Study guide test 3
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Study guide test 3
What adjusts the intensity of the ultrasound beam transmitted into the patient?
How does power control effect images?
Improves signal-to-noise ratio and enhances sensitivity
What reduces the signal-to-noise ratio and degrades sensitivity?
A loss of signal coherence during beam formation is called?
What is it when echo frequency is subdivided into frequency bands by filters, processed, then recombined?
What is the purpose of frequency compounding?
To emphasize penetration, resolution, or tissue texture (To improve contrast resolution)
What aquires multiple beam angles and averages the data, reduces acoustic noise while improving border definition of speculations reflectors
What improves the depiction of tissue boundaries and reduces noise variations?
What effect does compression have on an image?
Changes the grayscale mapping
What increases amplitude of low signals and decreases amplitudes of high signals so that all echo-induced signals are represented in the scan converter?
What improves image contrast but usually with a loss of weaker echoes?
Low dynamic range
What reduces image contrast but retains a broader extent of signal levels?
High dynamic range
What scanning technique creates a visual display of information that would be obtained by manual palpation?
What detects the relative tissue displacement between precompression (no stress) and compression (stress) measured by ultrasound?
What does it mean if strain is proportional to stress?
the material exhibits elastic behavior
As the sound wave propagates through the medium, ________ components intesify , and the waveform becomes more distorted.
What are present in the central portion of the transmitted beam but offset from the transducer face?
What are created as a result of propagation through tissue and are not produced upon reflection?
What is applied to remove the fundamental echo signal, and only the tissue harmonic component is processed for image formation?
harmonic band filter
What employs long waveforms during transmission to improve the signal-to-noise ratio and/or penetration?
What are two common methods to encode transmitted waveform?
1. frequency modulation
2. binary encoding
What eliminates low-level signals and noise below a certain level when selected by the operator?
Rejection of signals decreases what?
What removes weak signals and noise?
How does rejection remove weak signals and noise?
by passing only signals greater than a prescribed signal level
What can be applied to enhance spatial detail?
What are negative properties of persistence?
1. fast-moving objects become blurred with increased persistence
2. poor temporal resolution
What are positive properties of persistence?
1. allow high-quality abdominal scans to be ontained
2. reduces noise
The translation of the range of pixel values to brightness levels is called?
What is selected by the operator and can alter the presentation of the displayed image?
What does user-controlled compression modify?
What is a scan conversion method to assign echo amplitude to a pixel, which is not interrogated by a scan line?
Where is bilinear interpolation performed?
in axial and angular directions
What are the two types of acoustic noise?
What are "false" echo signals originating outside the main beam caused by side lobes, grating lobes, and scattering?
What are the bright and dark variations in the image from scattering of multiple small non-specular reflectors?
What is determined primarily by the spatial pulse length, which depends on the center frequency and the bandwidth of the transducer?
What defines the finite size of the detection sampling volume along the axial direction?
Spatial pulse length
What is the best axial resolution considered to be?
Half the spatial pulse length
What is determined primarily by the beam width and the scan-line density?
What depends on beam width and changes with depth?
What is contrast?
The difference in brightness levels
What has high signal levels and are readily seen?
What two components make up image contrast?
1. intrinsic (detection) contrast
2. displayed contrast
What do time gain compensation and dynamic range affect?
Displayed contrast translates pixel values to brightness levels on the monitor via what?
What describes the ability of a series of several frames aquired sequentially in time to depict the movement of structures?
What does decreasing scan range, scan-line density, persistence, or sector angle improve?
An increase in frame rate is usually accompanied by what?
Reduction in scan-line density
Frame rate, scan-line density, and scan range are all ____________
What does the inaccurate presentation of spatial relationships cause?
What can an improperly calibrated PACS interface or image recording device introduce?
What is the assignment of an intermediate signal level when the ultrasonic beam encompasses objects with different reflectivities?
Frequency and spatial compounding enhances signals from tissue features while ___________ ______
What is partially canceled when multiple images are added together?
What artifact can occur in-plane direction (lateral) or out-of-plane direction (slice thickness)?
High receiver gain or TGC increases the visibilty of what artifact?
What is another name for elevation plane?
What artifact can sample multiple tissues at once and blend the reflectors together?
Where is partial volume artifact typically seen?
Beyond the mechanical focal zone
What artifacts area is distal to low attenuation structure and has more intensity of reflections than surrounding tissue?
What artifact area is distal to high attenuation structure and has less intensity of reflections than surrounding tisue?
What artifact is seen in an area of fixed transmit focus where there is a greater intensity in the focal zone?
What causes banding artifact to be seen?
improper TGC setting
What artifact has multiple evenly spaced echoes, decreasing in intensity?
What artifact has a "ladder appearance" when sound bounces between two strong reflectors?
The mscle interface near the skin surface is often the source of what artifact?
What artifact is made up of small, highly reflective objects?
What artifact looks similar to reverberation, but more closely spaced together?
What artifact typically arises from the near wall or lumen of the gallbladder when crystaline deposits of cholrsterol are present?