Menon R S, Ogawa S, Tank D W, Uğurbil K
Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis 55455.
Magn Reson Med. 1993 Sep;30(3):380-6. doi: 10.1002/mrm.1910300317.
Multi-echo measurements of photic stimulation-induced signal changes in human visual cortex were made at 4 Tesla in order to quantify the nature of the signal change and its vascular origin, and to determine the optimum echo time for detection of the changes. Utilizing high resolution images, two distinct regions (ascribed to be microvasculature and visible venous vessels) were identified as giving rise to the signal increase. The fractional signal changes in gray matter areas depended linearly on echo time (TE) in the range of 10 to 60 ms and extrapolated to virtually zero for TE = 0, indicating that in-flow effects secondary to stimulation-induced blood flow increases were negligible in our functional imaging studies; instead, signal change due to photic stimulation originated from the increase in the apparent transverse relaxation rate, 1/T2*. This decrease in (1/T2*), brought about by the alterations in hemodynamic parameters, was 1.3 +/- 0.4 s-1 for gray matter and 3.0 +/- 0.7 s-1 (averaged over 10 individuals) for venous vessels visible in the images. The optimum choice of echo time was found to be TE > or = T2*.
为了量化光刺激引起的人类视觉皮层信号变化的性质及其血管起源，并确定检测这些变化的最佳回波时间，在4特斯拉磁场下对光刺激诱导的信号变化进行了多回波测量。利用高分辨率图像，确定了两个不同的区域（归因于微脉管系统和可见静脉血管）会引起信号增强。灰质区域的分数信号变化在10至60毫秒范围内与回波时间（TE）呈线性关系，并且对于TE = 0时外推至几乎为零，这表明在我们的功能成像研究中，刺激诱导的血流增加所继发的流入效应可忽略不计；相反，光刺激引起的信号变化源于表观横向弛豫率1/T2的增加。由血液动力学参数改变引起的(1/T2)的降低，对于灰质为1.3±0.4 s-1，对于图像中可见的静脉血管为3.0±0.7 s-1（10名个体的平均值）。发现回波时间的最佳选择是TE≥T2*。
