Using `mri_info` to get the resolution in each direction gives:
```
$ mri_info --res test.mgz
1.000 1.000 1.000 2.000
```
However, in nibabel getting the deltas I get:
```
>>> nib.load('test.mgz').get_header().get_zooms()
(3.7416575, 3.7416575, 3.7416575)
```
So, clearly, get_zooms() is doing something else that I mis-interpreted. I'm not sure where to get the equivalent information in nibabel, though...