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150 Cards in this Set
- Front
- Back
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What factors have an affect on the half value layer thickness?
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Dependent on the frequency and the medium through which the sound travels.
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List three factors which affect lateral resolution?
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1. Distance from transducer and focal zone settings
2. Number of cycles in a pulse 3. Frequency 4. Line Density |
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List three factors which the "Quality factor" is dependent upon?
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1. Crystal Damping
2. Crystal thickness 3. Operating frequency Q factor= Main frequency/Bandwidth |
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What two factors should allow for the transfer of sound from the transducer to the patient (and vice versa) more efficiently
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Grinding the matching layer to 1/4 wavelength of the velocity of sound through the matching material
Use of coupling gel |
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In order to eliminate image flicker, what frame rate is necessary in a real time imaging system
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> 15-20 frames per second
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What is the reciprocal of the pulse repetition frequency?
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Pulse Repetition Period
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The temporal resolution of a real-time scanner is dependent uponn which factor?
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Frame Rate
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What is the purpose of the scan converter?
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The scan converter is a device that stores imaging information in one scanning format and reads it out for display or archiving in another format, i.e. analog to digital.
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What is the purpose of changing the excitation time from one frame to the next (phase) in phased array transducers
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Allows for focusing and steering of the ultrasound pulse
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Lateral resolution will vary depending on: More than one answer may apply
A. Depth B. Beam diameter C. Transducer frequency D. focusing |
A,B,C,D (depth,beam diameter, frequency and focusing all affect lateral resolution).Lateral resolution is best where the sound beam is narrowest.
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An ultrasound transducer that has multiple concentric piezoelectric elements that are energized sequentially from the inside out allowing for circular symmetry of the beam is called:
A. Linear sequenced array B. Curvilinear Array C. Phased Array D. Annular phased Array |
D. Annular phased Array
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What function does the pulser of an ultrasound system have?
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Produces an electric voltage which:
1. Drives the transducer creating each individual pulse 2. Tells the display where the ultrasound pulses are produced |
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What is the pulse repetition frequency?
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PRF is the number of electrical pulses produced per second.
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List the imaging system components which determine the following ultrasound parameters:
1.Frequency 2. Speed 3. Attenuation 4. Lateral Resolution 5. PRF |
1. Transducer(crystal thickness)
2. Tissue (medium) 3. Transducer,tissue 4. Transducer, tissue 5. Sound source,pulser |
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List the factors which determine the ultrasound pulse amplitude and intensity:
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Both are determined by the sound source
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The loss of image contrast due to side lobe interference can be improved by apodization.
TRUE or FALSE |
True
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If the PRF is increased, what will happen to the duty factor?
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The duty factor will increase.
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List the five functions that the receiver performs:
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Amplification
Compression Compensation Rejection Demodulation |
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The ratio of output to input power is defined as:
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Gain
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What is the purpose of the amplification of the receiver?
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Increase small votages received from the transducer to larger ones suitable for processing.
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List three names which also describe compensation?
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Time Gain Compensation
Depth Gain Compensation Swept Gain Gain Compensation |
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What purpose does the compensation function have?
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Equalize differences in received reflection amplitudes due to reflector depth.
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List two terms which also describe rejection?
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Suppression and Threshold
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Demodulation converts the voltages delivered to the receiver from one form to another. This is done by what two processes?
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Smoothing and Rectification
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What is the purpose of the rejection function?
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Eliminates the smaller amplitude voltages produced by weaker reflections to eliminate noise
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Which three receiver functions are normally operator adjustable?
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Amplification,Compensation, Rejection
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What is the scan converter?
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A device which stores the ultrasound image information from the receiver in one format and converts it to another format to be displayed i.e)analog to digital
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What relationship does the following equations describe?
PRF= 77/Max Depth (cm) |
The relationship between PRF and the maximum imaging depth in soft tissue is inversly proportional. To image at greater depths the PRF must be lowered
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The maximum permissible PRF that will unambiguously image to a maximum depth of 20 cm is _____KHz
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3.85 KHz. This is determined by the formula:
PRF=77/max depth =77 divided by 20 = 3.85 KHz |
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What factor is the temporal resolution of a real time scanner depedent on
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Frame Rate
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List five factors which describe wave characteristics:
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Wavelength
Frequency Speed Period Amplitude |
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How is the propagation of sound in a medium related to the medium's stiffness and density?
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Speed is directly related to speed and inversly related to density. Stiffer the faster. Denser the slower
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What is the purpose of the depth gain compensation controls
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Compensate for attenuation of sound energy as distance from transducer to target increases
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what purpose does the gray scale display have
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Display a range of reflection amplitudes from white to black. Grayscale is important factor in contrast resolution
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What is a beam profiler
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A device designed to give three dimensional reflection amplitude information. It demonstrates beam characteristics including size (diameter) and intensity.
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If the frequency decreases, what will happen to the spatial pulse length?
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The spatial pulse length will increase or lengthen. Lower frequency have larger spatial pulse length.
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What type of transducer technology is utilized for creating variable focusing in two dimensions, is mechanically driven, but it is not capable of beam steering?
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Annular Array
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what is the Q factor?
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Q is the length of time that the sound persists. Low Q factor = short pulse length.
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What factor is the operating frequency dependent upon?
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Crystal thickness
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What type of scan converters are more commonly utilized today and Why?
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Digital scan converter. Digital scan converters overcome the inherent instability problems experienced with analog scan converters.
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The fraction of time that pulsed ultrasound is actually on describes what ultrasound factor?
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Duty Factor
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What is sensitivity?
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The ability of an imaging system to detect weak reflections
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What factor(s) is axial resolution primarily effected by?
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Spatial pulse length therefore the medium
Sound Source as frequency increases, spatial pulse length decreases, smaller dots are produced and axial resolution is improved |
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What is the duty factor of a CW doppler probe?
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1 (100% of the time)
A CW doppler transmit cystal is active 100% of the time |
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An annular array is a mechanical transducer
T or F |
True
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The focal zone is most correctly described as:
A. The region from the face of the transducer to the narrowest part of the beam B. The region where the sound beam is the narrowest. C. The region of the beam that is beyond the narrowest protion of the beam D. None of the Above |
B.
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How is a convex array (curvilinear array) transducer different from linear array and annular array transducers>
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1. Convex transducers are a hybrid of the linear and phased array. The convex have multiple elements with a curved face. A quasisector image is achieved with beam steering and can focus.
2. annular arrays are mechanical transducers with multiple elemnts pulsed from the inside out. The beam can be focused but not steered electronically. 3. Linear arrays have a rectangular image format and a large contact area. the beam can be focused and steered. |
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What is the range of PRF utilized in 2-D imaging?
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1-10 KHz
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Define bandwidth
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The difference between the highest and lowest frequency emitted by the transducer.
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How many piezolectric crystals does a CW Doppler transducer have?
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Two. One continuously transmits a signal and one continuously receives the signal.
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In order to travel or propagate sound requires a _____ to pass through
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Medium
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The spreading of the sound beamm as it moves farther from the sound source describes:
A. Scattering B. Interference C. Diffraction or divergence D. Reflection |
C.
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The number of cycles that an acoustic variable goes through in 1 second of time describes:
A. Frequency B. Period C. Wavelength D. Amplitude |
A.
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One megahertz=________Hz.
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1,000,000 Hz
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The time it takes one cycle to occur is called:
A. Frequency B. Period C. Wavelength D. Amplitude |
B.
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The length of space in which one cycle occurs is called:
A. Frequency B. Period C. Wavelength D. Amplitude |
C.
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The speed that a wave moves through a medium is called _________?
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Propagation Speed
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Using the formula frequency x wavelength will provide infromation regarding:
A. Amplitude B. Period C. Propagation Speed D. Duty Factor |
C.
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As frequency increases, the attenuation coefficient increasses.
True or False |
True
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If stiffness is increased, propagation speed will
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increase
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If the density of a medium is increased, propagation speed will:
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Decrease
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The number of pulses occurrring in a second describes:
A. PRF B. PRP C. Amplitude D. None of the above |
A.
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The time from the beginning of one pulse to the beginning of the next is called:
A. PRF B.PRP C. Amplitude D. Propagation Speed |
B.
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Sound scattering in all directions due to the reflector being much smaller than the pulse wavelength is referred to as:
A. Specular Reflector B. Backscatter C. Rayleigh Scattering D. All of the Above |
C.
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The damping material will increase the bandwidth of a transducer
True or False |
True
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Is the propagation speed for PW the same as CW in the same medium
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Yes
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Focusing the sound beam will increase the intensity of the sound beam
True or False |
True
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If the frequency of sound is increased, attenuation will ______?
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Increase
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As frequency increases, the depth of sound penetration will:
A. Increase B. Decrease C. Unaffected |
Decrease
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The more narrow the bandwidth, the more exact the frequency emitted by the transducer.
True or False |
True
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Longitudinal resolution is described as ________?
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Axial Resolution
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List three other terms synonymous with longitudinal resolution?
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Axial Resolution
Range Resolution Depth Resolution |
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If frequency is increased, the wave length will ______?
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decrease
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If frequency is increased, the depth of penetration will ________?
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decrease
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When performing an ultrasound exam of the abdomen on an obese person, which of the following transducer frequencies would be most helpful?
A. 10 MHz B. 5 MHz C. 3.5 MHz |
C
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Ultrasound transducers convert _____ energy into mechanical or ultrasound energy
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electrical
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The term piezoelectric means
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Pressure electric
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Describe the principle of piezoelectricity
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Transducer converts an electric signal into mechanical motion that results in ultrasound.
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List two factors that determine the operating frequency of the transducer
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speed of the material
Thickness of the element |
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CW transducers must have what two things in order to send and receive sound continuously.
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Source transducer element
Receiver transducer element |
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Transducers driven by voltage pulses are ________?
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PW transducers
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A PW transducer utilizess how many piezoelectric elements?
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One
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Describe the purpose of the damping material placed behind the transducer element.
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Reduce the number of cycles in each pulse, this improve axial resolution
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If pulse duration and spatial pulse length are reduced, what will happen to the axial resolution?
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It will improve
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What is the purpose of the matching layer on the face of the transducer
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Reduces reflection of the ultrasound at the element surface.
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Explain the purpose of the coupling agen used on a transducer
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Eliminate the layer of air between the transducer and body
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should a transducer be autoclaved before performing a procedure where a sterile invironment is necessary
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No-- the elements would be damaged
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List at least three things that determine beam diameter:
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Wavelength
Transducer diameter distance from transducer Lens (internal and external) Phasing |
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The area in which the sound beam diameter decreases as the distance from the transducer increases is called the _________?
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Near Zone
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The fresnel zone is another name for the _________?
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Near Zone
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The area of the sound beam where the beam diameter increases as the distance from the transucer increases is called the _________?
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Far zone
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Another name for the Far zone is _______?
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Fraunhofer Zone
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What does increasing frequency for a given transducer size (no change in diameter) do to the near zone length?
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Increases it
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What does increasing the frequency for a given transucer size do to the beam diameter?
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Decreases it
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The minimum reflector separation perpendicular to the sound path needed for separate reflections to be produced describes ________?
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Lateral resolution
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How is lateral resolution related to beam diameter?
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Lateral resolution is equal to beam diameter
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List three other names synonymous with lateral resolution
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Transverse resolution
Angular resolution Azimuthal resolution |
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If beam diameter is reduced, what will happen to the lateral resolution?
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It will improve
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To reduce beam diameter, what can be done to the sound
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It can be focused by curving the transducer element (internal), applying a fixed lens to the transducer assembly (external) or by employing electronically phased arrays.
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If the beam diameter is decreased and lateral resolution is increased, what will happen to the depth of penetration
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It will decrease
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What effect does curving the element of the transducer have on the sound beam
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One method of focusing the sound beam
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a transducer utilizing rectangular rows of elements that are pulsed at small time intervals refers to what type of transducer
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Linear Phased Array
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What effect will increasing the line density have on the following imaging characteristics
1. Image quality 2. PRF 3. Maximum imaging depth 4. Frame Rate |
Increaed line density will result in.
1. Improved image quality 2. Lower PRF 4. Lower Depth 5. Lower Frame Rate |
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The velocity of a sound wave is equal to ________ x _________
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Frequency, Wavelength
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If the frequency of sound in the body is doubled, what will happen to the velocity
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Remains the same
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the resonant frequency of a transducer is determined by the ______ and ________
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speed and thickness or the crystal
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Frequency of a sound wave is measured in ________
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Hertz
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Is an annular array beam mechanically steered?
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Yes
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Axial resolution directly depends upon ________?
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Spatial Pulse Length
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The Q-factor of the transducer is _______?
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Equal to the ratio of the operating frequency to the frequency bandwidth.
Low Q-factor=improved image quality |
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If the frequency is decreased wavelength will_______
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increase
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In the average pulsed ultrasound system the duty factor is always less than ______?
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one
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A low tranducer Q-factor will result in what kind of bandwidth
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Wide bandwidth
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Increasing the transducer frequency will have what effect on axial and lateral resolution
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It will improve both
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If the sector angle is doubled from 45 degrees to 90 degrees, how is the image quality, field of view, line density, PRF, frame rate and maximum depth affected?
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If sector angle is doubled, the following will occur
1. Image quality will be degraded 2. Field of view will increase 3. PRF and depth will be unchanged 4. Line density is unchanged, frame rate will lower 5. If line density is halve, frame rate will remain the same |
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the critical angle refers to
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The angle at which total reflection occurs
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If the frame rate is increased,how will it affect the following imaging characteristics?
1. Image Quality 2. Line Density 3. Maximum depth of penetration 4. PRF |
Increaing frame rate will:
1. Temporal resolution will increases but detail may decrease 2. The line density may limit the increase in frame rate or it (line density) will decrease 3. The maximum depth of imaging will be reduce if line density remain constant 4. PRF will increase |
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What percent of time is a pulsed ultrasound system capable of receiving sound
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> 99.0% of the time
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what is the wavelength of 1 MHz ultrasound in soft tissue
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1.54 mm
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What is the disadvantage of mechanical transducers in color flow imaging
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Increased color artifacts introduced by the moving elements. Blood which moves slower than the speed of the moving crystal will not be detected
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List at least two piezoelectric materials that are used in transducer cystals
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Ceramics
Lead zirconate titanate PZT Quartz Polymers polyvinylidene fluoride |
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As the number of focal zones increases, the frame rate will _______
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decrease
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There are two methods to achieve mechanical focusing of the ultrasound beam, internally and externally
True or False |
True
Internal refers to curving the elements to focus the beam External refers to putting a lens in front of the element to focus |
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One advantage of Annular Array transducers is dynamic aperture
True or False |
True
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which of the following is NOT a true statement regarding tissue Harmonic imaging?
A. Lower frequencies are sent and higher frequencies are received back B. The harmonic frequency is a multiple of the fundamental frequency C. Harmonic imaging improves the signal to noise ratio D. Harmonic imaging improves penetration |
D
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Harmonics should be used at all times to improve image quality
True or False |
False
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Give two ways that the ultrasound system components change to process the harmonic signal
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The receiver is set to listen at a higher frequency, a multiple of 2x or 3x that of the fundamental frequency
The receiver sets in a delay to listen not to the reflected signal but to a slightly later harmonic echo |
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Multi-dimensional arrays are smaller and less expensive to manufacture
True or False |
False
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How does a multi-dimensional transducer differ from a conventional phased or linear array transducer
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The footprint of the scan area is much larger, especially thicker which allows the transducer to obtain a volume of tissue sets of information rather than just a tomographic slice of information. It is most useful for rendering 3-D information
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List three ways for a system to obtain 3-D imaging from the transducer
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1. Multi-dimensional arrays for obtaining a volume of data sets of information
2. Articulating transducers or by using a potentiometer on the probe to register its orientation and location to the anatomy being scanned 3. Free Hand scanning which requires a steady sweep of the transducer to acquire a volume of data sets which has to be reconstructed into a 3-D image |
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Define apodization and tell what it is used for
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apodization of a transducer is useful to reduce or eliminate side-lobe artifacts
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If two transducers are the same frequency but one is larger in diameter than the other, which one would have the longer focal length.
A. The larger diameter probe B. The smaller diameter probe C. They would be the same D. Don't Know |
A
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What are the units for attenuation
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dB (decibels)
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What are the units for intensity
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W/cm squared.
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What term best describes the magnitude of a signal
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Amplitude
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List five factors which affect the acoustic impedance of a medium
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Compressibility
Velocity Temperature Stiffness Density |
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What two factors musst be known in order to calculate distance to a reflector
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Travel time
Speed |
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Describe acousic enhancement
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Strong echoes received from structures beyond or posterior to a weakly attenuating region that make the area more echogenic/brighter than the surrounding area.
This artifact may be helpful in differentiating some pathology |
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A unit less ratio that describes the distribution of the sound beam in space is called
A. Duty factor B. Beam uniformity coeffiecient C. Pulse duration D. Intensity transmission coefficient |
B
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No independently confirmed significant biological effects in mammalian tissue has been reported below what intensity
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100 mw/cm squared SPTA
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What term is used to describe a phenomenon produced by sound waves in a liquid or liquid like media which involves the expansion and compression of bubbles or cavities containing gas or vapors
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cavitation
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List four factors which are considered to contribute to the biological effects from diagnostic ultrasound
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Intracellular movement
Cavitation Shearing action Thermal effects |
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Video tapes are light sensitive
True or False |
False
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What is the upper limits of attenuated SPTA output intensities for CW Doppler instruments
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500 mw/cm squared
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The more bits per pixel, the more shades of gray can be assigned
True or False |
True
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A reduction in reflection amplitude from reflectors that lie behind a strongly reflecting or attenuating structure describes what type of artifact
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Shadowing
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What is refraction
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An artifact which occurs when the sound wave changes direction when traveling from one media to another. This results with the reflector being improperly positioned on the display
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What is the missing reflector artifact
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When two reflectors are seen as one resolution
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What is the cause of a multi-path artifact
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Multi-path artifacts are seen as a decrease in longitudinal resolution and overall degradation of image quality. It occurs when the path lengths of the pulse travels to and from a structure or reflector are of different lengths.
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List three factors which effect attenuation.
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Depth
Scattering Absorption |
