Part 2 - important (notes) Flashcards
-front t back, parallel to sound beam
-determined by SPL
-same at all depths, does not change
-best with short pulses, less cycles, high frequency
-LAARD
longitudinal, axial,radial,depth
axial resolution
- Side by side, perpendicular to beam
- Determined by beam width
- Best with narrowest beams
- Changes w/ Depth
- LATA – Lateral, angular, transverse, azimuthal
- Large Beam diameter , High Frequency – LESS divergence in far field
Lateral resolution
Determined by
thickness of PZT
propagation speed of PZT
Pulsed transducers
Thinner PZT
High frequency
Thick PZT
Low frequency
1/2 wavelength thick
PZT
1/4 wavelength thick
Matching layer
increases efficiency of sound transmission w/ impedance between skin & active element
Matching layer
Reduces ringing, shortens pulse duration & SPL
Damping material
Maximum Frequency - Minimum frequency equals ?
Bandwidth
- Pulses w/ short duration
- uses backing material
- reduced sensitivity
- wide bandwidth
- Low Q factor
- Improved axial resolution
Imaging transducer
- Continous wave
- no backing material
- increased sensitive
- narrow bandwidth
- high Q factor
- no image
Non - imaging transducer
- Small diameter
- lower frequency
- more divergence
Shallow focus
- large diameter
- higher frequency
- less divergence
Deep focus ( better lateral resolution in far field)
Determined by frame rate
Temporal resolution
Frame is determined by
Image depth # of pulses , focus, sector size, line density
Short go return time
Short Tframe
Higher frame rate
superior temporal resolution
Shallow imaging
Long go return time
Longer Frame
Low frame rate
Inferior temporal resolution
Deep imaging
Single focus
Narrow setor
Low line density
More pulses per frame
SUPERIOR TEMP RESOLUTION
High line density improves
Spatial resolution
Uses old data post processing larger pixel size same # of pixels as the original ROI unchanged temporal resolution
Read magnification
Aquires new data preprocessing smaller pixel size more pixels than original ROI improved spatial resolution May improve temporal resolution
Write magnification
Improves higher signal to noise ration
improved axial, spatial, contrast resolution
-deeper penetration
Coded excitation does this
A Mode
X -
Y -
X - depth
Y - amplitude
B Mode
X -
Y -
x - depth
z - amplitude
M - Mode
X - Time
Y - depth
first function of receiver take each signal and make them equally larger
Treats all signals the same
Amplification (receiver gain)
Second function of receiver is to correct for attenuation by creating an image uniformly bright from top to bottom. Signals treated differently
Compensation (TGC, DGC)
Gray scale mapping
max compression - high contrast , narrow dynamic range (black & white)
min compression - low contrast, wide dyanmic range
Compression (log compression, dynamic range)
Fourth function of receiver two part process that changes electrical signals within the receiver into a form for suitable CRT display
Demodulation
Two forms or demodulation
Rectifaction
Smoothing enveloping
Converting all negative voltage into positive voltages
Rectification
Eliminate small bumps in voltage signals
Smoothing enveloping
5th function Allow us to choose whether or not to dimply low level signals (gray scale info) strong signals remain unchanged
Reject (threshold suppression)
- Changes brightness of entire image
- alters signal to nosie ratio
- alters patient exposure
- has bio effect concert
Output power
- change brightness of entire image
- does not affect signal to noise
- does not change patients exposure
- no bio effect concerns
Receiver gain
If image is to dark
Increase receiver gain
If image is to bright
reduce output power
Image element
Image detail
Spatial resolution
All pertain to pixels
Computer memory
Gray shades
Contrast resolution
All pertain to bits
Maintains & organizes system timing
Master synchronizer
Converts electrical sdingals
Transducer
determines PRP, PRF & amplitude along with firing patterns
Pulser
Produces pictures to display
Receiver
CRT/ Television
Display
Archive
Storage
Created in tissue from non-linear behavior
Harmonics
Created during reflection
contrast harmonics
Created during transmission
Tissue harmonics
Fills in missin data, imrpoves spatial resolution
Fill-interpolation
For phases transducers only, frames are averages & improves signal to noise ratio, reduces artifact , improves station resolution, reduces temporal resolution
Spatial compounding
Advanced tecnquie that reduces speckle & noise , reflect signal is divided into subabnds of limited frequencies & an image is created from each sub band. Image from sub band combines into a single image
Frequency compounding
Image processing technique the continues to display information from older images then a smoother image with reduced noise, higher signal to noise ratio & improved image quality is produced
Temporal compounding (persistence)
Venous flow
Phasic flow
Cardiac contraction
Pulsatile
Constant speed, venous circulation
Steady flow
2 x velocity x transducer frequency x cos 0 / propagation speed
Doppler shift equation
0 or 180
Most accurate doppler shift
Clinically best
60
90
no measurement
Advantage - measure high velocities
Disadvantage - range ambiguity , lack of TGC
CW (non imaging) - no damping)
advantage - range resolution
disadvantage - inaccurate measurement of high velocities
aliasing can occur
Pulsed wave (uses damping)
- adjust scale
- low frequency
- shallow sample volume
- use cw transducer
- adjust baseline
Eliminate aliasing
Greater accuracy sensitive to low flow
disadvantage - more time to get imp, frame rate, and tamp resolution reduced
Packet/ ensemle length
multiple equally spaced, parraell to sound beam, deeper & along straight line
reverberation
single, solid hyper echoic line
comet tail/ ring down
structure above has high attenuation, shadow color same as background color, absence of true anatomy below
shadowing
refraction @ edge of circular structure, hypo due to refraction and beam spreading
edge shadowing
opposite of shadow, structure below has low attenuation, hyperechoic, parallel to sound beam
enhancement
ide by side form of enhancement, hyperechoic, high intensity in focal zone
Focal enhancement/ banding
– 2nd copy of reflector, artifact is DEEPER then real & equal distance from mirror
Mirror image
correct number of reflectors at improper depth, faster than soft tissue – shallow reflector, slower than soft tissue – deeper
Prop speed
obliquely 2nd copy of true reflector & media have different propagation speeds, appear side by side cannot tell which one is real & degrades lateral resolution
Refraction
- ONLY with mechincal single crystal transducer, 2nd copy of true reflector placed side by side
Side lobes
only with array transducers, 2nd copy of true reflector , side by side
Grating lobes
elevational resolution, beam has greater width than reflector, fill in anechoic structures also called partial volume artifact/ curried with a 1 ½ dimensional array transducer. Linear array = poor
slice thickness
Grainy appearance from interference effects of scattered sound
Speckle
late reflections appear to shallow on image, cured by a LOWER PRF. (incorrect depth)
Range ambiguity
reflector place incorrectly on display
Multipath
strategic pins located @ speed of soft tissue. Tests lateral & axial resolution. Cannot evaluate gray scale (no attenuation)
AIUM 100 mm test object
– pins mimic cysts & solid masses, has attenuation can evaluate gray scale
Tissue equivalent phantom
100 W/cm ^2
unfocused
1 w/cm^2
focused
measures acoustic output of transducer
Hydrophone
measures beam profiles from interactions of sound waves and light
Acoustic optics
– transducer turns acoustic energy into heat calculating total power
calorimeter
measures specific points in space and change in temp
Thermocouple
science to identify & measure characteristics of US relevant to potential bioeffects
Dosimetery
dynamic technique that produces images from sound reflections based on differing stiffness
Elastography
