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52 Cards in this Set
- Front
- Back
Sounds waves are comprised of: |
rarefactions and compressions
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7 parameters that describe sound wave:
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period
frequency amplitude power intensity propagation speed wavelength |
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Frequency affects:
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penetration and axial resolution (image quality)
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Formula for intensity:
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power (watts)
--------------------- beam area (cm2) |
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Speed of sound in soft tissue:
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1.54 km/s
1540 m/s 1.54 mm/us |
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Density and speed = ______ directions
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opposite
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Stiffness and speed = ______ directions
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same
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Propagation speed formula:
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frequency (hz) x wavelength (meters)
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The operator can change the:
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amplitude, power and intensity. The values of these parameters decrease as sound propagates through the body.
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Period, frequency and wavelength are changed when:
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a new transducer with a diff freq is used.
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What is determined by the sound source?
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period, frequency, amplitude, power, intensity
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What is determined by the medium:
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propagation speed
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What is determined by the sound source and the medium?
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the wavelength
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Pulse duration:
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the time from the start of a pulse to the end of that pulse, only the ACTUAL TIME that pulse is on.
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Pulse duration will be longer when using a new transducer with:
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lower frequency (longer period)
more ringing (more cycles in a pulse) |
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_____ Intensity is the most relevant to tissue heating.
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Spatial peak Temporal Average (SPTA)
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______ intensity has the highest value.
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Spatial peak temporal peak (SPTP)
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______ intensity has the lowest value.
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Spatial average Temporal average (SATA)
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___ intensity is maximum in time.
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Temporal peak (TP)
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__ intensity is averaged only during the pulse duration (on time only)
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peak average (PA)
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__ intensity is averaged during the pulse repetition period (both on and off times)
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temporal average (TA)
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The rank of intensities from the largest to the smallest is:
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SPTP, IM, SPPA, SPTA, SATA
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3 DB means _____
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2 times, the final intensity is 2 times bigger than the original intensity.
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6 dB means ______
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two times, two times.
The final is 4 times bigger than the original |
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20 dB means_____
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ten times, ten times. The final is 100 times bigger than the original intensity.
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The decrease in intensity, power and amplitude as the sound wave travels is termed:
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attenuation
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Units for attenuation is:
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dB (must be negative, since the attenuation causes intensity to decrease)
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In soft tissue, the _______ frequency, the _______ the attenuation.
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greater, greater. This is why we do not image deep with high freq sound.
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3 components of attenuation:
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absorption, scattering and reflection.
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Absorption:
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sound energy converted into heat energy
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If the boundary between 2 media has irregularities (with a size similiar to or a bit smaller than pulse's wavelength) then the wave maybe redirected into a number of different directions.
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scattering
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If the reflector is much smaller than the wavelength of sound, the ultrasounic energy is uniformly diverted in all directions. Higher frequency sound undergoes more of this. A rbc is this.
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Rayleigh scattering
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Reflection occurs when:
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some of the propagating sound energy strikes a boundary between 2 media and is returned toward the transducer.
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The amount of attenuation per centimeter is termed:
units: dB/cm |
attenuation coefficient.
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In soft tissue, attenuation coefficient (dB/cm) is estimated at approximately:
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half of the freq (Mhz), or 0.5 dB/cm/Mhz
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Impedance increases when:
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density increases or
propagation speed increases |
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Impedance formula:
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impedance (rayls) = density (kg/m3) x propagation speed (m/s)
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____________ ___________
does not change when path length changes. |
attenuation coefficient.
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________ is higher in both bone and in lung compared to soft tissue.
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attenuation
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IN SOFT TISSUE, the attenuation coefficient in dB per cm ranges from ____ to ____ times the ultrasonic frequency in MHz.
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0.5 to 1.1
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With oblique incidence:
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1) reflection angle = incident angle and
2) % transmission + % reflection = 100% |
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Refraction occurs when:
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there are different propagation speeds and oblique incidence.
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Snell's law:
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sine transmission angle prop speed2
___________________= __________ sine incident angle prop speed 1 |
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If propagation speed 2 is ____ than propagation speed 1, then the transmission angle is less than the incident angle.
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less
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If propagation speed 2 is greater than propagation speed 1, then the transmission angle is ________ than the incident angle.
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greater
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Reflection angle =
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incident angle
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In reflection with normal incidence you look for?
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diff impedance's
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Reflection with oblique incidence?
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we don't know!!
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This is derived from reflection information:
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transmission
% transmission + % of reflection = 100% |
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For refraction we need to look for?
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oblique incidence and different speeds
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13 usecs, the reflector is __ cm deep in the body
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1
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If the reflector is 4 cm deep in the body, how many us is that?
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52 usecs
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