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Biomedical subjects

F Grandori

Publications and source records attributed to F Grandori.

At least 37 records · Page 2Linked to original sources
PubMed1997

Optimal one- and two-dimensional filtering of transient-evoked otoacoustic emissions.

In the clinical use of evoked otoacoustic emissions the identification of the cochlear response and the reduction of the duration of the recording session are of great concern, especially if the recorded responses are to be used in hearing screening tasks. The aim of this paper is two-fold: to examine the potential and limits of optimal band-pass filtering to reduce the noise and increase identification of the cochlear response, and to introduce a technique of two-dimensional processing for reducing the acquisition time of TEOAEs. Band-pass filtering must guard against the loss of significant frequency components of the response; that is, the signals have to be filtered only when the filter bandwidth meets given conditions. As to test duration, preliminary results clearly indicate that two-dimensional filtering can substantially reduce the acquisition time, with only negligible losses in the basic response features, when a set of responses recorded at different stimulus levels is filtered.

Acoustic Stimulation↗
PubMed1997

Modeling peripheral nerve stimulation using magnetic fields.

The technique of magnetic stimulation (MS) has the potential to contribute to the study of the peripheral nervous system, but the uncertainty of the site of activation and problems in achieving supramaximal responses have prevented its extensive use. This paper discusses mathematical modeling of MS of the peripheral nerves. The work reveals recent theoretical advances, which may give new insight to the exact site of activation and help to understand the phenomena involved. The mechanisms of stimulation are examined: a solid comprehension of the stimulation event may boost new applications of the technique.

Animals↗
PubMed1997

High resolution time-frequency analysis of otoacoustic emissions.

High resolution time-frequency analysis of OAE signals evoked by stimuli of different strength was performed by means of the Matching Pursuit algorithm. The method relies on adaptive decomposition of a signal into waveforms of well-defined frequency and time localization. Energy of OAE as a function of time and frequency was evaluated for stimuli strength of 35-80 dB SPL. Dynamic characteristics of the signal were constructed. For strong stimuli decrease of the power of high frequency components was found. Matching Pursuit proved to be a method which offers high resolution parametrisation of OAE in time-frequency space and provides excellent possibilities of investigation of the signal generation mechanisms.

Acoustic Stimulation↗
PubMed1996

Transverse-field activation mechanism in magnetic stimulation of peripheral nerves.

The activating function of peripheral nerves in magnetic stimulation is thought to be the gradient of the induced electric field component parallel to the nerve. This implies that there are several orientations of the coil that should not excite nerves. We show that these orientations, however, often yield high-amplitude and even supramaximal muscle response, indicating that the model of the activating function has to be modified. We propose that the electric field component perpendicular to the nerve is responsible for these unexpected muscle responses. Our conclusion is based on practical experiments with different coils and on computer simulations of the induced electric field and its gradient.

Electric Stimulation↗
PubMed1996

A volume-conduction analysis of magnetic stimulation of peripheral nerves.

Magnetic stimulation is a method to study several nervous disorders as well as the intact nervous system in humans. Interest in magnetic stimulation of peripheral nerves has grown rapidly, but difficulties in locating the site of excitation have prevented it from becoming a routine clinical tool. It has been reasoned that the activating function of long and straight nerves is the first spatial derivative of the electric field component parallel to the nerves. Therefore, to predict the site of activation, one has to compute this field feature. We describe here an analytical mathematical model and investigate the influence of volume-conductor shape on the induced field. Predictions of the site of activation are given for typical stimulation coil arrangements and these results are compared with experimental and literature data. Comparisons suggest that the activating function is not simply the spatial gradient of the induced electric field, but that other mechanisms are also involved. The model can be easily utilized in the search for more efficient coil constructions and improved placements with respect to the target nerves.

Computer Simulation↗
PubMed1996

Analysis of temporal non-stationarities in EEG signals by means of parametric modelling.

A method for the analysis of variability of EEG signals is described. We examined simulated signals and real EEGs obtained from a normal subject and two epileptic patients. The first step of the method is based on autoregressive (AR) modelling of short EEG epochs. Prediction coefficients of the AR model were computed as a function of time from partially-overlapping moving windows of 2 s duration. The temporal behaviour of these coefficients was analysed to detect variability: quasi-stationary activity causes only smooth changes in the coefficients while variations in the amplitude and/or the frequency content of the signal are shown to produce sharp changes in the coefficients. A segmentation algorithm was developed to detect and quantify with a numerical value (Difference Measure, DM) the AR coefficients variations.

Algorithms↗
PubMed1995

An analytical model to predict the electric field and excitation zones due to magnetic stimulation of peripheral nerves.

The main unknown factor in understanding magnetic stimulation of peripheral nerves is the distribution of the induced electric field. We have applied the so-called reciprocity theorem and developed an analytical model to compute the electric field and its spatial derivatives inside pseudocylindrical structures. The results can be used to predict the site of excitation in magnetic stimulation of peripheral nerves.

Computer Simulation↗
PubMed1995

An optimal filtering technique to reduce the influence of low-frequency noise on click-evoked otoacoustic emissions.

There is a need for methods capable of increasing the detectability of transient-evoked otoacoustic emissions (TEOAE). Detection of an emission is based commonly on either visual inspection and cross-correlation between replicate recordings or cross-spectral analysis. Performance of these methods is obviously influenced by the residual noise level. Residual noise is often of low frequency and can be reduced by digital off-line filtering. For this purpose, an optimal high-pass filtering technique is proposed. Cross-correlation between replicates of TEOAEs was used to determine the cut-off frequency that maximizes the signal-to-noise (S/N) ratio. This is shown in a series of responses characterized by various S/N ratios. Data have been scored both visually and with quantitative methods before and after the use of high-pass filtering. The capability to detect the signal was increased with only a marginal decrease in the total power of the emissions.

Acoustic Stimulation↗
PubMed1993

Evoked otoacoustic emissions: nonlinearities and response interpretation.

Evoked otoacoustic emissions (EOAE's) are acoustic signals produced by the inner ear in response to transient acoustic stimuli and can be recorded in the external auditory canal. Since emissions can be reduced or even abolished by hearing losses of peripheral origin due to trauma and pathology, EOAE's are presently considered as the most sensitive clinical test for assessing the integrity of peripheral hearing. Recordings of emissions evoked in response to transient stimuli are contaminated by an initial artifact which in most clinical environments can be a very serious limitation. For this reason, a nonlinear estimation method is widely used (derived nonlinear response, DNLR), instead of classical synchronous averaging. Aims of this paper are: i) to justify theoretically the use of the DNLR technique by means of a simple model; ii) to compare the results obtained from the classical averaging (a linear estimation technique) with those obtained from the nonlinear DNLR technique. Some suggestions of practical interest are finally inferred from present analysis.

Artifacts↗
PubMed1993

Non-linearities of click-evoked otoacoustic emissions and the derived non-linear technique.

Averaged click-evoked and derived non-linear responses have been measured in normal ears to assess similarities and differences between the results obtained with the two methods. Computation of the input-output curves of click-evoked otoacoustic emissions with a short-time procedure reveals time-varying properties and the presence of saturation phenomena affecting, to various degrees, the linear content of emissions. Present preliminary results provide some guidelines towards the assessment of the relative role of the two techniques in otoacoustic emission testing.

Acoustic Stimulation↗
PubMed1992

A mathematical model for the computation of the forces exerted by the facial orthopedic mask.

This study presents a model for the computation of the forces exerted on the chin and on the forehead by the facial orthopedic mask in skeletal Class III malocclusions. Cephalometric data as well as geometry of the mask are taken into account to simulate in quantitative terms the entire approach. A computer program has been implemented to validate the model on a group of patients. Despite the approximations about the mechanical characteristics of the appliance and of the constraints (rigid body, ideal constraints) and despite the unavoidable errors in the estimation of the geometric parameters (dimensions and angles), it is shown that the computation of the forces (in orientation and in magnitude) at the forehead and at the chin is possible. Some practical applications of the model are presented.

Adolescent↗
PubMed1991

Individual versus averaged data in the analysis of auditory evoked electrical potentials.

Interpretation of multichannel electric potentials in terms of equivalent dipolar sources has often been based upon the analysis of averaged data, i.e. of the grand averages of the individual recordings obtained from normal subjects. Some considerations are presented here to show that the above procedure may lead to erroneous results. Examples of individual data fits are discussed in relation to the possibility of (i) defining a 'norm' and (ii) extracting some information about the 'resolving power' of the electric method.

Auditory Cortex↗
PubMed1991

Magnetic stimulation of the motor cortex--theoretical considerations.

The aim of this paper is to present a first approximation model for the computation of the electric fields produced in the brain tissues by magnetic stimulation. Results are given in terms of induced electric field and current density caused by coils of different radii and locations. Nontraditional coil locations and assemblies are also considered (multicoil arrangements). Model simulations show that a good control of the excitation spread can be achieved by proper positioning of the coil. It is also predicted that one of the major drawbacks of the technique, i.e., the poor ability to concentrate the current spread into a small brain area can be partially overcome by more effective coil positioning and/or assembly. Finally, some comparisons are made among the results obtained from electric and magnetic stimulation. This is thought to be of great help in the design of experiments aimed to understand the relative role of the different brain structures responsible for the motor response.

Brain↗
PubMed1991

Electric response audiometry in infants and preschool children. Long-term control of the results.

Two hundred and four infants and preschool children (mean age 2 years and 7 months +/- 9 months) with auditory impairment according to ABR and ECochG data, and 33 subjected to SVR were followed up for periods ranging from 1 year to 4 years and 6 months until a reliable conventional pure tone audiogram was obtained. One hundred and fifty-one children had conductive hearing loss, 75 sensorineural, 7 had ABR indicating disorders of the central auditory pathways, 5 were normal. Hit, false positive and false negative rates resulted as follows: 58.62%, 17.24% and 24.14% for SVR: 98.37%, 1.63% and 0% for ABR; 99.15%, 0.85% and 0% for ECochG. In the group with sensorineural hearing loss, 75% of the children gave ECochG detectable responses at 90 dB nHL, against 51.5% with ABR. With 1 kHz tonebursts, 64% of the tested subjects gave threshold responses to ECochG and 12% to ABR. The best strategy for children who failed the behavioral hearing tests, or in whom these tests were not applicable, was that based on ABR and middle ear impedance measures, complemented, when necessary, by ECochG.

Audiometry, Evoked Response↗
PubMed1988

Electrical stimulation of the motor cortex: theoretical considerations.

The aim of this paper is to present the results of a theoretical analysis of the intracranial fields produced by electrical stimulation of the unexposed motor cortex with surface electrodes in humans. Simulations of a first approximation model of the head indicate that the intensity and the spatial configuration of the intracranial fields can be controlled, to a great extent, by proper choice of the location and of the number of the stimulating electrodes. Fields are shown to be reasonably insensitive to changes of some crucial parameters, like the number of the stimulating electrodes and the ratio between the conductivity of the skull and that of the other tissues.

Electric Conductivity↗