Measurement of parenchymal extravascular R2* and tissue oxygen extraction fraction using multi‐echo vascular space occupancy MRI at 7 T. (17th December 2014)

• Record Type: Journal Article
• Authors: Cheng, Ying; van Zijl, Peter C. M.; Hua, Jun
• Is Part Of: NMR in biomedicine. Volume 28:Number 2(2015:Feb.)
• Page Start: 264
• Page End: 271
• Publication Date: 2014-12-17
• Subjects: Nuclear magnetic resonance -- Periodicals; Magnetic Resonance Spectroscopy -- Periodicals; 574
• DOI: 10.1002/nbm.3250
• Languages: English
• ISSNs: 0952-3480

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <p>Parenchymal extravascular <italic>R</italic><sub>2</sub>* is an important parameter for quantitative blood oxygenation level‐dependent (BOLD) studies. Total and intravascular <italic>R</italic><sub>2</sub>* values and changes in <italic>R</italic><sub>2</sub>* values during functional stimulations have been reported in a number of studies. The purpose of this study was to measure absolute extravascular <italic>R</italic><sub>2</sub>* 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 <italic>R</italic><sub>2</sub>* measurement at a spatial resolution of 2.5 × 2.5 × 2.5 mm<sup>3</sup> in healthy volunteers (<italic>n</italic> = 6). The ratio of changes in extravascular and total <italic>R</italic><sub>2</sub>* (Δ<italic>R</italic><sub>2</sub>*) was used to estimate the extravascular fraction of the BOLD effect. Extravascular <italic>R</italic><sub>2</sub>* values were found to be 44.66 ± 1.55 and 43.38 ± 1.51 s<sup>–1</sup> (mean ± standard error of the mean, <italic>n</italic> = 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 <italic>R</italic><sub>2</sub>* measurements, indicating an approximately 37% decrease compared with OEF at rest. Copyright © 2014 John Wiley & Sons, Ltd.</p> </abstract>