Influence of 100% and 40% Oxygen on Penumbral Blood Flow, Oxygen Level, and T*2-Weighted MRI in a Rat Stroke Model

Abstract

Accurate imaging of the ischemic penumbra is a prerequisite for acute clinical stroke research. T*2 magnetic resonance imaging (MRI) combined with an oxygen challenge (OC) is being developed to detect penumbra based on changes in blood deoxyhemoglobin. However, inducing OC with 100% O2 induces sinus artefacts on human scans and influences cerebral blood flow (CBF), which can affect T*2 signal. Therefore, we investigated replacing 100% O2 OC with 40% O2 OC (5 minutes 40% O2 versus 100% O2) and determined the effects on blood pressure (BP), CBF, tissue pO2, and T*2 signal change in presumed penumbra in a rat stroke model. Probes implanted into penumbra and contralateral cortex simultaneously recorded pO2 and CBF during 40% O2 ( n = 6) or 100% O2 ( n = 8) OC. In a separate MRI study, T*2 signal change to 40% O2 ( n = 6) and 100% O2 ( n = 5) OC was compared. Oxygen challenge (40% and 100% O2) increased BP by 8.2% and 18.1%, penumbra CBF by 5% and 15%, and penumbra pO2 levels by 80% and 144%, respectively. T*2 signal significantly increased by 4.56% ± 1.61% and 8.65% ± 3.66% in penumbra compared with 2.98% ± 1.56% and 2.79% ± 0.66% in contralateral cortex and 1.09% ± 0.82% and −0.32% ± 0.67% in ischemic core, respectively. For diagnostic imaging, 40% O2 OC could provide sufficient T*2 signal change to detect penumbra with limited influence in BP and CBF.