Pulse Check - Spectracular's NMR Blog

  Adiabatic RF pulses are well known for robust, B 1 -insensitive (i.e. changing the pulse amplitude above a minimum cut-off has little impact on its performance) and offset-independent inversion . But they can also be used for B 1 -insensitive narrow-band selective excitation .  How? Any inversion pulse, adiabatic or not, always produces transverse magnetization ( M xy ) centered around the transition band of the frequency profile. Take for instance this 30-ms Hyperbolic Secant adiabatic inversion pulse (HS1), with a time-bandwidth factor (R) of 20, and its simulated frequency profile. The transverse magnetization is excited centered around the transition bands of the inversion profile, and has an excitation bandwidth of ca. 155 Hz. This bandwidth depends on the pulse duration - longer the pulse, smaller the bandwidth - and also on the pulse shape. The offset of the excitation bands depends on the inversion bandwidth, and is ~±333 Hz. More importantly, this excitation is co...

What is slice selection? Routinely used in MRI, slice-selection refers to the excitation and observation of signals from only a specific, well-defined ‘slice’ of the sample, instead of the whole sample. In MRI, this could be a ‘slice’ of the human brain: Magnetic field gradient causes the center frequency ( F c ) of each slice to vary by position. The range of frequencies ( ΔF ) contained in a slice depends on slice thickness ( ΔF ) and the strength of the gradient ( G ss ). Source: https://mriquestions.com/slice-selective-excitation.html   From an high-resolution NMR perspective, it most often refers to selectively observing different parts of the typical NMR tube, as described here in Glenn Facey’s blog .  As also described in Facey’s blog, slice-selection is achieved by applying a linear gradient simultaneously with the excitation pulse, which is usually a shaped RF pulse. A key difference between slice selection in imaging applications vs high-resolution NMR is that imagi...