Flip angle calculation for consistent contrast in spoiled gradient echo imaging.

In spoiled gradient echo sequences, the T(1)-weighting of image contrast is strongly affected by a nonlinear interaction of two sequence parameters, repetition time (TR) and flip angle (alpha). If alpha is not properly adjusted to compensate for variation in TR due to changing resolution, bandwidth, or number of slices, any optimization of contrast-to-noise may be compromised. Currently, there is no direct way to compare or reproduce the contrast properties of one sequence to another with a different TR. Here, it is demonstrated that for short TRs alpha may be calculated and automatically adjusted such that relative contrast--the shape of the signal-versus-T(1) curve--remains consistent and signal scales proportionally to radicalTR in all tissues. TR is then free to vary to accommodate a range of sequence parameters without impacting relative contrast and the T(1)-weighting of one sequence can be compared to, or reproduced in, another study with a different TR. Copyright 2005 Wiley-Liss, Inc.