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XeUS: A second-generation automated open-source batch-mode clinical-scale hyperpolarizer. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2020; 319:106813. [PMID: 32932118 DOI: 10.1016/j.jmr.2020.106813] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2020] [Revised: 08/20/2020] [Accepted: 08/24/2020] [Indexed: 06/11/2023]
Abstract
We present a second-generation open-source automated batch-mode 129Xe hyperpolarizer (XeUS GEN-2), designed for clinical-scale hyperpolarized (HP) 129Xe production via spin-exchange optical pumping (SEOP) in the regimes of high Xe density (0.66-2.5 atm partial pressure) and resonant photon flux (~170 W, Δλ = 0.154 nm FWHM), without the need for cryo-collection typically employed by continuous-flow hyperpolarizers. An Arduino micro-controller was used for hyperpolarizer operation. Processing open-source software was employed to program a custom graphical user interface (GUI), capable of remote automation. The Arduino Integrated Development Environment (IDE) was used to design a variety of customized automation sequences such as temperature ramping, NMR signal acquisition, and SEOP cell refilling for increased reliability. A polycarbonate 3D-printed oven equipped with a thermo-electric cooler/heater provides thermal stability for SEOP for both binary (Xe/N2) and ternary (4He-containing) SEOP cell gas mixtures. Quantitative studies of the 129Xe hyperpolarization process demonstrate that near-unity polarization can be achieved in a 0.5 L SEOP cell. For example, %PXe of 93.2 ± 2.9% is achieved at 0.66 atm Xe pressure with polarization build-up rate constant γSEOP = 0.040 ± 0.005 min-1, giving a max dose equivalent ≈ 0.11 L/h 100% hyperpolarized, 100% enriched 129Xe; %PXe of 72.6 ± 1.4% is achieved at 1.75 atm Xe pressure with γSEOP of 0.041 ± 0.001 min-1, yielding a corresponding max dose equivalent of 0.27 L/h. Quality assurance studies on this device have demonstrated the potential to refill SEOP cells hundreds of times without significant losses in performance, with average %PXe = 71.7%, (standard deviation σP = 1.52%) and mean polarization lifetime T1 = 90.5 min, (standard deviation σT = 10.3 min) over the first ~200 gas mixture refills, with sufficient performance maintained across a further ~700 refills. These findings highlight numerous technological developments and have significant translational relevance for efficient production of gaseous HP 129Xe contrast agents for use in clinical imaging and bio-sensing techniques.
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Helium-rich mixtures for improved batch-mode clinical-scale spin-exchange optical pumping of Xenon-129. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2020; 315:106739. [PMID: 32408239 DOI: 10.1016/j.jmr.2020.106739] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2020] [Accepted: 04/24/2020] [Indexed: 06/11/2023]
Abstract
We present studies of spin-exchange optical pumping (SEOP) using ternary xenon-nitrogen-helium gas mixtures at high xenon partial pressures (up to 1330 Torr partial pressure at loading, out of 2660 Torr total pressure) in a 500-mL volume SEOP cell, using two automated batch-mode clinical-scale 129Xe hyperpolarizers operating under continuous high-power (~170 W) pump laser irradiation. In this pilot study, we explore SEOP in gas mixtures with up to 45% 4He content under a wide range of experimental conditions. When an aluminum jacket cooling/heating design was employed (GEN-3 hyperpolarizer), 129Xe polarization (%PXe) of 55.9 ± 0.9% was observed with mono-exponential build-up rate γSEOP of 0.049 ± 0.001 min-1 for the 4He-rich mixture (1000 Torr Xe/900 Torr He, 100 Torr N2), compared to %PXe of 49.3 ± 3.3% at γSEOP of 0.035 ± 0.004 min-1 for the N2-rich gas mixture (1000 Torr Xe/100 Torr He, 900 Torr N2). When forced-air cooling/heating was used (GEN-2 hyperpolarizer), %PXe of 83.9 ± 2.7% was observed at γSEOP of 0.045 ± 0.005 min-1 for the 4He-rich mixture (1000 Torr Xe/900 Torr He, 100 Torr N2), compared to %PXe of 73.5 ± 1.3% at γSEOP of 0.028 ± 0.001 min-1 for the N2-rich gas mixture (1000 Torr Xe and 1000 Torr N2). Additionally, %PXe of 72.6 ± 1.4% was observed at a build-up rate γSEOP of 0.041 ± 0.003 min-1 for a super-high-density 4He-rich mixture (1330 Torr Xe/1200 Torr 4He/130 Torr N2), compared to %PXe = 56.6 ± 1.3% at a build-up rate of γSEOP of 0.034 ± 0.002 min-1 for an N2-rich mixture (1330 Torr Xe/1330 Torr N2) using forced air cooling/heating. The observed SEOP hyperpolarization performance under these conditions corresponds to %PXe improvement by a factor of 1.14 ± 0.04 at 1000 Torr Xe density and by up to a factor of 1.28 ± 0.04 at 1330 Torr Xe density at improved SEOP build-up rates by factors of 1.61 ± 0.18 and 1.21 ± 0.11 respectively. Record %PXe levels have been obtained here: 83.9 ± 2.7% at 1000 Torr Xe partial pressure and 72.6 ± 1.4% at 1330 Torr Xe partial pressure. In addition to improved thermal stability for SEOP, the use of 4He-rich gas mixtures also reduces the overall density of produced inhalable HP contrast agents; this property may be desirable for HP 129Xe inhalation by human subjects in clinical settings-especially in populations with heavily impaired lung function. The described approach should enjoy ready application in the production of inhalable 129Xe contrast agent with near-unity 129Xe nuclear spin polarization.
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Batch-Mode Clinical-Scale Optical Hyperpolarization of Xenon-129 Using an Aluminum Jacket with Rapid Temperature Ramping. Anal Chem 2020; 92:4309-4316. [PMID: 32073251 DOI: 10.1021/acs.analchem.9b05051] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
We present spin-exchange optical pumping (SEOP) using a third-generation (GEN-3) automated batch-mode clinical-scale 129Xe hyperpolarizer utilizing continuous high-power (∼170 W) pump laser irradiation and a novel aluminum jacket design for rapid temperature ramping of xenon-rich gas mixtures (up to 2 atm partial pressure). The aluminum jacket design is capable of heating SEOP cells from ambient temperature (typically 25 °C) to 70 °C (temperature of the SEOP process) in 4 min, and perform cooling of the cell to the temperature at which the hyperpolarized gas mixture can be released from the hyperpolarizer (with negligible amounts of Rb metal leaving the cell) in approximately 4 min, substantially faster (by a factor of 6) than previous hyperpolarizer designs relying on air heat exchange. These reductions in temperature cycling time will likely be highly advantageous for the overall increase of production rates of batch-mode (i.e., stopped-flow) 129Xe hyperpolarizers, which is particularly beneficial for clinical applications. The additional advantage of the presented design is significantly improved thermal management of the SEOP cell. Accompanying the heating jacket design and performance, we also evaluate the repeatability of SEOP experiments conducted using this new architecture, and present typically achievable hyperpolarization levels exceeding 40% at exponential build-up rates on the order of 0.1 min-1.
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High Xe density, high photon flux, stopped-flow spin-exchange optical pumping: Simulations versus experiments. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2020; 312:106686. [PMID: 32006793 PMCID: PMC7436892 DOI: 10.1016/j.jmr.2020.106686] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/31/2019] [Accepted: 01/07/2020] [Indexed: 05/13/2023]
Abstract
Spin-exchange optical pumping (SEOP) can enhance the NMR sensitivity of noble gases by up to five orders of magnitude at Tesla-strength magnetic fields. SEOP-generated hyperpolarised (HP) 129Xe is a promising contrast agent for lung imaging but an ongoing barrier to widespread clinical usage has been economical production of sufficient quantities with high 129Xe polarisation. Here, the 'standard model' of SEOP, which was previously used in the optimisation of continuous-flow 129Xe polarisers, is modified for validation against two Xe-rich stopped-flow SEOP datasets. We use this model to examine ways to increase HP Xe production efficiency in stopped-flow 129Xe polarisers and provide further insight into the underlying physics of Xe-rich stopped-flow SEOP at high laser fluxes.
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A pulse programmable parahydrogen polarizer using a tunable electromagnet and dual channel NMR spectrometer. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2017; 284:115-124. [PMID: 29028543 PMCID: PMC5708540 DOI: 10.1016/j.jmr.2017.09.013] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2017] [Revised: 09/20/2017] [Accepted: 09/28/2017] [Indexed: 05/12/2023]
Abstract
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 B0/B1 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-1-13C-d3, where the 13C polarization was estimated to be P13C=20±2.5% corresponding to 13C signal enhancement approximately 25 million-fold at 9.1 mT or approximately 77,000-fold 13C enhancement at 3 T with respect to thermally induced polarization at room temperature.
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High-resolution hyperpolarized in vivo metabolic 13C spectroscopy at low magnetic field (48.7mT) following murine tail-vein injection. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2017; 281:246-252. [PMID: 28651245 PMCID: PMC5544012 DOI: 10.1016/j.jmr.2017.06.009] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Revised: 06/12/2017] [Accepted: 06/14/2017] [Indexed: 05/20/2023]
Abstract
High-resolution 13C NMR spectroscopy of hyperpolarized succinate-1-13C-2,3-d2 is reported in vitro and in vivo using a clinical-scale, biplanar (80cm-gap) 48.7mT permanent magnet with a high homogeneity magnetic field. Non-localized 13C NMR spectra were recorded at 0.52MHz resonance frequency over the torso of a tumor-bearing mouse every 2s. Hyperpolarized 13C NMR signals with linewidths of ∼3Hz (corresponding to ∼6ppm) were recorded in vitro (2mL in a syringe) and in vivo (over a mouse torso). Comparison of the full width at half maximum (FWHM) for 13C NMR spectra acquired at 48.7mT and at 4.7T in a small-animal MRI scanner demonstrates a factor of ∼12 improvement for the 13C resonance linewidth attainable at 48.7mT compared to that at 4.7T in vitro. 13C hyperpolarized succinate-1-13C resonance linewidths in vivo are at least one order of magnitude narrower at 48.7mT compared to those observed in high-field (≥3T) studies employing HP contrast agents. The demonstrated high-resolution 13C in vivo spectroscopy could be useful for high-sensitivity spectroscopic studies involving monitoring HP agent uptake or detecting metabolism using HP contrast agents with sufficiently large 13C chemical shift differences.
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Aqueous, Heterogeneous Parahydrogen-Induced 15N Polarization. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2017; 121:15304-15309. [PMID: 29238438 PMCID: PMC5723423 DOI: 10.1021/acs.jpcc.7b05912] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2017] [Revised: 06/20/2017] [Indexed: 05/20/2023]
Abstract
The successful transfer of parahydrogen-induced polarization to 15N spins using heterogeneous catalysts in aqueous solutions was demonstrated. Hydrogenation of a synthesized unsaturated 15N-labeled precursor (neurine) with parahydrogen (p-H2) over Rh/TiO2 heterogeneous catalysts yielded a hyperpolarized structural analog of choline. As a result, 15N polarization enhancements of over two orders of magnitude were achieved for the 15N-ethyl trimethyl ammonium ion product in deuterated water at elevated temperatures. Enhanced 15N NMR spectra were successfully acquired at 9.4 T and 0.05 T. Importantly, long hyperpolarization lifetimes were observed at 9.4 T, with a 15N T1 of ~6 min for the product molecules, and the T1 of the deuterated form exceeded 8 min. Taken together, these results show that this approach for generating hyperpolarized species with extended lifetimes in aqueous, biologically compatible solutions is promising for various biomedical applications.
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Robust Imidazole‐
15
N
2
Synthesis for High‐Resolution Low‐Field (0.05 T)
15
N Hyperpolarized NMR Spectroscopy. ChemistrySelect 2017. [DOI: 10.1002/slct.201700718] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
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NMR Spin-Lock Induced Crossing (SLIC) dispersion and long-lived spin states of gaseous propane at low magnetic field (0.05T). JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2017; 276:78-85. [PMID: 28152435 PMCID: PMC5452975 DOI: 10.1016/j.jmr.2017.01.014] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2016] [Revised: 01/17/2017] [Accepted: 01/19/2017] [Indexed: 05/22/2023]
Abstract
When parahydrogen reacts with propylene in low magnetic fields (e.g., 0.05T), the reaction product propane develops an overpopulation of pseudo-singlet nuclear spin states. We studied how the Spin-Lock Induced Crossing (SLIC) technique can be used to convert these pseudo-singlet spin states of hyperpolarized gaseous propane into observable magnetization and to detect 1H NMR signal directly at 0.05T. The theoretical simulation and experimental study of the NMR signal dependence on B1 power (SLIC amplitude) exhibits a well-resolved dispersion, which is induced by the spin-spin couplings in the eight-proton spin system of propane. We also measured the exponential decay time constants (TLLSS or TS) of these pseudo-singlet long-lived spin states (LLSS) by varying the time between hyperpolarized propane production and SLIC detection. We have found that, on average, TS is approximately 3 times longer than the corresponding T1 value under the same conditions in the range of pressures studied (up to 7.6atm). Moreover, TS may exceed 13s at pressures above 7atm in the gas phase. These results are in agreement with the previous reports, and they corroborate a great potential of long-lived hyperpolarized propane as an inhalable gaseous contrast agent for lung imaging and as a molecular tracer to study porous media using low-field NMR and MRI.
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Abstract
Nuclear spin polarization can be significantly increased through the process of hyperpolarization, leading to an increase in the sensitivity of nuclear magnetic resonance (NMR) experiments by 4-8 orders of magnitude. Hyperpolarized gases, unlike liquids and solids, can often be readily separated and purified from the compounds used to mediate the hyperpolarization processes. These pure hyperpolarized gases enabled many novel MRI applications including the visualization of void spaces, imaging of lung function, and remote detection. Additionally, hyperpolarized gases can be dissolved in liquids and can be used as sensitive molecular probes and reporters. This Minireview covers the fundamentals of the preparation of hyperpolarized gases and focuses on selected applications of interest to biomedicine and materials science.
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NMR SLIC Sensing of Hydrogenation Reactions Using Parahydrogen in Low Magnetic Fields. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2016; 120:29098-29106. [PMID: 28066517 PMCID: PMC5204359 DOI: 10.1021/acs.jpcc.6b07555] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Revised: 10/26/2016] [Indexed: 05/12/2023]
Abstract
Parahydrogen-induced polarization (PHIP) is an NMR hyperpolarization technique that increases nuclear spin polarization by orders of magnitude, and it is particularly well-suited to study hydrogenation reactions. However, the use of high-field NMR spectroscopy is not always possible, especially in the context of potential industrial-scale reactor applications. On the other hand, the direct low-field NMR detection of reaction products with enhanced nuclear spin polarization is challenging due to near complete signal cancellation from nascent parahydrogen protons. We show that hydrogenation products prepared by PHIP can be irradiated with weak (on the order of spin-spin couplings of a few hertz) alternating magnetic field (called Spin-Lock Induced Crossing or SLIC) and consequently efficiently detected at low magnetic field (e.g., 0.05 T used here) using examples of several types of organic molecules containing a vinyl moiety. The detected hyperpolarized signals from several reaction products at tens of millimolar concentrations were enhanced by 10000-fold, producing NMR signals an order of magnitude greater than the background signal from protonated solvents.
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Abstract
We report on a simple approach for efficient NMR proton hyperpolarization of propane using the parahydrogen-induced polarization (PHIP) technique, which yielded ≈6.2 % proton polarization using ≈80 % parahydrogen, a record level achieved with any hyperpolarization technique for propane. Unlike in previously developed approaches designed for continuous-flow operation, where reactants (propene and parahydrogen) are simultaneously loaded for homogeneous or heterogeneous pairwise addition of parahydrogen, here a batch-mode method is applied: propene is first loaded into the catalyst-containing solution, which is followed by homogeneous hydrogenation via parahydrogen bubbling delivered at ≈7.1 atm. The achieved nuclear spin polarization of this contrast agent potentially useful for pulmonary imaging is approximately two orders of magnitude greater than that achieved in the continuous-flow homogeneous catalytic hydrogenation, and a factor of 3-10 more efficient compared to the typical results of heterogeneous continuous-flow hydrogenations.
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Open-Source Automated Parahydrogen Hyperpolarizer for Molecular Imaging Using (13)C Metabolic Contrast Agents. Anal Chem 2016; 88:8279-88. [PMID: 27478927 PMCID: PMC4991553 DOI: 10.1021/acs.analchem.6b02130] [Citation(s) in RCA: 76] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
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An
open-source hyperpolarizer producing 13C hyperpolarized
contrast agents using parahydrogen induced polarization (PHIP) for
biomedical and other applications is presented. This PHIP hyperpolarizer
utilizes an Arduino microcontroller in conjunction with a readily
modified graphical user interface written in the open-source processing
software environment to completely control the PHIP hyperpolarization
process including remotely triggering an NMR spectrometer for efficient
production of payloads of hyperpolarized contrast agent and in situ quality assurance of the produced hyperpolarization.
Key advantages of this hyperpolarizer include: (i) use of open-source
software and hardware seamlessly allowing for replication and further
improvement as well as readily customizable integration with other
NMR spectrometers or MRI scanners (i.e., this is a multiplatform design),
(ii) relatively low cost and robustness, and (iii) in situ detection capability and complete automation. The device performance
is demonstrated by production of a dose (∼2–3 mL) of
hyperpolarized 13C-succinate with %P13C ∼ 28% and 30 mM concentration and 13C-phospholactate
at %P13C ∼ 15% and 25 mM concentration
in aqueous medium. These contrast agents are used for ultrafast molecular
imaging and spectroscopy at 4.7 and 0.0475 T. In particular, the conversion
of hyperpolarized 13C-phospholactate to 13C-lactate in vivo is used here to demonstrate the feasibility of ultrafast
multislice 13C MRI after tail vein injection of hyperpolarized 13C-phospholactate in mice.
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NMR Signal Amplification by Reversible Exchange of Sulfur-Heterocyclic Compounds Found In Petroleum. ChemistrySelect 2016; 1:2552-2555. [PMID: 27500206 DOI: 10.1002/slct.201600761] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
NMR hyperpolarization via Signal Amplification by Reversible Exchange (SABRE) was employed to investigate the feasibility of enhancing the NMR detection sensitivity of sulfur-heterocycles (specifically 2-methylthiophene and dibenzothiophenes), a family of compounds typically found in petroleum and refined petroleum products. SABRE hyperpolarization of sulfur-heterocycles (conducted in seconds) offers potential advantages of providing structural information about sulfur-containing contaminants in petroleum, thereby informing petroleum purification and refining to minimize sulfur content in refined products such as gasoline. Moreover, NMR spectroscopy sensitivity gains endowed by hyperpolarization potentially allows for performing structural assays using inexpensive, low-magnetic-field (ca. 1 T) high-resolution NMR spectrometers ideally suited for industrial applications in the field.
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Toward Production of Pure 13C Hyperpolarized Metabolites Using Heterogeneous Parahydrogen-Induced Polarization of Ethyl[1- 13C]acetate. RSC Adv 2016; 6:69728-69732. [PMID: 28042472 DOI: 10.1039/c6ra15808k] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Here, we report the production of 13C-hyperpolarized ethyl acetate via heterogeneously catalyzed pairwise addition of parahydrogen to vinyl acetate over TiO2-supported rhodium nanoparticles, followed by magnetic field cycling. Importantly, the hyperpolarization is demonstrated even at the natural abundance of 13C isotope (ca. 1.1%) along with the easiest separation of the catalyst from the hyperpolarized liquid.
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15N Hyperpolarization of Imidazole- 15N 2 for Magnetic Resonance pH Sensing via SABRE-SHEATH. ACS Sens 2016; 1:640-644. [PMID: 27379344 PMCID: PMC4924567 DOI: 10.1021/acssensors.6b00231] [Citation(s) in RCA: 100] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Accepted: 04/14/2016] [Indexed: 12/17/2022]
Abstract
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15N nuclear spins of imidazole-15N2 were
hyperpolarized using NMR signal amplification by reversible
exchange in shield enables alignment transfer to heteronuclei (SABRE-SHEATH).
A 15N NMR signal enhancement of ∼2000-fold at 9.4
T is reported using parahydrogen gas (∼50% para-) and ∼0.1
M imidazole-15N2 in methanol:aqueous buffer
(∼1:1). Proton binding to a 15N site of imidazole
occurs at physiological pH (pKa ∼
7.0), and the binding event changes the 15N isotropic chemical
shift by ∼30 ppm. These properties are ideal for in vivo pH
sensing. Additionally, imidazoles have low toxicity and are readily
incorporated into a wide range of biomolecules. 15N-Imidazole
SABRE-SHEATH hyperpolarization potentially enables pH sensing on scales
ranging from peptide and protein molecules to living organisms.
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Over 20% (15)N Hyperpolarization in Under One Minute for Metronidazole, an Antibiotic and Hypoxia Probe. J Am Chem Soc 2016; 138:8080-3. [PMID: 27321159 PMCID: PMC4937835 DOI: 10.1021/jacs.6b04784] [Citation(s) in RCA: 111] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Direct NMR hyperpolarization of naturally abundant (15)N sites in metronidazole is demonstrated using SABRE-SHEATH (Signal Amplification by Reversible Exchange in SHield Enables Alignment Transfer to Heteronuclei). In only a few tens of seconds, nuclear spin polarization P(15)N of up to ∼24% is achieved using parahydrogen with 80% para fraction corresponding to P(15)N ≈ 32% if ∼100% parahydrogen were employed (which would translate to a signal enhancement of ∼0.1-million-fold at 9.4 T). In addition to this demonstration on the directly binding (15)N site (using J(2)H-(15)N), we also hyperpolarized more distant (15)N sites in metronidazole using longer-range spin-spin couplings (J(4)H-(15)N and J(5)H-(15)N). Taken together, these results significantly expand the range of molecular structures and sites amenable to hyperpolarization via low-cost parahydrogen-based methods. In particular, hyperpolarized nitroimidazole and its derivatives have powerful potential applications such as direct in vivo imaging of mechanisms of action or hypoxia sensing.
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Aqueous NMR Signal Enhancement by Reversible Exchange in a Single Step Using Water-Soluble Catalysts. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2016; 120:12149-12156. [PMID: 27350846 PMCID: PMC4918635 DOI: 10.1021/acs.jpcc.6b04484] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2016] [Revised: 05/11/2016] [Indexed: 05/26/2023]
Abstract
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 1H signals of pyridine in water with only 1 atm of parahydrogen.
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Efficient Synthesis of Molecular Precursors for Para‐Hydrogen‐Induced Polarization of Ethyl Acetate‐1‐
13
C and Beyond. Angew Chem Int Ed Engl 2016. [DOI: 10.1002/ange.201600521] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Efficient Synthesis of Molecular Precursors for Para-Hydrogen-Induced Polarization of Ethyl Acetate-1-(13) C and Beyond. Angew Chem Int Ed Engl 2016; 55:6071-4. [PMID: 27061815 DOI: 10.1002/anie.201600521] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2016] [Revised: 02/18/2016] [Indexed: 12/15/2022]
Abstract
A scalable and versatile methodology for production of vinylated carboxylic compounds with (13) C isotopic label in C1 position is described. It allowed synthesis of vinyl acetate-1-(13) C, which is a precursor for preparation of (13) C hyperpolarized ethyl acetate-1-(13) C, which provides a convenient vehicle for potential in vivo delivery of hyperpolarized acetate to probe metabolism in living organisms. Kinetics of vinyl acetate molecular hydrogenation and polarization transfer from para-hydrogen to (13) C via magnetic field cycling were investigated. Nascent proton nuclear spin polarization (%PH ) of ca. 3.3 % and carbon-13 polarization (%P13C ) of ca. 1.8 % were achieved in ethyl acetate utilizing 50 % para-hydrogen corresponding to ca. 50 % polarization transfer efficiency. The use of nearly 100% para-hydrogen and the improvements of %PH of para-hydrogen-nascent protons may enable production of (13) C hyperpolarized contrast agents with %P13C of 20-50 % in seconds using this chemistry.
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Hyperpolarization of "Neat" Liquids by NMR Signal Amplification by Reversible Exchange. J Phys Chem Lett 2015; 6:1961-7. [PMID: 26029349 PMCID: PMC4442667 DOI: 10.1021/acs.jpclett.5b00782] [Citation(s) in RCA: 83] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2015] [Accepted: 05/08/2015] [Indexed: 05/20/2023]
Abstract
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.
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15N Hyperpolarization by Reversible Exchange Using SABRE-SHEATH. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2015; 119:8786-8797. [PMID: 25960823 PMCID: PMC4419867 DOI: 10.1021/acs.jpcc.5b01799] [Citation(s) in RCA: 181] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2015] [Revised: 03/28/2015] [Indexed: 05/14/2023]
Abstract
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% 15N-polarization (Theis, T.; et al. J. Am. Chem. Soc.2015, 137, 1404). Hyperpolarization on 15N (and heteronuclei in general) may be advantageous because of the long-lived nature of the hyperpolarization on 15N 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 15N 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 15N-hyperpolarization. The effects of parahydrogen pressure, flow rate, sample temperature, catalyst-to-substrate ratio, relaxation time (T1), and reversible oxygen quenching are studied on a test system of 15N-pyridine in methanol-d4. Moreover, we demonstrate the first proof-of-principle 13C-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 15N images (2 × 2 mm2 resolution). Importantly, this method enables hyperpolarization of molecular sites with NMR T1 relaxation times suitable for biomedical imaging and spectroscopy.
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Abstract
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.
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Propane- d6 Heterogeneously Hyperpolarized by Parahydrogen. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2014; 118:28234-28243. [PMID: 25506406 PMCID: PMC4259496 DOI: 10.1021/jp508719n] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Revised: 11/06/2014] [Indexed: 05/20/2023]
Abstract
Long-lived spin states of hyperpolarized propane-d6 gas were demonstrated following pairwise addition of parahydrogen gas to propene-d6 using heterogeneous parahydrogen-induced polarization (HET-PHIP). Hyperpolarized molecules were synthesized using Rh/TiO2 solid catalyst with 1.6 nm Rh nanoparticles. Hyperpolarized (PH ∼ 1%) propane-d6 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 mm3 and 17.7 s, respectively. Stopped-flow hyperpolarized propane-d6 gas was also detected at 0.0475 T with an observed nuclear spin polarization of PH ∼ 0.1% and a relatively long lifetime with T1,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 T1,eff of HP propane-d6 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 mm2 spatial and ∼0.7 s temporal resolution, respectively, at 0.0475 T.
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Irreversible catalyst activation enables hyperpolarization and water solubility for NMR signal amplification by reversible exchange. J Phys Chem B 2014; 118:13882-9. [PMID: 25372972 PMCID: PMC4259498 DOI: 10.1021/jp510825b] [Citation(s) in RCA: 117] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
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.
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In situ and ex situ low-field NMR spectroscopy and MRI endowed by SABRE hyperpolarization. Chemphyschem 2014; 15:4100-7. [PMID: 25367202 DOI: 10.1002/cphc.201402607] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2014] [Revised: 09/26/2014] [Indexed: 12/11/2022]
Abstract
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.
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Abstract
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.
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LIGHT-SABRE enables efficient in-magnet catalytic hyperpolarization. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2014; 248:23-6. [PMID: 25299767 PMCID: PMC6097635 DOI: 10.1016/j.jmr.2014.09.005] [Citation(s) in RCA: 140] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2014] [Accepted: 09/01/2014] [Indexed: 05/05/2023]
Abstract
Nuclear spin hyperpolarization overcomes the sensitivity limitations of traditional NMR and MRI, but the most general method demonstrated to date (dynamic nuclear polarization) has significant limitations in scalability, cost, and complex apparatus design. As an alternative, signal amplification by reversible exchange (SABRE) of parahydrogen on transition metal catalysts can hyperpolarize a variety of substrates, but to date this scheme has required transfer of the sample to low magnetic field or very strong RF irradiation. Here we demonstrate "Low-Irradiation Generation of High Tesla-SABRE" (LIGHT-SABRE) which works with simple pulse sequences and low power deposition; it should be usable at any magnetic field and for hyperpolarization of many different nuclei. This approach could drastically reduce the cost and complexity of producing hyperpolarized molecules.
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High-Resolution 3D Proton MRI of Hyperpolarized Gas Enabled by Parahydrogen and Rh/TiO 2Heterogeneous Catalyst. Chemistry 2014. [DOI: 10.1002/chem.201404052] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Cover Picture: High-Resolution 3D Proton MRI of Hyperpolarized Gas Enabled by Parahydrogen and Rh/TiO 2Heterogeneous Catalyst (Chem. Eur. J. 37/2014). Chemistry 2014. [DOI: 10.1002/chem.201490154] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Abstract
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.
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Abstract
We describe temperature-ramped spin-exchange optical pumping (TR-SEOP) in an automated high-throughput batch-mode (129)Xe hyperpolarizer utilizing three key temperature regimes: (i) "hot"-where the (129)Xe hyperpolarization rate is maximal, (ii) "warm"-where the (129)Xe hyperpolarization approaches unity, and (iii) "cool"-where hyperpolarized (129)Xe gas is transferred into a Tedlar bag with low Rb content (<5 ng per ∼1 L dose) suitable for human imaging applications. Unlike with the conventional approach of batch-mode SEOP, here all three temperature regimes may be operated under continuous high-power (170 W) laser irradiation, and hyperpolarized (129)Xe gas is delivered without the need for a cryocollection step. The variable-temperature approach increased the SEOP rate by more than 2-fold compared to the constant-temperature polarization rate (e.g., giving effective values for the exponential buildup constant γSEOP of 62.5 ± 3.7 × 10(-3) min(-1) vs 29.9 ± 1.2 × 10(-3) min(-1)) while achieving nearly the same maximum %PXe value (88.0 ± 0.8% vs 90.1% ± 0.8%, for a 500 Torr (67 kPa) Xe cell loading-corresponding to nuclear magnetic resonance/magnetic resonance imaging (NMR/MRI) enhancements of ∼3.1 × 10(5) and ∼2.32 × 10(8) at the relevant fields for clinical imaging and HP (129)Xe production of 3 T and 4 mT, respectively); moreover, the intercycle "dead" time was also significantly decreased. The higher-throughput TR-SEOP approach can be implemented without sacrificing the level of (129)Xe hyperpolarization or the experimental stability for automation-making this approach beneficial for improving the overall (129)Xe production rate in clinical settings.
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Abstract
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.
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High-resolution 3D proton MRI of hyperpolarized gas enabled by parahydrogen and Rh/TiO2 heterogeneous catalyst. Chemistry 2014; 20:11636-9. [PMID: 24961814 DOI: 10.1002/chem.201403604] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2014] [Indexed: 11/11/2022]
Abstract
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.
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Demonstration of heterogeneous parahydrogen induced polarization using hyperpolarized agent migration from dissolved Rh(I) complex to gas phase. Anal Chem 2014; 86:6192-6. [PMID: 24918975 PMCID: PMC4079322 DOI: 10.1021/ac5013859] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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Parahydrogen-induced polarization
(PHIP) was used to demonstrate
the concept that highly polarized, catalyst-free fluids can be obtained
in a catalysis-free regime using a chemical reaction with molecular
addition of parahydrogen to a water-soluble Rh(I) complex carrying
a payload of compound with unsaturated (C=C) bonds. Hydrogenation
of norbornadiene leads to formation of norbornene, which is eliminated
from the Rh(I) complex and, therefore, leaves the aqueous phase and
becomes a gaseous hyperpolarized molecule. The Rh(I) metal complex
resides in the original liquid phase, while the product of hydrogen
addition is found exclusively in the gaseous phase based on the affinity.
Hyperpolarized norbornene 1H NMR signals observed in situ were enhanced by a factor of approximately 10 000
at a static field of 47.5 mT. High-resolution 1H NMR at
a field of 9.4 T was used for ex situ detection of
hyperpolarized norbornene in the gaseous phase, where a signal enhancement
factor of approximately 160 was observed. This concept of stoichiometric
as opposed to purely catalytic use of PHIP-available complexes with
an unsaturated payload precursor molecule can be extended to other
contrast agents for both homogeneous and heterogeneous PHIP. The Rh(I)
complex was employed in aqueous medium suitable for production of
hyperpolarized contrast agents for biomedical use. Detection of PHIP
hyperpolarized gas by low-field NMR is demonstrated here for the first
time.
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Multidimensional mapping of spin-exchange optical pumping in clinical-scale batch-mode 129Xe hyperpolarizers. J Phys Chem B 2014; 118:4809-16. [PMID: 24731261 PMCID: PMC4055050 DOI: 10.1021/jp501493k] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
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We present a systematic, multiparameter
study of Rb/129Xe spin-exchange optical pumping (SEOP)
in the regimes of high xenon
pressure and photon flux using a 3D-printed, clinical-scale stopped-flow
hyperpolarizer. In situ NMR detection was used to study the dynamics
of 129Xe polarization as a function of SEOP-cell operating
temperature, photon flux, and xenon partial pressure to maximize 129Xe polarization (PXe). PXe values of 95 ± 9%, 73 ± 4%, 60
± 2%, 41 ± 1%, and 31 ± 1% at 275, 515, 1000, 1500,
and 2000 Torr Xe partial pressure were achieved. These PXe polarization values were separately validated by ejecting
the hyperpolarized 129Xe gas and performing low-field MRI
at 47.5 mT. It is shown that PXe in this
high-pressure regime can be increased beyond already record levels
with higher photon flux and better SEOP thermal management, as well
as optimization of the polarization dynamics, pointing the way to
further improvements in hyperpolarized 129Xe production
efficiency.
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Sub-second proton imaging of 13C hyperpolarized contrast agents in water. CONTRAST MEDIA & MOLECULAR IMAGING 2014; 9:333-41. [PMID: 24753438 DOI: 10.1002/cmmi.1579] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2013] [Revised: 09/05/2013] [Accepted: 10/14/2013] [Indexed: 11/07/2022]
Abstract
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), <P> ~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.
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Parahydrogen induced polarization of 1-(13)C-phospholactate-d(2) for biomedical imaging with >30,000,000-fold NMR signal enhancement in water. Anal Chem 2014; 86:5601-5. [PMID: 24738968 PMCID: PMC4063326 DOI: 10.1021/ac500952z] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
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The synthetic protocol for preparation
of 1-13C-phosphoenolpyruvate-d2, precursor for parahydrogen-induced polarization
(PHIP) of 1-13C-phospholactate-d2, is reported. 13C nuclear spin polarization of 1-13C-phospholactate-d2 was increased
by >30,000,000-fold (5.75 mT) in water. The reported 13C polarization level approaching unity (>15.6%), long lifetime
of 13C hyperpolarized 1-13C-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.
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The feasibility of formation and kinetics of NMR signal amplification by reversible exchange (SABRE) at high magnetic field (9.4 T). J Am Chem Soc 2014; 136:3322-5. [PMID: 24528143 PMCID: PMC3985893 DOI: 10.1021/ja501052p] [Citation(s) in RCA: 123] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2013] [Indexed: 12/16/2022]
Abstract
(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.
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XeNA: an automated 'open-source' (129)Xe hyperpolarizer for clinical use. Magn Reson Imaging 2014; 32:541-50. [PMID: 24631715 DOI: 10.1016/j.mri.2014.02.002] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2013] [Revised: 01/30/2014] [Accepted: 02/02/2014] [Indexed: 11/28/2022]
Abstract
Here we provide a full report on the construction, components, and capabilities of our consortium's "open-source" large-scale (~1L/h) (129)Xe hyperpolarizer for clinical, pre-clinical, and materials NMR/MRI (Nikolaou et al., Proc. Natl. Acad. Sci. USA, 110, 14150 (2013)). The 'hyperpolarizer' is automated and built mostly of off-the-shelf components; moreover, it is designed to be cost-effective and installed in both research laboratories and clinical settings with materials costing less than $125,000. The device runs in the xenon-rich regime (up to 1800Torr Xe in 0.5L) in either stopped-flow or single-batch mode-making cryo-collection of the hyperpolarized gas unnecessary for many applications. In-cell (129)Xe nuclear spin polarization values of ~30%-90% have been measured for Xe loadings of ~300-1600Torr. Typical (129)Xe polarization build-up and T1 relaxation time constants were ~8.5min and ~1.9h respectively under our spin-exchange optical pumping conditions; such ratios, combined with near-unity Rb electron spin polarizations enabled by the high resonant laser power (up to ~200W), permit such high PXe values to be achieved despite the high in-cell Xe densities. Importantly, most of the polarization is maintained during efficient HP gas transfer to other containers, and ultra-long (129)Xe relaxation times (up to nearly 6h) were observed in Tedlar bags following transport to a clinical 3T scanner for MR spectroscopy and imaging as a prelude to in vivo experiments. The device has received FDA IND approval for a clinical study of chronic obstructive pulmonary disease subjects. The primary focus of this paper is on the technical/engineering development of the polarizer, with the explicit goals of facilitating the adaptation of design features and operative modes into other laboratories, and of spurring the further advancement of HP-gas MR applications in biomedicine.
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Abstract
Three-dimensional printing with high-temperature plastic is used to enable spin exchange optical pumping (SEOP) and hyperpolarization of xenon-129 gas. The use of 3D printed structures increases the simplicity of integration of the following key components with a variable temperature SEOP probe: (i) in situ NMR circuit operating at 84 kHz (Larmor frequencies of (129)Xe and (1)H nuclear spins), (ii) <0.3 nm narrowed 200 W laser source, (iii) in situ high-resolution near-IR spectroscopy, (iv) thermoelectric temperature control, (v) retroreflection optics, and (vi) optomechanical alignment system. The rapid prototyping endowed by 3D printing dramatically reduces production time and expenses while allowing reproducibility and integration of "off-the-shelf" components and enables the concept of printing on demand. The utility of this SEOP setup is demonstrated here to obtain near-unity (129)Xe polarization values in a 0.5 L optical pumping cell, including ∼74 ± 7% at 1000 Torr xenon partial pressure, a record value at such high Xe density. Values for the (129)Xe polarization exponential build-up rate [(3.63 ± 0.15) × 10(-2) min(-1)] and in-cell (129)Xe spin-lattice relaxation time (T1 = 2.19 ± 0.06 h) for 1000 Torr Xe were in excellent agreement with the ratio of the gas-phase polarizations for (129)Xe and Rb (PRb ∼ 96%). Hyperpolarization-enhanced (129)Xe gas imaging was demonstrated with a spherical phantom following automated gas transfer from the polarizer. Taken together, these results support the development of a wide range of chemical, biochemical, material science, and biomedical applications.
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Low-field MRI can be more sensitive than high-field MRI. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2013; 237:169-174. [PMID: 24239701 PMCID: PMC3897717 DOI: 10.1016/j.jmr.2013.10.013] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2013] [Revised: 10/21/2013] [Accepted: 10/22/2013] [Indexed: 05/03/2023]
Abstract
MRI signal-to-noise ratio (SNR) is the key factor for image quality. Conventionally, SNR is proportional to nuclear spin polarization, which scales linearly with magnetic field strength. Yet ever-stronger magnets present numerous technical and financial limitations. Low-field MRI can mitigate these constraints with equivalent SNR from non-equilibrium 'hyperpolarization' schemes, which increase polarization by orders of magnitude independently of the magnetic field. Here, theory and experimental validation demonstrate that combination of field independent polarization (e.g. hyperpolarization) with frequency optimized MRI detection coils (i.e. multi-turn coils using the maximum allowed conductor length) results in low-field MRI sensitivity approaching and even rivaling that of high-field MRI. Four read-out frequencies were tested using samples with identical numbers of (1)H and (13)C spins. Experimental SNRs at 0.0475T were ∼40% of those obtained at 4.7T. Conservatively, theoretical SNRs at 0.0475T 1.13-fold higher than those at 4.7T were possible despite an ∼100-fold lower detection frequency, indicating feasibility of high-sensitivity MRI without technically challenging, expensive high-field magnets. The data at 4.7T and 0.0475T was obtained from different spectrometers with different RF probes. The SNR comparison between the two field strengths accounted for many differences in parameters such as system noise figures and variations in the probe detection coils including Q factors and coil diameters.
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48
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Efficient transformation of parahydrogen spin order into heteronuclear magnetization. J Phys Chem B 2013; 117:1219-24. [PMID: 23214962 DOI: 10.1021/jp3089462] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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.
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Abstract
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.
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A large volume double channel 1H-X RF probe for hyperpolarized magnetic resonance at 0.0475 T. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2012; 220:94-101. [PMID: 22706029 PMCID: PMC3510702 DOI: 10.1016/j.jmr.2012.04.012] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2011] [Revised: 04/03/2012] [Accepted: 04/07/2012] [Indexed: 05/20/2023]
Abstract
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).
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