Weibull A, Gustavsson H, Mattsson S, Svensson J
Department of Medical Radiation Physics, Lund University, SE-205 02 Malmö, Sweden.
Neuroimage. 2008 Jun;41(2):346-53. doi: 10.1016/j.neuroimage.2008.02.015. Epub 2008 Mar 10.
This work addresses the balance between temporal signal-to-noise ratio (tSNR) and partial volume effects (PVE) in functional magnetic resonance imaging (fMRI) and investigates the impact of the choice of spatial resolution and smoothing. In fMRI, since physiological time courses are monitored, tSNR is of greater importance than image SNR. Improving SNR by an increase in voxel volume may be of negligible benefit when physiological fluctuations dominate the noise. Furthermore, at large voxel volumes, PVE are more pronounced, leading to an overall loss in performance. Artificial fMRI time series, based on high-resolution anatomical data, were used to simulate BOLD activation in a controlled manner. The performance was subsequently quantified as a measure of how well the resulted activation matched the simulated activation. The performance was highly dependent on the spatial resolution. At high contrast-to-noise ratio (CNR), the optimal voxel volume was small, i.e. in the region of 2(3) mm(3). It was also shown that using a substantially larger voxel volume in this case could potentially negate the CNR benefits. The optimal smoothing kernel width was dependent on the CNR, being larger at poor CNR. At CNR >1, little or no smoothing proved advantageous. The use of artificial time series gave an opportunity to quantitatively investigate the effects of partial volume and smoothing in single subject fMRI. It was shown that a proper choice of spatial resolution and smoothing kernel width is important for fMRI performance.
这项工作探讨了功能磁共振成像（fMRI）中时间信噪比（tSNR）与部分容积效应（PVE）之间的平衡，并研究了空间分辨率和平滑处理选择的影响。在fMRI中，由于监测的是生理时间进程，tSNR比图像信噪比更为重要。当生理波动主导噪声时，通过增加体素体积来提高信噪比可能益处不大。此外，在大的体素体积下，PVE更为明显，导致整体性能下降。基于高分辨率解剖数据的人工fMRI时间序列被用于以可控方式模拟血氧水平依赖（BOLD）激活。随后将性能量化为所得激活与模拟激活匹配程度的一种度量。性能高度依赖于空间分辨率。在高对比噪声比（CNR）下，最佳体素体积较小，即在2(3)立方毫米的范围内。研究还表明，在这种情况下使用大得多的体素体积可能会抵消CNR带来的益处。最佳平滑核宽度取决于CNR，在CNR较差时更大。当CNR>1时，几乎不需要或根本不需要平滑处理。使用人工时间序列为定量研究单受试者fMRI中部分容积和平滑处理的影响提供了机会。结果表明，正确选择空间分辨率和平滑核宽度对fMRI性能很重要。
