Friday, 7 may 2010

Eric Raymond Muir^1,2, Qiang Shen², Timothy Q. Duong<sup>2

1</sup>Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA, United States; ²Research Imaging Institute, Ophthalmology/Radiology, UT Health Science Center San Antonio, San Antonio, TX, United States

The retina has two separate blood supplies, the retinal and choroidal vessels, located on either side of the retina. We recently showed that MRI at 42x42 µm can resolve layer-specific blood flow (BF) in both vascular layers, and the avascular layer in between in mice. In this study, we further developed this BF MRI technique to include inversion-recovery suppression of the vitreous and applied it to image layer-specific BF and BOLD changes during hypoxic challenge in mouse retinas. Basal BF and BF and BOLD responses to mild hypoxic challenge were markedly different between the retinal and choroidal vasculatures.

12:18 723. Effect of Hematocrit on MR Estimates of BVf, VSI and Local Blood Oxygen Saturation. an in Vivo Study.

Thomas Christen¹, Benjamin Lemasson¹, Nicolas Pannetier¹, Regine Farion¹, Christoph Segebarth¹, Chantal Remy¹, Emmanuel Louis Barbier<sup>1

1</sup>INSERM U836, Grenoble, France

We have investigated the influence of the hematocrit on the MR estimates of Blood Volume fraction (BVf), Vessel Size Index (VSI) and local SO2 (lSO2). In healthy rats, the hematocrit was either decreased using isovolumic hemodilution or increased using an intermittent hypoxia preconditionning. Measurements obtained with MR were compared to quantitative histology and blood gas analysis. Our results showed variations of lSO2 (consistent with a stable tissue oxygenation level), variations of BVf and no changes in VSI between groups of animals. In all cases MRI and biology remains correlated suggesting a linear effect of hematocrit on the MR estimates.