Mirko Gombia

Use of magnetic resonance imaging for monitoring Parma dry-cured ham processing.

Protocols were developed to apply Magnetic Resonance Imaging (MRI) to the dry-curing of Italian Parma ham. NMR relaxation analyses were performed on dry-cured hams at different processing stages to evaluate the ranges of variation of (1)H relaxation times T(1) and T(2) in representative ham muscle tissues, due to dehydration and salt uptake. MRI maps of the same ham sections were acquired, allowing T(1) and T(2) average values to be computed in selected Regions of Interest (ROI) inside muscle Semimembranosus, Semitendinosus and Biceps femoris. Chloride and moisture were determined by conventional chemical methods on the same ROIs, and MRI T(1) and T(1)/T(2) ratio were selected in a model (R(2)=0.90, P<0.05) fitting the salt content of the analysed muscle cores. Short Time Inversion Recovery (STIR) sequences were also applied to green and cured hams, but on fresh samples only, a bright image, displaying a clear separation between lean and fat tissue, was obtained.

Models of water imbibition in untreated and treated porous media validated by quantitative magnetic resonance imaging

Fluid imbibition affects almost every activity that directly or indirectly involves porous media, including oil reservoir rocks, soils, building materials, and countless others, including biological materials. In this paper, magnetic resonance imaging (MRI) has been applied to study water imbibition in a porous medium, in which capillary properties are artificially changed. As a model system, samples of Lecce stone, a material of cultural heritage interest, were analyzed before and after treatment with a protective polymer (Silirain-50 or Paraloid PB72). By using MRI, we can visualize the presence of water inside each sample and measure the height z(t) reached by the wetting front as a function of time during experiments of capillary absorption before and after treatment. The sorptivity S, defined as the initial slope of z versus t1/2, has been determined before treatment and through both treated and untreated faces after treatment. Very good fits to the data were obtained with theoretical and empirical m...

Nanopore Structure Buildup during Endodontic Cement Hydration Studied by time-Domain Nuclear Magnetic Resonance of Lower and Higher Mobility 1H

Time-domain nuclear magnetic resonance (TD-NMR) of (1)H nuclei has been used to monitor and model changes of endodontic cement pastes during hydration, from the initial reaction period up to hours and days. The (1)H in the samples are divided into two major spin groups by fitting each free induction decay, acquired after the second pulse of an inversion recovery (I-R) pulse sequence with variable interpulse delay, by the sum of a quasi-Gaussian (signal from low mobility nuclei) and an exponential (from higher mobility nuclei). The extrapolations to zero time of the signals from the two spin groups give two sets of I-R data that have been analyzed to give quasi-continuous T(1) distributions. After about a day, two clearly solid components appear. From a day to a few days, three liquid populations are identified, one of them mainly in the low-mobility spin group, which later merge, giving a single T(1) or T(2) peak. The rapid onset of the solid components, at the cost of the liquid, and the rapid changes of the relaxation time distributions of all components are clear indicators of the amount and kinetics of reaction products formation (C-S-H gel and Portlandite) and of the C-S-H micronanoporous structure buildup and evolution. At 30 days of hydration, the very short T(1) and T(2) liquid component (T(1) congruent with 200 micros and T(2) congruent with 50 micros) can be assigned to C-S-H intralayer water (thickness of the order of fractions of a nanometer) and the remaining liquid signal to interlayer water (thickness of the order of 1 nm). Comparisons are made among a widely used commercial endodontic cement paste and two more recent commercial pastes, with additive compounds to make the hydration process faster and to increase the workability. Parameters can be extracted from the data to characterize the different kinetics and nanostructure of the pore space formed up to 30 days. The parameters are in agreement with the expected effects of the additives, so the parameters can be used to optimize the formulation of new pastes, in order to improve their therapeutic performance.

Water vapor absorption in porous media polluted by calcium nitrate studied by time domain Nuclear Magnetic Resonance

Nuclear magnetic resonance relaxation analysis of liquid water (1)H nuclei in real porous media, selected for their similar composition (carbonate rocks) and different pore space architecture, polluted with calcium nitrate, is presented to study the kinetics of water condensation and salt deliquescence inside the pore space. These phenomena are responsible for deterioration of porous materials when exposed to environmental injury by pollution in a humid atmosphere. The theory is well described for simple pore geometries, but it is not yet well understood in real porous media with wide distributions of pore sizes and connections. The experiment is performed by following in time the formation of liquid water inside the pore space by T(1) and T(2) relaxation time distributions. The distributions allow one to see the effects of both the salt concentration and the pore space structure on the amount of water vapor condensed and its kinetics. It is shown that, for a given lithotype, even with different amounts of pollutant, the rate-average relaxation time T(1ra) tends to increase monotonically with NMR signal, proportional to the amount of liquid water. T(1ra) is often inversely associated with surface-to-volume ratio. This suggests a trend toward the filling of larger pores as amounts of liquid water increase, but it does not indicate a strict sequential filling of pores in order of size and starting with the smallest; in fact, relaxation time distributions show clearly that this is not the case. Increased amounts of salt lead to both markedly increased rates and markedly increased amounts of water absorption. NMR measurements of amounts of water, together with relaxation time distributions, give the possibility of information on the effect of pollution in porous materials exposed to humid atmospheres but sheltered from liquid water, even before the absorption of large amounts of moisture and subsequent damage. These phenomena are of importance also in other fields, such as the exploitation of geothermal energy.

Solid-liquid nuclear magnetic resonance relaxation and signal amplitude relationships with ranking of seasoned softwoods and hardwoods

In H1 NMR (nuclear magnetic resonance) relaxation measurements for a set of eight hardwood and softwood samples, each free induction decay (FID) is fitted by the sum of a “solid” signal of the form Aexp[−c(t∕TS)2][1−g(t∕TS)2+h(t∕TS)4] plus a “liquid” signal Bexp(−t∕T2-FID). Distributions of longitudinal (T1) relaxation times were computed separately for the solid and liquid components, giving also the solid/liquid H1 ratio α. From measurements on the samples dried, seasoned, and hydrated, the moisture content (liquid/solid weight ratio) was found to be approximately 0.50∕α. For each of the “seasoned” samples (10%–13% moisture content) a single T1 peak was found for the solid and two for the liquid, with the longer liquid T1 close to that of the solid, but with some differences exceeding perceived experimental uncertainties. None of the solid or liquid-long T1’s is much less than 20ms, even though liquid-short times go as low as 0.35ms, appearing to negate simple solid-to-liquid exchange on a millisecond t...

PERFIDI filters to suppress and/or quantify relaxation time components in multi-component systems: An example for fat–water systems

Parametrically Enabled Relaxation FIlters with Double and multiple Inversion (PERFIDI) is an experimental NMR/MRI technique devised to analyze samples/voxels characterized by multi-exponential longitudinal relaxation. It is based on a linear combination of NMR sequences with suitable preambles composed of inversion pulses. Given any standard NMR/MRI sequence, it permits one to modify it in a way which will attenuate, in a predictable manner and before data acquisition, signals arising from components with different r rates (r=1/T1). Consequently, it is possible to define relatively simple protocols to suppress and/or to quantify signals of different components. This article describes a simple way to construct low-pass, high-pass and band-pass PERFIDI filters. Experimental data are presented in which the method has been used to separate fat and water proton signals. We also present a novel protocol for very fast determination of the ratio between the fat signal and the total signal which avoids any time-consuming magnetization recovery multi-array data acquisition. The method has been validated also for MRI, producing well T1-contrasted images.

Inhomogeneity of rat vertebrae trabecular architecture by high-field 3D μ-magnetic resonance imaging and variable threshold image segmentation

To analyze the 3D microarchitecture of rat lumbar vertebrae by micro‐magnetic resonance imaging (μ‐MRI).

Improved pore space structure characterization by fusion of relaxation tomography maps

Quantitative Relaxation Tomography in porous media furnishes maps of internal sections where each pixel represents T1 or T2 of water 1H in the corresponding voxel, so that quantitative information on the pore space structure can be obtained. The porosity can be determined at different length scales by correcting pixel by pixel the signal intensity for T2 decay. Moreover, on the basis of the distribution of T1, the microporosity fraction can be computed, as well as several voxel-average porosities. Since T1 and T2 encode different pieces of information, fusion image techniques can improve the characterization of the pore space, showing simultaneously, on the same image, maps of the two parameters. Examples are given of application to a water-saturated travertine core and to a pig femur. Different kinds of look-up tables were tried by varying two of the three dimensions of the HSV color space in such a way as to optimize both the T1 and T2 contrasts simultaneously.