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This talk reports an fMRI method to detect the minute frequency shift caused by changes in the concentration of deoxyhemoglobin using the balanced steady state free precession (SSFP) technique.Since no geometric distortions are visually noticeable in balanced SSFP images,precise mapping of the functional activation areas with anatomic morphology is potentially achievable.In the original version of this approach using RF pulses at 500 to 700 flip angle,functional contrast is created by the sharp magnitude dip and phase transition band at the central reference frequency.This method is termed the passband SSFP fMRI.Miller et al.proposed a modification of this method by using small flip angle to increase functional sensitivity,termed the transition-band SSFP fMRI.With small flip angle,the signal magnitude across the functional sensitivity band,which also corresponds to sharp phase transition,remains relatively high rather than a low signal dip.This property allows transition-band SSFP fMRI to be suitable for detecting small functional changes in blood oxygenation with higher sensitivity.However,even if the feasibility of BOSS fMRI has been demonstrated,transition-band SSFP fMRI currently suffers from its native sensitivity to field heterogeneity,where an inappropriate setting of the reference frequency by 5 to 10Hz would lead to reductions of its functional sensitivity by a factor of 2 to 7.