Vascular Flashcards
(176 cards)
1
Q
Effect of age on arteries:
A
Arteries have properties to allow circulation propagation - as you get older these properties are lost, calcification occurs and vessels become less elastic = disease
2
Q
proximal =
A
towards heart
3
Q
distal =
A
away from heart
4
Q
antegrade flow =
A
away from heart
5
Q
retrograde flow =
A
towards heart
6
Q
arteries and veins have 3 layers
A
intima, media, adventitia
7
Q
intima
A
inner layer of vessel
vascular endothelium - provides lubrication
8
Q
media
A
middle layer of vessel
made of elastin, collagen, layers of smooth muscle
provides elasticity
9
Q
adventitia
A
outer layer of vessel
strong thick collagen layers with some elastin
fixes arteries in place
10
Q
vein walls
A
walls are thin and very elastic
media and adventitia are less well-defined
11
Q
distal veins have…
A
valves
12
Q
the trunk or portal venous system do not have…
A
valves
13
Q
How big are arterioles? What are walls made of? What do they do?
A
<1mm diameter
smooth muscle
control flow to distal capillary beds
14
Q
Aorta =
A
The main artery that comes out of heart - main blood vessel that supplies body with blood (oxygen).
It runs straight down the centre of the body – sits just in front of spine, slightly to the left.
15
Q
Ascending aorta
A
comes straight out of heart and into the aortic arch
16
Q
Abdominal aorta splits into…
A
bifurcates into left and rigth common iliac arteries (at the level of the belly button to supply both legs with blood)
17
Q
the thoracic aorta becomes the abdominal aorta at the level of the…
A
diaphragm
18
Q
Abdominal aorta can be further divided into…
A
suprarenal = above kidney
Infrarenal aorta = below the renal arteries which supply blood to the kidneys
19
Q
The abdominal aorta
A
Continuation of the descending thoracic aorta
Supplies all of the abdominal organs and the under surface of the diaphragm and parts of the abdominal wall. Its terminal goes on to supply the pelvis and lower limbs
20
Q
the normal diameter of the abdominal aorta =
A
<2cm in diameter
21
Q
Ultrasound: vein vs artery
A
arteries have thicker more muscular walls than veins
veins are easily compressed
central venous structures will fluctuate in size with respiration
22
Q
Definition of an aneurysm:
A
An abnormal dilatation of a blood vessel by more than 50% of its normal diameter.
23
Q
What diameter is considered an AAA?
A
> 3cm
24
Q
When is an AAA at risk of rupture?
A
> 5.5cm
25
If AAA ruptures...
causes massive internal haemorrhage = patient needs urgent 2-week wait referral to vascular surgery to discuss elective repair
26
What is the cause of AAA?
atherosclerosis
27
What are the risk factors for AAA?
smoking is biggest risk factor
age
males at higher risk
PAD/CAD
family history
hypertension
high cholesterol
connective tissue disorders
diabetes is protective - slower AAA growth
28
Pathophysiology of AAA:
dilation/swelling of the aortic wall causes gradual weakening due to inflammation, oxidative stress, proteolysis and biochemical wall stress = loss of structural integrity due to reduced structural proteins (elastin + collagen)
29
there are 3 types of AAA
fusiform = bulges out on all sides
saccular = bulges only on 1 side
pseudoaneurysm = outer layer of aortic wall becomes dilated
30
Symptoms of AAA:
normal no symtoms until rupture
back pain, abdominal pain, low blood pressure, tachycardia, collapse or pulsatile abdominal mass
31
National Abdominal Aortic Aneurysm Screening Programme:
Men aged 65 and over
uses abdominal ultrasound scan
two anterier posterior measurements are taken (longitudinal + transverse)
Measure aorta in peak systole due to slight changes in diameter during the cardiac cycle
inner-to-inner measurements of diameter used for consistency
<3 = no anyrsuym
3-4.4 = annual survallence
4.5-5.4 = 3 monthly survallance
>5.5 = intervention
32
B mode =
brightness mode = grey scale 2D image
33
Curvy linear probe =
lower frequency = better penetration at depth at expense of resolution
34
Advantages of Ultrasound in AAA surveillance:
- Non-invasive
- Safe – no ionizing radiation
- Quick
- Accurate
- Reproducible – can show increases in AAA over time
- High patient acceptance – just cold jelly on skin
35
Limitations of Ultrasound in AAA surveillance:
obesity - aorta sitting deeper
excess bowel gas can cause acoustic shadowing (ultrasound can not pass through gas)
variation of aortic diameters with the cardiac cycle
no visualisation of the thoracic aorta
inter-operator and intra-operator variability
36
When is intervention used for an AAA?
* Asymptomatic and 5.5 cm or larger
* Symptomatic AAA
* Asymptomatic, larger than 4.0 cm and has grown by more than 1 cm in 1 year
37
Types of AAA intervention:
open surgery (invasive, higher risk and longer recovery so only used when appropriate)
endovascular aneurysm repair (EVAR) = used when comorbidities or anesthetic risk = uses catheter and stent graft
38
EVAR has risk of..
endoleaks = requires yearly monitoring
AAA open surgery thus has better outcomes long term
39
Endoleak
complication of EVAR (endovascular aneurysm repair)
blood flows outside of stent but within aneurysm sac
can be better detected using contrast-enhance ultrasound (microbubbles injected into bloodstream)
40
Thrombus =
blood clot
41
Blood clots (thrombus) forms due to...
Virchow’s Triad
42
Virchow’s Triad =
1) blood stasis
2) changes in vessel wall (damage)
3) thrombogenic changes in blood (hypercoagulability)
43
Blood stasis
free-flowing blood doesn’t clot
blood can get caught in areas and pool
external compression can cause clotting – e.g. tumours/pregnancy/muscle swelling after extreme weight lifting
44
May-Thurner Syndrome
Left iliac vein is compressed by the right iliac artery = Artery is sitting over top of iliac vein, causing vein compression + repeated strain = blood will clot = DVT
45
Things that trigger the Virchow's triad
- major trauma
- congestive heart failure (inefficient pump) = oedema in legs, cooling of blood in reservoirs (veins)
- previous history
- central venous catheters
- hormone therapy
46
embolus =
detached mass able to travel in a vessel
47
embolism =
lodging of an embolus
48
Thrombo-embolism =
blockage by a thrombus that has travelled
49
Venous Thrombo-Embolic Disease (VTE):
Deep Vein Thrombosis (DVT) – usually in the lower limb
Pulmonary embolism (PE) - Sudden and life-threatening
50
DVT
Calf is painful, swollen, hot with reddened skin
Vein is non-compressible
Swelling around vein – oedema
51
Risk factors for Venous Thrombo-Embolic Disease (VTE):
surgery
immobility = sedentary lifestyle, elderly, surgery
age
malignancy
pregnancy
varicose veins (may not be causal)
thrombophilia (blood more likely to clot)
52
DVT NICE guidelines:
When DVT is suspected, the 2 level DVT Wells score is used to estimate the clinical probability of DVT.
53
Patients with a likely DVT Wells score (2 points or more):
A proximal leg vein ultrasound scan, with the result available within 4 hours if possible
A D dimer test if the scan result is negative, then offer a repeat proximal leg vein ultrasound scan 6-8 days later.
54
Why do DVTs need to be treated?
DVT can embolise to lungs = life-threatening
Blood clot in leg causes scaring = venous pooling = venous hypertension = cascade of inflammation = ulcer
Patients can develop Post Thrombotic Syndrome (PTS)
Normally working people are effected = significant impact to NHS costs but also independence/earning potential
55
Post Thrombotic Syndrome (PTS)
chronic pain and swelling, venous congestion, oedema, ulceration
different than claudication – Claudication is reproducible (same aggravating factor (walking) and same relieving factor (rest). Whilst PTS feels like leg is going to burst.
56
Management of DVT:
Elevation – gravity to help drainage
Stockings – compress leg to reduce swelling (improved blood flow)
Anticoagulation - thins blood to prevent clot forming (reduces further risk of VT)
57
Invasive intervention of DVT:
Remove the clot and restore blood flow
* Mechanical thrombectomy
* Thrombolysis infusion via venous catheter
* Angiojet / mechanical assisted lysis / EKOS (endovenous ultrasound-assisted)
58
Varicose veins:
Effects superficial (surface level) veins
Characterised by enlarged tortuous veins and failure of valves
Causes aching heavy legs
faulty valves
weak walls
failure of calf muscle pump
59
aetiology of varicose veins?
Unknown
?DVT
?occupational standing
?obesity
60
Venous Incompetence results in...
venous hypertension
* pigmentation
* ulceration
* lipodermato-sclerosis or woody leg –thickening
* varicose eczema- leaking components – inflame -
* mis-shaping-"inverted champagne bottle"
* swelling
61
Venous ulceration =
painless
wet/weeping
tissue hardening
hyperpigmentation
62
arterial ulceration =
painful
necrotic edges
63
Varicose veins treatment options:
- Endovenous ablation
- Foam Sclerotherapy
- Surgery / Stab avulsions
- Pull vein out of leg
64
Lower limb vein disease:
DVT
Telangiectasia
Superficial Thrombophlebitis
Kippel-Trenaunay-Weber Syndrome
65
Telangiectasia =
- SPIDER VEINS
- sun damage
- post radiation
- NOT LIFE THREATENING
- venous hypertension
- chronic flushing
- not treated on NHS? laser?
66
Superficial Thrombophlebitis =
Superficial vein thrombosis
inflammation of vein caused by clotting
painful in the inflammatory phase
feels like hard lumpy ‘rope’ under skin
episodic
complication of varicose veins
does not usually progress to DVT but can
IV drug use
67
Kippel-Trenaunay-Weber Syndrome =
- rare congenital condition
- port wine stain
- varicose veins
- hypertrophy of soft tissue and bone locally
- underdeveloped lymph system
68
Carotid artery stenosis =
the internal carotid artery and vertebral arteries supply the brain
high velocities are associated with stenoses
stenosis can lead to embolisation, TIA and stroke
69
Stroke can be...
Hemorrhagic (15%) = caused by a burst blood vessel - blood pools in brain, causing a buildup of pressure on the brain.
ischemic (85%) - blood flow is blocked plaque build up, thrombosis (plaque rupture and blood clot formation) or embolism (clot breaks off from somewhere else)
70
Risk factors for stroke are same as....
PAD
71
Carotid plaque
When there is stenosis (narrowing), blood is forced through narrow gap = high velocity = plaque more likely to be dangerous as more likely that emboli will travel up to brain.
72
neural crossover:
side of brain damaged is opposite to the side of body displaying symptoms
73
Stroke symptoms on left side of the body suggests...
right side of brain effected = blood supply to the right side of the brain is stopped.
right side of the brain is in charge of the left side of the body
look for right carotid disease
74
Symtoms of stroke and TIA
one sided weakness -
face/arm/leg numbness
Aphasia – loss of speech, coordination
Visual loss, double vision, amaurosis fugax
Symptoms last for 24hrs = stroke
Symptoms last less than 24hrs = TIA
75
Amaurosis fugax =
temporary and painless loss of vision - caused by a blockage of blood flow to the retina (ophthalmic artery)
76
Vertebro-basilar disease =
poor blood flow to the posterior (back) portion of the brain, which is fed by two vertebral arteries that join to become the basilar artery
dizziness + loss of balance
77
TIA (transient ischaemic attack) =
acute non-disabling stroke
<24 hours, often much less
78
Investigating carotid disease: Proximal arteries (aortic arch, proximal subclavian, brachiocephalic /innominate) are scanned using...
MRA - magnetic resonance angiography
CTA - Computed Tomography Angiography
79
Investigating carotid disease: the Intracranial arteries (MCA, PCA, ACA, BA) + Extracranial arteries (carotid arteries, vertebral arteries, subclavian) are scanned using...
Transcranial Doppler ultrasound
MRA
CTA
80
Ultrasound of diseased carotid arteries:
Plaque appearance can be hyperechoic (bright) or hypoechoic (dark).
The significance of a plaque may not clear from B-mode alone = Need colour and Doppler waveforms to establish significance.
81
Measuring stenosis in carotid arteries uses...
Peak systolic velocity
end diastolic velocity
82
Flow in the internal carotid artery and in the vertebral arteries is...
continuous throughout diastole: constant, steady perfusion of the brain
83
Treatment of stroke/TIA:
aspirin
carotid endarterectomy benefits patients with SYMPTOMATIC significant stenoses
stenting is an alternative interventional technique
84
ABPI
ankle brachial pressure index
used to assess peripheral arterial perfusion in lower limbs
ratio composed of blood pressure in upper arm (brachial artery) and lower limb (dorsalsis pedis in foot or posterior/anterior tibial artery in ankle)
85
If there is disease present in the lower limb (stenosis or blockages in arteries), the pressure distally (at ankle) will...
decrease
86
Equipment needed for APBI:
Sphygmomanometer = used to increase pressure of blood pressure cuff when measurements are taken
Hand held doppler device = continuous wave doppler
Ultrasound gel
87
Performing an ABPI:
Rest the patient in a supine position for 10min – to normalise pressure
Measure the systolic blood pressure bilaterally (both sides) in the posterior tibial artery/anterior tibial artery/dorsalis pedis artery
Measure the systolic blood pressure bilaterally in the branchial artery
Calculate the ratio for each
88
ABPI calculation =
highest ankle pressure / highest brachial pressure
89
How to measure systolic blood pressure:
Inflate the cuff above the pressure at which the Doppler pulse is no longer audible and then deflate the cuff slowly, noting the pressure at which you first detect a pulse from the Doppler. This represents the systolic pressure in the vessel being assessed.
For ABPI - doppler is used to listen to pulse (amplifies sound)
90
Incorrect ABPI can be measured due to:
Incorrectly positioned cuff
Irregular pulse (e.g. atrial fibrillation)
Calcified vessels (e.g. diabetes, renal disease) = False high readings due to non-compressible arteries.
Patient anxious and unrelaxed – increased blood pressure
Incorrect doppler probe/position of probe
91
ABPI >1.2
Calcified vessels often cause unusually high ABPI results. In this scenario, further assessments such as duplex ultrasound and angiography are advised to accurately assess perfusion.
92
ABPI 0.9-1.2
No evidence of significant peripheral arterial disease
93
ABPI 0.8-0.9
Mild arterial disease
94
ABPI 0.5-0.8
Moderate arterial disease: typically presenting with claudication
95
ABPI <0.5
Severe arterial disease: typically presenting with rest pain, ulceration and gangrene = critical limb ischaemia.
96
A 50% diameter stenosis leads to...
pressure drop after stenosis
due to turbulence and a loss of energy after a stenosis
97
Exercise ABPI:
look at changes in the ABPI post exercise
if there is disease expect ratio to decrease = A drop of >0.15 in ratio after exercise compared to at rest = diseased (normal people should be same or increase)
98
Vascular ultrasound uses...
sound waves to evaluate the body's circulatory system and help identify blockages in the arteries and veins and detect blood clots
99
why use ultrasound?
Ultrasound does not use ionizing radiation, has no known harmful effects, and provides images of soft tissues that don't show up on x-ray images.
100
Vascular ultrasound is performed to:
help monitor the blood flow to organs and tissues throughout the body.
locate and identify blockages (stenosis) and abnormalities like plaque or emboli and help plan for their effective treatment.
detect blood clots (DVT in the major veins of the legs or arms).
determine whether a patient is a good candidate for a procedure such as angioplasty.
evaluate the success of procedures that graft or bypass blood vessels.
determine if there is an enlarged artery (aneurysm).
evaluate varicose veins.
101
How does ultrasound work?
1. High-frequency sound waves are transmitted from a transducer.
2. These sound waves are then reflected by different tissue types in different ways.
3. The reflected sound waves are then picked up by the ultrasound transducer.
4. The sound waves are then transformed into an image by special software.
102
How do tissue types differ in their reflection of sound waves?
Bones, fat and stones =
produce a hyperechoic signal (appears bright as most ultrasound waves are reflected)
103
How do tissue types differ in their reflection of sound waves?
Cartilage and muscle =
produce a hypoechoic signal (appears dark as most waves pass through the tissue)
104
How do tissue types differ in their reflection of sound waves?
Fluid and fluid-filled structures =
produce an anechoic signal (appears black as there is no reflection of ultrasound waves)
105
There are 3 different types of ultrasound probe:
Linear
Curvilinear
Phased
106
linear probe:
High frequency (7-15MHz):
High resolution but superficial (1-6cm) depth
Good for vascular access, nerve blocks, assessment of testes and superficial lung tissue
107
Curvilinear:
Low frequency (2-5MHz)
Low resolution, but greater depth (10-20cm)
Useful for abdominal, pelvic, obstetric and deep lung tissue
108
Phased:
The lowest frequency (1-3MHz)
lower resolution but greater depth
Useful for echocardiography
109
dot/cross/line on the probe =
correlates with a dot on the left side of the screen.
This marker should be toward the patient’s right in transverse and head in longitudinal.
110
Gain:
adjusting the gain of an ultrasound changes the brightness of the image
The gain should be adjusted until fluid appears black and soft tissue appears mid-grey with some parts of the image appearing white
111
Depth:
Depth measures are shown in cm on the side of the ultrasound monitor
112
Tips for achieving optimal ultrasound view:
Use lots of gel
Make good contact between the probe and skin (whilst ensuring the patient is comfortable)
Dim the lights to improve your view of the monitor
Ensure the probe is perpendicular to the skin
113
Doppler =
an ultrasound technique that evaluates movement of materials in the body. It allows the evaluation of blood flow through arteries and veins in the body.
114
Doppler ultrasound can evaluate:
blockages to blood flow (such as clots)
narrowing of vessels
tumours and congenital vascular malformations
reduced or absent blood flow to various organs
increased blood flow (may be a sign of infection)
115
what does doppler look like when there is stenosis?
Drop in blood pressure after stenosis causes damped waveform
Duplex ultrasound imaging can show the degree of stenosis or narrowing, the site of occlusions or stenoses
116
Doppler records....
velocity of all RBCs
RBCs are fastest in the centre of vessel, vessel walls slow flow down = there are a range of velocities
Doppler waveform plots range of velocities (RBCs) not flow = doesn't tell us flow but gives us an idea about perfusion
The wave tells us how many RBCs are travelling at one speed.
As ventricles contract, blood is expelled into circulation and repeats – velocity changes in a pattern.
117
velocity increases when...
there is narrowing (area decreases) - up to a point where stenosis becomes too much (50% stenosis)
118
50% diameter stenosis leads to
Pressure drop
Volume flow is reduced
Perfusion to tissue is reduced
119
If vein doesn't compress...
?thrombus/DVT
120
Venous return and flow is modified by…
- one way valves
- calf pump
- respiratory pump
- gravity
121
If venous return is impaired this can cause...
either dilation of veins or transfer of fluid to interstitial spaces (oedema)
122
waveform repeating pattern corresponds to...
pulse = can be used to assess heart rate
123
The diastolic component of doppler waveforms can change due to...
sensitive to gravity, posture, temperature, disease, peripheral resistance
124
Vein doppler waveform:
no signature shapes like artery waveforms
lack of regular pulsatility
phasic with respiration
125
incompetent veins doppler waveform:
change in direction of flow
126
microcirculation =
arterioles, capillaries, venules
127
There are 3 modes of ultrasound:
B (brightness)
Colour
Doppler
128
Ultrasound waves are...
longitudinal: the vibration is parallel to the wave direction
Molecules vibrate and create pressure disturbances
The wave travels at the speed of sound
In soft tissue the speed of sound is constant
Sharp images (high spatial resolution) are produced with very high frequencies/small wavelengths.
129
Explain ultrasound waves...
Particles themselves vibrates but don’t move along, the wave moves along – a disturbance causes particle to vibrate and then the wave moves. Peaks = positions where molecules are close together. Wave moves in 3D outwards from disturbance.
130
ultrasound Frequency
Frequency is the number of cycles per unit of time
Ultrasound is 1MHz – 20MHz
131
ultrasound Wavelength
Wavelength is length of 1 cycle (distance between peaks)
the size of the wavelength determines the resolution of the image (smaller/low wavelength = sharper image)
132
Speed of sound
Wavelength and frequency are linked by the speed of sound. The speed of sound in all soft tissues is roughly the same (1540m/s) = allows imaging. Bone is much higher, air is much lower
133
Pulse echo and reflections
Probe acts as both a transducer and receiver
The ultrasound machine measures the time it takes for echoes to return
strength of echo is assigned a grey level
134
Probe send pulses into tissue...
some reflects of tissue but some carries on into tissue – we are interested in reflected pulses. When tissue changes in structure we get an echo – depending on density and stiffness. Differences in tissue properties cause reflections.
135
Z =
acoustic property of tissue
CHARACTERISTIC IMPEDANCE = Every tissue will respond to the passage of acoustic waves in a slightly different way
This depends on physical properties of density and speed of sound and stiffness.
Differences in tissue properties, cause reflections....ECHOES
136
Attenuation is frequency dependent
The echo strength decreases with depth
Attenuation is caused by a loss of signal
Absorption: ultrasound is converted to heat
Scattering: the pulse is re-directed into the tissue
High frequency ultrasound attenuates more than low frequency ultrasound
137
High frequency/small wavelength =
good spatial resolution
poor penetration into tissue (attenuation)
138
B-mode: blood
black
139
B-mode: fluid
black
140
B-mode: bone
bright white
141
B-mode: calcified plaque
bright white
142
Arterio-Venous Malformations
- Congenital
- "tangle" of vessels with direct arterial-venous communication
- Most common in cerebral circulation
- Can occur anywhere
- Direct connection
- Pulsatile flow in venous side
- Often found incidentally
- Hard to treat – can treat veins that symptomatic but will come back
143
Piezoelectric Transducer =
transducers can both produce and detect ultrasound
the ceramic is usually made from lead zirconate titanate (PZT)
in transmission mode a voltage makes the PZT crystal change shape, and waves are formed
an incoming wave can make the PZT change dimensions and produce a voltage. The ‘echo’ is detected
The backing layer of the PZT transducer absorbs unwanted waves, and the matching layers prevent unwanted internal reflections
144
ultrasound probes are made up of...
many transducer elements in a line (array)
145
transducer elements can...
can both transmit waves (pulses) and detect pulses, the ‘echoes’
pulses travel in a straight line; we call this the ultrasound beam
to create one 2D image the time taken is the frame rate
146
A mode
amplitude mode
is one line
'strength of echo’, signal amplitude is assigned a grey level
147
M mode
‘motion or movement’ is one line versus time
used during echo - e.g. to see opening and closing of valves
Dashed beam – one pulse travels along beam and that is plotted against time
0-10cm depth
148
Framerate –
how long it takes to build-up 2D image
149
B–mode
‘brightness’ (2D scan)
Skin surface is always at top of image
gives maximum signal: beam perpendicular to vessel wall
150
fluid on ultrasound
appears black – blood, cysts, interstitial fluid
151
plaque can be classified as...
hyperechoic (bright) - calcified
hypoechoic (dark)
152
To see extent of disease on ultrasound...
colour Doppler and spectral waveforms can be used
153
sharper image =
higher frequency
154
vessels in a diabetic
arteries can become calcified = appear brighter than surrounding tissue
155
Curvilinear Array
beams are perpendicular to probe surface
Beams are further apart at depth = spatial resolution isn't as sharp at depth
see more but at lower resolution
156
fat on ultrasound
cause image degradation, (diffraction and mis-registration artefacts)
images are blurred as beams are not travelling in a straight line.
157
fluid on ultrasound
blood, cysts, interstitial fluid, oedema, lipid cores all appear black
158
gain
intensity/brightness
159
TGC control
Allows to increase the gain at different depths – may just want a certain section to be brighter
160
phased array probe
Smaller than curvy + linear ray
Goes to a point at the top
161
Doppler effect =
There is a frequency shift if the target is moving.
(red blood cells, valves, vessel walls)
162
Doppler effect: if frequency increases =
moving towards probe
163
Doppler effect: if frequency decreases =
moving away from probe
164
The higher the frequency shift (pitch) =
the faster something is moving
165
MAXIMUM Doppler shift if
motion is parallel to the ultrasound beam
166
ZERO Doppler shift if
motion is perpendicular (90 degrees)
to the ultrasound beam
167
Continuous Wave Doppler:
one continuous beam
just sound no image
can be used to tell if something is moving
Point probe towards artery and sound is sent to speaker – tells us if there is blood movement (if there is a pulse)
168
Doppler Waveform-Spectral Doppler
The velocity is plotted versus time.
The number of RBCs travelling at each velocity is assigned a grey level.
169
the colour image consists of
many ultrasound beams
superimposed on the B mode image
170
Colour Flow Mapping
pulses allow imaging
the colour box is made up of many beams, superimposed on the B mode image
each pixel shows mean Doppler frequency at that position
direction displayed
poor spatial resolution compared with B mode
subject to aliasing (incorrect pixel colours)
171
Aliasing -
occurs when you get very high frequency shifts = very high velocities = cannot be displayed by colour
Indicates there is stenosis is present
Thus, just relying on B mode isnt good enough
172
Neck arteries that supply the brain have...
a positive component throughout the cardiac cycle, in response to highly tuned feedback mechanisms, ensuring that there is constant, continuous flow to the brain
173
The diastolic component of waveforms is sensitive to...
peripheral resistance - if distal arterioles dilate (hot foot, change in posture/gravity) then there may be a change in diastolic component in lower and upper limb arteries
disease can also change peripheral resistance
174
Why are there so many probes?
Probes operate at a range of frequencies
C = curvilinear
L = linear
V = 3D/vector
Numbers = frequency range
175
What probe to scan aorta?
deep structure
curvilinear 1-5MHz
176
What probe to scan carotid?
superficial
Linear 12-18MHz
