Biomedical subjects

Sune Nørhøj Jespersen

Publications and source records attributed to Sune Nørhøj Jespersen.

4 recordsLinked to original sources

PubMed2005

The influence of a cellular size distribution on NMR diffusion measurements.

In the magnetic resonance community, the usefulness of diffusion-weighted imaging is undisputed. However, the correct interpretation of multicomponent diffusion is not widely agreed upon, and progress in this direction is impeded by several confounding experimental results. It is thus of great importance to resolve possible interfering factors. The objective of the present study is to examine the influence of a cellular size distribution. Using the Kärger equations, numerical calculations show that even substantial cellular size variations induce only small changes in the estimated compartmental diffusion constants and volume fractions.

Animals↗

PubMed2005

Intravenous administration of Gd-DTPA prior to DWI does not affect the apparent diffusion constant.

MRI measurements of water diffusion and blood perfusion are increasingly used for the evaluation of organ functionality and tissue viability (e.g., in tumors). While diffusion-weighted imaging is performed without contrast agents, measurement of blood perfusion is normally performed based on the administration of paramagnetic substances such as gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA). Simultaneous measurements of these two parameters are often preferred. However, it may be argued that Gd-DTPA causes constriction of small blood vessels or alters hemodynamic parameters such as blood viscosity, thereby corrupting subsequent measurements of the apparent diffusion constant (ADC). The objective of the current study was to investigate the possible changes in the ADC in tumors following intravenous administration of 0.2 and 0.4 mmol/kg of Gd-DTPA in mice. The study was conducted with C3H mouse mammary carcinomas inoculated in the right foot of the animal subjects. The results were compared with findings in a sham group, demonstrating that Gd-DTPA had no significant impact on the ADC as measured in a 7-T animal system.

Analysis of Variance↗

PubMed2003

Transport properties of incipient gels.

We investigate the behavior of the shear viscosity eta(p) and the mass-dependent diffusion coefficient D(m,p) in the context of a simple model that, as the cross link density p is increased, undergoes a continuous transition from a fluid to a gel. The shear viscosity diverges at the gel point according to eta(p) approximately (p(c)-p)(-s) with s approximately 0.65. The diffusion constant shows a remarkable dependence on the mass of the clusters: D(m,p) approximately m(-0.69), not only at p(c) but well into the liquid phase. We also find that the Stokes-Einstein relation Deta proportional, variant k(B)T breaks down already quite far from the gel point.

Journal Article↗

PubMed2002

Cluster diffusion at the gelation point.

We use molecular dynamics simulations to study a model of the gelation transition with a dynamic bond forming procedure. After establishing evidence for three-dimensional (3D) percolation as the static universality class, we turn our attention to the dynamics of clusters at the gelation point, focusing in particular on the behavior of the diffusion constant D(s) as a function of cluster size s. We find a very clear power law behavior D(s) approximately s(-k) with a nontrivial exponent k approximately 0.69.

Journal Article↗