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Sonography Physics

Chapter 8: Axial Resolution

QuestionAnswer
What is resolution? The ability to image accurately
What is Axial Resolution? The ability of a system to display two structures that are close together
With axial resolution, where do the structures lie in relation to the sound beam's main axis? The structures lie parallel to the sound beam's main axis one in front of the other
What are the units for axial resolution? mm, any unit of distance
Axial resolution is determined by what? Spatial Pulse Length; medium and sound
What is the relationship between axial resolution and spatial pulse length? Shorter pules: better axial resolution
What is the mnemonic for the synonyms of axial resolution and what does it stand for. LARRD: longitudinal, axial, range, radial, depth
Can axial resolution be adjusted by the tech? Why or why not? no; because SPL is set by the TD
What are the typical values of axial resolution? 0.1-1.0mm
What type of numeric value improves image accuracy for axial resolution? Low numeric value
For best axial resolution, the pulse duration (PD) and SPL should by what? short
What are the equations for SPL? SPL = wavelength x # of cycles or SPL = propagation speed/frequency x # of cyles
What is the equation for axial resolution? axial resolution(mm)=SPL(mm)/2 or axial resolution(mm)=wavelength(mm)x #of cycles in pulse / 2
What is the equation for axial resolution in soft tissue? axial resolution(mm)=0.77x #cycles in pulse / frequency (MHz)
What two things create shorter pulses that improve axial resolution? Less ringing (dampen the crystal), higher frequency
When a crystal is dampened, how many cycles are in a pulse? 2-3 cycles
How does a higher frequency improve axial resolution? higher frequencies = shorter wavelength (with set medium)= shorter pulse
According to Kremkau, what is axial resolution and how does it run? It is the ability to produce 2 distinct structures and it runs "along scan line"
What is the useful frequency range for ultrasound? 2-15 MHz range
What happens when the frequency is less than 2MHz or more than 15MHz? less than 2MHz = not acceptable axial resolution more than 15MHz = not enough penetration depth
What are the two types of detail resolution? axial and lateral resolution
Created by: quietone055 on 2010-03-29



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