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After STE peparation with flip angle $\alpha$ and following the first imaging flip angle $\beta$, the FID and STE signal intesities are given by

$$ S_{0}^{STE} =\frac{1}{2}sin\beta sin^{2}\alpha \cdot M_{0} \tag{1} $$

and

$$ S_{0}^{FID} = sin\beta sin^{2}\alpha \cdot M_{0} \tag{2} $$

From these intensities, the peparation flip angle can be obtained acording to (16):

$$ B_{1}^{+} = \frac{\alpha}{\gamma \tau} \tag{3} $$

In case of an on-resonant STE preparation with block RF pulses, the magnitude of the driving B₁¹ field can then be obtained from the following identity:

$$ \alpha = arctan \sqrt{\frac{2S_{0}^{STE}}{S_{0}^{FID}}} \tag{4} $$

where $\gamma$ and $\tau$ denote the gyromagnetic ratio and the duration of the STE preparation pulse, respectively.