Test 4 Flashcards
What is the region in an unfocused beam that extends from the transducer surface to an axial distance where the field begins to diverge?
Fresnel Zone
Which change will make the near zone become longer?
Increased diameter of crystal
The near field length (blank) with increasing frequency
Increases
Which change will increase the rate of far field divergence?
decrease in frequency
For an unfocused transducer, what is the approximate beam width at the focal distance and twice the focal distance, given the crystal diameter of 5 mm?
2.5 mm, 5 mm
The transmitted beam diverges at which zone?
Fraunhofer Zone
True/False
If the number of cycles in the pulse are increased the axial resolution improves.
False
What will happen to the crystal if you heat a transducer above the Curie point?
it becomes depolarized
What is used to make most crystals in modern diagnostic sonographic transducers?
Lead zirconate titanate
Why is the piezoelectric effect employed in diagnostic medical ultrasound ?
To generate sound waves from electrical waves.
True/False
Intensity is uniform throughout the beam
False
What is the use of the transducer lens ?
Used to help focus the beam
What is the use of the transducers’ matching layers?
Lowers acoustic impedance mismatch between the transducer and patient
What is the use of the transducers piezoelectric material?
converts electrical to mechanical energy
What is the use of the transducers backing material?
Used to decrease the SPL, improve AR, increase transducer BW, & decrease transducer sensitivity
(Match response)
What is the most common natural piezoelectric material?
Quartz
The matching layers are cut to _____ the ______ of the crystal
1/4 the wavelength
An advantage of multiple transmit foci per line is improved _________ resolution.
However, ________ resolution will degrade.
Lateral resolution improves
Temporal resolution degrades
The velocity of sound waves is primarily dependent on the ?
Material in which the sound is being transmitted
One benefit of composite piezoelectric elements over natural elements is:
Acoustic impedance closer to that of soft tissue
True/False
The crystals in linear sequenced array transducers are fired off in groups to create a longer near zone.
True
True/False
If a crystal is damaged in a phased array transducer there will be a black line on the screen corresponding to that specific crystal
False
Huygen’s principle states that:
Numerous
wavelets that are produced form a new wave front using constructive interference
What primarily determines the operating frequency of an ultrasonic transducer?
Thickness of the crystal
In a real time scanner, the frame rate is influenced by…
Number of transmit focal regions
Number of lines per frame
Speed of sound in tissue
Depth of tissue examined
Note: NOT “Frequency bandwidth of the transducer”
True/False
Continuous wave probes have broad bandwidths due to their long pulse lengths
False
True/False
Electronic focusing is accomplished by delaying the electrical pulses to each crystal to cause the wave fronts to converge at variable focal points
True
What mode has NO grayscale image? It only has spikes representing how strong the retuning signal is.
A mode
This mode tracks the position of the transducer to place a dot on the screen corresponding to the transducer position (X, Y location), thus creating the 2-D image
B mode
True/False
Increasing the number of scan lines also increases the spatial resolution
True
True/False
For pulse wave imaging we want there to be a low Q factor
True
True/False
Mechanical transducers are steered with a motor and are focused by either internal or external methods.
True
What are the two other names for the operating frequency?
resonant and natural
The matching layer(s) are commonly composed of what in epoxy resin?
Aluminum powder
What is the pulse repetition period is the pulse repition frequency is 5 kHz?
0.2 ms
(Note: NOT 0.2 microsec)
If the number of cycles in a pulse is increase, but the wavelength remains the same, what is being increased or decreased?
The pulse duration is increased
What is the term for the time from the beginning of one pulse to the beginning of the next pulse?
Pulse repetition period
How does increasing the depth of effect the SPL?
No change
How does increasing the depth of effect the duty factor?
Decrease
How does increasing the depth of effect the Pulse repetition period ?
Increase
How does increasing the depth of effect the pulse duration?
No change
How does increasing the depth of effect the propagation speed?
No relation
How does increasing the depth of effect the number of cycles?
No relation
What change will cause the pulse duration to increase?
Frequency decreases
If the pulse repition period is 330 microseconds, what is the pulse repetition frequency?
3 kHz
What is the fraction of time the sound is actually on?
Duty factor
In diagnostic medical sonography, the beam would reach a reflector of approximately _______ deep in 20 microseconds
3 cm
In DMs, what is the most common unit for SPL?
mm
What is the unit for duty factor?
Unitless
What is the SPL if the wavelength is 2mm and there are 3 cycles in the pulse?
6 mm
PRF is the number of _______ occurring in 1 second
Pulses
If the Pulse Repetition Frequency decreases then what would happen as well?
Duty factor decreases
It took the beam 45.5 microseconds to reach the reflector. How deep did the beam travel?
7 cm
**typed
You are scanning with a 4 MHz transducer that has 2 cycles per pulse. You note a mass that is at a distance of 8 cm. What is the pulse repetition frequency ?
9.57 kHz
**typed
What is the relationship of frequency to absorption?
If the frequency is doubled, the absorption is doubled.
True/False
Continuous wave differs in that the probe has only one crystal to send and receive signals and pulse wave probes have two crystals
False
What determines the number of cycles in a pulse?
Backing layer
True/False
A longer spatial pulse length yields better image resolution.
False
What can the sonographer do to obtain the best image specular reflector?
The sonographer can turn their probe perpendicular to the interface.
**typed
What does a duty factor of 1 mean?
The machine is always on
**typed
You are scanning with a 3 MHz transducer that has 2 cycles per pulse. You note a mass that is at a distance of 11 cm. What is the pulse repetition frequency?
Round to two decimal places
6.96 kHz
**typed
