Transmitted light image of a 4TO7 tumor and adjacent normal tissue. ROIs for HbSat measurements in Figs. 234 are marked with the image. ROI 1, venule; ROI 2, arteriole; ROI 3, venule; ROI 4, arteriole; ROI 5, tumor feeding arteriole; ROI 6, tumor feeding arteriole; ROIs 7 to 9, tumor microvessels.