Barth M, Moser E
Institute for Medical Physics, University of Vienna, Austria.
Cell Mol Biol (Noisy-le-grand). 1997 Jul;43(5):783-91.
To further investigate the dependency of fMRI signal changes on echo time TE, we measured T2 and T2* values, obtained from human blood samples at various oxygenation levels and used them in a simple model to calculated signal enhancement in fMRI. In addition, the longitudinal relaxation time T1 of human blood was determined for reference. All measurements were performed at 23 degrees C to reduce blood cell metabolism during the measurement procedure. At 23 degrees C T1 values of 1434 +/- 48 ms for arterial human blood were obtained after correcting for hematocrit content, as hematocrit values ranged fro 28% to 34% only. The T2 relaxation times obtained are 181 +/- 23 ms for venous and 254 +/- 26 ms for arterial human blood, T2* relaxation times corrected for inhomogeneities of the static magnetic field (B0) are 42 +/- 2.8 ms and 254 +/- 32 ms, respectively. Furthermore, absolute and relative signal changes in fMRI experiments are calculated. The results from these model calculations reveal that contrast in fMRI can be optimised by choosing an appropriate echo time.
为了进一步研究功能磁共振成像（fMRI）信号变化对回波时间TE的依赖性，我们测量了在不同氧合水平下从人体血液样本中获得的T2和T2值，并将其用于一个简单模型中，以计算fMRI中的信号增强。此外，还测定了人体血液的纵向弛豫时间T1作为参考。所有测量均在23摄氏度下进行，以减少测量过程中血细胞的代谢。在23摄氏度下，校正血细胞比容含量后，动脉血的T1值为1434±48毫秒，因为血细胞比容值仅在28%至34%之间。获得的T2弛豫时间，静脉血为181±23毫秒，动脉血为254±26毫秒，针对静磁场（B0）不均匀性校正后的T2弛豫时间分别为42±2.8毫秒和254±32毫秒。此外，还计算了fMRI实验中的绝对和相对信号变化。这些模型计算的结果表明，通过选择合适的回波时间可以优化fMRI中的对比度。
