Design of a front-end integrated circuit for 3D acoustic imaging using 2D CMUT arrays

Integration of front-end electronics with 2D capacitive micromachined ultrasonic transducer (CMUT) arrays has been a challenging issue due to the small element size and large channel count. We present design and verification of a front-end drive-readout integrated circuit for 3D ultrasonic imaging using 2D CMUT arrays. The circuit cell dedicated to a single CMUT array element consists of a high-voltage pulser and a low-noise readout amplifier. To analyze the circuit cell together with the CMUT element, we developed an electrical CMUT model with parameters derived through finite element analysis, and performed both the pre- and postlayout verification. An experimental chip consisting of 4 X 4 array of the designed circuit cells, each cell occupying a 200 X 200 microm2 area, was formed for the initial test studies and scheduled for fabrication in 0.8 microm, 50 V CMOS technology. The designed circuit is suitable for integration with CMUT arrays through flip-chip bonding and the CMUT-on-CMOS process.     

Electronic transport properties of carbon nanotube based metal/semiconductor/metal intramolecular junctions

The electronic structure and the conductance of a carbon nanotube based metal/semiconductor/metal intramolecular junction is investigated numerically. The nature of electronic states at the interfaces and in the semiconductor section is analysed. The quantum conductance of the system is calculated in the coherent regime and its variations with energy and length are shown to be related to contributions from different kinds of electronic state.     

Anisoplanatic deconvolution of adaptive optics images

A modified method for maximum-likelihood deconvolution of astronomical adaptive optics images is presented. By parametrizing the anisoplanatic character of the point-spread function (PSF), a simultaneous optimization of the spatially variant PSF and the deconvolved image can be performed. In the ideal case of perfect information, it is shown that the algorithm is able to perfectly cancel the adverse effects of anisoplanatism down to the level of numerical precision. Exploring two different modes of deconvolution (using object bases of pixel values or stellar field parameters), we then quantify the performance of the algorithm in the presence of Poissonian noise for crowded and noncrowded stellar fields.     

Glucose biosensor based on carbon nanotube epoxy composites

A novel glucose biosensor based on a rigid and renewable carbon nanotube (CNT) based biocomposite is reported. The biosensor was based on the immobilization of glucose oxidase (GOx) within the CNT epoxy-composite matrix prepared by dispersion of multi-wall CNT inside the epoxy resin. The use of CNT, as the conductive part of the composite, ensures better incorporation of enzyme into the epoxy matrix and faster electron transfer rates between the enzyme and the transducer. Experimental results show that the CNT epoxy composite biosensor (GOx-CNTEC) offers an excellent sensitivity, reliable calibration profile, and stable electrochemical properties together with significantly lower detection potential (+0.55 V) than GOx-graphite epoxy composites (+0.90 V; difference deltaE = 0.35 V). The results obtained favorably compare to those of a glucose biosensor based on a graphite epoxy composite (GOx-GEC).     

Classification of EEG signals using neural network and logistic regression

Epileptic seizures are manifestations of epilepsy. Careful analyses of the electroencephalograph (EEG) records can provide valuable insight and improved understanding of the mechanisms causing epileptic disorders. The detection of epileptiform discharges in the EEG is an important component in the diagnosis of epilepsy. As EEG signals are non-stationary, the conventional method of frequency analysis is not highly successful in diagnostic classification. This paper deals with a novel method of analysis of EEG signals using wavelet transform and classification using artificial neural network (ANN) and logistic regression (LR). Wavelet transform is particularly effective for representing various aspects of non-stationary signals such as trends, discontinuities and repeated patterns where other signal processing approaches fail or are not as effective. Through wavelet decomposition of the EEG records, transient features are accurately captured and localized in both time and frequency context. In epileptic seizure classification we used lifting-based discrete wavelet transform (LBDWT) as a preprocessing method to increase the computational speed. The proposed algorithm reduces the computational load of those algorithms that were based on classical wavelet transform (CWT). In this study, we introduce two fundamentally different approaches for designing classification models (classifiers) the traditional statistical method based on logistic regression and the emerging computationally powerful techniques based on ANN. Logistic regression as well as multilayer perceptron neural network (MLPNN) based classifiers were developed and compared in relation to their accuracy in classification of EEG signals. In these methods we used LBDWT coefficients of EEG signals as an input to classification system with two discrete outputs: epileptic seizure or non-epileptic seizure. By identifying features in the signal we want to provide an automatic system that will support a physician in the diagnosing process. By applying LBDWT in connection with MLPNN, we obtained novel and reliable classifier architecture. The comparisons between the developed classifiers were primarily based on analysis of the receiver operating characteristic (ROC) curves as well as a number of scalar performance measures pertaining to the classification. The MLPNN based classifier outperformed the LR based counterpart. Within the same group, the MLPNN based classifier was more accurate than the LR based classifier.     

Accuracy of 3D MR microscopy for trabecular bone assessment: a comparative study on calcaneus samples using 3D synchrotron radiation microtomography

Magnetic resonance (MR) imaging is attractive for a noninvasive and radiation-free assessment of in vivo trabecular bone architecture. However the quantitative evaluation of architectural parameters could be biased by the limited sensitivity of MR. The aim of this study was to determine the accuracy of trabecular bone architectural parameters obtained from 3D high-resolution MR images, by comparison to reference images obtained by high-resolution X-ray microtomography using synchrotron radiation, from 29 samples of human calcaneus. MR images were obtained with a 66 m×66 m×66 m voxel size, using a 8.5 T MR microscope. Microtomography images were acquired with a 10 m×10 m×10 m voxel size, from the same samples. 3D architectural parameters characterizing the morphometry, topology, anisotropy, and orientation were computed from both modalities and carefully compared. To avoid errors, an identical region of interest was selected in the two corresponding images, and the same algorithms were run at identical spatial resolution. Our results establish that network connectivity, orientation and anisotropy are reliable from the MR data. The bone volume fraction, and morphometric parameters measured from the MR data, were found to be biased with respect to their values from the microtomography data, although there was a significant correlation between the two modalities.An erratum to this article can be found at     

Assessment of the preferred scout sagittal orientation for temporal lobe imaging with magnetic resonance

Oblique magnetic resonance imaging of the temporal lobe (tilted orientation) requires a stable reference line with minimum variability. In the clinical setting, where several observers carry out examination of the patients, there is a need to assure minimum inter-observer variability, in order to obtain comparable tilted anatomical planes. This is particularly relevant when performing quantitative imaging (qMRI) of the hippocampus, amygdala and para-hippocampal cortices. In this study, eight experienced observers tested the stability of four sagittal reference lines by manually tracing the posterior commissure-obex (PC-OB) line, the line tangential to the anterior surface of the pons at its most convex point and the lines orthogonal to the main axis of both hippocampi, in ten exams of healthy subjects. The stability of the tracing was assessed by comparing the inter-observer variability expressed by the variances of the measurements. The observers performance was assessed by comparing the precision of the tracing for each line. We tested the results statistically using Bartletts test (analysis of the variances of the four lines) followed by Fischer–Snedecor (in order to compare the two lines that had the smallest variance). The PC-OB line and the line tangential to the anterior surface of the pons had smaller inter-observer variances than the orthogonal lines (p<0.01). In addition, the variance of the PC-OB line was smaller than that of the line tangential to the pons (p<0.01). There were no significant intra-observer differences in the precision of tracing of any of the lines. We show quantitatively that the PC-OB line is the scout reference that yields the smallest inter-observer variance. Thus, this line should be preferred to improve the reproducibility of temporal lobe imaging while performing tilted coronal and axial sequences, to make quantitative assessments of the hippocampus, amygdala and para-hippocampal cortices.     

GC/MS profiling of gamma-hydroxybutyrate and precursors in various animal tissues using automatic solid-phase extraction. Preliminary investigations of its potential interest in postmortem interval determination

To quantify gamma-hydroxybutyrate (GHB) and its physiological metabolites, gamma-aminobutyric acid (GABA), 1,4-butanediol (1,4-BD), and gamma-butyrolactone (GBL) in various animal tissues (kidney, muscle, heart, liver, blood, brain cortex, thalamus, hypothalamus, hippocampus, or pons), an original gas chromatographic/mass spectrometric method with a automated solid-phase extraction by Oasis MCX cartridges on a Gilson Aspec Xli was developed. Using such apparatus allowed the limit of detection (LOD) of target compounds to be significantly lowered (LOD: 0.027, 0.025, and 5.7 microg/mL for GHB, 1,4-BD, and GABA, respectively, in 200 microL or microg of sample). After validation of each analytical step, the satisfactory performances of the apparatus in conjunction with the rapidity and ease of the extraction step make it suitable for simultaneous assay of GHB, 1,4-BD, GBL, and GABA. The method was used to test the correlation between GHB levels in tissues obtained at different times after death of male Sprague-Dawley rats and the postmortem interval. Preliminary results show a linear increase of GHB levels in relation to time of death in thoracic blood and central nervous system of animals kept at 15 and 20 degrees C.     

Study of normal incidence of three-component multilayer mirrors in the range 20-40 nm

We study theoretically and experimentally the increase of normal incidence reflectivity generated by addition of a third material in the period of a standard periodic multilayer, for wavelengths in the range 20 to 40 nm. The nature and thickness of the three materials has been optimized to provide the best enhancement of reflectivity. Theoretical reflectivity of an optimized B4C/Mo/Si multilayer reaches 42% at 32 nm. B4C/Mo/Si multilayers have been deposited with a magnetron sputtering system and a reflectivity of 34% at 32 nm has been measured on a synchrotron radiation source.     

Laser-ablated volume and depth as a function of pulse duration in aluminum targets

The ablated depth and volume per laser pulse from an aluminum target were measured for pulse durations that ranged from 80 fs to 270 ps at an average fluence of approximately 100 J/cm2 and a wavelength of 0.8 microm. The ablated volume showed a flat maximum for subpicosecond pulses and a minimum for approximately 6 ps. The crater diameters were rather constant up to pulse durations of approximately 6 ps and increased for larger pulse durations. As a result, the ablated depth also showed a plateau for subpicosecond pulses but decreased monotonically with pulse duration. A physical interpretation of these results and their consequences for laser applications are discussed.