Dear FS lists

When I measured subcortical GM volumes in the same subjects by using both version 5.1 and 5.3, I have observed a considerable difference in volumes between the two versions.
For instance, please see the left thalamic volumes below.
I cannot figure out why there is much difference between the versions.
Which result is more reliable?

Left-Thalamus-Proper_5.3 Left-Thalamus-Proper_5.1
10313 9757
8924.8 7746
9834.8 8287
7935.2 7034
8764.1 7747
9411.8 8037
7636.7 8051
9334.7 8255
10024.3 8171
8757.7 6900
9540.9 8316
9294.4 8369
8091 7366
9103.7 7818
9310.2 7974
7583 6872
9838.9 8911
8829.6 8004
9094.8 6973
9492.3 8922
8821.6 7691
7971.6 7376
9901.2 8936
9773.9 8855
9283.7 7615
8801.6 7690
8505.1 7325
8981 7258
9644.7 8860
9104.2 8298
8494.8 7402
9024.9 7721
8117.8 7226
8001.8 7548
8392.3 7668
8606.6 8173
9126.7 7595
8093 7885
8317.7 7157
10556 9307
8669.6 8374
8034.7 7338
8148.5 7276
9048.1 8064
8160.1 7014
8747.9 7894
8329.9 6866
8415.8 8189
9246.9 8256
8194.1 7183
9629.2 9579
7688.2 6398
8349.2 8238
8366.2 7348
8436.5 7616
8372.3 6977
9396.4 7589
9327.5 7684
10001.8 8627
9762.4 9228
8841 8532
8342.4 8024
8645.7 7725

Any comment would be appreciated.
Thank you.

Kim