1. Cognition And Neocortical Volume After Stroke
Qi Li
Heath Pardoe
Toby Cumming
Renee Lichter
Leif Ostergaard
Amy Brodtmann
Comparison of longitudinal cortical thickness measurement methods in a stroke population
Qi Li1, Heath Pardoe1,Toby Cumming1,Renee Lichter1,Leif Ostergaard2, Amy Brodtmann1
1 Florey Neuroscience Institutes, Heidelberg, Vic, Australia
2 Aarhus University, Copenhagen, Denmark
Corresponding author: Qi Li
Background: Accurate cortical thickness measurement is important for the image-based study of many neurodegenerative diseases. Cortical thickness measurement methods can be broadly classified into two categories: surface-based and voxel-based. There is considerable variability in cortical thickness measurements using different methods, even in similar patient populations, and there is no formal agreement on what constitutes the best cortical thickness measurement method. Most researchers have examined longitudinal change in dementia populations, showing significant decline in hippocampal regions. Minimal data in stroke patients have been published. The accuracy of different methods needs to be compared in order to demonstrate the optimal method of estimating cortical thickness changes over time in a stroke population. 56
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Methods
Participants
Stroke patients presenting with first-ever acute middle cerebral artery stroke were included, studied within 2 hours and serially over 3 months. We compared the 2 hour and 3 month scans with independently acquired control images, also taken 3 months apart.
Control patients were age-matched and free from significant psychiatric and neurological disease.
Imaging
Controls: 3D T1-weighted whole brain MPRAGE images acquired on a Siemens TRIO MRI scanner: echo time TE = 2.55 ms, inversion time TI = 900 ms, repetition time TR = 1900 ms, flip angle = 9º, voxel resolution = 1 mm isotropic.
Patients: 10 patients had 3D T1-weighted whole brain FSPGR images acquired on a GE Signa Excite 3T MRI scanner: echo time TE = 3 ms, repetition time TR = 625 ms, flip angle=20, voxel resolution = mm in plane, slice thickness = 1.3 mm. Two stroke patients were scanned on a GE Genesis Signa 1.5T MRI scanner: TE = 4.2 ms, TR = 830 ms, flip angle = 20, voxel resolution = mm in plane, slice thickness = 1.5 mm. Structural scans were processed using Freesurfer V 5.0 with default processing settings.
To further identify the accuracy of the 3 methods , three regions were chosen (as Figure 1) from patients group as regions of interest (ROI),which were related with stroke lesion areas, to do regional cortical thickness comparison.
Result and Discussion:
Ten control participants (5 men, mean age=67.2 years) and twelve stroke patients (9 men, 7 left-hemispheric, mean age=65.1 years, 10 subcortical, 2 cortical) were included.
Group-wise comparison ( Table 1):
There was no significant change either in mean cortical thickness (p=0.68 using FreeSurfer, p=0.36 using Laplacian and p=0.85 using registration) or change percentage (0.2%, 0.8% and 1.3%, respectively).
In patients group, significant changes over the time were found using FreeSurfer (1.7%±±, p=0.04) and Laplacian (-2.8%± p=0.02) methods. The registration method also detected a small decrease in thickness but this was not significant (-2.8%±, p=0.33). 3.
Regional comparison:
In patients with stroke who have large lesions in the white matter, FreeSurfer could provide more accurate results of cortical thickness than the Laplacian and Registration methods (Table 2).
Image analysis:
Surface-based analysis:
The structural scans were processed using Freesurfer V 5.0 with default processing settings. Cortical thickness measures were averaged at the lobar level using the inbuilt Freesurfer cortical parcellation procedure (“aparc”).
Voxel-based analyses:
Images were segmented into white matter, grey matter and CSF using ANTs ( Cortical thickness was separately measured by Laplacian and registration methods.
Method
Group
MD in 2hrs (SD)
MD in 3 months(SD)
MD change percentage
Cohen’d (ES)
T-test
FreeSurfer
Patient
2.39(0.14)
2.43(0.12)
1.67%(2.94%)
-0.32 (-0.16)
0.04
Control
2.43(0.13)
2.44(0.09)
0.44%(2.33%)
-0.06 (-0.03)
0.68
Laplacian
4.19(0.21)
4.08(0.20)
-2.63%(3.39%)
0.56 (0.27)
0.02
3.84(0.03)
3.87(0.17)
0.78%(15.28%)
-0.44 (-0.22)
0.36
Registration
0.78(0.08)
0.76(0.05)
-2.56%(8.45%)
0.31(0.15)
0.33
0.62(0.17)
0.63(0.15)
1.61%(27.18%)
-0.05(-0.03)
0.85
Conclusion:
In terms of longitudinal analysis for both patients and controls, these three methods perform equally well.
In comparison with Laplacian and Registration methods, the surface-based method provides more accurate results for regional comparison in patients with stroke.
MD=mean thickness
Table 1: Group-wise comparison of 3 methods in patients and controls
CANVAS
Cognition And Neocortical Volume After Stroke