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ultrasound2 prelim

# ultrasound2 prelim - 10.0 The Physics of Ultrasound...

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10.0 The Physics of Ultrasound Ultrasound is sound with frequencies higher than the highest frequency that can be heard by human beings >20KHz). Medical ultrasound operates typically between 1 and 10MHz. The propogation characteristics are defined in the theory of acoustics and medical ultrasound is principally concerned with compression waves rather than shear waves. Basic acoustic physics, wave equation Plane, spherical wave solutions of the wave equation Wave propogation in media, energy, intensity, reflection, refraction Transmission, reflection coefficients, attenuation in media, scattering Doppler effect Beam formation and focusing Beam patterns, diffraction formulation Paraxial, Fresnel and Fraunhofer approximations

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Important points from Ultrasound 1 Lecture Bulk compressibility, Ultrasound in tissue is principally a longitudinal (compressive) wave Wave equation in various geometries (plane wave, spherical wave) Speed of sound and density of various biological materials Acoustic Impedance Z= ρ c Acoustic Energy, Power Intensity. Transmission, Reflection for wave Amplitude and Intensity Quarter wave ( λ /4) matching layer concept dp dV V 1 1 c Animation courtesy of Dr. Dan Russell, Kettering University 2 1 2 1 2 Z Z Z Z I I R i r I 2 1 2 2 1 4 Z Z Z Z I I T i t I T I + R I =1 (pressure is different!)
http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm L. Braile, Purdue University ) 2 cos( 0 ft kx u u ) 2 cos( 0 0 0 ft kx cu cu p ) 2 sin( 2 2 0 ft kx f u f iu

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