Single‐Shot 2D Radial Echo Planar Imaging for Functional MRI

ABSTRACT Purpose To develop a novel single‐shot radial echo planar imaging (ss‐rEPI) technique for rapid, distortion‐free brain imaging in functional MRI experiments. Methods Radial multi‐gradient echo (radial mGRE) data were acquired on a 3T clinical scanner using a 2D ss‐rEPI readout with small golden‐angle rotations between echoes. Images were reconstructed using an iterative conjugate‐gradient method incorporating coil sensitivities, B 0 field inhomogeneities, transverse relaxation, and field‐drift correction to account for signal inconsistencies in the extended mGRE readout. Additional k ‐space‐weighted image contrast (KWIC) filtering prior to reconstruction helped reduce model mismatches at low spatial frequencies. Single‐shot rEPI image quality, contrast, and distortion were assessed against multi‐shot radial mGRE reference data. Retrospective adjustment of the KWIC filter and target TE in the reconstruction allowed the generation of multiple T 2 *weighted and phase contrast images from a single ss‐rEPI scan, enabling quantitative T 2 * mapping and QSM. Visual BOLD fMRI experiments were conducted and evaluated against Cartesian EPI measurements. Results Twenty‐four 3 mm thick slices of distortion‐free, multi‐contrast brain images were obtained at 2 × 2 and 1.5 mm 2 (ramp‐sampled) in‐plane resolution with an acquisition time of under 1.7 s. In multi‐session fMRI experiments on two subjects, ss‐rEPI demonstrated BOLD activation in the visual cortex comparable to standard EPI while also enabling functional T 2 * measurements. Conclusion Single‐shot rEPI enables rapid, distortion‐free 2D multi‐contrast brain imaging, offering a promising alternative to Cartesian EPI. Accurate ∆ B 0 modeling is critical for ss‐rEPI performance. Advanced reconstruction techniques and self‐calibration methods could further enhance its speed, performance, and applicability across diverse MRI techniques.