24 research outputs found
One- and two-dimensional spin correlation of complex fluids and the relation to fluid composition
Application of Optimal Control to CPMG Refocusing Pulse Design
We apply optimal control theory (OCT) to the design of refocusing pulses
suitable for the CPMG sequence that are robust over a wide range of B0 and B1
offsets. We also introduce a model, based on recent progress in the analysis of
unitary dynamics in the field of quantum information processing (QIP), that
describes the multiple refocusing dynamics of the CPMG sequence as a dephasing
Pauli channel. This model provides a compact characterization of the
consequences and severity of residual pulse errors. We illustrate the methods
by considering a specific example of designing and analyzing broadband OCT
refocusing pulses of length 10 t180 that are constrained by the maximum
instantaneous pulse power. We show that with this refocusing pulse, the CPMG
sequence can refocus over 98% of magnetization for resonance offsets up to 3.2
times the maximum RF amplitude, even in the presence of +/- 10% RF
inhomogeneity.Comment: 23 pages, 10 figures; Revised and reformatted version with new title
and significant changes to Introduction and Conclusions section
Cardiovascular disease in patients with rheumatoid arthritis: results from the QUEST-RA study
Correlation of Transverse and Rotational Diffusion Coefficient:Â A Probe of Chemical Composition in Hydrocarbon Oils
Signal optimization in inhomogeneous fields: application of quantum optimal control theory troy
We demonstrate that pulses derived using Optimal Control Theory (OCT) techniques can be used to significantly enhance the robustness of the Carr-Purcell-Meiboom-Gill sequence (CPMG) [1,2] to inhomogeneities in the static BB0 field. By numerically inverting the Liouville - von Neumann equation, OCT pulses were derived that can be used directly in place of hard pulses in the CPMG sequence to greatly improve the bandwidth of refocusing. To retain the echo stability achieved by the Meiboom-Gill correction to the Carr-Purcell sequence, the refocusing pulses were designed to perform a unitary π-rotation as opposed to just a state inversion transfer. To illustrate this approach we present an example of optimized pulses that show an improved CPMG-like behavior with complete excitation and multiple refocusing over a bandwidth of +/- 2.6 γB1,max B with a pulse duration limited to 10 t180