CT: This is short for computed tomography. This involves radiation similar to x rays. It is safe in patients with pacemakers. It is useful for trauma, excluding intracranial bleeds or hydrocephalus. It is less useful for investigating brain tumours and condition where more detail is required.
MRI: This is referred to a magnetic resonance imaging and involves no radiation. This is not suitable for patients with a pacemaker. It is better in evaluating soft tissues than CT.
Ultrasound: This investigation is more often used in babies before the fontanelle closed.
Myelogram: This involves injecting contrast into the spinal column by performing a LP. The flow of contrast can then be evaluated by taking x rays or performing a CT scan. The latter is used these days instead of x rays. This investigation is used to evaluate pathology of the spinal column and is used when a MRI of the spine is not possible.