A sonographer is an allied healthcare professional who specializes in the use of ultrasonic imaging devices to produce diagnostic images, scans, videos or three-dimensional volumes of anatomy and diagnostic data. The requirements for clinical practice vary greatly by country. Sonography requires specialized education and skills to acquire, analyze and optimize information in the image. Due to the high levels of decisional latitude and diagnostic input, sonographers have a high degree of responsibility in the diagnostic process. Many countries require medical sonographers to have professional certification. Sonographers have core knowledge in ultrasound physics, cross-sectional anatomy, physiology, and pathology.