Applications of time-varying gradients in existing magnetic resonance imaging systems

This paper describes several applications of magnetic resonance imaging (MRI) with time-varying gradients within the framework of existing imaging systems. An alternative form of slice selection is shown where a time-varying gradient is used, during the reception interval, to isolate the slice of interest (the reconstruction of the slice itself is treated by the conventional techniques). This system allows for precise control of the slice, thinner slices (less than 1 mm) and the ability to select multiple, closely packed slices using a single imaging sequence. All this is done by postprocessing so the slice(s) of interest can be selected after the measurements have been completed. It is also shown how time-varying gradients can be used to generate the signals required for conventional projection-reconstruction and two-dimensional Fourier transform techniques (yet achieving higher resolution and using a resonant gradient system). In addition to cross-sectional imaging, this same approach provides a simple system for projection imaging of the entire volume. All of these techniques constitute a good starting point for the exploitation of time-varying gradients for fast, high-resolution MRI with existing imaging systems.