Neurophotonics Center, Department of Biomedical Engineering, Boston University, Massachusetts.
Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts.
Magn Reson Med. 2019 Jun;81(6):3865-3874. doi: 10.1002/mrm.27660. Epub 2019 Jan 18.
The primary goal of this study was to estimate the value of , the exponent in the power law relating changes of the transverse relaxation rate and intra-extravascular local magnetic susceptibility differences as . The secondary objective was to evaluate any differences that might exist in the value of obtained using a deoxyhemoglobin-weighted distribution versus a constant distribution assumed in earlier computations. The third objective was to estimate the value of β that is relevant for methods based on susceptibility contrast agents with a concentration of higher than that used for BOLD fMRI calculations.
Our recently developed model of real microvascular anatomical networks is used to extend the original simplified Monte-Carlo simulations to compute from the first principles.
Our results show that for most BOLD fMRI measurements of real vascular networks, as opposed to earlier predictions of .5 using uniform distributions. For perfusion or fMRI methods based on contrast agents, which generate larger values for , for 9.4 T, whereas at 14 T can drop below 1 and the variation across subjects is large, indicating that a lower concentration of contrast agent with a lower value of is desired for experiments at high B .
These results improve our understanding of the relationship between R and the underlying microvascular properties. The findings will help to infer the cerebral metabolic rate of oxygen and cerebral blood volume from BOLD and perfusion MRI, respectively.
本研究的主要目的是估计 的值，即横向弛豫率变化与血管内外局部磁化率差异的幂律关系中的指数。次要目的是评估在使用去氧血红蛋白加权 分布与早期计算中假设的常数 分布获得的 值可能存在的差异。第三个目的是估计对于浓度高于用于 BOLD fMRI 计算的浓度的顺磁对比剂相关方法的β值。
我们最近开发的真实微血管解剖网络模型用于从第一性原理扩展原始简化的蒙特卡罗模拟，以计算 。
我们的结果表明，对于大多数真实血管网络的 BOLD fMRI 测量，与使用均匀 分布的早期预测的 .5 相反。对于基于对比剂的灌注或 fMRI 方法，由于 ， 对于 9.4 T ，而在 14 T 下 可以低于 1，并且个体之间的差异很大，这表明对于高 B 下的实验，需要具有较低值的较低浓度的对比剂。
这些结果提高了我们对 R 与潜在微血管特性之间关系的理解。这些发现将有助于分别从 BOLD 和灌注 MRI 推断脑氧代谢率和脑血容量。
