Effect of hematocrit on MR estimates of BVf, VSI and local blood oxygen saturation. An in vivo study

Introduction Using MRI and a contrast agent (CA), one can assess numerous characteristics of the microvasculaure: Blood Volume fraction (BVf), Vessel Size Index (VSI), or local SO2 (lSO2) [1] [2]. These MRI methods rely on infinite cylinders to model the vessels that contain the CA. In the vessel, one assumes that the CA is homogeneously distributed [3]. The contribution of red blood cells is at best taken into account using a constant scaling factor (hematocrit). There is however no evidence that red blood cells affect MRI estimates linearly. To evaluate the contributon of hematocrit to MRI estimates of BVf, VSI, and lSO2, hematocrit was experimentally modified in rats. MRI estimates were compared to values obtained from quantitative histology or blood gas analysis.