Ch. 10-11 Physics Flashcards
Ability to create accurate images
resolution
Measures the ability of the system to display two structures that are very close together with the structures parallel to the sound beams main axis
axial resolution
Axial resolution is related to
pulse duration, spatial pulse length
What pulses (in length and time) improve axial resolution
shorter
What frequencies have better axial resolution
higher
A short pulse is created in what 2 ways
less ringing (damping), higher frequency
A pulse is short if there are few cycles in a pulse is referred to as
less ringing (damping)
A pulse is short if each cycle in the pulse has a short wavelength is related to
higher frequency
LARRD axial resolution
longitudinal, axial, range, radial, depth
Image quality is better when axial resolution has a ____ numerical value
lower
Better axial resolution is associated with what 5 things
shorter SPL, shorter PD, higher frequencies, fever cycles per pulse, lower numerical values
Measures the ability of the system to display two structures that are very close together when they are ______ to the sound beams main axis is called ____
side-by-side/perpendicular, lateral resolution
Lateral resolution LATA
lateral, angular, transverse, azimuthal
Lateral resolution is determined by the beam
width
Beam width caries with
depth
Lateral resolution=
beam diameter
When two side-by-side reflectors are ____ together then the ____ of the beam, only one reflector is observed on the image
closer, width
____ frequencies improve axial and lateral resolution
higher
Is improved in the entire image because shorter pulses are associated with high frequency sound
axial resolution
Is improved at the focus AND in the far field because higher frequency pulses diverge less in the far field than low frequency pulses
Lateral resolution
Concentrates the sound energy into a narrower beam and thus improves lateral resolution
focusing
Three methods of focusing are
external, internal, phased array
With a FIXED lens (in a fixed focus transducer)
external focusing
In external focusing, the lens is placed
in front of the crystal
With a curved active element ( in a fixed focus transducer)
internal focusing
Use of a curved crystal
internal focusing
With the ELECTRONICS of the ultrasound system
phased array focusing
Phased array focusing is used only on ______ element transducers and never on a single element transducer
multiple active
A sound beam undergoes four distinct modifications when focused:
near field beam diameter and focal zone are reduced, focal depth is shallower, beam diameter in far zone increases, size of focal zone smaller
When focused, a sound beam diameter in the near field and focal zone is
narrowed/reduced
When focused, a sound beam focal depth is
shallower
When focused, a sound beam diameter in the far zone
increases
When focusing, a sound beam the size of the focal zone is
smaller
What are the determinants of sound beams
frequency in cw transducers, frequency in pw transducers, focal length, beam divergence, lateral resolution
Frequency in continuous wave transducers=
frequency of electoral signal from US system
Frequency in pulsed wave transducers are determined by
thickness of crystal and speed of sound in the crystal
Focal length is determined by
diameter of crystal and frequency of sound
Beam divergence is determined by
diameter of crystal and frequency of sound
Lateral resolution is determined by
beam width
Basic modes of display
a mode, b mode, m mode
A mode is called
amplitude mode
B mode is called
brightness mode
M mode is called
motion mode
Appears as a series of spikes
A mode
The height of the upward deflection is proportional to the
amplitude of the returning echo is A mode
A mode is accurate in determining the
depth of reflectors
In A mode, x-axis displays
depth of reflector (which is derived from time-of-flight)
In A mode, the y-axis represents
reflection amplitude
Appears as a line of dots of varying brightness
B mode
The brightness of the dot indicates
strength of reflection in B mode
Weaker reflections appear as
dark gray dots
Strong reflectors appear as
bright white dots
Is the basis of all other types of gray scale imaging, including real time imaging
B mode
In B mode, x-axis represents
reflector depth (derived from time-of-flight)
In B mode, y-axis represents
nothing
In B mode, z-axis is
brightness or amplitude
Appears as a group of horizontal wavy lines
M mode
M mode is the ONLY display mode that provides information about
reflectors changing location and depth with respect to time
In M mode, x-axis represents
time
In M mode, y axis represents (derived from time-of-flight)
depth
