Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
50 Cards in this Set
- Front
- Back
|
which of the following results in the wave with the greater intensity |
short distance, low frequency -sound attenuates least when traveling a short distance. low frequency sound attenuates less than high frequency sound |
|
|
a 10MHz sound beam travels through two medium. it attenuates 5db in medium A and 1db in medium B. What is the total attenuation that the sound bean undergoes as it travels through both media? |
6db, -as sound travels, attenuation simply adds, just like tolls add when you travel on the highway |
|
|
A 3 MHz sound beam travels 10 cm, 6cm in medium A and 4 cm in medium B. The total attenuation is 14 db. if the sound beam attenuated 4db in medium A, then how much attenuation occurred in medium B? |
10db, -as sound travels, attenuation simply adds just like tolls add when you travel on the highway. If 4 db of attenuation occurred in medium A then 10 db must occur in medium B. This would make the total attenuation 14db, as is given in the problem |
|
|
reflection and scattering |
specular-diffuse-scatter |
|
|
reflection |
occurs when propagating sound energy strikes a boundary between two media and some returns to the transducer |
|
|
specular reflection |
reflections from a smooth reflector (mirror) are specular and return in one direction -specular reflections also occur when the wavelength is much smaller than the irregularities in the boundary. |
|
|
diffuse reflection or backscatter |
the redirection of sound in all directions. when a boundary is rough, reflected sound is disorganized and random. diffuse is also called backscatter. -also occurs when the boundary has irregularities that are approximately the same size as the sounds wavelength |
|
|
rayleigh scattering |
if a reflector is much smaller than the wavelength of the sound, sound is uniformly distributed in all directions ("omnidirectional) higher frequency sound under goes more reighleigh scattering a red blood cell is a reighleigh scatter |
|
|
hint rayleigh |
rayleigh scattering is related to frequency |
|
|
atteuation coefficient defenition |
the amount of attenuation per centimeter. a way to report attenuation without dealing with distance. -attenuation coefficient is related to frequency |
|
|
units |
db/cm, decibles per centimeter |
|
|
as frequency increases.... |
the attenuation coefficient increases |
|
|
in soft tissue |
with higher frequency, there is more attenuation per centimeter, this is why higher frequency sound cannot penetrates deep |
|
|
equation |
total attenuation (db)=path length (cm) x attenuation coefficient (db/cm) |
|
|
impedance |
a number associated with a medium. impedance is calculated, it is not measured. |
|
|
units |
rayls, often represented by the letter "z" |
|
|
important note impedance |
reflection of an ultrasound wave depends upon different acoustic impedances of the media on either side of the boundary. |
|
|
ex of impedance |
two media A and B, have the same propagation speed. medium A's density is 10% higher than medium B's. thus, medium A's impedance is 10% higher than medium B's |
|
|
name the three components of attenuation. which of these 3 components is dominant contributor at attenuation |
absorption, reflection and scattering. absorption attenuates sound the most |
|
|
as the path length increases, attenuation of US in soft tissue |
increases |
|
|
total attenuation in soft tissue is related to ---&---? |
how far the wave travels (path length) and frequency of the sound |
|
|
attenuation in lung tissue is--- (less than, greater than, the same as) soft tissue |
greater than |
|
|
attenuation in bone is--- than soft tissue |
greater than |
|
|
attenuation in air is-- than soft tissue |
much greater than |
|
|
attenuation in water is---than soft tissue? |
much less than |
|
|
what are the units of attenuation |
decibles (db) |
|
|
what is the relationship between propagation speed and the attenuation coefficient in soft tissues? |
speed and attenuation coefficient are unrelated |
|
|
what is the relationship between us frequency and the attenuation coefficient in soft tissue |
in soft tissue, the attenuation coefficient in db per centimeter is about half of the ultrasonic frequency in MHz |
|
|
as the path length increases the attenuation coefficient of us in soft tissue |
remains the same |
|
|
acoustic impedance equals---x---? |
impedance -density (kg/m3) x propagation speed (m/s) |
|
|
impedance is important ---at boundaries? |
reflections |
|
|
which is better to use carotid artery, at 7.5 or 3.0 MHz transducer? |
7.5 because higher frequency |
|
|
in soft tissue,attenuation coefficient is directly related to ? |
frequency. if frequency doubles. att. coeff will double |
|
|
rayleigh scattering is related to? |
frequency 4 (if frequency doubles, rayleigh scattering increases by a factor of 16. 2x2x2x2=16 |
|
|
incidence "PORN" |
-perpendicular -orthogonal -right angle -ninety degrees -PORN |
|
|
oblique incidence |
anything other than 90 degrees; not at right angles -acute angles-are less than 90 degrees and are oblique -obtuse are greater than 90 degrees and are oblique |
|
|
incident intensity |
intensity of the sound wave at the instant prior to a striking boundary |
|
|
reflected intensity |
portion of the incident intensity that. after striking a boundary changes direction and returns back from where it came from |
|
|
transmitted intensity |
portion of the incident that, after striking a boundary, continues on in the same general direction that it was originally traveling |
|
|
units |
W/cm2 (they are all intensities) |
|
|
equation |
incident intensity=reflected intensity + transmitted intensity *conservation of energy "exists at a boundry |
|
|
intensity reflection coefficient (IRC) |
the percentage of the US intensity that bounces back when the sound strikes a boundary |
|
|
intensity transmission coefficient (ITC) |
the percentage of the incident intensity that, after striking a boundary, continues on in the same general direction that it was originally traveling |
|
|
units |
none, these are percentages |
|
|
typical values |
both IRC and ITC are unitless -range from 0% to 100% or 0 to 1.0 |
|
|
you get 100% if? |
impedance are identical |
|
|
equation |
100%=IRC (%) + ITC (%) |
|
|
when the IRC and ITC are added? |
the result is 100% |
|
|
when reflected and transmitted intensities are added? |
the result is incident intensity |
|
|
note intensities are reported in? |
units W/cm2 |
