k ‐ t 2 BLAST: Exploiting spatiotemporal structure in simultaneously cardiac and respiratory time‐resolved volumetric imaging

Multidimensional imaging resolving both the cardiac and respiratory cycles simultaneously has the potential to describe important physiological interdependences between the heart and pulmonary processes. A fully five‐dimensional acquisition with three spatial and two temporal dimensions is hampered, however, by the long acquisition time and low spatial resolution. A technique is proposed to reduce the scan time substantially by extending the k ‐ t BLAST framework to two temporal dimensions. By sampling the k ‐ t space sparsely in a lattice grid, the signal in the transform domain, x ‐ f space, can be densely packed, exploiting the fact that large regions in the field of view have low temporal bandwidth. A volumetric online prospective triggering approach with full cardiac and respiratory cycle coverage was implemented. Retrospective temporal interpolation was used to refine the timing estimates for the center of k ‐space, which is sampled for all cardiac and respiratory time frames. This resulted in reduced reconstruction error compared with conventional k ‐ t BLAST reconstruction. The k ‐ t 2 BLAST technique was evaluated by decimating a fully sampled five‐dimensional data set, and feasibility was further demonstrated by performing sparsely sampled acquisitions. Compared to the fully sampled data, a fourfold improvement in spatial resolution was accomplished in approximately half the scan time. Magn Reson Med 58:922–930, 2007. © 2007 Wiley‐Liss, Inc.