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Longitudinal designs
- There are few fMRI studies of test-retest reliability, and it is unknown whether fMRI data from adolescents are less stable than adults over time.
- Sources of variance include age-related anatomical differences, physiological variables (arousal, emotional state), time of day, site differences including personnel, and other contextual influences, all of which could be standardized in a protocol.
- Analysis parameters (percent signal change versus Z-score; region of interest (ROI) versus voxel-wise approaches; degree of smoothing) will influence stability and affect sensitivity. Measures that are highly sensitive to threshold levels, such as cluster extent, are unlikely to be stable or reliable.
- Some research has shown moderate reliability over 8 weeks when using percent signal change in an ROI as a measure. Z-scores were less reliable. Reliability was improved by defining an ROI based on a region of activation at time 1, as compared to an ROI defined by a Talairach atlas.
- The process of teasing apart signal components in independent components analysis (ICA) may function to reduce noise and increase reliability.
- Combining fMRI with other imaging measures (diffusion tensor imaging, perfusion) and physiological covariates (skin conductance response, pupil dilation, respiration, etc.) may reduce variability and increase reliability.