Controlling for Scanner-to-Scanner Variance in Multicenter FMRI Studies: Covariation with Signal-to-Fluctuation Noise Ratio (SFNR). Lee Friedman, Ph.D. And Gary Glover, Ph.D. Overall Goal. To evaluate scanner effects on brain activation patterns in multisite fMRI studies
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Controlling for Scanner-to-Scanner Variance in Multicenter FMRI Studies: Covariation with Signal-to-Fluctuation Noise Ratio (SFNR)
Lee Friedman, Ph.D.
Gary Glover, Ph.D.
Block trials, 15s “on”, 15s “off”, 8 blocks.
• Alternating contrast checkerboard.
• Binaural tones generated. This is an auditorily annoying, mistonal scale.
• Subject performs bilateral finger apposition at 3Hz, in time with visual and auditory cues.
Fixation cross, silence, no motion.
4 runs, 4.25 min each
- Analyses were conducted for separately for low-field scanners and high-field scanners, and for 8 ROIs (LA, RA, LC, RC, LM, RM, SM and the average, AV). Did not analyze visual cortex (why?)
-For each visit, each subject had only a single SFNR-GM-REST estimate from the resting-state data. So all four runs of the SM task were corrected with the same SFNR covariate.
-However, for SFNR-GM-RESID estimates based on the SM task rather than the resting state scan, each individual run of the SM task was corrected by an SFNR estimate from that same run.
Criteria for Ranking the SFNR Types:
(1) The number of statistically significant F-tests for the scanner effect in each model was calculated.
(2) The coefficient of variation (CV) was calculated for the estimated scanner means for each model.
“Anatomical Model of Normal Brain” described at:
A communality is the proportion
of variance in a variable accounted
for collectively by all the other
Low Field: F(scanner) = 103.2, p <.0001
High Field: F(scanner) = 15.6 , p <.0001
Low Field : F = 28.8, df = 1,4, p = 0.0058
high field: F = 17.8, df = 1,4, p = 0.0135
Low Field Scanners
High Field Scanners
Physiological Noise at 3T
At 3.0 T, the physiological noise is of increasing influence at higher excitation flip angles (larger signals) and results in the divergence of the SNR-to-SNR0 ratio from the line-of identity (dotted line). Kruger, Kastrup, and Glover, 2001