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Biomedical subjects

C Del Gratta

Publications and source records attributed to C Del Gratta.

24 records · Page 2Linked to original sources
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↗