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Comparison of the measurement methods of T1
The methods for determining the longitudinal relaxation time T1 are based on the same measuring principle:
First, the equilibrium magnetization of the sample (M0 ) is deflected at a certain angle, after which the system begins to relax. After certain waiting times (variable delays vd) the remaining magnetization (Mz ) and from it T1 certainly. In practice, two different methods are used, the inversion recovery method and the saturation recovery method.
- Tab. 1
- Compare inversion recovery and saturation recovery procedures
|Inversion recovery procedure||Saturation recovery procedure|
|more accurate measurement method||faster measurement method|
|It is possible to estimate the relaxation time during the measurement|
|Checking and possibly a correction of the set measurement parameters is possible without spending a great deal of time|
Both measurement methods have advantages and disadvantages that have to be weighed with regard to the desired result. When comparing different measurements, care should be taken to ensure that certain times are only compared with the same method in order to keep the influence of systematic errors as low as possible.
Because of the many external factors that can influence the relaxation of a substance, regardless of the measurement method used, careful sample preparation is a prerequisite for a successful measurement. For example, traces of oxygen must be removed before a measurement, since oxygen, like other paramagnetic substances, has a direct influence on the relaxation of a sample.