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The value of diagnostic imaging techniques in the management of diseases of the nervous system.

The Canadian Neurological Society recently stated its views on diagnostic imaging techniques.' The society was concerned that not only federal and provincial governments but also health care professionals were unaware of the advantages offered by these techniques in the management of diseases of the nervous system. Thus, it has reviewed the value of computerized tomography (CT) and other imaging techniques, emphasized potential cost effectiveness and made recommendations on future policy. As a research tool CT has provided new insight into disease processes. It is now firmly established as the definitive method of diagnosing diseases of the brain, particularly tumours, hemorrhage, abscesses and head injuries. These conditions present acutely and require aggressive treatment, such as brain surgery. For diseases that develop slowly, earlier and more accurate diagnosis helps the physician to establish more effective treatment and to provide a firm prognosis if treatment is ineffective. Patients and relatives welcome the minimal discomfort and risk. Earlier techniques, such as pneumoencephalography, radionuclide brain scanning and midline echoencephalography, have been largely superseded by CT scanning. Even skull roentgenography, electroencephalography, conventional plain-film tomography, cerebral angiography (in some hospitals) and positive contrast cisternography are now used less commonly.2 There is emerging evidence that CT scanning will be the first method of investigation of common spinal conditions, such as degenerative disc disease with nerve root compression,3 and of less common spinal diseases, such as spinal cord tumours. The increased accuracy of diagnosis may eliminate the need for myelography and clarify the indications for spinal surgery or other treatment. The development of CT scanners has been so intensive and complete that further improvements will only occur with costly research and development. However, related procedures are now emerging, the most significant being nuclear magnetic resonance (NMR), positron emission tomography (PET) and digital vascular imaging (DVI).4 NMR has several advantages over CT scanning.5-8 Because artefact created by adjacent bone is eliminated, the contents of the spine and posterior cranial fossa are