Physics Flashcards
1
Q
Anechoic
A
-without internal echoes
2
Q
Echogenic
A
- a region in an ultrasound image which has echoes
- synonymous terms: reflective, echo producing, echoic
3
Q
Heterogenous
A
-variable levels of echogenicity
4
Q
Homogeneous
A
-uniform echo texture
5
Q
Hyperechoic
A
-displayed echoes that are relatively brighter than the surrounding tissue
6
Q
Hypoechoic
A
-displayed echoes that are relatively darker than the surrounding tissue
7
Q
Isoechoic
A
-having the same echogenicity (brightness) as the surrounding tissue
8
Q
mega (M)
A
10^6
9
Q
kilo (k)
A
10^3
10
Q
deci (d)
A
10^-1
11
Q
centi (c)
A
10^-2
12
Q
milli (m)
A
10^-3
13
Q
micro (u)
A
10^-6
14
Q
What is sound?
A
- a travelling variation in acoustic variables
- a longitudinal, compressional wave
15
Q
What are acoustic variables?
What are some examples of acoustic variables?
A
- quantities that vary in a sound wave
- examples: pressure, density, and particle motion
16
Q
What is compression?
A
- when molecules are pushed together, it produces a region of increased density; creating a zone of high pressure
- compression describes the formation of a high pressure region
17
Q
What is rarefaction?
A
- when molecules release (or bounce back) there is a zone of decreased density
- the rarefaction describes the creation of this low pressure
18
Q
What is a longitudinal wave?
A
-a mechanical compressional wave in which back and forth particle motion is parallel to the direction of wave travel
19
Q
What is frequency?
A
-a count of how many complete variations in pressure (cycles) go through in one second
20
Q
What is the frequency range for audible sound?
A
20Hz - 20 000Hz
21
Q
What is the frequency range for ultrasound?
A
> 20 000Hz
22
Q
What is the period?
A
- a function time
- the time it takes for a sound wave to complete 1 cycle
23
Q
As frequency increases, what happens to the period and why?
A
- T decreases
- more cycles per second will equal shorter cycles
- they are inversely proportional
24
Q
What is wavelength?
A
-the length of space over which one cycle occurs
25
What is acoustic velocity (c)?
-the speed of a wave movement through a medium
26
If frequency increases, what will happen to wavelength and why?
-if frequency increases, wavelength decreases, because they are inversely related
27
What determines acoustic velocity?
-a medium's stiffness
28
What is stiffness?
-a medium's resistance to compression
29
Which materials have the highest acoustic velocity? (solids, liquids, gases)
solids > liquids > gases
30
What is the average acoustic velocity in soft tissue?
1.54 mm/us OR 1540 m/s
31
What materials are at the higher and lower ends of the scale for acoustic velocity?
- bone is higher than soft tissue
- lung is very low
- soft tissue is in the middle and are all within a tight range
32
Describe pulse echo technique in the use of ultrasound.
The transducer sends out a pulse which reflects off a boundary and returns to the transducer. The echo(es) is/are then represented as a dot on the screen. It's brightness depends on the strength of the returning echo.
33
Describe harmonics production.
The more dense/high pressure areas of the sound beam move faster than the less dense areas. This changes the waveform and produces multiples of the original fundamental frequency.
34
What are the first 3 odd harmonic frequencies of a sound wave with fundamental frequency=5MHz?
15MHz, 25mHz, 35MHz
35
What is CW?
-continuous wave transmission continuously emits a constant frequency with constant peak pressure amplitude sound waves from the force
36
What is pulsed ultrasound?
- not a continuous wave
| - a few cycles of ultrasound, separated by a gap of no sound
37
What is PRF and what is it's unit?
- the number of pulses occurring in a second
| - kHz
38
What is PRP and what is it's unit?
- the time from the beginning of one pulse to the beginning of the next
- ms
39
If PRF increases, what happens to PRP, and why?
- PRP will decrease
| - they are inversely proportional
40
What is PD?
- the time for one pulse to occur
| - from the beginning to the end of one pulse
41
What is the typical number of cycles in an ultrasound pulse?
2 or 3
42
What is the typical number of cycles in a doppler pulse?
5 to 30
43
If frequency increases, what will happen to PD and why?
-PD will decrease with an increase in frequency, because a higher frequency will generate a shorter period, which will decrease the PD
44
What is the advantage of a shorter PD?
-shorter PD = better image (resolution)
45
What is DF?
-the fraction of time that a pulsed ultrasound is on
46
If PD increases, what happens to DF and why?
-increasing PD will increase DF, because they are directly proportional
47
What is SPL, and what is it's significance?
- the length of space over which a pulse occurs
- unit is mm
- it is significant because it improves image resolution
- shorter pulse lengths improve resolution
48
If frequency increases, what happens to SPL?
- SPL will decrease with an increase in frequency
- SPL is directly related to wavelength and wavelength is inversely related to frequency, therefore any change in frequency will affect SPL indirectly
49
What affects bandwidth?
SPL
50
Which is better: a larger/smaller bandwidth?
-larger is better
51
Which is better: a QF of 3 or 0.4?
0.4
52
What is intensity?
-the rate at which energy passes through a unit area
53
If power increased, what would happen to intensity?
-intensity would increase proportionately with power
54
If the area increased, what would happen to intensity?
-intensity would decrease proportionately with the area
55
How do you change the area of an ultrasound beam?
-focus the beam
56
What is the amplitude of a wave?
- the maximum variation that occurs in an acoustic variable
| - measured from the baseline to the peak
57
What is power?
-the rate at which work is performed or energy is transmitted
58
Attenuation
-weakening of sound
59
weaker signal =
weaker echoes
60
TGC
- Time Gain Compensation
| - provides amplification of specific field echoes
61
What is attenuation is soft tissue?
0.5dB/cm MHz
62
Half Value Layer
- thickness of material that will half the original intensity
- distance it takes to drop 3dB
63
What is the opposite of reflection?
transmission
64
IRC + ITC =
1 or 100%
65
What is impedance directly proportional to?
density and propagation speed
66
What are specular reflectors?
- diaphragm
- fascia
- bone
- sound bounces back and produces a strong echo
67
When does scattering occur?
-when the boundary is not smooth
68
Scattering
-redirection of sound in many directions
69
What does scattering depend on?
-operational frequency and scatter size
70
Which is more likely to scatter? (a Lg or Sm wavelength)
-a large wavelength is more likely to scatter
71
Backscatter
-echo info that comes back to transducer
72
What does a large reflection mean?
-large difference between impedances (z)
73
What happens when there is a small difference between impedances (z)?
-most will transmit
74
What do contrast agents produce?
-harmonic frequencies
75
What is round trip travel time in soft tissue?
13us/cm
76
Is sound a mechanical wave?
Yes.
77
Is sound ionizing radiation?
No.
78
Is sound electromagnetic?
No. Electromagnetic waves do not require a medium.
79
Can sound converge/diverge?
Yes.
80
What are other words for a transducer?
- probe
- scan head
- transducer assembly
81
Transduce
- convert one form of energy into another
- voltage to sound
- sound to voltage
82
Piezoelectricity
piezo (press) + electron (amber)
83
Piezoelectric Effect
-sound to voltage
84
Converse/Reverse Piezoelectric Effect
-voltage to sound
85
Piezoelectric Element (aka crystal)
- adding a voltage causes thickness of the element to change
- creates a mechanical wave
- returning echo affects the element (creates a voltage)
86
1 cycle of alternating voltage =
2/3 cycles of pulse
87
longer AV =
longer pulse (doppler)
88
Quartz
-one of the first natural piezoelectric crystals
89
What piezoelectric elements do we use now?
-synthetic crystals (often ceramics)
1 Substance:
- lead
- zirconate
- titanate
- called PZT
-barium
90
What are piezoelectric elements usually made of?
- PZT
| - aka lead zirconate titanate
91
How do we realign molecular dipoles?
-place a strong magnetic field at a high temp. (350 degrees)
92
Polarization
-aligned dipoles
93
What do piezoelectric elements do while in magnetic field?
-cooled
94
Curie Point
-the temp. in which the magnetic properties of a sound can be changed
95
What is the curie point go PZT?
350 degrees
96
What would happen if thou brought the crystal back to the Curie Point, but without the magnetic field?
- dipoles will scatter
| - not piezoelectric anymore
97
What frequency does piezoelectric element (aka crystal) have?
- natural vibrational frequency
- fundamental frequency
- operational frequency
- resonance frequency
*they are all the same, just different names
98
What does operating frequency depend on?
-the element
99
Wavelength of US =
2x thickness of material (2 x th)
100
Multi Hertz Operation
-2 or 3 frequencies on the same element
101
How can operation frequency be adjusted?
-change voltage
102
Does PRF of voltage affect PRF of pulse?
Yes.
103
PRF volt =
PRF pulse
104
If you go further away, what do you have to decrease?
PRF
105
If you don't decrease PRF when you go further, what happens?
- range ambiguity (artifact)
- echo misplacement (artifact)
-happens from sending pulses too fast (before the other now is back)
106
pen
- penetration
| - aka depth
107
Damping Material
- aka backing material
- metal powder (tungsten) and plastic/epoxy resin
- on the back of the element
108
What is the damping materials impedance similar to?
crystal
109
What does a damping material reduce?
- ringing (ex. bell wrapped in rubber)
- cycles per pulse (n)
- amplitude (this is bad, weaker echo)
- sensitivity (this is bad, ability to detect weaker echoes)
110
What do a lower PD and a lower SPL result in?
better resolution
111
Does CW have damping material?
| What does this result in?
No.
- better sensitivity
- worse penetration
112
House Unit/Case
- usually same material as damping
- prevents moisture
- protects internal structures
- absorbs energy from sides of crystal
113
What is the purpose of matching layer?
-to reduce the difference in z
114
Footprint
-width of probe head
115
Do higher frequency transducers have smaller or larger footprints?
-smaller
116
What does a smaller beam width mean?
- stronger intensity (picks up more signals)
| - better resolution
117
What does focusing do?
-improves resolution (only in the NZL)
118
Where is beam width decreased?
-focal region
119
Focal Length
-distance from transducer to the focal region
120
Natural Focus
-beam will naturally come to focus
121
What are other names for the near zone?
- fresnel zone
| - near field
122
NZL
-region from transducer to min beam width
123
Beam Convergence
-beam width decreases with increasing distance from the transducer
124
What are other names for the far zone?
- fraunhofer zone
| - far field
125
Far Zone
-region beyond the NZL
126
Beam Divergence
-beam width increases with increasing distance from transducer
127
Aperture
- opening
| - width of element(s)
128
Beam Profile
-width (wb)
129
What does beam width change with?
| What does it affect?
- depth
| - affects resolution and intensity
130
Is intensity uniform within a beam?
No
131
Is power uniform within a beam?
Yes
132
What is the width at the focus?
0.5 aperture size
133
What is NZL determined by?
- size of element (aperture)
| - operating frequency
134
Focal Length
- aka NZL
| - distance to focus
135
Why is transducer care important?
- prevention of nosocomial infections
| - there is no infectious disease screening before exams
136
Critical
- device enters otherwise sterile tissue
- ex. intraoperative applications
Level of Disinfection: sterilization
137
Semi-Critical
- device contacts mucous membranes
- ex. endocavity applications
Level of Disinfection: high
138
Non-Critical
-device contacts intact skin
Level of Disinfection: intermediate or low
139
Transducer Care
- store in clean holders/racks
- keep cord off floor
- wipe probe and cord between patients
- use carrying case for transport
140
Low Level Disinfection
- use of sterilization wipes/solutions
- no bleach, ammonia or alcohol bases
- no sprays
- 5% hydrogen peroxide
- cavi wipes
- preempt (wipes)
141
High Level Disinfection
- invasive transducers are soaked
- cidex
- recert
142
Invasive Transducers
- transvaginal
- transrectal
- transesophageal
- catheter mounted
143
What are the benefits of invasive transducers?
- get us much closer to the tissue (higher resolution)
| - can use high frequency without worrying about attenuation
144
What is a drawback for invasive transducers?
-high risk of infection without proper sterile techniques
145
What does resolution allow for?
- the ability to image fine detail
- 'better' picture
- being able to separate distinct echoes
146
Why is a smaller resolution better?
-smaller details can be discerned
147
What happens if 2 reflectors are not separated sufficiently?
-they produce overlapping echoes
148
Axial Resolution
-minimum reflector separation along scan line to produce separate echoes
149
What are other names for axial resolution?
- longitudinal
- radial
- depth
- range
150
If the axial resolution is 2mm, structures 2mm apart will be seen as ___ structure(s).
2
151
If the axial resolution is 2mm, structures 1mm apart will be seen as ___ structure(s).
1
152
Do we want a smaller or larger AR?
-smaller is better
153
AR
Axial Resolution
154
How do we improve AR?
-reduce SPL
155
How do we reduce SPL?
- reduce 'n' by reducing damping layer
| - reduce wavelength by increasing operating f (will affect penetration)
156
What are some other names for lateral resolution?
- angular
- transverse
- azimuthal
157
Lateral Resolution
-minimum reflector separation perpendicular to scan LINE to produce separate echoes
158
LR
-lateral resolution
159
Do we want a sm or lg LR?
-smaller is better
160
How is LR improved?
-reducing beam width (by focusing)
161
Elevational Resolution
- minimum reflector separation perpendicular to scan PLANE to produce separate echoes
- 3rd dimension
162
A beam has slice thickness, which can also be known as __________ or __________.
- section thickness
| - elevational plane
163
What can elevational resolution produce?
-section thickness artifact (aka partial volume artifact)
164
What does elevational thickness do?
-filling in of cysts or other anechoic structures (ex. GB, vessels, urinary bladder)
165
What will a poor evolutional resolution show?
-echoes from outside the intended scan plane (especially with anechoic structures)
166
How do we fix elevational resolution artifact?
THI
- narrower and thinner beam
- less likely to pick up echoes from other plane
Spatial Compounding
167
Temporal Resolution
-being able to separate echoes in real time
168
What does poor temporal resolution visualize as?
-lag
169
Contrast Resolution
-being able to separate 2 different shades of grey
170
Useful Frequency Range
2 to 10 MHz
171
What do higher frequencies increase?
-resolution
172
What do higher frequencies decrease?
-max imaging depth
173
When may a frequency up to 50MHz be used?
- opthalmologic imaging
- dermatologic imaging
- intravascular imaging
174
What does electronic focus eliminate the need for?
- a lens
| - curved elements
175
How can focus be achieved in the third dimension (perpendicular scanning plane)?
- a lens
| - curved element
176
How can phasing be applied to focus in the third dimension electronically?
-with at least 3 rows of elements
177
What do 2D rays have the ability to do?
-steer and focus in 2 dimensions
178
1D array is...
-2D imaging
179
2D array is...
-3D imaging
180
4D imaging =
3D imaging + time
181
What is 3D imaging mostly used for?
- obstetrics
| - breast
182
What is 3D imaging also known as?
- volume imaging
| - volumetric scanning
183
Reception Steering
-listening from a particular direction
184
Dynamic Focusing
-continual change of the focus with increasing depth
185
Dynamic Aperture
-as the focus continues to change during echo reception, the aperture will increase to maintain a constant focal width
186
Annular Arrays
- concentric rings
| - piezoelectric material carved out in rings
187
Why aren't annular arrays used anymore?
-we can do the same thing with phasing and electronic phasing
188
Hemodynamics
-study of blood flow
189
What is the motion of heart and blood flow detected with?
- doppler effect
| - detects, quantify's and evaluate's blood flow
190
Circulatory System
- heart
- arteries
- arterioles
- capillaries
- venules
- veins
191
How many L of blood do humans have?
5L
192
What does blood consist of?
- plasma
- RBC
- WBC
- platelets
193
Blood Functions
- heat regulation
- oxygen
- carbon dioxide
- nutrients to cells
- removal of waste from cells
194
Heart
- 4 chambers: 2 atria, 2 ventricles
- cardiac muscles
- valves
195
Which arteries are oxygen poor?
-pulmonary arteries
196
Which veins are oxygen rich?
-pulmonary veins
197
Valves
- one way
- prevent back flow of blood
- in heart and veins
198
Stenotic Valves
-don't open enough (pathology)
199
Insufficiency/Regurgitation (valves)
-don't close enough (pathology)
200
Hydrostatic Pressure
- equivalent to the weight of a column of blood
| - increases with distance below the heart
201
What is the hydrostatic pressure in a supine patient?
0 mmHg
202
What is the hydrostatic pressure in a standing patient?
100 mmHg
| -pressure in veins is much higher
203
Respiration is also known as...
-phasicity
204
Inspiration
- diaphragm moves down
- increase in thorax volume, decrease in thoracic pressure
- allows air into lungs
- decrease in abdominal volume, increase in abdominal pressure
- stops venous return from the legs
205
Valsalva
- patient can be asked to hold their breath and 'bear down'
- increase in abdominal pressure
- stops venous return from legs
206
Expiration
- diaphragm moves up
- decrease in thoracic volume, increase in thoracic pressure
- increase in abdominal volume, decease in abdominal pressure
- venous blood returns from legs
207
Pressure
-driving force behind fluid flow
208
What is required for fluid flow?
-pressure difference/gradient
209
Which way does fluid flow?
-area of high pressure to area of low pressure
210
Volumetric Flow Rate
- volume of blood passing a point per unit of time
| - LONG STRAIGHT TUBE (we assume vessels in the body are long straight tubes)
211
R
resistance
212
Viscocity
-resistance to flow offered by fluid
213
What has the strangest effect on resistance?
-radius or diameter
214
What does resistance depend on?
-radius to the 4th power
215
If the radius doubles, what happens to R?
-decreases 16x
216
Vasoconstriction
- smaller blood vessels
| - restricts blood flow
217
Vasodilation
- larger blood vessels
| - allows more blood flow (when needed)
218
Types of Flow
- laminar
| - turbulent (non laminar)
219
Types of Laminar Flow
- plug flow
- parabolic
- disturbed flow
220
Plug Flow
- at the entrance to tubes
- blood moves as a unit
- same speed across the vessel
221
Parabolic/Laminar
- after entering the straight tube
| - fastest speeds in the centre of tube
222
Where do we assess in doppler?
-centre of the vessel (where it is fastest)
223
Where is the slowest speed?
- tube wall
| - at 0
224
Average flow speed =
1/2 of fastest speed
225
Disturbed Flow
- at stenosis
- at bifurcation
- still laminar, but streamlines are not straight
- non parabolic
226
Turbulent Flow
- usually after a significant stenosis
- chaotic, multidirectional, multispeed flow
- non laminar
- eddies
- overal forward flow
227
What time of flow may physicians heart bruit with?
-turbulent flow
228
What does turbulent flow depend on?
-Reynolds #
229
What is critical Reynolds number?
2000 for blood
| -flow must surpass a critical Reynolds # to cause turbulent flow
230
Stenosis
-partial blockage
231
Occlusion
-complete blockage
232
As heart beats...
-pressure and speed go up and down
233
what do we observe in compliant vessels?
1) added forward flow
| 2) reversal of flow
234
Compliance
-expansion and contraction of non ridging vessels during systole and diastole
235
Windkessel Effect
-aka added forward flow
236
Systole
-vessel expands
237
Diastole
- vessel contracts
| - results in extended flow w/o driving pressure from heart
238
Flow Reversal
During Diastole
- in AO, blood doesn't flow back because the aortic valve closes
- sometimes in distal circulation, when pressure decreases and vessel contracts, there will be reversal of flow (no valves to prevent back flow)
239
Continuity Rule
-speed goes up at a stenosis to keep volumetric flow rate (Q) constant at all 3 regions (before, at and after stenosis)
240
What happens to speed and pressure at a stenosis?
- speed goes up
| - pressure goes down
241
What does the continuity rule apply to?
- volumetric flow rate for a short segment (constant)
| - usually taking about a stenosis
242
Q = V x A
What happens when A decreases?
-V increases to keep the same amount of blood going through (continuity rule)
243
What is the point of the continuity rule?
- if we can figure out how fast the blood is going at a stenosis, we can figure out how much it is stenosed
- V will determine the severity
244
Bruit
-sound produced by a stenosis
245
Bernoulli Effect
-decrease in pressure in regions of high flow speed (at stenosis)
246
Before Stenosis:
| Bernoulli Effect
-pressure goes up to push blood through stenosis
247
At Stenosis:
| Bernoulli Effect
- pressure goes down to maintain energy
| - pressure energy to flow energy
248
After Stenosis:
| Bernoulli Effect
-flow energy to pressure energy
249
Ultrasound Basics
- sound wave is sent out at a particular frequency
- bounces off stationary structure
- returns at the same frequency that it was sent out
250
Doppler Effect
-change in frequency caused by the motion of a source, reflector or receiver
251
How do we know if the frequency will come back higher or lower?
-if the object is moving closer or further away
252
Doppler Shift
-difference between the sent a returning frequencies of a sound wave
253
What happens to the frequency if we are getting closer together?
-increases (positive shift)
254
What happens to the frequency if we are getting further apart?
-decreases (negative shift)
255
What shift does blood coming towards the transducer have?
-positive
256
what shift does blood moving away from the transducer have?
-negative
257
In Doppler...
- we fire a particular frequency
- measure the frequency that returns
- calculate how fast the object is moving
258
How do we affect the doppler shift?
-changing frequency
259
What can doppler shift calculate?
-velocity
260
Are we directly affecting the velocity by changing the frequency?
No.
261
Doppler effect Applications
- police speed detectors
- weather forecasting
- door openers
- burglar alarms
262
When does lesser doppler shift occur?
-if the angle of interrogation is non zero
263
What do we incorporate to compensate for lesser shift?
cos
264
Doppler Angle
-angle between the sound beam and the vessel
265
What does doppler shift depend on?
-cosine of doppler angle
266
cos 0 =
1
| -hitting vessel straight on
267
cos 30 =
0.87
268
cos 60 =
0.5
269
cos 90 =
0
| -hitting vessel perpendicular
270
What affects out calculated doppler shift?
-doppler angle
271
When is doppler shift less?
-when incorporating non zero angles
272
What does a decease in doppler shift measurement mean?
-decrease in velocity measurement
273
What happens if we don't incorporate cos?
-velocity measurements are off
274
What degree do we want to hit vessels at?
0
| -nearly impossible
275
What are some techniques to get close to a 0 doppler angle?
1) heel toe
2) phase (steer)
3) angle correct
276
Doppler Angle Correct
- we can tell the machine that we are off and it compensates
| - increased our velocity back to where it should be
277
When will there be an increased error in speed calculation?
-with a higher angle
278
What angle do we work under?
60
279
Doppler Blood Flow
- presence (yes/no)
- speed (slow/fast)
- character (laminar/turbulent)
- direction
280
Doppler Displays
- colour
- spectral
- audible
281
Colour Doppler
- aka colour flow imaging
- presence, speed, character and direction of blood flow
- assess a very large area at a time (vs. spectral doppler)
- colour superimposed on grey scale image
282
How do we steer colour doppler?
- phasing
- to get closer to 0 degrees
- to avoid if vessels are parallel to surface
283
How do we know if doppler shift has occurred?
-if the retiring echoes have a different frequency from the emitted
284
How do we know if flow is moving toward or away from transducer?
- depending on the sign of the doppler shift
| - colour is assigned to pixels
285
What is the difference in scan lines from colour and B mode?
Colour- multiple pulses are sent per scan line
B Mode- 1 pulse per scan line
286
what is doppler shift calculated within?
-signal processor
287
What does the signal processor detect?
Signal Processor Parameters:
- direction
- mean
- variance
- power
288
What is direction based on? (colour doppler)
+/- doppler shift
289
Mean/Average Velocity (colour doppler)
-average velocity of blood in an area is calculated and displayed
290
Variance (colour doppler)
- the variety within the blood flow
| - soft tissue deviation
291
Power/Strength of Echo (colour doppler)
- related to amplitude
| - depends on reflectors, impedance and concentration of RBC's
292
Reflectors
-specular reflection vs scattering
293
Impedance
higher impedance mismatch = more reflection
294
Concentration of RBC's
higher concentration = more reflection
295
Math Technique for Colour Doppler (autocorrelation)
- done with signal processor
| - determines mean and variance
296
How many pulses per scan line are sent out for colour doppler?
- 3 to 32 per scan line
| - usually 10 to 20
297
Ensemble Length
-# of pulses/scan line
298
More pulses for...
- accuracy of speed calculation
| - sensitivity (picking out weaker echoes/shifts)
299
Where does the data go once the instrument process it?
-to the display
300
What does the display use?
- hue
- saturation
- luminance
301
Hue
-what colour is shown
302
Saturation
-amount of colour
303
Luminance
- brightness
- echo intensity/power
- similar to 2D echo intensity
- stronger echoes will be brighter
304
What can a monographer do to affect the effectiveness of the colour doppler examination?
Change the size of the colour box/window.
- changes coverage
- affects frame rate/temporal resolution
305
What does colour map help to determine?
-mean velocities
-direction of flow
variance (change in colour from LT to RT)
306
What colour spectrum is most commonly used?
-red/blue
307
What shift does red usually indicate?
-positive
308
What shift does blue usually indicate?
-negative
309
Where is the + and - on the colour map?
+ on top
| - on bottom
310
Invert
- slips the colour map
| - does NOT change direction of flow
311
Baseline
- zero point (no doppler shift)
| - can move the baseline up or down based on what you want to fit on your map
312
Can you control PRF in doppler?
Yes.
313
Can you control PRF in 2D?
No.
314
What does changing the PRF in doppler do?
- changed the scale (cm/s)
| - increases or decreases speeds
315
decrease in PRF is a ______ in scale.
-decrease
316
An increase in PRF is a ______ in scale.
-increase
317
What happens if the PRF scale is set too high?
-slower flows go undetected?
318
What happens if your PRF scale is too high?
-faster flows alias
319
Aliasing
-shows wrap around colour
320
What does aliasing depend on?
Nyquist Limit
321
Nyquist Limit =
1/2 PRF
322
Are higher or lower velocities more likely to alias?
higher
323
When will aliasing often show?
within a stenosis if PRF is set too low
324
When can aliasing be good?
- can adjust your PRF for the normal flow
| - area of stenosis will show aliasing (highlights areas of highest velocity)
325
Colour Gain
- we can apply returning echo voltages (just like 2D)
| - we want wall to wall filling
326
Priority (colour control)
-aka echo write priority
Grayscale vs Colour Threshold
- echoes below cut off amplitude will show as colour
- stronger echoes show as grey scale
327
Wall Filter
- filters out noise (non useful info)
- keeps the useful signal
- eliminates any movement in the tissue that will produce doppler shifts
- sets a cut off point
328
Movement in Tissues that Produces Doppler Shifts
- tissue vibration, vessel movement
- aka clutter
- have lower velocities
329
Are arterial or venous speeds higher?
-arterial
330
How can you fix aliasing?
-increase PRF (not too much)
331
What happens if you increase PRF too much?
-echo misplacement
332
What may a tortuous vessel look like in colour doppler?
- flow reversal
| - aliasing
333
If you hit a vessel close o 90 degrees, what all it look like?
-no flow (occlusion)
334
What does an increase in doppler angle reduce?
- doppler shift
| - corresponding flow
335
Power Doppler
- strength/intensity of echo
- related to amplitude
- determines by concentration of moving RBC's
336
Can we display just the power?
Yes.
0shows only presence of flow
-no velocity, direction, flow character
337
Pro's of Power Doppler
1) increased sensitivity
- slow flow
- small or deep vessels
2) angle dependant
3) no aliasing
338
Con's of Power Doppler
- no speed/cannot quantify
- no direction
- no flow character to assess stenosis
339
Duplex Scanning
- doppler and gray scale
- we update between the 2 (transducer does 1 at a time)
- simultaneous (rapidly switches between the 2)
340
Spectral Doppler
-firing alone a single scan line
341
What is spectral doppler also called?
- pulsed doppler
| - pulsed wave doppler
342
How many cycles/pulse does spectral doppler have?
5 to 30 cycles/pulse
343
Spectral Doppler Parameters
-presence, speed, character and direction of blood flow
344
Sample Volume
- specific area that is being assessed
| - aka gate
345
Range Gating
-being able to select info from a specific depth
346
Effective Sample Length =
1/2 SPL + gate length
347
Sample Width =
beam width
348
Is sample volume (SV) user defined?
yes
349
Larger Gate Lengths
-looking for a vessel/signal
350
Smaller Gate Lengths
- more specific info
- less noise
- better quality of spectral waveform
351
With spectral doppler, samples are taken and then ______.
smoothes
352
Spectral Doppler
x axis =
y axis =
x axis = time
| y axis = soppler shift/velocity
353
Quadrature Phase Detector
- allows detection of bidirectional doppler
| - we can see +/- shifts
354
Spectral Analyzer
-determines each doppler shift frequency and it's strength
355
Fast Fourier Transform
- occurs within the spectrum analyzer
- math technique to figure out the frequency spectrum
- results sent to be displayed on the spectral display
356
What does spectral display show?
-spectral waveforms
357
Each point of spectral display shows...
- direction (+/-)
- magnitude (how fast)
- amplitude (brightness)
358
What affects direction of spectral waveform?
- whether its coming towards or away from the transducer
| - affected by direction of probe/steering
359
What affects magnitude (cm/s) of spectral display?
- speed of the blood flow
| - doppler angle
360
Doppler Angle
- between the scan line and the blood flow
| - can affect the calculated doppler velocity
361
larger doppler angle =
smaller doppler shift
| slower velocity calculated (w/o angle correct)
362
What affects amplitude of spectral doppler?
- brightness/intensity of returning echoes
| - concentration of RBC's/reflectors/impedances
363
Spectral Doppler Controls
- gate size/sample volume
- gain
- spectral invert
- baseline
-very similar to colour doppler controls
364
Gate Size/Smaple Volume (spectral controls)
-affects rangle resolution
365
Range Resolution
- knowing exactly where the signal is coming from
| - opposite of range ambiguity
366
Gain (spectral controls)
-amplification of incoming echo voltages
367
Invert (spectral controls)
- arteries are generally positive signals (above baseline)
| - veins are generally negative signals (below baseline)
368
Baseline (special doppler)
- xero point
| - ex. more + signals can move baseline down
369
Wall Filter (spectral controls)
- cuts off slower flows
| - used to get rid of clutter (tissue motion, valves)
370
PRF (spectral controls)
-PRF affects scale (which velocities we can display)
371
What will happen to any doppler shift over Nyquist Limit?
-alias
372
What happens if we decrease the PRF too much?
-aliasing (wrap around)
373
What happens if we increase the PRF too much?
-poor signal (wasted space)
374
Angle Correct (spectral control)
- increased angle, decreased doppler shift
| - makes it seem lower than it is
375
What happens when you correct the angle?
-brings the calculated speed back to it's true value
376
Higher frequencies will have a ______ pitch.
higher
377
What else can spectral doppler be converted to?
-audible sound
378
Volume (spectral Controls)
- audible signal can be turned up or down
| - we can listen for areas of high speeds (higher pitch)
379
Analyzing the Waveform
analyze spectral display with colour and grayscale info to assess for normal blood flow and pathology
380
Arterial Signals
- pulsatile
| - higher velocity waveforms
381
Venous Signals
- phasic
| - lower velocity waveforms
382
Analyzing the Resistance of Flow in a Waveform
-assess the systolic portion and the diastolic portion
383
High Resistance
- ECA, extremities
- quick upstroke
- low diastole
384
Low Resistance
- ICA/CCA, blood hungry organs (liver, renal, etc.)
- vasoldilation, slow upstroke
- higher diastole
385
Assessing Area of Stenosis
- remember continuity rule
- decrease in area, increase in velocity
- surpassing Reynolds # = turbulence
386
Spectral Broadening
wider range of spectra = more variety of shifts
- narrowing the window
- most obvious reason is stenosis
387
Spectral Limitations
- sonographers skill
- movement
- range gated to a specific depth
- aliasing
388
Fixing Aliasing
- adjust baseline
- lower operating f
- increase doppler angle (lowers all doppler shifts)
- increase PRF (increases Nyquist limit), allows for higher doppler shifts/velocities
389
Spectral Limitations
-body habits (depth) limits PRF
390
CW Doppler
- occasionally used
- 2 transducer elements (1 to send, 1 to receive)
- oscillator (CW beam former) produced a voltage
- sample volume = lg overlapping area
391
Can continuous wave doppler alias?
No.
-aliasing happens because the shift is more than Nyquist limit
Nyquist limit = 1/2 PRF
-no PRF in CW
-can pick up high maximum values without aliasing
392
CW Doppler Limitations
- large sample volume
- cant tell where its coming from
- poor range resolution
393
Does PW doppler have good range resolution?
excellent
