Plain X-rays
A plain X-ray provides useful information about the health, structure and alignment of bones but does not give reliable information about discs, nerve roots or muscles.
Magnetic Resonance Imaging (MRI)
The single most important development in medical diagnosis in the past two decades, MRI has become the investigation of choice for almost all spinal disorders. It essentially shows the presence of water in the body through the medium of magnetic fields rather than look at tissue density in the way X-rays do. It is safe and does not involve radiation. An MRI usually takes from three to ten minutes to complete. The majority of MRI machines are ‘closed’ which means the patient is placed in a rather confined space. ‘Open’ MRIs are available though image quality and resolution are somewhat diminished.
MRI is excellent for seeing soft tissues such as the spinal cord, nerve roots, discs, ligaments and musculature. If previous spinal surgery has been carried out, an intravenous contrast dye called Gadolinium is usually administered. This helps to distinguish between recurrent disc herniation and scar. Gadolinium is very safe, dissolves well in the blood stream and is quickly excreted in the urine.
Computed Tomography Scan (CT)
A CT scan uses radiation and computerised processing to provide a three dimensional image. They give good information about bone, including reliable dimensions of the spinal and nerve root canals. They also give reasonably good information about the lumbar discs and whether or not they are prolapsed. The test usually takes 15-20 minutes.
CTs are excellent for showing subtle spinal fractures. They are useful in patients who have pacemakers and other mechanical devices when MRI can cause device malfunction.
Discogram
A discogram is a procedure in which a radiologist inserts dye into a disc. The pressure within the disc usually rises and if the patients back pain is caused by a fault within that disc, his pain will be reproduced. This test is sometimes useful in localising which of a group of worn disc is causing the problem.
Electromyogaphy (EMG) and Nerve Condution Studies
EMG studies are performed by inserting an electrode under the skin and the response of the muscle to stimulation is viewed on a computer screen. In nerve conduction studies an electrode placed over the skin stimulates an underlying nerve and the speed and amplitude of the response can then be measured.
Both tests are complementary and usually carried out together by a neurologist with specialist training. They are used when a patient with neck or low back pain has suspected nerve or muscle damage.
