@article {306, title = {NMR spectroscopy in inhomogeneous B-0 and B-1 fields with non-linear correlation}, journal = {Journal of Magnetic Resonance}, volume = {175}, year = {2005}, note = {J Magn Reson939CPTimes Cited:8Cited References Count:38}, month = {Jul}, pages = {1-10}, abstract = {

Resolved NMR spectra from samples in inhomogeneous B-0 and B-1 fields can be obtained with the so-called \"ex situ\" methodology, employing a train of composite or adiabatic z-rotation RF pulses to periodically refocus the inhomogeneous broadening during the detection of the time-domain signal. Earlier schemes relied on a linear correlation between the inhomogeneous B0 and B, fields. Here the pulse length, bandwidth, and amplitude of the adiabatic pulses of the hyperbolic secant type are adjusted to improve the refocusing for a setup with non-linear correlation. The field correlation is measured using a two-dimensional nutation experiment augmented with a third dimension with varying RF carrier frequency accounting for off-resonance effects. The pulse optimization is performed with a computer algorithm using the experimentally determined field correlation and a standard adiabatic z-rotation pulse as a starting point for the iterative optimization procedure. The shape of the z-rotation RF pulse is manipulated to provide refocusing for the conditions given by the sample-, magnet-, and RF-coil geometry. (c) 2005 Elsevier Inc. All rights reserved.

}, keywords = {spectra}, isbn = {1090-7807}, doi = {Doi 10.1016/J.Jmr.2005.03.006}, url = {://WOS:000230050200001}, author = {Topgaard, D. and Sakellariou, D. and Pines, A.} } @article {323, title = {Self-diffusion measurements with chemical shift resolution in inhomogeneous magnetic fields}, journal = {Journal of Magnetic Resonance}, volume = {168}, year = {2004}, note = {J Magn Reson814XETimes Cited:5Cited References Count:27}, month = {May}, pages = {31-35}, abstract = {

A methodology for chemical shift resolved molecular self-diffusion measurements in time-independent static and radiofrequency field gradients is demonstrated. Diffusion encoding is provided by a stimulated echo Sequence with additional z-storage that allows for a change of diffusion time Without affecting the relaxation weighting. The signal is acquired stroboscopically between the pulses of a train of adiabatic double passages that induces a z-rotation Counteracting the phase spread resulting from precession in the inhomogeneous static field. as demonstrated in recent approaches to the goal of high-resolution \"ex situ\" NMR. Simulations of the pulse sequence show that the acquired signal results from the desired coherence pathway. Successful demonstrations of the experiment were performed on a Mixture of water and isopropanol. Published by Elsevier Inc.

}, keywords = {excitation}, isbn = {1090-7807}, doi = {Doi 10.1016/J.Jmr.2004.01.018}, url = {://WOS:000221006600004}, author = {Topgaard, D. and Pines, A.} } @article {324, title = {"Shim pulses" for NMR spectroscopy and imaging}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {101}, year = {2004}, note = {P Natl Acad Sci USA882PTTimes Cited:38Cited References Count:16}, month = {Dec 21}, pages = {17576-17581}, abstract = {

A way to use adiabatic radiofrequency pulses and modulated magnetic-field gradient pulses, together constituting a \"shim pulse,\" for NMR spectroscopy and imaging is demonstrated. These pulses capitalize on phase shifts derived from probe gradient coils to compensate for nonlinear intrinsic main magnetic field homogeneity for spectroscopy, as well as for deviations from linear gradients for imaging. This approach opens up the possibility of exploiting cheaper, less-than-perfect magnets and gradient coils for NMR applications.

}, keywords = {acquisition}, isbn = {0027-8424}, doi = {Doi 10.1073/Pnas.0408296102}, url = {://WOS:000225951500004}, author = {Topgaard, D. and Martin, R. W. and Sakellariou, D. and Meriles, C. A. and Pines, A.} }