Grey scale imaging (ultrasound)
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Commonly referred to as B (brightness) mode, the use of grey scale imaging in ultrasound renders a two-dimensional image in which the organs and tissues of interest are depicted as points of variable brightness. The formation of a B-mode image relies on the pulse-echo principle; assuming the speed of sound remains constant, the position of a target of interest may be inferred by the time taken from emission to its return to the transducer. In order to construct a cross-sectional image, the pulse-echo sequences from a multitude of neighboring scan lines are sequentially summated in real-time, generating a moving image 1.
Piezoelectric crystals within the footprint of the transducer convert electrical energy to mechanical energy by their deformation after a voltage is applied across them, acting as the generators of ultrasound waves. After the emission of these ultrasound waves the transducer "listens" for returning vibrations, which will deform the piezoelectric crystals transforming mechanical to electrical energy 2.
This current received during the listening phase is then analyzed by the ultrasound machine and is used to generate the B-mode image. The amplitude of the returning ultrasound waves are depicted as a function of brightness, hence the nomenclature.