Measurement of parenchymal extravascular R2* and tissue oxygen extraction fraction using multi‐echo vascular space occupancy MRI at 7 T |
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| Authors: | Ying Cheng Peter C. M. van Zijl Jun Hua |
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| Affiliation: | 1. F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, USA;2. Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, USA;3. The Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, The Johns Hopkins University School of Medicine, Baltimore, MD, USA |
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| Abstract: | Parenchymal extravascular R2* is an important parameter for quantitative blood oxygenation level‐dependent (BOLD) studies. Total and intravascular R2* values and changes in R2* values during functional stimulations have been reported in a number of studies. The purpose of this study was to measure absolute extravascular R2* values in human visual cortex and to estimate the intra‐ and extravascular contributions to the BOLD effect at 7 T. Vascular space occupancy (VASO) MRI was employed to separate out the extravascular tissue signal. Multi‐echo VASO and BOLD functional MRI (fMRI) with visual stimulation were performed at 7 T for R2* measurement at a spatial resolution of 2.5 × 2.5 × 2.5 mm3 in healthy volunteers (n = 6). The ratio of changes in extravascular and total R2* (ΔR2*) was used to estimate the extravascular fraction of the BOLD effect. Extravascular R2* values were found to be 44.66 ± 1.55 and 43.38 ± 1.51 s–1 (mean ± standard error of the mean, n = 6) at rest and activation, respectively, in human visual cortex at 7 T. The extravascular BOLD fraction was estimated to be 91 ± 3%. The parenchymal oxygen extraction fraction (OEF) during activation was estimated to be 0.24 ± 0.01 based on the R2* measurements, indicating an approximately 37% decrease compared with OEF at rest. Copyright © 2014 John Wiley & Sons, Ltd. |
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| Keywords: | BOLD VASO fMRI extravascular R2* high field CBV OEF |
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