Implementation and optimization by the simplex method of a 3D double echo sequence in steady-state free precession.

Under steady-state conditions, the resulting echoes have very complex T1 and T2 relationships. Many authors exploited these echoes in different sequences to produce either T1- or T2-weighted images. The simultaneous acquisition of two echoes in a single sequence provides two images of clearly different contrasts. We implemented such a sequence, in a 3D-acquisition mode, combining the advantages of thin and contiguous slices with those of a multi-echo sequence. The contrast of the images was correlated with theoretical results, derived from Bloch equations. In order to estimate the acquisition parameters (alpha, TE, TR) to obtain an optimal T1- or T2-contrast between two tissues, a computer simulation of these equations was used in conjunction with the simplex method. The results show that this sequence improves the clinical efficiency of MRI, particularly in neurological and articular disease.