The Not-so-Mighty, but pretty Handy Inversion Recovery Experiment

• if we tip the spins 180$^{\circ}$ away from the $z$-axis so that $M_{z}$ goes from $M_{0} \rightarrow -M_{0}$, we can see that on its return to equilibrium $M_{z} \equiv M_{0}$ it will have to pass through zero.

  
  
  
  
  
  
  
  
  
  
  
  
  
  

• Set up the equations for this, see
  

  $$M_{z}(t) = -M_{0} e^{-t/T_{1}} + M_{0}(1-e^{-t/T_{1}}) = M_{0}(1-2e^{-t/T_{1}}), \;\;\;\; 0<t<T_{I}$$ (8.17)

  
  

• plan to tip the longitudinal magnetization into the transverse plane at time $T_{I}$. see that we can choose $T_{I}$ in certain way, so that we can have 0 longitudinal magnetization available to tip. This occurs if
  

  $$T_{I,null} = T_{1} \ln 2$$ (8.18)

  
  

• Gives us a very accurate way to measure $T_{1}$, and/or a way to supress the signal from certain tissues based upon their value of $T_{1}$.

• advantage of IR experiment is that it is a very robust way to generate good contrast based upon $T_{1}$ for a specific tissue. Disadvantages are that it takes time to perform the inversion recovery (which makes the experiment longer), and reduces the signal from other tissues as well.