Institute of Electrical Engineering, Yanshan University, Qinhuangdao 066004, People's Republic of China. Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, United States of America.
J Neural Eng. 2018 Dec;15(6):066013. doi: 10.1088/1741-2552/aae0c9. Epub 2018 Sep 12.
Assessing an infant's brain development remains a challenge for neuroscientists and pediatricians despite great technological advances. As a non-invasive neuroimaging tool, functional near-infrared spectroscopy (fNIRS) has great advantages in monitoring an infant's brain activity. To explore the dynamic features of hemodynamic changes in infants, in-pattern exponent (IPE), anti-pattern exponent (APE), as well as permutation cross-mutual information (PCMI) based on symbolic dynamics are proposed to measure the phase differences and coupling strength in oxyhemoglobin (HbO) and deoxyhemoglobin (Hb) signals from fNIRS.
First, simulated sinusoidal oscillation signals and four coupled nonlinear systems were employed for performance assessments. Hilbert transform based measurements of hemoglobin phase oxygenation and deoxygenation (hPod) and phase-locking index of hPod (hPodL) were calculated for comparison. Then, the IPE, APE and PCMI indices from resting state fNIRS data of preterm, term infants and adults were calculated to estimate the phase difference and coupling of HbO and Hb. All indices' performance was assessed by the degree of monotonicity (DoM). The box plots and coefficients of variation (CV) were employed to assess the measurements and robustness in the results.
In the simulation analysis, IPE and APE can distinguish the phase difference of two sinusoidal oscillation signals. Both hPodL and PCMI can track the strength of two coupled nonlinear systems. Compared to hPodL, the PCMI had higher DoM indices in measuring the coupling of two nonlinear systems. In the fNIRS data analysis, similar to hPod, the IPE and APE can distinguish preterm, term infants, and adults in 0.01-0.05 Hz, 0.05-0.1 Hz, and 0.01-0.1 Hz frequency bands, respectively. PCMI more effectively distinguished the term and preterm infants than hPodL in the 0.05-0.1 Hz frequency band. As symbolic time series measures, the IPE and APE were able to detect the brain developmental changes in subjects of different ages. PCMI can assess the resting-state HbO and Hb coupling changes across different developmental ages, which may reflect the metabolic and neurovascular development.
The symbolic-based methodologies are promising measures for fNIRS in estimating the brain development, especially in assessing newborns' brain developmental status.
尽管技术取得了巨大进步，但评估婴儿的大脑发育仍然是神经科学家和儿科医生面临的挑战。作为一种非侵入性的神经影像学工具，功能近红外光谱（fNIRS）在监测婴儿大脑活动方面具有很大的优势。为了探索婴儿脑血流动力学变化的动态特征，提出了基于符号动力学的进样指数（IPE）、反模式指数（APE）和排列互信息（PCMI）来测量 fNIRS 中氧合血红蛋白（HbO）和脱氧血红蛋白（Hb）信号的相位差和耦合强度。
首先，使用模拟正弦振荡信号和四个耦合非线性系统进行性能评估。计算基于希尔伯特变换的血红蛋白相位氧合和去氧（hPod）测量值和 hPod 的相位锁定指数（hPodL）进行比较。然后，计算早产儿、足月儿和成人静息状态 fNIRS 数据的 IPE、APE 和 PCMI 指数，以估计 HbO 和 Hb 的相位差和耦合。通过单调性程度（DoM）评估所有指数的性能。使用箱线图和变异系数（CV）评估测量和结果的稳健性。
在模拟分析中，IPE 和 APE 可以区分两个正弦振荡信号的相位差。hPodL 和 PCMI 都可以跟踪两个耦合非线性系统的强度。与 hPodL 相比，PCMI 在测量两个非线性系统的耦合方面具有更高的 DoM 指数。在 fNIRS 数据分析中，与 hPod 类似，IPE 和 APE 可以分别在 0.01-0.05 Hz、0.05-0.1 Hz 和 0.01-0.1 Hz 频段区分早产儿、足月儿和成人。与 hPodL 相比，PCMI 更有效地在 0.05-0.1 Hz 频段区分足月儿和早产儿。作为符号时间序列测量，IPE 和 APE 能够检测不同年龄受试者的大脑发育变化。PCMI 可以评估不同发育年龄的静息状态 HbO 和 Hb 耦合变化，这可能反映了代谢和神经血管的发育。
基于符号的方法是评估 fNIRS 估计大脑发育的有前途的方法，特别是在评估新生儿大脑发育状况方面。
