Whole body T1 mapping of small animals using prospective gating and variable flip angle imaging

Prospective gating and automatic reacquisition of data corrupted by respiration motion were implemented in variable flip angle (VFA) and actual flip angle imaging (AFI) MRI scans to enable cardio-respiratory synchronised T1 mapping of the whole mouse. Stability tests of cardio-respiratory gating (CR-gating) and respiratory gating (R-gating) with and without reacquisition were compared with un-gated scans in 4 mice. The automatic and immediate reacquisition of data corrupted by respiration motion is observed to properly eliminate respiration motion artefact. CR-gated VFA scans with 16 flip angles and 32 k-lines per cardiac R-wave were acquired with R-gated AFI scans in a total scan time of less than 14 minutes. The VFA data were acquired with a voxel size of 0.075 mm3. T1 was calculated in the whole mouse with a robust and efficient nonlinear least squares fit of data. The standard deviation in the T1 measurement is conservatively estimated to be less than 6.2%. The T1 values measured from VFA scans with 32 k-lines per R-wave are in very good agreement with those measured from VFA scans with 8 k-lines per R-wave, even for myocardium. As such, it is demonstrated that prospective gating and reacquisition enables fast and accurate T1 mapping of small animals.