- Poster presentation
- Open Access
On the use of the "look-locker correction" for calculating T1 values from MOLLI
- Glenn S Slavin1
© Slavin; licensee BioMed Central Ltd. 2014
- Published: 16 January 2014
- Composite Curve
- Counterintuitive Effect
- Magnetization Recovery
- Rigorous Justification
- Single Excitation Pulse
MOLLI  uses interleaved Look-Locker (LL) blocks for cardiac T1 mapping. Data is fit to the equation A-B exp(-TI/T1*) to yield an "apparent" T1 (T1*), which is dependent on both the true T1 and imaging parameters. To estimate true T1, a "LL correction" T1est=(B/A-1)T1* [Eq. 1] has been proposed [1, 2]. Although this correction can provide reasonable estimates of true T1, we are not aware of a rigorous justification for its use. The purpose of this work was to investigate the applicability of this correction for MOLLI.
The MOLLI acquisition does not satisfy the requirements on which the LL correction is based. For a single LL block, each violation produces an error in T1est. When LL blocks are combined, however, the overestimation caused by interleaving LL blocks obtained with non-zero TI0 partially offsets the underestimation from the misapplied simplification and correction. Under certain conditions, this yields a reasonable estimate of T1, with the error being strongly dependent on the range of TI0. In practice, TI0 is typically too short to completely offset the effects of the LL correction, resulting in the observed systematic underestimation of T1.
The use of multiple LL blocks in MOLLI was intended to improve accuracy by increasing the sampling of the relaxation curve. Instead, it can be shown that this distinguishing feature of MOLLI has the unexpected effect of essentially averaging out errors introduced by the LL correction. However, T1 estimates derived from MOLLI using the LL correction cannot be consistently accurate because of the violated conditions of its use.
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.