Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • MULTIPLE SPIN ECHOES  (2)
Keywords
  • 1
    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
    Signatur Availability
    BibTip Others were also interested in ...
  • 2
    Keywords: Germany ; MODEL ; SAMPLE ; radiation ; TIME ; DOMAIN ; DYNAMICS ; SIGNAL ; FIELD ; RELAXATION ; EVOLUTION ; BETA ; SERIES ; SELECTION ; EQUATIONS ; ARTIFACTS ; BEHAVIOR ; DERIVATION ; molecular ; RE ; INCREASE ; MS ; NUCLEAR-MAGNETIC-RESONANCE ; analysis ; PHASE ; USA ; LOSSES ; VARIABLES ; COEFFICIENTS ; CIRCULATION ; INCREASES ; quantitative ; 1.5 T ; diffraction ; MULTIPLE SPIN ECHOES ; VALUES ; COMPOSITE ; COUPLINGS ; DIFFUSION MEASUREMENTS ; DISTANT DIPOLAR FIELD ; LIQUID NMR ; QUANTUM COHERENCES
    Abstract: The two-pulse COSY revamped by asymmetric Z-gradient echo detection (CRAZED) NMR experiment has the basic form 90 degrees-G delta-t(rec)-beta-nG delta-t(rec)-FID, with a phase-encoding gradient pulse G of length delta applied during the evolution time tau for transverse magnetization, readout pulse beta, rephasing gradient nG delta, and recovery time t(rec) prior to acquisition of the free-induction decay. Based on the classical treatment of the spatially modulated dipolar demagnetizing field and without invoking intermolecular multiple-quantum coherence, a new formulation of the first-order approximation for the theoretical solution of the nonlinear Bloch equations has been developed. The nth-order CRAZED signal can be expressed as a simple product of a scaling function C-n(beta,tau) and a signal amplitude function A(n)(t), where the domain t begins immediately after the beta pulse. Using a single-quantum coherence model, a generalized rf phase shift function has also been developed, which explains all known phase behavior, including nth-order echo selection by phase cycling. Details of the derivations are provided in two appendices as supplementary material. For n〉1, A(n)(t) increases from zero to a maximum value at t=t(max) before decaying and can be expressed as a series of n exponential decays with antisymmetric binomial coefficients. Fourier transform gives an antisymmetric binomial series of Lorentzians, where the composite lineshape exhibits negative wings, zero integral, and a linewidth that decreases with n. Analytical functions are presented for t(max) and A(n)(t(max)) and for estimating the maximal percent error incurred for A(n)(t(max)) when using the first-order model. The preacquisition delay Delta=delta+t(rec) results in the loss of the data points for t=0 to Delta. Conventional Fourier transformation produces time-zero truncation artifacts (reduced negative wing amplitude, nonzero integral, and reduced effective T-2 (*)), which can be avoided by time-domain fitting after right shifting the data by Delta. A doped water sample (9.93 mM NiSO4, 10 mm sample tube) was used to study the behavior of the CRAZED signal for n=1-4 with beta=90 degrees at 7 T (300 MHz H-1 frequency) as a function of Delta, with and without radiation damping. Pulse-acquire experiments were used to determine the relaxation times (T-1=61.8 ms and T*(2)=29.7 ms), and the radiation damping time constant T-rd=18.5 ms. When experimental CRAZED data sets were right shifted by Delta, excellent least-squares fits to the first-order model function were obtained for all n using a minimal set of free variables. Without radiation damping the fitted T*(2)values (29.7-30.2 ms) agreed with the reference value. With radiation damping the fitted effective T*(2) values were 16.2 ms for a 90 degrees pulse-acquire experiment and 18.8-20.2 ms for the CRAZED experiment with n=1-4 and signal amplitudes spanning a range of 10(5). (C) 2008 American Institute of Physics
    Type of Publication: Journal article published
    PubMed ID: 18681658
    Signatur Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...