Ultrasound Flashcards
Sound is a longitudinal wave
T
Sound requires a medium for propagation
T
Sound can propagate in a vaccuum
F (sound travels through the oscillation of particles in a medium, so it cannot propagate in a vacuum)
The human ear can detect sounds in the frequency range of 2 - 13 MHz
F (The human ear detects sounds between 20 Hz and 20 kHz - MHz are in the ultrasound range - far beyond human hearing)
Wavelength is inversely proportional to frequency
T
As the frequency of ultrasound increases, the wavelength in soft tissue decreases
T (inversely proportional)
The propagation velocity of US is faster in bone than in soft tissue
T
Propagation velocity varies depending on the medium
T
Acoustic pressure in tissue is unrelated to the energy of the sound wave
F (Acoustic pressure is directly related to the energy of the sound wave)
Sound waves require an elastic medium for propagation
T
Young’s Modulus measures elasticity, influencing how well sound propagates through the medium.
T
Acoustic Impedance (Z) is a measure of how ‘easy’ it is for sound to pass through a medium
T
A larger difference in acoustic impedance between two media leads to less reflection of sound waves
F (Larger differences in acoustic impedance cause stronger reflections at boundaries)
Big differences in acoustic impedance at an interphase will result in strong reflection of the sound wave
T
Impedances should be matched to allow for passage of sound waves through different mediums
T
Typical ultrasound absorption in tissue is approximately 10 dB per cm per MHz.
F (Typical ultrasound absorption in tissue is approximately 1 dB per cm per MHz.)
Refraction occurs when ultrasound travels between two media with the same propagation velocity.
F (Refraction occurs when there is a change in propagation velocity, causing the beam to bend.)
Refraction causes significant artefact
F
Diffraction is the bending of the ultrasound beam into the shadow of a strong absorber
T
Images in ultrasound are constructed based on the time it takes for the beam to return from a reflecting surface
T
The piezoelectric crystal in the transducer changes shape due to the application of electrical voltage.
T
The thickness of the transducer crystal is one-quarter of the ultrasound wavelength.
F (The thickness of the crystal is half the wavelength of the ultrasound beam.)
The matching layer of a transducer has a thickness of one quarter of the wavelength
T
Crystal layer thickness = ? wavelength of US beam
Matching layer thickness = ? wavelength of US beam
Crystal layer thickness = ½ wavelength of US beam
Matching layer thickness = ¼ wavelength of US beam
Ultrasound gel is used to prevent air layer reflection and improve contact between the probe and skin.
T
An ultrasound pulse contains 5 - 6 wavelengths
F (An ultrasound pulse contains 2 - 3 wavelengths
Pulse Duration (PD) is usually approx 1 microsecond
T
Increasing SPL, degrades spatial resolution
T
The higher the frequency, the shorter the SPL
T
Spatial resolution is heavily dependent on SPL
T
Shorter SPL results in improved spatial resolution
T
Longer SPL results in improved spatial resolution
F (Shorter SPL results in improved spatial resolution)
PRF determines the depth of tissue that we can interrogate
T
Increasing Pulse Repetition Frequency (PRF) decreases the depth of tissue that can be interrogated
T (Less time for echoes to return)
The thicker the tissue, the higher the PRF
F (The thicker the tissue, the lower the PRF eg. abdomen)
Max PRF = c / 2d
T
Increasing the SPL, decreases the bandwidth
T
In Doppler Imaging, a shorter SPL is used
F (In Doppler Imaging, a longer SPL is used)
In conventional U/S imaging, a shorter SPL and wider bandwidth is used
T
Bandwidth is obtained using Fourier analysis
T
Only lateral resolution is influenced by bandwidth
F (Both axial and lateral resolution are influenced by bandwidth.)
Axial spatial resolution is independent of the spatial pulse length
F (Axial resolution is directly related to SPL; shorter SPL improves axial resolution.)
Shorter SPL improves spatial resolution by allowing close objects to appear as separate structures.
T
Specular reflection occurs when the boundary between two structures is smooth
T
Mirror artefacts occur when sound waves reflect off multiple surfaces before returning to the transducer.
T
Lateral resolution depends on the focusing ability of the transducer and the aperture size.
T
Near Field = ? Zone
Far Field = ? Zone
Near Field = Fresnel Zone
Far Field = Fraunhofer Zone
The length of the near field is independent of the aperture
F (The length of the near field is dependent on the aperture)
The wider the aperture, the longer the near field, and vice verda.
T
Axial resolution is better than lateral resolution in ultrasound imaging
T
Axial resolution benefits from longer SPL, making it superior to lateral resolution.
F (Axial resolution benefits from shorter SPL, making it superior to lateral resolution.)
Time Gain Control (TGC) compensates for tissue attenuation with depth by amplifying echoes based on their time delay
T
Doppler techniques measure changes in sound velocity caused by moving blood cells.
F (Doppler measures changes in frequency, not velocity, to detect motion.)
Pulse Wave Doppler allows the analysis of echoes received from specific tissue depths.
T
The doppler shift can be used to determine the velocity of the flowing blood
T
The maximum doppler frequency shift that can be detected is determined by the SPL
F. (The maximum doppler frequency shift that can be detected is determined by the PRF)
The maximum doppler frequency shift that can be detected is determined by the PRF
T
Increasing PRF will increase the maximum doppler shift
T
Max doppler shift = PRF/2
T
Tissue Harmonic Imaging uses nonlinear propagation to generate harmonics for better image quality.
T
The velocity of sound in soft tissue is approximately 4080 m/s.
F (The velocity of sound in soft tissue is approximately 1500 m/s, while it is 4080 m/s in bone.)
A larger acoustic impedance mismatch between media leads to stronger sound transmission.
F (A larger impedance mismatch results in stronger reflection, not transmission.)
Ultrasound waves can experience absorption, reflection, refraction, and diffraction, similar to light waves.
T
The backing block in a transducer prevents backward transmission of ultrasound waves.
T
The matching layer between the transducer and the skin is half the wavelength in thickness.
F (The matching layer is one-quarter of the wavelength in thickness to optimize transmission.)
The spatial resolution of an ultrasound image degrades with depth due to increased SPL
T
Dispersion refers to the filtering out of higher frequencies in ultrasound imaging.
T
Lateral resolution depends on the width of the transducer’s beam
T
Higher PRF results in greater tissue depth interrogation.
F (Higher PRF reduces the time for echoes to return, limiting the depth that can be interrogated.)
The Doppler shift is proportional to the velocity of the blood flow
T
The maximum detectable Doppler shift is limited by PRF.
T
Scattering occurs when ultrasound encounters structures smaller than its wavelength.
T
Axial resolution improves as the spatial pulse length increases.
F (Axial resolution improves with shorter SPL)
Time Gain Control (TGC) ensures uniform brightness across all tissue depths.
T
The aperture size does not affect the focal plane or near field.
F (Aperture size influences the focal plane and near field depth, impacting lateral resolution.)
The far field (Fraunhofer zone) provides the best lateral resolution for imaging
F (Lateral resolution is best in the near field (Fresnel zone), where the beam is more focused.)
