Images - Back Pain
With all these techniques (X-rays – we call them radiographs as X-rays are "invisible”, bone scans, CT and MRI scans) we like to see the actual films and not just the reports.
You should retain ALL your own films indefinitely (even when they don’t seem relevant, eg, an X-ray of your chest, kidneys or colon usually shows the spine.
Hospitals often don’t release them and may destroy them after seven years. Radiologists don’t keep films although some scans are kept for a short period on disc. Radiologists will almost always have a copy of the report. If you have had X-rays taken by a specialist eg for an ACC report ask to have your films returned to you. The ACC don’t keep X-rays.
X RAYS / RADIOGRAPHS / ROENTGENOGRAMS
Plane (often miscalled plain) radiographs are planar images (in two planes) of bones, joints and soft tissues made by exposing the body part to X-rays (which are invisible) and recording the negative image on a photographic film. The higher the atomic number of the substance the more X-ray is absorbed, hence calcium in bone, with a high atomic number appears white on the film. Very useful information can be obtained from these images, especially in regard to possible surgically remediable causes of back pain. "Normal X-rays” are very reassuring but subtle changes can be missed and correlation with the symptoms and examination findings is required. This why I like to see the actual films.
The commonest radionuclide bone scan uses an artificially made substance Technetium. This is attached to diphosphonate and injected. It is taken up by bone in the body, especially in areas where there is higher bone turnover, e.g., in growing bone, healing bone (fractures) or bone destruction (tumours and infection). It is a very sensitive test but not specific. Improved localization can be done using the SPECT technique.
CT or CAT SCAN
Computerized (Axial) Topography uses the information from multiple radiographs and reformats them to produce axial images (cross sections). It is excellent for bones and joints but less good for soft tissues. It is used less commonly now in the spine, being largely superceded here by MRI scan.
Magnetic Resonance Imaging uses a very strong magnetic field to produce an effect on the hydrogen of water molecules. Different tissues of the body have different water contents allowing us to discriminate between fluid such as CSF (Cerebrospinal fluid), nerves, fat and discs. The resulting images are remarkable. However, they require the patient to lie very still in a tight tube (not for claustrophobics and difficult if you are in pain). Occasionally, to better differentiate disc prolapse and scar or tumour injection of Gadollinium is required. An open scanner is now available at the Manukau Radiology Institute (near Middlemore Hospital) for people with claustrophobia or who can’t fit in a standard scanner – see www.mri.co.nz
This can be assessed by CT scan or bone densitometry. These images are generally not helpful for other diagnostic purposes. For sequential measures it is best to use the same technique.