Hyperpolarized C-13 tracers: Technical advancements and perspectives for clinical applications

Hyperpolarized C-13 tracers offer a radiation-free option for metabolic imaging. Signal enhancement of an order of several thousand times with the dynamic nuclear polarization (DNP) technique allows the detection of these tracers and their immediate metabolites in living organisms with MRI/MRSI (magnetic resonance imaging/magnetic resonance spectroscopy imaging) methods in real time and with high temporal resolution. The initial 'target' application for DNP hyperpolarized tracers was prostate cancer, a condition that could hardly be diagnosed with the FDG PET. However, several Phase 2 clinical trials currently involve not only patients with prostate cancer but also pancreatic cancer, amyotrophic lateral sclerosis, transient ischemic attack, glioblastoma multiforme, mycosis fungiodes (skin cancer), and chronic heart failure. A large number of trials that started in the last three years indicate that there could be a potential for the application of hyperpolarized C-13 labeled pyruvate in the diagnosis of several conditions other than prostate cancer. One limitation for the hyperpolarized C-13-labelled tracers is their relatively short half-life. In this review, we discuss several emerging strategies for increasing tracer's lifetime that could allow either their transportation between facilities or improve the signal-to-noise ratio in the final acquisition. We also discuss some promising diagnostic applications. (C) 2021 Nalecz Institute of Biocybernetics and Biomedical Engineering of the Polish Academy of Sciences. Published by Elsevier B.V. All rights reserved.