Intracranial Cerebrovascular Flashcards
Intracranial doppler imaging is based on what
hemodynamics
what did intracranial imaging lag behind
it was difficult to penetrate the skull
intracranial imaging initally was developed to detect _________ following a what
vasospasm
subarachnoid hemorrhage
what is TCD
transcranial doppler
describe TCD
non invasive portable painless safe inexpensive repeatable
TCD measures and identifies what
measures velocity of flow
indentifies direction of flow
what was TCD imaging introduced
1982
TCD limitations
operator dependent - steady hand
blind vessel indentification - no image
anatomic variants - ex. incomplete circle of willis
skull difficult to penetrate
TCD clinical applications
occlusive disease cerebral emboli hemorrhage sickle cell disease subclavian steal head trauma cerebrovascular disease stroke migraine headaches aneurysms AV fistulas vasospasms eval of brain death eval of collateral flow
how is the blood delivered to the circle of willis
internal carotids and vertebrals form an anterior circulation and a posterior circulation respectively
what is the circle of willis
ring that permits communication between the right and left cerebral hemispheres and between the anterior and posterior systems
Thomas Willis in 1664
what does the circle of willis consist of
A1 segments of the 2 ACA’s, ACoA, 2 PCoA’s, 2 ICA’s, and P1 segment of the 2 PCA’s
describe the anterior circulation system
supplies majority of blood to both hemispheres
vessels: ICA, MCA, ACA, ACoA
describe the posterior circulation system
supplies the brainstem
vessels: vertebrals, basilar, PCA, PCoA
describe the internal carotid artery
origniates from the CCA
passes through the skull and gives off the FIRST major branch (ophthalmic artery)
gives off the posterior communicating arteries (PCoA) before dividing into middle cerebral arteries (MCA) and anterior cerebral arteries (ACA)
Internal carotid artery consists of what parts
cervical petrous lacerum cavernous supraclinoid ophthalmic communication
describe the opthalmic artery
first branch of the ICA
important role in collateral pathways
what is the portion of the ICA that forms 2 curves
carotid siphon
ICA bifurcates into what two terminal branches
anterior cerebral artery (ACA)
middle cerebral artery (MCA)
anterior circulation connects via what
posterior circulation connects via what
anterior communicating artery - ACOM
posterior communicating artery - PCOM
which vessel can you not see when doing a TCD
anterior communicating artery
describe MCA
larger terminal branch of the ICA
branches turn upward to the Sylvian fissure
four segments - M1 to M4
M1 and origin of M2 eval - TCD
describe ACA
smaller terminal branch of the ICA
A1 segment eval - TCD
ACA connected by ACoA
describe ACoA
can not be visualized with TCD
describe PCoA
courses from ICA to join the PCA
describe PCA
origniates from basilar
P1 segment eval - TCD
describe vertebral artery
branches of the subclavian
four segments
describe basilar artery
union of the vertebral
divides into the PCA to form part of the circle of willis
characteristics of TCD
phases array
PULSED doppler (cw can not be used)
2-5 MHz - for penetration - LOW FREQUENCY TRANSDUCER
assume 0 degree angle - shooting straight down the barrel
capture the entire circle of willis
what is the real time display of all doppler shift frequencies over time
doppler spectral waveform
______doppler shift = above the baseline, towards the transducer
______ doppler shift = below the baseline, away from the transducer
positive
negative
during TCD imaging, the doppler power should be _________ for adequate penetration
increased
what is the key for TCD
**depth
blue is away and red is towards
adjust power and gain
what are the four TCD windows
transtemporal
transorbital
transoccipital, suboccipital
submandibular
where is the transducer placed for a transtemporal scan
on the temporal bone cephalad to the zygomatic arch, and anterior to the ear
transtemporal imaging may be difficult because why
tortuous vessels - not located in up to 30% of patients
name the transtemporal vessels
MCA ACA MCA/ACA bifurcation - "butterfly sign" PCA ICA
______ PRF for slower flow in the ACA and PCA
decrease
how is transorbital scanning done
patient is supine and the transducer is gently placed on the closed eyelid
describe transorbital scanning
opthalmic artery - high resistance
carotid siphon
decrease power setting
ALARA principle
how is transoccipital scanning done
transducer is placed on the posterior aspect of the neck inferior to the nuchal crest
what vessels will be seen when scanning transoccipitally
vertebral
basilar
“Y sign”
submadicular scanning consists of what vessel
distal ICA
how do you achieve good quality color doppler images - TCD
increase color gain appropriately
maintain a small sector width and color box
change color PRF - depends on hemodynamics
be aware of color sensitivity and persistence settings
color and interpretation are important for TCD
TCD measures ______ flow velocity, not peak
mean
know charts for window, arteries, depth, mean velocity, and direction
slides 54-55
what 2 things are important when interpreting TCD
experience - w/o is difficult
knowledge of anatomy - essential
describe interpretations:
stenosis? occulusion? vasospasm? sickle cell anemia? vasoconstriction? AV malformation? brain death?
stenosis - increased velocities, turbulence
occulusion - no flow, insonating (angling) vessel key
vasospasm - increased velocities, sequential doppler
sickle cell anemia - increased velocities in the ICA and MCA
vasoconstriction - hemorrhage
AV malformation - increased velocities with low pulsatility, turbulence
brain death - suspected
physiologic factors of TCD velocities
age - lower velocities with increasing age
sex - slight increase in velocities with females
hematocrit - velocities increase with anemia
HR and cardiac output
describe stenosis
focal increases in velocity
local turbulence
poststenotic drop
PRF increased
describe occulsion
TCD is limited
lack of reliable data
describe vasospasm
vasoconstriction of the arteries
complication of hemorrhage
increase in velocity
describe hemorrhage
ruptured aneurysm
vascular tumor
head trauma
describe aneurysm
color flow appearing in an unexpected area
wider colo area
describe subclavian steal
associated with stenosis or occlusion of subclavian artery
vertebral becomes collateral - reversed flow
pressure difference of greater than 20 means obstruction on side with lower pressure
describe emboli detection
high intensity signal
hear a chirp/see a spike
describe emboli
use main MCA
transient signal
higher amplitude
unidirectional
audio sound - snap
describe sickle cell disease
inherited blood disorder
screen children
cerebral infarction associated with occlusion
