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Applications of parahydrogen induced polarization (PHIP) often warrant conversion of the chemically-synthesized singlet-state spin order into net heteronuclear magnetization. In order to obtain optimal yields from the overall hyperpolarization process, catalytic hydrogenation must be tightly synchronized to subsequent radiofrequency (RF) transformations of spin order. Commercial NMR consoles are designed to synchronize applied waves on multiple channels and consequently are well-suited as controllers for these types of hyperpolarization experiments that require tight coordination of RF and non-RF events. Described here is a PHIP instrument interfaced to a portable NMR console operating with a static field electromagnet in the milliTesla regime. In addition to providing comprehensive control over chemistry and RF events, this setup condenses the PHIP protocol into a pulse-program that in turn can be readily shared in the manner of traditional pulse sequences. In this device, a TTL multiplexer was constructed to convert spectrometer TTL outputs into 24 VDC signals. These signals then activated solenoid valves to control chemical shuttling and reactivity in PHIP experiments. Consolidating these steps in a pulse-programming environment speeded calibration and improved quality assurance by enabling the B 0 /B 1 fields to be tuned based on the direct acquisition of thermally polarized and hyperpolarized NMR signals. Performance was tested on the parahydrogen addition product of 2-hydroxyethyl propionate-1- 13 C-d 3 , where the 13 C polarization was estimated to be P 13C =20±2.5% corresponding to 13 C signal enhancement approximately 25 million-fold at 9.1 mT or approximately 77,000-fold 13 C enhancement at 3 T with respect to thermally induced polarization at room temperature., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Two synthetic strategies are investigated for the preparation of water-soluble iridium-based catalysts for NMR signal amplification by reversible exchange (SABRE). In one approach, PEGylation of a variant N -heterocyclic carbene provided a novel catalyst with excellent water solubility. However, while SABRE-active in ethanol solutions, the catalyst lost activity in >50% water. In a second approach, synthesis of a novel di-iridium complex precursor where the cyclooctadiene (COD) rings have been replaced by CODDA (1,2-dihydroxy-3,7-cyclooctadiene) leads to the creation of a catalyst [IrCl(CODDA)IMes] that can be dissolved and activated in water-enabling aqueous SABRE in a single step, without need for either an organic cosolvent or solvent removal followed by aqueous reconstitution. The potential utility of the CODDA catalyst for aqueous SABRE is demonstrated with the ∼(-)32-fold enhancement of 1 H signals of pyridine in water with only 1 atm of parahydrogen.

We report NMR Signal Amplification by Reversible Exchange (SABRE) hyperpolarization of the rare isotopes in "neat" liquids, each composed only of an otherwise pure target compound with isotopic natural abundance (n.a.) and millimolar concentrations of dissolved catalyst. Pyridine (Py) or Py derivatives are studied at 0.4% isotopic natural abundance ¹⁵N, deuterated, ¹⁵N enriched, and in various combinations using the SABRE-SHEATH variant (microTesla magnetic fields to permit direct ¹⁵N polarization from parahydrogen via reversible binding and exchange with an Ir catalyst). We find that the dilute n.a. ¹⁵N spin bath in Py still channels spin order from parahydrogen to dilute ¹⁵N spins, without polarization losses due to the presence of ¹⁴N or ²H. We demonstrate P(15N) ≈ 1% (a gain of 2900 fold relative to thermal polarization at 9.4 T) at high substrate concentrations. This fundamental finding has a significant practical benefit for screening potentially hyperpolarizable contrast agents without labeling. The capability of screening at n.a. level of ¹⁵N is demonstrated on examples of mono- and dimethyl-substituted Py (picolines and lutidines previously identified as promising pH sensors), showing that the presence of a methyl group in the ortho position significantly decreases SABRE hyperpolarization.

NMR signal amplification by reversible exchange (SABRE) is a NMR hyperpolarization technique that enables nuclear spin polarization enhancement of molecules via concurrent chemical exchange of a target substrate and parahydrogen (the source of spin order) on an iridium catalyst. Recently, we demonstrated that conducting SABRE in microtesla fields provided by a magnetic shield enables up to 10% 15 N-polarization (Theis, T.; et al. J. Am. Chem. Soc. 2015 , 137 , 1404). Hyperpolarization on 15 N (and heteronuclei in general) may be advantageous because of the long-lived nature of the hyperpolarization on 15 N relative to the short-lived hyperpolarization of protons conventionally hyperpolarized by SABRE, in addition to wider chemical shift dispersion and absence of background signal. Here we show that these unprecedented polarization levels enable 15 N magnetic resonance imaging. We also present a theoretical model for the hyperpolarization transfer to heteronuclei, and detail key parameters that should be optimized for efficient 15 N-hyperpolarization. The effects of parahydrogen pressure, flow rate, sample temperature, catalyst-to-substrate ratio, relaxation time ( T 1 ), and reversible oxygen quenching are studied on a test system of 15 N-pyridine in methanol- d 4 . Moreover, we demonstrate the first proof-of-principle 13 C-hyperpolarization using this method. This simple hyperpolarization scheme only requires access to parahydrogen and a magnetic shield, and it provides large enough signal gains to enable one of the first 15 N images (2 × 2 mm 2 resolution). Importantly, this method enables hyperpolarization of molecular sites with NMR T 1 relaxation times suitable for biomedical imaging and spectroscopy.

Two types of nanoscale catalysts were created to explore NMR signal enhancement via reversible exchange (SABRE) at the interface between heterogeneous and homogeneous conditions. Nanoparticle and polymer comb variants were synthesized by covalently tethering Ir-based organometallic catalysts to support materials comprised of TiO 2 /PMAA (poly methacrylic acid) and PVP (polyvinyl pyridine), respectively, and characterized by AAS, NMR, and DLS. Following parahydrogen (pH 2 ) gas delivery to mixtures containing one type of "nano-SABRE" catalyst particles, a target substrate, and ethanol, up to ~(-)40-fold and ~(-)7-fold 1 H NMR signal enhancements were observed for pyridine substrates using the nanoparticle and polymer comb catalysts, respectively, following transfer to high field (9.4 T). These enhancements appear to result from intact particles and not from any catalyst molecules leaching from their supports; unlike the case with homogeneous SABRE catalysts, high-field ( in situ ) SABRE effects were generally not observed with the nanoscale catalysts. The potential for separation and reuse of such catalyst particles is also demonstrated. Taken together, these results support the potential utility of rational design at molecular, mesoscopic, and macroscopic/engineering levels for improving SABRE and HET-SABRE (heterogeneous-SABRE) for applications varying from fundamental studies of catalysis to biomedical imaging.

Parahydrogen is demonstrated to efficiently transfer its nuclear spin hyperpolarization to nitrogen-15 in pyridine and nicotinamide (vitamin B(3) amide) by conducting "signal amplification by reversible exchange" (SABRE) at microtesla fields within a magnetic shield. Following transfer of the sample from the magnetic shield chamber to a conventional NMR spectrometer, the (15)N NMR signals for these molecules are enhanced by ∼30,000- and ∼20,000-fold at 9.4 T, corresponding to ∼10% and ∼7% nuclear spin polarization, respectively. This method, dubbed "SABRE in shield enables alignment transfer to heteronuclei" or "SABRE-SHEATH", promises to be a simple, cost-effective way to hyperpolarize heteronuclei. It may be particularly useful for in vivo applications because of longer hyperpolarization lifetimes, lack of background signal, and facile chemical-shift discrimination of different species.

By using 5.75 and 47.5 mT nuclear magnetic resonance (NMR) spectroscopy, up to 10(5)-fold sensitivity enhancement through signal amplification by reversible exchange (SABRE) was enabled, and subsecond temporal resolution was used to monitor an exchange reaction that resulted in the buildup and decay of hyperpolarized species after parahydrogen bubbling. We demonstrated the high-resolution low-field proton magnetic resonance imaging (MRI) of pyridine in a 47.5 mT magnetic field endowed by SABRE. Molecular imaging (i.e. imaging of dilute hyperpolarized substances rather than the bulk medium) was conducted in two regimes: in situ real-time MRI of the reaction mixture (in which pyridine was hyperpolarized), and ex situ MRI (in which hyperpolarization decays) of the liquid hyperpolarized product. Low-field (milli-Tesla range, e.g. 5.75 and 47.5 mT used in this study) parahydrogen-enhanced NMR and MRI, which are free from the limitations of high-field magnetic resonance (including susceptibility-induced gradients of the static magnetic field at phase interfaces), potentially enables new imaging applications as well as differentiation of hyperpolarized chemical species on demand by exploiting spin manipulations with static and alternating magnetic fields., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Long-lived spin states of hyperpolarized propane- d 6 gas were demonstrated following pairwise addition of parahydrogen gas to propene- d 6 using heterogeneous parahydrogen-induced polarization (HET-PHIP). Hyperpolarized molecules were synthesized using Rh/TiO 2 solid catalyst with 1.6 nm Rh nanoparticles. Hyperpolarized ( P H ∼ 1%) propane- d 6 was detected at high magnetic field (9.4 T) spectroscopically and by high-resolution 3D gradient-echo MRI (4.7 T) as the gas flowed through the radiofrequency coil with a spatial and temporal resolution of 0.5 × 0.5 × 0.5 mm 3 and 17.7 s, respectively. Stopped-flow hyperpolarized propane- d 6 gas was also detected at 0.0475 T with an observed nuclear spin polarization of P H ∼ 0.1% and a relatively long lifetime with T 1,eff = 6.0 ± 0.3 s. Importantly, it was shown that the hyperpolarized protons of the deuterated product obtained via pairwise parahydrogen addition could be detected directly at low magnetic field. Importantly, the relatively long low-field T 1,eff of HP propane- d 6 gas is not susceptible to paramagnetic impurities as tested by exposure to ∼0.2 atm oxygen. This long lifetime and nontoxic nature of propane gas could be useful for bioimaging applications including potentially pulmonary low-field MRI. The feasibility of high-resolution low-field 2D gradient-echo MRI was demonstrated with 0.88 × 0.88 mm 2 spatial and ∼0.7 s temporal resolution, respectively, at 0.0475 T.

Activation of a catalyst [IrCl(COD)(IMes)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; COD = cyclooctadiene)] for signal amplification by reversible exchange (SABRE) was monitored by in situ hyperpolarized proton NMR at 9.4 T. During the catalyst-activation process, the COD moiety undergoes hydrogenation that leads to its complete removal from the Ir complex. A transient hydride intermediate of the catalyst is observed via its hyperpolarized signatures, which could not be detected using conventional nonhyperpolarized solution NMR. SABRE enhancement of the pyridine substrate can be fully rendered only after removal of the COD moiety; failure to properly activate the catalyst in the presence of sufficient substrate can lead to irreversible deactivation consistent with oligomerization of the catalyst molecules. Following catalyst activation, results from selective RF-saturation studies support the hypothesis that substrate polarization at high field arises from nuclear cross-relaxation with hyperpolarized (1)H spins of the hydride/orthohydrogen spin bath. Importantly, the chemical changes that accompanied the catalyst's full activation were also found to endow the catalyst with water solubility, here used to demonstrate SABRE hyperpolarization of nicotinamide in water without the need for any organic cosolvent--paving the way to various biomedical applications of SABRE hyperpolarization methods.

Parahydrogen induced polarization was employed to prepare a relatively long-lived correlated nuclear spin state between methylene and methyl protons in propane gas. Conventionally, such states are converted into a strong NMR signal enhancement by transferring the reaction product to a high magnetic field in an adiabatic longitudinal transport after dissociation engenders net alignment (ALTADENA) experiment. However, the relaxation time T1 of ∼0.6 s of the resulting hyperpolarized propane is too short for potential biomedical applications. The presented alternative approach employs low-field MRI to preserve the initial correlated state with a much longer decay time TLLSS =(4.7±0.5) s. While the direct detection at low-magnetic fields (e.g. 0.0475 T) is challenging, we demonstrate here that spin-lock induced crossing (SLIC) at this low magnetic field transforms the long-lived correlated state into an observable nuclear magnetization suitable for MRI with sub-millimeter and sub-second spatial and temporal resolution, respectively. Propane is a non-toxic gas, and therefore, these results potentially enable low-cost high-resolution high-speed MRI of gases for functional imaging of lungs and other applications., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We demonstrate the feasibility of microscale molecular imaging using hyperpolarized proton and carbon-13 MRI contrast media and low-field (47.5 mT) preclinical scale (38 mm i.d.) 2D magnetic resonance imaging (MRI). Hyperpolarized proton images with 94 × 94 μm(2) spatial resolution and hyperpolarized carbon-13 images with 250 × 250 μm(2) in-plane spatial resolution were recorded in 4-8 s (largely limited by the electronics response), surpassing the in-plane spatial resolution (i.e., pixel size) achievable with micro-positron emission tomography (PET). These hyperpolarized proton and (13)C images were recorded using large imaging matrices of up to 256 × 256 pixels and relatively large fields of view of up to 6.4 × 6.4 cm(2). (13)C images were recorded using hyperpolarized 1-(13)C-succinate-d2 (30 mM in water, %P(13C) = 25.8 ± 5.1% (when produced) and %P(13C) = 14.2 ± 0.7% (when imaged), T1 = 74 ± 3 s), and proton images were recorded using (1)H hyperpolarized pyridine (100 mM in methanol-d4, %P(H) = 0.1 ± 0.02% (when imaged), T1 = 11 ± 0.1 s). Both contrast agents were hyperpolarized using parahydrogen (>90% para-fraction) in an automated 5.75 mT parahydrogen induced polarization (PHIP) hyperpolarizer. A magnetized path was demonstrated for successful transportation of a (13)C hyperpolarized contrast agent (1-(13)C-succinate-d2, sensitive to fast depolarization when at the Earth's magnetic field) from the PHIP polarizer to the 47.5 mT low-field MRI. While future polarizing and low-field MRI hardware and imaging sequence developments can further improve the low-field detection sensitivity, the current results demonstrate that microscale molecular imaging in vivo is already feasible at low (<50 mT) fields and potentially at low (~1 mM) metabolite concentrations.

Several supported metal catalysts were synthesized, characterized, and tested in heterogeneous hydrogenation of propene with parahydrogen to maximize nuclear spin hyperpolarization of propane gas using parahydrogen induced polarization (PHIP). The Rh/TiO2 catalyst with a metal particle size of 1.6 nm was found to be the most active and effective in the pairwise hydrogen addition and robust, demonstrating reproducible results with multiple hydrogenation experiments and stability for ≥1.5 years. 3D (1) H magnetic resonance imaging (MRI) of 1 % hyperpolarized flowing gas with microscale spatial resolution (625×625×625 μm(3) ) and large imaging matrix (128×128×32) was demonstrated by using a preclinical 4.7 T scanner and 17.4 s imaging scan time., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Indirect proton detection of (13)C hyperpolarized contrast agents potentially enables greater sensitivity. Presented here is a study of sub-second projection imaging of hyperpolarized (13)C contrast agent addressing the obstacle posed by water suppression for indirect detection in vivo. Sodium acetate phantoms were used to develop and test water suppression and sub-second imaging with frequency-selective RF pulses using spectroscopic and imaging indirect proton detection. A 9.8 mm aqueous solution of (13)C PHIP hyperpolarized 2-hydroxyethyl-(13)C-propionate-d2,3,3 (HEP),

 ~25% was used for demonstration of indirect proton sub-second imaging detection. Balanced 2D FSSFP (fast steady-state free precession) allowed the recording of proton images with a field of view of 64 × 64 mm(2) and spatial resolution 2 × 2 mm(2) with total acquisition time of less than 0.2 s. In thermally polarized sodium 1-(13)C-acetate, (13) C to (1)H polarization transfer efficiency of 45.1% of the theoretically predicted values was observed in imaging detection corresponding to an 11-fold overall sensitivity improvement compared with direct (13)C FSSFP imaging. (13)C to (1)H polarization transfer efficiency of 27% was observed in imaging detection, corresponding to a 3.25-fold sensitivity improvement compared with direct (13)C FSSFP imaging with hyperpolarized HEP. The range of potential applications and limitations of this sub-second and ultra-sensitive imaging approach are discussed., (Copyright © 2014 John Wiley & Sons, Ltd.)

The application of low magnetic fields to heteronuclear NMR has expanded recently alongside the emergence of methods for achieving near unity polarization of spin ensembles, independent of magnetic field strength. The parahydrogen induced hyperpolarization methods in particular, often use a hybrid arrangement where a high field spectrometer is used to detect or image polarized molecules that have been conjured on a separate, dedicated polarizer instrument operating at fields in the mT regime where yields are higher. For controlling polarizer chemistry, spare TTL channels of portable NMR spectrometers can be used to pulse program reaction timings in synchrony with heteronuclear RF transformations. The use of a spectrometer as a portable polarizer control module has the advantage of allowing detection in situ, simplifying the process of optimizing polarization yields prior to in vivo experimental trials. Suitable heteronuclear spectrometers compatible with this application are becoming more common, but are still sparsely available in comparison to a large existing infrastructure of single channel NMR consoles. With the goal of expanding the range of these systems to multinuclear applications, the feasibility of rotating a pair of heteronuclear spins ((13)C and (1)H) at 12mT was investigated in this study. Nonlinear phase and amplitude modulated waveforms designed to simultaneously refocus magnetization at 128kHz ((13)C) and 510kHz ((1)H) were generated numerically with optimal control. Although precise quantitative comparisons were not attempted due to limitations of the experimental setup, signals refocused at heteronuclear frequencies with this PANORAMIC approach (Precession And Nutation for Observing Rotation At Multiple Intervals about the Carrier) yielded amplitudes comparable to signals which were refocused using traditional block pulses on heteronuclear channels. Using this PANORAMIC approach to heteronuclear NMR at low field would reduce expense as well as hardware complexity and bulk, weighed against the caveat that elaborate pulses are required. More work will be necessary to test this method on the targeted application of parahydrogen induced hyperpolarization as well as to quantify efficiency, but upon further development we anticipate that this method may offer a viable 'software' approach to heteronuclear manipulations of spins at low magnetic fields., (Copyright © 2014 Elsevier Inc. All rights reserved.)

A novel variant of an iridium-based organometallic catalyst was synthesized and used to enhance the NMR signals of pyridine in a heterogeneous phase by immobilization on polymer microbead solid supports. Upon administration of parahydrogen (pH2) gas to a methanol mixture containing the HET-SABRE catalyst particles and the pyridine, up to fivefold enhancements were observed in the (1)H NMR spectra after sample transfer to high field (9.4 T). Importantly, enhancements were not due to any residual catalyst molecules in solution, thus supporting the true heterogeneity of the SABRE process. Further significant improvements may be expected by systematic optimization of experimental parameters. Moreover, the heterogeneous catalyst is easy to separate and recycle, thus opening a door to future potential applications varying from spectroscopic studies of catalysis, to imaging metabolites in the body without concern of contamination from expensive and potentially toxic metal catalysts or accompanying organic molecules., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The synthetic protocol for preparation of 1-(13)C-phosphoenolpyruvate-d2, precursor for parahydrogen-induced polarization (PHIP) of 1-(13)C-phospholactate-d2, is reported. (13)C nuclear spin polarization of 1-(13)C-phospholactate-d2 was increased by >30,000,000-fold (5.75 mT) in water. The reported (13)C polarization level approaching unity (>15.6%), long lifetime of (13)C hyperpolarized 1-(13)C-phospholactate-d2 (58 ± 4 s versus 36 ± 2 s for nondeuterated form at 47.5 mT), and large production quantities (52 μmoles in 3 mL) in aqueous medium make this compound useful as a potential contrast agent for the molecular imaging of metabolism and other applications.

(1)H NMR signal amplification by reversible exchange (SABRE) was observed for pyridine and pyridine-d5 at 9.4 T, a field that is orders of magnitude higher than what is typically utilized to achieve the conventional low-field SABRE effect. In addition to emissive peaks for the hydrogen spins at the ortho positions of the pyridine substrate (both free and bound to the metal center), absorptive signals are observed from hyperpolarized orthohydrogen and Ir-complex dihydride. Real-time kinetics studies show that the polarization build-up rates for these three species are in close agreement with their respective (1)H T1 relaxation rates at 9.4 T. The results suggest that the mechanism of the substrate polarization involves cross-relaxation with hyperpolarized species in a manner similar to the spin-polarization induced nuclear Overhauser effect. Experiments utilizing pyridine-d5 as the substrate exhibited larger enhancements as well as partial H/D exchange for the hydrogen atom in the ortho position of pyridine and concomitant formation of HD molecules. While the mechanism of polarization enhancement does not explicitly require chemical exchange of hydrogen atoms of parahydrogen and the substrate, the partial chemical modification of the substrate via hydrogen exchange means that SABRE under these conditions cannot rigorously be referred to as a non-hydrogenative parahydrogen induced polarization process.

Commonly used neuroimaging approaches in humans exploit hemodynamic or metabolic indicators of brain function. However, fundamental gaps remain in our ability to relate such hemo-metabolic reactivity to neurotransmission, with recent reports providing paradoxical information regarding the relationship among basal perfusion, functional imaging contrast, and neurotransmission in awake humans. Here, sequential magnetic resonance spectroscopy (MRS) measurements of the primary inhibitory neurotransmitter, γ-aminobutyric acid (GABA+macromolecules normalized by the complex N-acetyl aspartate-N-acetyl aspartyl glutamic acid: [GABA(+)]/[NAA-NAAG]), and magnetic resonance imaging (MRI) measurements of perfusion, fractional gray-matter volume, and arterial arrival time (AAT) are recorded in human visual cortex from a controlled cohort of young adult male volunteers with neurocognitive battery-confirmed comparable cognitive capacity (3 T; n=16; age=23±3 years). Regression analyses reveal an inverse correlation between [GABA(+)]/[NAA-NAAG] and perfusion (R=-0.46; P=0.037), yet no relationship between AAT and [GABA(+)]/[NAA-NAAG] (R=-0.12; P=0.33). Perfusion measurements that do not control for AAT variations reveal reduced correlations between [GABA(+)]/[NAA-NAAG] and perfusion (R=-0.13; P=0.32). These findings largely reconcile contradictory reports between perfusion and inhibitory tone, and underscore the physiologic origins of the growing literature relating functional imaging signals, hemodynamics, and neurotransmission.

Spin order obtained in the strong coupling regime of protons from parahydrogen-induced hyperpolarization (PHIP) is initially captured as an ensemble of singlet states. For biomedical applications of PHIP, locking this spin order on long-lived heteronuclear storage nuclei increases spectral dispersion, reduces background interference from water protons, and eliminates the need to synchronize subsequent detection pulse sequences to accrued singlet-state evolution. A variety of traditional sequences such as INEPT or HMQC are available to interconvert heteronuclear single quantum coherences at high field, but new approaches are required for converting singlet states into heteronuclear single quantum coherences at low field in the strong coupling regime of protons. Described here is a consolidated pulse sequence that achieves this transformation of singlet-state spin order into heteronuclear magnetization across a wide range of scalar couplings in AA'X spin systems. Analytic solutions to the spin evolution are presented, and performance was validated experimentally in the parahydrogen addition product, 2-hydroxyethyl 1-(13)C-propionate-d(3). Hyperpolarized carbon-13 signals were enhanced by a factor of several million relative to Boltzmann polarization in a static magnetic field of 47.5 mT (~13% polarization). We anticipate that this pulse sequence will provide efficient conversion of parahydrogen spin order over a broad range of emerging PHIP agents that feature AA'X spin systems.

Reported here is a water soluble Rh(I)-based catalyst for performing parahydrogen induced polarization (PHIP). The [Rh(I)(norbornadiene)(THP)(2)](+)[BF(4)](-) catalyst utilizes the monodentate phosphine ligand tris(hydroxymethyl)phosphine (THP). The monodentate PHIP catalyst is less susceptible to oxygenation by air and THP ligand and is significantly less expensive than bidentate water-soluble PHIP ligands. In situ PHIP detection with this monodentate Rh(I) based catalyst in water yielded 12% (13)C polarization for the parahydrogen addition product, 2-hydroxyethyl 1-(13)C-propionate-d(2,3,3) (HEP), with a (13)C T(1) relaxation of 108 seconds at 0.0475 T. PHIP polarization yields were high, reflecting efficient hydrogenation even under conditions of high content of the oxidized phosphine form of the THP ligand.

Applications of PASADENA in biomedicine are continuing to emerge due to recent demonstrations that hyperpolarized metabolic substrates and the corresponding reaction products persist sufficiently long to be detected in vivo. Biomedical applications of PASADENA typically differ from their basic science counterparts in that the polarization endowed by addition of parahydrogen is usually transferred from nascent protons to coupled storage nuclei for subsequent detection on a higher field imaging instrument. These pre-imaging preparations usually take place at low field, but commercial spectrometers capable of heteronuclear pulsed NMR at frequencies in the range of 100 kHz to 1 MHz are scarce though, in comparison to single channel consoles in that field regime. Reported here is a probe circuit that can be used in conjunction with a phase and amplitude modulation scheme we have developed called PANORAMIC (Precession And Nutation for Observing Rotations At Multiple Intervals about the Carrier), that expands a single channel console capability to double or generally multiple resonance with minimal hardware modifications. The demands of this application are geared towards uniform preparation, and since the hyperpolarized molecules are being detected externally at high field, detection sensitivity is secondary to applied field uniformity over a large reaction volume to accommodate heterogeneous chemistry of gas molecules at a liquid interface. The probe circuit was therefore configured with a large (40 mL) Helmholtz sample coil for uniformity, and double-tuned to the Larmor precession frequencies of (13)C/(1)H (128/510 kHz) within a custom solenoidal electromagnet at a static field of 12 mT. Traditional (on-resonant) as well as PANORAMIC NMR signals with signal to noise ratios of approximately 75 have been routinely acquired with this probe and spectrometer setup from 1024 repetitions on the high frequency channel. The proton excitation pulse width was 240 μs at 6.31 W, compared to a carbon-13 pulse width of 220 μs at 2.51 W. When PANORAMIC refocusing waveforms were transmitted at a carrier frequency of 319 kHz, integrated signal intensities from a spin-echo sequence at both proton (510 kHz) and carbon-13 (128 kHz) frequencies were within experimental error to block pulse analogs transmitted on resonance. We anticipate that this probe circuit design could be extended to higher and lower frequencies, and that when used in conjunction with PANORAMIC phase and amplitude modulated arrays, will enable low field imaging consoles to serve as multinuclear consoles., (Copyright © 2012 Elsevier Inc. All rights reserved.)

In this work we describe a large volume 340 mL (1)H-X magnetic resonance (MR) probe for studies of hyperpolarized compounds at 0.0475 T. (1)H/(13)C and (1)H/(15)N probe configurations are demonstrated with the potential for extension to (1)H/(129)Xe. The primary applications of this probe are preparation and quality assurance of (13)C and (15)N hyperpolarized contrast agents using PASADENA (parahydrogen and synthesis allow dramatically enhanced nuclear alignment) and other parahydrogen-based methods of hyperpolarization. The probe is efficient and permits 62 μs (13)C excitation pulses at 5.3 W, making it suitable for portable operation. The sensitivity and detection limits of this probe, tuned to (13)C, are compared with a commercial radio frequency (RF) coil operating at 4.7 T. We demonstrate that low field MR of hyperpolarized contrast agents could be as sensitive as conventional high field detection and outline potential improvements and optimization of the probe design for preclinical in vivo MRI. PASADENA application of this low-power probe is exemplified with (13)C hyperpolarized 2-hydroxyethyl propionate-1-(13)C,2,3,3-d(3)., (Copyright © 2012 Elsevier Inc. All rights reserved.)

We demonstrate that potassium 1-(13)C-phosphoenolpyruvate becomes hyperpolarized potassium 1-(13)C-phospholactate with (13)C T(1) = 36 s after molecular hydrogenation by PASADENA (Parahydrogen and Synthesis Allows Dramatically Enhanced Nuclear Alignment). This proof-of-principle study was conducted with a fully protonated molecular precursor. (13)C was polarized to a level of 1%, corresponding to nearly 4000-fold sensitivity enhancement at 3 T. The relevant homo- and heteronuclear spin-spin couplings are reported., (© 2012 American Chemical Society)

A device is presented for efficiently enriching parahydrogen by pulsed injection of ambient hydrogen gas. Hydrogen input to the generator is pulsed at high pressure to a catalyst chamber making thermal contact with the cold head of a closed-cycle cryocooler maintained between 15 and 20K. The system enables fast production (0.9 standard liters per minute) and allows for a wide range of production targets. Production rates can be systematically adjusted by varying the actuation sequence of high-pressure solenoid valves, which are controlled via an open source microcontroller to sample all combinations between fast and thorough enrichment by varying duration of hydrogen contact in the catalyst chamber. The entire enrichment cycle from optimization to quantification and storage kinetics are also described. Conversion of the para spin-isomer to orthohydrogen in borosilicate tubes was measured at 8 min intervals over a period of 64 h with a 12 T NMR spectrometer. These relaxation curves were then used to extract initial enrichment by exploiting the known equilibrium (relaxed) distribution of spin isomers with linear least squares fitting to a single exponential decay curve with an estimated error less than or equal to 1%. This procedure is time-consuming, but requires only one sample pressurized to atmosphere. Given that tedious matching to external references are unnecessary with this procedure, we find it to be useful for periodic inspection of generator performance. The equipment and procedures offer a variation in generator design that eliminate the need to meter flow while enabling access to increased rates of production. These tools for enriching and quantifying parahydrogen have been in steady use for 3 years and should be helpful as a template or as reference material for building and operating a parahydrogen production facility., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Magnetic resonance imaging (MRI) has played an important role in the diagnosis and management of cancer since it was first developed, but other modalities also continue to advance and provide complementary information on the status of tumors. In the future, there will be a major continuing role for noninvasive imaging in order to obtain information on the location and extent of cancer, as well as assessments of tissue characteristics that can monitor and predict treatment response and guide patient management. Developments are currently being undertaken that aim to provide improved imaging methods for the detection and evaluation of tumors, for identifying important characteristics of tumors such as the expression levels of cell surface receptors that may dictate what types of therapy will be effective and for evaluating their response to treatments. Molecular imaging techniques based mainly on radionuclide imaging can depict numerous, specific, cellular and molecular markers of disease and have unique potential to address important clinical and research challenges. In this review, we consider what continuing and evolving roles will be played by MRI in this era of molecular imaging. We discuss some of the challenges for MRI of detecting imaging agents that report on molecular events, but highlight also the ability of MRI to assess other features such as cell density, blood flow and metabolism which are not specific hallmarks of cancer but which reflect molecular changes. We discuss the future role of MRI in cancer and describe the use of selected quantitative imaging techniques for characterizing tumors that can be translated to clinical applications, particularly in the context of evaluating novel treatments., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Presented here is a centrally controlled, automated parahydrogen-based polarizer with in situ detection capability. A 20% polarization, corresponding to a 5,000,000-fold signal enhancement at 48 mT, is demonstrated on 2-hydroxyethyl-1-(13)C-propionate-d(2,3,3) using a double-tuned antenna and pulsed polarization transfer. In situ detection is a refinement of first-generation devices enabling fast calibration of rf pulses and B(0), quality assurance of hyperpolarized contrast agents, and stand-alone operation without the necessity of high-field MR spectrometers. These features are essential for biomedical applications of parahydrogen-based hyperpolarization and for clinical translation. We demonstrate the flexibility of the device by recording (13)C signal decay due to longitudinal relaxation of a hyperpolarized contrast agent at 48 mT corresponding to 2 MHz proton frequency. This appears to be the longest recorded T(1) (101 ± 7 s) for a (13)C hyperpolarized contrast agent in water.

Gamma-aminobutyric acid (GABA) and glutamate (Glu) levels, normalized to total creatine (tCr), were measured in the anterior cingulate and cerebellar vermis in healthy adults (n=19, age=24.6±6.4 years) using ¹H MRS at 3 T, and metabolite correlations across regions and subjects were determined. Mean anterior cingulate and cerebellar GABA/tCr ratios were 0.31 (0.08) and 0.23 (0.06), respectively, while corresponding Glu levels were 1.16 (0.10) and 0.70 (0.07), respectively. Anterior cingulate and cerebellar glutamate levels were correlated (r=0.6103, P=.0140), although it is noted that when adjusted for multiple comparisons, all correlations reported here cluster to a P value of .0583. It is unlikely that this correlation is driven by correlations in tCr, since interregional correlations were not observed for other metabolites referenced to tCr. Correlations were also observed among metabolites in both the anterior cingulate and cerebellar vermis. In the former, N-acetylasparate was linearly dependent on glutamate (r=0.6577, P=.0063) and, at or below this significance threshold, four metabolites were correlated in the cerebellar vermis (Ins/tCh: r=0.6261, P=.0109. NAA/tCh: r=0.6426, P=.0082. NAA/Glu: r=0.6412, P=.0085. tCh/Glu: r=0.6193, P=0.0122)., (Copyright © 2011 Elsevier Inc. All rights reserved.)

gamma-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter in human brain and has been implicated in several neuropsychiatric disorders. In vivo human brain GABA concentrations are near the detection limit for magnetic resonance spectroscopy ( approximately 1 mM), and because of overlap with more abundant compounds, spectral editing is generally necessary to detect GABA. In previous reports, GABA spectra edited by J-difference spectroscopy vary considerably in appearance. We have evaluated the factors that affect GABA spectra and the conditions necessary for robust acquisition of J-difference spectra from arbitrary brain regions. In particular, we demonstrate that variations in spectral quality can be explained in part by the incoherent addition of transients that results from shot to shot frequency and phase variations. An automated time-domain spectral alignment strategy that enables reproducible acquisition of high-quality GABA spectra at 3 T with a standard 30-cm T/R volume coil is presented. Representative GABA spectra from human frontal lobe, an area where susceptibility-induced frequency and phase variations are especially troublesome, that demonstrate the robustness of the acquisition and data handling strategy used in this study are presented.

Complete (17)O chemical shielding (CS) and quadrupole coupling (QC) tensors and their molecular orientations were determined for the central residues in two tripeptides Gly-Gly-Val (GGV) and Ala-Gly-Gly (AGG) by single-crystal NMR methods. Tensor orientations in the two peptides are very similar, however, principal components are different. The most shielded CS and smallest magnitude QC components are normal to the peptide plane, while the most deshielded CS and largest QC components are in the peptide plane either at an angle of 17 degrees (CS) or perpendicular (QC) to the C=O bond. Comparisons of principal components from experiment and DFT calculations indicate that the smaller shielding tensor span in GGV (549 ppm) compared to AGG (606 ppm) is likely due to two factors: a shorter "direct" H-bond distance to the peptide carbonyl oxygen and an "indirect" H bond of the peptide NH to a carboxylate rather than a carbonyl. We anticipate that (17)O NMR should be generally useful for probing H-bonding and local electrostatic interactions in proteins and polypeptides. Using the single-crystal data as an accurate reference, we show that a useful subset of the NMR parameters, QC and CS principal components and their relative orientation, can be obtained with reasonable accuracy from a very high-field (21.2 T), stationary sample powder spectrum.

Li(+) and Ca(2+) binding to the carbonyl oxygen sites of a model peptide system has been studied by (17)O solid-state NMR spectroscopy. (17)O chemical shift (CS) and quadrupole coupling (QC) tensors are determined in four Gly-(Gly-(17)O)-Gly polymorphs by a combination of stationary and fast magic-angle spinning (MAS) methods at high magnetic field, 19.6 T. In the crystal lattice, the carbonyl oxygen of the central glycyl residue in two gly-gly-gly polymorphs form intermolecular hydrogen bonds with amides, whereas the corresponding carbonyl oxygens of the other two polymorphs form interactions with Li(+) and Ca(2+) ions. This permits a comparison of perturbations on (17)O NMR properties by ion binding and intermolecular hydrogen bonding. High quality spectra are augmented by density functional theory (DFT) calculations on large molecular clusters to gain additional theoretical insights and to aid in the spectral simulations. Ion binding significantly decreases the two (17)O chemical shift tensor components in the peptide plane, delta(11) and delta(22), and, thus, a substantial change in the isotropic chemical shift. In addition, quadrupole coupling constants are decreased by up to 1 MHz. The effects of ion binding are found to be almost an order of magnitude greater than those induced by hydrogen bonding.

15N shielding tensors were determined for the central peptide groups in GGV, AGG, and APG by single-crystal NMR. We find that the angle between the downfield component (delta11) and the N-H or the N-C(delta) (pro) bonds is in the range of 20-23 degrees and in accord with previous solid-state NMR measurements. However, AGG, unlike APG or GGV, has a distorted peptide plane, and delta11 lies approximately in the plane of N, C(alpha), and H rather than in the peptide plane defined by heavy atoms. Accurate orientations of delta22 and delta33 were determined, and the usual assumption that delta22 is along the peptide normal was found only in APG which has a highly nonaxial tensor. More generally, delta22 and delta33 are rotated about the delta11 axis (36 degrees in GGV). These results are compared with DFT calculations to gain a structural understanding of the effects of intermolecular interactions on shielding tensor principal components and orientations. Trimeric clusters containing H-bonded neighbors predict the orientations of the principal components within 2-3 degrees, but calculated principal components are less quantitative. Possible reasons for this disagreement are explored.

15N chemical shielding parameters are reported for central glycyl residues in crystallographically characterized tripeptides with alpha-helix, beta-strand, polyglycine II (3(1)-helix), and extended structures. Accurate values of the shielding components (2-5 ppm) are determined from MAS and stationary spectra of peptides containing [2-(13)C,(15)N]Gly. Two dipolar couplings, (1)H-(15)N and (13)C(alpha)-(15)N, are used to examine (15)N shielding tensor orientations in the molecular frame and the results indicate that the delta(11), delta(33) plane of the shielding tensor is not coincident with the peptide plane. The observed isotropic shifts, which vary over a range of 13 ppm, depend on hydrogen bonding (direct and indirect) and local conformation. Tensor spans, delta(span) = delta(11) - delta(33), and their deviations from axial symmetry, delta(dev) = delta(22) - delta(33), vary over a larger range and are grouped according to 2 degrees structure. Augmented by previously reported (13)C(alpha) shielding parameters, a prediction scheme for the 2 degrees structure of glycyl residues in proteins based on shielding parameters is proposed.