Diagnostic ultrasound (also known as sonography or ultrasonography) is a non-invasive diagnostic technique used to image inside the body.
The word “ultrasound” in physics, refers to all sound with a frequency that humans cannot hear. In diagnostic sonography the ultrasound is usually between 2 and 18MHz .Ultrasound waves are produced by a transducer (a hand-held probe), which can both emit ultrasound waves, as well as detect the ultrasound echoes reflected back. In most cases, the active elements in ultrasound transducers are made of special ceramic crystal materials called piezoelectrics.
These materials are able to produce sound waves when an electric current passes through them, but can also work in reverse, producing electricity when a sound wave hits them. When used in an ultrasound scanner, the transducer sends out a directed beam of sound waves into the body, and the sound waves are reflected back to the transducer from the tissues and organs in the path of the beam.
When these echoes hit the transducer, they generate electrical signals that the ultrasound scanner converts into images of the tissues and organs. .Higher frequencies provide better quality images but are more readily absorbed by the skin and other tissue so they cannot penetrate as deeply as lower frequencies. Lower frequencies can penetrate deeper but the image quality is inferior.
Diagnostic ultrasound is a highly operator dependent imaging modality that requires the user to make optimum use of the scanning equipment.