Oxygen, can be added to the hp gas for inhalation but paramagnetic O2 also leads to an increase in relaxation, for instance the T1 value drops to approximately 15 s for 129Xe in breathable mixtures containing 20% O2 . Special care should be taken as xenon becomes a general anesthetic when its alveolar concentration is in the realm of 70% . However a 70% mixture of xenon with 30% N2, inhaled for a single breath-hold
of 20–40 s, will usually only result in an alveolar concentration Selleckchem PI3K inhibitor of xenon ≈ 35% . Moreover, it has been recently reported that 3–4 repeated inhalation cycles with undiluted one liter boluses of hp 129Xe are well tolerated in patients with mild to moderate COPD . The most common in vivo hp noble gas imaging protocols are still using the concept of FLASH (Fast-Low-Angle-Shot) as their core. Variable flip angle (VFA) MRI sequences, first developed by Zhou et al.
, are based on an innovative concept that makes full use of the entire hp spin state and therefore lead to improved MR image quality. VFA results in constant signal amplitude (assuming the absence of noticeable T1 relaxation) until the hp state is completely ‘used up’ ( Fig. 3) . Although this methodology has rarely been used for MRI check details of lungs to date, as it requires careful calibration of the rf pulse power, it can be tremendously beneficial for experiments where low signal intensity is a concern , Technological developments
in hardware, computing and image reconstruction might lead to orders of magnitude faster data collection and processing compared to the first in vivo attempts. Improvements utilizing echo planar imaging (EPI) and spiral imaging acquisition schemes are already in place for dynamic ventilation imaging with hp 3He, however spatial resolution is usually sacrificed for speed. Three-dimensional (3D) dynamic imaging with hp 3He within one breath-hold has also been reported . These PRKACG improvements might be translated to other hp noble gases (129Xe, 83Kr) given that sufficient advances in SEOP of these species will be achieved. NMR and MRI velocimetry methods have been extensively reviewed . In principal, the methods can be translated directly to study gas phase flow and dynamics though experiments must be designed with consideration to the specific requirements for gas phase measurements. In non-turbulent flow of liquids, the coherent motion dominates, while contributions from the stochastic dispersion (i.e. diffusion driven) term are negligible. In flowing gases however, stochastic terms may be on the same order of magnitude as the coherent terms arising from the flow. As shown in Fig. 4, this can lead to a strong interplay between coherent flow and Brownian motion depending on the time Δ between the gradient pulses used for displacement encoding. Whilst at shorter Δ times xenon displaces as predicted numerically (Fig.