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A Pasquarelli

Publications and source records attributed to A Pasquarelli.

At least 19 recordsLinked to original sources
PubMed2004

Calibration of a vector-MEG helmet system.

The MEG system Argos 500, recently installed at the University of Ulm, is designed for clinical application and routine use, to allow investigation of a large number of patients per day. To reach this goal, the system design meets the requirements of reliability, high field sensitivity, minimal set-up overhead before each measurement and an easy-to-handle user interface. The sensor system consists of a 163 vector-magnetometer array oriented and located in a suitable way to cover the whole head of the patient. Four additional triplets are available as references to build software gradiometers. To use this system at a high performance level, it must be properly calibrated, with these goals: to determine the actual geometry of the sensors array, which can deviate from the design specifications, and to determine the actual sensitivity of each sensor. The calibrating source consists of 31 coils placed at the corners of a head-size dodecahedron. Various details of the calibration system and process are presented here.

Calibration↗
PubMed2004

Argos 500: operation of a helmet vector-MEG.

We here describe the MEG system recently installed at the University of Ulm; it is specifically designed for clinical application and routine use, to allow investigation of a large number of patients per day. To reach this goal, the system design meets the requirements of reliability, high field sensitivity, minimal set-up time before each measurement and an easy-to-handle user interface. The sensor system consists of a 163 vector-magnetometers array oriented and located in a suitable way to cover the whole head of the patient. Four additional triplets are available as references to arrange software gradiometers. The helmet shaped sensor system is positioned to accommodate the patient in a supine position. Simultaneously to the MEG, there are 64 EEG channels. Other relevant patient information can be recorded up to a total number of 660 acquisition channels. Noise level of a single magnetometer is about 5 fT/square root of Hz. Maximum sampling rate is 4200 Hz.

Electroencephalography↗
PubMed2004

Multi-channel magnetocardiography for detecting beat morphology variations in fetal arrhythmias.

OBJECTIVE: Over the last few years, a number of studies have shown that fetal magnetocardiography (fMCG) is useful in describing fetal cardiac activity. A 55-channel MCG system in Ulm was used to record fetal cardiac activity in 12 pregnant women (with normal fetal heart activity in echocardiography) and in 5 pregnant women in whom the echocardiography showed fetal arrhythmias. METHOD: The recorded MCG data were treated in order to eliminate the maternal signal and three MCG channels with the best signals were used to emulate a standard electrocardiogram (ECG) recording so that standard MCG analysis could be performed. RESULTS: The results in assessing fetal electrophysiology, demonstrating its potential, are presented here for two fetuses with recorded supraventricular extrasystoles (SVES) and for one with ventricular extrasystoles (VES). Concerning the SVES, the analysis software OMEGA was able to separate three different beat morphologies. The VES could be detected exactly and have been confirmed by postnatal ECG. CONCLUSION: The beat morphology and the beat-to-beat variations allow new insights into the electrophysiology of the fetal heart.

Arrhythmias, Cardiac↗
PubMed1998

Cell membrane lipid molecular dynamics in a solenoid versus a magnetically shielded room.

The generalized polarization function of the fluorescent probe 2-dimethylamino-6-lauroylnaphthalene has been used to evaluate the lipid dynamics in Friend erythroleukemia cell membrane. The values of this function varied during the culture growth cycle, showing decreased lipid dynamics 24-48 h from the cell seeding. When the cycle occurred in a solenoid producing a magnetic field of 70 microT at 50 Hz in addition to the 45 microT DC of the earth (short-term 4-day exposure), the membrane lipid dynamics during this same time-period decreased by about 10% (P < .04). After long-term (184 days) or extremely long-term (395 days) exposure of the cells to the magnetic field, little additional variation in the membrane lipid dynamics was observed, suggesting an adaptation phenomenon. A variation of membrane lipid dynamics was also observed due to in vitro cell differentiation (P < .02). Nevertheless, the exposure of both undifferentiating and differentiating cells to a highly attenuated magnetic field in a magnetically shielded room (20 nT DC plus 2.5 pT AC) did not induce any modification of membrane lipid dynamics.

Animals↗
PubMed1997

Cell-cycle kinetics of Friend erythroleukemia cells in a magnetically shielded room and in a low-frequency/low-intensity magnetic field.

This work was undertaken to compare the behavior of Friend erythroleukemia cells in a solenoid, where the magnetic field was 70 microT at 50 Hz (plus 45 microT DC of Earth) with that of the same cells in a magnetically shielded room, where the magnetic field was attenuated to 20 nT DC and 2.5 pT AC. The control laboratory magnetic field corresponded to 45 microT DC and a stray 50 Hz field below 0.2 microT. The culture growth cycle of cells maintained inside the solenoid was slightly accelerated compared with that of cells maintained outside the solenoid (P < .05). This stimulation probably depended on sensitivity of cell cycle to a magnetic field, because, inside the solenoid, the percentage of G1 cells slightly increased during the culture growth cycle, whereas that of S cells slightly decreased. Acceleration of growth was detected soon after exposure of the cultures to the solenoid field, and growth did not change further if the action of this field continued for a long time, accounting for adaptation. The solenoid field also caused a small increase of cell survival without influencing cell volume. By contrast, the culture growth cycle of cells maintained inside the magnetically shielded room was slightly decelerated compared with that of cells maintained outside the room (P < .05). The essential absence of any field inside the magnetically shielded room also caused a small increase of cell volume, whereas, during the culture growth cycle, the percentage of G1 cells decreased, and that of S cells increased. The majority of these events did not change in cells induced to differentiate hemoglobin through dimethylsulfoxide.

Animals↗
PubMed1997

The study of steady magnetic fields associated with primary and secondary ST shift in ischaemic rabbit hearts.

The study of injury potentials associated with DC currents that generate the primary or secondary ST shifts during cardiac ischaemia is possible only through the invasive technique of the DC electrogram. Clinical surface ECG recordings are AC coupled and cannot be used. This paper reports the use of non-invasive and unshielded magnetocardiographic measurements to evaluate the DC injury currents associated with ST shifts during coronary artery occlusions in the isolated rabbit heart. The effect on the magnetic ST shift is studied under different ischaemic conditions including regional ischaemia, global ischaemia, global ischaemia following long periods of regional ischaemia, regional ischaemia after repeated episodes of reversible global ischaemia, and bilateral regional ischaemia. Recording of DC magnetic fields allows the characterization of primary and secondary ST displacement for each induced ischaemic condition. Our measurements show that the ST shift starts earlier when inducing ischaemia in hearts previously subjected to ischaemic episodes than in hearts where the ischaemia was produced for the first time.

Animals↗
PubMed1996

Topography and sources of electromagnetic cerebral responses to electrical and air-puff stimulation of the hand.

SEPs and SEFs after air-puff stimulation of index and little fingers have been studied and compared to the responses following electrical stimulation of the same digits and of the median nerve at the wrist in 5 subjects. The differences in morphology of the evoked signals are described and the generator characteristics are analysed for SEFs by means of a moving dipole model inside a homogeneous sphere. In our measurements the magnetic fields following electrical finger stimulation show a 30 msec component, which was absent following air-puff stimulation. This could not be seen in the electric field activity. The generators of the first component of SEFs after air-puff finger stimulation proved to be deeper (8 mm on average across all subjects and for both fingers) than in the case of electrically evoked SEFs. A similar behaviour was also observed for the second component of SEFs for the 2 stimulus modalities.

Adult↗
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↗
PubMed1994

Short-term brain 'plasticity' in humans: transient finger representation changes in sensory cortex somatotopy following ischemic anesthesia.

Transient rearrangements of finger representation in primary somatosensory cortex induced by an anesthetic block of the sensory information from adjacent fingers have been shown invasively in animals. Such a phenomenon has been now replicated in seven healthy human volunteers. Somatosensory Evoked Fields (SEFs) have been recorded during separate electrical stimulation of the 1st, 3rd, or 5th finger. Recordings were obtained in control conditions (stage A), following complete ischemic anesthesia of the 4 non-stimulated fingers (stage B), and after regaining sensation (stage C). SEFs were recorded using a 28-channel DC-SQUID magnetometer; a single position of the sensor was enough to identify the source of N20m, P30m and following components using the Equivalent Current Dipole (ECD) model. The amount of afferent input during stages A through C was monitored with surface electrodes placed on the nerve at wrist and elbow. No variation of the nerve compound potential was observed during stages A through C. In stage A, the localizing algorithm was able to discriminate the individual finger representation in accordance with the somatotopic organisation of the sensory homunculus. It was observed that the ECDs responsible for the cortical responses from the unanesthetized finger were significantly changing following a relatively brief period of sensory deprivation from the adjacent fingers. Such changes of the ECDs with respect to the control conditions were characterized by an increase in strength and deepening for the middle finger, and by a shift on the coronal plane for the thumb and the little finger (medial for the former, lateral for the latter). Such changes became progressively evident in stage B, but were persisting in stage C.

Action Potentials↗
PubMed1994

Analysis of interhemispheric asymmetries of somatosensory evoked magnetic fields to right and left median nerve stimulation.

This paper represents the first neuromagnetic systematic investigation of the asymmetries between the sources activated in the right and left hemispheres after electric median nerve stimulation. We focused our attention on the location and strength of the equivalent sources activated in the primary somatosensory cortex contralateral to the stimulated nerve in the 50 msec post-stimulus epoch. The spatial coordinates of the equivalent sources did not differ statistically significantly in the two hemispheres. Minor individual asymmetries are shown to be related to the interhemispheric differences in the position of the central sulcus as revealed by MRI investigation. The equivalent sources were significantly stronger in the left hemisphere. When comparing the location of the generators across individuals, we show that interhemispheric differences fluctuate less than absolute values. A quantitative evaluation of these findings is also given. Based on these results, a normative data set has been established, to be used as a baseline in following up changes of interhemispheric asymmetries due to hemispheric lesions and subsequent cortical reorganization.

Adult↗
PubMed1994

Magnetocardiography and exercise testing.

Twenty healthy male subjects (age range, 15-25 years; median, 21 years) underwent magnetocardiography during physical exercise. Significant ST-segment displacements of the magnetic signal were found during exercise at a heart rate of 120 beats/min compared to the magnetic signal at rest (P < .001). Since no significant ST-segment changes were found in the electrocardiogram recorded simultaneously with the magnetocardiogram, it is concluded that the magnetocardiogram shows junctional ST-T segment changes earlier than the electrocardiogram.

Adolescent↗
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

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↗