Technical Note: A deuterated ¹³ C-urea reference for clinical multiparametric MRI prostate cancer studies including...

Metabolic magnetic resonance imaging (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.

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.

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 in ¹ 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 ¹³ C signal was unaffected.

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.