T1? MRI CONTRAST IN THE HUMAN BRAIN ADIABATIC RF PULSE

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 人脑的T1？MRI对比度：绝热射频脉冲期间纵向旋转框架松弛快门速度的调制 在这项工作中，我们发展了一种在绝热脉冲过程中获得T1弛豫的方法。我们证明了T1？是一系列AFP脉冲(没有脉冲间时间间隔)在激发之前的主要松弛机制，并展示了如何利用使用不同调制函数构建的AFP脉冲来在人脑图像中产生组织对比度。我们证明了偶极弛豫通道对T1弛豫有贡献。对于两个完全相同的自旋之间的偶极相互作用，时间常数对AFP脉冲调制函数的依赖对于转动相关时间1 ns来说并不显著。我们还表明，用不同的调制函数(HS1和HS4)得到的绝热速率常数差可以用两位点交换(2SX)模型很好地描述。这可以在体内提供发生平衡交换的特定位置A(或B)的本征弛豫参数。绝热T1？和T2？方法的一个重要特征如下：由于绝热1H2O T1？对比度主要来自偶极弛豫路径，而绝热T2对比度似乎主要来自交换和扩散的平均，这两种测量方法可能提供互补的对比度，从而改善无创组织特征。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. T1¿ MRI Contrast in the Human Brain: Modulation of the Longitudinal Rotating Frame Relaxation Shutter-Speed During an Adiabatic RF Pulse In this work, we developed a method to access T1¿ relaxation during adiabatic pulses. We demonstrated that T1¿ is the dominant relaxation mechanism during a train of AFP pulses (with no interpulse time intervals) place prior the excitation, and showed how AFP pulses constructed using different modulation functions can be exploited to generate tissue contrast in human brain images. We demonstrated that dipolar relaxation channels contribute to the T1¿ relaxation. For the dipolar interaction between two identical spins, the dependence of the T1¿ time constant on the AFP pulse modulation functions is insignificant for the rotational correlation times ¿c < 1 ns. We also show that the adiabatic R1¿ rate constant differences obtained using different modulation functions (HS1 and HS4) can be quite well described by a two-site-exchange (2SX) model. This can provide intrinsic relaxation parameters in-vivo of the specific site A (or B) undergoing equilibrium exchange. An important feature of the adiabatic T1¿ and T2¿ methods is the following: Because adiabatic 1H2O T1¿ contrast originates predominantly from dipolar relaxation pathways, while adiabatic T2¿ contrast appears to originate mainly from the averaging of exchange and diffusion, these two measurements are likely to provide complementary contrasts, and thus, improved non-invasive tissue characterization.