title: Multivariate detrending of fMRI signal drifts for real-time multiclass pattern classification.
abstract: Signal drift in functional magnetic resonance imaging (fMRI) is an unavoidable artifact that limits classification performance in multi-voxel pattern analysis of fMRI. As conventional methods to reduce signal drift, global demeaning or proportional scaling disregards regional variations of drift, whereas voxel-wise univariate detrending is too sensitive to noisy fluctuations. To overcome these drawbacks, we propose a multivariate real-time detrending method for multiclass classification that involves spatial demeaning at each scan and the recursive detrending of drifts in the classifier outputs driven by a multiclass linear support vector machine. Experiments using binary and multiclass data showed that the linear trend estimation of the classifier output drift for each class (a weighted sum of drifts in the class-specific voxels) was more robust against voxel-wise artifacts that lead to inconsistent spatial patterns and the effect of online processing than voxel-wise detrending. The classification performance of the proposed method was significantly better, especially for multiclass data, than that of voxel-wise linear detrending, global demeaning, and classifier output detrending without demeaning. We concluded that the multivariate approach using classifier output detrending of fMRI signals with spatial demeaning preserves spatial patterns, is less sensitive than conventional methods to sample size, and increases classification performance, which is a useful feature for real-time fMRI classification.
authors.affiliation: BK21 PLUS Project for Medical Science, Yonsei University College of Medicine, Seoul, Republic of Korea; Department of Nuclear Medicine, Department of Radiology, Department of Psychiatry, Severance Hospital, Yonsei University College of Medicine, Seoul, Republic of Korea; Severance Biomedical Science Institute, Yonsei University College of Medicine, Seoul, Republic of Korea.
authors.forename: Dongha
authors.initials: D
authors.lastname: Lee
authors.affiliation: BK21 PLUS Project for Medical Science, Yonsei University College of Medicine, Seoul, Republic of Korea; Department of Nuclear Medicine, Department of Radiology, Department of Psychiatry, Severance Hospital, Yonsei University College of Medicine, Seoul, Republic of Korea.
authors.forename: Changwon
authors.initials: C
authors.lastname: Jang
authors.affiliation: BK21 PLUS Project for Medical Science, Yonsei University College of Medicine, Seoul, Republic of Korea; Department of Nuclear Medicine, Department of Radiology, Department of Psychiatry, Severance Hospital, Yonsei University College of Medicine, Seoul, Republic of Korea. Electronic address: parkhj@yonsei.ac.kr.
authors.forename: Hae-Jeong
authors.initials: HJ
authors.lastname: Park
mesh_terms: D000328:Adult; D016477:Artifacts; D001921:Brain / Q000033:anatomy & histology / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D015999:Multivariate Analysis; D060388:Support Vector Machine; D055815:Young Adult
keywords: Multi-voxel fMRI classification; Multi-voxel pattern analysis (MVPA); Real-time fMRI; Support vector machine (SVM); Voxel-wise detrending