BROADBAND METHOD FOR SIGNAL AMPLIFICATION OF MAGNETIC RESONANCE CONTRAST AGENTS WITHIN SECONDS AND THEIR PURIFICATION

Abstract

The present invention relates to a method for transferring a two-spin order of a molecule (e.g. parahydrogen) into a hyperpolarization of at least one heteronucleus, the method comprising the steps of: providing a molecule (e.g. parahydrogen pH.sub.2) comprising two protons and at least one heteronucleus (S.sub.3, S.sub.4), the protons having nuclear spins being coupled to a nuclear spin of the at least one heteronucleus; exposing the protons and the at least one heteronucleus to an e.g. homogeneous magnetic field (B.sub.0) in a z-direction, the z-direction forming a right-handed orthogonal coordinate system with an x- and a y-direction; and applying a sequence of radio frequency pulses to the protons and the at least one heteronucleus in order to transfer said two-spin order into the hyperpolarization of the at least one heteronucleus, wherein said sequence of radio frequency pulses comprises a first, a second, and a third group (N.sub.A, N.sub.B, N.sub.C) of 180 radio frequency pulses, wherein the first group (N.sub.A) of 180 radio frequency pulses is consecutively applied n.sub.A times during a first time interval (.sub.A) and wherein the second group (N.sub.B) of 180 radio frequency pulses is consecutively applied n.sub.B times during a second time interval (.sub.B) after the last first group, and wherein the third group (N.sub.C) of 180 radio frequency pulses is consecutively applied n.sub.C times during a third time interval (.sub.C) after the last second group, wherein n.sub.A, n.sub.B, n.sub.C are integer numbers, respectively.

Claims

1. A method for transferring a two-spin order of a molecule into a hyperpolarization of at least one heteronucleus (S.sub.3, S.sub.4), the method comprising the steps of: providing a molecule comprising two protons (H.sub.1, H.sub.2) and at least one heteronucleus (S.sub.3, S.sub.4), the protons having nuclear spins being coupled to a nuclear spin of the at least one heteronucleus (S.sub.3, S.sub.4); exposing the protons and the at least one heteronucleus to a magnetic field (B.sub.0) in a z-direction, the z-direction forming a right-handed orthogonal coordinate system with an x-direction and a y-direction; applying a sequence of radio frequency pulses to the protons and the at least one heteronucleus (S.sub.3, S.sub.4) in order to transfer said two-spin order into the hyperpolarization of the at least one heteronucleus, wherein said sequence of radio frequency pulses comprises a first, a second, and a third group (N.sub.A, N.sub.B, N.sub.C) of 180 radio frequency pulses, wherein the first group (N.sub.A) of 180 radio frequency pulses is consecutively applied n.sub.A times during a first time interval (.sub.A) and wherein the second group (N.sub.B) of 180 radio frequency pulses is consecutively applied n.sub.A times during a second time interval (.sub.B) after the last first group, and wherein the third group (N.sub.C) of 180 radio frequency pulses is consecutively applied n.sub.C times during a third time interval (.sub.C) after the last second group, wherein n.sub.A, n.sub.B, n.sub.C are integer numbers, respectively.

2. The method according to claim 1, wherein the first group (N.sub.A) of 180 radio frequency pulses comprises a first 180 radio frequency pulse (P1) having a phase .sub.11 and acting on the protons, and a second 180 radio frequency pulse (P2) having a phase .sub.21 and acting on the at least one heteronucleus (S.sub.3), and wherein the first group (N.sub.A) of 180 radio frequency pulses comprises a third 180 radio frequency pulse (P3) having a phase .sub.12 and acting on the protons, and a fourth 180 radio frequency pulse (P4) having a phase .sub.22 and acting on the at least one heteronucleus (S.sub.3).

3. The method according to one of the preceding claims, wherein the second group (N.sub.B) of 180 radio frequency pulses comprises a first 180 radio frequency pulse (P5) having a phase .sub.13 and acting on the protons and a succeeding second 180 radio frequency pulse (P6) having a phase .sub.14 and acting on the protons.

4. The method according to claim 1 or 2, wherein the second group (N.sub.B) of 180 radio frequency pulses comprises a first 180 radio frequency pulse (P11) having a phase .sub.23 and acting on the at least one heteronucleus (S.sub.3) and a succeeding second 180 radio frequency pulse (P5) having a phase .sub.13 and acting on the protons, and wherein the second group (N.sub.B) of 180 radio frequency pulses comprises a third 180 radio frequency pulse (P12) having a phase .sub.24 and acting on the at least one heteronucleus (S.sub.3) and a succeeding fourth 180 radio frequency pulse (P6) having a phase .sub.14 and acting on the protons, wherein the third and the fourth 180 radio frequency pulses (P12, P6) of the second group (N.sub.B) are applied after the second 180 radio frequency pulse (P5) of the second group (N.sub.B).

5. The method according to one of the preceding claims, wherein the third group (N.sub.C) of 180 radio frequency pulses comprises a first 180 radio frequency pulse (P7) having a phase .sub.15 and acting on the protons, and a second 180 radio frequency pulse (P8) having a phase .sub.25 and acting on the at least one heteronucleus (S.sub.3), and wherein the third group (N.sub.C) of 180 radio frequency pulses comprises a third 180 radio frequency pulse (P9) having a phase .sub.16 and acting on the protons, and a fourth 180 radio frequency pulse (P10) having a phase .sub.26 and acting on the at least one heteronucleus (S.sub.3).

6. The method according to one of the preceding claims, wherein said sequence of radio frequency pulses further comprises a first 90 radio frequency pulse (RF1) having a phase .sub.11 and acting on the protons, wherein the first group (N.sub.A) of 180 radio frequency pulses is consecutively applied n.sub.A times during said first time interval (.sub.A) after said first 90 radio frequency pulse (RF1), and wherein said sequence of radio frequency pulses further comprises a second 90 radio frequency pulse (RF2) having a phase .sub.12 and acting on the protons, which second 90 radio frequency pulse (RF2) succeeds the first 90 radio frequency pulse (RF1) and is applied to the protons at an end of the first time interval (.sub.A), wherein the second group (N.sub.B) of 180 radio frequency pulses is consecutively applied n.sub.B times during said second time interval (.sub.B) after said second 90 radio frequency pulse (RF2), and wherein said sequence of radio frequency pulses further comprises a third 90 radio frequency pulse (RF3) having a phase .sub.13 and acting on the protons, which third 90 radio frequency pulse (RF3) succeeds the second 90 radio frequency pulse (RF2) and is applied to the protons at an end of the second time interval (.sub.B), wherein the third group (N.sub.C) of 180 radio frequency pulses is consecutively applied n.sub.C times during said third time interval (.sub.C) after said third 90 radio frequency pulse (RF3).

7. The method according to claim 6, wherein said sequence of radio frequency pulses further comprises a fourth 90 radio frequency pulse (RF4) having a phase .sub.22 and acting on the at least one heteronucleus (S.sub.3) and a succeeding fifth 90 radio frequency pulse (RF5) having a phase .sub.23 and acting on the at least one heteronucleus (S.sub.3), wherein particularly the third 90 radio frequency pulse (RF3) is simultaneous with said fourth 90 radio frequency pulse (R4).

8. The method according to claim 6 or 7, wherein the phases .sub.11, .sub.12, .sub.13 of the first, second and third 90 radio frequency pulse (RF1, RF2, RF3) are collinear, and/or wherein the phase (.sub.23) of the fifth 90 radio frequency pulse (RF5) is orthogonal to the phase (.sub.22) of the fourth 90 radio frequency pulse (RF4), wherein particularly .sub.11=.sub.12=.sub.13=x, .sub.22=x, .sub.23=y.

9. The method according to claim 7 or 8, wherein said sequence of radio frequency pulses further comprises a sixth 90 radio frequency pulse (RF6) having a phase .sub.14 and acting on the protons, wherein said sequence of radio frequency pulses further comprises a seventh 90 radio frequency pulse (RF7) having a phase .sub.21 and acting on the at least one heteronucleus (S.sub.3), wherein particularly the sixth 90 radio frequency pulse (RF6) is simultaneous with the fifth 90 radio frequency pulse (RF5), and wherein particularly the seventh 90 radio frequency pulse (RF7) is simultaneous with the first 90 radio frequency pulse (RF1).

10. The method according to claim 9, wherein the phases .sub.11, .sub.12, .sub.13, .sub.14 of the first, second, third, and sixth 90 radio frequency pulse (RF1, RF2, RF3, RF6) are collinear, and wherein the phase .sub.21 of the seventh 90 radio frequency pulse (RF7) corresponds to .sub.21=.sub.23+, wherein particularly .sub.11=.sub.12=.sub.13=.sub.14=x, .sub.22=x, .sub.23=y, and .sub.21=y.

11. The method according to one of the claims 1 to 8, wherein the step of providing a molecule and at least one heteronucleus also comprises providing a further heteronucleus (S.sub.4), the nuclear spin of the at least one heteronucleus (S.sub.3) being coupled to the a nuclear spin of the further heteronucleus (S.sub.4), and wherein the step of exposing the protons and the at least one heteronucleus to a magnetic field (B.sub.0) in the z-direction, also comprises to expose the further heteronucleus (S.sub.4) to said magnetic field (B.sub.0), and wherein the step of applying a sequence of radio frequency pulses to the protons and the at least one heteronucleus (S.sub.3) in order to transfer said two-spin order into the hyperpolarization of the at least one heteronucleus (S.sub.3) also comprises transfer of the two-spin order into hyperpolarization of the further heteronucleus (S.sub.4), wherein particularly the heteronucleus and the further heteronucleus can be of the same species or can belong to a different species.

12. The method according to claim 11, wherein said sequence of radio frequency pulses further comprises a sixth radio frequency pulse (RF8) of angle having a phase .sub.24 and acting on the heteronuclei (S.sub.3, S.sub.4) and being spaced apart by a fourth time interval (.sub.D) from the third 90 radio frequency pulse (RF3), and wherein said sequence of radio frequency pulses comprises a seventh 90 radio frequency pulse (RF9) having a phase .sub.25 and acting on the heteronuclei (S.sub.3, S.sub.4), wherein the seventh 90 radio frequency pulse (RF9) is spaced apart from said sixth radio frequency pulse (RF8) of angle by a fifth time interval (.sub.E).

13. The method according to claims 7 and 12, wherein said sequence of radio frequency pulses further comprises a 180 radio frequency pulse (P13) having a phase .sub.27 and acting on the heteronuclei (S.sub.3, S.sub.4) after said fifth 90 radio frequency pulse (RF5) and prior to said sixth radio frequency pulse (RF8) of angle , and wherein said sequence of radio frequency pulses further comprises a 180 radio frequency pulse (P14) having a phase .sub.28 and acting on the heteronuclei (S.sub.3, S.sub.4) after the sixth radio frequency pulse (RF8) of angle and prior to said seventh 90 radio frequency pulse (RF9).

14. The method according to claim 11, wherein said sequence of radio frequency pulses further comprises a single continuous wave irradiation acting on the two heteronuclei (S.sub.3, S.sub.4) and comprising a power larger than a chemical shift difference between the two heteronuclei (S.sub.3, S.sub.4), particularly so as to modulate a polarization over the two heteronuclei (S.sub.3, S.sub.4).

15. The method according to one of the preceding claims, wherein for obtaining a hyperpolarized contrast agent comprising the at least one heteronucleus (S.sub.3), prior to said step of applying a sequence of radio frequency pulses to the protons and the at least one heteronucleus in order to transfer said two-spin order into the hyperpolarization of the at least one heteronucleus (S.sub.3), said molecule is added to one of: a mediator, the mediator not being part of the hyperpolarized contrast agent in the end, a precursor of the hyperpolarized contrast agent, which precursor is finally part of the hyperpolarized contrast agent, wherein the at least one heteronucleus (S.sub.3) is comprised by the precursor, a precursor of the hyperpolarized contrast agent, which precursor is then split to obtain the contrast agent that comprises the at least one heteronucleus (S.sub.3). a contrast agent, wherein the at least one heteronucleus is comprised by the contrast agent.

16. The method according to one of the preceding claims, wherein the respective radio frequency pulse is one of; a rectangular pulse, a frequency selective pulse, a shaped pulse having a shape deviating from a rectangular shape.

17. The method according to one of the preceding claims, wherein a final radio frequency pulse on the heteronucleus is one of: used to tilt the magnetization along the z axis or used to tilt the magnetization in an arbitrary direction, particularly for observing a fraction directly and for storing a rest of the magnetization, omitted in case it would tilt the magnetization along the z axis to allow observing all the magnetization directly.

18. A method for transferring a two-spin order of a molecule into a hyperpolarization of at least one heteronucleus (S.sub.3, S.sub.4), the method comprising the steps of: providing a molecule comprising two protons (H.sub.1, H.sub.2) and at least one heteronucleus (S.sub.3, S.sub.4), the protons having nuclear spins being coupled to a nuclear spin of the at least one heteronucleus (S.sub.3, S.sub.4), wherein the J-coupling between a proton and the at least one heteronucleus is larger than the J-coupling between the two protons, and transferring the two spin-order to the at least one heteronucleus using radio frequency pulses.

19. The method according to one of the preceding claims, wherein said hyperpolarization of the at least one heteronucleus is conducted with help of a catalyst in an organic solvent, wherein after hyperpolarization of the at least one heteronucleus, an aqueous solution is added to the organic solvent, and wherein the aqueous solution may comprise a cleaving agent that is configured to cleave a precursor comprising the at least one hyperpolarized heteronucleus to obtain a hyperpolarized contrast agent, and wherein for capturing the catalyst a complexing agent can be added to the organic solvent before or after adding the aqueous solution to the organic solvent, and wherein the organic solvent is evaporated or removed by using a stripping gas, and wherein for obtaining an injectable solution comprising the contrast agent, the aqueous solution is filtered to remove by-products and/or impurities that precipitated upon evaporation; or wherein said hyperpolarization of the at least one heteronucleus forming part of a contrast agent is conducted in a solvent, the solvent being one of: an aqueous solution, an organic solution, a mixture of an aqueous and an organic solution, wherein the solvent is evaporated or removed by using a stripping gas, leaving the hyperpolarized contrast agent behind, particularly in a solid form, and wherein the contrast agent is washed with a solvent in which the contrast agent does not dissolve, and wherein for obtaining an injectable solution comprising the contrast agent, the contrast agent is added to a solution.

20. A method for obtaining an injectable solution comprising a contrast agent, wherein a hyperpolarization of at least one heteronucleus is conducted with help of a catalyst in an organic solvent, wherein after hyperpolarization of the at least one heteronucleus, an aqueous solution is added to the organic solvent, and wherein the aqueous solution may comprise a cleaving agent that is configured to cleave a precursor comprising the at least one hyperpolarized heteronucleus to obtain a hyperpolarized contrast agent, and wherein for capturing the catalyst a complexing agent can be added to the organic solvent before or after adding the aqueous solution to the organic solvent, and wherein the organic solvent is evaporated or removed by using a stripping gas, and wherein for obtaining an injectable solution comprising the contrast agent, the aqueous solution is filtered to remove by-products and/or impurities that precipitated upon evaporation; or wherein a hyperpolarization of at least one heteronucleus forming part of a contrast agent is conducted in a solvent, the solvent being one of: an aqueous solution, an organic solution, a mixture of an aqueous and an organic solution, wherein the solvent is evaporated or removed by using a stripping gas, leaving the hyperpolarized contrast agent behind, particularly in a solid form, and wherein the contrast agent is washed with a solvent in which the contrast agent does not dissolve, and wherein for obtaining an injectable solution comprising the contrast agent, the contrast agent is added to a solution.

21. The method according to claim 19 or 20, wherein the evaporation of organic solvent is facilitated by applying a vacuum, wherein particularly the evaporation of organic solvent is facilitated by a stripping gas flow through the solution.

Description

[0098] Further embodiments, features and advantages of the present invention will be described below with reference to the Figures, wherein

[0099] FIG. 1 shows a nuclear spin network with relevant couplings J.sub.12: J-coupling between the two protons of parahydrogen, .sub.HH: chemical shift between the two protons J.sub.13: Coupling between one proton and the heteronucleus S.sub.3, and J.sub.23: Coupling of the other proton with the heteronucleus S.sub.3;

[0100] FIG. 2 shows a diagram of an embodiment of a method according to the present invention for efficient polarization transfer comprising three (particularly different) time intervals .sub.A, .sub.B and .sub.C and three repeatable groups (also denoted as blocks) of 180 pulses N.sub.A, N.sub.B and N.sub.C;

[0101] FIG. 3 shows the transfer efficiency of the method according to the present invention in relation to couplings and the time interval .sub.A in the strong non-equivalent regime;

[0102] FIG. 4 shows a representation of the broadband transfer efficiency (left), as well as an example for a fixed time in the strong non-equivalent regime;

[0103] FIG. 5 shows an embodiment of the method using an extended spin system with additional heteronucleus;

[0104] FIG. 6 shows a pulse sequence for transferring spin order to two heteronuclei as indicated in FIG. 5. Key is a pulse with the angle , which allows to split spin order between several heteronuclei (e.g. S.sub.3 and S.sub.4 of FIG. 5), and

[0105] FIG. 7 shows an example of the sequence applied for SABRE, wherein TD is a delay to allow release of the substrate bound to the H.sub.2-catalyst complex at the end of the sequence.

[0106] As indicated in FIG. 2, the present invention provides an efficient broadband method that can be used to amplify a large number of contrast agents within seconds. Advantageously the method can be used for both PHIP and SABRE. It uses the robust two-spin order generated by the protons H.sub.1, H.sub.2 of parahydrogen pH.sub.2 (cf. FIG. 1), but achieves a high efficiency (>90%) even when there are only small differences (>0.1 Hz) between the individual J-couplings. Radio frequency pulses are used to efficiently convert this order into hyperpolarization of the hetero nuclear spins. An exemplary NMR pulse sequence for achieving this spin order transfer is shown in FIG. 2. Particularly, according to an embodiment (cf. FIGS. 1 and 2), the method comprises the steps of: providing a molecular system such as parahydrogen (pH.sub.2) comprising two protons and at least one heteronucleus S.sub.3, the protons H.sub.1 and H.sub.2 (cf. FIG. 1) having nuclear spins being coupled to a nuclear spin of the at least one heteronucleus S.sub.3 (the parahydrogen can be added to precursors or mediators involved in producing an contrast agent in different ways that will be described further below); exposing the protons and the at least one heteronucleus to a magnetic field B.sub.0 in a z-direction (particularly, the magnetic field B.sub.0 can be a homogeneous magnetic field), the z-direction forming a right-handed orthogonal coordinate system with an x and a y-direction; and applying a sequence of radio frequency (RF) pulses to the protons H.sub.1 and H.sub.2 and the at least one heteronucleus S.sub.3 in order to transfer said two-spin order into the hyperpolarization of the at least one heteronucleus S.sub.3, wherein said sequence of radio frequency pulses comprises 180 RF pulses in three repeatable groups (also denoted as blocks) N.sub.A, N.sub.B, N.sub.C, wherein integers n.sub.A, n.sub.B, n.sub.C indicate the number of repetitions of the respective group. A first time interval .sub.A indicates the time duration of all repetitions of the first group N.sub.A. Likewise, a second and a third time interval .sub.B and .sub.C indicated these time durations for the second and third group N.sub.B, N.sub.C.

[0107] Particularly, the example in FIG. 2 corresponds to n.sub.A=n.sub.B=n.sub.C=1 and .sub.A=.sub.C.

[0108] The first group N.sub.A and the third group N.sub.C each comprise two 180 radio frequency pulses P1, P3 and P7, P9 in the proton channel .sup.1H having phases .sub.11, .sub.12 and .sub.15, .sub.16 and two 180 radio frequency pulses P2, P4 and P8, P10 in the heteronucleus channel S having phases .sub.21, .sub.22 and .sub.25, .sub.26 wherein pulse P1 is simultaneous with pulse P2, pulse P3 is simultaneous with pulse P4, pulse P7 is simultaneous with pulse P8, and pulse P9 is simultaneous with pulse P10. However, the respective simultaneity is not strict and pulse pairs P1 and P2, P3 and P4, P7 and P8, and P9 and P10 can each be separated in time by a time interval. What is implied is that the evolution induced by chemical shifts, J-couplings and RF offsets is negligible during the time separation between pulses on the .sup.1H and S channels. Particularly, a time interval between to preferably simultaneous RF pulses (e.g. P1 and P2, P3 and P4, P7 and P8, and P9 and P10) is less than 100 ms, particularly less than 10 ms, particularly less than 1 ms.

[0109] Particularly, the second group N.sub.B merely comprises two succeeding 180 pulses P5, P6 in the proton channel having phases .sub.13, .sub.14.

[0110] Furthermore, the sequence of radio frequency pulses further comprises a first, a second, and a third 90 radio frequency pulse RF1, RF2, RF3 in the proton channel having phases .sub.11, .sub.12, .sub.13 as indicated in FIG. 2 that act one after the other in the proton channel, as well as a 90 radio frequency pulse RF4 having phase .sub.22 and a 90 radio frequency pulse RF5 having phase .sub.23 that act one after the other in the heteronucleus channel S.sub.3.

[0111] As indicated in FIG. 2, the respective group N.sub.A, N.sub.B, N.sub.C of 180 pulses is applied between succeeding 90 pulses RF1, RF2; R2, RF3/RF4; RF3/RF4, RF5.

[0112] Particularly, the 90 radio frequency pulse RF3 is applied to the protons H.sub.1, H.sub.2 at the same time T3 said 90 radio frequency pulse RF4 is applied to the at least one heteronucleus S.sub.3. Furthermore, particularly, the 90 pulses in the two channels are separated from one another in the shown pulse sequence by said time intervals .sub.A, .sub.B, and .sub.C. Further, the respective second 180 pulse P3, P4, P6, P9, P10 of the last repetition of each group immediately precedes the succeeding 90 pulse RF2, RF3/RF4, RF5 as shown in FIG. 2.

[0113] Particularly, these 180 pulses P3, P4, P6, P9, P10 of the last repetition of each group N.sub.A, N.sub.B, N.sub.C that immediately precede the succeeding 90 pulse RF2, RF3/RF4, RF5 are omitted in an embodiment and the phases of the 90 RF pulses are adjusted accordingly.

[0114] Furthermore, optionally, the second group N.sub.B can comprise further 180 RF pulses P11, P12 in the heteronucleus channel having phases .sub.23 and .sub.24. These optional RF pulses P11, P12 can also be present in the other embodiments (cf. FIGS. 6 and 7) of the method according to the present invention. At low magnetic field these optional 180 RF pulses P11, P12 help to increase the efficiency of the sequence if the conditions move towards the equivalence of the protons.

[0115] A specific choice of the phases of the individual RF pulses which correspond to the direction of the respective RF pulse with respect to a coordinate system in which the z-direction is aligned with the magnetic field B.sub.0 is e.g. given by: [0116] All phases .sub.11, .sub.12, .sub.13 of the first, second and third 90 radio frequency pulse RF1, RF2, RF3 are collinear, [0117] the phase .sub.23 of the fifth 90 radio frequency pulse RF5 is orthogonal to the phase .sub.22 of the fourth 90 radio frequency pulse RF4.

[0118] In a specific embodiment, one can select: .sub.11=.sub.12=.sub.13=x, .sub.22=x, .sub.23=y, i.e. the first, second and third 90 RF pulse RF1, RF2, RF3 are in the x-direction, the fourth 90 RF pulse is in the x-direction and the fifth 90 RF pulse is in the y-direction.

[0119] Furthermore, the phases of the 180 pulses in each channel of each group can be shifted with respect to one another by 180. Particularly, the phases of the 180 pulses in each channel of each group can alternate between x and x.

[0120] Particularly, in an embodiment, the phases of the 180 RF pulses can be

[00002]${}_{11}={}_{13}={}_{13}=x,{}_{12}={}_{14}={}_{16}=-x,{}_{21}={}_{25}=x,\mathrm{and}{}_{22}={}_{26}=-x$

[0121] Particularly, if 180 RF pulses P11 and P12 are present one can select .sub.23=.sub.21 and .sub.24=.sub.26.

[0122] In general, one can distinguish three processes to obtain a desired contrast agent, which process can make use of the above-described transfer mechanism: [0123] 1) Parahydrogen is added to a mediator, which is not part of the signal amplified molecule at the end. This is either an unsaturated bond (PHIP) of a contrast agent precursor or a metal complex (SABRE) which is only temporarily stable. Subsequently, the spin order is transferred from parahydrogen to a heteronucleus within the desired compound. Subsequently, the temporarily stable molecule decays or the precursor is decomposed to obtain the desired contrast agent. [0124] 2) Parahydrogen is added to a contrast agent precursor (or to the contrast agent) and is finally part of the contrast agent. The spin order is also transferred to a heteronucleus to produce amplified signals. Protective groups can also be used here, for example to stabilize unsaturated precursors for hydrogenation. These are then split off to obtain the contrast agent. [0125] 3) Parahydrogen is added to a precursor, which is then split to obtain the contrast agent. Only after the splitting is the spin order transferred to a heteronucleus. This process is particularly useful if the proton polarization after addition has a long lifetime. In addition, this process can be useful to create a coupling network more suitable for the transfer.

[0126] Each of the general procedures listed under points 1) to 3) greatly benefits from the robust and efficient broadband spin order transfer method according to the present invention.

[0127] Furthermore, particularly, the method according to the present invention can be used in one of at least three scenarios: [0128] A) The considered spins are all weakly coupled (all chemical shifts are larger than the J-couplings) as a prerequisite for the generation of the two-spin order. In the following this will be referred to as the high field case. [0129] B) The hydrogenation reaction takes place in the high field, under conditions mentioned under A), and is brought to a lower magnetic field B.sub.0 for the transfer experiment, where the conditions do not apply. By means of the method according to the present invention, it is still possible to produce the desired polarization of the heteronuclei. This will be referred to as the low field case in the following. [0130] C) The method can be used field-independently if a proton-heteronucleus coupling is much larger than all other couplings, particularly at least 3 times as large, particularly at least 5 times as large, particularly at least 10 times as large.

High Field Case

[0131] In the high field case the conditions n.sub.A=n.sub.B=n.sub.C=1 and .sub.A=.sub.C are preferably used according to an embodiment. To assess the transfer efficiency of spin order |f.sub.WC|, the following abbreviations are introduced:

[00003]${}_J=.Math..Math.J_{13}.Math.-.Math.J_{23}.Math..Math.$${.Math.}_J=.Math.J_{13}.Math.+.Math.J_{23}.Math.$

[0132] By means of these relationships, it is possible to select, with respect to the different time intervals .sub.A, .sub.B, .sub.C, optimal transfer conditions. The transfer efficiency is shown in FIG. 3.

[0133] For a simplified representation, FIG. 4 shows the one-dimensional projections of the efficiency and a possible parameter path from FIG. 3.

[0134] In particular, the representation of the efficiency shows that the method can be used broadband and thus goes beyond the state of the art.

[0135] The same sequence of FIG. 2 can be used for the case described above under C), more precisely for a very large proton-heteronucleus coupling.

[0136] The following tables 1, 2, and 3 state examples of relevant molecules and their optimized parameters. The most relevant molecules are pyruvate, acetate and lactate as well as other carboxylic acids, which all have a similar coupling network.

[0137] Particularly, in the tables below, ethyl acetate and cinnamyl acetate each form a precursor of a contrast agent, while phospholactate corresponds to a contrast agent.

TABLE-US-00001 TABLE 1 HH/ J.sub.12/ J.sub.13/ J.sub.23/ Molecule ppm Hz Hz Hz Ethyl acetate 3.0 7.1 3.6 0.1 [00001] Cinnamyl acetate (1) 1.0 11.5 11.0 0.1 [00002] Cinnamyl acetate (2) 1.0 11.5 160.0 5.0 [00003] Phospholactate 3.0 6.9 4.1 3.8 (.sup.13C transfer) [00004] Phospholactate 3.0 6.9 8.6 0.0 (.sup.31P transfer) [00005] Ir-Imes (SABRE) 0.1 8.0 25.5 0.5 [00006] [00007]

TABLE-US-00002 TABLE 2 Molecule B.sub.0/T .sub.A/ ms .sub.B/ms .sub.C/ms Ethyl acetate 7 135.1 71.1 135. 1 1 135.1 76.7 135. 1 [00008] 0.020 1216 774 1486 Cinnamyl acetate (1) 7 45.0 46.0 45.0 1 45.0 45.2 45.0 [00009] 0.020 495 478 45 Cinnamyl acetate (2) 7 3.0 44.3 3.0 1 3.0 44.8 3.0 [00010] 0.020 3.0 44.3 3.0 Phospholactate (.sup.13C 7 1709 360 1709 transfer) 1 1709 504 1709 [00011] 0.020 2215 1521 2088 Phospholactate (.sup.31P 7 135 73.9 58.1 transfer) 1 58.1 68.1 58.1 0.020 174 657 58.1 [00012] Ir-Imes (SABRE) 7 96.1 309.4 19.2 1 19.2 1040 19.2 [00013] 0.020 19.2 787 19.2 [00014]

TABLE-US-00003 TABLE 3 Molecule n.sub.A n.sub.B n.sub.C ||/ % Ethyl acetate 1 1 1 99.6 1 1 1 98.5 [00015] 2 9 5 58.8 Cinnamyl acetate (1) 1 1 1 99.5 1 1 1 97.5 [00016] 6 3 3 74.5 Cinnamyl acetate (2) 1 1 1 98.8 1 1 1 96.0 [00017] 1 1 1 97.0 Phospholactate (.sup.13C 1 1 1 99.7 transfer) 1 1 1 99.6 5 10 1 46.9 [00018] Phospholactate (.sup.31P 1 1 1 99.8 transfer) 1 1 1 92.1 1 2 11 83.2 [00019] Ir-Imes (SABRE) 3 1 15 92.7 1 1 1 91.5 [00020] 11 6 15 98.3 [00021]

Low Field Case

[0138] In the above-described case B), the highest possible efficiency is achieved with the shown pulse sequence of FIG. 2, if n.sub.A, n.sub.B and n.sub.C as well as the times .sub.A, .sub.B and .sub.C are considered differently from each other and optimized with respect to the couplings.

Signal Amplifier of Several Heteronuclei

[0139] In addition to amplifying the signal of only one heteronucleus, it may be useful to hyperpolarize several heteronuclei, e.g. to observe different metabolic pathways. By extending the sequence shown in FIG. 2, this is also possible. The considered spin system is shown in FIG. 5 and is extended by another heteronucleus S.sub.4. This adds another chemical shift .sub.SS and J.sub.34 between the two heteronuclei. The extension of the previously described sequence is shown in FIG. 6.

[0140] According thereto, the sequence of radio frequency pulses used to accomplish the transfer of the spin order further comprises a radio frequency pulse RF8 of angle having a phase .sub.24 (e.g. this pulse can be in the x-direction) and acting in the heteronuclei channel S and being spaced apart by a fourth time interval .sub.D from the 90 radio frequency pulse RF3. Furthermore, the sequence comprises a further 90 radio frequency pulse RF9 having a phase .sub.25 (e.g. y-direction) and acting in the heteronuclei channel S, which further 90 radio frequency pulse RF9 is spaced apart from said radio frequency pulse of angle RF8 by a fifth time interval .sub.E.

[0141] Particularly, .sub.D and .sub.E can be selected according to:

[00004]${}_D=n.Math.\frac{1}{2J_{34}},\mathrm{and}{}_E=\frac{1}{2J_{34}},$

wherein n is an integer, and wherein J.sub.34 is the J-coupling between the two heteronuclei S.sub.3 and S.sub.4 (cf. FIG. 5).

[0142] Furthermore, another 180 radio frequency pulse P13 having phase .sub.27 (e.g. x-direction) is applied in the heteronuclei channel S after said 90 radio frequency pulse RF5 and prior to said radio frequency pulse of angle RF7. Furthermore, a 180 radio frequency pulse P14 having phase .sub.28 (e.g. x-direction) is applied in the heteronuclei channel S after the radio frequency pulse of angle RF7 and prior to the 90 radio frequency pulse RF9.

[0143] Furthermore, for the sequence of FIG. 6 representing the transfer to S3 and S4 a decoupling on .sup.1H can be added starting at the time point T4 and the RF pulses P13, RF8 and P14 can be exchanged by a single continuous wave (CW) irradiation comprising a power much larger than the chemical shift difference between S.sub.3 and S.sub.4, so as to modulate the polarization over S.sub.3 and S.sub.4.

[0144] Furthermore, also in the sequence according to FIG. 6 the second group N.sub.B can comprise the optional further 180 RF pulses P11, P12 in the heteronucleus channel having phases .sub.23 and .sub.24.

[0145] Furthermore, according to yet another modification of the sequence shown in FIG. 6, the radio frequency pulse RF5 can be omitted.

[0146] Further, FIG. 7 shows a further embodiment of the method according to the present invention, which relates to a SABRE sequence. Particularly, SABRE refers to a PHIP method in which the parahydrogen molecule, the catalyst and the substrate (and other assisting co-ligands including the solvent) come together to form a labile complex. The complex persists for long enough to transfer polarization from the parahydrogen to a target heteronucleus of the substrate. The substrate is then released in a chemically unmodified form, and the catalyst remains ready for another transfer cycle when the hydrogen molecule is also released.

[0147] As for hydrogenative PHIP, there are two ways of transferring parahydrogen order to a target heteronucleus in SABRE: a first mode makes essential use of passing the sample at different magnetic fields (field cycling method) and a second make use of radiofrequency pulses and delays at one fixed magnetic field (RF method).

[0148] By suitable modifications, the known ESOTHERIC pulse sequence (cf. Pulsed Magnetic Resonance to Signal-Enhance Metabolites within Seconds by utilizing para-Hydrogen, ChemistryOpen 2018, 7, 344-348, Sergey Korchak, Shengjun Yang, Salvatore Mamone, and Stefan Glggler) can be adapted to transfer spin order in PHIP-SABRE. In SABRE polarization transfer, one has to take in account the existence of two substrate pools: one in which the substrate is bound to the catalyst-H.sub.2 complex and a second one in which the substrate is free.

[0149] In the following it is assumed that [0150] there are no nuclear spins directly j-coupled to the heteronucleus except for the H.sub.2 in the bound hydrogen-catalyst-substrate, which may necessitate deuteration of the substrate or [0151] if protons directly j-coupled to the heteronucleus are present, they can be selectively decoupled or the induced evolution can be refocused by a suitable choice of timing.

[0152] Compared to the original ESOTHERIC, the modifications particularly consist in the following: [0153] for the molecules in which a H.sub.2-catalyst-substrate complex is formed and maintained for all the duration of the sequence I.sub.1zI.sub.2z.fwdarw.fS.sub.3z.sup.b/2; where f is the efficiency of the transfer [0154] after a delay .sub.D the complex dissociates: S.sub.3z.sup.b.fwdarw.aS.sub.3z.sup.f+(1a)S.sub.3z.sup.b [0155] on the heteronuclear channel, a 90 pulse is added in the first bock and two 180 degree pulses at and of the second block, respectively. Overall S.sub.3z.sup.f.fwdarw.S.sub.3z.sup.f for the free substrate pool magnetization; [0156] on the 1H channel a 90 degree in the end of the last block ensures that I.sub.1zI.sub.1z.fwdarw.I.sub.1zI.sub.1z for all the H2 molecules that are either free or in a (H2-catalyst-no substrate complex). This pulse is optional. [0157] finally, a loop is added to pump polarization from the pool of bound substrate into the pool of free substrate.

[0158] It is important that maximum spin order I.sub.1zI.sub.2z is present at the H.sub.2-catalyst-substrate complex at every cycle in the loop. This can be achieved by introducing a bubbling time at the beginning of the loop cycle or by continuous bubbling of para-H.sub.2.

[0159] In this simplified model, it is possible to show that the maximum polarization reachable on the free substrate is

[00005]$p\frac{f}{1+f}$

when the relaxation of S.sub.3z.sup.f is negligible during the application of the repeated sequence.

[0160] For f=1, a maximum of 50% polarisation can transferred to the free substrate.

[0161] Particularly, as shown in FIG. 7, the sequence comprises three groups of 180 RF pulses, the first group N.sub.A comprising 180 RF pulses P1, P3 in the proton channel and 180 RF pulses P2, P4 in the heteronucleus channel, the pulses P1, P3, P2, P4 having phases .sub.11, .sub.12, .sub.21, .sub.22. Furthermore, the second group N.sub.B comprising 180 RF pulses P5, P6 in the proton channel and 180 RF pulses P11, P12 in the heteronucleus channel, the pulses P5, P6, P11, P12 having phases .sub.13, .sub.14, .sub.23, .sub.24. Further, the third group N.sub.C comprising 180 RF pulses P7, P9 in the proton channel and 180 RF pulses P8, P10 in the heteronucleus channel, the pulses P7, P9, P8, P10 having phases .sub.15, .sub.16, .sub.25, .sub.26

[0162] In each group the 180 RF pulses are applied during a first, a second and a third time interval .sub.A, .sub.B and .sub.C. Particularly, as an example, the respective time interval can be three seconds or less.

[0163] Particularly, the fourth time interval .sub.D is a delay to allow release of the substrate bound to the H.sub.2-catalyst complex at the end of the sequence. In practical embodiments of the sequence, the following values can be chosen for the phases (directions) of the RF pulses: [0164] each sub-block, the phases of the two 180 pulses in the same channel are shifted by 180 degrees relative to each other. [0165] the phases of the 90 pulses on the 1H channel (.sub.11, .sub.12, .sub.13, .sub.14) are collinear [0166] the phases .sub.22 can be chosen at will [0167] the phase .sub.23 is orthogonal to .sub.22 [0168] the phase .sub.21=.sub.23+. A specific choice is all the phases in each sub-block alternate between x and x, .sub.11=.sub.12=.sub.13=.sub.14=x, .sub.22=x, .sub.23=y; .sub.21=y.

[0169] In other practical embodiment of the sequences, any of the 180 pulses preceding a 90 pulse can be dropped, with appropriate adjustments of the phases of the subsequent 90 degree pulses.

[0170] Again, optionally, the second group N.sub.B can comprise the further 180 RF pulses P11, P12 in the heteronucleus channel having phases .sub.23 and .sub.24.

[0171] Particularly, if 180 RF pulses P11 and P12 are present one can select .sub.23=.sub.21 and .sub.24=.sub.26.

Purification of the Contrast Agent

[0172] The reaction for signal amplification and processing of the contrast agent can be conducted according to the examples described in the following.

[0173] Particularly, hyperpolarization is achieved by means of a catalyst in organic solvents. Ideally, the solvents do not form an azeotrope with water but form a phase. Such solvents are for example acetone and methanol. After signal amplification of the heteronucleus (e.g. as described herein), aqueous solution is added to the reaction mixture. The aqueous solution may contain a substance (e.g. acids or bases or enzymes) that splits metabolite precursors to obtain the signal amplified metabolite. In addition, complexing reagents may be added to the solution to capture the catalyst used. Complexing agents are for example microparticles with thiol groups that bind the metal or other ligands that are poorly soluble in the complex. This step can already be carried out before the addition of water in the organic solvent. The organic solvent is then evaporated, wherein evaporation can also mean to remove the solvent via a stripping gas. The evaporation with or without stripping gas can be facilitated by applying a vacuum. The stripping gas can be added intentionally or be result of residual pressure of gas in the setup (e.g. hydrogen) after applying vacuum.

[0174] During this process by-products and impurities may precipitate (catalyst, side chains after splitting, etc.), which are then removed by filtering the aqueous solution. Finally, a pure injection solution with contrast agent is obtained. For contrast media that are hardly soluble in water, organic solvent in the form of e.g. ethanol can be added to the injection solution.

[0175] Alternatively, the contrast agent can be hyperpolarized in an aqueous or organic solution or a mixture thereof. The solvent is then evaporated, leaving the contrast agent behind. It can then be washed with a solvent in which the contrast agent does not dissolve. Absorption of the contrast agent in a solution results in a pure injection solution.

[0176] According to a specific example (particularly relating to the context of PHIP), 0.5 ml solution of 100 mM phenylacetylene pyruvate in acetone-d6 and 2 mM rhodium catalyst is hydrogenated at 50 C using 7 bars p-H2 for 20 s giving cinnamyl pyruvate. The pressure is released. 0.1 ml of 10 mM chelating agent (dithizone or another non-soluble in water) is added to the acetone solution. 0.5 ml of 100 mM sodium carbonate in water is added to hydrolyse the precursor in 2 s to free pyruvate and cinnamyl alcohol. The acetone is evaporated under vacuum (where residual hydrogen gas flows through the solution and mixes it thus facilitating evaporation) and 0.2 ml concentrated PBS buffer is added. The solution is filtered to remove cinnamyl alcohol, complexed rhodium and insoluble catalyst leftovers, leaving pure pyruvate in physiological PBS buffer.

[0177] Furthermore, according to yet another specific example (relating to the context of SABRE), 0.5 ml solution of 100 mM 15N-nicotinic acid in methanol-d3 and 2 mM iridium catalyst is supplied with hydrogen at 30 C using 7 bars p-H2 for 20 s. The pressure is released. 0.1 ml of 10 mM chelating agent (dithizone or another non-soluble in water) is added to the methanol solution. 0.5 ml of biological PBS buffer is added. The methanol is evaporated under vacuum. The solution is filtered to remove complexed iridium and insoluble catalyst leftovers, leaving pure nicotinic acid in physiological PBS buffer.

[0178] Furthermore, according to an embodiment, in all sequences described herein or shown in FIGS. 2, 6, 7 the last radio frequency pulse on the heteronucleus is used to tilt the magnetization along the z axis. In principle it can be any value if one wants to observe a fraction directly and store the rest of the magnetization. It can be removed if one wants to observe directly all the magnetization.

[0179] The invention further encompasses, but is not limited to, the following items. Consequently, each item can also be formulated as a patent claim of the present application that can relate to other claims according to the dependencies stated in the items. The reference numerals stated in parentheses relate to the Figures described above. [0180] Item 1: A method for transferring a two-spin order of a molecule into a hyperpolarization of at least one heteronucleus, the method comprising the steps of: [0181] providing a molecule comprising two protons and at least one heteronucleus (S.sub.3, S.sub.4), the protons having nuclear spins being coupled to a nuclear spin of the at least one heteronucleus; [0182] exposing the protons and the at least one heteronucleus to a magnetic field (B.sub.0) in a z-direction, the z-direction forming a right-handed orthogonal coordinate system with an x and a y-direction; [0183] applying a sequence of radio frequency pulses to the protons and the at least one heteronucleus in order to transfer said two-spin order into the hyperpolarization of the at least one heteronucleus, wherein said sequence of radio frequency pulses comprises a first, a second, and a third group (N.sub.A, N.sub.B, N.sub.C) of 180 radio frequency pulses, wherein the first group (N.sub.A) of 180 radio frequency pulses is consecutively applied n.sub.A times during a first time interval (.sub.A) and wherein the second group (N.sub.B) of 180 radio frequency pulses is consecutively applied n.sub.B times during a second time interval (.sub.B) after the last first group, and wherein the third group (N.sub.C) of 180 radio frequency pulses is consecutively applied n.sub.C times during a third time interval (.sub.C) after the last second group, wherein n.sub.A, n.sub.B, n.sub.C are integer numbers, respectively. [0184] Item 2: The method according to item 1, wherein the first group (N.sub.A) of 180 radio frequency pulses comprises a first 180 radio frequency pulse (P1) having a phase .sub.11 and acting on the protons, and a second 180 radio frequency pulse (P2) having a phase .sub.21 and acting on the at least one heteronucleus (S.sub.3), and wherein the first group (N.sub.A) of 180 radio frequency pulses comprises a third 180 radio frequency pulse (P3) having a phase .sub.12 and acting on the protons, and a fourth 180 radio frequency pulse (P4) having a phase .sub.22 and acting on the at least one heteronucleus (S.sub.3). [0185] Item 3: The method according to one of the preceding items, wherein the second group (N.sub.B) of 180 radio frequency pulses comprises a first 180 radio frequency pulse (P5) having a phase .sub.13 and acting on the protons and a succeeding second 180 radio frequency pulse (P6) having a phase .sub.14 and acting on the protons. [0186] Item 4: The method according to item 1 or 2, wherein the second group (N.sub.B) of 180 radio frequency pulses comprises a first 180 radio frequency pulse (P11) having a phase .sub.23 and acting on the at least one heteronucleus (S.sub.3) and a succeeding second 180 radio frequency pulse (P5) having a phase .sub.13 and acting on the protons, and wherein the second group (N.sub.B) of 180 radio frequency pulses comprises a third 180 radio frequency pulse (P12) having a phase .sub.24 and acting on the at least one heteronucleus (S.sub.3) and a succeeding fourth 180 radio frequency pulse (P6) having a phase .sub.14 and acting on the protons, wherein the third and the fourth 180 radio frequency pulses (P12, P6) of the second group (N.sub.B) are applied after the second 180 radio frequency pulse (P5) of the second group (N.sub.B). [0187] Item 5: The method according to one of the preceding items, wherein the third group (N.sub.C) of 180 radio frequency pulses comprises a first 180 radio frequency pulse (P7) having a phase .sub.15 and acting on the protons, and a second 180 radio frequency pulse (P8) having a phase .sub.25 and acting on the at least one heteronucleus (S.sub.3), and wherein the third group (N.sub.C) of 180 radio frequency pulses comprises a third 180 radio frequency pulse (P9) having a phase .sub.16 and acting on the protons, and a fourth 180 radio frequency pulse (P10) having a phase .sub.26 and acting on the at least one heteronucleus (S.sub.3). [0188] Item 6: The method according to one of the preceding items, wherein the first time interval (.sub.A) is different from the second time interval (.sub.B), and/or wherein the first time interval (.sub.A) is equal to the third time interval (.sub.C). [0189] Item 7: The method according to one of the preceding items, wherein said integer numbers n.sub.A, n.sub.B, n.sub.C are selected to be n.sub.A=1, n.sub.B=1, and n.sub.C=1. [0190] Item 8: The method according to one of the preceding items, wherein in each group (N.sub.A, N.sub.B, N.sub.C) the phases of the 180 radio frequency pulses acting on the protons are shifted by 180 relative to one another, and/or wherein in each group (N.sub.A, N.sub.B, N.sub.C) the phases of the 180 radio frequency pulses acting on the at least one heteronucleus are shifted by 180 relative to one another. [0191] Item 9: The method according to one of the preceding items, wherein in the n.sub.A.sup.th applied first group (N.sub.A) the third and the fourth 180 radio frequency pulse (P3, P4) are omitted, and/or wherein in the n.sub.B.sup.th applied second group (N.sub.B) the second 180 radio frequency pulse (P6) or the fourth 180 radio frequency pulse (P6) is omitted, and/or wherein in the n.sub.C.sup.th applied third group (N.sub.C) the third and the fourth 180 radio frequency pulse (P9, P10) are omitted. [0192] Item 10: The method according to one of the preceding items, wherein said sequence of radio frequency pulses further comprises a first 90 radio frequency pulse (RF1) having a phase .sub.11 and acting on the protons, wherein the first group (N.sub.A) of 180 radio frequency pulses is consecutively applied n.sub.A times during said first time interval (.sub.A) after said first 90 radio frequency pulse (RF1), and wherein said sequence of radio frequency pulses further comprises a second 90 radio frequency pulse (RF2) having a phase .sub.12 and acting on the protons, which second 90 radio frequency pulse (RF2) succeeds the first 90 radio frequency pulse (RF1) and is applied to the protons at an end of the first time interval (.sub.A), wherein the second group (N.sub.B) of 180 radio frequency pulses is consecutively applied n.sub.B times during said second time interval (.sub.B) after said second 90 radio frequency pulse (RF2), and wherein said sequence of radio frequency pulses further comprises a third 90 radio frequency pulse (RF3) having a phase .sub.13 and acting on the protons, which third 90 radio frequency pulse (RF3) succeeds the second 90 radio frequency pulse (RF2) and is applied to the protons at an end of the second time interval (.sub.B), wherein the third group (N.sub.C) of 180 radio frequency pulses is consecutively applied n.sub.C times during said third time interval (.sub.C) after said third 90 radio frequency pulse (RF3). [0193] Item 11: The method according to item 10, wherein said sequence of radio frequency pulses further comprises a fourth 90 radio frequency pulse (RF4) having a phase .sub.22 and acting on the at least one heteronucleus (S.sub.3) and a succeeding optional fifth 90 radio frequency pulse (RF5) having a phase .sub.23 and acting on the at least one heteronucleus, wherein particularly the third 90 radio frequency pulse (RF3) is simultaneous with said fourth 90 radio frequency pulse (R4). [0194] Item 12: The method according to item 10 or 11, wherein the phases .sub.11, .sub.12, .sub.13 of the first, second and third 90 radio frequency pulse (RF1, RF2, RF3) are collinear, and/or wherein the phase (.sub.23) of the fifth 90 radio frequency pulse (RF5) is orthogonal to the phase (.sub.22) of the fourth 90 radio frequency pulse (RF4), wherein particularly .sub.11=.sub.12=.sub.13=x, .sub.22=x, .sub.23=y. [0195] Item 13: The method according to item 11 or 12, wherein said sequence of radio frequency pulses further comprises a sixth 90 radio frequency pulse (RF6) having a phase .sub.14 and acting on the protons, wherein said sequence of radio frequency pulses further comprises a seventh 90 radio frequency pulse (RF7) having a phase .sub.21 and acting on the at least one heteronucleus (S.sub.3), wherein particularly the sixth 90 radio frequency pulse (RF6) is simultaneous with the fifth 90 radio frequency pulse (RF5), and wherein particularly the seventh 90 radio frequency pulse (RF7) is simultaneous with the first 90 radio frequency pulse (RF1). [0196] Item 14: The method according to item 13, wherein the phases .sub.11, .sub.12, .sub.13, .sub.14 of the first, second, third, and sixth 90 radio frequency pulse (RF1, RF2, RF3, RF6) are collinear, and wherein the phase .sub.21 of the seventh 90 radio frequency pulse (RF7) corresponds to .sub.21=.sub.23+, wherein particularly .sub.11=.sub.12=.sub.13=.sub.14=x, .sub.22=x, .sub.23=y, and .sub.21=y. [0197] Item 15: The method according to item 13 or 14, wherein said sequence of radio frequency pulses is repeated after lapsing of a fourth time interval (.sub.D) after applying said fifth and/or sixth 90 radio frequency pulses (RF5, RF6), wherein particularly said sequence of radio frequency pulses is repeated n times, n being an integer. [0198] Item 16: The method according to one of the items 1 to 12, wherein the step of providing a molecule and at least one heteronucleus also comprises providing a further heteronucleus (S.sub.4), the nuclear spin of the at least one heteronucleus (S.sub.3) being coupled to a nuclear spin of the further heteronucleus (S.sub.4), and wherein the step of exposing the protons and the at least one heteronucleus to a magnetic field (B.sub.0) in the z-direction, also comprises to expose the further heteronucleus (S.sub.4) to said magnetic field (B.sub.0), and wherein the step of applying a sequence of radio frequency pulses to the protons and the at least one heteronucleus (S.sub.3) in order to transfer said two-spin order into the hyperpolarization of the at least one heteronucleus (S.sub.3) also comprises transfer of the two-spin order into hyperpolarization of the further heteronucleus (S.sub.4). [0199] Item 17: The method according to claim 16, wherein the heteronucleus and the further heteronucleus can be of the same species or belong to a different species. [0200] Item 18: The method according to item 16 or 17, wherein said sequence of radio frequency pulses further comprises a sixth radio frequency pulse (RF8) of angle having a phase .sub.24 and acting on the heteronuclei (S.sub.3, S.sub.4) and being spaced apart by a fourth time interval (.sub.D) from the third 90 radio frequency pulse (RF3), and wherein said sequence of radio frequency pulses comprises a seventh 90 radio frequency pulse (RF9) having a phase .sub.25 and acting on the heteronuclei (S.sub.3, S.sub.4), wherein the seventh 90 radio frequency pulse (RF9) is spaced apart from said sixth radio frequency pulse (RF8) of angle by a fifth time interval (.sub.E). [0201] Item 19: The method according to items 11 and 18, wherein said sequence of radio frequency pulses further comprises a 180 radio frequency pulse (P13) having a phase .sub.27 and acting on the heteronuclei (S.sub.3, S.sub.4), particularly after said fifth 90 radio frequency pulse (RF5) and/or prior to said sixth radio frequency pulse (RF8) of angle , and wherein said sequence of radio frequency pulses further comprises a 180 radio frequency pulse (P14) having a phase .sub.28 and acting on the heteronuclei (S.sub.3, S.sub.4) after the sixth radio frequency pulse (RF8) of angle and prior to said seventh 90 radio frequency pulse (RF9). [0202] Item 20: The method according to item 16, wherein said sequence of radio frequency pulses further comprises a single continuous wave irradiation acting on the two heteronuclei (S3, S4) and comprising a power larger than a chemical shift difference between the two heteronuclei (S3, S4), particularly so as to modulate a polarization over the two heteronuclei (S3, S4). [0203] Item 21: The method according to one of the preceding items, wherein for obtaining a hyperpolarized contrast agent comprising the at least one heteronucleus (S.sub.3), prior to said step of applying a sequence of radio frequency pulses to the protons and the at least one heteronucleus in order to transfer said two-spin order into the hyperpolarization of the at least one heteronucleus (S.sub.3), said molecule is added to one of: [0204] a mediator, the mediator not being part of the hyperpolarized contrast agent in the end, [0205] a precursor of the hyperpolarized contrast agent, which precursor is finally part of the hyperpolarized contrast agent, wherein the at least one heteronucleus (S.sub.3) is comprised by the precursor, [0206] a precursor of the hyperpolarized contrast agent, which precursor is then split to obtain the contrast agent that comprises the at least one heteronucleus (S.sub.3). [0207] a contrast agent, wherein the at least one heteronucleus is comprised by the contrast agent. [0208] Item 22: The method according to one of the preceding items, wherein said at least one heteronucleus (S.sub.3, S.sub.4) is one of: [0209] .sup.13C contained in pyruvate; [0210] .sup.13C contained in an acetate, [0211] .sup.13C contained in ethyl acetate; [0212] .sup.13C contained in cinnamyl acetate (1); [0213] .sup.13C contained in cinnamyl acetate (2); [0214] .sup.13C contained in a lactate; [0215] .sup.31P contained in phospholactate; [0216] .sup.13C contained in phospho-enol-lactate; [0217] .sup.31P contained in phospho-enol-lactate; [0218] .sup.13C contained in acetoacetate; [0219] .sup.13C contained in 3-hydroxybutyrate; [0220] .sup.13C contained in an amino acid; [0221] .sup.13C contained in a fatty acid; [0222] .sup.13C contained in cinnamyl pyruvate; [0223] .sup.13C contained in cinnamyl lactate. [0224] Item 23: The method according to one of the preceding claims, wherein the respective radio frequency pulse is one of; a rectangular pulse, a frequency selective pulse, a shaped pulse having a shape deviating from a rectangular shape. [0225] Item 24: The method according to one of the preceding claims, wherein a final radio frequency pulse on the heteronucleus is one of: [0226] used to tilt the magnetization along the z axis or used to tilt the magnetization in an arbitrary direction, particularly for observing a fraction directly and for storing a rest of the magnetization, [0227] omitted in case it would tilt the magnetization along the z axis to allow observing all the magnetization directly. [0228] Item 25: [0229] A method for transferring a two-spin order of a molecule into a hyperpolarization of at least one heteronucleus (S.sub.3, S.sub.4), the method comprising the steps of: [0230] providing a molecule comprising two protons (H1, H2) and at least one heteronucleus (S3, S4), the protons having nuclear spins being coupled to a nuclear spin of the at least one heteronucleus (S3, S4), wherein the J-coupling between a proton and the at least one heteronucleus is larger than the J-coupling between the two protons, and [0231] transferring the two spin-order to the at least one heteronucleus using radio frequency pulses. [0232] Item 26: The method according to one of the preceding items, wherein said hyperpolarization of the at least one heteronucleus is conducted with help of a catalyst in an organic solvent. [0233] Item 27: The method according to item 26, wherein after hyperpolarization of the at least one heteronucleus, an aqueous solution is added to the organic solvent. [0234] Item 28: The method according to item 27, wherein the aqueous solution comprises a cleaving agent that is configured to cleave a precursor comprising the at least one hyperpolarized heteronucleus to obtain a hyperpolarized contrast agent. [0235] Item 29: The method according to one of the items 26 to 28, wherein for capturing the catalyst a complexing agent is added to the organic solvent before or after adding the aqueous solution to the organic solvent. [0236] Item 30: The method according to item 29, wherein the organic solvent is evaporated or removed by using a stripping gas. Particularly, the evaporation of organic solvent is facilitated by applying a vacuum. Particularly, the evaporation of organic solvent is facilitated by a stripping gas flow through the aqueous solution. The stripping gas can be any gas or steam, preferably an inert gas, e.g. nitrogen, hydrogen. [0237] Item 31: The method according to item 30, wherein for obtaining an injectable solution comprising the contrast agent, the aqueous solution is filtered to remove by-products and/or impurities that precipitated upon evaporation. [0238] Item 32: The method according to one of the items 1 to 25, wherein said hyperpolarization of the at least one heteronucleus forming part of a contrast agent is conducted in a solvent, the solvent being one of: an aqueous solution, an organic solution, a mixture of an aqueous and an organic solution. [0239] Item 33: The method according to item 32, wherein the solvent is evaporated or removed by using a stripping gas, leaving the hyperpolarized contrast agent behind, particularly in a solid form. Particularly, the evaporation of organic solvent is facilitated by applying a vacuum. Particularly, the evaporation of organic solvent is facilitated by a stripping gas flow through the solution. The stripping gas can be any gas or steam, preferably an inert gas, e.g. nitrogen, hydrogen. [0240] Item 34: The method according to item 33, wherein the contrast agent is washed with a solvent in which the contrast agent does not dissolve. [0241] Item 35: The method according to item 34, wherein for obtaining an injectable solution comprising the contrast agent, the contrast agent is added to a solution. [0242] Item 36: A method for obtaining a hyperpolarized contrast agent, the method comprising the steps of: [0243] Adding a molecule comprising two protons forming a two-spin order to a precursor of the contrast agent, [0244] Splitting the precursor to obtain the contrast agent, [0245] Transferring the two-spin order into a hyperpolarization of at least one heteronucleus of the contrast agent to obtain the hyperpolarized contrast agent. [0246] Item 37: The method according to item 36, wherein transferring the two-spin order into hyperpolarization of the at least one heteronucleus is conducted using a method according to one of the items 1 to 20, 22 to 35 [0247] Item 38: A method for obtaining an injectable solution comprising a contrast agent, wherein [0248] a hyperpolarization of at least one heteronucleus is conducted with help of a catalyst in an organic solvent, wherein after hyperpolarization of the at least one heteronucleus, an aqueous solution is added to the organic solvent, and wherein the aqueous solution may comprise a cleaving agent that is configured to cleave a precursor comprising the at least one hyperpolarized heteronucleus to obtain a hyperpolarized contrast agent, and wherein for capturing the catalyst a complexing agent can be added to the organic solvent before or after adding the aqueous solution to the organic solvent, and wherein the organic solvent is evaporated or removed by using a stripping gas, and wherein for obtaining an injectable solution comprising the contrast agent, the aqueous solution is filtered to remove by-products and/or impurities that precipitated upon evaporation; [0249] or wherein [0250] a hyperpolarization of at least one heteronucleus forming part of a contrast agent is conducted in a solvent, the solvent being one of: an aqueous solution, an organic solution, a mixture of an aqueous and an organic solution, wherein the solvent is evaporated or removed by using a stripping gas, leaving the hyperpolarized contrast agent behind, particularly in a solid form, and wherein the contrast agent is washed with a solvent in which the contrast agent does not dissolve, and wherein for obtaining an injectable solution comprising the contrast agent, the contrast agent is added to a solution. [0251] Item 39: The method according to claim 38, wherein the evaporation of organic solvent is facilitated by applying a vacuum, wherein particularly the evaporation of organic solvent is facilitated by a stripping gas flow through the solution.