Inversion group (IG) fitting: A new T 1 mapping method for modified look‐locker inversion recovery (MOLLI) that allows arbitrary inversion groupings and rest periods (including no rest period)

Purpose The Modified Look‐Locker Inversion Recovery (MOLLI) technique is used for T 1 mapping in the heart. However, a drawback of this technique is that it requires lengthy rest periods in between inversion groupings to allow for complete magnetization recovery. In this work, a new MOLLI fitting algorithm (inversion group [IG] fitting) is presented that allows for arbitrary combinations of inversion groupings and rest periods (including no rest period). Theory and Methods Conventional MOLLI algorithms use a three parameter fitting model. In IG fitting, the number of parameters is two plus the number of inversion groupings. This increased number of parameters permits any inversion grouping/rest period combination. Validation was performed through simulation, phantom, and in vivo experiments. Results IG fitting provided T 1 values with less than 1% discrepancy across a range of inversion grouping/rest period combinations. By comparison, conventional three parameter fits exhibited up to 30% discrepancy for some combinations. The one drawback with IG fitting was a loss of precision—approximately 30% worse than the three parameter fits. Conclusion IG fitting permits arbitrary inversion grouping/rest period combinations (including no rest period). The cost of the algorithm is a loss of precision relative to conventional three parameter fits. Magn Reson Med 75:2332–2340, 2016. © 2015 Wiley Periodicals, Inc.