Speaker
Description
INTRODUCTION: The vast majority of emerging hyperpolarized MRI contrast agents employ heteronuclei (e.g. 13C or 129Xe) for transient storage of hyperpolarization and detection due to much longer lifetimes of the HP state and the lack of background signal. However, clinical MRI scanners are often poorly suited for excitation and detection of heteronuclei as they typically lack the corresponding RF hardware and software. While multi-nuclear detection capability exists on clinical research MRI scanners, to date their number (<0.5%) is inconsequential for the purpose of achieving widespread implementation of HP MRI.
METHODS/RESULTS: We report on our progress in developing three distinct approaches to enable detection of HP contrast media on clinical MRI scanners equipped with proton-only hardware and software. The first strategy employs proton sensing of 13C-hyperpolarized metabolites in vivo (most notably hyperpolarized pyruvate and its downstream metabolites). The second approach relies on the use of ultrafast electronics to “translate” excitation pulses at proton frequency to a given heteronuclear frequency. In this approach, a transmit-receive RF coil is required to transmit excitation pulses and detect the heteronuclear signal. The detected signal is then “translated” back to the proton frequency of the MRI scanner, and can be “fed” to the MRI scanner for image visualization or processed off-line. Radiofrequency Amplification by Stimulated Emission of Radiation (RASER) is the third most promising approach. RASER signals are created via stimulated emission by “negatively” hyperpolarized spins without external radio-frequency excitation pulses (and thus not requiring the RF excitation coil and the pulse-sequence-synchronization) and without any background signal. The recently demonstrated feasibility of RASER MRI, 13C RASER, and the tracking of chemical transformation, and achieving ultra-high Q of 1 million of detecting NMR RF chain will be discussed. Together, these advances suggest the feasibility of 13C and 129Xe RASER imaging in vivo, using heteronuclear purpose-built high Q detection electronics for clinical MRI scanners.
