Hyperpolarization (physics)

Hyperpolarization is the spin polarization of the atomic nuclei of a material in a magnetic field far beyond thermal equilibrium conditions determined by the Boltzmann distribution.

[5] During this process, circularly polarized infrared laser light, tuned to the appropriate wavelength, is used to excite electrons in an alkali metal, such as caesium or rubidium inside a sealed glass vessel.

While different sizes of glass vessels (also called cells), and therefore different pressures, are used depending on the application, one amagat of total pressure of noble gas and nitrogen is sufficient for SEOP and 0.1 amagat of nitrogen density is needed to quench fluorescence.

[3] Great improvements in 129Xe hyperpolarization technology have achieved > 50% level at flow rates of 1–2 L/min, which enables human clinical applications.

This is done by first optically pumping alkali metal, then transferring the polarization to a noble gas nucleus to increase the population of the spin up state.

[3] Once the spins are depolarized (return to the ms=-1/2 state), they are excited again by the continuous wave laser light and the process repeats itself.

In order to use hyperpolarized noble gases in applications such as lung imaging, the gas must be transferred from the experimental setup to a patient.

As soon as the gas is no longer actively being optically pumped, the degree of hyperpolarization begins to decrease until thermal equilibrium is reached.

The application desired is what governs the design of the optical pumping cell and is dependent on laser diameter, optimization needs, and clinical use considerations.

Additionally, an IR iris is placed behind the mirror, providing information of laser light absorption by the alkali metal atoms.

As the cell is heated, the rubidium enters the vapor phase and starts to absorb laser light, causing the percent transmittance to decrease.

Ideally, the laser should be continuous wave to ensure the alkali metal and noble gas remains polarized at all times.

In principle, any alkali metal can be used for SEOP, but rubidium is usually preferred due to its high vapor pressure, allowing experiments to be carried out at relatively low temperatures (80 °C-130 °C), decreasing the chance of damaging the glass cell.

[27] Our target is to identify the infection or disease (cancer, for example) anywhere in our body like cerebral, brain, blood, and fluid, and tissues.

[28] There are a lot of biomarkers are considering as being cancer: Hepatitis C virus ribonucleic acid (HCV-RNA), International Normalized Ratio (INR), Prothrombin Time (PT), Monoclonal Protein (M protein), Cancer Antigen-125 (CA-125), Human Immunodeficiency Virus -Ribonucleic Acid (HIV RNA), B-type Natriuretic Peptide (BNP).27and Lymphoma cell (Ramos cell lines and Jurkat cell lines) a form of cancer.

[30] This disease-causing verdict agent is the biomarker is existing extremely trace amount especially initial state of the disease.

If it is possible to gather the acceptable and clearly interpretable data from NMR or MRI experiment by using the contrasting agent, then experts can take a right initial step to recover the patients who already have been suffering from cancer.

This is demonstrated by the experimental data values when NMR spectra are acquired at different magnetic field strengths.

[22] A couple of important points from experimental data are: (Figure 11) Longitudinal spin relaxation time (T1) is very sensitive with an increase of magnetic field and hence enhance the NMR signals is noticeable in SEOP in case of 129Xe.

However, satisfactory increment in T1delay time (354±24 minutes) when data was collected in presence of 3000 mT magnetic field.

Third, at cold condition, the level of hyperpolarization of 129Xe gas at least can get the (at human body's temperature) imaging although during the transferring into the Tedlar bag having poor percentage of 87Rb (less than 5 ng/L dose).

[37] Multiparameter analysis of 87Rb/129Xe SEOP at high xenon pressure and photon flux could be used as 3D-printing and stopped flow contrasting agent in clinical scale.

[38] All of those polarization values of 129Xe has been approved by pushing the hyperpolarized 129Xe gas and all MRI experiment also done at lower magnetic field 47.5 mT.

[38] Finally demonstrations indicated that such a high pressure region, polarization of 129Xe gases could be increment even more that the limit that already has been shown.

[21] This is done by first optically pumping cesium vapor, then transferring the spin polarization to CsH salt, yielding an enhancement of 4.0.

[21] Unreacted hydrogen was removed, and the process was repeated several times to increase the thickness of the CsH film, then pressurized with nitrogen gas.

The process of MEOP is very efficient (high polarization rate), however, compression of the gas up to atmospheric pressure is needed.

The 13C polarization levels in solid compounds can reach up to ≈64% and the losses during dissolution and transfer of the sample for NMR measurements can be minimized to a few percent.

10,000-fold increased intensity[45] can be obtained compared to NMR signals of the same organic molecule without PHIP and thus only "thermal" polarization at room temperature.

Compared to orthohydrogen or organic molecules, a much greater fraction of the hydrogen nuclei in parahydrogen align with an applied magnetic field.

Figure 1. Excitation transitions of a rubidium electron.
Figure 2. Effect of applied magnetic field on spin where there is energy splitting in the presence of a magnetic field, B 0 .
Figure 3. Transitions that occur when circularly polarized light interacts with the alkali metal atoms.
Figure 4. Transfer of polarization via A) binary collisions and B) van der Waals forces.
Figure 5. Photo of 2" diameter 10" length optical cells.
Figure 6. Structure of SurfaSil.
Figure 7. Experimental setup that involves illuminating an optical cell containing alkali metal, a noble gas, and nitrogen gas.
Figure 8. Diagram above shows the highest temperature and pressure at which xenon gas can exist in liquid and gaseous states simultaneously.30
Figure 10. Measurements of the Polarization of 129 Xe(g) in presence of low and intermediate magnetic fields. All (A-D) figures are NMR signal amplitude in μV/KHz vs Larmor Frequency in KHz. (A) Enhanced 129 Xe(g) NMR signal at 62 kHz Larmor Frequency from the SEOP cell; Xenon(g) has 1545 torr and Nitrogen(g) has 455 torr pressure and NMR data was collected in presence of 5.26mT magnetic field. (B) Reference NMR signal for water Proton Spin (111M), doping with CuSO 4. 5H 2 O(s), 5.0mM and polarization has been created thermally in presence of 1.46 mT magnetic fields (number of scans was 170,000 times). (C) NMR data for Hyperpolarized 129 Xe was collected in presence of 47.5mT magnetic fields.( 129 Xe was 300 torr and N 2 was 1700 torr).(D) Reference NMR signal for 13 C was collected from 170.0mM CH 3 COONa(l) in presence of 47.5mT magnetic field. 32
Figure 11. 129 Xe(g) MRI studying in presence of high field vs T 1 (longitudinal Spin Relaxation Time) during the decaying of hyperpolarization of 129 Xe(g) in presence of magnetic field different strengths; 3.0 T for blue triangle, approximately 1.5 mT for red circles and approximately 0.0 mT for white squares. Hyperpolarized 129 Xe(g) has transferred to kids bags then counted the decay time T 1 in presence of different magnetic fields separately. Increasing the magnetic field strength (1.5mT to 3000mT) causing the decay time approximately up to eight-fold increments.