NMR Imaging Using Second Order Quadrupole Broadened Resonances

Solid-state 27Al MRI and NMR thermometry for catalytic applications with conventional (liquids) MRI instrumentation and techniques

“…For broad resonances, rf pulses excite only certain molecular orientations. Correction terms broaden the resonance, with the extent of broadening depending of the sample size, which has been demonstrated for 63 Cu imaging of powdered Cu 2 O [22].…”

“…One of the approaches relies on an active line narrowing using sample rotation (e.g., magic angle spinning (MAS) with synchronized sample and magnetic field gradient rotation), multi-pulse line-narrowing sequences, and combination thereof [11][12][13][14][15][16]. Another general strategy to overcome substantial line broadening is based on the utilization of large static (e.g., in stray field imaging (STRAFI) [17][18][19][20]), pulsed [21,22] or oscillating [23,24] magnetic field gradients. Another possible course of action is the utilization of very short delays between the creation of the transverse magnetization and signal detection, sometimes in combination with rapidly oscillating gradients, or switching on the gradient before the excitation rf pulse and keeping it on while signal is detected, which forms the basis of most projection-reconstruction MRI studies [25,26].…”

“…This reversal is possible because the large broadening of NMR spectra in solids is inhomogeneous in nature. Next, for quadrupolar nuclei with half-integer spin including 23 Na (I = 3/2), 27 Al (I = 5/2), and 51 V (I = 7/2), central transition (1/2 M À1/2) is broadened only to second order in perturbation theory [22,42]. This implies that relatively long rf pulses and limited digitizer bandwidth should be enough to excite and detect the central transition of these nuclei.…”