Imaging the Effects of Oxygen Saturation Changes in Voluntary Apnea and Hyperventilation on Susceptibility-Weighted Imaging

Axial SWI MIP venogram at baseline (A), breath-holding (B), and hyperventilation (C) in a healthy subject. D–F, Magnified portions of the SWI venogram at baseline, breath-holding, and hyperventilation, respectively. The signal intensity changes in the venous architecture are caused by oxygenation level alterations during the respiratory challenges. There is a slight increase in signal intensity within venous structures during breath-holding (B) and marked signal decrease during hyperventilation (C) as a result of different responses of vascular tone to changes of blood CO₂, which is a vasoactive modulator.