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

Abstract

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