Ph.D Thesis

Ph.D StudentKatz Itai
SubjectNew Approaches for Improving the Sensitivity of Magnetic
Resonance Imaging
DepartmentDepartment of Chemistry
Supervisor PROF. Aharon Blank
Full Thesis textFull thesis text - English Version


Magnetic resonance imaging (MRI) is consensually recognized as one of the most useful probing techniques, with applications in multiple scientific fields.  However, this method suffers from poor sensitivity and thus imaging resolution is limited and/or acquisition times are impractically long.  The scope of this research work was to offer ways to enhance sensitivity in MRI.  We pursued two separate. The first involved electrical detection of Electron Spin Resonance (ESR) signals in an imaging experiment conducted on a photovoltaic device based on amorphous silicon.  In semiconductors, some conduction processes are spin dependent, facilitating gating of conduction by spin manipulations available in magnetic resonance methodology.  Electrical detection offers much enhanced sensitivity as the detected quants of energy are of the order of 1eV - the voltage across the device, several orders of magnitude larger than typical energy quants in conventional induction detection magnetic resonance.  The new methodology we developed enabled us to obtain functional images of the device with micron scale resolution, compared to mm-scale resolution in previous publications.  The second project dealt with improving the sensitivity of nuclear magnetic resonance (NMR) experiments by means of dynamic Nuclear Polarization (DNP).  DNP enables to transfer polarization (spin magnetization) from strongly polarized unpaired electrons (termed polarizing agent) to weakly polarized nuclei, potentially enhancing NMR signal by 2-3 orders of magnitude.  This requires thorough mixing between polarizing agent and sample and thus poses great challenges for the use of DNP in clinical MRI.  We have developed a new class of polarizing agent that can be formed directly on the examined sample, rather than supplemented externally.  These radicals are inherently unstable, simple to obtain and can be annihilated at will, after performing the task of polarization enhancement. Our radicals demonstrated strong enhancement factors comparable to the ones achieved with conventional established polarizing agents.