Influence of 100% and 40% oxygen on penumbral blood flow, oxygen level, and T2☆-weighted MRI in a rat stroke model

Accurate imaging of the ischemic penumbra is a prerequisite for acute clinical stroke research. T-2(star) 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% O-2 induces sinus artefacts on human scans and influences cerebral blood flow (CBF), which can affect T-2(star) signal. Therefore, we investigated replacing 100% O-2 OC with 40% O-2 OC (5 minutes 40% O-2 versus 100% O-2) and determined the effects on blood pressure (BP), CBF, tissue pO(2), and T-2(star) signal change in presumed penumbra in a rat stroke model. Probes implanted into penumbra and contralateral cortex simultaneously recorded pO(2) and CBF during 40% O-2 (n = 6) or 100% O-2 (n = 8) OC. In a separate MRI study, T-2(star) signal change to 40% O-2 (n = 6) and 100% O-2 (n = 5) OC was compared. Oxygen challenge (40% and 100% O-2) increased BP by 8.2% and 18.1%, penumbra CBF by 5% and 15%, and penumbra pO(2) levels by 80% and 144%, respectively. T-2(star) 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% O-2 OC could provide sufficient T-2(star) signal change to detect penumbra with limited influence in BP and CBF. Journal of Cerebral Blood Flow & Metabolism (2011) 31, 1799-1806; doi:10.1038/jcbfm.2011.65; published online 11 May 2011