It has been only 10 years since the introduction of X-ray computed tomography (CT) revolutionised the practice of neuroradiology and neurosurgery (Ambrose, 1973; Hounsfield, 1973). Today it ap pears that medicine is on the verge of another rev olution in imaging. The recent development of nu clear magnetic resonance (NMR) as an imaging method shows great promise, not only as a method for displaying human anatomy and gross pathology but also for recording in vivo biochemical and phys iological changes. Not only does it make it possible to demonstrate differences in cellular metabolism and display them in a manner similar to that of X ray CT (i.e., as axial tomographic sections), it can achieve this without the use of ionising radiation. The NMR phenomenon has been known since 1945 (Bloch, 1946; Purcell et aI., 1946), and it has been used extensively since then as an analytical technique in chemistry and physics. In 1971, the concept of using the NMR technique for detecting malignant tissue in vitro was introduced (Damadian, 1971), and by 1973, less than a year after X-ray CT had been discovered, NMR images of phantoms had been made (Lauterbur, 1973). These observations attracted a number of scientists to the field of NMR research, both in Europe and in North America, with the result that rapid progress was made toward developing a human imaging system. Three years after Lauterbur's work with phantoms, the first im ages of human volunteers were made (Damadian et aI., 1977). These early images were extremely crude, but they indicated that NMR imaging of the body was possible. Further development of the technique led to improved images of the extremities (Hinshaw et aI., 1979) and head (Moore et aI., 1980) in normal