DMS 216 FINAL EXAM QUESTIONS
AND ANSWERS | ALREADY
PASSED
What are the differences between CW and PW Doppler - Answer- CW: requires 2
crystals in the transducer. One crystal constantly transmits while the second crystal
continuously receives
PW: Only one crystal that alternates between transmitting and receiving
What is a liquid crystal - Answer- Certain ones change color based on their
temperature. When a sound beam strikes the crystals the sound energy is absorbed.
The change in crystal temperature causes a change in their color providing insight into
the shape and strength of the sound beam
What are the differences between the mechanistic and empirical approach - Answer-
The mechanistic approach searches for a relationship between cause and effect
The empirical approach searches for a relationship between exposure and response
*strongest conclusions are made when there is an agreement
What are the advantages of CW and PW Doppler - Answer- Advantages of CW: The
greatest advantage is its ability to accurately measure very high velocities
Advantages of PW: Being able to select the exact location where velocities are
measured called range resolution, range specificity, or freedom from range ambiguity
artifact
What factors and system settings affect frame rate - Answer- Factors affecting FR:
speed of sound in the medium
Imaging depth
System settings that affect FR: imaging depth
Number of pulses per frame
How does imaging depth affect temporal resolution - Answer- Fig 13.1- Shallow
imaging: Short go-return time Shorter T frame
Higher FR
Superior temporal resolution
Deep imaging: Long go-return time
Longer T frame
Lower FR
, Inferior temporal resolution
What are the disadvantages of CW and PW Doppler - Answer- Disadvantages of CW:
Primary disadvantage is that the exact location of the moving blood cells can't be
determined. Signals arise from all blood cells in the region of overlap between the
transmit and receive beams. This limitation is called range ambiguity. Another
disadvantage is its lack of TGCs
Disadvantages of PW: Primary disadvantage is inaccurate measurement of high
velocities. High velocity flow in one direction is inaccurately displayed as traveling the
opposite direction. This inaccuracy is called aliasing
Fundamental Frequency - Answer- The frequency of sound created by the transducer
and transmitted into the body
Harmonic frequency - Answer- Twice the fundamental frequency (also called second
harmonic frequency)
Linear behavior - Answer- Linear means proportional or symmetrical. Linear systems
respond in an even manner. Ex: an elevator takes 10 seconds to travel to each hospital
floor so it is linear bc it is even
Nonlinear behavior - Answer- Nonlinear means irregular or disproportionate. A system
is nonlinear when it behaves unevenly. Ex: different times between each hospital floor.
*harmonic frequency sound arises from nonlinear behavior
What is mechanical index - Answer- The amount of contrast harmonics produced may
be estimated by a number called the mechanical index (MI) The MI depends on the
frequency of the transmitted sound and the rarefraction pressure of the sound wave.
Mechanical index as it relates to power and frequency - Answer- Lower MI: small
pressure variation and higher frequency
Higher MI: large pressure variation and lower frequency
Electrical and overall safety considerations (pg 417) - Answer- Electrical safety: the
greatest risk comes from electrical shock from a cracked transducer housing
Overall safety considerations: Only perform studies with valid medical justification
Do not prolong studies without valid medical justification. Minimize exposure time while
performing a complete diagnostic exam. Exam time is the primary determinant of patient
exposure
Use minimum output power and maximum amplification to optimize image quality.
ALARA
In summary be: prudent, careful, judicious
Hemodynamics - Answer- Hemodynamics is the study of blood moving through the
circulatory system.
AND ANSWERS | ALREADY
PASSED
What are the differences between CW and PW Doppler - Answer- CW: requires 2
crystals in the transducer. One crystal constantly transmits while the second crystal
continuously receives
PW: Only one crystal that alternates between transmitting and receiving
What is a liquid crystal - Answer- Certain ones change color based on their
temperature. When a sound beam strikes the crystals the sound energy is absorbed.
The change in crystal temperature causes a change in their color providing insight into
the shape and strength of the sound beam
What are the differences between the mechanistic and empirical approach - Answer-
The mechanistic approach searches for a relationship between cause and effect
The empirical approach searches for a relationship between exposure and response
*strongest conclusions are made when there is an agreement
What are the advantages of CW and PW Doppler - Answer- Advantages of CW: The
greatest advantage is its ability to accurately measure very high velocities
Advantages of PW: Being able to select the exact location where velocities are
measured called range resolution, range specificity, or freedom from range ambiguity
artifact
What factors and system settings affect frame rate - Answer- Factors affecting FR:
speed of sound in the medium
Imaging depth
System settings that affect FR: imaging depth
Number of pulses per frame
How does imaging depth affect temporal resolution - Answer- Fig 13.1- Shallow
imaging: Short go-return time Shorter T frame
Higher FR
Superior temporal resolution
Deep imaging: Long go-return time
Longer T frame
Lower FR
, Inferior temporal resolution
What are the disadvantages of CW and PW Doppler - Answer- Disadvantages of CW:
Primary disadvantage is that the exact location of the moving blood cells can't be
determined. Signals arise from all blood cells in the region of overlap between the
transmit and receive beams. This limitation is called range ambiguity. Another
disadvantage is its lack of TGCs
Disadvantages of PW: Primary disadvantage is inaccurate measurement of high
velocities. High velocity flow in one direction is inaccurately displayed as traveling the
opposite direction. This inaccuracy is called aliasing
Fundamental Frequency - Answer- The frequency of sound created by the transducer
and transmitted into the body
Harmonic frequency - Answer- Twice the fundamental frequency (also called second
harmonic frequency)
Linear behavior - Answer- Linear means proportional or symmetrical. Linear systems
respond in an even manner. Ex: an elevator takes 10 seconds to travel to each hospital
floor so it is linear bc it is even
Nonlinear behavior - Answer- Nonlinear means irregular or disproportionate. A system
is nonlinear when it behaves unevenly. Ex: different times between each hospital floor.
*harmonic frequency sound arises from nonlinear behavior
What is mechanical index - Answer- The amount of contrast harmonics produced may
be estimated by a number called the mechanical index (MI) The MI depends on the
frequency of the transmitted sound and the rarefraction pressure of the sound wave.
Mechanical index as it relates to power and frequency - Answer- Lower MI: small
pressure variation and higher frequency
Higher MI: large pressure variation and lower frequency
Electrical and overall safety considerations (pg 417) - Answer- Electrical safety: the
greatest risk comes from electrical shock from a cracked transducer housing
Overall safety considerations: Only perform studies with valid medical justification
Do not prolong studies without valid medical justification. Minimize exposure time while
performing a complete diagnostic exam. Exam time is the primary determinant of patient
exposure
Use minimum output power and maximum amplification to optimize image quality.
ALARA
In summary be: prudent, careful, judicious
Hemodynamics - Answer- Hemodynamics is the study of blood moving through the
circulatory system.
