Sound Waves Part 3 Flashcards
Interactions of US with Tissue
A beam of ________ is produced outside the patient’s body
The xrays are subsequently ________ (absorbed and scattered) as they pass through tissue
Ultimately, the transmitted ________ are recorded on film
For diagnostic US, the recorded image is based on the ________, not transmitted energy
X-ray
Attenuated
Photons
Reflected
The device that generates US waves and then detects the reflected energy is the ________
US wave is directed into the body to interact with ________, each tissue on its own characteristic way
Results of these interactions are then recorded for diagnosis in the form of ________ US
Sound may be:
________ - ________ - ________
Transducer Tissues Reflected Incident Transmitted Reflected
________ is the major interaction of interest
4 factors affecting reflected echo strength
________ = the junction of two media with different acoustic properties
________ of incidence = the angle from the normal (perpendicular or 90 degrees) at which the sound beam strikes the interface
________ / Normal incidence = a sound beam (incidence sound) intersects a smooth surface ( the boundary between two tissues). Larger than the width of the beam, at 90 degrees
________ incidence = a sound beam that intersects a smooth surface larger than the width of the beam, at less than 90 degrees (NOT perpendicular)
Interface
Angle
Perpendicular
Oblique
4 factors affecting reflected echo strength
Sound Attenuation
Sound __________ = The decrease in strength/intensity as a beam traverses a medium; the reduction in the intensity (amplitude) of an US beam as it travels through a medium; the weakening of sound as it propagates
Encompasses ________, ________, and ________; reflection may be included
Attenuation limits imaging ________ and must be compensated for
Sound ________ = the conversion of sound to heat; it is normally the dominant contribution to attenuation (in ST)
Attenuation Absorption Scattering Divergence Depth Absorption
Attenuation
How loud is too loud?
Noise-induced hearing damage is related to the duration and volume if exposure. Government research suggests the safe exposure limit is _____ decibels for eight hours a days. Some common decibel levels:
Raindrops = 40 dB Normal conversation = 60 dB Busy city traffic = 85 dB Hair dryers = 90 dB Rock concerts = 105 dB Chainsaws = 110 dB An iPod at peak volumes = 115 dB Jack hammers = 120 dB Gunshot, fireworks = 140 dB
for ST:
Attenuation (dB) = 1/2 x _____ (MHz) x _______ (cm)
As frequency _______, attenuation _______
As pathlength _______, attenuation _______
ST = 1/2 ____/____/____
for a 1 MHz transducer, ____ dB of intensity is lost for ____ cm of travel
85 frequency pathlength increases increases increases increases dB cm MHz 1/2 1
4 Factors Affecting Reflected Echo Strength
_______ = The spreading out of a beam that results from a source of small physical dimensions or diffraction or scattering. Divergence degrades the US image by creating a loss of beam intensity and decreasing Lateral Resolution ( = beam width)
Rate of divergence increases
- As the distance from sound source _______
- As the diameter of sound source _______
- Frequency of the sound source _______
Divergence
increases
decreases
increases
The magnitude of a cyclic variations gives an idea of the strength of _______
_______, _______, and _______ are the parameters relevant
sound
amplitude
power
intensity
Amplitude
Relates to the _______ of the sound wave
Equals the maximum variation of an _______ variable; maximum value minus the normal value; difference between average value and maximum value
NOT the difference between _______ and _______ values
Units are any unit of an acoustic variable
- temperature = _______
- pressure = _______ (Pa, MPa)
strength acoustic maximum minimum degrees pascal's
Power
Rate at which _______ (capability of doing work) is transmitted; rate at which work is done; rate of energy flow over ENTIRE beam
Unit = _______ (W), _______ (mW)
Relates to the _______ of the sound wave
energy
watts
milliWatts
strength
Intensity
The concentration of _______ in a sound beam
The _______ of the beam divided by the beam’s cross sectional area
Relates to the _______ of the sound beam
_______ (Watts) per unit area (m^2)
Unit = W/m^2, mW/cm^2
energy
power
strength
power
Relationship Between Amplitude, Intensity, Power
Determined by the _______ source
Changes as they propagates through the body
Intensity is proportional to _______
Power is _______ = Intensity is _______
Power is _______ = Intensity is _______
Intensity is proportional to the wave’s _______ SQUARED
Amplitude is _______ = Intensity is _______
Amplitude is _______ = Intensity is reduced to _______-_______ of its original value
Power is proportional to the wave’s _______ SQUARED
sound power doubled doubled halved halved amplitude Doubled quadrupled quatered one-sixteenth amplitude
4 Factors Affecting Reflected Echo Strength
Acoustic Impedance
The measure of ________ to sound traveling through a medium
Specular Reflectors
________ interfaces, ________ then the beam width
Produce ________-intensity, ________ reflections
Very ________ dependant
These are responsible for major organ outlines as seen by US; ________, ________
Resistance Smooth Larger High Unidirectional Angle Diaphragm Pericardium
NonSpecular
________ - Tiny, punctate reflectors that scatter a small portion of the beam in almost all directions
________ Reflectors - may be scattered by a rough boundary between tissues or within tissues due to their heterogenous character.
________ provide the US texture within organs
Very ________ dependant
RBCs are a specific type of scattered called ________ scatterers
Scatterers Diffuse Scatterers Frequency Rayleigh
4 Factors Affecting Reflected Echo Strength
The degree of ________ impedance mismatch
Inherent ________ of the incidence ultrasound beam
The ________ at which the US beam strikes a reflecting surface
________ of the reflector
Acoustic
Strength
Angle
Size
Degree of Acoustic Impedance Mismatch of the Materials Making up the Reflecting Interface/Boundary
Acoustic Impedance
The measure of ________ to sound traveling through a medium
Unit = kg / m^3 / s or simply, the Rayl
Impedance = Density (kg/m^3) x Prop Speed (m/s)
Z = pc
Determined by the ________
Density ________ - Impedance ________
Prop Speed ________ - Impedance ________
Impedance is ________ PROPORTIONAL to Density and/or Propagation Speed
Acoustic Impedance
In Perpendicular incidence the amount of sound reflected depends on: incident ________ and ________ Mismatch of the 2 Media
No impedance difference = No ________
________ in impedance difference - ________ in reflection
The difference in acoustic impedance causes some portion of the sound to be ________ at an interface, which allows visualization of ST structures with US
Resistance Medium Increase Increase Increases Increases Directly Intensity Impedance Reflection Increase Increase Reflected
Inherent Strength of the Incidence Ultrasound Beam
A powerful US pulse generates stronger ________ than week pulse
Why not use strong pulses always?
If ________ are too strong they overwhelm the US receiver causing a “white out”
Excessive beam strength can cause ________ damage
Excessive beam strength could generate ________ perceptible to the patient
Reflections
Echoes
Tissue
Heat
Angle at which the US Beam Strikes a Reflecting Surface
To obtain maximum detection of the reflected signal, we must orient the transducer so the generated sound beam will strike an interface ________
Perpendicularly
Size of the Reflector
Significantly affects strength of an US reflection; fall into 2 classes
Specular Reflectors
________ interfaces, ________ than the beam width
Produce ________-intensity, ________ reflections
Very ________ dependant
These are responsible for major organ outlines as seen by US; ________, ________
Scatterers
Tiny, punctate reflectors that ________ a small portion of the beam in almost all directions
________ provide the US texture within organs
Very ________ dependant
RBCs are a specific type of scatterer called ________ scatterers
Smooth Larger High Unidirectional Angle Diaphragm Pericardium Scatter Scatterers Frequency Rayleigh
The B-Mode Display and “One” and “Two” Dimensional Displays
B-Mode Display
All standard ultrasound images are _______ modulated, or “B-Mode” images
Bright dots, or _______ (short for picture element) make up the picture
The _______ shade or brightness of each pixel is modulated (adjusted) in proportion to the strength or amplitude of each echo
The location of the dot relates to the _______ of the reflecting structure
One and Two Dimensional Displays
The B-mode display from a single US crystal is a ____-dimensional series of bright dots; this is an “ice-pick” or “searchlight” view
A single “ice-pick” line of B’mode information is of little application; however if the information can be stored in memory and multiple lines added to it then a ____ dimensional image (width and height) can be formed = B-scan
brightness pixels gray depth one two
One and Two Dimensional Displays
With _______ array (contains multiple elements that can be fired singly or in groups) devices, multiple “ice-pick” views are lined up side-by-side, like the teeth of a comb
The elements of a linear array are fired beginning at one end and proceeding to the other, resulting in a series of “echo lines” that collectively are called a _______
When the frame is complete, it is displayed on a TV screen, and the process of accumulating a new set of _____ “lines” begins again
In summary; each frame of an US image is made of individual scan lines; a single scan line is created by a _______ from the transducer
When several frames are acquired and presented in each second of time, it is called _____-time or _______ display
linear frame echo pulse real dynamic
Temporal Resolution
The Ability to Evaluate Rapid Motion
The ability to distinguish closely spaced events in time; improves with _______ frame rate’ scanning speed is expressed as the frame rate and is closely related to temporal resolution
The _______ the frame rate, the better the ability to image rapidly moving structures, to overcome patient motion artifacts (breathing), perform rapid survey scans of a region
When discussing frame rate, consider:
Each frame is made up of multiple _______ lines
Each scan line requires a _______
After each pulse, the system must wait to collect all echoes emerging from that line; the amount of wait time is _______ dependant on the maximum depth setting
Each _______ on each scan line requires a pulse
increased higher scan pulse directly focus
Temporal Resolution
Abbreviations, Definitions, Terms used to define scanning speed limitations
PRF = _______ _______frequency = number of pulses per second
FR = _______ rate - The number of frames or images created each second; reported in units per second or Hz
LPF or N = Number of _____ per frame - Each frame of an US image is made of individual scan lines; a single scan line is created by a pulse from the transducer
NF = Number of _______ regions - Each focal zone along a particular line of site requires an individual pulse
P or R = Image _______/maximum depth of _______ - Depth of the frame; Not how deep the anatomy is displayed on the frame
The relationship of lines per frame, frame rate, number of focuses and maximum imaging depth (ST) is
P x LPF x FR x NF < 77,000
77,000 is a constant - it never changes
if, PRF (Hz) = LPF x FR x NF
then,
P x PRF < 77,000
An improvement in any parameter must be at the expense of another parameter
pulse repetition frame lines focal depth penetration
Transducer Types
Multiple Element Construction
Arranged in construction as
_______ - _______ - _______
Multiple Element Operation
Arranged by operation as
_______ / _______ / _______ - _______ - _______
Multiple Element Construction
Arranged in construction as
Linear - Curvilinear - Annular
_______ Array = Multiple small rectangular crystals in a straight row = a wavelength wide
Curved/Convex/_______ Array = Multiple small rectangular crystals about a wavelength wide, in a curved row arranged along an arc
_______ Array = Elements are concentrically arranged ring
Linear Curvilinear Annular sequenced switched segmental vector phased linear curvilinear annular
Transducer Types
Multiple Element Operation
Arranged by operation as
Sequenced / Switched / Seqmental - Vector - Phased
Sequenced / Switched / Segmental
Each Crystal or group produces an US beam and receives the returning echo along ____ line of sight
Vector
Scan lines originate from different points across the top of display and travel out in different directions
Transducers have a flat _____ and small _____ print
Image similar to _______ array
Phased
Contains compact line of elements, each about ____ wavelength wide
All crystals excited at or nearly at the same time (less than ____ ms time difference)
Entire array produces ____ line of sight each time the crystal elements
Resulting _____ pulse sent in specific direction
one face foot convex 1/4 1 one sound
Transducer Care and Maintenance
Heat Sterilization
If heated above the Curie temperature, depolarization of transducer will occur resulting in loss of _______ properties
Check manufacturer for preferred agents for _______ and _______
Dropping / Impact
May damage _______ interior
Cracked transducer surface may lead to _______ shock
Cable Damage
Damage may lead to loss of _______, Intermittent operation, and/or excessive _______ noise on the display
piezoelectric cleaning sterilization probe electrical sensitivity electrical
Basics of Beam Formation, Steering and Focusing
Many US instruments utilize a “phased-array” US crystal to _______, _______, and _______ the US beam
Each crystal elements produces a “wavelet” , or little US wave; the wavelets merge at a short distance from the crystal to form a unified “____-front”
create
steer
focus
wave
Beam Steering
Performed to sweep US beams over a scanned volume during imaging require transmission _____ delay lines
Time Delays are accomplished by offsetting the firing of crystals by small _____ delays (10^-9 sec)
Array transducers produce only ____ line of sight each time the elements are excited
The beam must be steered throughout the _____ of view to allow data collection along different lines of sight
Direction of the ____ is changed electronically by altering the excitatior sequence of the crystal elements
time time one field beam
Beam Steering
Time delays associated with beam steering are longer than _______, but less than microseconds
Greater the difference in delays, the _______ the sector angle
nanoseconds
greater
Beam Focusing
Performed to improve lateral resolution and slice thickness; improves _______ resolution within the focal zone
Because most crystals in an array belong to multiple firing groups, focusing requirements cannot be achieved by _______ means
Phasing, using time delay lines, is usually performed to _______ the beam
Accomplished by offsetting the firing of crystals by _______ time delays (10^-9 sec)
spatial
mechanical
focus
small
