Whole Body MRI T1 Mapping of Small Animals using Prospective Gating and Variable Flip Angle Imaging

Paul Kinchesh, Philip D Allen, John S Beech, Stuart Gilchrist, Ana L Gomes, Veerle Kersemans, 
Robert G Newman, Borivoj Vojnovic, Michael Brady, Ruth J Muschel, Sean C Smart

Cancer Research UK and Medical Research Council Oxford Institute for Radiation Oncology, 
Department of Oncology, University of Oxford, Oxford, United Kingdom

Summary

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 ungated 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. Data were acquired on 21st and 22nd January 2016.

Funding

This work was supported financially by Cancer Research UK (CRUK grants C5255/A12678, C2522/A10339), 
the Engineering and Physical Sciences Research Council (EPSRC grant C2522/A10339) and 
the Medical Research Council Unit Grant for the Oxford Institute for Radiation Oncology.

Files in Repository

Data are available for each of 4 mice.  
The *.nii files are NIfTI-1 formatted image files, http://nifti.nimh.nih.gov/
ImageJ is a suitable viewer, http://imagej.nih.gov/ij/

M#_CRNstab.nii:  Stability of CR-gating without reacquisition, mouse #.
M#_CRNstdev.nii: Standard deviation image of M#_CRNstab.nii
M#_CRRstab.nii:  Stability of CR-gating with reacquisition, mouse #.
M#_CRRstdev.nii: Standard deviation image of M#_CRRstab.nii
M#_Nstab.nii:    Stability without gating, mouse #.
M#_Nstdev.nii:   Standard deviation image of M#_Nstab.nii
M#_RNstab.nii:   Stability of R-gating without reacquisition, mouse #.
M#_RNstdev.nii:  Standard deviation image of M#_RNstab.nii
M#_RRstab.nii:   Stability of R-gating with reacquisition, mouse #.
M#_RRstdev.nii:  Standard deviation image of M#_RRstab.nii
M#_T1_8.nii:     T1 map generated from M#_T1_VFA8.nii and M#_T1_FA.nii
M#_T1_32.nii:    T1 map generated from M#_T1_VFA32.nii and M#_T1_FA.nii
M#_T1_FA.nii:    R-gated Flip Angle map with reacquisition for a prescribed flip of 64 degrees, mouse #.
M#_T1_VFA8.nii:  CR-gated Variable Flip Angle scan with reacquisition, 8 k-lines per R-wave, mouse #.  
M#_T1_VFA32.nii: CR-gated Variable Flip Angle scan with reacquisition, 32 k-lines per R-wave, mouse #.  

# = [1,4]
The TR of the VFA scans was 2.8 ms.
The 16 prescribed flip angles of the VFA scans were (in degrees):
1.815,2.259,2.703,3.147,3.591,4.035,4.479,4.923,5.367,5.811,6.255,6.699,7.143,7.587,8.031,8.475.