JP5224461B2 - Method for producing contrast medium - Google Patents

Description

  The present invention relates to a method effective for improving NMR signal detection sensitivity of a sample to be analyzed in biodiagnosis using NMR (Nuclear Magnetic Resonance), molecular structure analysis of organic chemistry, and the like. More specifically, a method for producing an organic radical species using ultraviolet rays, and an NMR signal detection by further performing dynamic nuclear polarization (hereinafter referred to as DNP if necessary) on the organic radical species. The present invention relates to a method for producing a contrast agent with improved sensitivity and a contrast agent produced by the method.

  NMR refers to a resonance phenomenon that occurs when a sample to be measured containing nuclei having a magnetic moment is placed in a strong magnetic field of several Tesla and an electromagnetic wave having a frequency satisfying the resonance condition is applied thereto. The magnetic moment of a nucleus is called a nuclear spin, and NMR observes the energy absorption and emission processes of the nuclear spin. Normally, the nuclear spin emission energy immediately after stopping the electromagnetic wave having the resonance frequency is detected as an electric signal by a search coil, and the detected electric signal is called an NMR signal. Although NMR is considered useful for biodiagnosis and molecular structure analysis, it has the inherent disadvantage of low NMR signal detection sensitivity, and various technological developments related to improving NMR signal detection sensitivity have been conducted. It has been broken.

The main technological developments are:
1) Further strong magnetic field
2) Low noise in NMR signal detection circuit
3) Adoption of dynamic nuclear spin polarization method is mentioned, and the present invention relates to 3) dynamic nuclear spin polarization method.
The dynamic nuclear spin polarization method increases the intensity of an NMR signal by applying a strong magnetic field and microwaves to a radical species having electron spin to shift the electron spin polarization to nuclear spin polarization.

In order to perform dynamic nuclear spin polarization, there must be about 10 ¹⁹ spins / cm ³ of radicals in the sample. Until now
A. Incorporating stable radicals such as trityl radicals and nitroxy radicals,
B. Generate radicals in a cryogenic solid sample by electron beam irradiation (see Non-Patent Documents 1 and 2),
Uses photoexcited spin triplet such as C. pentacene (see Non-Patent Document 3)
Methods have been reported. As a device for performing dynamic nuclear spin polarization, HyperSense (registered trademark) of Oxford Instruments is known (see Non-Patent Document 4).

D.G.Crabb et al. Phys. Rev. Lett. 64, 2627 (1990) S. T. Goertz et al. Nucl. Inst. Meth. A 526, 43 (2004) M.Iinuma et al. Phys. Rev. Lett. 84,171 (2000) Catalog of HyperSense (registered trademark) of Oxford Instruments Molecular Biotools Ltd. (Hyp / 01 / A / 0306) E. R. McCarney and S. Han, J. Mag. Res. 190,307 (2008) J. H Ardenkjaer-Larsen et al. Appl. Phys. Sci. 100, 10158 (2003)

The DNP method is a technique for obtaining a nuclear spin polarization equivalent to an electron spin by performing a polarization transfer from an electron spin mixed in a sample to a nuclear spin. The polarization degree of hydrogen nuclear spins at room temperature under a magnetic field of 3.5 Tesla is only about 10 ^-4 %. However, if the DNP method is used at an extremely low temperature, it can be raised to nearly 100% in principle. The NMR signal intensity is proportional to the nuclear spin polarization. An NMR signal whose signal intensity is 6 digits higher in principle if the cryogenic sample in the high nuclear spin polarization state obtained in the DNP apparatus is melted, transferred to the NMR apparatus, and measured before the nuclear spin relaxation time. Can be obtained.

Returning to the previous section, the above-mentioned A. is a technique that can introduce radicals most easily into a sample, and is a technique that has been generally used in DNP experiments, but has the following two problems.
Since stable radicals remain even after the sample is melted and promotes a decrease in the degree of nuclear spin polarization, a sample mixed with stable radicals cannot maintain the effect as a contrast agent for a long time.
Toxicity of stable radicals in animal NMR measurements.

  In order to solve this problem, there is a study (see Non-Patent Document 5) that separates radicals from a polarized solution by attaching stable radicals to the airgel. However, the maximum degree of polarization is slightly less than that at room temperature thermal equilibrium. It is about 40 times, which is much lower than the reported value using the method of B. (> 10000, see Non-Patent Document 6).

Unlike the stable radical of A., the radical generated in the cryogenic solid sample by the method of B. disappears with melting, so the effect as a contrast agent lasts longer than the method of A. There is no need to consider. But,
Since an electron beam bends in a magnetic field, the dynamic nuclear spin polarization device must be demagnetized or the sample must be irradiated at a location more than a certain distance away. The irradiated sample must be transported to a dynamic nuclear spin polarization device while maintaining a cryogenic environment.
Furthermore, since the electron beam has a low material permeability, a very low temperature sample must be taken out from the container and irradiated.
Measures such as radiation protection are required.
Since the electron beam irradiation experiment is very complicated, this method has hardly been used.

  C. can be used only in very limited media such as naphthalene crystals because pentacene has a low solubility in organic solvents and requires high transparency even though it is a solid sample when laser light is incident.

  An object of the present invention is to provide a method for producing an organic radical species that is easy to produce organic radicals, and a method for producing a contrast agent using a dynamic nuclear spin polarization method that has low toxicity and maintains a contrast effect. It is in providing the contrast agent manufactured by this.

  In order to achieve the aforementioned object, in the method for producing an organic radical species according to one aspect of the present invention, a small amount of photodissociable molecules are added to an organic solvent, irradiated with ultraviolet rays at an extremely low temperature, An organic radical is generated. The amount of the photolabile molecule added to the organic solvent is 0.1 to 1 wt%.

  In addition, in the method for producing a contrast agent according to another aspect of the present invention, dynamic nuclear spin polarization is performed using an organic radical generated by irradiating ultraviolet light to a cryogenic organic solvent mixed with a photolabile molecule. Is doing.

  Molecular dissociation and its side reactions are induced by adding a small amount of photodissociable molecules in an organic solvent and irradiating ultraviolet rays at an extremely low temperature. Using this phenomenon, a large amount of radicals used for dynamic nuclear spin polarization can be produced. Unlike electron beams, ultraviolet rays are small and do not require radiation protection. In particular, ultraviolet rays having a wavelength of 200 nm or more are easy to handle and highly safe because they do not cause ozonization of oxygen in the air. In addition, if the sample cell is made of quartz or the like without being bent by the magnetic field, the sample can be irradiated without being taken out of the cell. In addition, it is possible to easily guide ultraviolet light to the sample portion at the center of the dynamic nuclear spin polarization apparatus using an optical fiber.

  In the production of the contrast agent described above, butanol containing 0.1 to 1 weight percent (wt%) phenol as a photolabile molecule is preferably used as the organic solvent.

  Further, in the production of a contrast agent, the organic solvent containing the photolabile molecule is placed in a dynamic nuclear spin polarization device, and ultraviolet rays are guided to the organic solvent via an ultraviolet transmission optical fiber. By performing irradiation and dynamic nuclear spin polarization at the same location, it is possible to avoid the hassle of transporting a low-temperature solid sample from the ultraviolet irradiation section to the dynamic nuclear spin polarization apparatus while preventing melting.

  The contrast agent according to still another aspect of the present invention is to perform dynamic nuclear spin polarization using an organic radical generated by irradiating ultraviolet light to a cryogenic organic solvent mixed with a trace amount of photolabile molecules. Can be manufactured with extremely simple equipment. The radical generated in the cryogenic sample by ultraviolet decomposition is generally highly reactive, and immediately disappears through a recombination reaction with another radical immediately after thawing to become a molecule having low reactivity and toxicity. Therefore, the problem of toxicity and depolarization after thawing, which has been a problem with the technique using stable radicals, is solved.

  According to the present invention, with the same degree of effort as the method of A. described above, it has been obtained only by the complicated method of B. A large amount of radicals that do not cause harm can be generated. Therefore, according to the present invention, a contrast agent having extremely high NMR signal detection sensitivity can be obtained.

It is a schematic explanatory drawing of the apparatus for enforcing the manufacturing method of the contrast agent by performing dynamic nuclear spin polarization concerning one embodiment of the present invention. It is a schematic explanatory drawing of the experimental apparatus for verifying the generation of radicals by ultraviolet rays and the dynamic nuclear spin polarization. It is a figure which shows the result obtained by experiment, Comprising: The intensity | strength change of the NMR signal before (at the time of thermal equilibrium) and after (at the time of nuclear spin polarization) which raise | generates dynamic nuclear spin polarization using the contrast agent of this invention is shown. It is a figure for demonstrating. It is a figure which shows the correlation with the radical concentration and ultraviolet irradiation time in a 77K butanol / phenol (0.1 wt.%) Sample determined by the electron spin method. It is a figure which shows the ultraviolet signal irradiation time to a butanol / phenol (0.3 wt.%) Sample, and the relationship of the NMR signal intensity at the time of 4.2K polarization with respect to the NMR signal intensity at the time of 4.2 K thermal equilibrium. It is a figure which shows the relationship between a phenol concentration and the ratio of the NMR signal intensity at the time of 1.5K polarization with respect to the NMR signal intensity at the time of 4.2 K thermal equilibrium.

  The present invention makes it very easy to create radicals that are stable only in cryogenic solids, such as those produced by electron beam irradiation, and that disappear instantaneously upon melting, using the ultraviolet decomposition method. Unlike radiation, the extinction coefficient and decomposition probability of ultraviolet light strongly depend on the shape of the molecule.In one embodiment of the present invention, phenol that is susceptible to ultraviolet decomposition is applied to a polarized sample. It is mixed as a photolabile molecule.

  The photolabile molecule is preferably an optical fiber, a quartz window, or a molecule that decomposes with ultraviolet rays having a wavelength that is highly permeable to the atmosphere to generate hydrogen atoms. Since the bonding force of carbon-hydrogen bonds of most organic substances is smaller than the hydrogen-hydrogen bonding force of hydrogen molecules, hydrogen atoms generated by ultraviolet irradiation draw hydrogen atoms from organic solvents and unpair with carbon sites. Create radicals with electrons. A radical having an unpaired electron at a carbon site is likely to cause dynamic nuclear spin polarization because the g-value anisotropy of electron spin resonance is small and the line width of the strong magnetic field electron spin resonance spectrum is narrow.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic explanatory diagram of an apparatus for carrying out a method for producing a contrast agent by performing dynamic nuclear spin polarization according to an embodiment of the present invention. In FIG. 1, 20 is an NMR apparatus, 19 is a microwave generator, 11 is a dynamic nuclear spin polarization apparatus, and 12 and 13 are ultraviolet generators. In addition, 14 is an ultraviolet transmission optical fiber, 15 is a polarization coil, 16 is a sample, 17 is a polarized sample transport tube, 18 is attached to the tip of the polarized sample transport tube 17, and a contrast agent is injected into the living body. It is a work implement to do.

The UV transmissive optical fiber 14 is provided between the UV generators 12 and 13 made of a mercury lamp or a laser and the sample 16 of the dynamic nuclear spin polarization device 11, and polarizes the UV generated by the UV generators 12 and 13. It leads to the pole sample. The polarized sample in the sample 16 is mixed with a small amount of photolabile molecules such as phenol. A sample cooled to a very low temperature is irradiated with ultraviolet rays to generate radicals, and then irradiated with microwaves generated by the microwave generator 19, thereby performing dynamic nuclear spin polarization at the same location. The dynamic nuclear spin-polarized sample, like the polarized sample using stable radicals, is instantly melted by using, for example, hot water, and then instantaneously reaches the NMR apparatus 20 (or NMR apparatus) through the transport tube 17. Transport. Here, the dynamic nuclear spin polarization device 11, the transport tube 17 extending from the dynamic nuclear spin polarization device 11 to the NMR device 20, and the work tool 18 provided at the tip of the transport tube 17 are all used in conventional NMR diagnosis. It has the same structure as the device and instrument.
<Experimental example>

  In order to verify the method for producing a contrast agent according to the present invention, in a verification experiment, after performing ultraviolet irradiation using an apparatus (container) different from the dynamic nuclear spin polarization apparatus 11, dynamic nuclear spin polarization is performed. The sample was transferred to the apparatus 11 for dynamic nuclear spin polarization. FIG. 2 is a schematic explanatory diagram of an experimental apparatus for verifying generation of radicals by ultraviolet rays and dynamic nuclear spin polarization. In the figure, the same reference numerals as those in FIG. 1 denote components having substantially the same function, 21 is a quartz liquid nitrogen dewar, 22 is a glass liquid helium dewar, and each dewar uses a conventional one. And installed independently. The nuclear spin polarization was measured using the NMR apparatus 23 for measuring nuclear spin polarization.

A butanol sample containing phenol was inserted into a quartz dewar 21 filled with 77K liquid nitrogen and solidified. After solidification, ultraviolet rays (Minaga Electric SUPERCURE-352S, central wavelength 365 nm, 5000 mW) from a mercury xenon lamp were irradiated from outside Dewar 21 for about 1 hour to generate about 10 ¹⁹ spins / cm ^{3 of} butanol radicals. Unlike at room temperature, butanol radicals do not disappear at 77K. After irradiation, the sample was quickly transferred (within 10 seconds) to the dynamic nuclear spin polarization device 11 filled with liquid helium, and after measuring the NMR signal of hydrogen in thermal equilibrium under 4.2K, 1.18 Tesla, liquid helium The sample was cooled to 1.5K by depressurizing and dynamic nuclear spin polarization was performed by microwave irradiation (33.2 GHz, 50 mW).

FIG. 3 shows the result of measuring the state of dynamic nuclear spin polarization with the NMR device 23 for measuring nuclear spin polarization. FIG. 3 shows the NMR signal intensity of hydrogen nuclei in butanol / phenol (0.3 wt%) material irradiated with ultraviolet rays. In FIG. 3, the NMR signal intensity (arb.) On the vertical axis (not shown) is proportional to the nuclear spin polarization. From the signal intensity ratio between 4.2K thermal equilibrium and dynamic nuclear spin polarization, it is clear that the degree of polarization is up to about 50 times. As shown in FIG. 3, the intensity of the NMR signal reached 14% for 4.2K dynamic polarization and 48% for 1.5K dynamic polarization with respect to the 4.2K thermal equilibrium signal. . This value is more than 3000 times the degree of polarization 4 × 10 ⁻⁴ % at 1.l8 Tesla room temperature thermal equilibrium. It is considered that a higher absolute polarization can be obtained if a similar experiment is performed with a higher magnetic field using a superconducting magnet.

  FIG. 4 shows the relationship between the radical concentration in the butanol / phenol sample and the ultraviolet irradiation time determined by the electron spin resonance method. In the sample with 1 wt% of phenol added, the radical concentration once saturated after 20 minutes of irradiation, but the concentration increased again when the sample was rotated. From this result, it can be seen that when 1 wt% of phenol is added, the ultraviolet light does not pass through the sample having an inner diameter of 3.2 millimeters and the photodissociation reaction occurs only on the surface, and the entire sample cannot be polarized uniformly.

  FIG. 5 shows the relationship between the amplification factor (arb.) Of the NMR signal and the ultraviolet irradiation time (hour). In FIG. 5, the horizontal axis represents the time of ultraviolet irradiation (hours) on the butanol / phenol (0.3 wt%) sample, and the vertical axis represents the NMR signal intensity at 4.2 K polarization relative to the NMR signal intensity at 4.2 K thermal equilibrium. The ratio (times) is shown. The experiment was performed three times: 0.5 hour irradiation, 1 hour irradiation, and 2 hour irradiation. As a result, the highest degree of polarization was obtained with the sample irradiated for 1 hour.

  FIG. 6 is a graph showing the relationship between the phenol concentration and the ratio of the NMR signal intensity at 1.5 K polarization to the NMR signal intensity at 4.2 K thermal equilibrium. From FIG. 6, it can be seen that even when the phenol concentration is 0.1 wt%, a 33-fold increase in polarization is obtained, but at a phenol concentration of 0.3 to 1 wt%, the polarization increase is nearly 50 times.

  It is well known that general radicals such as butanol radicals disappear instantaneously due to recombination of radicals at the same time as the sample is melted. If dynamic nuclear spin polarization using the ultraviolet decomposition method demonstrated using the apparatus of FIG. 2 is performed with the apparatus of FIG. 1, liquid NMR and diagnostic imaging measurements can be performed while maintaining a higher degree of polarization than before.

  The present invention is not limited to the above embodiments, and all modifications should be construed as being included in the claims of the present application without departing from the scope of the technical idea of the present invention. For example, in the above-described experimental examples, phenol is used as a photolabile molecule and butanol is used as an organic solvent. However, the present invention is not limited to these substances and combinations, and other substances may be used without departing from the spirit of the present invention. Substances and combinations may be used. For example, it is considered that halides having high photodissociation properties such as hydrogen iodide can be used. In the above-described embodiment, the present invention has been described with respect to NMR. However, the present invention is not limited to this, and the present invention can be applied to an apparatus using the same principle, for example, MRI.

DESCRIPTION OF SYMBOLS 11 Dynamic nuclear spin polarization apparatus 12, 13 Ultraviolet generator 14 Ultraviolet transmission type optical fiber 15 Polarization coil 16 Sample 16 'Sample after transfer 16' Polarized sample transport pipe 18 For injecting contrast agent into living body Work tool 19 Microwave generator 20 NMR device 21 Dewar for liquid nitrogen 22 Dewar for liquid helium 23 NMR device for nuclear spin polarization measurement

Claims (2)

Butanol containing 0.3 wt% phenol as a photolabile molecule is irradiated with ultraviolet rays at extremely low temperatures to generate butanol radicals, and the generated butanol radicals are irradiated with microwaves to perform dynamic nuclear spin polarization. A method for producing a contrast agent. The method for producing a contrast agent according to claim 1, wherein the butanol radical generation and the dynamic nuclear spin polarization are performed in the same apparatus.

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