Ultrasound Flashcards
what is the audible range of sound waves?
1-20Hz
20-2000 Hz
20-20,000 Hz
20-20,000Hz. Hz= cycles per second. ultrasound is anything above 20,000Hz
What is the frequency range for medical ultrasound?
20-20,000Hz
1-2MHz
2-18MHz
10-18MHz
2-18MHz = 2-18 million cycles per second
what things effect the speed of sound through an object?
the stiffness of the tissue (bulk modulus) and the density
how can you calculate the speed of sound (c) in relation to the stiffness (B) and density (p)?
see picture
how are the speed of sound, frequency and wavelength related in an equation?
c = f λ (f = frequency; λ = wavelength)
what is the speed of sound through soft tissue?
1540 m/s
define the frequency of a sound wave?
how many times per second the compression phase passes any single point in the medium, measured in megahertz (MHz).
what is a period?
The period (T) of a wave is the time between successive compressions (or rarefactions) at a single position in the medium. The time taken for 1 complete cycle. Inversely related to frequency.
T=1/f
what is the definition of a wavelength?
The wavelength (λ) of a wave is the distance between successive compressions (or rarefactions) at a single point in time.
what is the speed of sound in air?
330m/s
what is the speed of sound in bone?
4080m/s
a decrease in 10 decibels is equal to what change in intensity?
10 fold decrease in intensity
a decrease in 3 decibels is equal to what change in intensity?
halves the intensity
Intensity (dB ratio) =
10 log10 (I1 / I2) (I1 = intensity 1; I2 = intensity 2)
what is acoustic impedence?
Acoustic impedance (Z) describes the resistance experienced by an ultrasound beam in the medium. It depends on density (ρ) and elasticity and is, for practical purposes, independent of frequency. Acoustic impedance is measured in Rayls (kg/m2s).
What is the calculation for acoustic impedence?
Acoustic impedence (Z, kg m-2 s-1) = density (p) x speed of sound in that material (c)
how do you calculate the reflection coefficient?
Reflection coefficient (R) = Z2 – Z1)2 / Z2 + Z1)2
how can you calculate the Nyquist limit if you have the pulse repetition frequency?
Nyquist limit = PRF / 2
what is snells law?
The angle of refraction is determined by the change in the speed of sound and is related to the angle of incidence. The angle can be smaller or larger depending on which material the sound is slower through. If the sound speeds up the transmittance angle increases, right image below.
what is axial resolution and the axial resolution limit?
Axial (or depth) resolution is the ability to separate two interfaces along the same scan line at varying depths. If the interfaces are too close together, the echo pulses will overlap and be recorded as a single interface- this is the axial resolution limit. It is determined by the spatial pulse length. Axial resolution is about (just above) half the pulse length. If they are closer than this they won’t be differentiated.
SPL= #cycles x λ
what calculation is used by an ultrasound machine to plot the depth of an object?
T= time, c= speed (1540). divided by 2 as there and back again
define the pulse duration?
Pulse duration (PD): the time taken for an entire pulse to be emitted from the ultrasound machine. (#cycles x time)
define the spatial pulse length
SPL (spatial pulse length): the length of the pulse as it moves through space. Cycles x wavelength. Distance measurement.
define the pulse repetition period
Pulse repetitions period: the amount of time between the start of one pulse and the start of the next pulse (PD + receive time). Inversely proportional to the pulse repetition frequency.
PRP=1/PRF
define the pulse repetition frequency
Pulse repetition frequency: determines the number of pulses you can fit in one second.
As PRP increased we can image a greater depth, this reduces the PRF. The opposite is also true.
Pulse repetition frequency (PRF) = frame rate x lines per frame
what is the doppler equation to calculate the speed?
F(d)= detected frequency, F(t)= transmitted frequency
what determines the fundamental frequency a transducer has?
thickness of the PZT. Frequency (f)= c/2x thickness of the PZT. the thickness of the PZT is half a wavelength.
what is the curie temperature?
the temperature above which you remove the dipoles in the PZT material (350 degrees c)
which part of the probe stops all the sound waves being reflected by the skin surface?
matching layer
what is the purpose of the backing layer
dampening. Therefore dampening shortens the spatial pulse length.
It also stops the sound from being transmitted backward into the transducer.
It also stops the sound from being a pure frequency, and a few other frequencies are produced- more bandwidth
what is the q factor
measures the purity of frequencies from the transducer. Q=f0/f(range). – A high Q-factor transducer indicates a narrow bandwidth and a long SPL.
o “High Q” transducers are commonly used in Doppler ultrasound application, where a
narrow bandwidth is needed to accurately quantify flow rate.
– A low Q-factor transducer indicates a broad bandwidth and a short SPL. Heavy dampening.
what is the modified Bernoulli equation?
ΔP=4×v ^2 ‘4vsquared’
where:
Δ 𝑃
ΔP is the pressure gradient in mmHg,
𝑣 v is the peak velocity of the regurgitant jet in m/sec.
what is the pulse duration for 5 cycles of 5MHz ultrasound?
Time for 1 wavelength (period, T)= 1/f. PD=Numberofcycles×T. therefore the answer is 1microsecond
what is azimuthal resolution?
lateral resolution. Azimuthal resolution in ultrasound imaging refers to the ability to distinguish between two points that are side by side (perpendicular to the direction of the ultrasound beam) within the same imaging plane.
in ultrasound, as pulse repetition frequency increases, the duty factor…
DutyFactor= PulseRepetitionPeriod/PulseDuration.
As the pulse repetition frequency (PRF) increases, the duty factor also increases. This is because the time between pulses (PRP) decreases while the pulse duration remains constant, leading to a higher proportion of time during which the transducer is actively emitting ultrasound waves.
Q factor is determined by:
a) bandwidth only
b) impedence and bandwidth
c) frequency and band width
d) pulse duration and bandwidth
C.
Q= fundamental frequency/ renge of frequencies (or band width)
Low-frequency ultrasound transducers have
A Longer wavelengths and less penetration
B Shorter wavelengths and greater penetration
C Shorter wavelengths and less penetration
D Longer wavelengths and greater penetration
D
Which Doppler angle yields the greatest Doppler shift?
A 60 degrees
B 0 degrees
C 45 degrees
D 90 degrees
B
lateral resolution is primarily determined by…
a) frequency
b) inherent to the transducer
c)beam diameter
C
which is true about harmonic ultrasound?
a) a returning harmonic signal will be attenuated to a lesser degree than a returning fundamental signal
b) harmonic production decreases with depth
c) fewer artifacts are detected with fundamental imaging than with tissue harmonic imaging
d) the bandwidth of the transducer determines the range of harmonic frequencies that can be detected by the transducer
a,d???
if the frequency of a sound wave increases what happens to the spatial pulse length?
decreases
does wavelength have a greater effect on axial, lateral, temporal or far zone resolution in ultrasound
axial. Axial resolution is directly related to the pulse duration, which is determined by the wavelength of the ultrasound wave. Specifically, better axial resolution is achieved with shorter wavelengths. This is because shorter wavelengths result in shorter pulse durations, allowing the system to distinguish smaller reflectors that are closer together along the beam axis.
arrange the following media in terms of ultrasound speed from highest to lowest?
fat, air, bone, muscle
bone, muscle, fat, air
the speed of sound depends on which of the following?
frequency,
wavelength,
amplitude,
the medium
primarily on the medium.
Frequency: The frequency of sound (the number of cycles per second) does not directly affect the speed of sound in a specific medium. Frequency relates to the pitch of the sound (higher frequencies correspond to higher pitches) and is related to the wavelength and speed of sound, but it does not dictate the speed itself.
Wavelength: Wavelength is inversely proportional to frequency (λ = v / f, where λ is wavelength, v is velocity, and f is frequency). While wavelength is related to frequency and speed of sound, it does not independently determine the speed of sound in a medium.
Amplitude: Amplitude refers to the intensity or loudness of sound, which is related to the energy carried by the sound wave. Amplitude affects the perception of sound (loudness), but it does not affect the speed of sound in a given medium.
a red blood cell is an example of a:
specular reflector,
mirror reflector,
Rayleigh reflector,
strong reflector
A red blood cell is an example of a Rayleigh reflector in the context of ultrasound imaging.
Here’s why:
Rayleigh scattering occurs when the size of the scatterer (such as a red blood cell) is much smaller than the wavelength of the incident ultrasound wave. In this case, the scattered waves are dispersed equally in all directions.
Red blood cells are much smaller than the wavelength of ultrasound waves commonly used in medical imaging (typically in the range of 1-15 MHz), making them effectively scatterers that contribute to Rayleigh scattering.
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