Shim gradient

Table 3.4. Shim gradients found on high-resolution spectrometers...

Shim gradient Gradient order Interacting shim gradients... 

Table 3.6. Shim gradients found on high-resolution spectrometers. Lower field instruments (<500 MHz) may utihse only 20 or so gradients (such as those in the left panel), whilst higher field spectrometers may employ in excess of 30. Shims up to third order are those most likely to need periodic optimisation as part of longterm spectrometer maintenance for which the most significant interacting shims are Usted. Those shown in square brackets interact less strongly with the listed gradient whilst those that interact with Z° (the main field) may cause momentary disruption of the lock signal when adjusted...

Shim gradient Gradient order Principle interacting shim gradients Shim gradient Gradient order... 

Cryostat Active Shield Main Magnet Coil Passive Shims Active Shims Gradient Coil RF Coil... 

Cryostat ctive Shield ain Magnet Coil assive Shims. ctive Shims. Gradient Coil RF Coil. Patient Bed... 

NMR microscopy systems are built as add-ons to NMR spectrometers. The general technology of an NMR spectrometer is not the subject of this chapter, only the parts that are of particular importance in NMR microscopy applications, such as the magnets, the shim systems, the gradient systems, the NMR microscopy probes and the gradient amplifiers, will be described in some detail. 

The whole NMR imaging sensor system usually consists of a magnet, a shim system mounted inside the room-temperature bore of the magnet, a gradient system mounted inside the shim system and the rf coil mounted inside the gradient system. In the case of a saddle coil or a birdcage resonator, open access can be realized from the bottom to the top of the entire system with the coil diameter. 

This makes the straightforward shim procedure on the lock-level impossible. As most NMR probes are nowadays equipped with -gradients, shimming is usually accomplished by gradient-shimming on the acetonitrile signal. 

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