The 3D T1 images obtained for the two subjects with the two scanners in the supine position are reported in Figure 1.
The 3D T1 images of Subject 2 in the supine and sitting position at 0.25 T are shown in Figure 2.
Fig. 1: 3DT1 of the two subjects, acquired with the two scanners and in different positions. Subject 1 (A and B) and Subject 2 (C and D) at 1.5 T (A, C) and at 0.25 T (B, D). Corresponding axial exemplificative slices were chosen for a proper comparison.
References: Fondazione Don Carlo Gnocchi ONLUS, Milan, Italy
Fig. 2: Comparison of 3DT1 of Subject 2, acquired at 0.25 T while he was sitting and supine. Corresponding axial exemplificative slices were chosen for a proper comparison.
References: Fondazione Don Carlo Gnocchi ONLUS, Milan, Italy
Tissue segmentation and volumes
The performance of the GM segmentation obtained with the two scanners is shown in Figure 3,
where the GM obtained at 0.25 T was coregistered and superimposed to the GM obtained at 1.5 T.
The differences between the corresponding volumes obtained at 1.5 T vs 0.25 T,
normalized by their average,
are shown in the 2nd and 3rd columns of Table 1 (one for each subject),
where positive values mean that the tissue of interest is overestimated at 0.25 T compared to 1.5 T.
The differences between supine and sitting position at 0.25 T,
normalized by their average,
are reported in the 4th column of Table 1.
Positive values mean higher values in the supine vs sitting position.
The repeatability obtained at 1.5 T is reported in the 5th column of Table 1.
Positive values mean higher values for the first acquisition,
compared to the second one.
Table 1.
Comparisons between scanners,
positions,
and runs.
The difference of corresponding tissue volumes,
normalized by their average,
is reported.
Legend: GM=grey matter; pGM=peripheral GM; SGM=subcortical GM; WM=white matter; vCSF=ventricular cerebrospinal fluid; Brain=brain =GM+WM.
Tissue
|
Subject 1:
1.5 vs 0.25 T
|
Subject 2:
1.5 vs 0.25 T
|
Subject 2:
Supine vs WB
|
Subject2:
scan 1 vs scan 2
|
GM
|
5.67%
|
-1.21%
|
-3.10%
|
0.96%
|
pGM
|
10.33%
|
2.35%
|
1.09%
|
0.35%
|
SGM
|
3.60%
|
0.73%
|
0.06%
|
2.68%
|
WM
|
-1.35%
|
-3.02%
|
-4.77%
|
-1.51%
|
vCSF
|
0.08%
|
-9.35%
|
-4.67%
|
0.12%
|
Brain
|
2.33%
|
-2.08%
|
-3.90%
|
-0.22%
|
SNR
The SNR obtained with the two scanners in the whole brain was: 9.22 and 54.39 for the Subject 1 at 0.25 T and 1.5 T respectively; 9.90 and 10.29 for the Subject 2 at 0.25 T in the supine and sitting positions respectively,
and 48.86 and 54.59 for the two different acquisitions of Subject 2 at 1.5 T.
Contrasts
The differences of the contrasts obtained at 1.5 T vs 0.25 T,
normalized by their average,
are reported in Table 2 for the two subjects.
All the values are positive,
which means higher SNR at 1.5 T.
Table 2.
Differences between 1.5 T and 0.25 T contrasts,
normalized by their average.
|
Subject 1
1.5 vs 0.25 T
|
Subject 2
1.5 vs 0.25 T
|
WMvsGM
|
1.55%
|
4.81%
|
WMvsCSF
|
10.17%
|
3.80%
|
GMvsCSF
|
14.64%
|
4.02%
|