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Keywords:

  • inline image mapping;
  • flip angle;
  • RF inhomogeneity;
  • actual flip angle imaging (AFI)

Purpose

A new approach to mapping the flip angle quickly and efficiently in 3D based on the Look-Locker technique is presented.

Methods

We modified the accelerated 3D Look-Locker T1 measurement technique to allow rapid measurement of flip angle. By removing the inversion pulses and interleaving two radio frequency pulses with different amplitude, it is possible to fit directly for the true flip angle using a reduced number of parameters. This technique, non-inverted Double Angle Look-Locker, allows quick and efficient mapping of the flip angle in 3D.

Results

non-inverted Double Angle Look-Locker is validated in vitro against the actual flip angle imaging technique for a range of flip angles and T1 values. Flip angle maps produced with non-inverted Double Angle Look-Locker can be acquired in approximately 1 min, and are accurate to within 10% of the actual flip angle imaging measurement. It is shown to accurately measure the excited slab profile of several different pulses. An application to correcting in vivo DESPOT T1 data is presented.

Conclusion

The presented technique is a rapid method for mapping flip angles across a 3D volume, capable of producing a flip angle map in approximately 1 min. Magn Reson Med 71:591–598, 2014. © 2013 Wiley Periodicals, Inc.