Virgincar Rohan S, Robertson Scott H, Nouls John, Degan Simone, Schrank Geoffry M, He Mu, Driehuys Bastiaan
Center for In Vivo Microscopy, Duke University Medical Center, Durham, North Carolina, USA.
Biomedical Engineering, Duke University, Durham, North Carolina, USA.
Magn Reson Med. 2017 Apr;77(4):1438-1445. doi: 10.1002/mrm.26229. Epub 2016 Apr 5.
Xe interacts with biological media to exhibit chemical shifts exceeding 200 ppm that report on physiology and pathology. Extracting this functional information requires shifts to be measured precisely. Historically, shifts have been reported relative to the gas-phase resonance originating from pulmonary airspaces. However, this frequency is not fixed-it is affected by bulk magnetic susceptibility, as well as Xe-N , Xe-Xe, and Xe-O interactions. In this study, we addressed this by introducing a robust method to determine the 0 ppm Xe reference from in vivo data.
Respiratory-gated hyperpolarized Xe spectra from the gas- and dissolved-phases were acquired in four mice at 2T from multiple axial slices within the thoracic cavity. Complex spectra were then fitted in the time domain to identify peaks.
Gas-phase Xe exhibited two distinct resonances corresponding to Xe in conducting airways (varying from -0.6 ± 0.2 to 1.3 ± 0.3 ppm) and alveoli (relatively stable, at -2.2 ± 0.1 ppm). Dissolved-phase Xe exhibited five reproducible resonances in the thorax at 198.4 ± 0.4, 195.5 ± 0.4, 193.9 ± 0.2, 191.3 ± 0.2, and 190.7 ± 0.3 ppm.
The alveolar Xe resonance exhibits a stable frequency across all mice. Therefore, it can provide a reliable in vivo reference frequency by which to characterize other spectroscopic shifts. Magn Reson Med 77:1438-1445, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
氙与生物介质相互作用时会表现出超过200 ppm的化学位移，这些位移反映了生理和病理情况。提取这些功能信息需要精确测量位移。从历史上看，位移是相对于源自肺空域的气相共振来报告的。然而，这个频率不是固定的——它受体磁化率以及氙-氮、氙-氙和氙-氧相互作用的影响。在本研究中，我们通过引入一种稳健的方法从体内数据确定0 ppm氙参考值来解决这个问题。
在2T场强下，从四只小鼠胸腔内的多个轴向切片采集呼吸门控的超极化氙气和溶解相的光谱。然后在时域对复杂光谱进行拟合以识别峰。
气相氙表现出两个不同的共振峰，分别对应于传导气道中的氙（从-0.6±0.2到1.3±0.3 ppm变化）和肺泡中的氙（相对稳定，为-2.2±0.1 ppm）。溶解相氙在胸部表现出五个可重复的共振峰，分别位于198.4±0.4、195.5±0.4、193.9±0.2、191.3±0.2和190.7±0.3 ppm。
肺泡氙共振在所有小鼠中表现出稳定的频率。因此，它可以提供一个可靠的体内参考频率，用于表征其他光谱位移。《磁共振医学》77:1438 - 1445, 2017。© 2016国际磁共振医学学会。
