Local flip angle correction for improved volume T1-quantification in three-dimensional dGEMRIC using the Look-Locker technique.

ABSTRACT

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.