Quiz 5 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
What change while make the near zone become longer?
Increased diameter of crystal
Which statement regarding the near field or the far field zones is true?
The near field length increases with increasing frequency
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 a crystal diameter of 5mm ?
2.5 mm, 5 mm
The transmitted beam diverges is 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?
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?
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 effect?
Converts electrical to mechanical energy
What is the use of the transducers backing material?
Used to decrease the SPL, improve AR, increase transducer BW, and decrease transducer sensitivity.
What is the most common natural piezoelectric material?
Quartz
The matching layers are cut to _______ the _______ of the crystal.
1/4 of the wavelength
An advantage to multiple transmit foci per line is improved _____ resolution, however, ______ resolution will degrade.
Lateral, temporal
The velocity of sound waves is primarily dependent on the…
Material in which the sound is being transmitted
One benefit of composit 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 phase array transducer there will be a black line on the screen corresponding to that specific crystal.
False
Huygens 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 all of the following:
- 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
At a frame rate of 2 FPS, what is the time for a single frame to occur?
0.05 second
(20 frames/1second = 1frame / x second)
True/False:
Electronic focusing is accomplished by delaying the electrical pulses in each crystal to cause the wave fronts to converge at variable focal points
True
Which mode has NO grayscale image? It only has spikes representing how strong the returning signal is.
a mode
Which 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
Increase in 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
Your crystal diameter is 9 mm and your frequency is 4 MHZ, what is the near zone length?
54 mm
True/False:
Mechanical transducers are steered with a motor and are focused by either internal or external methods
True
Written
What are the two other names for the operating frequency?
Resonant and natural
written
The matching layers are commonly composed of what in epoxy resin?
Aluminum powder
In which of the following is the amplitude height of the echo proportional to its strength?
A-mode
In M-mode, the vertical axis represents:
Depth
The ‘A’ in A-mode stands for:
Amplitude
If the echo amplitude increases, the echo brightness:
Increases
What is determined by the range equation?
Depth of the reflector
The number of frames generated per second is called:
Frame Rate
The major limitation in scanning speed is:
Time it takes for the sound wave to propagate through tissue
The ability to resolve two events related by times is:
Temporal resolution
Higher frame rate and temporal resolution are:
Directly related
Frame rates can be improved by:
Decreasing the depth
Maximum depth x line per frame x number of focal zones x frame rate is less than:
77,000
The image depth controls the:
PRF
The relationship between the spatial resolution and temporal resolution can be described as:
Indirectly related
Another name for the depth control is:
Field of view
What organ is scanned with the highest temporal resolution?
Pediatric heart
Spatial resolution includes…
-longitudinal resolution
-elevational resolution
-lateral resolution
(Note: NOT temporal resolution)
How many microseconds does it take for the ultrasound instrument to put an echo 6cm deep on the image?
78
A voxel is a 3-D picture element which includes all of the following:
-length
-width
-thickness
