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C Del Gratta

Publications and source records attributed to C Del Gratta.

15 recordsLinked to original sources
PubMed2001

Linear inverse source estimate of combined EEG and MEG data related to voluntary movements.

A method for the modeling of human movement-related cortical activity from combined electroencephalography (EEG) and magnetoencephalography (MEG) data is proposed. This method includes a subject's multi-compartment head model (scalp, skull, dura mater, cortex) constructed from magnetic resonance images, multi-dipole source model, and a regularized linear inverse source estimate based on boundary element mathematics. Linear inverse source estimates of cortical activity were regularized by taking into account the covariance of background EG and MEG sensor noise. EEG (121 sensors) and MEG (43 sensors) data were recorded in separate sessions whereas normal subjects executed voluntary right one-digit movements. Linear inverse source solution of EEG, MEG, and EEG-MEG data were quantitatively evaluated by using three performance indexes. The first two indexes (Dipole Localization Error [DLE] and Spatial Dispersion [SDis]) were used to compute the localization power for the source solutions obtained. Such indexes were based on the information provided by the column of the resolution matrix (i.e., impulse response). Ideal DLE values tend to zero (the source current was correctly retrieved by the procedure). In contrast, high DLE values suggest severe mislocalization in the source reconstruction. A high value of SDis at a source space point mean that such a source will be retrieved by a large area with the linear inverse source estimation. The remaining performance index assessed the quality of the source solution based on the information provided by the rows of the resolution matrix R, i.e., resolution kernels. The i-th resolution kernels of the matrix R describe how the estimation of the i-th source is distorted by the concomitant activity of all other sources. A statistically significant lower dipole localization error was observed and lower spatial dispersion in source solutions produced by combined EEG-MEG data than from EEG and MEG data considered separately (P < 0.05). These effects were not due to an increased number of sensors in the combined EEG-MEG solutions. They result from the independence of source information conveyed by the multimodal measurements. From a physiological point of view, the linear inverse source solution of EEG-MEG data suggested a contralaterally preponderant bilateral activation of primary sensorimotor cortex from the preparation to the execution of the movement. This activation was associated with that of the supplementary motor area. The activation of bilateral primary sensorimotor cortical areas was greater during the processing of afferent information related to the ongoing movement than in the preparation for the motor act. In conclusion, the linear inverse source estimate of combined MEG and EEG data improves the estimate of movement-related cortical activity.

Dura Mater↗
PubMed2000

Topographic organization of the human primary and secondary somatosensory areas: an fMRI study.

The topographical organization of SI and SII somatosensory areas was investigated using fMRI at 1.5 T and electrical sensory stimulation. Electrical stimuli were delivered unilaterally to the median nerve at the wrist and to the tibial nerve at the medial malleolus, during a block paradigm study. In all subjects, activation was observed, contralaterally to the stimulated side, in the post-central gyrus, in the posterior parietal cortex, in the mesial pre-frontal region and, bilaterally, in the supratemporal region at the level of the Sylvian fissure. The latter region, corresponding presumably to SII, showed a rough but clearcut topographical organization, with the median nerve areas located more posteriorly. In addition, weaker activations were observed in some subjects in the ipsilateral mesial prefrontal region and in the ipsilateral posterior parietal cortex. Information contained in the present study represent an interesting database for future investigations on the effects of sensorimotor learning in normal individuals on plastic reorganization following a lesion of the primary sensorimotor centers, i.e. in stroke patients, on the topography and balance between upper and lower limb representations in primary and secondary somatosensory cortices.

Adult↗
PubMed2000

Integration of high resolution EEG and functional magnetic resonance in the study of human movement-related potentials.

Cortical sources of human movement-related potentials (i.e. unilateral finger extension) were modeled using functional magnetic resonance imaging (fMR) data as a constraint of a linear inverse source estimation from highly sampled (128 channels) EEG data. Remarkably, this estimation was performed within realistic subject's MR-constructed head models by boundary element techniques. An appropriate figure of merit served to set the optimal amount of fMR constraints. With respect to standard linear inverse source estimates, fMR-constrained ones presented increased spatial detail and provided a more reliable timing of activation in bilateral sensorimotor cortical regions of interest.

Adult↗
PubMed1999

The use of an inhomogeneous applied field improves the spatial sensitivity profile of an in vivo SQUID susceptometer.

We present a SQUID susceptometer with a non-homogeneous magnetizing field which is null at the sensing coil and increases towards the patient position with a constant gradient plus a cubic term at large distances. Compared with the magnetizing fields of similar instruments described in the literature, our gradient field enhances the signal due to internal organs with respect to the signal due to superficial tissue. Preliminary measurements have been performed on phantoms of known magnetic susceptibility. The advantage of using a non-homogeneous field compared with a uniform field has been investigated in the case of a double-layer phantom.

Electron Spin Resonance Spectroscopy↗
PubMed1998

Hand motor cortical area reorganization in stroke: a study with fMRI, MEG and TCS maps.

The anatomical and functional correlates of the hand sensorimotor areas was investigated in a stroke patient with a malacic lesion in the left fronto-parieto-temporal cortex. The patient presented hemiplegia and motor aphasia 12 months earlier, followed by an excellent motor recovery. Transcranial magnetic stimulation mapping, functional magnetic resonance and magnetoencephalography were used as methods of functional imaging and all yielded consistent results. In particular, an asymmetrical enlargement and posterior shift of the sensorimotor areas localized in the affected hemisphere were found with all three techniques. Aspects related to brain 'plasticity' for functional recovery are discussed.

Cerebrovascular Disorders↗
PubMed1996

A SQUID based AC susceptometer for the investigation of large samples.

We developed a SQUID based susceptometer with a large available magnetized volume for the investigation of large objects. The magnetizing field is generated by a pair of Helmoltz coils. To achieve a high signal-to-noise ratio, the susceptometer is operated in a lock-in mode with an AC magnetizing field. A negative feedback control allows the rejection of the applied field with a relative residual of 1 x 10(-7). The apparatus was tested with substances of known magnetic susceptibility. The overall sensitivity, stated in terms of the magnetic moment, is better than 7 x 10(-11) A m2 for small samples.

Humans↗
PubMed1995

Detection and counting of specific cell populations by means of magnetic markers linked to monoclonal antibodies.

We report on experiments aimed at the assessment of a new method for cell marking. This method combines superparamagnetic particles, commonly used for cell separation, linked to monoclonal antibodies, and biomagnetic instrumentation featuring an extremely high magnetic field sensitivity. The final goal of the method is to locate and estimate specific cell populations in the human body. In this experiment, quantitative features of the method are evaluated in vitro with lymphocytes and carcinoma cells. Comparison between estimation and direct counting of cells is quite satisfactory and motivates further development of the technique.

Antibodies, Monoclonal↗
PubMed1993

[The use of magnetic tracers in hemodynamics. A proposed model study].

Velocity of blood flow is critical in specific clinical situations. Available non invasive blood velocimeters gives only qualitative informations; quantitative estimates can be obtained invasively. We investigated the possibility of estimating the velocity of fluids using magnetic tracer. A model for the laminar blood flow inside a vessel was developed. A biomagnetometer was used to measure the fluid tracer velocity. The experimental setup was designed to mimic blood flow. A PVC tube simulated the vessel. The tube was connected to a bottle of normal saline. The tracer injection took place 25 cm distal to the saline bottle. The system was calibrated to a constant flow velocity of about 1 cm/s. A paramagnetic fluid (Magnevist, Schering, Berlin) was adopted as a tracer. In each session an amount of 2 cm3 was injected into the tube within 5 seconds. The recording equipment consisted of a second order gradiometer (baseline 7 cm, pick-up coil diameter 1.5 cm) coupled to a rfSQUID magnetometer. The recording bandwidth was dc-3 Hz, the sampling rate 32 Hz with 12 bit digitalization. The biomagnetic system was positioned immediately above the tube 55 cm away from the injection site. The total recording time for each session was 240 seconds. The injection of the tracer took place 60 seconds after the beginning of the data acquisition. Five measuring sessions in the earth magnetic field were performed at first and showed a low signal-to-noise ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Flow Velocity↗
PubMed1992

Measurement of segmental transit through the gut in man. A novel approach by the biomagnetic method.

The techniques commonly used to evaluate the transit of contents through the gut feature some limitations for being either inaccurate, invasive, inconvenient, or potentially dangerous for the subjects. Aim of this study was to establish a safe, noninvasive and accurate technique for the measurement of segmental oroanal transit time. We localized an orally ingested magnetic marker by means of a biomagnetic instrumentation that allows us to identify in a three-dimensional pattern the position of a biomagnetic source inside the body. The biomagnetic localizations were compared with the anatomical data obtained by magnetic resonance imaging investigations. The study was performed in 12 healthy subjects, and scans were taken every hour up to the arrival of the marker into the cecum; thereafter, scans were taken every 4 hr up to the elimination of the marker. In 99% of the isofield maps obtained from each field scan, the marker was localized within the bowel walls. The mean oroanal transit time was 56 +/- 5 hr, the mouth-to-cecum transit time was 13 +/- 1.7 hr, and the total colonic transit time was 43.5 +/- 5 hr (mean +/- SEM). Segmental colon transit did not show major differences among the regions considered, although most of the time was spent in the right colon. In fact, a good correlation was found between transit time through the right colon and oroanal and total colonic transit (r = 0.77, P < 0.02, r = 0.79, P < 0.02 respectively). In conclusion, this method might be a safe alternative to the techniques presently used in the clinical setting for the measurement of intestinal transit.

Administration, Oral↗
PubMed1991

Calculation of static susceptibility maps using the reciprocity theorem.

In performing measurements of magnetic susceptibility of human tissues, it is useful to calculate the field produced by a magnetisation distribution over a relatively large measurement area. This involves costly computations that can be made easier by the use of the reciprocity theorem.

Humans↗
PubMed1991

Multichannel hybrid system for neuromagnetic measurements.

This paper describes progress toward the development of a 28-multichannel system for neuromagnetic measurements. A novel 'hybrid' design consisting of 16 first-order axial gradiometers and 12 first-order planar gradiometers was chosen, which optimises the use of the available cylindrical volume of the dewar tail. This configuration maintains the symmetry of the detected pattern with respect to rotation of a biomagnetic source located under the centre of the array and features a localisation power considerably better than an array of all first-order planar gradiometers. The detecting array permits simultaneous magnetic measurements over a circular scalp region of 16 cm diameter. The magnetic sensors used are Nb/PbAuIn DC SQUIDs fabricated at the IBM. The devices incorporate resonant damping resistors shunting the inductance, resulting in smooth flux-voltage characteristics and, consequently, very low noise figures in a flux-locked loop configuration. A simple and low cost electronic system has been designed and fabricated for the DC SQUID sensors.

Equipment Design↗
PubMedDate not supplied

[Magnetic fields evoked by auditory stimuli: a normative study].

After outlining the fundamentals of biomagnetism and their possible clinical applications, the authors report the results of a normative study on auditory magnetic fields performed on 18 normally hearing subjects between the ages of 25 and 30. Having presented a thorough review of the literature, they then describe the recording technique employed, the dcSQUID biomagnetic system for signal detection, the shielded room, the characteristics of the stimulus. The auditory magnetic response is characterized by three main waves (P4Om, N100m, P200m) whose latency and amplitude values were calculated. Moreover, in order to localize dipolar activity, certain parameters, such as P and T, were taken into consideration. Localizations were made using a spherical volume conductor or with MRI, which was in any case employed in all the subjects. The waves, especially the N100m recorded contralaterally to the stimulus, showed a reduced latency and an increased amplitude when compared to those recorded ipsilaterally. Moreover, a systematic posterior shift of the N100m source into the left hemisphere with respect to the right one was detected. In conclusion, the authors emphasize the need to study electric as well as magnetic responses in order to better understand auditory cortical functions.

Acoustic Stimulation↗