Pole‐To‐Pole 3D Radial Trajectory Designs Improve Image Quality and Quantitative Parametric Mapping in the Brain and Heart

PURPOSE: To design 3D radial spiral phyllotaxis trajectories aimed at removing phase inconsistencies, improving image quality, and enhancing parametric mapping accuracy by acquiring nearly opposing spokes starting from both hemispheres in 3D radial k-space. METHODS: Two 3D radial trajectories, pole-to-pole and continuous spiral phyllotaxis, were developed and implemented on a 3T MRI scanner in a phase-cycled balanced steady-state free precession (bSSFP) and a spoiled gradient-echo (GRE) sequence. Image quality and k-space center phase variations were evaluated in a spherical phantom using the original and new radial phyllotaxis designs. T1/T2 was quantified and compared using phase-cycled bSSFP data acquired with the new radial trajectory designs, as well as the original phyllotaxis trajectory and a Cartesian trajectory as references, in both an MRI system phantom and the brains of three healthy volunteers. ECG-triggered whole-heart GRE data were acquired using the original and pole-to-pole phyllotaxis trajectories in three healthy volunteers and compared for image quality improvement. RESULTS: All 3D radial trajectory designs showed variations in the k-space center phase depending on the orientation of the readout spokes. Image quality improved when using the pole-to-pole and continuous phyllotaxis over the original trajectory. Scans using the original trajectory had higher T1/T2 estimation errors in comparison to the new trajectories and the Cartesian trajectory. The pole-to-pole and continuous trajectories improved T1/T2 maps of the brain and image quality for all cardiac images. CONCLUSION: Acquiring nearly opposing spokes in 3D radial trajectory designs compensates phase inconsistencies without requiring additional corrections, which improves quantitative imaging and anatomical visualizations.