We present a novel imaging procedure using multiple receiver coils. This circumvents the sequential acquisition of signals required by conventional imaging strategies. The advantage of this technique over existing subsecond imaging techniques is that (a) contrast can be maintained and (b) there is no magnetic field gradient switching involved. o 1988 Academic Press, Inc.
Although magnetic resonance is in wide use as an imaging technique, the time taken to construct the image is clearly an undesirable feature, although recently, considerable progress has been made in reducing imaging time (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11). What all the current procedures have in common is that they are based ultimately on two-dimensional Fourier transforms (2DFT; or the related back-projection technique) and furthermore employ only one (Helmholtz) detector. It has been shown that a reduction in imaging time using these procedures places certain restrictions on contrast (12).
In conventional 2DlT strategies, a spatial location is encoded using a magnetic field gradient in a particular direction. Thus, dipoles within the object will absorb and emit radiation at frequencies that correspond to their spatial location. However, these frequencies are not unique, and therefore entire lines of pixels within the object field are subject to the same magnetic field strength and absorb at the same frequency. Removal of this ambiguity requires the imposition of N different, and successive, field gradients. The set of N echoes then contains enough information to determine the amplitude of an emitter at a particular space-time point within the object. Comparison with a subsequent set of N echoes then leads directly to the relaxation parameters T I and T,, which are the quantities of interest. Current fast scan strategies employ essentially the same methodology but rely on reducing the flip angle of the dipoles in the object field (7,8). Recently progress has been reported in shortening image acquisition times with partial flip angle imaging and short TR values, while maintaining the contrast obtained in longer TR sequences (10).
A novel procedure is outlined here, in which imaging time might in principle be reduced to a fraction of a second, without any change in contrast and without the need for magnetic field gradient switching. This is because all signals from the object are obtained simultaneously with a full 90" flip angle for the spin. The key innovation