Science Waves
Ultrasound – Sendwavesintobodywhicharereflectedattheinterfacesbetween tissue – Returntimeofthewavestellsusofthedepthofthereflectingsurface History – Firstpracticalapplication,1912unsuccessfulsearchforTitanic – WWIIbroughtmassivemilitaryresearch-SONAR(SOundNavigation And Ranging) – Mid-centuryusedfornon-destructivetestingofmaterials – Firstusedasdiagnostictoolin1942forlocalizingbraintumors – 1950’s2Dgrayscaleimages – 1965orsoreal-timeimaging Sonography – relativelyportable,inexpensive,andsafesoisoftenthefirstchoiceof a medical imaging method where feasible Sound waves • Sound wave propagate by longitudinal motion (compression/expansion), but not transverse motion (side-to-side) • Can be modeled as weights connected by springs 1Ultrasonic Waves and properties • Mechanical waves are longitudinal compression waves • “Ultrasound” refers to frequencies greater than 20kHz, the limit of human hearing • For Medical imaging typically 100 Times higher frequency than audible by human typically 2 to 20 MHz Transmission and Reflection 2 Propagation of ultrasound waves in tissue Scattering • Specular reflector is a smooth boundary between media (conventional view of reflections • Acoustic scattering arises from objects that are size of wavelength or smaller • Most organs have characteristic structure that gives rise to defined scatter “signature” Specular -echoesoriginatingfromrelativelylarge,regularlyshapedobjectswith smooth surfaces. These echoes are relatively intense and angle dependent. (i.e. valves) - Reflection from large surfaces Scattered - echoes originating from relatively small, weakly reflective, irregularly shaped objects