Download Ultrasound Physics: Attenuation, Reflection, and Refraction and more Exams Health Physics in PDF only on Docsity! DO NOT COPY SPI chapter 6 Test Questions Answered (Latest Update 2023- 2024 Verified Answers) Define attenuation - correct answer ✅Decrease in "bigness" (intensity, power &litude) of a wave as it travels How are attenuation and speed related - correct answer ✅UNRELATED. Three components of attention - correct answer ✅1) absorption 2) scattering 3) reflection Attention unit - correct answer ✅dB (must be negative since attenuation causes intensity to decrease) Less attenuation - correct answer ✅shorter distances, lower frequencies More attenuation - correct answer ✅longer distances, higher frequencies Attenuation in different media - correct answer ✅Air>> bone&lung>> Soft tissue>> blood Attenuation & penetration - correct answer ✅In soft tissue lower frequency = less attenuation, we can penetrate further with lower frequency To find total attenuation - correct answer ✅+/- dB NEVER multiply Reflection - correct answer ✅Occurs when propagating sound strikes a boundary between two media and some return to the tx Page 1 of 7 specular reflection - correct answer ✅-reflection from a smooth surface and return in ONE direction, strikes at 90degrees When does specular reflection occur? - correct answer ✅When the wavelength is smaller than boundary irregularities diffuse reflection/ backscatter - correct answer ✅Redirection of sound in ALL directions When does scattering occur? - correct answer ✅When boundary is rough, reflected sound is disorganized, hits at acute or obtuse angle, also when boundary has irregularities that are the same size as wavelength Rayleigh scattering - correct answer ✅If reflector is MUCH smaller than wavelength, sound is uniformly distributed in all directions (OMNIDIRECTIONAL) As frequency increases, scattering - correct answer ✅Increases (higher frequency undergoes more Rayleigh scattering) Organized reflection - correct answer ✅Specular Disorganized reflection - correct answer ✅diffuse or back scatter Organized scattering - correct answer ✅Rayleigh Disorganized scatter - correct answer ✅Scattering Page 2 of 7 IRC AND ITC unit - correct answer ✅UNITLESS they are percentages IRC AND ITC equation - correct answer ✅100% = IRC + ITC When they are added together the result is ALWAYS 100% Reflection With NORMAL incidence - correct answer ✅Reflection occurs only if The two media and the boundary have different acoustic impedances IRC formula - correct answer ✅(Z2-z1)/(z2+z1)2 Z2 is what impedance? - correct answer ✅transmitted impedance (tissue sound is entering) Z1 is what impedance? - correct answer ✅reflected impedance (medium the sound is currently in) With greater impedance differences - correct answer ✅The IRC increases and the amount of reflection increases Transmission with NORMAL incidence - correct answer ✅What ever is not transmitted is reflected Reflection & transmission with OBLIQUE incidence - correct answer ✅Transmission and reflection MAY or MAY NOT occur. (Remember with oblique incidence we are uncertain so just say I DONT KNOW) Page 5 of 7 What we do know of OBLIQUE incidence - correct answer ✅Law of conservation of energy conservation of energy formula for incident intensity - correct answer ✅Incident intensity = transmitted+reflected Reflection angle = - correct answer ✅Incident angle Refraction - correct answer ✅Transmission with a bend (change in direction as sound transmits from one medium to another) Refraction requires - correct answer ✅Oblique incidence AND different speeds Refraction CAN NOT occur with - correct answer ✅normal incidence or identical prop speeds Snell's Law - correct answer ✅the ratio between the angle of incidence and the angle of refraction Snell's law equation - correct answer ✅Sin (transmission angle)/sin (incident angle) = propagation speed 2/ propagation speed 1 Same prop speed = - correct answer ✅No refraction Page 6 of 7 M2 slower than M1 - correct answer ✅Transmission angle less than incident angle M2 fast than M1 - correct answer ✅Transmission angle greater than incident angle Page 7 of 7
