Phycis And Instrumentation Flashcards
What is the most important physical parameter influencing absorption of the sound beam
Frequency
Absorption of energy from attenuation of the ultrasound beam as it travels through tissues is highest in
Bone
Function that equalizes the ultrasound signals received from various depths and displays them with equal reflections
Time gain compensation
TGC
What function controls the number of ultrasound pulses transmitted per second and is dependent on depth of penetration and sample volume
PRF
Why is it important to choose the correct sample volume size
Small sample volume prevents interference from the blood flow in nearby vessels
A sample volume too small will not allow parts to flow
Sample volume should be adapted to fit the diameter of the vessel being interrogated
In order to obtain the most precise image the area of interest should be focused in what part of the sound beam
Near field
What phenomenas associated with the passage of the ultrasound beam through body tissues are classified as bioeffects
Thermal and mechanical effects
The rise in temp in tissues under the influence of ultrasound energy is controlled by the power level settings on the us machine. What is considered an INSIGNIFICANT rise in temp ?
< 2.0 degree Celsius
Best description of Alara principle
Keeping both output power and exposure time as low as reasonably achievable
Where does maximum tissue heating occur during the ultrasound
Between the transducer surface and focal zone
Optimal transducer frequency for a fetal echo
5-7 mhz
The transducer emits a sound beam across the field of view. What term describes the location where the sound beam reaches its narrowest diameter
Focal zone
What adjustments will eliminate aliasing
Changing the angle of insonation
Shifting the baseline
Lowering the frequency
Increasing the PRF
Shadowing occurs when the object of interrogation has a high level of
Attenuation
What artifact caused by two strong reflectors with a large surface area is displayed in the near field and has multiple equally spaced echoes that extend into the far field
Reverberation artifact
What can you do to eliminate shadowing in a image
Decrease the frequency
Adjust the angle of insonation to avoid scanning through fetal ribs
Adjust frame rate
Adjust rejection
Which type of artifact is produced by interference patterns and results in the granular appearance of the image
Speckle
What function is used to eliminate low frequency noise and artifacttual clutter caused by the movement Of the vessel walls
Wall filter
What is the term for a frequency shift that exceeds the Nyquist limit during pulsed wave or color Doppler imaging
Aliasing
Color Doppler imaging gives info on
Blood flow velocity
Blood flow direction
Frequent shift
Blood flow disturbances
In order to Visualize flow in vessels with low flow states such as the pulmonary veins what adjustment should the sonographer make
Decrease the PRF
What are the benefits of power Doppler when compared to color Doppler
Power Doppler is less dependent on the angle of insonation
Power Doppler is not subjective to aliasing
Power Doppler less dependent of direction is blood flow
Power Doppler is useful in slow flow velocity states
In a Doppler wave form across the mitral valve the A wave represents
Atrial systole
Normal patent foreman ovale flow is
Biphasic 20-40 cm/sec
Pulsatile flow in the umbilical vein seen with Doppler most likely represents
Congestive heart failure and volume overload
If a fetus has a cardiac defect with reduced cardiac inflow the DV waveform will be abnormal the abnormal waveform will have
Reduced A wave toward the baseline reversed flow of the A wave during atrial contraction
Which modality of ultrasound transmits the GREATEST amount of energy into the fetus
Pulsed Wave Doppler
A peak systolic velocity in the ductus arteriosus that exceeds ——— cm per second has been reported in cases of ductal constriction
> 140
Increasing PRF decreases
Aliasing
As depth increases the PRF
Decreases
Increasing the the PRF will ______ the number of pulses transmitted per second eliminating the noise and scatter of the ultrasound frequencies
Decrease
