Signal fluctuations induced by non-T1-related confounds in variable TR fMRI experiments.

PURPOSE

To assess and model signal fluctuations induced by non-T(1)-related confounds in variable repetition time (TR) functional magnetic resonance imaging (fMRI) and to develop a compensation procedure to correct for the non-T(1)-related artifacts.

MATERIALS AND METHODS

Radiofrequency disabled volume gradient sequences were effected at variable offsets between actual image acquisitions, enabling perturbation of the measurement system without perturbing longitudinal magnetization, allowing the study of non-T(1)-related confounds that may arise in variable TR experiments. Three imaging sessions utilizing a daily quality assurance (DQA) phantom were conducted to assess the signal fluctuations, which were then modeled as a second-order system. A modified projection procedure was implemented to correct for signal fluctuations arising from non-T(1)-related confounds, and statistical analysis was performed to assess the significance of the artifacts with and without compensation.

RESULTS

Assessment using phantom data reveals that the signal fluctuations induced by non-T(1)-related confounds was consistent in shape across the phantom and well-modeled by a second-order system. The phantom exhibited significant spurious detections (at P < 0.01) almost uniformly across the central slices of the phantom.

CONCLUSION

Second-order system modeling and compensation of non-T(1)-related confounds achieves significant reduction of spurious detection of fMRI activity in a phantom.