Emmanuel Perrin

nth-order fractional Brownian motion and fractional Gaussian noises

A generalization of fractional Brownian motion (fBm) of parameter H in ]0, 1[ is proposed. More precisely, this work leads to nth-order fBm (n-fBm) of H parameter in ]n-1, n[, where n is any strictly positive integer. They include fBm for the special case n=1. Properties of these new processes are investigated. Their covariance function are given, and it is shown that they are self similar. In addition, their spectral shape is assessed as 1/f/sup /spl alpha// with /spl alpha/ belonging to ]1; +/spl infin/[, providing a larger framework than classical fBm. Special interest is given to their nth-order stationary increments, which extend fractional Gaussian noises. The covariance function and power spectral densities are calculated. The properties and signal processing tasks such as a Cholesky-type synthesis technique and a maximum likelihood estimation method of the H parameter are presented. The results show that the estimator is efficient (unbiased and reaches the Cramer-Rao lower bound) for a large majority of tested values.

Development of cochlear active mechanisms in humans differs between gender

Despite onset of function early during the third term of gestation, the human auditory system demonstrates continued maturation, thought previously to occur primarily at the neural level. The electromotile properties of outer hair cells appear to contribute substantially to hearing sensitivity and frequency selectivity and lead to the generation of otoacoustic emissions (OAEs). This report demonstrates continued development of cochlear active mechanisms (i.e. end-organ level) after onset of cochlear function, as reflected by OAEs. Significant gender differences also are reported, corresponding to recently observed intersex differences in cochlear length and precursory to gender differences observed in the adult.

Fast and exact synthesis for 1-D fractional Brownian motion and fractional Gaussian noises

In this letter, it is shown that fast and exact fractional Brownian motion (fBm) and fractional Gaussian noise (fGn) signals can be synthesized by the circulant embedding method (CEM). CEM consists in embedding the N/spl times/N covariance matrix of the stationary fGn process in a larger 2M/spl times/2M circulant matrix such that M /spl ges/N-1. CEM is exact, since second-order statistics of the generated data are those of the Gaussian fGn. CEM is fast, since the optimal case M=N-1 can be reached. Fast and exact fBm sequences can be easily recovered from fGn ones.

Contralateral acoustic stimulation induces a phase advance in evoked otoacoustic emissions in humans

In 28 normal-hearing human subjects, the medial olivocochlear efferent system was activated by contralateral acoustic stimulation which is able to mimic the inhibitory effects of electrical stimulation of the crossed olivocochlear bundle. A first experiment on 16 subjects demonstrated that a contralateral white noise of 35 dB SL was able to induce temporal changes on transiently evoked otoacoustic emissions in response to clicks of 63 dB SPL. These temporal changes consisted of an advance of click-evoked otoacoustic signals in 87% of cases and is referred to as phase-shift effect. The phase advance, quantified using two signal processing methods in both time and frequency domains, was found to be mainly associated with lower frequencies, with a maximal effect at 1.5 kHz and minimal effects around 3.5 and 4 kHz. In a second experiment, carried out on 12 subjects, a negative relationship was found to exist between the ipsilateral stimulation level (level of clicks ranging from 57 to 69 dB SPL) and the phase-shift effect (PSE). Specifically in the range of levels tested (25-45 dB SL), a linear relationship presenting no obvious saturation effect was observed between the contralateral level and the PSE. The PSE was examined in 6 additional subjects exhibiting pathological symptoms; 2 of 3 individuals, who had no contralateral stapedial reflexes unilaterally, showed the PSE whereas this response was reduced or absent in 3 other subjects in the ear with severed efferents associated with a vestibular neurotomy. The integrity of olivocochlear efferents was, therefore, necessary to obtain a full effect, but the absence of stapedial reflex did not prevent the effect from occurring.

Assessment of radiofrequency self‐heating around a metallic wire with MR T1‐based thermometry

Heat produced by a magnetic resonance (MR) imaging sequence in the vicinity of a conductive wire (pacemaker, electrodes, or catheter), is a subject of interest for the assessment of patient safety during imaging. For this purpose, the measurement of temperature rises during an MR imaging sequence using MR T1‐based thermometry provides several advantages, mainly in its ability to retrieve in situ real‐time thermal maps. Recent studies investigated the heat produced by an independent radiofrequency pulse, assessing MR imaging sequence heating using a specific MR thermometry sequence. This study focuses on self‐heating for which the radiofrequency pulses used for measuring temperature create the heat. An experimental design was set up to evaluate T1‐based thermometry self‐heating using a coupled/decoupled wire and to compare it with a reference temperature gathered by an optical fiber device. For the tested experimental set up, T1‐based thermometry is in fairly good agreement with optical fiber reference temperature. Magn Reson Med, 2011.

Piecewise fractional Brownian motion

Starting from fractional Brownian motion (fBm) of unique parameter H, a piecewise fractional Brownian motion (pfBm) of parameters H/sub o/, H/sub i/, and /spl gamma/ is defined. This new process has two spectral regimes: It behaves like an fBm of parameter H/sub o/ for low frequencies |/spl omega/|</spl gamma/ and like an fBm of parameter H/sub i/ for high frequencies |/spl omega/|/spl ges//spl gamma/. When H/sub o/=H/sub i/, or for limit cases /spl gamma//spl rarr/0 and /spl gamma//spl rarr//spl infin/, pfBm becomes classical fBm. It is shown that pfBm is a continuous, Gaussian, and nonstationary process having continuous, Gaussian, and stationary increments, namely, piecewise fractional Gaussian noises. The asymptotic self-similarity of pfBm is shown according to the considered regime: At large scale, the process is self-similar with parameter H/sub o/ and with parameter H/sub i/ at low scale.

Integrated RF micro-coils on porous silicon

Porous silicon (PS) of up to 400 /spl mu/m with high porosity (70%) has been studied to integrate high-performance micro-coils on heavily doped Si substrates (7-15 m/spl Omega/cm). 2 /spl mu/m-thick Au spiral inductors with L/spl sim/15 nH were fabricated; they demonstrate a quality factor Q up to 8 in the 0,1 to 2 GHz frequency range. Substrate loss is greatly lowered, down to /spl sim/12 /spl Omega/ at 400 MHz, which offers attractive potentialities for high resolution RMN (80-500 MHz) spectroscopy integrated devices.

RF induced temperature elevation near metallic wires in clinical magnetic resonance imaging

Heating of biological tissues along metallic wires placed in MRI scanner has become an important question with the development of interventional MRI. In order to assess thermal response to RF exposure during MR procedures, the temperature elevation was studied near metallic non-magnetic wires. All tests have been performed on a 1.5 T clinical scanner. The major issue is to insure patient safety against potential heating of tissues located in the metallic wire vicinity. Three experiments were conducted: the first investigate the wire diameter, the second the excitation angle, and the third, the temperature distribution along the wire. This study shows that the temperature decreases with the diameter wire. The temperature range increases quadratic with excitation angle. Heating has also been observed along the wire, and results indicate that heating peaks are located according to electrical length of the wire. In the close vicinity of the wire, an important heating (40 /spl deg/C rise) has been observed. Electromagnetic simulations of experimental set up were made assuming a plane wave excitation with FEKO software. Correlations between measured and calculated values of electric field are presented.

Towards optical characterization of biological media: analysis of backscattered images in linearly polarized light, simulations and experiments

Optical imaging is a non invasive way to characterise turbid media, which is of real interest for investigating biological tissues for diagnosis purposes. A method called Integral Reflectance (IR) has already been developed [1]. The media being illuminated by a laser beam (670 nm, <1 mW), the backscattered light is captured by a 2D CCD camera. The reduced scattering coefficient μs and the absorption coefficient μa are determined from the image. Having μs and μa, the objective is to improve the characterization by estimating the anisotropy factor g, using polarized light. Different patterns depending on g are produced in these images, presenting some lobes, centred in the entry point of the laser beam, whose number and shape vary with g. To assess a simple description of these patterns, a circular outline of the image, at a given radius, is studied by Fourier series decomposition, namely Fourier descriptors, whose indices, modulus and phase provide the number, the size and the orientation of the lobes, respectively. Backscattered images of turbid media with g in the range [0.006 ; 0.93] (μs = 10, 20, 40 cm-1 ; μa = 0.01, 1, 5 cm-1), were simulated using a Monte Carlo code for polarized light. Tables of Fourier descriptors were obtained as function of g, μs and μa. Five reference solutions made of polystyrene spheres in liquid, with g varying from 0.71 to 0.919 (tissue phantoms) were tested. The Fourier descriptors were compared to simulations, and g could be retrieved with a maximum error of 10%.

Acoustical recognition of laryngeal pathology using the fundamental frequency and the first three formants of vowels.

The recognition of laryngeal pathology by analysis of the voice is investigated. The fundamental frequency and the first three formants are considered. The recognition strategy is based on comparison with normal ranges calculated over 200 ordinary voices, grouped in ten age classes ranging from 20 to 70 years, for males and females. 220 test voices are studied divided into four groups: normal voices, functional dysphonia, nodules and recurrent nerve palsy. Each subject is marked according to his/her normal range. Parameters (or items) are calculated on the Interactive Laboratory System workstation. The vocalic material is composed of 11 vowels taken from a sentence. Results are given in terms of the number of values out of the normal ranges. Statistical analysis considers both parameter ability and error rates in pathology recognition. Pathology recognition shows the following error percentages: 23% for dysphonia, 14% for nodules and 33% for recurrent nerve palsy. Parameters do not show the same efficiency for voice pathology characterisation. Formants appear to be better than the fundamental frequency.