78. ULTRASOUNDS: RESOLUTION Flashcards
- What does the Spatial Resolution of an Ultrasound device determine?
- it determines the ability to separate two adjacent
objects - it allows us to differentiate between 2 objects that are
very close together
- What 3 planes do we consider Spatial Resolution in?
- Depth (Axial) Resolution
- Lateral Resolution
- Elevation Resolution
- this is the height of the slice
- What do these Test images of phantoms show?
- they show circular regions
- they are echo free
- they mimic the presence of cysts of varying sizes
- What are the diameters of these circular, echo free regions?
- 10 mm
- 8 mm
-6 mm
-4 mm
-3 mm
-2 mm
- What is the relation between the holes and the frequency?
LOW FREQUENCY TRANSDUCERS
- have more echo free holes
- they also have a larger focal length
HIGH FREQUENCY TRANSDUCERS
- have less echo free holes
- they also have a shorter focal length
- they also have a better resolution
- we can define the echo free regions better
- What 2 concerns must be balanced when we set the frequency for Ultrasound imaging?
- The depth to which the image will be formed
- The Spatial resolution of the image
- What do we use lower frequency waves to image?
- they image deep within the abdomen
- this is because they have longer wavelengths
- What do we use higher frequency waves to image?
- they image finer details that can be resolved
- the parts of the body they image are close to the
surface - this is because they have shorter wavelengths
- What other body part can higher frequency waves image?
- they can be used for Breast ultrasounds
- these are about 7.5-10 MHz
THIS IS BECAUSE:
- much shallower regions of the body must be imaged
in the latter procedure
- What other advantage do high frequency sound waves bring about?
- they have a higher spatial resolution
- this helps with introducing the transducer into the
body near the tissues to be imaged
- What does Axial Resolution determine?
- it determines the ability to separate two objects that
are lying along the axis of the beam
- What does Axial Resolution tell us about?
- it tells us about the minimum distance that two
structures can be away from each other - while still producing two distinct echos on an image
THESE STRUCTURES:
- are positioned front to back
- What is Axial Resolution determined by?
- it is determined by the pulse length
- it is measured in mm
- What is the Pulse Length?
- this is the wavelength
MULTIPLIED BY - the number of cycles in the pulse
- What do lower numerical values of the Axial Resolution indicate?
- they indicate a shorter pulse
- What kind of images do shorter pulses create?
- they create more accurate images
- What kind of Axial Resolution results in a better image quality?
- Axial Resolutions that have a lower numerical value
- How do we mathematically describe Axial Resolution?
- How do we calculate Pulse Length?
- What are some characteristics Higher Frequency?
- they have a lower axial resolution
- What relation do wavelength and frequency have to one another?
- they are inversely proportional
- What relation do the number of cycles in a pulse and the frequency have to one another?
- they are inversely proportional
- What echo and interface distances produce a better Axial Resolution?
THERE WILL BE A BETTER RESOLUTION:
- when there is a smaller distance between the echos
- larger distances between the interfaces
THIS MEANS THAT THE:
- signals will be more clear
- the values and signals are discrete
- What echo and interface distances produces a lower Axial Resolution?
THERE WILL BE A LOWER RESOLUTION:
- when there is a larger distance between the echos
- smaller distances between the interfaces
THIS MEANS THAT THE:
- signals will combine
- the transducer will receive signals that are very close
together
- this worsens the resolution
