To measure Modulation Transfer Function (MTF), the signal intensity of the beads in the 4 bead ramps are examined from the central slice. The ramps are made from 0.18mm beads. The bead with the strongest signal is chosen for analysis.
The line spread function (LSF) of the strongest bead is measured in both x and y directions. The Fourier transforms of the x and y LSF’s are used to produce the MTF curves.
The Nyquist frequency shows the maximum frequency before aliasing and other undesirable effects start occurring. It is calculated as 1 / (2*pixel size [cm]) = Nyquist frequency [cm-1]. For anisotropic pixel sizes, the Nyquist frequency for the MTF calculated along a particular direction is calculated from the corresponding pixel size in that direction.
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