Ultrasound imaging is a medical diagnostic technique where sound waves are being used to image various parts of the body. Other terms for ultrasound imaging are sonograms, US and sonography. Ultrasound is widely used these days as it is painless and safe to adults, children and foetuses. There are no side effects such as the ones associated with radiation. During the ultrasound scan, the sonographer rests a small probe over the skin. This probe produces sound waves i.e pulsations that travel through the tissues. Some of the sound waves are being reflected back to the transducer and the computer analyses the returning echoes and produces the image on the screen. It is the same principle as the sonar the navy uses. Ultrasound is being used to image mostly solid organs such as liver, kidneys, uterus and ovaries, muscles and blood vessels and babies in the womb. It has, however, limited value in organs such lungs, bone, stomach and bowel/colon. Ultrasound images are black and white but colour Doppler is being used to evaluate organ and blood vessel blood flow and this is what the red and blue colours on the screen are.