Which real-time instrument measures the displacement of tissue when a force is applied?
If the transmitted frequency is 2 MHz, what is the frequency of the second harmonic?
Which device applies dynamic receive focusing?
recive beam former
Which operator control adjusts the transmitted peak intensity?
Which operator control can improve the visualization of weak reflectors, yet increases patient exposure?
Which operator control eliminates low-amplitude noise from the B-mode image?
Which B-mode operator control allows multiple sequential frames to be added together for display in real-time?
What does activation of the cine function accomplish?
review of sequence of acquired images
How is averaging effect enhanced in spatial compounding?
additional beam angles
What are 2 advantages of the frequency compounding in B-mode imaging?
1. emphasize penetration, resolution, or tissue texture
2. acoustic noise reduction to improve contrast resolution
What is the image processing technique that translates pixel values to brightness levels in the displayed image?
gray scale map
At which processing stage does dynamic receive focusing take place?
receive beam formation
What signal processing technique eliminates low signal levels and redistributes the remaining signal levels throughout the gray scale prior to display?
What is the purpose of bilinear interpolation?
to interpolate (insert; introduce) the scan data a long the axial and angular directions
Which zoom adjustment can improve the spatial resolution in B-mode imaging?
What is a disadvantage of write zoom?
field of view is limited
Which operator control alters image contrast? (2)
1. frequency compounding
2. dynamic range
What is the purpose of reject control?
removes weak signals and noise
What is the purpose of persistence?
increase signal to noise ratio
What is clutter?
"false" echo signals originating outside the main beam caused by side lobes, grating lobes, and scattering
What is speckle?
the bright and dark variations in the image, from scattering of multiple small, non-specular reflectors
What is contrast resolution?
the ability to resolve two objects with similar reflective properties as separate entities
What is geometric distoration?
deviation from true spatial relationships corresponding to anatomic structures
What is temporal resolution?
the ability to depict the movement of structures accurately
Which B-mode imaging technique suppresses speckle?
Which adjstment would improve temporal resolution in B-mode imaging?
decrease number of transmit focal zones
What are the 8 assumptions the machine makes
1. transmitted wave travels in straight line path
2. attenuation is uniform along the path
3. beam dimensions are small
4. all echoes originate from axis of main beam only
5. all received echoes come from most recent transmitted pulse
6. ultrasound wave travels through body at 1540 m/s
7. each reflector contributes a single echo
8. every signal is derived from a single object and is related to its reflective properties
Another term for elevational resolution is?
What effect can the slice thickness artifact have on an image?
fills in hollow structures
What are the three types of refraction artifacts?
1. misregistration refraction
2. defocusing refraction
3. ghost image
The artifact that occurs due to vibrations of gas bubbles being insonated by ultrasound is called?
When specular reflectors are isonated at oblique angles, resulting in incorrect axial placement of an interface, it is called?
multiple path reflections (artifact)
Velocity error occurs when?
the actual acoustic velocity in the medium deviates from the calibrated velocity and the measured elapsed time is not accurately converted to depth
What artifact occurs when sound reflects off a strong reflector and part of the sound energy is redirected toward the same structure, resulting in a duplicated display of the structure placed deeper in the image?
What are two beneficial artifacts?
Bending of the sound beam after striking a curved reflector, causing edge shadowing, is called?
What is the doppler effect?
phenomenon in which an apparent change from the transmitted frequency is relative motion between the source of sound and the receiver
What is observed for a reflector moving at constant velocity with a dopler angle of 90 degrees?
echo frequency is the same as transmit fequency
What is the sign indicator of the doppler shift frequency if a reflector approaches the transducer at constant velocity?
Which parameters are included in the equation for doppler shift frequency?
1. velocity of sound in medium
2. angle betwen directions of movement and beam
3. transmitted frequency
4. velocity of interface / reflector
What is a feature of continuous wave doppler?
no upper velocity limit for moving reflectors
What is the purpose of the wall filter?
to eliminate low frequency doppler shifts from moving anatomy rather than from moving blood cells
Which signal processing technique enables the direction of motion in pulsed wave spectral doppler?
What is the artifactual display of a high-frequency doppler shift at a frequency lower than the true value?
What is a feature of duplex scanning using B-mode and spectral doppler?