Hyperpolarization without a polarizer: in vivo 13C-MRI using SAMBADENA
Andreas B. Schmidt1,2, Stephan Berner1,3,4, Moritz Braig1, Mirko Zimmermann1, Jürgen Hennig1, Dominik von Elverfeldt1, and Jan-Bernd Hövener2,4

1Radiology - Medical Physics, University Medical Center Freiburg, Freiburg, Germany, 2Radiology and Neuroradiology, University Medical Center Schleswig-Holstein, Kiel, Germany, 3German Consortium for Cancer Research (DKTK), Heidelberg, Germany, 4German Cancer Research Center (DKFZ), Heidelberg, Germany


Hyperpolarization (HP) enhances the sensitivity of MR by several orders of magnitude and allows the detection of metabolism non-invasively and in vivo. However, well-established methods are costly, complex and require a dedicated “polarizer” next to the MRI system. SAMBADENA is, to date, the simplest and most cost-effective method to generate 13C-HP > 20 % for MRI. Within seconds HP is achieved within the MRI and little additional hardware is required. Here, the first in-vivo applications of SAMBADENA are reported, demonstrating its potential to be a fast, simple, low-cost alternative method for HP-MRI.


The sensitivity of MRI to monitor metabolism non-invasively and in vivo can be dramatically enhanced by means of nuclear hyperpolarization (HP).1–3 Dissolution dynamic nuclear polarization (dDNP1) is well established and was used in human studies2,3, but suffers from high cost, complexity and long HP cycles. Parahydrogen (pH2)-based methods are less costly and faster but less advanced. Recently, a PASADENA (pH2 and synthesis allow dramatically enhanced nuclear alignment4) experiment was realized on a commercial MRI system: by Synthesis Amid the Magnet Bore, A Dramatically Enhanced Nuclear Alignment (SAMBADENA)5,6 with a 13C-polarization of P > 20% was achieved in vitro. Here, we present the first 13C-images acquired in vivo from SAMBADENA-hyperpolarized agents, putting the method to a real-life test with respect to the complex requirements of in-vivo imaging, namely anesthesia, animal monitoring, biocompatibility of the tracer solution (temperature, pressure) and well-controlled injection.


pH2 was enriched to >90% as described elsewhere.6
Samples were prepared as before5 using aqueous 13C-, 2H3-labeled hydroxyethyl-acrylate (HEA) at cHEA=5.5mM, 22mM or 80mM and catalyst with concentration of ccat=2mM or 4mM. pH2, was catalytically added to HEA and 13C polarization was obtained by means of spin-order transfer (SOT) using the sequence l-PH-INEPT+.8,9
Setup: For HP and MRI a 7T preclinical MRI system (Biospec 7/20,Bruker,Germany) was used in combination with a dual-resonant 1H-13C-transmit-receive volume resonator (Rapid,Germany). A high-pressure and high-temperature reactor was custom-made to yield fast hydrogenation (inner volume ≈2ml, PSU 1000). The reactor was mounted to a custom-built mouse bed that allows animal heating, control and anesthesia (Fig. 1).
Hyperpolarization: The heated reactor (≈80°C) was filled with the hot precursor solution (≈80°C), closed and moved into the magnet. Hydrogenation was initialized by injecting pressurized pH2 (ppH2≈15-30bar) from the bottom of the reactor. After the variable hydrogenation time th the SOT was executed. 13C-HP was quantified assuming 100% hydrogenation and pH2-enrichment using a sample of thermally polarized n.a. acetone.
In-vivo SAMBADENA: The reactor was connected to the tail vein of a mouse (30g, 14 weeks old) that was placed next to it via a syringe using a catheter and a one-way check-valve (IDEX, USA). An HP-tracer solution was produced and ≈300µl were injected over a period of 10s. Another 5s later, the distribution of the tracer was imaged using a single-shot 13C-RARE sequence (90/180°, RARE-factor: 38, FOV: (8.4cm)2, zerofilled to 128x96px, interpolated to 256x192px, one 6cm slice, TR=0.487s, TE=79ms, acquisition time:0.487s). 1H-MRI was acquired for coregistration (1H-Turbo-RARE,90/180°, RARE-factor:8, matrix:2562, TR=2.5s, TE=33ms, acquisition time:161s). SNR was calculated as maximum intensity divided by standard deviation of the noise.


HP at high tracer concentrations: HP was measured as function of cHEA and an inverse correlation was observed (P=(22±2)%,(17±2)% and (7±1)% at cHEA=5.5mM, 22mM and 80mM, respectively; pH2 pressure of 15bar; N=2 each). The experiment was repeated with 80 mM solution at ppH2=20bar, 25bar and 30bar and HP was quantified to (8±1)%, (8±1)% and 13%, respectively (Fig. 2). Note that the latter could not be repeated as some equipment was damaged by the elevated pressure.
In-vivo SAMBADENA: After the intravenous injection of HP HEP (300ml, ccat=4mM, cHEA=80mM, P≈7 %), strong 13C signal was imaged with an SNR of 168. The highest signal intensities originated from the vena cava, aorta and femoral arteries of the rodent (Fig. 3).


For any biomedical application, highly concentrated, highly polarized samples are needed to achieve sufficient signal in vivo. While the received signal (~cHEA*P) increased with the tracer concentration, the overall HP yield decreased suggesting incomplete hydrogenation. As expected and discussed before10, the HP yield was enhanced by supplying pH2 at a higher pressure which increased the pH2 available. While MRI definitely can be improved and it is expected that HP can be further enhanced along with dissolved pH2 and by optimization of the reaction (temperature, ccat) the HP levels were sufficient to demonstrate the in vivo applicability of SAMBADENA with a 13C-angiography of an adult mouse. The results show the potential of SAMBADENA to be a fast, simple and cost-efficient alternative method for the production and application of HP 13C-tracers. The HP of biomolecules like succinate11,12, lactate13–15, pyruvate or acetate16 is currently investigated.


In-vivo 13C-MRI of agents hyperpolarized by SAMBADENA without a dedicated polarizer was successfully demonstrated. With respect to recent advances in pH2-based methods concerning metabolic tracers, SAMBADENA appears well placed to simplify the research on - and application of - HP metabolic tracers. The next crucial step will be to adapt SAMBADENA to these new methods and metabolically active molecules.


Support by the DFG (HO 4604/1-1 and HO 4604/2-1), the DKTK and the Heinrich-Böll-Stiftung (ABS, P131623) and the contribution of the COST Action TD1103 is greatly acknowledged. All animals were measured under the approval of the local ethics committee.


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Figure 1: Hyperpolarization without a polarizer: The tracer is produced in situ within the MRI at the application site. The required components are a reactor, valves and tubing, pH2, an animal bed, and a 13C-MRI system. The latter is used for the HP process and MRI.5

Figure 2: HP vs. pressure: HP was quantified with different concentrations of the precursor molecule HEA (squares: ccat=2mM, cHEA=5.5mM; diamonds: ccat=4mM, cHEA=22mM; asterisks: ccat=4mM, cHEA=80mM). When the concentration of the tracers is increased from 5.5mM to 80mM the HP drops from P=(22±2)% to P=(7±1)%, although the acquired signal (~cHEP*P) is increasing. This effect suggests a lack of pH2 and incomplete pH2-hydrogenation. For the 80mM solution the HP could be increased again to P=13% by applying higher pH2 pressures. Data points and error bars represent the mean value and st.dev. (N=2; at 30bar N=1 as equipment was damaged by high pressures).5

Figure 3: In vivo SAMBADENA: To demonstrate the in-vivo feasibility of SAMBADENA, an HP tracer solution was injected into the tail vein of an in-vivo mouse (300µl, concentration of tracer of cHEP=80mM, P≈7%, in H2O; 30g, 14 weeks old). About 5s later the distribution of the 13C-tracer was imaged using a single-slice, single-shot 13C-RARE sequence (a). Coregistration with a subsequently recorded 1H-TurboRARE-3D MRI (b) revealed the tracer in the vascular system of the rodent, most prominently in the vena cava, aorta and femoral arteries ((c) and (d)). (d): www.biologycorner.com; CC BY-NC-SA 4.0.

Proc. Intl. Soc. Mag. Reson. Med. 26 (2018)