Two-dimensional radial acquisition technique with density adaption in sodium MRI.

Conventional 2D radial projections suffer from losses in signal-to-noise ratio efficiency because of the nonuniform k-space sampling. In this study, a 2D projection reconstruction method with variable gradient amplitudes is presented to cover the k-space uniformly. The gradient is designed to keep the average sampling density constant. By this, signal-to-noise ratio is increased, and the linear form of the radial trajectory is kept. The simple gradient design and low hardware requirements in respect of slew rate allow an easy implementation at MR scanners. Measurements with the density-adapted 2D radial trajectory were compared with the conventional projection reconstruction method. It is demonstrated that the density-adapted 2D radial trajectory technique provides higher signal-to-noise ratio (up to 28% in brain tissue), less blurring, and fewer artifacts in the presence of magnetic field inhomogeneities than imaging with the conventional 2D radial trajectory scheme. The presented sequence is well-suited for electrocardiographically gated sodium heart MRI and other applications with short relaxation times.