Sound waves with frequencies above 20 kHz are called ultrasoundUltrasound. Ultrasound is frequently used to decipher the underground and underwater structures. Ultrasound signals of appropriate frequency are now often used to generate images of internal body organs, in determining their size and the depth from the body skin. Since ultrasoundUltrasound signalsSignal are non-toxic and non-ionizing, they do not damage or harm body cells; one may therefore take several ultrasound scans without any damage to the body. Using the Doppler effectDoppler effect, ultrasound signals may also be used to generate the image of blood flow pattern in different body parts. Details of ultrasound imaging are provided in this chapter.