What is cross-relaxation in NMR?
The cross-relaxation is a process in which the energy of excitation, initially localized on one ion, is partially transferred to a neighboring ion, leaving both ions in lower energy levels, which decay rapidly to the ground state.
How do you calculate relaxation rate?
Thus, the relaxation time can be determined, by measuring the time it takes for X0 to decrease to X0/2.718. In other words, it is the time in which the relaxation process carries the system a fraction 1/e toward the equilibrium position. Thus, τ is a time interval like the half-life t1/2.
What is cross-relaxation?
Cross-relaxation (also sometimes called self-quenching) occurs between two identical molecules (ions), when a first molecule (or ion) initially in an excited state exchanges energy with a second molecule (ion) that is initially in the ground state, resulting in both molecules (ions) simultaneously changing to excited …
What is relaxation rate?
Relaxation is the process by which the spins in the sample come to equilibrium with the surroundings. At a practical level, the rate of relaxation determines how fast an experiment can be repeated, so it is important to understand how relaxation rates can be measured and the factors that influence their values.
What is T1 and T2 relaxation time?
This slower motion is closer to the Larmor frequency. Examples of T1 and T2 in biological tissues include: CSF, T1=1.9 seconds and T2=0.25 seconds; brain white matter, T1=0.5 seconds and T2=0.07 seconds (70 msec).
How is T2 relaxation time calculated?
Mathematically, T2 is defined by the equation Magxy/Magxy_max = e -t/T2, and is measured by fitting the observed loss of magnetization in the xy plane over time to an exponential . N T2 of less than 60 msec may be too short to support structural determination.
What is relaxation constant?
Electronics: RC circuit. is called the relaxation time or RC time constant of the circuit. A nonlinear oscillator circuit which generates a repeating waveform by the repetitive discharge of a capacitor through a resistance is called a relaxation oscillator.
What is T1 and T2 relaxation times?
The approach of the system to thermal equilibrium is known as relaxation and T1 and T2 are relaxation times (relaxation rates R1(2)=1/T1(2) are also used). Both relaxation times are time constants used to characterize what are assumed to be first order rate processes.
What is T2 * sequence?
T2*-weighted sequences are used to depict paramagnetic deoxyhemoglobin, methemoglobin, or hemosiderin in lesions and tissues.
What are the time constants T1 and T2?
T1 (longitudinal relaxation time) is the time constant which determines the rate at which excited protons return to equilibrium. It is a measure of the time taken for spinning protons to realign with the external magnetic field….
| TR (msec) | TE (msec) | |
|---|---|---|
| T2-Weighted (long TR and TE) | 4000 | 90 |
| Flair (very long TR and TE | 9000 | 114 |
How is stress relaxation time calculated?
The relationship between E and η is given by the equation τ = η / E where τ is known as the relaxation time for a mechanical system exposed to a controlled stress.