by autolysis of Crambe abyssinica L seed and with published mass spectra. The presence of 1-cyano-2,3-epithiopropane in volatile extracts of unblanched, frozen stored Brussels sprouts is also reported.