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Joint myocardial T1 and T2 mapping
Journal of Cardiovascular Magnetic Resonance volume 17, Article number: Q1 (2015)
Recent studies suggest that quantitative myocardial T1 mapping allows assessment of focal and diffuse fibrosis in the myocardium . Quantitative T2 mapping has also been proposed to overcome challenges associated with T2 weighted imaging . These maps are traditionally acquired with different sequences, necessitating image registration to evaluate them jointly. A sequence that can jointly estimate T1 and T2 maps has been proposed , but it requires multiple relaxation cycles, which necessitates a lengthy free-breathing acquisition. In , an alternative joint estimation sequence was proposed based on the inversion-recovery SSFP curve. In this study, we sought to develop a saturation-recovery based heart-rate independent sequence that can be acquired in a breath-hold and that allows for simultaneous estimation of quantitative T1 and T2 maps.
The sequence diagram is depicted in Figure 1. At every heartbeat, a saturation pulse is applied to eliminate the magnetization history. The longitudinal magnetization then recovers for Tsat based on the T1 value. Subsequently a T2-prep pulse  with echo length TEprep is applied to generate the additional T2 weighting, after which a single shot SSFP image is acquired. The process is repeated for 13 heartbeats with various (Tsatk, TEprepk) corresponding to heartbeat k, to sample different T1-T2 weighted images. The first heartbeat is acquired with no magnetization preparation.
The T1 and T2 maps were estimated jointly by voxel-wise least squares fitting to a 4-parameter signal model, A (1- exp(-Tsatk/T1)) exp(-TEprepk/T2) + B. Phantom imaging of 14 vials with different T1/T2 values were performed and compared to inversion-recovery and CPMG spin-echo references, respectively. Breath-held in-vivo imaging was performed on 5 healthy adult subjects, and the maps were compared to SASHA T1 maps  and to T2 maps .
Phantom imaging resulted in T1 and T2 values not significantly different than the references (P = 0.481 and 0.479 respectively). Example in-vivo T1 and T2 maps are depicted in Figure 2, comparing various techniques. The T1 and T2 values were in good agreement (1211 ± 82 ms vs. 1210 ± 92 ms for T1; 49.0 ± 5.8 ms and 47.3 ± 6.5 ms for T2).
The proposed sequence allows for the simultaneous estimation of accurate and jointly registered quantitative T1 and T2 maps with similar accuracy and precision to saturation-based T1 mapping and to T2 mapping of same duration.
Mewton : JACC. 2011
Giri : JCMR. 2009
Sinclair : JMRI. 2009
Santini : MRM. 2014
Brittain : MRM. 1995
Chow : MRM. 2013
Akçakaya : MRM. 2014
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Akçakaya, M., Weingärtner, S., Basha, T.A. et al. Joint myocardial T1 and T2 mapping. J Cardiovasc Magn Reson 17, Q1 (2015). https://doi.org/10.1186/1532-429X-17-S1-Q1
- Sequence Diagram
- Simultaneous Estimation
- Joint Estimation
- Phantom Imaging
- Longitudinal Magnetization