Ch. 16
As a general rule, the dynamic range of information (blank), the more it is processed
decreases
Sound with a frequency of 4MHz is created by a transducer. What is the fundamental frequency?
4MHz
The arterial pressure generated by the heart in a patient who is standing upright is 140mmHg. What is the arterial pressure measured in the toe of the upright patient?
240mmHg
What technique is used to perform spectral analysis on color doppler data?
Autocorrelation
What does the wall filter eliminate?
Low velocity flow
Mirror images artifacts always appear … than the true anatomy
Deeper
What are the 3 devices that perform quality assurance?
Tissue equivalent phantom, doppler phantom, and beam profile/slice thickness phantom
When can a patient revoke consent?
Any time
What component of the ultrasound system is most likely to expose a patient to danger?
Transducer
What are the 3 rules when it comes to the signals of compression of dynamic range?
1. The largest signal remains the largest.
2. The smallest signal remains the smallest.
3. The range of signals is reduced.
What nonlinear behavior creates tissue harmonics?
Sound travels faster in compressions and slower in rarefactions
What happens to venous flow in the legs during inspiration?
Downward movement of diaphragm=decreases
Colors above the doppler shift means that blood cells are….
Moving towards the transducer
What is the term for when color is set too high and appears throughout the color box?
Color confetti
What are the two ways of reducing lobe artifacts?
Subdicing and apodization
What standard is best used in a quality assurance program?
Objective
If a patient arrives in your room sedated and without a wristband confirming who they are, what do you do?
Call the nurse
What are the two forms of cavitation?
Stable and Transient
An uncompressed signal has a dynamic range of 85 dB. The signal undergoes 30 dB of compression. What is the dynamic range of the compressed signal?
55dB.
What nonlinear behavior creates contrast harmonics?
Microbubbles expand to a greater extent than they compress
During expiration, venous flow to the legs?
Diaphragm moves upward=increases
What doppler has NO aliasing?
CW Doppler
T/F Color will appear in a vessel when the direction of flow and sound are perpendicular
FALSE
Lobe artifact degrades
Lateral resolution
What form of resolution is evaluated by visualizing closely spaced pins that are parallel to the sound beam’s main axis?
Axial resolution
What term provides the basis for informed consent?
Autonomy
The …. to the patient outweighs the …
benefits, risks
Means fewer shades of gray
Narrow dynamic range (high contrast)
What is associated with the highest MI?
Low frequency, extreme peak rarefactional pressure
When venous flow to the legs decrease, venous return to the heart?
Increases
Color doppler reports …. velocities
average or mean
What direction do you steer the color box?
Parallel to the vessel
What assumption does shadowing violate?
The strength of the reflection is related to the characteristics of the tissue creating the reflection
If I want to evaluate my transducer to ensure it is imaging the grayscale properly, what phantom would I use?
Tissue equivalent phantom
What is associated with the lowest tissue temperature elevation?
Gray scale imaging
An alternative description of dynamic range is?
Number of choices
Higher MI’s are associated with what?
Bubble disruption
Arterial blood pressure measured in a supine patient’s arm is 140 mmHg. What is the hydrostatic pressure at all locations within the arterial circulation?
0 mmHg
When you adjust your scale, what are you actually doing?
Increasing the Nyquist limit
What assumption does comet tail violate?
Sound travels directly to the reflector and back
Define the dead zone
Region closest to the transducer where images are inaccurate
In vitro research is performed …
Outside the living body/artificial environment
Shallow gate (High PRF) results in … aliasing
Less
5 ways to avoid aliasing:
Adjust scale to max, new window (shallower sample gate), low frequency transducer, baseline shift, and CW doppler
At what angle between the sound beam and the direction of motion will the doppler shift be the highest?
0 or 180 degrees