Entwicklung und Charakterisierung von mikrostrukturierten Planarspulen für Kernspinresonanz-Anwendungen

• Development and characterisation of micro structured planar coils for nuclear magnetic resonance applications

Ellersiek, Dennis; Mokwa, Wilfried (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2010)
Dissertation / PhD Thesis

Aachen, Techn. Hochsch., Diss., 2010

Abstract

Systems based on nuclear magnetic resonance have become indispensable to analyse non-metallic specimen. Magnetic resonance imaging methods can resolve a specimen structure with a micrometer-scale resolution. A major part of the current systems uses magnetic fields of several Teslas. This allows the analysis of small objects, with the disadvantage of high costs and immobility. Portable low field devices, commonly based on solenoid coils of conventional copper wire, have already been developed to analyse centimetre-sized objects. However, the demand for a portable device, which enables a millimetre-sized structure analysis, was not fulfilled, especially to image small near-surface areas of large specimen. For instance, such system should be capable to verify if birthmarks are cancerous or not. The object of this work is the realisation of such system. For this purpose, a portable system was developed consisting of the necessary radio frequency coil, gradient coils, a matching circuit for the use with conventional spectrometers and a 0.4-T permanent magnet. This device can be approached indefinitely close to the specimen. The less than 50 µm thin planar coils consist of two polyimide layers and two gold layers. The coils were optimised for this special purpose with the help of electrical parameter calculations, magnet field simulations and measurements. The systems fabricated and characterised are dedicated to analyse optimally areas of 2 mm² and 5 mm² of large specimen with a resolution down to 50 µm. Due to the small coil size, a combination of several independent systems is possible at a distance of a few centimetres, which is not the case for large coils. To test the system, a 20-hour measurement with a conventional spectrometer was performed in order to image a 5-mm² area with a resolution of 150 µm from a microfludic system. Adapted electronics and optimised analysis software should decrease the measuring time considerably. The same technology and a similar optimisation were applied to develop additional resonant circuits, which, when used on a catheter, enable its localisation with magnetic resonance imaging and allow the monitoring of minimally invasive medical procedures with magnetic resonance imaging. This has been difficult until now due to a poor contrast between the catheter and the surrounding tissue. Existing systems increase the contrast insufficiently or require complicated assembly technologies. Often their dimensions result in a considerable change of the catheter properties. Within this work, monolithically integrated biocompatible resonant circuits, which can be fully integrated in catheters of 3-French (1 mm) and 5-French (1.67 mm) diameter without decreasing their qualities, were developed. Different devices for 1.5-T and 3.0-T magnetic resonance scanners were fabricated and tested successfully in water and isotonic saline solution.

Institutions

• Chair of Materials in Electrical Engineering I and Institute of Materials in Electrical Engineering [611510]