Numerical method for adjusting magnetic arrays for medical NMR imaging

Nuclear magnetic resonance is expected to replace CAT scan as a leading diagnostic tool because of its non invasive nature. The magnet generating the static field is a major part of the cost because of the high level of field homogeneity required for imaging, Two or three further magnetic sources generate a gradient field. I propose replacing these sources with an array of adjustable magnetic sources and I provide a preliminary numerical method of determining adjustments so that static field inhomogeneities will be removed at the same time as the gradient field is inserted, This reduces cost by relaxing the homogeneity requirements for the large static field magnet. Field measurements across the image plane are used as input to the computer inversion algorithm. The magnetic moments required to compensate the inhomogeneities and add the gradient field are computed. I show for a simple configuration that the accuracy of the field is a function of the number of elements in the magnetic array.