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  • methods  (2)
  • 1
    Keywords: brain ; IMAGES ; imaging ; SYSTEM ; TISSUE ; CONTRAST ; MR ; MRI ; SEQUENCE ; SEQUENCES ; SIGNAL ; FIELD ; WATER ; magnetic resonance imaging ; NMR ; PARAMETERS ; MR imaging ; HEALTHY-VOLUNTEERS ; methods ; technique ; correlation ; Sensitivity and Specificity ; LIQUID ; PHANTOMS ; DISTANCES ; Image Processing,Computer-Assisted ; Protons ; Quantum Theory
    Abstract: Dipole-dipole interactions in 1H NMR of liquids permit a new tissue contrast in MR imaging (MRI). For this purpose, the CRAZED (COSY Revamped by Asymmetric Z-gradient Echo Detection) sequence which simply consists of two radiofrequency pulses of delay tau and a magnetic field gradient pulse of strength G, is applied to create intermolecular multiple-quantum coherences of dipolar-coupled ensembles of water protons with spatial distance d = pi/(gammaGtau). As a consequence, the measured signal originates from "sources" that have a tunable dimension. CRAZED was first applied to MR imaging at 1.5 T by Zhong et al. To study the contrast properties and influence of sequence parameters of this technique, we implemented different sequences of this type on a clinical 1.5-T whole-body tomograph. The sequences were optimized in experiments with agar gel phantoms. We obtained images with dipolar contrast from the brain of healthy volunteers. The gradient system enabled correlation distances d in the range of 0.05 mm to 1 mm
    Type of Publication: Journal article published
    PubMed ID: 16986458
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  • 2
    Keywords: Germany ; MICROSCOPY ; INFORMATION ; SYSTEMS ; DISTINCT ; SAMPLES ; SEQUENCE ; treatment ; SIGNAL ; FIELD ; SPECTROSCOPY ; COMPONENT ; RE ; SPINS ; methods ; technique ; USA ; function ; physics ; GEOMETRY ; GRADIENT ; RESONANCE ; CRAZED ; DEMAGNETIZING FIELD ; diffraction ; distant dipolar field (DDF) ; intermolecular multiple-quantum coherence ; LIQUIDS ; MULTIPLE SPIN ECHOES ; QUANTUM COHERENCE ; SOLUTION NMR
    Abstract: 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 2) 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 distanced = pi/(gamma G tau) 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 equal 2 coherences, i.e., a dominant continuous course as a function of a (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. (C) 2006 Elsevier Inc. All rights reserved
    Type of Publication: Journal article published
    PubMed ID: 17110144
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