Table 2. Major fMRI QA metrics.

Metrics	Test goal	Implementations	Relevant references
SNR	Temporal SNR provides information about system stability, and image SNR can be applied to evaluate data quality	Simmons et al. proposed a QA protocol including daily measure of SNR and long-term stability of SNR	(7,11,16,18,44)
CNR	A measure to assess fMRI system performance and data quality. CNR can be helpful to compare fMRI studies between different sessions, subjects, and sites. CNR also reflects the validity of the statistical analysis	–	(8,9,18,23,45)
SFNR	The SFNR reflects system stability such as RF amplifier, gradient system. SFNR related-measures can identify noise sources from physiological motion and thermal contributions	FBIRN recommended a daily inspection before scan schedules (17)	(16,17,45)
PSC/PSF	PSC/PSF can reflect fMRI system instability. An increase in PSC/PSF reflects a decrease in system stability	Same as above (17)	(9,15,16,18,45)

fMRI, functional magnetic resonance imaging; QA, quality assurance; SNR, signal-to-noise ratio; CNR, contrast-to-noise ratio; SFNR, signal-to-fluctuation-noise ratio; PSC, percentage signal change; PSF, percent signal fluctuation; RF, radiofrequency.