= Medical ultrasound
{wiki}
= Ultrasonography
{synonym}
<Ultrasonography> forms medical images using <ultrasound>. In <pulse-echo imaging>, a <piezoelectric transducer> emits a short acoustic pulse and receives echoes from changes in <acoustic impedance>. If an echo returns after <time> $\Delta t$ from a reflector at distance $d$ in a uniform medium with <sound speed> $c$, the round trip gives $d=c\Delta t/2$. Scanning the beam assembles spatial information from many such measurements.<Ultrasound by National Institute of Biomedical Imaging and Bioengineering>[How does it work?: piezoelectric emission and reception, echo timing and acoustic coupling]{ref}
A water-tank experiment with two reflectors at known separations tests the depth calculation without biological interpretation. An incorrect assumed <sound speed> changes the inferred depths; overlapping pulses limit the separation of nearby reflectors. In tissue, <acoustic attenuation>, scattering and the geometry of the beam further affect the image. These mechanisms explain why the displayed anatomy depends on both physical propagation and the acquisition model.
Back to article page
