Magnetic resonance imaging of the spine. Technology and technique

Perhaps in no other area of radiology is the appearance of the images as dependent on the technique used to obtain them as is the case in magnetic resonance imaging (MRI). In some instances, such as decreasing signal-to-noise ratios at the periphery of surface coils or obvious difficulties in localizing the level of an abnormality detected in spinal images, the technical dependence is obvious. There are many instances, however, in which the influence of technology may be more subtle, although no less important. It is far less of a problem to have difficulty localizing a level when this difficulty is recognized than it is when ambiguity concerning the level of an abnormality goes undetected. Obsessive attention to accurate localization of levels is necessary to avoid potentially dangerous mistakes. Terms such as "T1-weighted" rarely provide an accurate description of the contrast characteristics of an MRI image. Careful use of terminology, or at a minimum clear thinking concerning the determinants of image contrast will avoid confusion in image interpretation. The "weighting" of an image usually cannot be defined in terms of a single parameter, and attempts to do so often obfuscate more than they clarify. As technology evolves, a variety of different "T1-weighted" pulse sequences may be introduced. Each of these may display different contrast characteristics. It will be important to identify the specific pulse sequence, rather than "weighting" to understand the signal intensities observed on images.