Adiabatic rf pulses: Applications toin vivo NMR

Multiparametric Saturation Transfer MR Fingerprinting Using Rosette‐Accelerated Readout

“…The T 2 preparation module consisted of a hard 90° tip-down RF pulse followed by a pair of adiabatic inversion pulses to refocus the spins. The magnetization was returned to the longitudinal axis by a 90° tip-up RF pulse 38 , 40 , 41 . A crusher gradient was applied following the T 2 preparation.…”

Robust dual‐angle T1 measurement in magnetization transfer spectroscopy by time‐optimal control

“…For comparison of the optimized RF pulses, adiabatic and block RF shapes are introduced. For the adiabatic, BIR‐4 RF pulses designed with the respective flip angles are suggested 15,22 . The parameters are sech/tanh shape with maximum amplitude , bandwidth , RF constant = 5.3, pulse duration , and time‐step length .…”

“…[18][19][20][21] Compared with conventional pulses, adiabatic RF pulses benefit from additional modulation of the RF frequency and exhibit high robustness to B þ 1 inhomogeneities, courtesy of the adiabatic passage. In particular, the class of BIR-4 excitation pulses 15,22 is of great interest, as it allows the design of arbitrary flip angles, modulated using distinct phase jumps. However, adiabatic pulses often require a longer pulse duration and come with high energy requirement.…”

“…For the adiabatic, BIR-4 RF pulses designed with the respective flip angles are suggested. 15,22 The parameters are sech/tanh shape with maximum amplitude r max ¼ 500μT, bandwidth Δω ¼ AE5kHz, RF constant β = 5.3, pulse duration T p ¼ 4ms, and time-step length τ ¼ 0:0024ms. Both BIR-4 RF pulses are depicted in Figure 1 AE5 kHz showed the desired performance with flip angle-errors of ≈ 1% at 100%B þ 1,nom ' and <12% at 40% B þ 1,nom .…”

Quantification of blood–brain barrier water exchange and permeability with multidelay diffusion‐weighted pseudo‐continuous arterial spin labeling

“…M1 gradients were placed on two sides of the first refocusing pulse (Figure 3B, blue lobes); a small deviation from a complete 180° refocusing will reduce the efficacy of motion compensation. We implemented a BIR4 (B 1 ‐insensitive rotation) nonselective refocusing pulse (Figure 3B) to replace the first 180°‐sinc pulse for robust refocusing and motion compensation in the presence of B 1 + /B 0 field inhomogeneities 47 . Amplitude‐modulated and frequency‐modulated hyperbolic tangent functions were optimized for a range of B 1 + (80%–130%) and B 0 (−500–500 Hz) with constraints of pulse duration (7.68 ms) and maximal scanner transmit voltage (550 V) 48 .…”