Figure 6.

Simulated dictionary elements for different relaxation times. A, The simulated normalized absolute signal intensities for tissues with a T₁ of 500 ms (blue) is plotted together with the signal evolution for tissues with a T₁ of 1000 ms (red). Solid lines show simulation results for T₂ values of 50 ms, while dotted lines show results for T₂ values of 150 ms. Comparison of the red and blue graphs shows that the difference in T₁ is encoded mostly in the first half of the MRF sequence, whereas T₂ is encoded over the entire train. Comparison of the solid and dotted graphs shows that the second half helps to further encode differences in T₂. B, The same results are plotted for a T₁ of 3500 ms (blue) and 4000 ms (red), showing much smaller differences between the 2 simulated signal evolutions for the same absolute difference in relaxation times. This indicates that a certain difference in T₁ is easier detected for lower T₁ values with the current MRF train. Optimization of the MRF train might increase the encoding capability for large T₁ values. For all simulations the B₁ ⁺ fraction was set to 1