A multispectral microscope for in vivo oximetry of rat dorsal 1 spinal cord vasculature 2 3

14 Quantification of blood oxygen saturation (SO2) in vivo is essential for understanding the 15 pathogenesis of diseases in which hypoxia is thought to play a role, including inflammatory 16 disorders such as multiple sclerosis (MS) and rheumatoid arthritis (RA). We describe a low-cost 17 multispectral microscope and oximetry technique for calibration-free absolute oximetry of 18 surgically exposed blood vessels in vivo. We imaged the vasculature of the dorsal spinal cord in 19 healthy rats, and varied inspired oxygen (FiO2) in order to evaluate the sensitivity of the imaging 20 system to changes in SO2. The venous SO2 was calculated as 67.8 ± 10.4% (average ± standard 21 deviation), increasing to 83.1 ± 11.6% under hyperoxic conditions (100% FiO2) and returning 22 to 67.4 ± 10.9% for a second normoxic period; the venous SO2 was 50.9 ± 15.5% and 29.2 ± 23 24.6% during subsequent hypoxic states (18% and 15% FiO2 respectively). We discuss the 24 design and performance of our multispectral imaging system, and the future scope for extending 25 this oximetry technique to quantification of hypoxia in inflamed tissue. 26 27