Magnetic-field homogeneity

The magnetic field homogeneity is the next important requirement for MRI magnets. In many MRI applications, the magnetic field homogeneity of around... 

It is normal in conventional NMR to work with deuterated solvents, which serve both for optimising magnetic field homogeneity (lock, shim) and for avoiding the presence of the unwanted strong signals from protonated solvents. 

Figure 2.1 Sample depth and magnetic field homogeneity.

Figure 2.2 Undissolved material causing loss of magnetic field homogeneity.

Shimming The process of adjusting current flowing through the room temperature shim coils in order to achieve optimal magnetic field homogeneity prior to the acquisition of NMR data. The process may be performed manually or under automation. 

Facilities for a variety of multiple-resonance experiments, including broad-band, homo- or hetero-nuclear decoupling, are now generally built into the spectrometer, instead of being provided by auxiliary audio-oscillators. Oscilloscopes for optimization of magnetic-field homogeneity, precalibrated recorder-charts, and frequency counters for accurate calibration of charts and frequencies for multiple... 

Before attempting to interpret an NMR spectrum, it is wise to ascertain whether it has been obtained under suitable experimental conditions so that it is meaningful. The symmetry and sharpness of the line due to TMS (or other reference) provides an indication of magnetic field homogeneity and general spectrometer performance. Most spectrometers designed for routine studies are sufficiently automated that reasonable sets of instrument parameters are selected, but it is possible to misset parameters for acquisition or data processing and obtain distorted spectra. 

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