It’s a CT (computerized tomography) scan. It still uses X-rays but the results are in 3D so one can view “slices” of the image from different perspectives.

The sternum is in the the same plane as the spine from this angle, so that’s why there’s only the slightest hint of a ribcage and only the sternum - this slice is well past rib bones.

Similarly the shoulder is much closer to the viewer’s perspective in the 3d model, so it’s not shown at all.

Edit: misinterpreted CT slice location.