Medical ultrasonography uses high frequency broadband sound waves in the megahertz range that are reflected by tissue to produce images. Important uses include imaging the abdominal organs, heart, breast, muscles, tendons, arteries and veins. While it may provide less anatomical detail than techniques such as CT or MRI, it has several advantages which make it ideal in numerous situations, in particular that it studies the function of moving structures in real-time and emits no ionizing radiation. It is also relatively inexpensive and quick to perform. Ultrasound scanners can be taken to critically ill patients in intensive care units, avoiding the danger caused while moving the patient to the radiology department. Doppler capabilities on modern scanners allow the blood flow in arteries and veins to be assessed.