These are two images of the axillary and brachial arteries. The image on the left is taken earlier, and that on the right, later. The contrast was injected via a catheter which was placed into the subclavian artery/axillary artery junction. Notice that on the later image, the axillary artery isn't as visible, as unopacified blood flows into the axillary artery and mixes with and dilutes the x-ray dye.