Biomedical subjects

G Tognola

Publications and source records attributed to G Tognola.

At least 19 recordsLinked to original sources

PubMed2001

A hospital based universal neonatal hearing screening programme using click-evoked otoacoustic emissions.

Since 1997 a hospital-based universal hearing screening programme (Milan Programme) has been carried out at the Neurophysiopathology Unit of the Mangiagalli Clinic in Milan, for the early identification of hearing loss in neonates (5650 well babies, 749 newborns from the Neonatal Pathology Unit (NPU) without risk for hearing loss and 118 newborns at risk for hearing loss). As a result, considering the well baby population, three pathological neonates (one profound bilateral and two unilateral hearing loss) were identified. Three additional cases were found among the NPU newborns, whereas 16 cases with bilateral and 11 with unilateral hearing loss were found among the at-risk babies.

Acoustic Stimulation↗

PubMed2001

Analysis of spontaneous and click-evoked otoacoustic emissions in newborns.

This paper addresses the quantitative investigation of the contribution of spontaneous (SOAE) to click-evoked (TEOAE) otoacoustic emissions in newborns. The hypothesis was that a weighted linear combination of the spontaneous peaks is strongly similar to the corresponding click-evoked emissions. After identification of the main spontaneous peaks for each subject, a best fit procedure was applied to find the amplitude and phase of each spontaneous tone in the weighted summation. The comparison of the weighted signal (SpTEOAE) with the actual click-evoked response (TEOAE) from the same subject was performed, obtaining correlation coefficient higher than 50% in more than 100 ears over 132.

Factor Analysis, Statistical↗

PubMed2001

Time-frequency analysis of neonatal click-evoked otoacoustic emissions.

Click-evoked otoacoustic emissions (CEOAEs) of full-term babies were considered. By means of the wavelet transform, each CEOAE was decomposed into frequency bands. The rms amplitude and test-retest correlation were computed from these bands. The results indicated that both the amplitude and correlation were not invariant with time but reached a maximum in specific time windows, depending on the frequency of the component. For all components, the correlation was greatly decreased for latencies > 12.5 ms. As a result, comparison between the performance of the default ILO 88 window (2.5-20 ms) and the 2.5-12.5 ms window showed that for all frequencies in the 1.5-6 kHz range there was a statistically significant improvement in the correlation.

Factor Analysis, Statistical↗

PubMed2001

"Linear" and "derived" otoacoustic emissions in newborns: a comparative study.

OBJECTIVE: To investigate the effects of a specific aspect of the acquisition procedure, the averaging technique, on the evaluation of click-evoked otoacoustic emissions (CEOAEs) in newborns. DESIGN: CEOAEs were recorded by an Otodynamic ILO88 system from 89 full-term newborns at the third day after delivery. For each ear and in the same test session, CEOAEs were evoked by 75 to 85 dB pSPL acoustic clicks and averaged according to two different modes: the "linear" (classic average) and the "derived" mode, which allows the cancellation of linear behaving components (such as acoustic artifacts). All examined ears had a normal auditory function as assessed by conventional ABR between the ages of 2 and 4 mo. CEOAEs obtained by both averaging techniques were compared on the basis of several quantitative parameters: the waveform similarity; the levels of signal and noise and the inter-test reproducibility of the broadband response and of four different frequency bands centered at 1.6, 2.4, 3.2, and 4 kHz; the amplitude as a function of time; the test time. To eliminate the contribution of the stimulus artifact, linear CEOAEs were windowed 6 to 20 msec, whereas derived emissions were windowed using the default ILO88 window (2.5 to 20 msec). Additionally, CEOAEs were classified as "pass" or "fail" accordingly to screening criteria used in the daily clinical practice. RESULTS: Linear and derived emissions had very similar wave shapes and no time shifts during the first 12.5 msec. On the contrary, clear differences in the waveforms and time shifts were observed at longer latencies. The use of both averaging techniques resulted in identical CEOAE levels for both the broadband response and for the first two tested frequencies. For the last two frequencies, emission levels were lower when averaged with the linear technique owing to the use of the time window 6 to 20 msec, which reduces the amplitudes of high-frequency components. The residual noise in derived traces is 6 dB higher than that from linear traces. Also, derived CEOAEs had a lower inter-test reproducibility in both the broadband compound emission and in the four frequency bands examined here. The greatest difference in reproducibility was observed at the lowest band (1.2 to 2 kHz). Scoring of emissions was influenced by the averaging technique: 14% CEOAEs obtained with linear averaging and scored as passes were classified as fails when averaged with the derived mode. Moreover, if a CEOAE was scored as pass when using the derived technique, it also was scored as pass when using linear averaging. The increased number of false positives most likely was due to the higher noise floor/lower signal to noise ratio (SNR) of CEOAEs obtained with the derived technique. CONCLUSIONS: In the tested newborns and at the levels of stimulation used in this study, the emissions obtained with the derived technique were noisier than those obtained with the linear technique, this being intrinsically due to the type of averaging. Therefore, screening criteria based on the evaluation of the SNR (or similar parameters) could be influenced by the type of averaging used during the acquisition.

Acoustic Stimulation↗

PubMed2001

Data processing options and response scoring for OAE-based newborn hearing screening.

Scoring of click-evoked otoacoustic emissions (CEOAEs) is typically achieved by the evaluation of the reproducibility of the whole emission and/or within narrow bands. Screening outcomes are influenced not only by the specific combination of the subdivision scheme (i.e., the number, position, and bandwidth of the narrow bands) and the threshold used to determine pass and refer, but also by the accuracy with which the reproducibility is estimated. This study was designed to examine what factors affect the accuracy of the reproducibility estimate and how the accuracy of the reproducibility estimate together with the choice of the subdivision scheme/thresholds affect CEOAE scoring. Simulations with real CEOAEs corrupted with synthesized noise indicated that the reproducibility estimate is influenced by time-windowing and band-pass filtering: the longer the time-window or the broader the bandwidth of the filter, the more accurate the estimate. Quantitative figures on numerical scoring were given in terms of the referral rate and were derived from CEOAEs recorded in a clinical environment from more than 3400 newborns. The narrow bands were extracted according to 12 different subdivision schemes covering the 1.5-4-kHz range. The referral rate was found to depend on the subdivision scheme being used: (i) the worst results were obtained considering four narrow bands at 1.6-2.4-3.2-4 kHz; (ii) the best results were obtained considering two narrow bands at 2.25 and 3.75 kHz; (iii) bandwidths greater than 1 kHz resulted in the lowest referral rates. Also, scoring based on the extraction of four narrow bands produced the most unstable results, i.e., a small change in the threshold might cause even a great change in the referral rate.

Female↗

PubMed2000

Frequency and temporal analysis of contralateral acoustic stimulation on evoked otoacoustic emissions in humans.

Previous studies have shown that the effect of contralateral acoustic stimulation (CAS) on ipsilateral evoked otoacoustic emissions (EOAE) depends somewhat upon the spectrum of the eliciting stimulus. The latency of the EOAE, however, is itself frequency-dependent. Consequently, two general ways of analyzing the effects of CAS may be considered: by frequency band or by temporal segment. In this study, we analyzed the effects of CAS both ways in the same subjects, essentially simultaneously. The frequency analysis of the EOAE derived from the wavelet transform (WT). The WT is known to provide a robust approach to the analysis of non-stationary signals and was anticipated to avoid possible time-frequency confounds of the cochlear mechanical system. For comparison, a more basic analysis - using a temporal moving window - was employed. The results largely support earlier findings and confirm that in humans the greatest suppression of EOAEs by CAS is obtained for lower frequency and/or longer latency EOAE components. Despite expectations for the WT analysis, the more basic, temporal, analysis tended to yield the clearer results.

Acoustic Stimulation↗

PubMed1998

Wavelet analysis of click-evoked otoacoustic emissions.

Time-frequency distribution methods are being widely used for the analysis of a variety of biomedical signals. Recently, they have been applied also to study otoacoustic emissions (OAE's), the active acoustic response of the hearing end organ. Click-evoked otoacoustic emissions (CEOAE's) are time-varying signals with a clear frequency dispersion along with the time axis. Analysis of CEOAE's is of considerable interest due to their close relation with cochlear mechanisms. In this paper, several basic time-frequency distribution methods are considered and compared on the basis of both simulated signals and real CEOAE's. The particular structure of CEOAE's requires a method with both a satisfactory time and frequency resolution. Results from simulations and real CEOAE's revealed that the wavelet approach is highly suitable for the analysis of such signals. Some examples of the application of the wavelet transform to CEOAE's are provided here. Applications range from the extraction of normative data from adult and neonatal OAE's to the extraction of quantitative parameters for clinical purposes.

Adult↗

PubMed1998

Two-dimensional filter to facilitate detection of transient-evoked otoacoustic emissions.

This paper implements a filtering technique to enhance the signal-to-noise ratio (SNR) and, in turn, the detection of transient-evoked otoacoustic emissions (TEOAE's), generated by healthy human cochlea. One can increase the SNR by compiling an image of recorded TEOAE from more than one stimulus intensity, averaged over a few sweeps, which can be further processed by means of two-dimensional spatial mean filters. Averaging some 60 sweeps recorded to stimuli at several intensity levels requires one-forth of the collection time needed for a classical set of responses (average of 260 sweeps), and obtains approximately the same final SNR. The relation between the performances of the proposed technique and the SNR of the rapidly acquired responses before filtering is also investigated.

Acoustic Stimulation↗

PubMed1998

Time-frequency distribution methods for the analysis of click-evoked otoacoustic emissions.

Click-evoked otoacoustic emissions (CEOAEs) are time-varying signals with a clear frequency dispersion along with the time axis. Analysis of CEOAEs is of considerable interest due to their close relation with cochlear mechanisms. The particular structure of CEOAEs requires a time-frequency method with both a satisfactory time and frequency resolution. In this paper, several basic time-frequency distribution methods are considered and compared on the basis of both simulated signals and real CEOAEs. Results from simulations and real CEOAEs revealed that the wavelet approach is highly suitable for the analysis of such signals. Some examples of the application of the Wavelet Transform to CEOAEs are provided here. Applications range from the extraction of normative data from adult OAEs to the extraction of quantitative parameters for clinical purposes.

Acoustic Stimulation↗

PubMed1997

Time-frequency distributions of click-evoked otoacoustic emissions.

Emissions evoked by broad-band stimuli, such as clicks, show a 'frequency dispersion' reminiscent of the place-frequency distribution along the cochlea. Analysis of the time-frequency properties of transiently evoked otoacoustic emissions (TEOAEs) is therefore of considerable interest due to their close relation with cochlear mechanisms. In particular, since OAEs in response to click stimuli are expected to evoke a cumulative response from the whole cochlea, the analysis of click-evoked OAEs can yield a global view of cochlear function. Wavelet analysis is performed to obtain time-frequency distributions of click-evoked OAEs at various intensity levels from normal ears. By means of the inverse wavelet transform, the recorded responses are decomposed into elementary components representing the contribution within a narrow frequency band to the cumulative OAE. The relationship between the frequency of the elementary components, latency and level of stimulation is described.

Acoustic Stimulation↗

PubMed1997

Electric versus magnetic transcranial stimulation of the trigeminal system in healthy subjects. Clinical applications in gnathology.

This investigation is focused on the analysis of the masseter responses evoked by means of magnetic and electric stimulation of the cortex and root of the trigeminal system of 20 healthy subjects. Moreover, in order to determine jaw elevation in centric occlusion, the analysis also focused on the motor response of the trigeminal bilateral roots evoked simultaneously using two stimulators. The masseter responses show a high level of symmetry in both latency and amplitude. The difference between the hinge axis in natural centric occlusion (CO) and in centric relation (CR) as determined by electric and magnetic transcranial stimulation is lesser than 2.5 mm. This is due to two main factors: (i) the response is evoked from the trigeminal motor neural pool involving all the masticatory muscles and hence simulating the natural 'muscular coactivation'; (ii) there is no manual manipulation to guide the jaw into the centric relation (CR). This method could be of some help for diagnosis in patients suffering from TMJ dysfunction who have lost stereognostic control over the jaw and display obvious signs of deviation during closure of the mandible.

Adult↗

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 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↗