Optimal Echo Time for Functional MRI of the Infant Brain Identified in Response to Noxious Stimulation
Blood oxygen level dependent (BOLD) brain activity, measured using functional MRI (fMRI), is dependent on the echo time (TE) and the reversible spin–spin relaxation time constant (Symbol) that describes the decay of transverse magnetization. Use of the optimal TE during fMRI experiments allows maximal sensitivity to BOLD to be achieved. Reports that Symbol values are longer in infants (due to higher water concentrations and lower lipid content) have led to the use of longer TEs during infant fMRI experiments; however, the optimal TE has not been established.Methods:
In this study, acute experimental mildly noxious stimuli were applied to the heel in 12 term infants (mean gestational age = 40 weeks, mean postnatal age = 3 days); and the percentage change in BOLD activity was calculated across a range of TEs, from 30 to 70 ms, at 3 Tesla. In addition, Symbol maps of the whole brain were collected in seven infants.Results:
The maximal change in BOLD occurred at a TE of 52 ms, and the average Symbol across the whole brain was 99 ms.Conclusion:
A TE of approximately 50 ms is recommended for use in 3T fMRI investigations in term infants.