研究显示:fNIRS采用692和830nm波长组合信噪比高
指一个设备或系统中信号与噪声的比例。如在音频放大器中,我们希望的是该放大器除了放大信号外,不应该添加任何其它额外的东西。因此,信噪比应该越高越好。
是一种利用不同波长的近红外光来检测组织中氧合血红蛋白(oxy-Hb)和脱氧血红蛋白(deoxy-Hb)浓度变化的技术,常用于非侵入性的人脑功能测量。
fNIRS通常使用位于oxy-Hb和deoxy-Hb光吸收相等点(约在800nm处)两侧的波长,但尚未确定最佳的波长组合。
日本学者HirokiSato等人,通过比较五个波长(678、692、750、782和830nm)与830nm配对,以期找到最佳配对的波长组合。结果发现,692和830nm波长组合信噪比最高。一种理论认为,将较短的波长与830nm配对可以提供更高的灵敏度,因为两个波长之间的血红蛋白吸收系数存在较大差异。该研究在四个皮质区域(额叶、枕叶、顶叶和颞叶)测量的变化表明,当678nm、692nm和750nm波长与830nm配对时,噪声水平通常低于782nm波长与830nm配对时的噪声水平,这与理论预测一致。此外,在所有区域和受试者中检测到的功率信噪比(S/NS)和波长依赖关系表明,692nm配对具有最高的信噪比(oxy-Hb和deoxy-Hb在692nm配对的S/NS约为782nm配对的1.52和1.63倍)。根据观测值中误差与观测值函数中误差之间关系的定律(即误差传播定律)预测,当使用较短的波长(如678nm)时,会有更高的信噪比,但实际并非如此,这表明最佳波长不能仅由波长(Hb物种的吸收系数)决定,必须考虑测量区域的光学性质。请注意,最佳波长还取决于系统特性,如辐照光强度和检测设备。本研究结果证明了使用约690nm改善近红外测量脑功能研究的实用性。因此,对于与830nm配对以测量皮质激活引起的血红蛋白变化而言,692nm波长是比780nm左右的波长更理想的选择。
HirokiSato,MasashiKiguchi,FumioKawaguchi,etal.Practicalityofwavelengthselectiontoimprovesignal-to-noiseratioinnear-infraredspectroscopy[J].NeuroImage,(2004)1554-1562.
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