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Hello, I need to help solids lab at our UCI site - they have a custom probe and need to orient it properly in order to ease the shimming procedure.

My question is - how to determine orientation of X and Y shims?

We have 800 MHz 63 mm Oxford magnet (+ Varian UnityInova console)

asked Apr 28 '10 at 10:29

Evgeny%20Fadeev's gravatar image

Evgeny Fadeev

updated Apr 28 '10 at 13:58

2 Answers:
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Assuming that the probe is an MAS or solenoid coil type, you can make use of the geometry of the sample. Both of these have typical sample volumes that are longer in one direction. You can use a 1-D projection imaging technique to find the coil axes.

Examine the probe and make a mark on the bottom of the probe (where it will still be visible when the probe is in the magnet) indicating the long axis of the sample coil. Fill the sample volume with water (or paraffin for protons, or something else that gives a good SNR on a single pulse). Put the probe in the magnet and establish a pulse sequence (e.g. 1pulse) which gives a good signal. Ramp the X (or Y) shim to a large value. Record the spectrum again. Note the linewidth. Now rotate the probe in small increments, taking a spectrum after each rotation. The minimum linewidth will occur when the sample is perpendicular to the X (or Y) axis. You can then mark the probe mount, by reference to the mark you made earlier on the probe.

For best accuracy, you should probably plot the linewidths vs. rotation angle. Then you can smooth and interpolate the curve. You could get a plastic protractor from the bookstore, cut out the center, and fasten it to the bottom of the magnet as a reference for the angle measurements.


answered Apr 29 '10 at 09:12

Carl%20Gregory's gravatar image

Carl Gregory

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For room temperature shims, a good starting point is always the direction in which the shim cable attaches to the shim base. The cable direction is normally along one of the X or Y axes.

For magnet internal cryoshims, the X direction is normally marked on the exterior of the magnet, or indicated in the magnet manual.


answered Sep 13 '10 at 08:46

Jerry%20Hirschinger's gravatar image

Jerry Hirschinger

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