Partial Fourier reconstruction for improved resolution in 3D hyperpolarized 13 C EPI

Abstract

Purpose: Asymmetric in-plane k-space sampling of EPI can reduce the minimum achievable TE in hyperpolarized ${13}^{}C$ with spectral-spatial radio frequency pulses, thereby reducing $T_2^{*}$ weighting and signal-losses. Partial Fourier image reconstruction exploits the approximate Hermitian symmetry of k-space data and can be applied to asymmetric data sets to synthesize unmeasured data. Here we tested whether the application of partial Fourier image reconstruction would improve spatial resolution from hyperpolarized [1- ${13}^{}C$ ]pyruvate scans in the human brain.

Methods: Fifteen healthy control subjects were imaged using a volumetric dual-echo echo-planar imaging sequence with spectral-spatial radio frequency excitation. Images were reconstructed by zero-filling as well as with the partial Fourier reconstruction algorithm projection-on-convex-sets. Resulting images were quantitatively evaluated with a no-reference image quality assessment.

Results: The no-reference image sharpness metric agreed with perceived improvements in image resolution and contrast. The [1- ${13}^{}C$ ]lactate images benefitted most, followed by the [1- ${13}^{}C$ ]pyruvate images. The ${13}^{}C$ -bicarbonate images were improved by the smallest degree, likely owing to relatively lower SNR.

Conclusions: Partial Fourier imaging and reconstruction were shown to improve the sharpness and contrast of human HP ${13}^{}C$ brain data and is a viable method for enhancing resolution.

Keywords: Dual-Echo; EPI; bicarbonate; brain; hyperpolarized ${13}^{}C$; lactate; metabolic imaging; partial Fourier; pyruvate.