Current Status of Magnetic Resonance Imaging of the Central Nervous System
At the present level of development, clinical trials of magnetic resonance imaging have established that for the brain and spinal cord its depiction of gross structure now rivals those of computed tomography (CT) and is superior in its ability to detect pathological change in normal tissue. Magnetic resonance, however, is not a generic technique, but by manipulation of the applied spin sequences a whole range of different image classes can be generated which have varying weightings by proton density, the relaxation times Tt and T2 and bulk flow. It has to be realised that in practical terms the use of an inappropriate sequence may fail to disclose pathology and the application of even a representative selection of sequences may be precluded by considerations of time. Much work is now being directed towards both defining the optimal sequence for a given pathological condition and exploring the specificity of the information which can be derived from the images. The hope has long been expressed that magnetic resonance imaging would allow a more precise prediction of tissue type than is possible with computed tomography. Pathological tissues, particularly in tumours, are seldom homogeneous and it is not surprising, therefore, that a wide range of spin relaxation values can be found in a single tumour. The biophysical basis underlying such changes in the relaxation times observed in pathological tissues is imperfectly understood.
KeywordsMeningioma Neuroma Cholesteatoma Methaemoglobin
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