3 Results
3.2 T1 relaxation in the primary visual cortex and VOTC (Pipeline Part 2)
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Figure 3.13: Median RPD estimation in the T1 map in occipital-temporal ROIs extracted from the Wang atlas (V1d and V1v) and VisfAtlas (V2d, V2v, V3d, V3v, IOG, ITG, MTG, LOS, hMT, pFus, OTS, mFus and CoS), ordered from posterior to
an-terior. Each participant's median RPD can be identified by their distinct colors.
3.2 T1 relaxation in the primary visual cortex and VOTC (Pipeline
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Figure 3.14: Sagittal view of the (a) UNIT1 and (b) T1 map at 0.375 mm isotropic resolution; (c) UNIT1 and (d) T1 map without background and skull at 0.375 mm isotropic resolution. The last column shows the gained spatial resolution with the up-sampling step, using T1 map as an example. The T1 map at 0.75 mm isotropic resolution and up-sampled T1 map to 0.375
mm isotropic resolution in the region identified in (d) T1 map with a red rectangle are respectively identified in (e) and (f) (sub-001, session 1).
Figure 3.15: Sagittal view of the six cortical layers equally distanced for (a) whole-brain and (b) magnified in the primary visual cortex (sub-001, session 1).
The ROIs V1d and V1v were moved from the MNI space to the native space of each participant using the deformation field returned by the bidspm segmentation workflow. These ROIs can be visual-ized in Figure 3.16 in the native space of one of the participants. The cortical layers in V1d and V1v are represented in Figure 3.17 in gradual shades of orange and red, respectively. The lighter shades of orange and red represent cortical layer I, which is closer to the CSF, becoming darker towards cortical layer VI, which is closer to the WM. T1 values were extracted from the T1 map in each of the six cortical layers that compose these ROIs.
The ROIs V1d and V1v were merged to represent the T1 laminar profile in V1 as the T1 laminar profiles of the two sub-ROIs were very similar. The T1 laminar cortical profile in V1 is depicted in
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Figure 3.18 for the two hemispheres. The plots show the mean of the T1 values for each subject in each layer, as well as the mean and standard deviation of all values in each layer. The T1 laminar profile shows for both hemispheres a decrease in T1 from the layer closest to the CSF to the layer closest to the WM, which suggests an increase in myelin density from the supragranular to the infragranular layers.
Figure 3.16: Sagittal, axial and coronal view of V1 dorsal (V1d) and V1 ventral (V1v) extracted from the Wang atlas and moved to the individual space (sub-001, session 1). V1d and V1v are represented in orange and red, respectively.
Figure 3.17: Sagittal, axial and coronal view of the cortical layers in V1d and V1v (Wang atlas) in the individual space (sub-001, session 1). The six equidistant cortical layers are represented in different shades of orange (V1d cortical layers) and red (V1v cortical layers). The lighter shades of orange and red represent cortical layer I, which is closer to the cerebrospinal fluid
(CSF), becoming darker towards cortical layer VI, which is closer to the white matter (WM).
Figure 3.18: T1 relaxation laminar profile in the primary visual cortex (V1) for left and right hemisphere, from the CSF neighbor layer to the WM neighbor layer. The mean of the T1 values in each layer is represented for each participant with
distinct shapes in blue. The means of the three participants T1 values and standard deviation are represented in red.
The same process was performed for pFus, mFus and CoS regions in the VOTC. Each corresponding binary mask and cortical layers in individual space are depicted in Figure 3.19.
The cortical layers in pFus, mFus and CoS are represented in shades of light green, dark green and dark blue, respectively. The lighter shades of each color represent cortical layer I and become darker
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as they approximate the cortical layer VI. T1 values were extracted from the T1 map in each of the six cortical layers that compose these ROIs. The T1 relaxation laminar profile was plotted for pFus, mFus and CoS and are depicted in Figure 3.20 for both hemispheres. The plots show the mean of the T1 values for each subject in each layer, as well as the mean and standard deviation of all values in each layer.
Similarly as in V1, the T1 laminar profile shows for both hemispheres a decrease in T1 from the closest layer to CSF to the closest layer to WM, which suggests an increase in myelin density from supragran-ular to infragransupragran-ular layers in pFus, mFus and CoS.
In order to perform a better comparison between ROIs, the average T1 relaxation laminar profiles of V1, pFus, mFus and CoS were plotted in Figure 3.21. The plot shows T1 relaxation values ranged between 1.6 s and 2.7 s, decreasing from cortical layers near CSF to layers near WM.
Figure 3.19: Sagittal, coronal and axial views of pFus, mFus and CoS binary masks in individual space (sub-001, session 1) in the first row. In the second row, the sagittal, coronal and axial views of the cortical layers in pFus, mFus and CoS are rep-resented in the individual space (sub-001, session 1). The lighter shades of the assigned color to each region represents
corti-cal layer I, which is closer to the CSF, becoming darker towards corticorti-cal layer VI, which is closer to the WM.
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Figure 3.20: T1 relaxation laminar profile in the posterior lateral fusiform gyrus (pFus), mid-lateral fusiform gyrus (mFus) and collateral sulcus (CoS), from the CSF neighbor layer to the WM neighbor layer. The mean of the T1 values in each layer
is represented for each participant with distinct shapes in blue. The means of the three participants T1 values and standard deviation are represented in red. The results for both hemispheres are plotted in the figure with the left hemispheres in the
first column and the right hemispheres on the second column.
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Figure 3.21: T1 relaxation laminar profile in the primary visual cortex (V1), posterior lateral fusiform gyrus (pFus), mid-lateral fusiform gyrus (mFus) and colmid-lateral sulcus (CoS), from the CSF neighbor layer to the WM neighbor layer. The
aver-age of the subjects T1 values in each layer is represented for each of the four regions of interest with distinct colours. The results for both hemispheres are plotted in the figure.
Discussion
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