Technical Note: A Deuterated 13C‐Urea Reference for Clinical Multiparametric Prostate Cancer Studies Including Hyperpolarized Pyruvate

PURPOSE: Metabolic MRI using hyperpolarized [1-(13) C]-pyruvate offers unprecedented new insight into disease and response to therapy. (13) C-enriched reference standards are required to enable fast and accurate calibration for (13) C studies, but care must be taken to ensure that the reference is compatible with both (13) C and (1) H acquisitions. The goal of this study was to optimize the composition of a (13) C-urea reference for a dual-tuned (13) C/(1) H endorectal coil and minimize imaging artifacts in metabolic and multiparametric MRI studies involving hyperpolarized [1-(13) C]-pyruvate. METHODS: Due to a high amount of Gd doping for the purpose of reducing the spin-lattice relaxation time (T1) of urea, the (1) H signal produced by a reference of (13) C-urea in normal water was rapidly relaxed, resulting in severe artifacts in heavily T1-weighted images. Hyperintense ringing artifacts in (1) H images were mitigated by reducing the (1) H concentration in a (13) C-urea reference via deuteration and lyophilization. Several references were fabricated and their SNR was compared using (1) H and (13) C imaging sequences on a 3T MRI scanner. Finally, (1) H prostate phantom imaging was conducted to compare image quality and (1) H signal intensity of normal and deuterated urea references. RESULTS: The deuterated (13) C-urea reference provides strong (13) C signal for calibration and an attenuated (1) H signal that does not interfere with heavily T1-weighted scans. Deuteration and lyophilization were fundamental to the reduction of (1) H signal and hyperintense ringing artifacts. There was a 25-fold reduction in signal intensity when comparing the non-deuterated reference to the deuterated reference, while the (13) C signal was unaffected. CONCLUSION: A deuterated reference reduced hyperintense ringing artifacts in (1) H images by reducing the (1) H signal produced from the (13) C-urea in the reference. The deuterated reference can be used to improve anatomical image quality in future clinical (1) H and hyperpolarized [1-(13) C]-pyruvate MRI prostate imaging studies.