Mixture and dissolution of laser polarized noble gases: Spectroscopic and imaging applications

Controlling diffusion of 3He by buffer gases: a structural contrast agent in lung MRI.

Purpose: To study the influence of admixing inert buffer gases to laser-polarized 3 He in terms of resulting diffusion coefficients and the consequences for image contrast and resolution. Materials and Methods: The diffusion coefficient of 3 He was altered by admixing buffer gases of various molecular weights ( 4 He, N2, and SF6). The influence of the pulse sequence and the diffusion coefficient on the appearance of MRI of (laserpolarized) gases was analyzed by comparison of basic theoretical concepts with demonstrative experiments. Results: Excellent agreement between theoretical description and observed signal in simple gradient echoes was observed. A maximum signal gain can be predicted …

Phenylene motion in polycarbonate and polycarbonate/additive mixtures

Pulsed deuteron NMR line shapes have been analysed to characterize type and time scale of the phenylene group motion in glassy bisphenol-A polycarbonate. The motional mechanism involvesπ-flips about theC1C4 axis augmented by small angle fulctuations about the same axis, reaching a rms amplitude of ±35‡ at 380 K. The distribution of correlation times for theπ-flips is heterogeneous in nature and can be described either by a log-Gaussian or an asymmetric distribution with a more rapid decay at high correlation times comparable to the Williams-Watts distribution. From both distributions essentailly the same mean activation energy of 37 kJ/mol is obtained, whereas the temperature dependent widt…

Development of MR active contrast agents via Parahydrogen Induced Polarization

Parahydrogen Induced Polarization provides dramatic MR signal enhancement that can be exploited for molecular imaging. This method allows amongst others for Magnetic Resonance Imaging of 13C and 15N, which is usually constrained by the low MR sensitivity of these nuclei. By combining hydrogenation of barbiturates with parahydrogen under special experimental conditions (PASADENA under pressure) with a polarization transfer sequence we demonstrate the transfer of the initial 1H polarization to 13C. The polarization transfer yields a signal increase for 13C of more than 1000. Hence, the role of certain target compounds such as anesthetics like the barbituric acid derivatives could be investiga…

Development of a Polarizer and Biocompatible Polarizing Agents for Use in Dynamic Nuclear Polarization DNP-Enhanced NMR and MRI

The application of 13C (or other low γ nuclei) NMR spectroscopy and imaging for clinical diagnosis has been constrained by the extremely long imaging and spectroscopy acquisition times that are required to obtain high SNR under physiological conditions (low natural abundance of 13C, low concentration of 13C-compounds, physiological temperature etc.). However, this obstacle could be overcome by in vitro hyperpolarization of a 13C-containing molecule with long spin lattice relaxation time via dynamic nuclear polarization (DNP) and subsequent injection into the animal or patient of investigation [1, 2]. DNP is achieved by resonant excitation of electron spins of radicals (electron paramagnetic…