Yang Zhangyan, Arabinda Mishra, Wang Feng, Chen Li Min, Gore John C
Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA.
Magn Reson Med. 2025 Mar;93(3):1314-1328. doi: 10.1002/mrm.30326. Epub 2024 Oct 7.
Previous studies have shown varied BOLD signals with gradient echo (GE) across cortical depth. To interpret these variations, and understand the effects of vascular geometry and size, the magnitudes and layer distributions of GE and spin-echo (SE) BOLD functional MRI signals were compared in the somatosensory cortex of squirrel monkeys during tactile stimulation and in a resting state at high spatial resolution and high field.
A block-design stimulation was used to identify tactile-evoked activation signals in somatosensory Areas 3b and 1. Layer-specific connectivities were calculated using resting-state data. Signal power spectra were compared by depth and pulse sequence. The measured ratios of transverse relaxation rate changes were compared with Anderson and Weiss's model.
SE signals showed a 26% lower percentage signal change during tactile stimulation compared with GE, along with a slower time course. SE signals remained consistent but weaker in lower layers, whereas GE signals decreased with cortical depth. This pattern extended to resting-state power spectra. Resting-state functional connectivity indicated larger connectivity between the top layers of Area 3b and Area 1 for GE, with minimal changes for SE. Comparisons with theory suggest vessel diameters ranging from 19.4 to 9 microns are responsible for BOLD effects across cortical layers at 9.4 T.
These results provide further evidence that at high field, SE BOLD signals are relatively free of contributions from sources other than microvascular changes in response to neural activity, whereas GE signals, even in the superficial layers, are not dominated by very large vessels.
先前的研究表明，梯度回波（GE）在整个皮层深度的血氧水平依赖（BOLD）信号各不相同。为了解释这些变化，并理解血管几何形状和大小的影响，在松鼠猴体感皮层进行触觉刺激时以及在高空间分辨率和高场强的静息状态下，对GE和自旋回波（SE）BOLD功能磁共振成像信号的大小和层分布进行了比较。
采用组块设计刺激来识别体感3b区和1区的触觉诱发激活信号。使用静息状态数据计算层特异性连接性。通过深度和脉冲序列比较信号功率谱。将测得的横向弛豫率变化比值与安德森和韦斯的模型进行比较。
与GE相比，SE信号在触觉刺激期间的信号变化百分比低26%，且时间进程较慢。SE信号在较低层保持一致但较弱，而GE信号随皮层深度降低。这种模式扩展到静息状态功率谱。静息状态功能连接性表明，GE在3b区和1区顶层之间的连接性更大，而SE的变化最小。与理论的比较表明，在9.4T时，直径范围为19.4至9微米的血管负责跨皮层层的BOLD效应。
这些结果进一步证明，在高场强下，SE BOLD信号相对不受神经活动引起的微血管变化以外的其他来源的影响，而GE信号即使在表层也不由非常大的血管主导。
