Inductively coupled, transmit-receive coils for proton MRI and X-nucleus MRI/MRS in small animals.

We report several inductively coupled RF coil designs that are very easy to construct, produce high signal-to-noise ratio (SNR) and high spatial resolution while accommodating life support, anesthesia and monitoring in small animals. Inductively coupled surface coils were designed for hyperpolarized 13 C MR spectroscopic imaging (MRSI) of mouse brain, with emphases on the simplicity of the circuit design, ease of use, whole-brain coverage, and high SNR. The simplest form was a resonant loop designed to crown the mouse head for a snug fit to achieve full coverage of the brain with high sensitivity when inductively coupled to a broadband pick-up coil. Here, we demonstrated the coil's performance in hyperpolarized 13 C MRSI of a normal mouse and a glioblastoma mouse model at 4.7 T. High SNR exceeding 70:1 was obtained in the brain with good spatial resolution (1.53 mm × 1.53 mm). Similar inductively coupled loop for other X-nuclei can be made very easily in a few minutes and achieve high performance, as demonstrated in 31 P spectroscopy. Similar design concept was expanded to splitable, inductively coupled volume coils for high-resolution proton MRI of marmoset at 3T and 9.4T, to easily accommodate head restraint, vital-sign monitoring, and anesthesia delivery.

Development of Dissolution Dynamic Nuclear Polarization of [15 N3 ]Metronidazole: A Clinically Approved Antibiotic.

We report dissolution Dynamic Nuclear Polarization (d-DNP) of [15 N3 ]metronidazole ([15 N3 ]MNZ) for the first time. Metronidazole is a clinically approved antibiotic, which can be potentially employed as a hypoxia-sensing molecular probe using 15 N hyperpolarized (HP) nucleus. The DNP process is very efficient for [15 N3 ]MNZ with an exponential build-up constant of 13.8 min using trityl radical. After dissolution and sample transfer to a nearby 4.7 T Magnetic Resonance Imaging scanner, HP [15 N3 ]MNZ lasted remarkably long with T1 values up to 343 s and 15 N polarizations up to 6.4 %. A time series of HP [15 N3 ]MNZ images was acquired in vitro using a steady state free precession sequence on the 15 NO2 peak. The signal lasted over 13 min with notably long T2 of 20.5 s. HP [15 N3 ]MNZ was injected in the tail vein of a healthy rat, and dynamic spectroscopy was performed over the rat brain. The in vivo HP 15 N signals persisted over 70 s, demonstrating an unprecedented opportunity for in vivo studies.