Albert M S, Schepkin V D, Budinger T F
Department of Radiology, Brigham & Women's Hospital, Boston, MA, USA.
J Comput Assist Tomogr. 1995 Nov-Dec;19(6):975-8. doi: 10.1097/00004728-199511000-00025.
The major obstacle to the use of 129-xenon (I = 1/2) as a new source of contrast in magnetic resonance is its low sensitivity. The hyperpolarized 129Xe-MRI technique using laser optical pumping of rubidium promises to resolve this problem. The potential of xenon-based MRI for the body tissues other than the lung air spaces depends on the 129Xe polarization lifetime (T1) in the blood at a magnetic field of commonly available clinical MRI systems.
Xenon with natural abundance of 129Xe (26%) was dissolved in human blood and studied at 36 degrees C in a 2.35 T 40 cm bore MRI spectrometer (27.6 MHz). Zeeman relaxation (T1) of six blood samples was measured by the progressive saturation method for periods of 4-8 h each.
NMR spectra revealed two peaks at 216.0 ppm (A) and 194.0 ppm (B) relative to the xenon gas above the blood volume. Assignment and 129Xe T1 values were 4.5 +/- 1 s for red blood cells (A), 9.6 +/- 2 s for plasma (B) and 11.9 +/- 1.6 s for xenon gas at atmospheric oxygen pressure. Xenon dissolved in distilled water appears at 189.8 ppm and has T1 = 26.3 +/- 1.4 s.
These relaxation times, though shorter than expected, are comparable to the transport time of blood, and are long enough to encourage use of hyperpolarized xenon for MRI studies in tissues, in addition to lung.
将129氙（I = 1/2）用作磁共振成像新的对比剂的主要障碍是其灵敏度较低。利用铷的激光光泵浦的超极化129Xe-MRI技术有望解决这一问题。基于氙的MRI对肺气腔以外身体组织的潜在应用取决于在常用临床MRI系统磁场中血液中129Xe的极化寿命（T1）。
将天然丰度为129Xe（26%）的氙溶解在人血中，并在36℃下于一台2.35 T、40 cm孔径的MRI光谱仪（27.6 MHz）中进行研究。通过逐次饱和法对六个血样的塞曼弛豫（T1）进行测量，每个血样测量4 - 8小时。
核磁共振谱显示相对于血样上方的氙气，在216.0 ppm（A）和194.0 ppm（B）处有两个峰。在大气氧压下，红细胞（A）的归属和129Xe T1值为4.5±1秒，血浆（B）为9.6±2秒，氙气为11.9±1.6秒。溶解在蒸馏水中的氙出现在189.8 ppm处，T1 = 26.3±1.4秒。
这些弛豫时间虽然比预期的短，但与血液的传输时间相当，并且足够长，足以鼓励除肺部之外，将超极化氙用于组织中的MRI研究。
