Exam 1 Study Questions Flashcards
What is time per cycle?
Period
What is it called when there is a large, smooth interface?
Specular reflection
What is the maximum variation per cycle?
Amplitude
Less than 20 Hz
Infrasound
What is length per cycle?
Wavelength
What is cycles per second?
Frequency
What is the speed of a wave through a medium?
Propagation speed
When the structure’s dimensions are much smaller than the beams wavelength (red blood cells)
Rayleigh scattering
When the incident sound beam strikes the boundary at exactly 90 degrees
Normal incidence
Backscatter
Diffuse reflection
Define axial resolution
The ability to clearly define two separate reflectors that are very close together and parallel to the sound beam
List 3 of the acoustic parameters and their applicable units
Period
Frequency
Amplitude
Power
Intensity
Wavelength
Propagation speed
Define constructive interference
A pair of in-phase waves results in the formation of a single wave of greater amplitude
Define destructive interference
A pair of out-of-phase waves results in the formation of a single wave of lesser amplitude
Define specular reflection
A sound wave is reflected off of a smooth, flat surface and in one direction
Define diffuse reflection
A sound wave is reflected off a rough, uneven surface in multiple directions (backscatter)
Define half-value layer/half-value thickness
The distance sound travels in a tissue that reduces the intensity of sound to one-half its original value.
If system A has a wavelength of 5mm for a two-cycle pulse and system B has a wavelength of 2mm for a two-cycle pulse, which one is going to provide the best axial resolution?
System B
Define impedance
Acoustic resistance to sound traveling in a medium
What is the formula for impedance?
Impedance = density x propagation speed
z=c(p)
If the intensity at the start of the path is 10 mW/cm2 and the attenuation over the path is 6dB, the intensity at the end of the path is _____ mW/cm2
-6 = ¼ (10 x ¼) = 2.5 mW/cm2
If the intensity at point A is 20 mW/cm and at point B it is 10 mW/cm, the attenuation from A to B is _____ dB.
-3 dB
-3 = ½ 20 x ½ = 10
If the incident angle is 40 degrees and the transmission angle is 30 degrees, what is the change is speed from Medium 1 to Medium 2 ____
Decreases
Propagation speed increases if stiffness ____
Increases
If power is doubled and area remains the same, intensity ____
Increases
Destructive interference results in a wave where the amplitude ____
Decrease
As a wave travels through a medium, the intensity of the wave ____
Increases
- Frequency decreases as period ____
Increases
If the frequency is increased, the attenuation ____
Increases
If the wavelength increases, frequency ____
Decreases
The depth is changed from 6 cm to 12 cm, the pulse repetition frequency ____
Decreases
- How many mm are in 8 km
8,000,000
Which is adjustable by the sonographer?
Amplitude
Refraction occurs when ____
An interface is encountered at oblique incidence with different propagation speeds
Which of the sequences of metric abbreviations are in increasing order?
u, m, c, d, M
Spatial pulse length is determined by:
Both the sound source and medium
If the frequency is doubled, the wavelength is:
Halved
What is a unit for intensity?
mW/cm^2
How are pulse repetition period and depth related?
Directly
A wave is non-perpendicular at an interface. The propagation speed of medium 1 is higher than medium 2. The transmitted wave will have an angle that _______ the incident angle
Is less than
What determines attenuation?
Path length and frequency
How are cholesterol level and life span related?
Inversely
What is the fraction of time that ultrasound is emitted?
Duty factor
Which one of the following contributes the most to attenuation?
Absorption
_____ is measured in Rayls
Impedance
The horizontal axis on a graph is the _______ axis.
x-axis
Convert 12 inches to centimeters (2.54 cm = 1 inch)
30.48 cm
What is 1,300,000 in scientific notation?
1.3x10^6
What is 0.000000351 in scientific notation?
3.51x10^-7
All sound waves carry __________ from one location to another.
Energy
What type of wave is a sound wave?
Longitudinal
What is the definition of density?
Concentration of mass in a volume
Acoustic parameters include:
Period, frequency, amplitude, power, intensity, wavelength, and propagation speed
A _________ is a collection of cycles that travel together.
Pulse
________ are desirable for imaging because they create images with better axial resolution.
Shorter pulses
What determines axial resolution?
Spatial resolution
A cycle includes ________.
One positive half wave and one negative half wave
Used to help focus the beam
Lens
Converts electrical to mechanical energy
Piezoelectric materials
Lowers the acoustic impedance mismatch between the transducer and the patient
matching layer
Delivers the drive voltage to the crystal and echo voltage to the recievers
Wires
Dampening component
Backing material
The ability to distinguish between two structures
Resolution
The operating or main frequency
Resonant frequency
Where the beam reaches its minimal diameter
Focus
Fresnal
Near field zone
Fraunhofer
Far field zone
True or false: damping lengthens the pulse
False
True or false: PZT stands for lead zirconate titanate
True
In the near zone beam width ____ as distance from the transducer increases.
Decreases
Doubling the aperture ____ the near zone length.
Increases
A higher-frequency transducer produces more or less divergence in the far field?
Less
True or false: in pulse-echo system, the desired Q factor is an large as possible
False
True or false: the beam diameter is constant in the near zone
False
Divergence of a sound beam of an unfocused transducer occurs in the ____ zone
Fraunhofer
In a sound wave, regions where the pressure is higher than normal are called regions of ____.
Compression
Bandwidth can be increased by increasing ____.
Damping
What is the depth of the object if the go-return time is 7 us?
1.54 x 7 / 2 = 5.39 mm
At what part of the beam is the intensity the greatest?
At the focus
What is the name given to describe electronic focusing of multi-element transducers?
Phasing
According to the range equation, which of the following are necessary to calculate the distance to the reflector?
Propagation speed and go-return time.
When a sonographer increases the maximum imaging depth during an exam, what happens to the PRF?
It decreses
The reverse piezoelectric effect describes the ____ of a sound wave.
Transmission
The thickness of the element is equal to ____ the wavelength of the resonate frequency.
1/2
Reflection of the sound beam from a large interface with a rough surface is called ____.
Diffuse reflection
The optimal impedance of the matching layer would be about ____ rayls if the element is 25 rayls and tissue is 3.5 rayls.
15 rayls
The optimal thickness of the matching layer is ____ of the wavelength of resonant frequency.
25%
For modern day ultrasound scanners, the most favorable resolution factor is ____.
Axial
The size of the focus of a 2 MHz, 8mm diameter single element unfocused transducer is ____
4 mm
The most commonly used material in modern transducer elements is ____.
Lead zirconate titanate
What determines the PRF of a sound wave?
Imaging depth
Backing material improves____ axial resolution.
Improves
Heating a transducer above the ____ ____ will cause depolarization.
Curie point
Two ultrasound systems have near zone lengths of 8cm. At the focus System G has a lateral resolution of 3.0mm, whereas System p has a lateral resolution of 5.0mm. Which system is more likely to produce higher quality pictures at the focus?
System G
Slice thickness can be improved by ____.
Curving the element or using a lens
Which of the following transducers would give the shallowest focus?
Diameter = 1mm; Frequency = 2 MHz (smaller diameter and lower frequency)
What is the most common form of fixed focusing?
Internal
The range equation relates ____, ____, and ____.
Distance, velocity, and time.
Two crystals of the same thickness are used for transducers A and B. The propagation velocity on transducer A’s crystal is twice that of transducer B. Which means transducer ____ operates at ____ the operating frequency.
A; twice
Which quantity is unitless?
Q-factor
The Q value of a transducer is determined by ____.
Bandwidth
What can be used to focus an ultrasound beam?
Curved crystal, acoustic lens, and phasing.
