Local flip angle correction for improved volume T1‐quantification in three‐dimensional dGEMRIC using the look‐locker technique

Purpose

To present an evaluation method for three‐dimensional Look‐Locker (3D‐LL) based T1 quantification, calculating correct T1 values independent of local flip angle (FA) variations. The method was evaluated both in phantoms and in vivo in a delayed Gadolinium Enhanced MRI of Cartilage (dGEMRIC) study with 33 subjects.

Materials and Methods

T1 was measured with 3D‐LL, using both local FA correction and a precalculated FA slice profile, and compared with standard constant FA correction, for all slices in phantoms and in both femur condyles in vivo. T1 measured using two‐dimensional Inversion Recovery (2D‐IR) was used as gold standard.

Results

Due to the FA being slice dependent, the standard constant FA correction results in erroneous T1 (systematic error = 109.1 ms in vivo), especially in the outer slices. With local FA correction, the calculated T1 is excellent for all slices in phantoms (<5% deviation from 2D‐IR). In vivo the performance is lower (systematic error = ?57.5 ms), probably due to imperfect inversion. With precalculated FA correction the performance is very good also in vivo (systematic error = 13.3 ms).

Conclusion

With the precalculated FA correction method, the 3D‐LL sequence is robust enough for in vivo dGEMRIC, even outside the centermost slices. J. Magn. Reson. Imaging 2009;30:834–841. © 2009 Wiley‐Liss, Inc.