Use vector diagrams, similar to those of Fig. 4.25 on page 65, to show what happens during

Question:

Use vector diagrams, similar to those of Fig. 4.25 on page 65, to show what happens during the spin echo sequence
90°(x) - τ - 180°(y) - τ -
Also, draw up a phase evolution diagram appropriate for this sequence. In what way does the result differ from a spin echo in which the 180° pulse is about the x-axis?
Without drawing up further detailed diagrams, state what the effect of applying the refocusing pulse about the -x-axis would be.