title: Regional quantification of cerebral venous oxygenation from MRI susceptibility during hypercapnia.
abstract: There is an unmet medical need for noninvasive imaging of regional brain oxygenation to manage stroke, tumor, and neurodegenerative diseases. Oxygenation imaging from magnetic susceptibility in MRI is a promising new technique to measure local venous oxygen extraction fraction (OEF) along the cerebral venous vasculature. However, this approach has not been tested in vivo at different levels of oxygenation. The primary goal of this study was to test whether susceptibility imaging of oxygenation can detect OEF changes induced by hypercapnia, via CO2 inhalation, within selected a priori brain regions. Ten healthy subjects were scanned at 3T with a 32-channel head coil. The end-tidal CO2 (ETCO2) was monitored continuously and inspired gases were adjusted to achieve steady-state conditions of eucapnia (41±3mmHg) and hypercapnia (50±4mmHg). Gradient echo phase images and pseudo-continuous arterial spin labeling (pcASL) images were acquired to measure regional OEF and CBF respectively during eucapnia and hypercapnia. By assuming constant cerebral oxygen consumption throughout both gas states, regional CBF values were computed to predict the local change in OEF in each brain region. Hypercapnia induced a relative decrease in OEF of -42.3% in the straight sinus, -39.9% in the internal cerebral veins, and approximately -50% in pial vessels draining each of the occipital, parietal, and frontal cortical areas. Across volunteers, regional changes in OEF correlated with changes in ETCO2. The reductions in regional OEF (via phase images) were significantly correlated (P<0.05) with predicted reductions in OEF derived from CBF data (via pcASL images). These findings suggest that susceptibility imaging is a promising technique for OEF measurements, and may serve as a clinical biomarker for brain conditions with aberrant regional oxygenation.
authors.affiliation: Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, USA; Radiology, Athinoula A. Martinos Center for Biomedical Imaging, 149 Thirteenth Street, Charlestown, MA, USA. Electronic address: apfan@mit.edu.
authors.forename: Audrey P
authors.initials: AP
authors.lastname: Fan
authors.affiliation: Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, USA; Psychiatry, Massachusetts General Hospital East, 149 Thirteenth Street, Charlestown, MA, USA. Electronic address: kcevans@partners.org.
authors.forename: Karleyton C
authors.initials: KC
authors.lastname: Evans
authors.affiliation: Radiology, Athinoula A. Martinos Center for Biomedical Imaging, 149 Thirteenth Street, Charlestown, MA, USA; Harvard-MIT Health Sciences and Technology, Institute of Medical Engineering and Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, USA. Electronic address: jstout@mit.edu.
authors.forename: Jeffrey N
authors.initials: JN
authors.lastname: Stout
authors.affiliation: Radiology, Athinoula A. Martinos Center for Biomedical Imaging, 149 Thirteenth Street, Charlestown, MA, USA; Harvard-MIT Health Sciences and Technology, Institute of Medical Engineering and Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, USA. Electronic address: bruce@nmr.mgh.harvard.edu.
authors.forename: Bruce R
authors.initials: BR
authors.lastname: Rosen
authors.affiliation: Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, USA; Radiology, Athinoula A. Martinos Center for Biomedical Imaging, 149 Thirteenth Street, Charlestown, MA, USA; Harvard-MIT Health Sciences and Technology, Institute of Medical Engineering and Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, USA. Electronic address: elfar@mit.edu.
authors.forename: Elfar
authors.initials: E
authors.lastname: Adalsteinsson
mesh_terms: D000328:Adult; D001931:Brain Mapping; D002245:Carbon Dioxide / Q000378:metabolism / Q000494:pharmacology; D002536:Cerebral Arteries / Q000033:anatomy & histology / Q000378:metabolism; D002550:Cerebral Veins / Q000033:anatomy & histology / Q000378:metabolism*; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000097:blood*; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology*; D017397:Prefrontal Cortex / Q000378:metabolism; D013113:Spin Labels; D055815:Young Adult
chemical_list: D013113:Spin Labels; D002245:Carbon Dioxide
keywords: Hypercapnia; Oxygen extraction fraction; Oxygenation imaging; Quantitative susceptibility