Fourier approximation of slice profile for SINC excitation pulse having different flip angles from 10° to 180°

This plot shows slice profiles of SINC pulses for different flip angles ranging from 10° to 180° and their fourier approximations. Slice profile is a distribution of transverse magnetization over slice thickness. At small flip angles, slice profile of an RF pulse can be approximated by directly taking the fourier transform of the RF pulse shape. Fourier transform of a SINC pulse gives the rectangular slice profile. Ideal rectangular slice profile can not be achieved because of the finite duration of a SINC pulse. It can be seen from the plot that this fourier approximation holds quite well for flip angles upto 30° and the slice profile of such a low flip angle pulse is nearly identical to fourier transform of SINC pulse shape. Nonlinearities start to emerge at flip angles higher than 30° and this approximation breaks down severely above flip angles of 90°.