Article

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

University of Bologna, Engineering Faculty, Italy.
Magnetic Resonance Imaging (Impact Factor: 2.06). 02/1994; 12(2):209-12. DOI: 10.1016/0730-725X(94)91518-0
Source: PubMed

ABSTRACT 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.

0 Bookmarks
 · 
56 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Longitudinal and transverse proton relaxation from several sets of paired surgical samples of human epithelial tumors and associated histologically uninvolved tissues were studied at 37C and at 20 MHz. Broad distributions of exponential terms fit allT 1 andT 2 decays well. The tumor times showed over twice the scatter of the associated tissue times but no clear trends. Although the nontumor relaxation show little variability, the tumor curves can have either longer or shorter times and different shapes.
    MAGMA Magnetic Resonance Materials in Physics Biology and Medicine 09/1994; 2(3):405-407. · 1.86 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Summary The water retention characteristic provides the traditional data set for the derivation of a soil's pore-size distribution. However, the technique employed to achieve this requires that assumptions be made about the way pores interconnect. We explore an alternative approach based on stray field nuclear magnetic resonance (STRAFI-NMR) to probe the water-filled pores of both saturated and unsaturated soils, which does not require information relating to pore connectivity. We report the relative size distributions of water-occupied pores in saturated and unsaturated samples of two sets of glass beads of known particle size, two sands, and three soils (a silty loam, a sandy loam and a loamy sand), using measurements of the NMR T1 proton relaxation time of water. The T1 values are linearly related to pore size and consequently measured T1 distributions provide a measure of the pore-size distribution. For both the sands and the glass beads at saturation the T1 distributions are unimodal, and the samples with small particle sizes show a shift to small T1 values indicating smaller voids relative to the samples with larger particles. Different matric potentials were used to reveal how the water-occupied pore-size distribution changes during drainage. These changes are inconsistent with, and demonstrate the inadequacies of, the commonly employed parallel-capillary tube model of a soil pore space. We find that not all pores of the same size drain at the same matric potential. Further, we observe that the T1 distribution is shifted to smaller values beyond the distribution at saturation. This shift is explained by a change in the weighted average of the relaxation rates as the proportion of water in the centre of water-filled pores decreases. This is evidence for the presence of pendular structures resulting from incomplete drainage of pores. For the soils the results are similar except that at saturation the T1 distributions are bimodal or asymmetrical, indicative of inter-aggregate and intra-aggregate pore spaces. We conclude that the NMR method provides a characterization of the water-filled pore space which complements that derived from the water retention characteristic and which can provide insight into the way pore connectivity impacts on drainage.
    European Journal of Soil Science 02/2005; 56(1):135-143. · 2.65 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Understanding the relations between sensory/physical parameters and the underlying microstructural features is an essential step for designing and manufacturing novel food products. ‘Deductive’ strategies to derive such structure–property relationships operate on time-scales, which do not match with the currently required pace of research and development. In this work an ‘inductive’ approach has been outlined that deploys benchtop spectroscopic NMR and NIR measurements and multi-variate data analysis in order to generate explorative models that relate microstructure and functional parameters. Using protein-stabilised oil-in-water model emulsions, the use of a partial least squares and a multi-linear regression approach for processing and analysis of time-domain NMR data is demonstrated, and benchmarked against the deployment of NIR spectroscopy.
    Food Research International. 01/2007;