Ultrasound

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Ultrasound is high frequency mechanical vibrations or pressure waves above a frequency the human ear can hear. Ultrasound uses sound waves above 20 KHz.


Ultrasound or ultrasonography is a medical imaging technique that uses high frequency sound waves and their echoes to aid in the diagnosis and treatment of patients. Ultrasound uses a pulse-echo technique of imaging the body. Pulses transmitted into patient and give rise to echoes when they encounter interfaces/reflectors caused by variations in the "acousitc impedence" between different tissues.


Echo signals are amplified electronically and displayed on a monitor using shades of grey (from black to white), stronger reflectors = brighter shades of grey and appear white in an image. Those with no echoes will appear black, such as a full bladder.


The ultrasound image (sonographic / echographic) is based on mechanical oscillations of the crystal excited by electrical pulses (piezoelectric effect). Numerous crystals are assembled to form the transducer. A transducer converts one type of energy into another. Based on the pulse-echo principle occurring with ultrasound piezoelectric crystals, ultrasound transducers convert electricity into sound.


The ultrasound waves (pulse of sound) are sent from the transducer and propagate through different tissues and then return reflected as echoes to the transducer. Those returned echoes are then converted back into electrical impulses by the transducer crystals and are further processed in order to form the ultrasound image presented on the screen.


 

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