Appendicitis. Power Doppler ultrasound scan of increased blood flow (orange) to the appendix (not seen), resulting from acute appendicitis in a 70- year-old woman. The appendix is a thin tube leading off the beginning of the large intestine. It has no known function and can become infected and inflamed, causing the abdominal pain of appendicitis. The inflamed appendix needs to be surgically removed before it bursts. Doppler ultrasound scanning detects moving fluids, such as blood, by the frequency change they cause when reflecting high-frequency sound waves. Power Doppler scans use colour to show the moving fluid, but do not show the direction of the flow.