Towards molecular imaging by means of MRI

Towards molecular imaging by means of MRI

Norek, M.

Sheldon, R.A. (promotor)
Peters, J.A. (promotor)

Applied Sciences

2008-05-13

The work presented in the thesis is focused on the design of highly efficient contrast agents for molecular imaging by means of MRI based on the detailed physical characterization of the given material. Specifically, attention is paid on the development of contrast agents for magnetic fields higher than 1 Tesla. In Chapter 2 the transversal relaxivity r2 of aqueous suspensions of lanthanide oxide nanoparticles is investigated. These nanoparticles are characterized by a very efficient T2 shortening of water protons, which increases with the magnetic field, B, and the square of the effective magnetic moment of the lanthanide of interest. A significant difference between r2* and r2, as determined by the classical CPMG pulse sequence, was explained by the presence of xanthan gum, which forms a thick layer on the particles surface and was used as an emulsifier to prevent particles agglomeration in magnetic field. A semi-empirical model was developed to rationalize the relaxation behavior in these systems. In Chapter 3, the dysprosium oxide nanoparticles are further investigated. The attention is focused to the effect of the size of the particles and the strength of external magnetic field, B, on the r2 relaxivity. The optimal particle size for each magnetic field is determined. The relaxivity enhancement is found to be mainly affected by the diffusion of water nearby the particles surface and the strength of the local field inhomogeneities caused by the single magnetic perturber. In Chapter 4, magnetization measurements of the samples obtained by lyophylization of a colloidal solution of Dy2O3 nanoparticles (rp: 1 and 50 nm) in water and dextran, and at temperatures varying between 1.4 K and 298 K, is presented. Two components were distinguished in the magnetization curves: one associated with the simple paramagnetic behavior of the core dysprosium ions, and another, ascribed to the canting Dy3+ at the particles surface. The nanosize effects of the Dy2O3 material on M (B) curves are discussed. In Chapter 5, a detailed analysis of transversal relaxation of an aqueous suspension of the mesoporous material Ln-AV-9 is given. The relaxivity, as measured by the CPMG method, is always much smaller than the corresponding value of r2* (up to 20 times in the case of Dy-AV-9), because of the big size of the magnetic entities (5 to 20 microns). A simple model is developed to describe the system, taking into account the residual diffusion effects in the static dephasing regime (SDR). In Chapter 6, the longitudinal water relaxivity r1 is investigated in the presence of Gd3+ loaded nanozeolites NaY. The main interest is the influence of the pore size and the Si/Al ratio on r1. With respect to the former parameter, the mesoporous material Al-TUD1, loaded with Gd3+, is included in the study.

mri
molecular imaging
contrast agents
the transversal relaxivity r2
the longitudinal water relaxivity r1
lanthanide oxide nanoparticles
ln-av-9 mesoporous material
gd(iii)-nay nanozeolite

http://resolver.tudelft.nl/uuid:8db390c3-ccc9-4b79-9533-c493f8e00c26

Institutional Repository

doctoral thesis

(c) 2008 M. Norek