For every RF (slice) excitation, there will be one k-space, analogous to a spreadsheet where the signal measurements are stored. In 2DFT imaging, each slice will come from a unique “sheet” of k-space. In 3DFT imaging, k-space is actually a 3D grid where the entire volume that is excited by the slice selective RF will be encoded in that grid. Thus, for the common case of 2DFT there will be a “sheet” of k-space for each slice. If a series has 30 slices, there will be 30 separate “sheets” of k-space. If the series is acquired using 3DFT, the entire series of 30 slices would have only one “sheet” of k-space, but that k-space would have 3 dimensions and might therefore seem like a stack of 30 separate 2D “sheets” of k-space.