Radial multi-echo bSSFP and IDEAL chemical shift separation in k-space for high-speed 3D hyperpolarized ¹³C metabolic...

Hyperpolarized (HP) carbon-13 (¹³C) MRSI provides real-time information about metabolic processes but lacks high temporal and spatial resolution. This study introduces a multi-echo-balanced steady-state free precession (ME-bSSFP) method with a 3D radial readout trajectory in a spiral phyllotaxis pattern as a method for non-Cartesian HP ¹³C MRSI that allows for flexible reconstruction with high spatiotemporal resolution.

The approach uses ME-bSSFP with iterative decomposition of echo asymmetry and least-squares estimation (IDEAL) for separating ¹³C metabolite signals. The method was evaluated using thermally polarized ¹³C-enriched phantoms and in vivo experiments in healthy rats injected with HP [1-¹³C]pyruvate.

The method successfully acquired and separated thermally polarized and HP ¹³C metabolite signals, demonstrating its versatility and effectiveness. This approach allows for the extraction of high temporal- or high spatial-resolution 3D MRI from the same measurement. In vivo, dynamic HP metabolite intensities were extracted at a temporal resolution of 16 ms, and dynamic 3D metabolite images were generated with an isotropic FOV of 356 mm and a spatial resolution of 5.56 mm in 4.8 s.

The proposed radial ME-bSSFP method with iterative decomposition of echo asymmetry and least-squares estimation decomposition provides a flexible, efficient, and robust approach for HP ¹³C MRSI. It opens new possibilities for monitoring metabolic processes with unprecedented temporal resolution, generating dynamic 3D metabolite maps, and applying rapid acquisition and undersampling schemes. The method's ability to optimize imaging temporal resolution and facilitate kinetic modeling paves the way for innovative applications in dynamic HP metabolic MRI.