CHART Flashcards
Typical value of frequency
2-15MHz
Typical value of intensity
0.001-100 watts/cm^2
Typical value of propagation speed in soft tissue
1,540m/s
- 54Km/s
- 54mm/us
order of speed in media slow to fastes
air 330 lung 300-1200 fat 1450 soft tissue 1540 tendon 1850 bone 2000-4000
air
Typical value of pulse duration
0.5-3us
made of 2-4 cycles
Shallow imaging
High PRF
High duty factor
Short PRP
Deep imaging
Low PRF
Low Duty factor
long PRP
3 Commandments of intensity
- Intensities may be reported in various ways with respect to space and time
- Intensity is the key parameter with regard to bioeffects. the different intensities are important in the study of bioeffects, SPTA is the most relevant with respect to tissue heating
- Peak is greater than average
Intensities highest to lowest
SPTP SATP SPTA most important for thermal bioeffects SATA SPPA SAPA
attenuation is related to
frequency and path length
high frequency
long path length
more attenuation
low frequency
short path length
less attenuation
attenuation in media from greatest to least
air (greatest)
lung, bone
soft tissue
water(least)
refraction requires
Oblique incidence
different speeds
Imaging transducer characteristics
backing material short SPL short pulse duration low sensitivity wide bandwidth low Q factor decreased output power
What determines the resonant frequency for continuous wave transducer
electrical frequency equals sounds frequency
What determined the resonant frequency for pulsed wave transducer
thickness of the element
propagation speed of the element
thin crystal
fast PZT
higher frequency
Thick crystal
slow PZT
lower frequency
two factors that determine focal depth
transducer diameter (aperture) frequency
shallow focus
small diameter
low frequency
deep focus
large diameter
high frequency
beam divergence is determined by
aperture of ceramic
frequency
less divergence
narrower beam in the far field
large aperture
high frequency
improved lat res in the far field
More divergence
wider beam in the far field
small aperture
low frequency
degraded lat res in the far field
higher frequency sound
improves axial resolution in entire image
improves lateral resolution in the far field
how does focusing alter the beam
- narrower waist in the us beam
- shallower focus
- smaller focal zone
what are the two types of focusing
fixed and adjustable
mechanical, conventional and phased array
what are the three specific methods of focusing
1 lens (external)
- curved PZT (internal)
- electronic
image shape of mechanical transducer
sector
what type of transducers have mechanical steering
mechanical
annular
what type of transducers dont have any steering
switched (sequential)
what type of transducers have fixed focusing
mechanical
annular
linear sequential
Frame rate is determines by
imaging depth # of pulses per image
Frame rate is limited by
the speed of sound in the medium
imaging depth
four settings that affect temporal resolution
- maximum imaging depth
- # of pulses per scan line
- sector size
- line density
what results in high temporal resolutuion
high frame rate shallow imaging fewer pulses per image single focusing narrow sector low line density
what results in low temporal resolution
low frame rate deep imaging more pulses per image multifocusing wide sector high line density ( improves spatial resolution)
what is the typical value of frame rate
20-100Hz
what is associated with a better movie but lower quality image
high temporal resolution
what is associated with a poor quality movie but high quality image
low temporal resolution
What are the six components of an ultrasound system
master synchronizer transducer pulser receiver display storage
what are the five functions of the receiver
amplification compensation compression demodulation rejection
Higher frequency undergoes_________ TGC
more
Lower frequency undergoes ___________ TGC
less
what are the 5 requirements for contrast agents
safe strong reflectors long persistence small enough to pass through capillaries metabolically inert
what are the characteristics of Bistable displays
2 choices, black or white on or off high contrast narrow dynamic range poor contrast resolution
what are the characteristics of gray scale displays
many shades of gray multiple levels low contrast wide dynamic range good contrast resolution
what are forms of preprocessing
TGC log compression write magnification fill in interpolation persistence ( frame averaging) spatial compounding
what are forms of postprocessing
read magnification
3-D rendering
give the order of information flow through the ultrasound system
Master synchronizer Pulser Beam former Transducer (preamplification) Receiver Scan converter Display Image archive (PACS)
Read Magnification
does not rescan, only reads image in memory reads old data postprocessing same line density larger pixel unchanged spatial resolution unchanged temporal resolution
Write Magnification
rescans and acquires new data, discards old image data
writes new data
preprocessing
increased line density
more pixels
improved spatial resolution
temporal resolution can change (Improved if image is shallow)
Spatial compounding is created with different ____________and has ___________ temporal resolution
different views
reduced temporal resolution
Temporal compounding (persistence) is created with different _________ and has _____________ temporal resolution
different times
reduces temporal resolution
Frequency compounding is created with different ____________ and has ___________ temporal resolution
different frequency
unchanged temporal resolution
Narrow dynamic range has
few choices
bistable (black and white)
high contrast
Wide dynamic range has
many choices
gray scale
low contrast
Transducers process data with the
widest dynamic range
the recording device has data with the
narrowest dynamic range
Pulsatile flow is
arterial
cardiac contraction
high rate
higher pressure
Phasic flow is
venous
respiration
low rate
lower pressure
Volume
how much?
volume/time
liters/ min
flow
speed
how fast?
distance/ time
meters/ sec
velocity
stenosis causes
change in flow direction increased velocity in the stenosis * highest velocity, low pressure at the lumen ( bernoullis principle turbulent flow at exit pressure gradient across the stenosis loss of pulsatility in arterial flow
what are the factors that determine resistance (ohms)
- Radius of the lumen
- Length
- VIscosity of fluid
At the most narrowed location of stenosis (bernoullis principle)
velocity is the highest
kinetic energy is the highest
pressure is the lowest
Hydrostatic pressure order
-50mmHg at fingertip with hand elevated above head
-30mmHg at head
0 mmHg at heart
50mmHg at waist
75mmHg at knee
100mmHg at ankle
Vessels collapse when opposing vessel walls touch each other, blood pressure is zero
coaptation
what is the equation for hydrostatic pressure
measured pressure= circulatory + hydrostatic
During inspiration
diaphragm descends into abd
pressure in thorax decreases
venous flow from legs decreases
venous return to the heart increases
During expiration
diaphragm ascends into thorax
pressure in the abd decreases
venous flow to the legs increases
venous return to the heart decreases
Doppler shift=
Doppler shift = received frequency - transmitted frequency
Doppler shift equation
Doppler Shift=2 x reflector speedx incident freq. x cos
———————————————————–
propagation speed
equation for nyquist limit
Nyquist limit (KHz) = PRF/2
what are the five ways to eliminate aliasing
- use CW DOPPLER
- use a low frequency transducer
- select a new view with a shallow sample volume
- increase the scale, same view
- baseline shift (for appearances only)
small sample volume creates
clean, large window
large sample volume creates
spectral broadening or fill in
what kind of velocity does color doppler measure
mean/ average
what kind of velocity does spectral Doppler measure
Peak velocity (CW AND PW)
Imaging requires
normal incidence
higher frequency= better resolution
Pulsed wave only
1 Crystal
Doppler requires
0 or 180 degrees incidence
lower frequency ( less aliasing)
pulsed or CW
SMALL PACKETS HAVE
less accurate Doppler
less sensitive to low velocity
high frame rate, high temporal resolution
LARGE PACKETS HAVE
more accurate
more sensitive to low velocities
low frame rate, low temporal
Identifies high velocity jets anywhere along the length os the beam ( range ambiguitity)
no aliasing
Continuous wave Doppler
accurately identifies the location of the flow (range resolution)
Good temporal resolution
Good range resolution
aliasing
Pulsed wave Doppler
provides 2-D flow information directly on anatomic image
size of color jet is most affected by color Doppler Gain settings
Multiple packets= poor temporal resolution
Pulsed US
Range resolution
aliasing
Color Flow Doppler
allows the use of color with low velocities or small volumes of blood flow
greatest sensitivity
Power Mode Doppler
Color angio
energy mode
which spectral analysis is less accurate but faster
autocorrelation
What are the things to do to optimize Color Doppler
- check if the angle (color box postition)
- check the color gain (gain)
3, check the color scale (velocity scale)
Eliminates low magnitude Doppler shifts that are created by moving anatomy rather than RBC’S
High pass wall filter
serve as reject, exclude low level only Doppler shifts around the baseline, reject clutter
wall fillters
what are the six basic assumptions of imaging systems
- sound travels in a straight line
- sound travels directly to a reflector and back
- sound travels at exactly 1,540m/s
- reflections arise from structures positioned along the beam’s main axis
- intensity of the reflections is related to the scattering characteristics of the tissue
- the imaging plane is extremely thin
what kind of transducers create side lobe artifacts
mechanical
what kind of transducers create grating lobe artifact
arrays
how can one reduce grating lobes
with subdicing and apodization
lobe artifacts degrade
lateral resolution
linear array transducers have poor
elevational resolution
cross talk is an artifact that happens in doppler only, what are the two causes
Doppler gain is set too high
incident angle near 90 degrees when flow is at the focus
what are the requirements for quality assurance
multiple evaluations of the system’s components
repairs
preventative maintenance
record keeping
what are the goal for quality assurance
proper equipment operation
detect gradual changes
minimize downtime
reduce number of repeat scans
what are the methods of quality assurance
test under known, defined conditions
constant instrument settings
use phantom with measurable characteristics
image in identical environments
a phantom is an
objective standard
contains a medium similar to soft tissue, strategically located pins and structures that mimic cysts, masses . . .
evaluates gray scale
tissue equivalent phantom
used to assess the accuracy of PW, CW, and color flow doppler
Vibrating strings and moving belt phantom
Doppler phantom
Commercially available, array of strategically located pins
speed of soft tissue
does not have the same attenuating properties as soft tissue
cannot evaluate gray scale
AIUM 100mm Test Object- Water filled phantom
measures the pressure in a sound beam
hydrophone
a transducer which turns acoustic energy into heat
total heat gain+ time= total power
calorimeter
measures the intensity at specific locations
thermocouple
thermal index
bioeffects
mechanical index
cavitation
what 2 things are related to mechanical index
peak refraction pressure
lower frequency
bubbles do not burst
shear stresses
microstreaming
stable cavitation
formula for mechanical index
MI= Peak refraction pressure devided by the square root of frequency
also known as normal, inertial( TIN)
bubbles burst
highly localized
transient
