Qualitative and quantitative assessment of the local contrast agent aggregations using MRI
Major issues of qualitative and quantitative assessment of the contrast agent aggregations using 1H and 19F MRI are addressed in this thesis. The dynamic assessment of the migration of the cells labeled with custom-designed Iron oxide loaded Poly-(L-LActide) (iPLLA) nanoparticles as a new multimodal contrast agent into the target tissue is shown. To overcome the limitations of the "dark spot" imaging using negative contrast agents, Off-resonance Modulating Pre-Pulse (OMPP) preparation scheme for modulating the magnetization according to the local field distortions caused by susceptibility-generating objects is applied to generate the positive contrast images. Whereas localization based on contrast modulation is possible, quantification of contrast agent concentration remains difficult, because the effective agent relaxivity in tissue is affected by several factors including a nonlinear relation between concentration and relaxation constants. Moreover the accuracy is limited by the precision of the T2/T2* estimates which heavily depend on the method of fitting of the T2/T2* decay curve. The importance of proper choice of the fitting model is investigated for myocardial quantitative T2 mapping. In contrast to methods based on iron-oxide contrast agents, “hot-spot” imaging using 19F nucleus enables rather direct detection without any background signal, making 19F MRI potentially quantitative. However, quantification of local 19F concentrations is depending on the uniform spin excitation and signal reception. A method allowing for correction of transmit/receive field inhomogeneities enabling accurate 19F quantification with acquisition times suitable for use in vivo is introduced in this thesis.
Subject HeadingsKernspintomografie [GND]
Cell tracking [MeSH]
Contrast media [MeSH]
Magnetic resonance imaging [MeSH]