Improved Contrast in Ultra-Low-Field MRI with Time-Dependent Bipolar Prepolarizing Fields: Theory and NMR Demonstrations
| Autor: | Lutz Trahms, Jens Voigt, Risto J. Ilmoniemi, Hans J. Scheer, Martin Burghoff, Jaakko O. Nieminen, Stefan Hartwig |
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| Rok vydání: | 2013 |
| Předmět: |
Physics
medicine.diagnostic_test Ultra low field Physics::Medical Physics Spin–lattice relaxation Magnetic resonance imaging Polarization (waves) 01 natural sciences 030218 nuclear medicine & medical imaging Magnetic field 03 medical and health sciences 0302 clinical medicine Nuclear magnetic resonance Signal strength Control and Systems Engineering 0103 physical sciences Time course medicine 010306 general physics Dispersion (chemistry) Instrumentation |
| Zdroj: | Metrology and Measurement Systems; Vol 20 |
| ISSN: | 0860-8229 |
| Popis: | The spin-lattice (T1) relaxation rates of materials depend on the strength of the external magnetic field in which the relaxation occurs. This T1 dispersion has been suggested to offer a means to discriminate between healthy and cancerous tissue by performing magnetic resonance imaging (MRI) at low magnetic fields. In prepolarized ultra-low-field (ULF) MRI, spin precession is detected in fields of the order of 10-100 μT. To increase the signal strength, the sample is first magnetized with a relatively strong polarizing field. Typically, the polarizing field is kept constant during the polarization period. However, in ULF MRI, the polarizing-field strength can be easily varied to produce a desired time course. This paper describes how a novel variation of the polarizing-field strength and duration can optimize the contrast between two types of tissue having different T1 relaxation dispersions. In addition, NMR experiments showing that the principle works in practice are presented. The described procedure may become a key component for a promising new approach of MRI at ultra-low fields |
| Databáze: | OpenAIRE |
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