Impact of intravascular signal on quantitative measures of cerebral oxygen extraction and blood volume under normo- and hypercapnic conditions using an asymmetric spin echo approach

An asymmetric spin echo (ASE) single shot echo planar imaging (EPI) sequence is proposed for obtaining quantitative estimates of R2′, cerebral venous blood volume fraction (vCBV), and oxygen extraction fraction (OEF) noninvasively in normal volunteers. The impact of the presence of intravascular signal on the estimates of vCBV and OEF were examined in five subjects with different levels of flow attenuation. A significant reduction in the estimates of vCBV and a small increase in the measurements of OEF were observed in the presence of flow suppression gradients. In addition, mild hypercapnia was induced in normal subjects (n = 4). R2′, vCBV, and OEF were measured under both normocapnia and experimentally induced hypercapnia. In agreement with the well-documented cerebral vascular responses to hypercapnia, estimates of R2′ and OEF decrease, while measures of vCBV increase during hypercapnia.