This includes tilted excitation methods [42] and [43] and a method where additional refocusing pulses are applied for recovering the magnetization after the orthogonal excitation and refocusing pulses HDAC inhibitor [44]. Future work in eddy-current correction would benefit from improvements that have been made to field-camera technology to allow continuous monitoring of the phases using a time-interleaved approach [45], which would allow monitoring of the phases during the diffusion-encoding pulse itself. It is also
possible to compute the impulse-response function by deconvolution methods [34] and [35]. The gradient impulse-response function could be computed once and applied to any gradient waveform including the diffusion-encoding gradients. In addition, concurrent field-monitoring can be achieved with fluorine-based field probes [46] and [47], which would allow simultaneous acquisition of the imaging data and measurement of field offsets for eddy-current correction. The use of a field camera is a valuable approach for characterizing the time-varying nature of eddy
currents of higher spatial orders. This study has demonstrated that there are higher levels of second- and third-order eddy-currents in the unipolar spin-echo diffusion sequence compared to the bipolar diffusion sequence. Second-order eddy-current correction results in improved image quality and reduced misalignment artifacts, particularly for the unipolar diffusion sequence. In choosing between the unipolar and bipolar sequences BMS-777607 ic50 for performing diffusion imaging in the presence of bulk motion, both the echo time and the level of higher-order eddy-current O-methylated flavonoid contributions should be considered. The unipolar sequence offers shorter echo times, while the bipolar sequence, as well as being velocity-compensated, offers the advantage of reduced higher-order eddy currents. This work is supported by UK Engineering and Physical Sciences Research Council (EPSRC) (Grant: EP/I018700/1) and supported by the National Institute for Health Research University College London Hospitals
Biomedical Research Centre. “
“Many chemical systems analysed by NMR spectroscopy spontaneously undergo dynamical changes that lead to variation in the isotropic chemical shift over time. When the frequency of these processes is similar to the frequency of the chemical shift difference, interference effects lead to changes in the intensity, linewidth and frequency of observed resonances. Collectively termed chemical exchange phenomena, these effects can be quantitatively probed with suitable experiments to provide insight into the underlying molecular processes [1] and [2]. CPMG experiments [3] and [4] are a notable example [5] that can provide kinetic and thermodynamic information describing the exchange process, and also structures of the interconverting states [29], [30], [31] and [32], even when the population of one of the interconverting conformers is as low as 1%.
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