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SPI Chapter 10

Axial and Lateral Resolution

QuestionAnswer
What is resolution? the ability to create accurate image
What is axial resolution? deals with structures that are parallel to the sound beam and details found in an image
What are the units of axial resolution? mm or any unit of distance
What is axial resolution related to? spatial pulse length and pulse duration
What is spatial pulse length determined by? both sound and the medium
What does shorter pulses improve? axial resolution
What are synonyms for axial resolution? longitudinal, range, radial, or depth resolution
Is axial resolution adjustable by the sonographer? No
What are the typical values for axial resolution? 0.1 to 1.0 mm
What is the formula of axial resolution? axial resolution (mm) = spatial pulse length (mm)/2 or axial resolution (mm) = wavelength (mm) x #cycles in pulse/2
What is the formula resolution in soft tissue? axial resolution (mm) = 0.77 x #cycles in pulse/frequency (MHz)
What is axial resolution determined by? pulse length
What 2 ways is a short pulse created? less ringing and higher frequency
What is less ringing? a pulse is short if there are few cycles in the pulse
What is lateral resolution? identify two structures that are very close, they are side by side or perpendicular
What are the units of of lateral resolution? mm, cm, or any unit of distance
What is lateral resolution determined by? width of the sound beam
What are synonyms of lateral resolution? angular, transverse, or azimuthal resolution
Which zone is lateral resolution good with? focal zone
What does lateral resolution equal? beam diameter (mm)
In clinical situation, why is axial resolution is better than lateral resolution? because ultrasound pulses are shorter than they are wide
Between axial and lateral resolution, which numerical value should be less? axial resolution
What does axial resolution improve? the entire image because shorter pulses are associated with high frequency
What does lateral resolution improve? the far field only because high frequency pulses diverge less in the far field than low frequency pulses
What is focusing? concentrates the sound energy into a narrower beam and improves lateral resolution
What is the 3 methods of focusing? external, internal, and phased array focusing
What is external focusing? with a lens
What is internal focusing? with a curved active element
What is phased array focusing? with the electronics of the ultrasound system
What is fixed focusing? conventional or mechanical focusing, includes both external and internal techniques.
What does phased phases array mean? adjustable or multiple focusing
What is frequency-continuous wave determined by? frequency of electrical signal from ultrasound system
What is frequency-pulsed wave determined by? thickness of ceramic and speed of sound in ceramic
What is focal length and beam divergence determined by? diameter of ceramic and frequency of sound
What is lateral resolution determined? beam width
Created by: Lazacha
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