Other Saturation-Recovery T1 Mapping techniques#

Several variations of the inversion recovery pulse sequence were developed to overcome challenges like those specified above. Amongst them, the Look-Locker technique [Look and Locker, 1970] stands out as one of the most widely used in practice. Instead of a single 90° acquisition per TR, a periodic train of small excitation pulses θ are applied after the inversion pulse, {θ180 – 𝛕 – θ – 𝛕 – θ – …}, where 𝛕 = TR/n and n is the number of sampling acquisitions. This pulse sequence samples the inversion time relaxation curve much more efficiently than conventional inversion recovery, but at a cost of lower SNR. However, because the magnetization state of each TI measurement depends on the previous series of θ excitation, it has higher sensitivity to B1-inhomogeneities and imperfect spoiling compared to inversion recovery [Stikov et al., 2015, Gai et al., 2013]. Nonetheless, Look-Locker is widely used for rapid T1 mapping applications, and variants like MOLLI (Modified Look-Locker Inversion recovery) and ShMOLLI (Shortened MOLLI) are widely used for cardiac T1 mapping [Messroghli et al., 2004, Piechnik et al., 2010].

Another inversion recovery variant that’s worth mentioning is saturation recovery, in which the inversion pulse is replaced with a saturation pulse: {θ90 – TI – θ90}. This technique was used to acquire the very first T1 map [Pykett and Mansfield, 1978]. Unlike inversion recovery, this pulse sequence does not need a long TR to recover to its initial condition; every θ90 pulse resets the longitudinal magnetization to the same initial state. However, to properly sample the recovery curve, TIs still need to reach the order of ~T1, the dynamic range of signal potential is cut in half ([0, M0]), and the short TIs (which have the fastest acquisition times) have the lowest SNRs.

References

1

Neville D Gai, Christian Stehning, Marcelo Nacif, and David A Bluemke. Modified look-locker t1 evaluation using bloch simulations: human and phantom validation. Magnetic resonance in medicine, 69(2):329–336, 2013. doi:10.1002/mrm.24251.

2

David C Look and Donald R Locker. Time saving in measurement of nmr and epr relaxation times. Review of scientific instruments, 41(2):250–251, 1970. doi:10.1063/1.1684482.

3

Daniel R Messroghli, Aleksandra Radjenovic, Sebastian Kozerke, David M Higgins, Mohan U Sivananthan, and John P Ridgway. Modified look-locker inversion recovery (molli) for high-resolution t1 mapping of the heart. Magnetic Resonance in Medicine: An Official Journal of the International Society for Magnetic Resonance in Medicine, 52(1):141–146, 2004. doi:10.1002/mrm.20110.

4

Stefan K Piechnik, Vanessa M Ferreira, Erica Dall'Armellina, Lowri E Cochlin, Andreas Greiser, Stefan Neubauer, and Matthew D Robson. Shortened modified look-locker inversion recovery (shmolli) for clinical myocardial t1-mapping at 1.5 and 3 t within a 9 heartbeat breathhold. Journal of cardiovascular magnetic resonance, 12(1):1–11, 2010. doi:10.1186/1532-429X-12-69.

5

IL Pykett and Peter Mansfield. A line scan image study of a tumorous rat leg by nmr. Physics in Medicine & Biology, 23(5):961, 1978. doi:10.1088/0031-9155/23/5/012.

6

Nikola Stikov, Mathieu Boudreau, Ives R. Levesque, Christine L. Tardif, Joëlle K. Barral, and G. Bruce Pike. On the accuracy of t1 mapping: searching for common ground. Magnetic Resonance in Medicine, 73(2):514–522, 2015. arXiv:https://onlinelibrary.wiley.com/doi/pdf/10.1002/mrm.25135, doi:10.1002/mrm.25135.