Brain and spinal cord imaging has considerably extended our ability to understand the structure and function of the normal and disordered central nervous system. Data from imaging techniques can be obtained in living patients and permits an evaluation of a disease, not only at a given point in time, but over the progression of the disease. Some of the techniques reviewed in this chapter also have the potential to demonstrate an effect of drug therapy. Although, currently, these techniques are probably not sensitive enough to demonstrate a therapeutic response in an individual patient over time, it is possible that certain techniques may be capable of assessing changes due to therapy in a treatment group. This approach has been particularly powerful in disorders which are characterized by exacerbations and remissions, such as multiple sclerosis, where it has been possible to monitor changes in total cortical plaque load in response to treatment with β-interferon (Paty and Moore, 1997). Serial measurements using brain imaging will undoubtedly yield new insights, even in disorders marked by variable progression, such as ALS. To a large extent, imaging techniques can be thought of as an extension of pathological or biochemical measurements on brain tissue in situ.

The roles of imaging techniques in ALS are threefold. First, they are used to exclude causes of bulbar or limb weakness due to compressive lesions or other causes. Secondly, imaging techniques can identify abnormal signals that might be supportive of a diagnosis of ALS.