The rapidly growing interest in production of hyperpolarized noble gasses (HpG), predominantly 3He and l29Xe for Nuclear Magnetic Resonance (NMR) experiments is driven by potentially attractive medical applications. Neither helium nor xenon is normally present in the body, so the experiments do not suffer from unwanted background signals. Among the potential medicine applications, the opportunity to image organs with low water content and/or with air spaces, such as colon or lungs, has raised a considerable interest. Current conventional imaging techniques cannot provide good images of these hollow spaces. These applications show that HpG may become a useful tool for non-invasive investigation of human lung ventilation, giving access to static imaging during breathhold, dynamics of inspiration/expiration, and functional imaging. This paper describe the way of optical pumping of Rb vapour by Ti:Sa laser which is necessary for attainment hyperpolarized state of 129Xe
In this thesis I discuss experiments to create hyperpolarised noble gases. In particular, we have constructed an apparatus to hyperpolarise helium and xenon gases and used these resources to image the lungs of living rats and probe the physical properties of mesoporous solids. The apparatus uses a line-width narrowed laser diode array to optically pump rubidium vapour which then polarises the noble gases through spin-exchange collisions. We have also developed techniques to optimise both the amount and rate of polarisation. Using these techniques, we have shown that the apparatus can produce hyperpolarised helium in 350mL volumes with a polarisation of up to 25%. It can also produce hyperpolarised xenon in a continuous flow which results in 10% polarisation of the xenon at a rate of 1018 polarised atoms per minute with only four watts of laser light incident on the cell. The optical feedback system for laser diode arrays was improved to correct for the divergence of the beam caused by curvature in the array of diode elements. This curvature of the array is an artifact of the manufacturing process and causes an increase in the full width half maximum (FWHM) achievable for the spectral profile of the array when using optical feedback to spectrally narrow the laser diode array. The optical feedback allowed the tenfold narrowing of the laser line-width with the additional treatment of the “smile” giving a further 30% improvement. The feedback allowed more efficient absorption of the light at much lower pressures. A probe was designed and constructed to measure the polarisation of the rubidium atoms in the two possible levels of the 5S ground state. This probe enabled the rapid optimisation of the polarisation of the rubidium atoms which in turn led to the best polarisation rates measured for the equipment. We have successfully used the hyperpolarised helium from our apparatus to produce high resolution images of lungs of rats that have been kept alive for the duration of the experiments on a ventilator system. These images far surpass the quality of lung images from standard MRI techniques. We also used the hyperpolarised xenon gas to measure pore sizes in mesoporous solids by detecting the shift in the xenon resonance frequency caused by the interaction with the material, and we investigated the effect on the frequency shift of water absorbed in the material. The pore sizes of the materials ranged from 2.5 to 16 nm.
This paper shows the possibility of the use of a solid-state alexandrite laser as a radiation source for the method of spin-exchange optical pumping of noble gases (xenon, krypton). The use of dispersive optical elements in the laser cavity will allows the adjusting of the radiation wavelength exactly in the rubidium spectral absorption lines 794.7 nm and 780 nm. To obtain a hyperpolarized state of noble gases, it is necessary to excite rubidium atoms for further spin-exchange process with the noble gas nuclei. This fact will allow the increasing of the magnetic resonance imaging contrast in the field of diagnosis of respiratory organs diseases.
We present the experimental results of generation and of detection of hyperpolarized xenon obtained by 4.7 T, 200 MHz magnetic resonance (MR) system. Xenon 129 was hyperpolarized by the spin-exchange with Rubidium pumped first by Ti:Sa laser and also by extended cavity laser system based on a high-power laser diode optimized for maximum efficiency of the optical pumping process. The application of the arrangement with semiconductor laser system is oriented medicine, especially to continuous production of hyperpolarized Xenon (HpXe) which serves as an contrast media in MR imaging systems.
In recent years, hyperpolarized noble gas MRI attracts attention. Spin-exchange optical pumping (SEOP) is often used for hyperpolarizing nuclear spin of noble gas. Although there are many reports on rare gas hyperpolarization devices using SEOP, most of them use high power CW lasers exceeding 10 W. Large output laser has high risk of exposure, high cost and high energy consumption. However, in SEOP, only a very small amount coincident with D1 line works and almost all other power is abandoned. Therefore, in this study, we development that Xe hyperpolarizing system using narrow linewidth Ti:Sapphire laser and demonstrated that this system can pump with lower pawer by tuning wavelength to D1 line. As a result, we show that system using narrow linewidth laser can get equally or lager signal augment ratio by 1/45 times lower irradiation power than conventional system.
Here we present a $\mathrm{Rb}\text{\ensuremath{-}}^{129}\mathrm{Xe}$ spin-exchange optical pumping polarizer capable of rapid generation of large volumes of highly polarized
129Xe gas. Through modeling and measurements we maximize the
129Xe nuclear spin polarization output to enable the generation of polarized
129Xe gas imaging volumes (
300 cm3) every 5 min within a clinical setting. Our model is verified by experiment to correctly predict the optimum Rb vapor density for maximum
129Xe nuclear polarization for a flux
3.4 W/cm2 of circularly polarized Rb
D1 photons incident on an 80 cm long cylindrical optical cell. We measure a
129Xe magnetization production efficiency of ${\ensuremath{\eta}}_{\mathrm{pr}}=1.8%$, which approaches the photon efficiency limit ${\ensuremath{\eta}}_{\ensuremath{\gamma}}=3.3%$ of this system and enables the polarization of $2.72\ifmmode\times\else\texttimes\fi{}{10}^{22}$
129Xe spins per hour, corresponding to
1013 cm3 of 100% polarized
129Xe at STP. This magnetization production rate is threefold higher than the highest previously published
129Xe magnetization production rate and has enabled routine clinical lung magnetic resonance imaging (MRI) with hyperpolarized
129Xe doses available on demand at run time, as well as high-SNR
129Xe MRI of the human brain and kidneys.