Chapter 10 Flashcards
______ is the ability to create accurate images
resolution
______ describes one measure of the detail found in an image
axial resolution (measures in mm), it is also called longitudinal, range, radial, or depth resolution
axial resolution measures the ability of a system to display two structures that are very close together when the structures are ______ to the sound beams main axis
parallel
axial resolution is related to the ______
spatial pulse length (determined by both sound source and the media)
______ pulses improve axial resolution, and is also related to pulse duration
short
what is the typical values for axial resolution?
0.1 to 1 mm, lower numerical values indicate shorter pluses and improve image accuracy
to remember axial resolution synonyms use LARRD, which means
Longitudinal, Axial, Range, Radial, Depth
what is the equation for axial resolution?
axial resolution (mm) = spatial pulse length (mm) / 2 In soft tissue it is 0.77 x # cycles in phase / frequency (MHz)
what are the two ways that short pulses are created?
less ringing and higher frequency
one way to reduce ringing is to ______ the crystals after it has been excited by an electrical signal from the system
dampen
if the pulse is short because there are few cycles in the pulse its known as _____
less ringing
is the pulse is short because each cycle in the pulse has a short wavelength its known as ______
higher frequency sound
what all is the axial resolution associated with?
shorter spatial pulse length, shorter pulse duration, higher frequencies, fewer cycles per pulse, and lower numerical value
______ is the ability to distinctly identify two structures that are vary close together when they are side by side or perpendicular to the sound beams main axis
lateral resolution (mm or cm)
what is the lateral resolution determined by?
width of the sound beam
______ beams have better resolution
narrower; beam diameter varies with depth and lateral resolution changes with depth
to remember the synonyms for lateral resolution use LATA which means?
Lateral, Angular, Transverse, Azimuthal
Lateral resolution is best at the _____, where the beam is narrowest
focus
what is the equation for lateral resolution?
lateral resolution (mm) = beams diameter (mm)
axial resolution is better that lateral resolution because ultrasound pulses are ______ than they are wide
shorter; thus the numerical value is less
when two side-by-side reflectors are closer to each other than the width of the beam, only ______ reflection is observed on the image
one
______ frequencies improve both lateral and axial resolutions
higher
______ is improved in the entire image with higher frequency because shorter pulses are associated with high frequency sound.
axial resolution
______ is improved by high frequency only in the far field because high frequency pulses diverge less in the far field
lateral resolution
changes with depth, smallest diameter crystals are best in near field, largest diameter and highest frequency is best in far field
lateral resolution
same at all depths, does not change, shortest pulses are best in far and near fields
axial resolution
what are the three methods of focusing?
external focusing (with a lens), internal focusing (with a curved active element), and phased array focusing (with the electronics of the ultrasound system)
______, also called conventional or mechanical focusing, includes both external and internal techniques
fixed focusing
with external focusing a ______ is placed in front of the piezoelectric material
lens
as the arc of the lens becomes more prominent, the degree of focusing ______ and the beam narrows in the focal zone
increases
with internal focusing a ______ concentrates that sound energy into a narrower or tighter beam (most common form of fixed focusing)
curved piezoelectric crystal
as the curvature of the PZT becomes more pronounced, the degree of focusing ______
increases
______ means adjustable or multiple focusing
phased array
in phases array transducers, the systems ______ focus the sound beam
electronics
what is the effects of focusing the sound beam?
beam diameter in near field and focal zone is reduced, focal depth is shallower, beam diameter in the far zone increases, and focal zone is smaller
