Measurement of regional blood oxygenation and cerebral hemodynamics

✍ Scribed by Bernice E. Hoppel; Robert M. Weisskoff; Keith R. Thulborn; John B. Moore; Kenneth K. Kwong; Bruce R. Rosen

• Publisher: John Wiley and Sons
• Year: 1993
• Tongue: English
• Weight: 925 KB
• Volume: 30
• Category: Article
• ISSN: 0740-3194
• DOI: 10.1002/mrm.1910300609

✦ Synopsis

Abstract

An echo planar linewidth mapping technique, Shufflebutt, has allowed temporal measurements of changes in linewidth caused by static inhomogeneities (ΔLWSI) and transverse relaxation rate (ΔR2) in models of hypoxia and hypercapnia. We demonstrate these changes are due to intravascular susceptibility differences(Δ~X~) between the blood and tissue. Contrast agent injections at a /Δ~X~ equivalent to that of deoxygenatetd blood showed a twofold difference between the contrast agent and physiological anoxia values. Hypercapnia decreased both Δ__LWSI__ and Δ__R2__ consistent with an increase in blood oxygenation. We attribute these findings to constant oxygen extraction during an increase in blood flow, resulting in less deoxygenated venous blood and thus reduced Δ~X~. For in vivo__perturbations we found that Δ__R/Δ__R__2′ ≈ 0.33, a ratio much different from that measured in whole blood phantoms (Δ__R__/Δ__R__2′ ≈ 2). This demonstrates that signal changes in these studies are produced predominantly by dephasing of extravascular protons due to field inhomogeneities produced by intravascular deoxygenated hemoglobin (deoxyHb).