In order to run FASTMAP, you need to load the fastestmap parameter file (It is in systemdir/parlib) into a suitable experiment, e.g., exp3 or exp4. Execution of an acquisition should now be prevented automatically with the display of a menu that reminds you to check the settings of a few parameters, as shown below.
Among the parameters to be adjusted are:
lro - the FOV (cm), which together with sw defines the gradient strengths. The choice of lro should take into account the dimensions of most subjects/orgrans scanned in this particular setup, and should also take into account that fastmap always centers the projection at the ROI center. Examples of recommened settngs are lro=30 for volume coils and head scans, lro=20 for human head scans using surface coils, lro=6-10 for rodents and small mammals.
thk - the thickness of the bar in mm (two-dimensional slice selection), the compromise here is to make sure thk is at least three times smaller than the typical ROI being shimmed. Examples, are thk=10 for most human head scans, thk=2 for rodents. In cases of excellent signal-to-noise ratios, thk can be further reduced, which can further improve shim performance, especially in situations of poor initial shims.
tpwr - RF power setting for all pulses used in the sequence (dB). Although fastmap is fully adiabatic, it is recommened to consider the tpwr setting, especially when using a small surface coil with a strong RF amplifier, in order not to damage the RF coil. An initial setting that assumes a peak gB1 of approximately 0.5 - 1kHz should be adequate.
tof - set the tof to be on-resonance with the water frequency.
resto - should be set to on-resonance to water and thus equal to tof (resto=tof).
More adjustments can be found with the button continue setup,
which will bring you to the following menu:
For a description of these adjustments on a routine basis, click here. For a description of the recommended settings for the calibration process, see below:
tau - For calibration it is recommended to set tau=0.01, a compromise between setting a large value without setting it too large to avoid uncorrectable discontinuities in the phase projections.
nt - if sensitivity is adequate, set nt=1, if time is not an issue nt=2 might be safer (the sequence does have a +- phase cycle)
diam (mm) - For whole body systems use 40 mm, for animal systems, 6-10 mm shuld work.
epi=n - Because of issues with eddy current compensation and its quality, it is recommended to turn epi mode off, this does result in two fold longer acquisition, but this should not be a problem, since this adjustment needs to be done only once for a given configuration.
Low B1 - It is recommended to use the Low B1 setting, this requires a tpwr setting corresponding to a B1 of 0.5 - 1 kHz.
Next make sure that X0=0 Y0=0 Z0=0 (location at the isocenter), set tr=3 and tof to the water frequency.