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Objective. Recently developed magnetoelectric nanoparticles (MENPs) provide a potential tool to enable different biomedical applications. They could be used to overcome the intrinsic constraints posed by traditional neurostimulation techniques, namely the invasiveness of electrodes-based techniques, the limited spatial resolution, and the scarce efficiency of magnetic stimulation. Approach. By using computational electromagnetic techniques, we modelled the behaviour of recently designed biocompatible MENPs injected, in the shape of clusters, in specific cortical targets of a highly detailed anatomical head model. The distributions and the tissue penetration of the electric fields induced by MENPs clusters in each tissue will be compared to the distributions induced by traditional transcranial magnetic stimulation (TMS) coils for non-invasive brain stimulation positioned on the left prefrontal cortex (PFC) of a highly detailed anatomical head model. Main results. MENPs clusters can induce highly focused electric fields with amplitude close to the neural activation threshold in all the brain tissues of interest for the treatment of most neuropsychiatric disorders. Conversely, TMS coils can induce electric fields of several tens of V m−1 over a broad volume of the PFC, but they are unlikely able to efficiently stimulate even small volumes of subcortical and deep tissues. Significance. Our numerical results suggest that the use of MENPs for brain stimulation may potentially led to a future pinpoint treatment of neuropshychiatric disorders, in which an impairment of electric activity of specific cortical and subcortical tissues and networks has been assumed to play a crucial role.

Deep transcranial magnetic stimulation (dTMS) is a neurostimulation technique for deep brain structures that has recently been successfully applied in the clinic for the treatment of addiction. In contrast to the conventional magnetic stimulation, which uses planar coils [Figure-of-Eight (FoE)] to target specific superficial regions of the brain, dTMS requires the design of complex 3-D coils in order to induce deeply penetrating fields. Recent clinical studies have focused on the use of H4 coils, which utilizes a left–right symmetric structure for bilateral stimulation of the prefrontal cortex, and demonstrated efficacy for therapy such as smoking cessation. The mechanism of activity, however, remains poorly understood, in part because the affected regions of the brain are not known in detail. To this purpose, computational techniques applied to highly detailed inhomogeneous tissue phantoms provide a powerful tool for testing coil efficacy. In this work, we quantified both electric field ${\mathbf E}$ distribution and its penetration depth in the prefrontal cortex, induced by a specific Hesed-coil, H4, designed for the addiction treatment and by the traditional FoE coil for comparison. Results show that H4 coil preferentially targets the insula and cingulate cortex. Moreover, it can induce in the deepest tissues E amplitude ranging between 20% and 40% of the cortical peak, and it can penetrate the cortex up to 4 cm with a E > 50% of the cortical peak, thus noticeably increasing the penetration depth of the traditional TMS systems.

In the last two decades, motor cortex stimulation has been recognized as a valuable alternative to pharmacological therapy for the treatment of neuropathic pain. Although this technique started to be used in clinical studies, the debate about the optimal settings that enhance its effectiveness without inducing tissue damage is still open. To this purpose, computational approaches applied to realistic human models aimed to assess the current density distribution within the cortex can be a powerful tool to provide a basic understanding of that technique and could help the design of clinical experimental protocols. This study aims to evaluate, by computational techniques, the current density distributions induced in the brain by a realistic electrode array for cortical stimulation. The simulation outcomes, summarized by specific metrics quantifying the efficacy of the stimulation (i.e., the effective volume and the effective depth of penetration) over two cortical targets, were evaluated by varying the interelectrode distance, the stimulus characteristics (amplitude and frequency), and the anatomical human model. The results suggest that all these parameters somehow affect the current density distributions and have to be therefore taken into account during the planning of effective electrical cortical stimulation strategies. In particular, our calculations show that (1) the most effective interelectrode distance equals 2 cm; (2) increasing voltage amplitudes increases the effective volume; (3) increasing frequencies allow enlarging the effective volume; and (4) the effective depth of penetration is strictly linked to both the anatomy of the subject and the electrode placement.

Exposure to electromagnetic fields (EMFs) has prominently increased during the last decades due to the rapid development of new technologies. Among the various devices emitting EMFs, those based on Radio-frequency identification (RFID) technologies are used in all aspects of everyday life, and expose people unselectively. This scenario could pose a potential risk for some groups of the general population, such as pregnant women, who are expected to be possibly more sensitive to the thermal effects produced by EMF exposure. This is the first paper that addresses the estimation of temperature rise in two pregnant women models exposed to ultrahigh frequency RFID by computational techniques. Results show that the maximum temperature increase of the fetus and of the pregnancy-related tissues is relatively high (even about 0.7 °C), not too far from the known threshold of biological effects. However, this increase is confined to a small volume in the tissues.

Literature studies showed the ability to treat neuropsychiatric disorders using H1 coil, developed for the deep Transcranial Magnetic Stimulation (dTMS). Despite the positive results of the clinical studies, the electric field (E) distributions inside the brain induced by this coil when it is positioned on the scalp according to the clinical studies themselves are not yet precisely estimated. This study aims to character- ize the E distributions due to the H1 coil in the brain of two realistic human models by computational electromagnetic techniques and to compare them with the ones due to the figure-of-8 coil, traditionally used in TMS and positioned as such to simulate the clinical experiments. Despite inter-individual differences, our results show that the dorsolateral prefrontal cortex is the region preferentially stimulated by both H1 and figure-of-8 coil when they are placed in the position on the scalp according to the clinical studies, with a more broad and non-focal distribution in the case of H1 coil. Moreover, the H1 coil spreads more than the figure-of-8 coil both in the prefrontal cortex and medial prefrontal cortex and towards some deeper brain structures and it is characterized by a higher penetration depth in the frontal lobe. This work highlights the importance of the knowledge of the electric field distribution in the brain tissues to interpret the outcomes of the experimental studies and to optimize the treatments.

Objective: A procedure to personalize the electrode to stimulate specific cortical regions by transcranial electric stimulations has been recently proposed. This study aims to assess the distribution of the electric field (E) induced by tES via the personalized (RePE) and the nonpersonalized (ReNPE) electrode. Methods: We used two anatomical models on which we shaped and placed the RePE, based on brain anatomy, and the ReNPE to target the bilateral primary motor (M1) or somatosensory cortex (S1) with the reference on the occipital area in both cases. The effect of shifts of the ReNPE position has been also evaluated. Results: The RePE induced higher E peak and median values than the ReNPE along the bilateral primary motor sensory cortices, up to their lateral regions, on a great percentage of volume of these cortices along all their extent. The shift of the ReNPE electrode toward the inion still induced higher E peak and median values than the ReNPE not shifted, but less than the RePE, mainly in the central region and, in a lower percentage of volume, in the lateral regions of these cortices. Conclusion: The E distributions induced for both targets (M1 and S1) by the RePE are different from the ones due to the ReNPE, along the whole extent of the bilateral primary sensorimotor cortices. The shift in the ReNPE positioning can modify the E distributions mainly in the more central region of these cortices. Significance: These results strengthen the suitability of personalized electrodes in targeting extended cortical regions.

Objective: Deep transcranial magnetic stimulation (dTMS) has been recently used in several clinical studies as diagnostic and therapeutic tool. However, electric field ( E ) distributions induced in the brain by dTMS are still unknown. This paper provides a characterization of the induced E distributions in the brain of a realistic human model due to 16 different coil configurations. Methods: The scalar potential finite-element method was used to calculate the E distributions differentiating the brain structures, e.g., cortex, white matter, anterior cingulated cortex, cerebellum, thalamus, hypothalamus, nucleus accumbens, amygdale, and hippocampus. Results: Our results support that the double cone coils and the large diameter circular coils are more prone to activate deeper brain structures but are also characterized by a reduced focality on the surface of the cortex, with the consequent possible counter effect of stimulating regions not of interest. The Hesed coils, although their ability to reach deep brain tissues is lower, seem to be more able to reduce the effect on other brain regions where the stimulation is undesired. Conclusion: All the coil configurations resulted subjected to a depth-focality tradeoff. Significance: Since there is not a configuration that is capable of achieving a stimulation both deep and focal, the selection of the most suitable coil settings for a specific clinical application should be based on a balanced evaluation between these two different needs.

The aim of this study was to evaluate the cochlear functionality of Sprague-Dawley rats exposed to electromagnetic fields at 900 MHz and to gentamicin by distortion product otoacoustic emissions, which are a well-known indicator of the status of the cochlea's outer hair cells. A population of 32 rats was divided into four groups: group 1 was treated with daily intramuscular injections of 150 mg/kg body weight gentamicin for 15 days; group 2 was treated with daily intramuscular injections of 150 mg/kg body weight gentamicin for 15 days and exposed to electromagnetic fields; group 3 was exposed to electromagnetic fields; group 4 was sham-exposed. Rats were exposed 2 h/day, 5 days/week for 4 weeks at a local SAR of 4 W/kg in the ear (continuous wave at 900 MHz). Distortion product otoacoustic emissions tests were carried out before, during and after the combined exposure. The analysis of the data showed no subchronic exposure to electromagnetic fields on the inner auditory system of rats in either normal ears or ears exposed to a well-recognized pathological agent.

Polynomial Chaos (PC) is a decomposition method used to build a meta-model, which approximates the unknown response of a model. In this paper the PC method is applied to the stochastic dosimetry to assess the variability of human exposure due to the change of the orientation of the B- field vector respect to the human body. In detail, the analysis of the pregnant woman exposure at 7 months of gestational age is carried out, to build-up a statistical meta-model of the induced electric field for each fetal tissue and in the fetal whole-body by means of the PC expansion as a function of the B-field orientation, considering a uniform exposure at 50 Hz.

Recently we developed a new procedure to personalize the electrode to selectively stimulate specific cortical regions by transcranial electric stimulations (tES) [Tecchio et al.,2013] and we showed that tES via this innovative personalized electrode shaped on individual brain MRI can relieve multiple sclerosis fatigue [Tecchio et al., 2014]. This study aims to assess by computational approach the distriution of the intra-cerebral electric field induced by tES through the personalized in comparison with a non-personalized electrode in two realistic human models.

Excitable tissue can be stimulated non-invasively by means of externally applied changing magnetic fields. This paper considers theoretically magnetic stimulation to functionally stimulate the tissue. We optimize the stimulating coil to accomplish functional magnetic stimulation (FMS) with the minimum cost expressed in terms of driving energy needed to provoke excitation. Magnetic stimulation is less discomfortable than functional electrical stimulation (FES) and therefore, the use of FMS opens up completely new views to the restoration of movement and therapy in patients with neuromuscular system impairment. Advances in coil design can make FMS a promising application field for magnetic stimulation. Copyright (C) 1998 Elsevier Science S.A. Excitable tissue can be stimulated non-invasively by means of externally applied changing magnetic fields. This paper considers theoretically magnetic stimulation to functionally stimulate the tissue. We optimize the stimulating coil to accomplish functional magnetic stimulation (FMS) with the minimum cost expressed in terms of driving energy needed to provoke excitation. Magnetic stimulation is less discomfortable than functional electrical stimulation (FES) and therefore, the use of FMS opens up completely new views to the restoration of movement and therapy in patients with neuromuscular system impairment. Advances in coil design can make FMS a promising application field for magnetic stimulation.

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.

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.

This paper provides a characterization of the induced electric field distributions in the brain of a realistic human model due to 16 different coil configurations. We used the scalar potential finite element method to calculate the induced electric field distributions differentiating the brain structures, e.g. cortex, white matter, cerebellum, thalamus, hypothalamus, hippocampus, pons and midbrain. We found that, despite the presence of a depth-focality tradeoff, some configurations are able to reach subcortical white matter tracts at effective electric field level.

Extremely low frequency magnetic fields (ELF-MF) have been considered as a possible risk factor for childhood leukemia by several epidemiological studies. In this work the exposure assessment of fetuses at 3, 7 and 9 months of Gestational Age (GA) to differently polarized uniform magnetic fields at the frequency of 50 Hz by means of high resolution numerical models of pregnant women is carried out. This set of models is used to analyze the fetal tissue-specific induced electric fields and current densities as a function of both the incident magnetic field polarization and the GA.

Deep brain stimulation is a clinical technique for the treatment of parkinson’s disease based on the electric stimulation, through an implanted electrode, of specific basal ganglia in the brain. To identify the correct target of stimulation and to choose the optimal parameters for the stimulating signal, intraoperative microelectrodes are generally used. However, when they are replaced with the chronic macroelectrode, the effect of the stimulation is often very different. Here, we used numerical simulations to predict the stimulation of neuronal fibers induced by microelectrodes and macroelectrodes placed in different positions with respect to each other. Results indicate that comparable stimulations can be obtained if the chronic macroelectrode is correctly positioned with the same electric center of the intraoperative microelectrode. Otherwise, some groups of fibers may experience a completely different electric stimulation.

Exposure from electromagnetic (EM) devices has increased during the last decades due to the rapid development of new technologies. Among them, radiofrequency identification (RFID) applications are used in almost every aspect of everyday life, which could expose people unselectively. This scenario could pose potential risks for certain groups of general population, such as pregnant women, who are more sensitive to thermal effects produced by EM exposure. In this paper, the temperature rise at the steady state in two pregnant women models exposed to UHF RFID has been assessed. Results show that heating of tissues is far from the threshold of biological effects indicated by radiation protection guidelines.

Generally, physiological modeling and biomedical signal processing constitute two important paradigms of biomedical engineering (BME): their fundamental concepts are taught starting from undergraduate studies and are more completely dealt with in the last years of graduate curricula, as well as in Ph.D. courses. Traditionally, these two cultural aspects were separated, with the first one more oriented to physiological issues and how to model them and the second one more dedicated to the development of processing tools or algorithms to enhance useful information from clinical data. A practical consequence was that those who did models did not do signal processing and vice versa. However, in recent years,the need for closer integration between signal processing and modeling of the relevant biological systems emerged very clearly [1], [2]. This is not only true for training purposes(i.e., to properly prepare the new professional members of BME) but also for the development of newly conceived research projects in which the integration between biomedical signal and image processing (BSIP) and modeling plays a crucial role. Just to give simple examples, topics such as brain–computer machine or interfaces,neuroengineering, nonlinear dynamical analysis of the cardiovascular (CV) system,integration of sensory-motor characteristics aimed at the building of advanced prostheses and rehabilitation tools, and wearable devices for vital sign monitoring and others do require an intelligent fusion of modeling and signal processing competences that are certainly peculiar of our discipline of BME.

This paper investigates the spatial distribution of the electric field and of the current density in the brain tissues induced by transcranial direct current stimulation of the primary motor cortex. A numerical method was applied on a realistic human head model to calculate these field distributions in different brain struc- tures, such as the cortex, the white matter, the cerebellum, the hippocampus, the medulla oblongata, the pons, the midbrain, and the thalamus. The influence of varying the anode area, the cathode area, and the injected current was also investigated. An electrode area as the one typically used in clinical practice (i.e., both elec- trodes equal to 35 cm2 ) resulted into complex and diffuse amplitude distributions over all the examined brain structures, with the re- gion of maximum induced field being below or close to the anode. Variations in either the anode or cathode area corresponded to changes in the field amplitude distribution in all the brain tissues, with the former variation producing more diffuse effects. Vari- ations in the injected current resulted, as could be expected, in linearly correlated changes in the field amplitudes.

Deep Brain Stimulation (DBS) is a clinically suitable technique for the treatment of the Parkinson's disease. Recently, also other neurological disorders such as Tourette syndrome, obsessive-compulsive disorder, epilepsy are being to be treated with DBS. However, the debate on its therapeutic mechanisms of action is still open. In order to a better understanding of such mechanisms, in this work the attention is focused on the DBS micro-stimulation. Indeed, a micro electrodes registration and stimulation is a fundamental step, during the surgical phase, to optimize the technique in terms of DBS lead positioning and DBS signal parameters. In this paper a dosimetric analysis with micro electrodes has been carried out, showing a more focused distribution of the electrical potential induced in the neuroanatomical tissues and changes of the excited/inhibited regions, respect to a macro electrodes stimulation.

In recent years there has been considerable interest in the study of glucose-induced dielectric property variations of human tissues as a possible approach for non-invasive glycaemia monitoring. We have developed an electromagnetic sensor, and we tested in vitro its ability to estimate variations in glucose concentration of different solutions with similarities to blood (sodium chloride and Ringer-lactate solutions), differing though in the lack of any cellular components. The sensor was able to detect the effect of glucose variations over a wide range of concentrations (similar to 78-5,000 mg/dL), with a sensitivity of similar to 0.22 mV/(mg/dL). Our proposed system may thus be useful in a new approach for non-invasive and non-contact glucose monitoring.

To improve planning of maxillofacial surgery, a novel method for maxillary-, mandibular-, and facial-nerve 3-D image reconstruction was implemented and optimized. A set of images acquired by a computed tomography (CT) scanner was segmented to reconstruct the 3-D model of the maxilla and mandible. Particular attention was given to the segmentation of the facial nerve, which was obtained through the gradient-vector-flow (GVF) snake method. After segmentation, precise anatomical 3-D plastic models were fabricated through stereolithography from CT scans of five clinical cases that will undergo either dental implant surgery or bone distraction. For all cases, 3-D models delivered essential visual and tactile information for the planning and simulation of surgery as well as for customized implant preparation.

Cochlear implants are electronic devices used to restore partial hearing to people with severe hearing impairment. This study aims to evaluate the effects of an external microwave at 2.4 GHz on the SAR distribution inside a head model with a cochlear implant. Results show no harmful effects in the cochlear tissues due to the described interaction.

This paper investigates the internal electric and magnetic field distribution and the specific absorption rate (SAR) values in a magnetic resonance imaging-based model of the inner hearing system exposed to 900 and 1800 MHz. The internal fields distributions were calculated using the Finite Integration Technique. The estimation of the field values was evaluated along lines passing through that target organ, specifically from the vestibular to the cochlear region and from the apex to the base of the cochlea. The specific findings are: 1) higher internal fields strength and SAR value in the vestibular region rather than in the auditory region, especially for the inner ear closer to the external source; 2) higher internal fields strength in the basal and apical region of the cochlea than in the middle one; 3) local differences in the internal fields distribution and SAR value, comparing the head models including or not the inner auditory system model; 4) results' variability evaluated by changing the head-source mutual position and the dielectric properties of the inner hearing system.

The design and development of an experimental setup to measure in-vitro electric potential distribution delivered by a multichannel cochlear implant varying conditions and parameter of usage is described, with particular attention to the spatial distribution of the electric potential generated by this implant. This study enables a better comprehension of the relationships between parameters of stimulations and the electric potential delivered by the cochlear implant, fundamental to develop a more efficient and spatially localized stimulation of the nervous tissues.

The electric potential pattern generated by a cochlear implant was modeled using the finite-element method. The pattern, which is a response to bipolar current pulses from the implant electrode array, was investigated for different values of the electrical parameters of the human cochlea and of the array. Simulated data are compared with measurements in a water tank. Numerical simulations were carried out for different electrode configurations. Electrode configurations were found to affect the resulting potential, and the measurements confirmed our modeling approach. This study provides a better understanding of the relationship between the stimulation parameters and the delivered electric field, which is crucial to develop more efficient and spatially localized excitations of cochlear neural tissues.

Distortion product otoacoustic emissions (DPOAE) can be used to study cochlear function in an objective and non-invasive manner. One practical and essential aspect of any investigating measure is the consistency of its results upon repeated testing of the same individual/animal (i.e., its test/retest repeatability). The goal of the present work is to propose two indices to quantitatively assess the repeatability of DPOAE in laboratory animals. The methodology is here illustrated using two data sets which consist of DPOAE subsequently collected from Sprague-Dawley rats. The results of these experiments showed that the proposed indices are capable of estimating both the repeatability of the true emission level and the inconsistencies associated with measurement error. These indices could be a significantly useful tool to identify real and even small changes in the cochlear function exerted by potential ototoxic agents.

Electric potential field distribution induced in the physiological tissues by bipolar current pulses, generated by a cochlear implant electrode array, was calculated by mathematical modeling the electrical properties of the human cochlea and of the electrode array, using a finite element method. At the same time it was planned an experimental setup to compare simulated data to the potential distributions measured in-vitro using a saline solution bath. Theoretical measurements were done under different stimulation conditions, i.e., by considering different electrode shapes and configurations, stimulus intensities, pulse stimulation rates, and pulse durations. All these parameters were found to affect the resulting field potentials. Preliminary results of this study provide a deeper knowledge of the relationship between the stimulation parameters and the actually delivered electric field, which is crucial to develop more efficient and spatially focused excitations of cochlear neural tissues

The rapid diffusion of environmental electromagnetic radiations, in particular in the radiofrequency range, is determining increasing interest on their possible consequent health effects. A particular attention is deserved to those subjects who are considered to be more sensitive such as people who use cochlear implants. Cochlear implants (CI) are electronic devices that restore partial hearing to deaf or severely hard of hearing people. Aim of this study was to analyze the possible functional interactions of RF microwaves with CI. Results of this study show that the electrode array inside a cochlea exposed to an external radiofrequency EMF source at 900 MHz produced peaks on the amplitude of the electric and magnetic fields near the implant and a consequent local increase of the absorbed power and tissue temperature. Moreover, peaks of current density in correspondence of the electrodes were found, with average values of about 4 ?A.

Human excitable cells can be stimulated noninvasively with externally applied time-varying electromagnetic fields. The stimulation can be achieved either by directly driving current into the tissue (electrical stimulation) or by means of electromagnetic induction (magnetic stimulation). While the electrical stimulation of the peripheral neuromuscular system has many beneficial applications, peripheral magnetic stimulation has so far only a few. This paper analyzes theoretically the use of multiple magnetic stimulation coils to better control the excitation and also to eventually mimic electrical stimulation. Multiple coils allow electronic spatial adjustment of the shape and location of the stimulus without moving the coils. The new properties may enable unforeseen uses for peripheral magnetic stimulation, e.g., in rehabilitation of patients with neuromuscular impairment. Human excitable cells can be stimulated noninvasively with externally applied time-varying electromagnetic fields. The stimulation can be achieved either by directly driving current into the tissue (electrical stimulation) or by means of electromagnetic induction (magnetic stimulation). While the electrical stimulation of the peripheral neuromuscular system has many beneficial applications, peripheral magnetic stimulation has so far only a few. This paper analyzes theoretically the use of multiple magnetic stimulation coils to better control the excitation and also to eventually mimic electrical stimulation. Multiple coils allow electronic spatial adjustment of the shape and location of the stimulus without moving the coils. The new properties may enable unforeseen uses for peripheral magnetic stimulation, e.g., in rehabilitation of patients with neuromuscular impairment.

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.

Introduction Non-invasive transcutaneous spinal direct current stimulation (tsDCS) induces changes in spinal cord function in humans (Cogiamanian et al., 2012). The physiological mechanisms underlying these changes however remain speculative. A relevant issue to better understand this innovative non-invasive neuromodulation technique is the estimation of the spatial distribution of the current density in the spinal cord during tsDCS. Objective To evaluate the current density ( J ) induced by dorsal tsDCS in the spinal cord using electromagnetics computational techniques applied to realistic human models of different age and gender. Materials and methods The computation was conducted using the simulation platform SEMCAD X (Schmid & Partner Engineering AG, Zurich, Switzerland) solving the Laplace equation. Three realistic human models of the Virtual Family (Christ et al., 2010) were used. The models are based on high resolution magnetic resonance images of healthy volunteers (a 26-years-old female adult model "Ella"; a 34years-old male adult model "Duke"; an 11years old female adolescent model "Billie"). The models consist of up to 77 different tissues, the dielectric properties of which were assigned on the basis of the data at low frequency (Gabriel et al., 1996). In this preliminary study three electrode montages were modeled in which the anode was always over the spinal process of the tenth thoracic vertebra and the cathode was placed: (i) above the right deltoid (ii) over the umbilicus; (iii) over Cz. The injected current was 3mA. The electrodes were conductors within rectangular sponges. Results Preliminary data indicates that in the dorsal spinal cord below the stimulating electrode the peaks of J across the models are of 0.02 A/m 2 , 0.03 A/m 2 and 0.06 A/m 2 for the three electrode montages, respectively. Conclusion The electric field generated by tsDCS reaches the spinal cord at physiologically effective strength.

Knowledge of the electric field that is induced in the brain or the limbs is of importance in magnetic stimulation of the nervous system. Here, an analytical model based on the reciprocity theorem is used to compare the induced electric field in unbounded, semi-infinite, spherical, and cylinder-like volume conductors. Typical stimulation coil arrangements are considered, including the double coil and various orientations of the single coil. The results can be used to determine when the influence of the boundaries is negligible enough to allow the use of more simplified geometries.

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.

Short-latency (10-50 ms) median nerve somatosensory evoked potentials (SEPs) from four normal subjects were analysed by means of temporal segmentation techniques and source derivation methods. In each case the responses were recorded using 32 electrodes. Dipolar optimization was carried out with a time-varying technique, using three different approaches: regional sources estimation, spherical source estimation (one radial and one tangential component), and multiple dipolar approach. This was to assess the relative influence on the dipolar solution of the different optimization techniques. The effect of the different number of channels in the estimation procedures has been also investigated. The methods of optimization are crucial, particularly for the orientation of P22. In all cases the source location estimated with the 32-electrode montage was shifted towards the centre of the spheres.

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. An approximation model for the computation of the electric fields produced in the brain tissues by magnetic stimulation is presented. 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. Some comparisons are made among the results obtained from electric and magnetic stimulation. This is thought to be helpful in the design of experiments aimed at understanding the relative role of different brain structures responsible for the motor response.

Hearing aid shells (or earmolds) must couple the hearing aid with the user's ear. Earmolds have to fit the subject's outer ear canal properly to ensure a good performance of the aid. Because of the great variability in the anatomical pattern of the ear, earmolds are custom made. At present, an impression of the subject's ear canal is taken and used to fabricate the silicon-made mold. The postimpression activities that typically are performed during the fabrication process modify the physical dimensions of the resulting earmold and thus affect the fit of the product. A novel system for 3-D laser scanning and mesh reconstruction of the surface of ear canal impressions is presented. The reconstructed impression can be digitally stored and passed directly to dedicated CAD 3-D printing machines to model the silicon earmold and thus achieve the best possible fit. The proposed system is based on a couple of cameras and a commercial laser for the surface digitization and on a straightforward algorithm, based on the deformation of a geometric model, for the reconstruction of the acquired surface. Measurements on objects of well-known geometric features and dimensions are performed to assess the accuracy and repeatability levels of this 3-D acquisition system. Robustness to noise of the proposed reconstruction algorithm is determined by simulations with a synthetic test surface. Finally, the first measurements (acquisition+reconstruction) of closed surfaces from ear canal impressions are reported.

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.