Biomedical subjects

P Fantazzini

Publications and source records attributed to P Fantazzini.

7 recordsLinked to original sources

PubMed1994

Taking, processing, and interpreting spin-echo data in porous media and tissues.

Measurements of T2 by the Carr-Purcell-Meiboom-Gill (CPMG) method without externally applied field gradients for fluids in porous media are affected by locally inhomogeneous fields from susceptibility differences. Diffusion leads to a substantial range of correlation times tau c for change of local field. Wide distributions often lead to the dependence of 1/T2 on tau (half pulse spacing) of the form 1/T2 approximately R1 + R2 tan-1 (R3 tau), while narrow distributions require the extra term (R2R3/R4)exp(-R4 tau). To determine tau-dependence, the effects of different ranges of data coverage can be minimized by using only data within the time range common to all measurements and by adding a virtual n = 0 point to each data set, where n is echo number and this point is determined by extrapolating echo amplitudes for the small tau values.

Animals↗

PubMed1994

Water-air saturation changes in restricted geometries studied by proton relaxation.

The results are reported of a systemic T1 and T2 investigation of natural (sandstones) and artificial (microporous porcelain) porous media, after each step of a water desaturation process by centrifugation in air. The analysis of the relaxation curves permitted distinguishing well the different behaviour of the natural samples as compared to the artificial ones, which can be explained by the different pore structures. In both kinds of samples the evolution of the relaxation time distributions yielded a clear picture of the changes of the water distribution in the pore framework following the displacement process, until irreducible water saturation was attained. The results are compatible with the assumption of a fixed amount of surface area contributing to the relaxation of decreasing amounts of fluid as SW is reduced.

Air↗

PubMed1994

A comparison among different inversion methods for multi-exponential NMR relaxation data.

The inversion of data to be represented by sums or continuous distributions of exponentials is done by different algorithms and compared. The published CONTIN program presents a chosen solution with an appropriate amount of detail. An in-house program EXDISTR allows operative choice of various constraints in order to show the consequences in quality of fit of allowing various features such as extra maxima or minima. Another in-house program based on the system theory approach, IDENT, treats the data as the output samples of a linear, time-invariant, autonomous dynamic system.

Algorithms↗

PubMed1994

A dedicated MRI apparatus for medical and industrial applications.

So far, one of the major obstacles to the development of special purpose MRI imaging apparatus has been the lack of a magnetic technology that could cater to the need for a light, compact and efficient magnet, capable of providing the required field uniformity at a reasonable cost. Today, recent advances in magnet design permit attaining, with the use solely of ferrite, low-cost, small-scale scanners, which can open up new areas of application of MRI, in both medical and industrial fields. A novel apparatus (ARTOSCAN) is described and some examples of applications in different fields are shown. The apparatus has been designed specifically for the imaging of extremities, but possible applications on the industrial side are numerous and not yet all identified. Such a device could be used, for example, in the agricultural, food, and oil industries, where some of the needs for nondestructive quality-control devices could be fulfilled. Some tests have been performed that demonstrate the potential of the apparatus in the study of rock properties, of the drying process of pasta and wood, and to display flaws that could be present in ceramic materials before firing.

Equipment Design↗

PubMed1990

Water 1H spin-lattice relaxation as a fingerprint of porous media.

The 1H spin-lattice relaxation curves of water in samples of natural porous media can be thought of as "fingerprints" of the porous samples. Also the whole of traditional petrophysical properties (permeability, irreducible water saturation, etc.) can be thought of as "fingerprints" of the porous samples. The characteristics of the pore space determine on one hand the relaxation curve shape, and on the other the petrophysical properties. The understanding of this correspondence can contribute to a better definition of the concept of the architecture of a porous medium. At this purpose we have obtained 1H spin-lattice relaxation curves from a collection of standard sandstone cores of known petrophysical properties and characterized by the same surface properties. The results corroborate the idea that the structure of relaxation curves contains information on the distance scale and on the architecture of the pore space, even if it is difficult to extract it without ambiguities. Different methods of curve fitting were performed and compared with the aim of getting the maximum information from the relaxation curves. Several aspects of this kind of investigation indicate the analogies between 1H response of water confined in porous media and in biological tissues.

Magnetic Resonance Spectroscopy↗

PubMed1984

The water proton spin-lattice relaxation time measurements in liver samples from hepatectomized and sham-operated rats.

We report the proton spin-lattice relaxation times (T1) of rat liver samples taken at different times after partial hepatectomy. The T1 values obtained are compared with those of liver samples from sham-operated rats and of liver samples from rats that had not undergone any surgical treatment. The results show that surgical stress significantly influences the T1 values of sham-operated rats both in their absolute value and in their dependence on the time after the operation, while it induces only a modest early increase of the water content. Possible effects of liver regeneration on 1H-T1 are almost completely concealed by the changes due to the surgical operation. These results emphasize the importance of the choice of a suitable control for T1 measurements in biological systems.

Animals↗

PubMedDate not supplied

Variations of the 1H spin-lattice relaxation in a fatty liver model as compared to normal liver.

We report the results of an in vitro study on ethionine-injected rat liver (EI) and on normal rat liver (C) performed analyzing with iterative fitting procedures the 1H spin-lattice relaxation curves detected by IR pulse sequence at 20 MHz and at 37 degrees C on fresh excised samples. Single-exponential functions did not adequately describe the experimental curves both in EI and in C group. The analysis of the curves by two-exponential hypothesis showed a small portion of the signal characterizable by a time constant of about 80 ms, common both to EI and to C samples. A slowing of about 30% in the relaxation characterized the remaining portion of the curve (90-95%) in EI as compared to C samples. The hypothesis that the 1H of the triglycerides vacuoles present in EI livers had a relaxation curve additional to the remaining signal was checked by three-exponential analysis. The results were not in contrast with the known value of the triglycerides percentage content and with the spin-lattice relaxation time of the -CH2 group 1H obtained in different experimental conditions in the same fatty liver model. The negative results of the three-exponential analysis on normal liver curves as well as the favorable controls performed to test the analysis procedure supported further this hypothesis. The remaining signal after subtraction of the triglycerides contribution showed still the small fast portion and the increase of the relaxation time of the major portion (from approximately 300 ms up to approximately 400 ms) as compared to C samples.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗