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Sonography Physics
Chapter 8: Axial Resolution
| Question | Answer |
|---|---|
| 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
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