Improved recovery of the hemodynamic response in diffuse optical imaging using short optode separations and state-space modeling

• Published in: NeuroImage (Orlando, Fla.) Vol. 56; no. 3; pp. 1362 - 1371
• Main Authors: Gagnon, Louis, Perdue, Katherine, Greve, Douglas N., Goldenholz, Daniel, Kaskhedikar, Gayatri, Boas, David A.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.06.2011; Elsevier Limited
• Subjects: Adaptive filtering; Adult; Algorithms; Biomechanical Phenomena; Brain - anatomy & histology; Brain - physiology; Cerebrovascular Circulation - physiology; Diagnostic Imaging - methods; Diffuse optical imaging; Hemodynamic response; Hemodynamics - physiology; Hemoglobins - analysis; Hemoglobins - metabolism; Human subjects; Humans; Image Processing, Computer-Assisted; Kalman filtering; Least-Squares Analysis; Linear Models; Magnetic Resonance Imaging; Medical imaging; Methods; Models, Statistical; Multidistance measurements; Normal Distribution; Oxygen - blood; Physiology; Principal components analysis; Respiration; Spectroscopy, Near-Infrared; Adaptive filtering; Multidistance measurements; Kalman filtering; Diffuse optical imaging; Hemodynamic response
• ISSN: 1053-8119; 1095-9572; 1095-9572
• DOI: 10.1016/j.neuroimage.2011.03.001

Diffuse optical imaging (DOI) allows the recovery of the hemodynamic response associated with evoked brain activity. The signal is contaminated with systemic physiological interference which occurs in the superficial layers of the head as well as in the brain tissue. The back-reflection geometry of the measurement makes the DOI signal strongly contaminated by systemic interference occurring in the superficial layers. A recent development has been the use of signals from small source-detector separation (1cm) optodes as regressors. Since those additional measurements are mainly sensitive to superficial layers in adult humans, they help in removing the systemic interference present in longer separation measurements (3cm). Encouraged by those findings, we developed a dynamic estimation procedure to remove global interference using small optode separations and to estimate simultaneously the hemodynamic response. The algorithm was tested by recovering a simulated synthetic hemodynamic response added over baseline DOI data acquired from 6 human subjects at rest. The performance of the algorithm was quantified by the Pearson R2 coefficient and the mean square error (MSE) between the recovered and the simulated hemodynamic responses. Our dynamic estimator was also compared with a static estimator and the traditional adaptive filtering method. We observed a significant improvement (two-tailed paired t-test, p<0.05) in both HbO and HbR recovery using our Kalman filter dynamic estimator compared to the traditional adaptive filter, the static estimator and the standard GLM technique. ► Small optode separations measurements help remove systemic interference in NIRS data. ► Simultaneous filtering and estimation allows better recovery of the HRF. ► Dynamic filtering take into account the non-stationary behavior of the interference. ► Works well even if the baseline short-long correlation is as low as 0.1.