Investigation of Low Frequency Drift in fMRI Signal

• Published in: NeuroImage (Orlando, Fla.) Vol. 9; no. 5; pp. 526 - 533
• Main Authors: Smith, Anne M., Lewis, Bobbi K., Ruttimann, Urs E., Ye, Frank Q., Sinnwell, Teresa M., Yang, Yihong, Duyn, Jeff H., Frank, Joseph A.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.05.1999; Elsevier Limited
• Subjects: Adult; Aged; BOLD; Cadaver; Cadavers; Case-Control Studies; Drift; Functional magnetic resonance imaging; functional magnetic resonance imaging (fMRI); Humans; low frequency drift; Magnetic Resonance Imaging - methods; Male; Middle Aged; Motion; Noise; Normal Distribution; Phantoms, Imaging; Physiology; Pricing policies; Time series; functional magnetic resonance imaging (fMRI); BOLD; low frequency drift; artifacts
• ISSN: 1053-8119; 1095-9572
• DOI: 10.1006/nimg.1999.0435

Low frequency drift (0.0–0.015 Hz) has often been reported in time series fMRI data. This drift has often been attributed to physiological noise or subject motion, but no studies have been done to test this assumption. Time series T*2-weighted volumes were acquired on two clinical 1.5 T MRI systems using spiral and EPI readout gradients from cadavers, a normal volunteer, and nonhomogeneous and homogeneous phantoms. The data were tested for significant differences (P=0.001) from Gaussian noise in the frequency range 0.0–0.015 Hz. The percentage of voxels that were significant in data from the cadaver, normal volunteer, nonhomogeneous and homogeneous phantoms were 13.7–49.0%, 22.1–61.9%, 46.4–68.0%, and 1.10%, respectively. Low frequency drift was more pronounced in regions with high spatial intensity gradients. Significant drifting was present in data acquired from cadavers and nonhomogeneous phantoms and all pulse sequences tested, implying that scanner instabilities and not motion or physiological noise may be the major cause of the drift.