在Resting-state fMRI下以Seed-Based分析評估不同磁場、掃描時間和Seed ROI半徑造成的功能性連結變化

Abstract

Resting-state functional magnetic resonance imaging (rs-fMRI) is widely used for investigating spontaneous brain activities and subsequently revealing functional connectivity. Resting-state brain connectivity has been proven to provide insight into the neuropathophysiology of clinical condition. Previous studies have shown that different preprocessing and data acquisition parameters that vary across laboratories account for the variations of connectivity maps in terms of the strength and spatial extent. However, the effects of remaining procedures were rarely investigated and the significance of different data acquisition parameters and analysis steps on rs-fMRI need to be studied. Therefore, the main purpose of this study is to evaluate the effects of different magnetic field strength and scan duration during acquisition steps, and the size of seed selection in analysis procedures to provide recommendations for optimization that can be useful in clinical rs-fMRI applications. Nineteen volunteers were recruited for the rs-fMRI study. The experiments were conducted on 1.5 T and 3.0T scanners, respectively. To study the optimal scan duration, a total of 900 measurements were scanned using TR=2s, corresponding to 30 minutes of total acquisition time. 8 sets of data with different scan duration ranging from 200 to 1600 sec with 200 sec increment were then grouped for a further seed-based correlation analysis on 5 brain networks (i.e. motor, default, visual, amygdala, and hippocampus networks). The effect of seed size on rs-fMRI was evaluated using 10 various sizes of seed with the radius ranged from 3 to 30 mm with 3 mm increment. Overall, duration of about 200 sec (3 minutes) of resting state data acquisition was found to provide a good compromise between total experiment time and robust functional connectivity in both 1.5 T and 3.0 T rs-fMRI studies. However, due to the nature of lower signal-to-noise ratio of 1.5 T MRI, a longer scans (up to 800 sec, 13 min) are preferable especially for networks like amygadala and hippocampus. Meanwhile, the size of seed selection had shown the effects on the strength and the spatial extent of the connectivity maps and the radius of seed size ranging from 3 to 9mm were found to produce every network robustly. In conclusion, duration of 3 minutes of 3T resting state data acquisition is preferable in rs-fMRI studies; however, to provide better rs-fMRI results in 1.5T MRI if access to 3T MRI is impossible, using a slightly longer scan duration depending on the networks of interest and selecting seed size of 3 mm to 9 mm radius is recommended.