ac hopping admittance in spinel manganate negative temperature coefficient thermistor electroceramics

In this work, the ac admittance of a thick film nickel manganate spinel negative temperature coefficient thermistor ceramic system containing a glass phase is investigated. The dominating relaxation process is a grain boundary (GB) effect and has been investigated comprehensively. We present double-logarithmic plots of the specific admittance σ' vs ω and (σ'/σ_(dc)) vs ω, and specific impedance z vs −z"/ω and [(ρ_(dc)/z')−1] vs ω, in order to characterize GB charge transport. Using the complex admittance notation (σ*), an unusually low Jonscher exponent of frequency ~0.007 was obtained and the GB relaxation displayed close to ideal behavior

Cross-Correlation of Motor Activity Signals from dc-Magnetoencephalography, Near-Infrared Spectroscopy, and Electromyography

Neuronal and vascular responses due to finger movements were synchronously measured using dc-magnetoencephalography (dcMEG) and time-resolved near-infrared spectroscopy (trNIRS). The finger movements were monitored with electromyography (EMG). Cortical responses related to the finger movement sequence were extracted by independent component analysis from both the dcMEG and the trNIRS data. The temporal relations between EMG rate, dcMEG, and trNIRS responses were assessed pairwise using the cross-correlation function (CCF), which does not require epoch averaging. A positive lag on a scale of seconds was found for the maximum of the CCF between dcMEG and trNIRS. A zero lag is observed for the CCF between dcMEG and EMG. Additionally this CCF exhibits oscillations at the frequency of individual finger movements. These findings show that the dcMEG with a bandwidth up to 8 Hz records both slow and faster neuronal responses, whereas the vascular response is confirmed to change on a scale of seconds

Quantification of mutant huntingtin protein in cerebrospinal fluid from Huntington's disease patients.

Quantification of disease-associated proteins in the cerebrospinal fluid (CSF) has been critical for the study and treatment of several neurodegenerative disorders; however, mutant huntingtin protein (mHTT), the cause of Huntington's disease (HD), is at very low levels in CSF and, to our knowledge, has never been measured previously

Characterization of homogeneous tissue phantoms for performance tests in diffuse optics

Solid homogeneous turbid phantoms can be employed to mimic the attenuation and angular distribution of light emerging from tissue, e.g., to assess the responsivity of the detection system of diffuse optics instrumentation and to support standardized performance tests of functional near-infrared spectroscopy devices. We present three methods to quantify the wavelength-dependent diffuse transmittance, relying on (1) measurement of radiance exiting the phantom by a detector far from the exit aperture, (2) simple recording of radiance by a power meter close to the exit aperture and correction for the finite distance between phantom surface and detector, (3) determination of the reduced scattering and absorption coefficients by time-resolved diffuse transmittance measurements and forward calculation of the time-integrated diffuse transmittance based on the diffusion model. The implications of the different approximations related to these approaches are discussed. The various methods were applied to characterize solid slab phantoms, and the results were compared. Specifically, for an epoxy-resin based phantom having a thickness of 2 cm, a reduced scattering coefficient of about 0.5/mm and an absorption coefficient of about 0.01/mm, the diffuse transmittance values obtained by the three different methods were found to agree within about 10%

Non-contact time-resolved diffuse reflectance imaging at null source-detector separation

We report results of the proof-of-principle tests of a novel non-contact tissue imaging system. The system utilizes a quasi-null source-detector separation approach for time-domain near-infrared spectroscopy, taking advantage of an innovative state-of-the-art fast-gated single photon counting detector. Measurements on phantoms demonstrate the feasibility of the non-contact approach for the detection of optically absorbing perturbations buried up to a few centimeters beneath the surface of a tissue-like turbid medium. The measured depth sensitivity and spatial resolution of the new system are close to the values predicted by Monte Carlo simulations for the inhomogeneous medium and an ideal fast-gated detector, thus proving the feasibility of the non-contact approach for high density diffuse reflectance measurements on tissue. Potential applications of the system are also discussed. © 2011 Optical Society of America

Characterization of a time-resolved non-contact scanning diffuse optical imaging system exploiting fast-gated single-photon avalanche diode detection

We present a system for non-contact time-resolved diffuse reflectance imaging, based on small source-detector distance and high dynamic range measurements utilizing a fast-gated single-photon avalanche diode. The system is suitable for imaging of diffusive media without any contact with the sample and with a spatial resolution of about 1 cm at 1 cm depth. In order to objectively assess its performances, we adopted two standardized protocols developed for time-domain brain imagers. The related tests included the recording of the instrument response function of the setup and the responsivity of its detection system. Moreover, by using liquid turbid phantoms with absorbing inclusions, depth-dependent contrast and contrast-to-noise ratio as well as lateral spatial resolution were measured. To illustrate the potentialities of the novel approach, the characteristics of the non-contact system are discussed and compared to those of a fiber-based brain imager

Design and construction of a solid switchable phantom for diffuse optical imaging

We propose a simple and reliable solid phantom for mimicking realistic localized absorption changes within a diffusive medium. The phantom is based on a solid matrix holding a movable black inclusion embedded in a rod. Translating the rod parallel to the phantom surface, the inhomogeneity can be positioned beneath the source-detector pair (perturbed case) or far from it (unperturbed case). Examples of time-resolved transmittance measurements and time-resolved reflectance scans are shown to demonstrate the properties and the versatility of the phantom