What is off-resonance?

Several students has asked about “off-resonance decoupling” in 13C NMR spectroscopy (p. 539 Carey). This technique removes all of the carbon-hydrogen coupling from a signal except those between nuclei that are directly bonded to one another.

What happens when the RF pulse is switched off?

When RF Pulse is switched off, the protons start to realign themselves back in a low energy state or equilibrium state, i.e., the main magnetic field’s direction. This is called relaxation. Relaxation occurs in two different ways, i.e., T1 and T2 relaxation.

What is RF pulse in MRI?

Every MRI patient has an RF coil placed near the part of the body being scanned. This coil is a radio transceiver that can communicate with your hydrogen atoms via radio frequency (RF) waves. The technologist uses that coil to send RF pulses at the body part under examination.

What is off resonant excitation?

Off-resonance excitation is used as a method for collisional excitation of ions in an ion cyclotron resonance (ICR) cell [1, 2].

What is gated decoupling?

The gated decoupling mode is used when the user would like to preserve the coupling information between nuclei and get the benefits of NOE (note that NOE can sometimes decrease signal intensity, like in the case of 15N and 29Si). You can also see that the signal to noise ratio on the left spectrum is higher due to NOE.

What is on resonance and off resonance?

On resonance, the measured signal has only a real component, independent of the RF field strength. Off-resonance, the out-of-phase component becomes important.

Why do we use RF pulses?

Radiofrequency pulses are used to tilt these protons away from their alignment, shifting them to a higher energy state.

What is meant by a soft RF pulse?

the case of soft (selective) pulses appears more subtle. Unlike hard pulses applied at a. common carrier frequency, soft pulses usually have different frequency offsets in the. same sequence and their nutation phase cannot be directly linked with the RF phase.

Why are RF pulses used?

RF pulses are used in the spin preparation phase of a pulse sequence, which prepare the spin system for the ensuing measurements. In many sequences, RF pulses are also applied to the volumes outside the one to be measured. This is the case when spatial presaturation techniques are used to suppress artifacts.

How do RF coils work?

When used as receivers, RF-coils are responsible for detecting the MR signal. The oscillating net magnetic flux from the excited spin system can be captured by the coil in which an induced electric current is generated. This current is then amplified, digitized, and filtered to extract frequency and phase information.

What is spin tickling?

Spin tickling experiments involve irradiation of single lines in the spectrum with a weak field, He, (~,H2/2~ < l J I) while simultaneuosly with a second field, HI, observing which of the unperturbed lines are split into doublets; transitions having an energy level in common with the tickled transition are split.

Why is decoupling important?

Impact decoupling means maintaining economic outputs while reducing the negative environmental impact of any activity. Resource decoupling is very common in agriculture. An example is increasing crop yields, which means higher crop production on the basis of the same resource, meaning land.

What happens when a pulse is off resonance?

In most elementary treatments, this transformation is used only to derive the condition for the RF pulse widths on resonance. However, a deeper understanding of the spin dynamics can be learned by considering what happens when the RF frequency of the pulse is off-resonance.

What is the duration of a RF pulse?

When an rf pulse of magnitude B1 is applied to an ensemble of spin-1/2 nuclei, each spin rotates around the rf field vector at a rate given by the nutation frequency ωnut = ω1, for a pulse of duration τp [ 32, 33 ].

How does a RF pulse generate phase coherence?

If only the spins in the lower energy (α) state are considered (precessing around a cone facing upward), there is no phase coherence in the ensemble and the random orientations of the precessing spins cancel out their motions (no measurable signal). The RF pulse synchronizes the spins (gets them in phase and generates phase coherence ).

How are off resonance studies used in NMR?

The off-resonance studies help the student firm up his or her grasp of pulsed NMR theory. Participants will learn the basics of NMR physics, how to set up and control pulse sequence parameters, how to use such sequences to measure relaxation times, and how to interpret the signal produced when the RF frequency is tuned away from resonance.