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C2 Modules CLINICAL > Doppler Ultrasound > Flashcards

Doppler Ultrasound Flashcards

1
Q

What is the Doppler effect used to measure?

A

Blood speed

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2
Q

What is the ultrasound Doppler shift measured by?

A

Comparing transmitted and received ultrasound signals (usually pulses)

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3
Q

What is found within a single location?

A

Spectral Doppler

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4
Q

Over a region: (colour/power)

A

Doppler Imaging

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5
Q

What is doppler shift proportional to?

A

Blood speed (m/s or cm/s) for a fixed angle between artery (direction of blood flow) and ultrasound beam direction

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6
Q

Why do you need to calibrate the machine?

A

Get a good estimate of the speed of blood

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7
Q

How do you calculate the sped in m/s?

A

Calculate the cross-sectional area and multiply the speed by that cross sectional area
= units of m3/second

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8
Q

What gives an indication of blood flow?

A

Measure the average of speed and multiple that by cross section

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9
Q

What is B-more image?

A

Grey-level image that is displayed

Provide anatomical information but doesn’t tell anything about speed or blood

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10
Q

What is blood flow colour coded according to?

A

Direction

The direction is relative to ultrasound waves

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11
Q

What is veins displayed as?

A

Shades of blue and green

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12
Q

What is spectral Doppler trace?

A

Measuring speed of blood at a particular point

Measuring within middle of artery - between 2 little gates

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13
Q

Why is the line angled so that it is in same direction as the artery?

A

So it will be close to the direction of blood

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14
Q

Where is the ultrasound transducer placed on?

A

Skin

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15
Q

What is it called when we want to measure at a specific speed?

A

Sample volume

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16
Q

What is aligned with the vessel?

A

Angle correction line

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17
Q

What does the spectral Doppler trace tend to measure?

A

Blood velocity which corresponds to the blue line which is the envelope

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18
Q

What is the envelope in the spectral Doppler trace?

A

Maximum velocity speed that is being measured

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19
Q

What gives the spectral broadening shape?

A

Spread of speed within a sample of small volume

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20
Q

Where is there a proportionality between?

A

Doppler shift and speed of blood

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21
Q

What is kept constant in the Doppler equation?

A

speed of sound

Around 15-40m/second

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22
Q

What is measured by the ultrasound scanner?

A
  1. Doppler shift
  2. Received frequency
  3. Transmitted frequency
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23
Q

What is set by the scanner operator?

A

Doppler angle < = 60 deg

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24
Q

What is known by ultrasound scanner?

A
  1. transmitted frequency

2. Speed of sound

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25
What is doppler shift thereotically?
0 | Theta=90degree
26
What is the best practice for doppler velocity measurement?
Theta < 60 degree and fixed
27
What are doppler frequencies?
Audible - listen to sound | Doppler shifts are in the audible range - 20kHz
28
What is filtered out using a wall filter?
Signal from vessel walls - High amplitude - Low Doppler shifts
29
Why are measurements inaccurate ?
1. Number of sources of error | 2. Subject to significant inter- inter observer variability if not performed carefully
30
What are examples of Doppler ultrasound device?
1. Continuous wave (CW) 2. Pulsed wave (PW) 3. Doppler Imaging
31
What is continuous wave?
Measures velocities over a wide range of depths
32
What is pulsed wave?
Gated to measure velocity at a particular depth (I.e. within a sample volume) - pulse repetition frequency - pulsed wave Doppler
33
What is pulse repetition frequency?
~2-8kHz | Determines the maximum velocity that can be measured
34
What is pulsed wave Doppler?
Measures velocities in just a small region Change depth of region called gating Screen out other parts of the signal and just retain signal that is of a particular depth of where you want to measure speed of blood
35
What is Doppler imaging?
Colour Doppler Colour = velocity + direction Power Doppler Colour= strength of Doppler signal (~flow/no flow)
36
What is not accurate enough to be used quantitatively?
Colour Doppler
37
What are examples of colour Doppler artefacts?
1. Noise/flash artefact that is due to tissue movement or moving probes of the surface 2. Brief of random colour all the way across the image 3. Vessel is being obsecured by flash artefacts 4. Aliasing 5. Very high speeds are actually being mapped as low speed in opposite direction
38
What does doppler give a good indication of?
Surface of plaque
39
What represents the power of the received Doppler shift signal?
Pixel colour
40
What does power Doppler not give?
No velocity information
41
What are the advantages of power Doppler imaging?
1. Relative independence to vessel orientation 2. Sensitivity to low blood flow 3. Useful for visualising complex vascular geometries (e.g. in brain)
42
What are the clinical applications of Doppler?
1. Extracranial | 2. Intracranial
43
What are features of extracranial clinical applications?
1. Assessment of carotid atherosclerosis stenosis 2. Arterial dissection 3. Carotid body and had and neck tumours
44
What are features of intracranial clinical applications?
1. Assessment of arterial stenosis 2. Evaluation of collateral flow and arterial malformations 3. Aneurysm detection 4. Investigation of dynamic cerebrovascular response 5. Embolus detection 6. Intraoperative monitoring
45
What are the main uses of Doppler ultrasound?
Look for disease in the carotid arteries
46
What does common carotid artery split into?
1. ICCA | 2. ECCA
47
What is a common site for atherosclerosis?
Carotid bifurcation
48
What is the pathology for atherosclerosis?
1. The interior of the artery is narrowed 2. Histological cross-section slide 3. The lumen of the artery is narrowed 4. Plaque may become “unstable” rupture and produce emboli, leading to brain infarction
49
What are the problems of assessing carotid stenosis?
1. Several different definitions of stenosis 2. Little standardisation in measurement between centres 3. Accuracy of methods used for clinical measurement is often limited
50
What is the NASCET trial?
1. One major stroke prevented for every 6 patients treated 2 years after surgery if degree of stenosis is 70-99% - 1 in 22 of degree of stenosis is 50-69%
51
What did the ACST trial suggest?
Asymptomatic patients with high grade stenosis may also benefit from surgery
52
What are the advantages of x-ray/CT/MR angiography
1. Invasive: a contrast agent is usually required 2. Only the lumen is visualised 3. Ionising radiation dose in case of x-ray or CT
53
What are the problems of 3D diagnostic scanners?
1. Not portable in general 2. Expensive 3. Not suitable for real-time imagine
54
What is the problem for traditional projection angiography?
Vessel diameter measurements are highly dependent on the projection plane
55
What are the advantages of Doppler ultrasound?
1. Low cost equipment 2. Portable 3. Real-time imaging 4. Visualisation of vessel wall as well as blood 5. Multimodal (imaging + velocity measurements) 6. Also possible using some MRI techniques, such as black blood MRI
56
What are the 2 methods to estimate the amount of disease?
1. Direct measurements from transverse images | 2. Measure velocity
57
What are the principle of Doppler-based methods?
1. Velocity increases with degree of stenosis 2. Relate velocity to stenosis 3. As lumen narrows, higher velocity - varies with individual patients
58
When do you measure velocity?
At site of maximal stenosis | Located visually or find location with maximum velocity
59
What are the problems with Doppler-based stenosis estimation?
1. Large variability: PSV only loosely related to stenosis | 2. Errors in Doppler velocity measurements
60
What is doppler clinically useful for?
Discriminating moderate to severe stenosis
61
why is PSV only loosely related to stenosis?
1. Variation in blood velocity between patients unrelated to carotid disease can be due to - cardiac output - blood pressure - contralateral disease 2. Inter-observer and inter-equipment variability 3. Variability in reference measurement adopted
62
What is transcranial Doppler?
1. Ultrasound passes somewhere through the skull 2. Most commonly the temporal window on side of skull 3. Get spectral Doppler traces 4. Characteristics of waveform vary depending on which vessel we are making measurements in
63
TCD ultrasound
1. Measurement of cerebral blood velocities 2. Low frequency vs diagnostic ultrasound 3. Access via temporal or occipital windows or eye 4. Temporal window: MCA > circle of Willis 5. Occipital window: basilar arteries 6. Stenosis, aneurysm, vasopasm and embolus detection 7. Useful for monitoring neurovascular surgical procedures
64
What are the advantages of TCD?
1. Low cost 2. Portable 3. Real time velocity monitoring 4. No constraint agent required
65
What are examples of real time velocity monitoring?
1. Carbon dioxide reactivity 2. Dynamic autoregulation investigations 3. Cerebral lateralisation 4. Intraoperative and bedside monitoring
66
What are the limitations of TCD?
1. Access limited due to limited numbers of numbers 2. Not all patients have an acoustic window 3. The sample Gate is positioned blind 4. Higher end equipment combines imaging and Doppler velocity measurement 5. Doppler angle cannot be estimated accurately 6. Poor resolution
67
Real time velocity measurement during surgery
1. Usually MCA 2. Indicates velocity changes and emboli 3. Used to determine co-lateral blood flow and necessity for shunt insertion 4. Indicates linking of shunt or poor air seal

C2 Modules CLINICAL (26 decks)

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