Correcting inter‐scan motion artifacts in quantitative R 1 mapping at 7T

Yaël Balbastre (1, 2) , Ali Aghaeifar (1) , Nadège Corbin (3, 1) , Mikael Brudfors (1) , John Ashburner (1) , Martina F. Callaghan (1)

1 UCL - University College of London [London]
2 HMS - Harvard Medical School [Boston]
3 CRMSB - Centre de résonance magnétique des systèmes biologiques

Purpose:Inter-scan motion is a substantial source of error inR1estimationmethods based on multiple volumes, for example, variable flip angle (VFA), andcan be expected to increase at 7T whereB1fields are more inhomogeneous. Theestablished correction scheme does not translate to 7T since it requires a bodycoil reference. Here we introduce two alternatives that outperform the estab-lishedmethod.Sincetheycomputerelativesensitivitiestheydonotrequirebodycoil images.Theory:The proposed methods use coil-combined magnitude images to obtainthe relative coil sensitivities. The first method efficiently computes the rela-tive sensitivities via a simple ratio; the second by fitting a more sophisticatedgenerative model.Methods:R1maps were computed using the VFA approach. Multiple datasetswere acquired at 3T and 7T, with and without motion between the acquisi-tion of the VFA volumes.R1maps were constructed without correction, withthe proposed corrections, and (at 3T) with the previously established correctionscheme. The effect of the greater inhomogeneity in the transmit field at 7T wasalso explored by acquiringB+1maps at each position.Results:At 3T, the proposed methods outperform the baseline method.Inter-scan motion artifacts were also reduced at 7T. However, at 7T repro-ducibility only converged on that of the no motion condition if position-specifictransmit field effects were also incorporated.Conclusion:The proposed methods simplify inter-scan motion correction ofR1maps and are applicable at both 3T and 7T, where a body coil is typically notavailable. The open-source code for all methods is made publicly available

Mots clés: 7T; generative modeling; inter-scan motion; sensitivity; qMRI; R1

Domaines: Imagerie

Yaël Balbastre, Ali Aghaeifar, Nadège Corbin, Mikael Brudfors, John Ashburner, et al.. Correcting inter‐scan motion artifacts in quantitative R 1 mapping at 7T. Magnetic Resonance in Medicine, In press, ⟨10.1002/mrm.29216⟩. ⟨hal-03646797⟩