Intracranial Doppler (Midterm) Flashcards
what is TCD (transcranial doppler)?
Noninvasive method for assessing cerebral hemodynamics and Evaluating intracranial cerebrovascular disease
what are used in TCD?
power doppler
duplex sonography
contrast agents
what applications are required for TCD?
large signal -to- noise ratio
do transcranial instrumetns have a higher or lower bandwidth?
lower
what is the transcranial sample volume?
Larger less defined sample volume than most other pulsed doppler devices
what freqency is necessary for TCD?
2-MHZ pulsed range gated Doppler device with good directional resolution is necessary
what power is transmitted in TCD?
10 and 100 mW/cm/s
how far from the probe do we focus in TCD?
40-60 mm
what are the indications for TCD?
- Detection of intracranial stenosis and occlusions in the major arteries
- Evaluation of intracranial hemodynamics and collateral flow where there is extracranial disease
- Monitoring of intracranial vessel recanalization in acute stroke
- Monitoring intracranial hemodynamics
- Detection of right to left shunts
- Detection of cerebral microemboli
- During functional tests
when do we monitor intracranial hemodynamics?
after:
- hemorrhage
- endarterectomy/angioplasty
what functional tests may we use TCD during?
- Stimulation with vasoconstrictive drugs
- External stimulation of visual cortex
- Before neurosurgery
- During open heart surgery
what must a sonographer have a knowledge of in TCD study?
- Probe and settings
- Circle of Willis anatomy
- Appropriate patient positioning
- Nomenclature of cerebral arteries
- Normal depths of vessels
- Normal velocities of vessels
- Low resistant flow signals
how many segments does the ACA have?
2 (A1 and A2)
where is the carotid siphon?
just proximal to ICA intracranial branches
how many segments are in the carotid siphon?
3 (C1 and C2 and C3)
where does the ophthalmic artery branch?
junction of C2 and C3
how many segments does the MCA have?
2 (M1 and M2)
how many segments does the PCA have?
2 (P1 and P2)
where are segments 1 located?
closest to midline of the brain
what are the 4 ultrasonic windows for TCD?
Temporal approach
Orbital
Submandibular
Suboccipital
where is the probe directed in the submandibular approach?
The probe is directed upward toward the proximal intracranial ICA
where is the submandibular window located?
below the mandible at the angle-using the carotid triangle
how is the patient lying for the suboccipital approach?
-Patient is positioned lying on their
left side,with back toward you
-Head must be tucked in at the chin
toward the chest
where is the probe located in the suboccipital approach?
Probe is placed at the base of the skull
and directed upward into the
foramen
what is seen in the transorbital approach?
carotid siphon and opthalmis artery
where is the probe directed in the transorbital approach?
Probe is directed toward the orb to locate the OA,then followed to the carotid siphon-distal intracranial ICA
how is the patient laying in the transtemporal approach?
patient in supine position
where is the probe places (average) for transtemporal approach?
Probe is placed on temporal aspect of head Cephalad to zygomatic arch
-Immediately anterior and slightly superior to tragus of ear
which position of the transtemporal apprach is the most adequate?
Position 1 of the image is most often adequate as a window
Immediately anterior and slightly superior to tragus of ear
what do we visualize in the anterior orientation of transttemporal approach?
- M1and M2 segments of MCAS
- C1 segment of carotid siphon(CS)
- A1 segment of ACA & anterior communicating artery
what do we visualize in the posterior orientation of transttemporal approach?
- insonates P1 and P2 segments of PCA
- Top of the basilar artery and the posterior communicating arteries
what is the Suboccipital-transforaminal approach essential for?
screening distal vertebral arteries(V4 segment) and the Basilar artery throughout its entire length
where is the probe placed for the Suboccipital-transforaminal approach?
between the posterior margin of the foramen magnum and the spinous process of C1 vertebra
where is the beam aimed for the Suboccipital-transforaminal approach?
aimed at the bridge of the nose
who pose a difficulty for the Suboccipital-transforaminal approach?
elderly individuals or arthritic necks
what can be insonated in the transorbital approach?
- The opthalmic artery can be insonated as well as components of the anterior cerebral circulation
- Not used as much as the transtemporal and suboccipital approach
what is the submandibular useful for?
- Useful compliment to extracranial studies
- Probe is placed in the retromandibular area
- Useful for detecting carotid dissection-and chronic ICA occlusion with collaterals
insonation depth for the transtemporal arteries?
MCA-50 ACA-70 Carotid siphon-65 PCA-65-70 Basilar- 75
velocities for transtemporal areries?
MCA-55 ACA-50 Carotid siphon-39 PCA-40 Basilar-40
how do you identify cerebal vessels?
- Insonation depth
- Direction of flow at insonation depth
- Flow velocity(mean flow velocity and systolic or diastolic peak flow velocity)
- Probe position ie- what window is being used
- Direction of the ultrasonic beam ie-posterior,anterior,sub-occipital,submandibular
- Traceability of vessels
- Low resistant flow spectrum similar to ICA flow
what is an important factor when identidying cerebral vessels?
Low resistant flow spectrum similar to ICA flow
what approach do you start with in the exam?
transtemporal
how do you start the exam?
- Start with the transtemporal approach
- Identify the midline of the brain
- If the midline is not visible,then the exam may be futile
- Once it is identified,turn on the color
- The MCA is identified on either side of the midline at a depth of 50-55 mm
- Track the ipsilateral arterial network,by angling he probe anteriorly toward the ACA and then posteriorly toward the PCA
what does traceability refer to?
Refers to the fact the MCA and the other arteries can be tracked in incremental steps from a more shallow insonation depth(35mm) to deeper sites(55mm)
is flow normally toward or away from the transducer?
Flow is normally toward the probe as the MCA flows out toward the cerebrum
what may indicate disease?
Changes in the character of the flow profile and flow direction
what indicates insonation of A1 segment?
When tracking the MCA medially(65-70mm depth),an abrupt change in flow direction-away from the probe-indicates
at 65-70mm depth what does flow towards the probe usualy emanate?
usually emanate from the carotid siphon at its junction with the MCA
when can you pick up the P1 segment of the PCA with the transtemporal appraoch?
By angling the beam more posteriorly from this transtemporal approach
what is an important feature for identifying the PCAs?
The PCA can be tracked medially to its junction with the basilar artery and from there to the contralateral PCA
why is hemodialysis created?
sustain patients with end stage renal disease
what does hemodialysis remove?
waste products
creatinine
urea
excess water
what are patients with hemodialysis likely to undergo?
multiple revisions, fistulas, grafts
what is the role of the sonographer pre-operative for hemodialysis?
Assess arterial inflow and to determine the suitability of efferent(outflow) veins for hemodialysis access creation
what is the role of the sonographer for post-operative for hemodialysis?
- Assess fistulas and grafts for defects,stenosis or occlusion
- Evaluate the access for aneurysms,pseudoaneurysms and perigraft abscess
what are the indications for a hemodialysis?
- Pre-op assessment
- Distal limb ischemia
- Absence of palpable fistula “thrill”
- Peri-graft fluids or mass
- Poor dialysis
- Elevated pressures during dialysis
- Access recirculation of 12% or greater
- Unexplained urea reduction ratio <60%
- Difficult cannulation or thrombus aspiration
what are the 3 types of access for hemodialysis?
1-Central venous catheter
2-synthetic AV bridge graft
3-primary AV fistula
what does an access for hemodialysis create?
creates a way for blood to be removed from the body, circulate through the dialysis machine, and then return to the body at a rate that is higher than can be achieved through a normal vein
what are other names for an access?
fistula or shunt
what is the insertion point for a central venous cathedar?
IJV or subclavian vein
is central venous cathedar a long or short term solution?
short term solution
why is central venous cathedar sometimes tunneled under the skin?
to be less obstructive and for easier access
what is a primary AV fistula?
a surgical procedure
that creates a direct connection between
an artery and a vein
where is a primary AV fistula done?
often done in the lower arm but can be done in the upper arm as well
what is the preferred type of vascular access?
primary AV fistula
what is another name for priary AV fistula?
Native access fistula
which arm is the primary AV fistula usually created?
non-dominant arm
what is the Primary AV fistula called?
Brescia-Cimino fistula
what fistula is usually created in primary AV fistula?
- Radial artery to Cephalic vein fistula is most common
- Brachial artery to Basilic vein is also common
AVF are _______ and known for________________
AVF are autogenous and known for long term patency and low complication rate
why must AVF be allowed to mature prior to use?
adequate flow volume may not occur
When the fistula is created,and has matured ,the superficial efferent vein is used for __________
dialysis puncture
when and why does the superficial efferent vein become lumpy and sausage shaped?
increased intraluminal pressure when the fistula is created
when are flow volumes difficult to obtain?
difficult to obtain in the efferent vein due to inconsistent vein diameter
what do we do when a patients arm veins are not suitable for creating a fistula?
synthetic bridge graft
-a surgeon can use a flexible rubber tube
to create a path between an artery and vein and the graft sits under the skin
how is synthetic bridge graft different from fistula?
Used in much the same way as the fistula except that the needles used for hemodialysis are placed into the graft material rather than the patient’s own vein
where is the synthetic tube graft placed?
between an artery and vein
synthetic tube graft is used for __________
dialysis puncture
when is tube graft used?
when veins are not adequate
-useful when fistulas have failed
how many people are not canidates for AVF?
50%
what is a synthetic graft made out of and its shape?
teflon (gore-Tex) and sometimes polyurethrane and may be straight or looped
what can some synthetic access grafts be used for?
Some are self sealing and can be used for cannulation soon after implantation
how do synthetic graft tubes reduce flow volume?
may be tapered at the arterial end
does AVF or grafts have a shorter duration and lower patency rate?
grafts
where are grafts and fistulas usually created?
initially in the forearm
what happens when grafts and fistualas fail?
more proximal vasculature is used to create a new access
what are other access locations for synthetic access grafts?
- Brachial A to Basilica V
- Subclavian A to Jugular v
- Femoral A to Long saphenous V
what are complications with a graft and fistula?
- thrombus/occlusion
- stenosis
- Arterial steal:may result in digit or hand ischemia
- Distal venous hypertension
- Aneurysms and pseudoaneurysms(common)
- Elevated right heart pressure due to excessive graft flow
- Infection(mostly with synthetic grafts)
where are stenosis locations within a graft or fistula?
- proximal and distal anastomosis
- within the graft
- in venous outflow tract due to intimal hyperplasia or thrombus
what is the sonographers role for fistulas and grafts?
- Must be aware of the type of graft prior to exam
- 2-D images to R/O visible thrombus
- Doppler to demonstrate patency,stenosis,or occlusion
- Aneurysms and pseudoaneurysms must be ruled out
what is the normal spectral doppler for the feeding artery?
monophasic with large diastolic component
what is the normal spectral doppler for the anastomosis?
perivascular tissue vibration;turbulent flow over long stretch
what is the normal spectral doppler for the draining vein?
pulsatile flow-arterialized
what should the volume flow be in graft and fistula?
500ml/min
what is done after several years of use with fistula or graft?
Dilatation of feeding artery and draining vein after several years of use
what are indications for looking at the graft and fistula?
- Difficulty with needle placement
- Increased dialysis time
- Pain, swelling, or discoloration of the limb or digits (fingers/toes)
- Loss of pulse in the graft
- Palpable mass in the graft or limb
- Abnormal lab values
- Increased venous pressure during dialysis
what should the flow be in a graft and fistula?
artery side to venous side
what resoltuion is used when looking at a graft or fistula?
9 MHz
what do we evaluate with graft?
- Artery feeding the graft
- The arterial anastomosis
- The graft body
- The venous anastomosis
- The draining vein
where is doppler and PSV assessed within a graft?
- 2 cm cranial to the arterial anastomosis within the feeding artery
- 2 cm caudal to the venous anastomosis within the graft
- At the arterial and venous anastomoses
- Mid graft
- A PSV ratio is calculated at the anastomosis and at any visible stenosis
what PSV shows a >50% diameter reduction
PSV ratio >2
whar PSV shows a >75% diameter reduction
PSV ratio with a 75% stenosis
how is diameter reduction confirmed?
angiography
what should be evaluated for respiratory phasicity and transmitted cardiac pulsations?
The IJV adn SCV
in the presence of an uper arm graft, what may be seen in the SCV in the absence of a central stenosis?
monophasic flow
what is monophasic flow is SCV related to?
This is related to the high volume of blood flow and low resistance pattern of flow in the graft
when does an arterial steal distal to the arterial anastomosis occur?
when the venous outflow from the graft exceeds the capacity of the inflow artery
what does arterial steal cause?
cause symptoms of arterial insufficiency,particularly during dialysis
where is doppler spectral assessed for arterial steal?
from the radial artery caudal to the graft insertion-usually at the wrist
what is complete steal?
the direction of flow is reversed caudal to the graft
what is partial steal?
The spectral waveform is biphasic(some flow on both sides of the baseline)
what is asymptomatic steal common with?
no clinical significance
what may symtomatic patients for arterial steal require?
graft ligation
