Berlin 2005 – wissenschaftliches Programm
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ST: Strahlen- und Medizinphysik
ST 2: Medizinphysik: Bildgebung II
ST 2.1: Fachvortrag
Montag, 7. März 2005, 14:00–14:15, TU HL1
Intermolecular multiple quantum coherences in liquid NMR - A new probe for investigation of biological structures? — •Stefan Kirsch and Peter Bachert — Deutsches Krebsforschungszentrum (DKFZ), Abt. Medizinische Physik in der Radiologie, Heidelberg
Collective 1H dipole-dipole interactions provide a new approach for exploring microscopic structures by liquid NMR. In liquid phase dipole-dipole interactions vanish due to Brownian molecular motion. Surprisingly, anisotropies owing to strong magnetic field gradients generate residual dipole-dipole interactions. This effect was first observed in solid 3He, liquid 3He and 1990 in water. Residual dipole-dipole interactions give rise to intermolecular multiple-quantum coherences (iMQCs), which exhibit properties different from those of single-quantum coherences detected in the classical NMR experiment. iMQCs can be explained semi-classically by introduction of the "demagnetizing" field or by a quantum-mechanical density matrix treatment. An interesting property of iMQCs is, that they originate predominantly from dipole-dipole interactions of protons with mutual distance d, which depend on the strength G and the duration τ of the magnetic field gradient: d=π /(γ G τ). Theory predicts the possibility to use the dependence on distance of iMQCs to study biological structures similar to a conventional diffraction experiment. We were able to verify the diffraction-like behavior of iMQCs in experiments with periodically structured phantoms.