Mandeville Joseph B, Leite Francisca P, Marota John J A
Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital (MGH), Massachusetts Institute of Technology (MIT), Harvard Medical School (HMS), Boston, Massachusetts, USA.
Magn Reson Med. 2007 Oct;58(4):769-76. doi: 10.1002/mrm.21380.
While most functional MRI studies using exogenous contrast agent employ gradient-echo (GE) signal, spin echo (SE) imaging would represent an attractive alternative if its detection power were more comparable with GE imaging. This study demonstrates that SE methods systematically underestimate functional changes in microvascular cerebral blood plasma volume (CBV), so that SE detection power in brain tissue cannot match that provided by GE signal. Empirically, the in vivo response of SE-CBV was about 40% smaller than that of GE-CBV in rat brain at low basal values of CBV, a result that is consistent with physics predictions under the simplifying assumption of uniform vessel dilation. However, increasing values of basal CBV were associated with monotonically increasing mean vessel sizes and monotonically decreasing GE to SE ratios of functional changes in CBV (fCBV). This result suggests the presence of large but weakly reactive conduit vessels at high basal values of CBV. Hence, we conclude that GE imaging is the method of choice for functional MRI (fMRI) using exogenous contrast agent in most cases, although SE methods may represent a more spatially linear representation of underlying neural activity that becomes most apparent in regions with high basal CBV, such as the cortical surface.
虽然大多数使用外源性造影剂的功能磁共振成像（fMRI）研究采用梯度回波（GE）信号，但如果自旋回波（SE）成像的检测能力能与GE成像更具可比性，那么它将是一个有吸引力的替代方法。本研究表明，SE方法系统性地低估了脑微血管血浆容积（CBV）的功能变化，因此脑组织中的SE检测能力无法与GE信号提供的检测能力相匹配。根据经验，在CBV的低基础值时，大鼠脑内SE-CBV的体内反应比GE-CBV小约40%，这一结果与在血管均匀扩张的简化假设下的物理预测一致。然而，基础CBV值的增加与平均血管大小的单调增加以及CBV功能变化（fCBV）的GE与SE比值的单调降低相关。这一结果表明，在高基础CBV值时存在大但反应性弱的导血管。因此，我们得出结论，在大多数情况下，GE成像是使用外源性造影剂进行功能磁共振成像（fMRI）的首选方法，尽管SE方法可能代表了潜在神经活动在空间上更线性的表现，这在高基础CBV的区域（如皮质表面）最为明显。
