EPI-BOLD fMRI of human motor cortex at 1.5 T and 3.0 T: sensitivity dependence on echo time and acquisition bandwidth.
OBJECTIVE
To investigate the sensitivity dependence of BOLD functional imaging on MRI acquisition parameters in motor stimulation experiments using a finger tapping paradigm.


METHODS
Gradient-echo echo-planar fMRI experiments were performed at 1.5 T and 3.0 T with varying acquisition echo time and bandwidth, and with a 4 mm isotropic voxel size. To analyze the BOLD sensitivity, the relative contributions of BOLD signal amplitude and thermal and physiologic noise sources were evaluated, and statistical t-scores were compared in the motor area.


RESULTS
At 1.5 T, the number of activated pixels and the average t-score showed a relatively broad optimum over a TE range of 60-160 msec. At 3.0 T, an optimum range was observed between TEs of 30-130 msec. Averaged over nine subjects, maxima in the number of pixels and t-score values were 59% and 18% higher at 3.0 T than at 1.5 T, respectively, an improvement that was lower than the observed 100% to 110% increase in signal-to-noise ratio at 3.0 T.


CONCLUSIONS
The somewhat disappointing increase in t-scores at 3.0 T was attributed to the increased contribution of physiologic noise at the higher field strength under the given experimental conditions. At both field strengths, reducing the effective image acquisition bandwidth from 35 to 17 Hz per pixel did not affect or only marginally affect the BOLD sensitivity.
Fera
Francesco
F
Clinical Brain Disorder Branch, National Institutes of Mental Health, NIH, Bethesda, Maryland 20892, USA.
Yongbi
Martin N
MN
van Gelderen
Peter
P
Frank
Joseph A
JA
Mattay
Venkata S
VS
Duyn
Jeff H
JH
D000328:Adult; D017352:Echo-Planar Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007089:Image Enhancement; D007091:Image Processing, Computer-Assisted; D008297:Male; D009044:Motor Cortex / Q000033:anatomy & histology* / Q000502:physiology; D012044:Regression Analysis; D012680:Sensitivity and Specificity