The main problem is that all volume rendering presets assume that background is darker than the object that you would like to see. In your case, the object is dark and background box is bright, therefore you’ll only see a solid box.
The simplest is probably to invert your image by using SimpleFilters module: Filter = ShiftScaleImageFilter, Scale = -1.
If you don’t want to change your input image then you need to adjust volume rendering transfer functions to make bright values transparent. Something like this should work:
I’ve added an “inverted” volume rendering preset, CT-Air, which will be available in nightly builds that you download tomorrow or later. If you choose this preset and adjust “Shift” slider then dark structures should show up in the 3D view.