Liau Joy, Perthen Joanna E, Liu Thomas T
Center for Functional Magnetic Resonance Imaging and Department of Radiology, University of California San Diego, La Jolla, CA, USA.
Neuroimage. 2008 Aug 1;42(1):296-305. doi: 10.1016/j.neuroimage.2008.04.177. Epub 2008 Apr 23.
Measures of the spatial extent of functional activation are important for a number of functional magnetic resonance imaging (fMRI) applications, such as pre-surgical planning and longitudinal tracking of changes in brain activation with disease progression and drug treatment. The interpretation of the data from these applications can be complicated by inter-subject or inter-session variability in the measured fMRI signals. Prior studies have shown that modulation of baseline cerebral blood flow (CBF) can directly alter the functional CBF and blood oxygenation level dependent (BOLD) responses, suggesting that the spatial extents of functional activation maps based on these signals may also depend on baseline CBF. In this study, we used a caffeine dose (200 mg) to decrease baseline CBF and found significant (p<0.05) reductions in both the CBF activation extent and contrast-to-noise ratio (CNR) but no significant changes in the BOLD activation extent and CNR. In contrast, caffeine significantly changed the temporal dynamics of the BOLD response but not the CBF response. The decreases in the CBF activation extent and CNR were consistent with a significant caffeine-induced decrease in the absolute CBF change accompanied by no significant change in the residual noise. Measures of baseline CBF also accounted for a significant portion of the inter-subject variability in the CBF activation map area and CNR. Factors that can modulate baseline CBF, such as age, medication, and disease, should therefore be carefully considered in the interpretation of studies that use functional CBF activation maps.
功能激活空间范围的测量对于许多功能磁共振成像（fMRI）应用都很重要，比如术前规划以及随着疾病进展和药物治疗对大脑激活变化进行纵向追踪。这些应用中数据的解读可能会因测量的fMRI信号存在个体间或不同扫描时段的变异性而变得复杂。先前的研究表明，基线脑血流量（CBF）的调节可直接改变功能性CBF和血氧水平依赖（BOLD）反应，这表明基于这些信号的功能激活图的空间范围可能也取决于基线CBF。在本研究中，我们使用一剂咖啡因（200毫克）来降低基线CBF，发现CBF激活范围和对比噪声比（CNR）均显著降低（p<0.05），但BOLD激活范围和CNR无显著变化。相比之下，咖啡因显著改变了BOLD反应的时间动态，但未改变CBF反应。CBF激活范围和CNR的降低与咖啡因引起的绝对CBF变化显著降低一致，同时残余噪声无显著变化。基线CBF的测量值在CBF激活图面积和CNR的个体间变异性中也占了很大一部分。因此，在解释使用功能性CBF激活图的研究时，应仔细考虑能够调节基线CBF的因素，如年龄、药物和疾病。
