HYPERPOLARISATION METHOD AND PRODUCT

Abstract

In a method for preparing a hyperpolarised sample, for example for a magnetic resonance procedure, a starting solution comprising alpha-ketoglutaric acid and 13C-labelled molecules is frozen to form a frozen solution. The solution is irradiated with ultraviolet and/or visible radiation, to generate free radicals. The frozen solution is then hyperpolarised by applying a magnetic field to the solution while irradiating it with frequency-modulated microwave radiation.

Claims

1. A method for preparing a hyperpolarised sample comprising the steps of: freezing a solution comprising alpha-ketoglutaric acid and .sup.13C-labelled molecules to form a frozen solution; irradiating the frozen solution with ultraviolet and/or visible radiation; hyperpolarising the frozen solution by applying a magnetic field to the solution while irradiating the frozen solution with frequency-modulated microwave radiation.

2. A method according to claim 1, in which the microwave radiation is frequency-modulated at a rate between 1 Hz and 1 MHz with an amplitude between 1 Hz and 100 MHz.

3. A method according to claim 1, in which the concentration of alpha-ketoglutaric acid in the frozen solution is in the range of 10 mM to 500 mM.

4. A method according to claim 1, in which the step of irradiating with ultraviolet and/or visible radiation generates free radicals in the frozen solution.

5. A method according to claim 4, in which a free-radical concentration of 10-100 mM is generated in the frozen solution.

6. A method according to claim 1, in which the step of freezing the solution comprises reducing the temperature of the solution to below 190K.

7. A method according to claim 1, in which the magnetic field strength is between 3 and 15 T.

8. A method according to claim 1, in which the .sup.13C-labelled molecules comprise one or more of pyruvic acid, lactic acid, acetic acid, glutamine, fumaric acid, urea, or glucose.

9. A method according to claim 1, in which the step of irradiating the frozen solution with ultraviolet and/or visible radiation is carried out with the frozen solution at a first temperature below 190K, and the step of hyperpolarising the frozen solution is carried out with the frozen solution at a second temperature below 2K.

10. A method according to claim 9, in which after hyperpolarisation the temperature of the frozen solution is raised to a third temperature above 200K within a magnetic field of at least 0.5T in order to reduce the concentration of free radicals in the frozen solution, and is then reduced to a fourth temperature below 78 K for storage in a magnetic field of 0.1T or above.

11. A method according to claim 1, in which the solution further comprises a glass forming agent, preferably ethanol, dimethyl sulfoxide or glycerol.

12. A method according to claim 1, further comprising the step of dissolving or melting the polarised frozen solution for use in a magnetic resonance application such as NMR, MRS or MRI.

13. A hyperpolarised sample for use in NMR, MRS or MRI prepared according to a method as defined in claim 1.

14. A hyperpolarised sample for use in NMR, MRS or MRI containing alpha-KG at a concentration of less than 50 mM and containing succinic acid at a concentration of less than 20 mM.

15. A hyperpolarised sample according to claim 14 containing alpha-KG at a concentration of less than 25 mM and/or containing succinic acid at a concentration of less than 5 mM.

Description

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

[0041] Specific embodiments of the invention will now be described by way of example, with reference to the accompanying drawings in which;

[0042] FIG. 1 is a schematic illustration of the formation and UV-Vis irradiation of glassy beads of a sample for low-temperature dynamic nuclear polarization (DNP), according to an embodiment of the invention;

[0043] FIG. 2 shows ESR spectra measured at 77 K for different irradiation times of the sample;

[0044] FIG. 3 is a plot of deduced radical concentration as a function of the irradiation time for the sample;

[0045] FIG. 4 is a schematic illustration of a DNP polarizer for polarising samples embodying the invention;

[0046] FIG. 5 illustrates a microwave sweep with and without microwave frequency modulation measured inside the DNP polarizer;

[0047] FIG. 6 is a plot of a liquid-state hyperpolarized .sup.13C MR signal decay for the sample; and

[0048] FIG. 7 shows a summed .sup.13C MR spectra acquired in a rat liver following the intravenous injection of a hyperpolarised solution embodying the invention.

[0049] In a first embodiment of the method of the invention, the first step consists in preparing a starting solution containing alpha-KG and photo-inducing the free radical. FIG. 1 shows a quartz dewar (1) insulated with a vacuum chamber (2) and filled with liquid nitrogen (3). Droplets of a 10M aqueous solution of [1-13C]lactic acid containing 300 mM of alpha-KG are snap frozen in the liquid nitrogen to form glassy beads that fall into the tail of the quartz dewar (4). The glassy frozen beads are subsequently irradiated with UV-Vis light (5) for 30 s using a Dymax Bluewave 200 W broadband UV-Vis lamp (Dymax, Wiesbaden, Germany) set to maximum output intensity. At the end of the irradiation time, the tail of the quartz dewar can be inserted in an X-band ESR spectrometer to determine the concentration of photo-induced free radicals. FIG. 2 shows the ESR spectra measured at 77 K for various irradiation times for samples irradiated as in FIG. 1 and FIG. 3 is a plot showing the deduced radical concentration as a function of the irradiation time (to deduce the concentration the double integral of the ESR spectrum was compared to a calibration curve, created from a set of known concentrations of the persistent radical compound, 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl).

[0050] The second step of the method consists in polarizing the .sup.13C spins of the sample by low-temperature dynamic nuclear polarization (DNP) using a polarizer such as the one sketched in FIG. 4. The polarizer comprises a liquid helium cryostat (6), a superconducting magnet (7), and a frequency-modulated microwave source (8) connected to a waveguide (9) directing the microwaves inside the sample space (10) of the polarizer. The sample space is filled with liquid helium. In a preferred embodiment, the sample, in the form of frozen beads, (11) is enclosed in a leak-tight assembly (12) through which a fluid such as a liquid, such as hot water, or a gas, such as helium or nitrogen gas, can be supplied from an entry port (13) to an exit port (14) to raise the temperature of the sample above 200 K once the sample is sufficiently polarized and the assembly containing the sample is raised out of the liquid helium bath of the sample space. The photo-induced radicals will then be quenched and the sample can either be extracted from the polarizer and directly used for MR experiments, or be extracted from the polarizer for storage in an external device and subsequently used for MR experiments, or be placed back in the sample space of the polarizer for storage.

[0051] FIG. 5 displays microwave sweeps with and without microwave frequency modulation measured inside the DNP polarizer. Comparing these measurements clearly illustrates the unexpectedly large beneficial effect of frequency modulation in embodiments of the invention. The sweeps are shown in FIG. 5 as plots of 13C solid-state NMR signal vs. center microwave frequency measured in a photo-irradiated frozen [1-13C]lactic acid solution containing 300 mM of alpha-KG polarized via DNP in a 7 T and 1.35 K polarizer. The microwave was frequency modulated at a rate of 1.5 kHz and an amplitude of 52 MHz. The dashed line linking the measurement points is to guide the eye.

[0052] FIG. 6 is an example of liquid-state hyperpolarized .sup.13C MR signal decay measured at 14.1 T (a 10-degree radiofrequency pulse was applied every 3 s) in a room-temperature [1-13C]lactate solution hyperpolarized using the free-radical photo-induced in alpha-KG.

[0053] FIG. 7 shows the sum of a series of .sup.13C MR spectra acquired in a rat liver following the intravenous injection of a sample embodying the invention. The sample was 1 ml of a 42 mM [1-13C]lactate solution hyperpolarized using the free-radical photo-induced in alpha-KG. In addition to [1-13C]lactate (182.8 ppm), the following downstream metabolites could be detected: [1-13C]pyruvate (170.7 ppm) and [1-13C]pyruvate hydrate (179 ppm), [1-13C]alanine (176.7 ppm), [1-13C]malate (175.2 ppm), and [13C]bicarbonate (160.8 ppm). The data was acquired in preclinical horizontal-bore 9.4T MRI system using a 10-mm diameter 13C surface coil and a series of 20-degree radiofrequency pulses applied every 2 s.