In figure A,
![The Actual Formula](ch15/img/formul169.png)
pulse is applied, followed by a
![The Actual Formula](ch15/img/formul170.png)
phase shift of the field vector
![The Actual Formula](ch15/img/formul173.png)
Thus the Bloch vector processes around
![The Actual Formula](ch15/img/formul174.png)
with a small angle. In figure B. an exact
![The Actual Formula](ch15/img/formul170.png)
pulse is applied, followed by a
![The Actual Formula](ch15/img/formul170.png)
phase shift of the field vector. Thus the Bloch vector is fixed
![The Actual Formula](ch15/img/formul171.png)
no change in the evolution of