Axis-matching excitation pulses for CPMG-like sequences in inhomogeneous fields

Transmit Array Spatial Encoding (TRASE) using broadband WURST pulses for RF spatial encoding in inhomogeneous B0 fields

“…While simple swept WURST pulses are used in this proof-of-concept to demonstrate TRASE in an inhomogeneous B 0 field, there is a whole class of composite, shaped, adiabatic, and optimal control pulses that could be explored for enabling TRASE imaging of broadband samples [48]. To take one promising example, “symmetric phase-alternating” composite refocusing pulses with equal duration to a narrowband hard pulse have been shown to provide increased CPMG signal amplitudes from samples with wide bandwidths [49].…”

“…To take one promising example, “symmetric phase-alternating” composite refocusing pulses with equal duration to a narrowband hard pulse have been shown to provide increased CPMG signal amplitudes from samples with wide bandwidths [49]. These refocusing pulses work most efficiently when their imperfections are compensated by an “axis-matched” excitation pulse [48]. …”

Concurrently optimized cooperative pulses in robust quantum control: application to broadband Ramsey-type pulse sequence elements

“…We also would like to point out the mutual cancellation of pulse errors in decoupling sequences [65][66][67]. A recent example, where one pulse (an individually optimized refocusing pulse) was given and a second pulse (an excitation pulse) was then optimized to find the best match is found in [28]. (In contrast, in the following we demonstrate how pulses can be concurrently optimized to find the best match without fixing one of them, providing additional degrees of freedom.)…”

“…in NMR, ESR or optical spectroscopy with a large range of offset frequencies or highly inhomogeneous line widths, the performance of simple rectangular pulses is not satisfactory and improved performance can be achieved by using shaped or composite pulses [9,[11][12][13].Depending on the application, experimental limitations and imperfections that need to be taken into account include (a) limited pulse amplitude due to amplifier constraints, (b) limited pulse energy in order to reduce heating effects, which are of particular concern in medical applications [3], (c) scaling of the pulse amplitudes due to errors in pulse calibration or due to the spatial inhomogeneity of the control field [9, 14, 15], (d) amplitude and phase transients [16][17][18] and (e) noise on the control amplitude [19,20]. Many different approaches have been used to optimize robust pulses [9,[11][12][13][21][22][23][24][25][26][27][28][29][30]. In addition to pulse imperfections, noisy fluctuations of classical or quantum nature in the environment leads to relaxation losses.…”