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Conventional magnetic resonance (MR) images are reconstructed by Fourier transformation and have uniform spatial resolution across the entire field of view (FOV). The present paper describes a way of creating MR images which have higher spatial resolution in some areas than in others. Such locally focused images can be acquired in less scan time than that required to image the entire FOV with uniformly high resolution. After the user specifies the spatial resolution desired in each portion of the FOV,the algorithm automatically generates image basis functions which oscillate most rapidly in the zones with highest resolution. Images are reconstructed by summing a series of these basis functions, with coefficients calculated from a subset of the usual phase-encoded signals required to create an image with uniformly high spatial resolution. The algorithm also determines which phase-encodings are optimal for this purpose, and these are usually non-uniformly scattered in k-space. Functional and interventional imaging may benefit from this technique, which makes it possible to acquire a rapid series of dynamical images which have high resolution in areas of expected change and lower resolution elsewhere.>
Cao et al. (Tue,) studied this question.