School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN, USA.
Neuroimage. 2010 Feb 15;49(4):3027-38. doi: 10.1016/j.neuroimage.2009.11.051. Epub 2009 Dec 4.
A confound for functional magnetic resonance imaging (fMRI), especially for auditory studies, is the presence of imaging acoustic noise generated mainly as a byproduct of rapid gradient switching during volume acquisition and, to a lesser extent, the radiofrequency transmit. This work utilized a novel pulse sequence to present actual imaging acoustic noise for characterization of the induced hemodynamic responses and assessment of linearity in the primary auditory cortex with respect to noise duration. Results show that responses to brief duration (46 ms) imaging acoustic noise is highly nonlinear while responses to longer duration (>1 s) imaging acoustic noise becomes approximately linear, with the right primary auditory cortex exhibiting a higher degree of nonlinearity than the left for the investigated noise durations. This study also assessed the spatial extent of activation induced by imaging acoustic noise, showing that the use of modeled responses (specific to imaging acoustic noise) as the reference waveform revealed additional activations in the auditory cortex not observed with a canonical gamma variate reference waveform, suggesting an improvement in detection sensitivity for imaging acoustic noise-induced activity. Longer duration (1.5 s) imaging acoustic noise was observed to induce activity that expanded outwards from Heschl's gyrus to cover the superior temporal gyrus as well as parts of the middle temporal gyrus and insula, potentially affecting higher level acoustic processing.
功能磁共振成像（fMRI）的一个混杂因素，特别是对于听觉研究，是成像声噪声的存在，其主要是在容积采集过程中快速梯度切换的副产品产生的，在较小程度上，是由射频发射产生的。这项工作利用了一种新的脉冲序列来呈现实际的成像声噪声，以描述诱导的血流动力学反应，并评估初级听觉皮层对噪声持续时间的线性度。结果表明，对短暂持续时间（46 毫秒）的成像声噪声的响应是高度非线性的，而对较长持续时间（>1 秒）的成像声噪声的响应变得近似线性，右侧初级听觉皮层的非线性程度高于左侧，对于研究的噪声持续时间。本研究还评估了成像声噪声引起的激活的空间范围，结果表明，使用模型化的响应（特定于成像声噪声）作为参考波形，揭示了在使用典型伽马变量参考波形时未观察到的听觉皮层中的额外激活，这表明提高了对成像声噪声诱导活动的检测灵敏度。观察到较长持续时间（1.5 秒）的成像声噪声会引起从 Heschl 回向外扩展的活动，覆盖颞上回以及部分颞中回和岛叶，可能会影响更高水平的声音处理。
