CHART Flashcards
(115 cards)
1
Q
Typical value of frequency
A
2-15MHz
2
Q
Typical value of intensity
A
0.001-100 watts/cm^2
3
Q
Typical value of propagation speed in soft tissue
A
1,540m/s
- 54Km/s
- 54mm/us
4
Q
order of speed in media slow to fastes
A
air 330 lung 300-1200 fat 1450 soft tissue 1540 tendon 1850 bone 2000-4000
air
5
Q
Typical value of pulse duration
A
0.5-3us
made of 2-4 cycles
6
Q
Shallow imaging
A
High PRF
High duty factor
Short PRP
7
Q
Deep imaging
A
Low PRF
Low Duty factor
long PRP
8
Q
3 Commandments of intensity
A
- 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
9
Q
Intensities highest to lowest
A
SPTP SATP SPTA most important for thermal bioeffects SATA SPPA SAPA
10
Q
attenuation is related to
A
frequency and path length
11
Q
high frequency
long path length
A
more attenuation
12
Q
low frequency
short path length
A
less attenuation
13
Q
attenuation in media from greatest to least
A
air (greatest)
lung, bone
soft tissue
water(least)
14
Q
refraction requires
A
Oblique incidence
different speeds
15
Q
Imaging transducer characteristics
A
backing material short SPL short pulse duration low sensitivity wide bandwidth low Q factor decreased output power
16
Q
What determines the resonant frequency for continuous wave transducer
A
electrical frequency equals sounds frequency
17
Q
What determined the resonant frequency for pulsed wave transducer
A
thickness of the element
propagation speed of the element
18
Q
thin crystal
fast PZT
A
higher frequency
19
Q
Thick crystal
slow PZT
A
lower frequency
20
Q
two factors that determine focal depth
A
transducer diameter (aperture) frequency
21
Q
shallow focus
A
small diameter
low frequency
22
Q
deep focus
A
large diameter
high frequency
23
Q
beam divergence is determined by
A
aperture of ceramic
frequency
24
Q
less divergence
A
narrower beam in the far field
large aperture
high frequency
improved lat res in the far field
25
More divergence
wider beam in the far field
small aperture
low frequency
degraded lat res in the far field
26
higher frequency sound
improves axial resolution in entire image
| improves lateral resolution in the far field
27
how does focusing alter the beam
1. narrower waist in the us beam
2. shallower focus
3. smaller focal zone
28
what are the two types of focusing
fixed and adjustable
| mechanical, conventional and phased array
29
what are the three specific methods of focusing
1 lens (external)
2. curved PZT (internal)
3. electronic
30
image shape of mechanical transducer
sector
31
what type of transducers have mechanical steering
mechanical
| annular
32
what type of transducers dont have any steering
switched (sequential)
33
what type of transducers have fixed focusing
mechanical
annular
linear sequential
34
Frame rate is determines by
```
imaging depth
# of pulses per image
```
35
Frame rate is limited by
the speed of sound in the medium
| imaging depth
36
four settings that affect temporal resolution
1. maximum imaging depth
2. # of pulses per scan line
3. sector size
4. line density
37
what results in high temporal resolutuion
```
high frame rate
shallow imaging
fewer pulses per image
single focusing
narrow sector
low line density
```
38
what results in low temporal resolution
```
low frame rate
deep imaging
more pulses per image
multifocusing
wide sector
high line density ( improves spatial resolution)
```
39
what is the typical value of frame rate
20-100Hz
40
what is associated with a better movie but lower quality image
high temporal resolution
41
what is associated with a poor quality movie but high quality image
low temporal resolution
42
What are the six components of an ultrasound system
```
master synchronizer
transducer
pulser
receiver
display
storage
```
43
what are the five functions of the receiver
```
amplification
compensation
compression
demodulation
rejection
```
44
Higher frequency undergoes_________ TGC
more
45
Lower frequency undergoes ___________ TGC
less
46
what are the 5 requirements for contrast agents
```
safe
strong reflectors
long persistence
small enough to pass through capillaries
metabolically inert
```
47
what are the characteristics of Bistable displays
```
2 choices, black or white
on or off
high contrast
narrow dynamic range
poor contrast resolution
```
48
what are the characteristics of gray scale displays
```
many shades of gray
multiple levels
low contrast
wide dynamic range
good contrast resolution
```
49
what are forms of preprocessing
```
TGC
log compression
write magnification
fill in interpolation
persistence ( frame averaging)
spatial compounding
```
50
what are forms of postprocessing
read magnification
| 3-D rendering
51
give the order of information flow through the ultrasound system
```
Master synchronizer
Pulser
Beam former
Transducer (preamplification)
Receiver
Scan converter
Display
Image archive (PACS)
```
52
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
```
53
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)
54
Spatial compounding is created with different ____________and has ___________ temporal resolution
different views
| reduced temporal resolution
55
Temporal compounding (persistence) is created with different _________ and has _____________ temporal resolution
different times
| reduces temporal resolution
56
Frequency compounding is created with different ____________ and has ___________ temporal resolution
different frequency
| unchanged temporal resolution
57
Narrow dynamic range has
few choices
bistable (black and white)
high contrast
58
Wide dynamic range has
many choices
gray scale
low contrast
59
Transducers process data with the
widest dynamic range
60
the recording device has data with the
narrowest dynamic range
61
Pulsatile flow is
arterial
cardiac contraction
high rate
higher pressure
62
Phasic flow is
venous
respiration
low rate
lower pressure
63
Volume
how much?
volume/time
liters/ min
flow
64
speed
how fast?
distance/ time
meters/ sec
velocity
65
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
```
66
what are the factors that determine resistance (ohms)
1. Radius of the lumen
2. Length
3. VIscosity of fluid
67
At the most narrowed location of stenosis (bernoullis principle)
velocity is the highest
kinetic energy is the highest
pressure is the lowest
68
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
69
Vessels collapse when opposing vessel walls touch each other, blood pressure is zero
coaptation
70
what is the equation for hydrostatic pressure
measured pressure= circulatory + hydrostatic
71
During inspiration
diaphragm descends into abd
pressure in thorax decreases
venous flow from legs decreases
venous return to the heart increases
72
During expiration
diaphragm ascends into thorax
pressure in the abd decreases
venous flow to the legs increases
venous return to the heart decreases
73
Doppler shift=
Doppler shift = received frequency - transmitted frequency
74
Doppler shift equation
Doppler Shift=2 x reflector speedx incident freq. x cos
-----------------------------------------------------------
propagation speed
75
equation for nyquist limit
Nyquist limit (KHz) = PRF/2
76
what are the five ways to eliminate aliasing
1. use CW DOPPLER
2. use a low frequency transducer
3. select a new view with a shallow sample volume
4. increase the scale, same view
5. baseline shift (for appearances only)
77
small sample volume creates
clean, large window
78
large sample volume creates
spectral broadening or fill in
79
what kind of velocity does color doppler measure
mean/ average
80
what kind of velocity does spectral Doppler measure
Peak velocity (CW AND PW)
81
Imaging requires
normal incidence
higher frequency= better resolution
Pulsed wave only
1 Crystal
82
Doppler requires
0 or 180 degrees incidence
lower frequency ( less aliasing)
pulsed or CW
83
SMALL PACKETS HAVE
less accurate Doppler
less sensitive to low velocity
high frame rate, high temporal resolution
84
LARGE PACKETS HAVE
more accurate
more sensitive to low velocities
low frame rate, low temporal
85
Identifies high velocity jets anywhere along the length os the beam ( range ambiguitity)
no aliasing
Continuous wave Doppler
86
accurately identifies the location of the flow (range resolution)
Good temporal resolution
Good range resolution
aliasing
Pulsed wave Doppler
87
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
88
allows the use of color with low velocities or small volumes of blood flow
greatest sensitivity
Power Mode Doppler
Color angio
energy mode
89
which spectral analysis is less accurate but faster
autocorrelation
90
What are the things to do to optimize Color Doppler
1. check if the angle (color box postition)
2. check the color gain (gain)
3, check the color scale (velocity scale)
91
Eliminates low magnitude Doppler shifts that are created by moving anatomy rather than RBC'S
High pass wall filter
92
serve as reject, exclude low level only Doppler shifts around the baseline, reject clutter
wall fillters
93
what are the six basic assumptions of imaging systems
1. sound travels in a straight line
2. sound travels directly to a reflector and back
3. sound travels at exactly 1,540m/s
4. reflections arise from structures positioned along the beam's main axis
5. intensity of the reflections is related to the scattering characteristics of the tissue
6. the imaging plane is extremely thin
94
what kind of transducers create side lobe artifacts
mechanical
95
what kind of transducers create grating lobe artifact
arrays
96
how can one reduce grating lobes
with subdicing and apodization
97
lobe artifacts degrade
lateral resolution
98
linear array transducers have poor
elevational resolution
99
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
100
what are the requirements for quality assurance
multiple evaluations of the system's components
repairs
preventative maintenance
record keeping
101
what are the goal for quality assurance
proper equipment operation
detect gradual changes
minimize downtime
reduce number of repeat scans
102
what are the methods of quality assurance
test under known, defined conditions
constant instrument settings
use phantom with measurable characteristics
image in identical environments
103
a phantom is an
objective standard
104
contains a medium similar to soft tissue, strategically located pins and structures that mimic cysts, masses . . .
evaluates gray scale
tissue equivalent phantom
105
used to assess the accuracy of PW, CW, and color flow doppler
Vibrating strings and moving belt phantom
Doppler phantom
106
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
107
measures the pressure in a sound beam
hydrophone
108
a transducer which turns acoustic energy into heat
| total heat gain+ time= total power
calorimeter
109
measures the intensity at specific locations
thermocouple
110
thermal index
bioeffects
111
mechanical index
cavitation
112
what 2 things are related to mechanical index
peak refraction pressure
| lower frequency
113
bubbles do not burst
shear stresses
microstreaming
stable cavitation
114
formula for mechanical index
MI= Peak refraction pressure devided by the square root of frequency
115
also known as normal, inertial( TIN)
bubbles burst
highly localized
transient
