Figure 4.

Controlling excitation T₂ selectivity by relaxation-matching pulse dimensions can be used to create sensitivity in the steady state of a spoiled gradient echo (SPGR) sequence (here, for 0.5 s T₁ in SPGR with 8 ms TR). The difference in excitation profiles for two different pulses highlights a specific range of T₂ (a, top). If the pulses are alternated to allow interleaved image encodes, the steady-state T₂ profiles are altered slightly, with a some added emphasis of short-T₂ magnetization (a, middle). When the alternate pulses also tip to different angles, the difference profile creates heightened short-T₂ sensitivity and ‘inverted’ longer-T₂ signal (a, bottom).

For imaging, the sensitivity profiles created by subtracting images acquired at different echo times but with only one pulse rate (b, top) or with different pulse rates but at the same echo time (b, middle) are shaped differently from that of the proposed subtraction (b, bottom).