Purpose: MRI methods sensitive to functional changes in cerebral blood volume (CBV) may map neural activity with better spatial specificity than standard functional MRI (fMRI) methods based on blood oxygen level dependent (BOLD) effect. The purpose of this study was to develop and investigate a vascular space occupancy (VASO) method with high sensitivity to CBV changes for use in human brain at 7 Tesla (T).
Methods: To apply 7T VASO, several high-field-specific obstacles must be overcome, e.g., low contrast-to-noise ratio (CNR) due to convergence of blood and tissue T1 , increased functional BOLD signal change contamination, and radiofrequency field inhomogeneities. In the present method, CNR was increased by keeping stationary tissue magnetization in a steady-state different from flowing blood, using slice-selective saturation pulses. Interleaved acquisition of BOLD and VASO signals allowed correction for BOLD contamination.
Results: During visual stimulation, a relative CBV change of 28% ± 5% was measured, confined to gray matter in the occipital lobe with high sensitivity.
Conclusion: By carefully considering all the challenges of high-field VASO and filling behavior of the relevant vasculature, the proposed method can detect and quantify CBV changes with high CNR in human brain at 7T.
Keywords: 7 Tesla; cerebral blood volume; fMRI acquisition techniques; slab-selective VASO; vascular space occupancy.
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