Abstract
Subject motion has long since been known to be a major confound in functional MRI studies of the human brain. For resting-state functional MRI in particular, data corruption due to motion artefacts has been shown to be most relevant. However, despite 6 parameters (3 for translations and 3 for rotations) being required to fully describe the head's motion trajectory between timepoints, not all are routinely used to assess subject motion. Using structural (n = 964) as well as functional MRI (n = 200) data from public repositories, a series of experiments was performed to assess the impact of using a reduced parameter set (translationonly and rotationonly) versus using the complete parameter set. It could be shown that the usage of 65 mm as an indicator of the average cortical distance is a valid approximation in adults, although care must be taken when comparing children and adults using the same measure. The effect of using slightly smaller or larger values is minimal. Further, both translationonly and rotationonly severely underestimate the full extent of subject motion; consequently, both translationonly and rotationonly discard substantially fewer datapoints when used for quality control purposes (“motion scrubbing”). Finally, both translationonly and rotationonly severely underperform in predicting the full extent of the signal changes and the overall variance explained by motion in functional MRI data. These results suggest that a comprehensive measure, taking into account all available parameters, should be used to characterize subject motion in fMRI.
Highlights
Subject motion has long since been known to be a major confound in functional MRI studies of the human brain [1]
Functional MRI data from adults was obtained by randomly picking 20 subjects each from 10 randomly selected participating sites’ datasets from the fcon_1000 project (MRI dataset 3; n = 200 [27,28]); details of this dataset are described in Table 2 and are given in the Supplement S3
There is a further increase in adulthood across the age range studied, but the slope is much less steep
Summary
Subject motion has long since been known to be a major confound in functional MRI studies of the human brain [1]. For resting-state functional MRI (rsfMRI) and functional connectivity analyses in particular, even minimal motion was recently found to be highly problematic [2,3,4,5]. Both prospective [6,7,8] and retrospective approaches [9,10] to motion correction have been suggested, but the most commonly-used approach still is retrospective ‘‘motion correction’’ by using a rigid-body translation [11,12]. As the -detected extent of subject motion is commonly used to identify and remove bad datasets (‘‘motion scrubbing’’ [4,18,19]), accurately describing motion is most important
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