Technical Note: A deuterated C-urea reference for clinical multiparametric MRI prostate cancer studies including hyperpolarized pyruvate.

Purpose: Metabolic magnetic resonance imaging (MRI) using hyperpolarized [1- C]-pyruvate offers unprecedented new insight into disease and response to therapy. C-enriched reference standards are required to enable fast and accurate calibration for C studies, but care must be taken to ensure that the reference is compatible with both C and H acquisitions. The goal of this study was to optimize the composition of a C-urea reference for a dual-tuned C/ H endorectal coil and minimize imaging artifacts in metabolic and multiparametric MRI studies involving hyperpolarized [1- C]-pyruvate.

Methods: Due to a high amount of Gd doping for the purpose of reducing the spin-lattice relaxation time (T ) of urea, the H signal produced by a reference of C-urea in normal water was rapidly relaxed, resulting in severe artifacts in heavily T -weighted images. Hyperintense ringing artifacts in H images were mitigated by reducing the H concentration in a C-urea reference via deuteration and lyophilization. Several references were fabricated and their SNR was compared using H and C imaging sequences on a 3T MRI scanner. Finally, H prostate phantom imaging was conducted to compare image quality and H signal intensity of normal and deuterated urea references.

Results: The deuterated C-urea reference provides strong C signal for calibration and an attenuated H signal that does not interfere with heavily T -weighted scans. Deuteration and lyophilization were fundamental to the reduction in H signal and hyperintense ringing artifacts. There was a 25-fold reduction in signal intensity when comparing the nondeuterated reference to the deuterated reference, while the C signal was unaffected.

Conclusion: A deuterated reference reduced hyperintense ringing artifacts in H images by reducing the H signal produced from the C-urea in the reference. The deuterated reference can be used to improve anatomical image quality in future clinical H and hyperpolarized [1- C]-pyruvate MRI prostate imaging studies.