A New Class of Encoding Techniques using a Transmit Array: Illustration with Cylindrical Encoding

Introduction In nearly all magnetic resonance imaging (MRI) applications, gradient coils are used for data encoding. Although an arbitrarily oriented slice can be selected, gradient coils limit the field-of-view (FOV) to a rectangular region and the slice to a plane. However, in a considerable fraction of MRI applications, the region of interest (ROI) is merely a portion of the selected slice. Hence, all the FOV needs to be imaged. Because the gradients encode all the FOV data producing uniform pixels, either the resolution of the ROI has to be decreased or the total imaging time has to be increased. Although using multi-dimensional pulses, a certain region can be excited and the FOV can be decreased, due to the fact that the FOV needs to be rectangular, this method is useful if the ROI is rectangular too. If the ROI is convex, or encloses a region which is not of interest, the efficiency is still low.