Example: For shimming the zonal shims (z,z2,z3, etc.) only measurements along the
z-axis (at x=y=0) are needed. Typically, the lateral dimension (here: x,y) is chosen to be
small compared to the ROI to avoid any lateral phase term to influence the phase along the
z projection. The tau parameter defines the time by which the first echo time is offset to
encode B0 and typically is chosen between 0.005 and 0.03 s.
Two-dimensional localization using either STEAM or fully adiabatic PRESS is available
currently. The measurement is done by having the one-dimensional projections intersect at
a common point, typically the center-of mass of the defined VOI, which must currently be
determined outside this package.
Two types of experiments are implemented:
i - Measurement of the three main gradient axes, which in conjunction with linear fitting
allows to determine the 1st order shims X,Y,Z.(3 projections)
ii- Measurement of the orientations corresponding to the six side diagonals of the cube,
i.e. xy, yx, yz, zy, xz, zx, which allows to calculate all 1st and
2nd-order shims. (6 projections)