CT scans can show the disc cartilage between vertebrae so they can detect disc protrusions.  CT is still considered the best first test for finding a disc protrusion as it is non-invasive, quick and less expensive than MRI.  It has a large opening and the subject can move some between scan “slices” without ruining the study. It does involve some exposure to ionizing radiation and isn’t as good as MRI for detecting spinal stenosis.