fMRI at 1.5, 3 and 7 T: characterising BOLD signal changes

Neuroimage. 2009 Oct 1;47(4):1425-34. doi: 10.1016/j.neuroimage.2009.05.015. Epub 2009 May 14.


Blood oxygenation level dependent (BOLD) signal changes occurring during execution of a simple motor task were measured at field strengths of 1.5, 3 and 7 T using multi-slice, single-shot, gradient echo EPI at a resolution of 1x1x3 mm(3), to quantify the benefits offered by ultra-high magnetic field for functional MRI. Using four different echo times at each field strength allowed quantification of the relaxation rate, R(2)* and the change in relaxation rate on activation, DeltaR(2)*. This work adds to previous studies of the field strength dependence of BOLD signal characteristics, through its: (i) focus on motor rather than visual cortex; (ii) use of single-shot, multi-slice, gradient echo EPI for data acquisition; (iii) co-registration of images acquired at different field strengths to allow assessment of the BOLD signal changes in the same region at each field strength. DeltaR(2)* was found to increase linearly with field strength (0.51+/-0.06 s(-1) at 1.5 T; 0.98+/-0.08 s(-1) at 3 T; 2.55+/-0.22 s(-1) at 7 T), while the ratio of DeltaR(2)*/R(2), which dictates the accessible BOLD contrast was also found to increase (0.042+/-0.002 at 1.5 T; 0.054+/-0.002 at 3 T; 0.084+/-0.003 at 7 T). The number of pixels classified as active, the t-value calculated over a common region of interest and the percentage signal change in the same region were all found to peak at TE approximately T(2)* and increase significantly with field strength. An earlier onset of the haemodynamic response at higher field provides some evidence for a reduced venous contribution to the BOLD signal at 7 T.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Brain Mapping / methods*
  • Evoked Potentials, Motor / physiology*
  • Female
  • Humans
  • Image Enhancement / methods*
  • Magnetic Resonance Imaging / methods*
  • Male
  • Motor Cortex / physiology*
  • Oxygen Consumption / physiology*
  • Sensitivity and Specificity