Diffraction-like phenomena in a periodic magnetization distribution at 1.5 T using the distant dipolar field (DDF).
In the CRAZED experiment (COSY revamped by asymmetric Z-gradient echo detection, Warren et al.), a spatially anisotropic magnetization distribution is created by application of a magnetic field gradient (strength G, duration tau) which in turn generates a response called the distant dipolar field (DDF). The DDF is a source of intermolecular multiple-quantum coherences (iMQC) which contain information on the distance d=pi/(gammaGtau) between pairs of dipolar-coupled spins. Diffraction-like phenomena may result for periodically structured samples. In this study, we report the observation of diffraction owing to the DDF at 1.5 T using a clinical whole-body tomograph. Based on the semi-classical treatment of the problem by Robyr and Bowtell, diffraction conditions were obtained for a CRAZED-type pulse sequence that selects iMQC of order N. The predicted distinct difference in N=2 and N not equal2 coherences, i.e., a dominant continuous course as a function of tau (N=2) and prominent diffraction peaks otherwise, could be verified in CRAZED experiments in a periodically structured sample selecting coherence orders N=2 and N=3. The diffractive signal component contains information on the geometric structure of the sample. Applications of this technique may permit the detection of changes in composition and geometry of periodic structures.
Kirsch
Stefan
S
Department of Medical Physics in Radiology, German Cancer Research Center (dkfz), D-69120 Heidelberg, Germany.
Bachert
Peter
P
D003198:Computer Simulation; D004574:Electromagnetic Fields; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008956:Models, Chemical; D012031:Refractometry / Q000379:methods*; D055672:Static Electricity