Sound & Waves
What are the acoustic variables of sound?
Pressure, density, distance
What transducer uses concentric ring elements?
Annular phased array
What improves axial resolution?
Shorter spatial pulse length
What is aliasing?
Wraparound of Doppler signal due to low PRF
What causes shadowing?
High attenuation structures
If frequency increases, what happens to wavelength?
Wavelength decreases
What is the purpose of the matching layer?
To increase the amount of sound transmitted
What affects lateral resolution?
Beam width
What does CW Doppler lack?
Range resolution
What artifact mimics a second structure along the beam path?
Mirror image
Define temporal resolution.
Ability to locate moving structures in time
Define focal depth.
Distance from transducer to focus
Which resolution is best in near field?
Lateral resolution
What is the Doppler shift if f_recv = 5.003 MHz, f_trans = 5 MHz?
3 kHz
Name a QA phantom type.
Tissue equivalent phantom
Name the unit of intensity.
Watts/cm^2
What is Huygens’ Principle?
Each point on the transducer is a sound source and wave interference results in an hourglass shaped beam
What is another term for elevational resolution?
Slice thickness resolution
What causes spectral broadening?
Turbulent flow or wide sample volume
What is comet tail artifact?
Reverberation with closely spaced echoes
What is the duty factor?
Percentage of time the system is transmitting
What determines beam divergence?
Transducer diameter and frequency
How can we improve lateral resolution?
Focus the beam
What does the Doppler equation calculate?
Frequency shift from motion
What is the purpose of QA testing?
Ensure consistent image quality and safety