Because in general the Z2 coil intrincically produces a B0 (frequency) shift, this needs to be taken into account for the calibration. To start this, load into another experiment the parameter file sh2pul.par that is provided in $FASTMAP/parlib. After adjusting frequency (tof), pw, tpwr and gain to get an appreciable signal without ADC overflow, manually shim at least x1, y1 and z1(c) to optimum. Then collect a single-shot spectrum and adjust the phase and display the spectrum fully : ph f full. Of course fn (e.g. 32k), np, sw (20kHz) should be reasonably set.
NEED to have $vnmruser/fastmap dir created. Change fastmap.upload accordingly !!
NOTE:
Some systems generate a transient frequency shift with a time constant on the order of
minutes upon abrupt changes in the Z2 coil. To assess such drifts run the macro get_z2drift. The macro will array d1=60 and then 3 s thereafter and
for the first element deviate the z2 shim from the good setting and start the
acquisition automatically. The output of the ensuing peak picking is displayed on line3
and written to the file $vnmruser/fastmap/<gcoil>_z2drift. In this file is the
output of the peak picked arrayed experiment above, which is shown in the text output
window and the spectra are shown with dss at the end to visually check for temporal
drifts. Check after what time the field is stable and this will define the repetition time
needed for making changes to the Z2 coil.
The next step is to establish the field (frequency) change induced by the Z0 impurity of the Z2 shim coil. This is done by running the macro get_z2z0 in the same experiment from which get_z2drift was run (see above NOTE). This macro will increasingly and symmetrically deviate from the current (optimum) setting of the Z2 coil and automatically abort, when it finds excellent correlation and that the change in frequency with Z2 DAC is less than 5% after running 4 measurements. The output is stored in the file $vnmruser/fastmap/<gcoil>_<name of Z2 parameter>z0, which is used in the Calibration (see below).