It is a non-invasive imaging technique that creates detailed images of the back of the head, the foramen magnum (hole in the base of the skull), the first two cervical vertebrae, and surrounding soft tissues. Your doctor may advise this test to diagnose obstructive hydrocephalus (blockage of cerebrospinal fluid) and syringomyelia. It is also used to detect stenosis and compression of the brain stem/spinal cord, which leads to neckaches, headaches and neck aches.