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248 Cards in this Set
- Front
- Back
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What is the range of the average diameter of basal cerebral arteries? |
2 to 4 mm |
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It is estimated that 18% to 54% of individuals display variations at the level of the circle of Willis. What are some of these variations? |
1) Variation of caliber of vessels 2) Variation of the course of vessels 3) Variation of the origin of branches |
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What are the parasellar, genu, and supraclinoid segments part of? |
The carotid siphon |
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Where is the anterior communicating artery located? |
Above the optic chiasm |
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Both the anterior cerebral arteries communicate via... |
the anterior communicating artery |
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Both the cerebral arteries course in what direction? |
Medially to the internal carotid arteries |
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What is a typical characteristic of a non-imaging transducer for transcranial Doppler? |
1 to 2 Mhz pulsed wave |
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What is the Doppler frequency range in standard duplex imaging system for transcranial? |
2 to 3 MHz |
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What is the initial target vessel to be explored through the transtemporal acoustic window? |
The middle cerebral artery |
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What are the Lindegaard and the Basilar artery/vertebral artery ratios both useful for the the categorization of? |
Vasospasm |
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What does the relation, MCA>ACA>PCA=BA=VA, represent? |
Relative flow velocities |
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What are some of the criterion used for the identification of vessels or vessel segments in the intracranial circulation? |
1) the direction of flow in relation to the transducer 2) The sample volume depth 3) The vessel flow velocity |
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The accurate caluculation of flow velocities with TCD are... |
operator dependent |
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What are some primary diagnostic features of the Doppler signals for evaluation of intracranial vessels? |
1) Changes in velocity from established criteria 2) Changes in flow pulsatility from established standards 3) Changes in flow direction from established standards |
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What collateral pathways will not show direct evidence of significant carotid artery disease? |
Leptomenigeal collateralization |
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Pulsatility index is not used as... |
a part of the five primary criteria used to identify intracranial arterial segment. |
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Can a limited transcranial Doppler or transcranial duplex imaging exam be ordered to evaluate for sickle cell anemia? |
No |
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Nuances in signal can be heard before... |
they can be seen on the Doppler spectrum |
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What kind of signals could be missed by turbulent flow on the Doppler spectrum? |
High velocity |
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What is the Atlas loop approach used for? |
Obtaining data to characterize basilar artery vasospasm |
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To ensure patient safety when using the transorbital approach, which technical setting should you always adress? |
Decrease the acoustic intensity |
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At a depth of approximately 65 mm from the trans-temporal window, with a Doppler sample gate of 5 to 10 mm, you should obtain two Doppler spectra (one on each side of the baseline). What do these Doppler spectra correspond to? |
MCA to ACA |
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When is evidence of vasospasm usually seen following subarachnoid hemorrhaging? |
3 to 4 days after the bleed started |
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On average, the center of the Circle of Willis is approximately the size of |
a thumbnail |
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The anterior intracranial arterial circulation is formed as a continuation of the |
internal carotid artery |
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In 18% to 27% of the population, the posterior cerebral arteries receive blood flow (at least partly) from the |
internal carotid artery |
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The anterior inferior cerebellar and superior cerebellar arteries are branches of the |
basilar artery |
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The posterior inferior cerebellar arteries are typically branches of the |
vertebral arteries |
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The best acoustic window to insonate the vertebral and basilar arteries is through the |
foramen magnum |
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On non-imaging transcranial Doppler, a visual colored roadmap of vessels is possible because of the addition of |
M-mode |
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Independently of the technique use (TCD OR TCDI), the documentation of data obtained on intracranial arteries is based on |
spectral waveforms |
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All of the arteries examined during a TCD or TCDI examination supply the brain except the |
ophthalmic artery |
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When the transducer is placed 1.25 inches below the mastoid process and posterior to the sternocleidomastoid muscle, the technique is called the |
atlas loop approach |
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The Gosling index expresses the (blank) of the Doppler signal |
pulsatility |
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The MCA mean velocity divided by the submandibular ICA mean velocity represents the calculation for the |
Lindegaard ratio |
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Ipsilateral increased velocities observed in the ACA and PCA with a signifcant stenosis or occlusion of the MCA is a result of |
leptomeningeal colateralization |
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Evaluation of the MCA from a temporal window with a more posterior location will require aiming the transducer |
slightly anterior |
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The location at the temporal window resulting in a neutral orientation of the transducer to evaluate the MCA is |
middle |
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A "fifth" accoustic window is sometimes used for transcranial examination; this window is the |
Atlas Loop approach |
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The two anterior cerebral arteries are usually connected by an anterior communicating artery at what level? |
Above the optic chiasm |
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The frequency found in most TCD (non-imaging) transducers is typically |
1 to 2 MHz |
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The imaging frequency found in most TCDI (duplex) transducers is typically |
4 MHz |
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The Doppler frequency found in most TCDI (duplex) transducers is typically |
2 to 3 MHz |
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With transcranial Doppler, why is spectral broadening unavoidable? |
The sample gate is relatively large compared to the size of the artery evaluated |
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Why are velocities acquired during a transcranial exam usually referred to as mean velocities? |
They typically represent the time-averaged velocities throughout an entire cardiac cycle |
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What are the main quantitative values used for diagnostic purposes in a transcranial exam? |
The mean velocities and the pulsatility index |
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All Doppler spectra obtained from examination of intracranial arteries should have low-resistance characteristics except those obtained in what artery? |
The ophthalmic artery |
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Because of individual variations of the temporal window, the area is often subdivided into what locations? |
Posterior, middle, anterior, and frontal locations |
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Circle of Willis |
A roughly circular anastomosis of arteries located at the base of the brain |
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collateral |
a vessel that parallels another vessel; a vessel that is important to maintain blood flow around another stenotic or occluded vessel |
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Lindegaard ratio |
middle cerebral artery mean velocity divided by the submandibular internal carotid artery mean velocity; this ratio is useful in differentiating increased volume flow from decreased diameter when high velocities are encountered in the MCA or intracranial ICA |
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Abbreviation for middle cerebral artery |
MCA |
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Abbreviation for internal carotid artery |
ICA |
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pulsatility |
expressed as Gosling's pulsatility index (peak systolic velocity minus end-diastolic velocity divided by the time averaged peak velocity) |
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Sviri ratio |
ratio calculation used to determine vasospasm from hyperdynamic flow in the posterior circulation; the bilateral vertebral artery velocities taken at the atlas loop are added together and averaged; this averaged velocity is then divided into the highest basilar mean velocity |
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transcranial Doppler |
A noninvasive test that uses ultrasound to measure the velocity of blood flow through the intracranial cerebral vessels |
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What is the abbreviation for transcranial Doppler? |
TCD |
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transcranial duplex imaging |
a noninvasive test on the intracranial cerebral blood vessels that uses ultrasound and provides both an image of the blood vessels as well as a graphical display of the velocities within the vessels |
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vasospasm |
A sudden constriction in a blood vessel causing a restriction in blood flow |
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What is the abbreviation for transcranial duplex imaging? |
TCDI |
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Who introduced TCD and TCDI? |
Rune Aaslid in 1982 |
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What patients did Aaslid apply TCD and TCDI to? |
patients with vasospasm secondary to subarachnoid hemorrhage. |
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What is the abbreviation for subarachnoid hemorrhage? |
SAH |
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What does TCD and TCDI provide? |
diagnostic information in patients with a variety of cerebrovascular diseases. |
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What complements the neuroimaging techniques of computed tomography with contrast, magnetic resonance imaging with contrast, and cerebral angiography? |
Transcranial Doppler and transcranial duplex imaging by providing physiological data in real time that can be repeated. |
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What is a valuable tool when considering the complex dynamics of cerebral blood flow? |
The ability to provide physiological data in real time that can be repeated by transcranial Doppler and transcranial duplex imaging. |
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What do TCD examination directly study? |
the intracranial conducting arteries that lie at the base of the brain, including the arterial anatomists called the circle of Willis and the major anterior and posterior arteries that supply the circle. |
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What does the numerical classification system of the cerebral arteries describe? |
Each arterial segment by name and number with the number referring to either the anatomical course or a branch point. |
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What is the abbreviation for the internal carotid artery? |
ICA |
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What is the anterior circulation of the circle of Willis formed by? |
The intracranial continuation of the internal carotid artery. |
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Where does the the ICA first become accessible by TCD exam? |
in the cavernous portion. |
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what is the cavernous portion usually referred to as? |
The carotid "siphon" because of its tortuous course. |
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What are the three segments the carotid siphon is broken down into? |
1) The parasellar 2) the Genu 3) the supraclinoid |
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What is the number classification of the parasellar? |
C4 |
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What is the number classification of the genu? |
C3 |
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What is the number classification of the supraclinoid? |
C2 |
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The ICA pierces the dura, then enters the subarachnoid space, and terminates C1 by |
dividing into the middle cerebral and anterior cerebral arteries. |
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What is the abbreviation for middle cerebral artery? |
MCA |
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What is the abbreviation for anterior cerebral artery? |
ACA |
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What are the significant branches to a TCD study that arise from from the distal ICA? |
The ophthalmic artery and the posterior communicating arteries. |
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What is the abbreviation for ophthalmic artery? |
OA |
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What is the abbreviation for posterior communicating artery? |
PCOA |
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What is the path of the middle cerebral artery? |
The MCA branches and courses laterally from the ICA as the main trunk (or M1 segment) and bifurcates or trifurcates into M2 branches that quickly angle upward into the insular area. |
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Is there any asymmetry between the left and right middle cerebral arteries? |
Very little |
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What is the ACA known as? |
A1 or precommunicating segment |
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Where does the ACA begin? |
It begins and courses medially from the ICA for a short distance before passing forward as the A2 or postcommunicating segment. |
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Where are the two ACAs connected? |
Above the optic chiasm by the anterior communicating artery (or the ACOA). |
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What do the frequent variations of between the two ACAs mainly consist of? |
Differences in diameter or curvature |
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What is the intracranial posterior circulation a continuation of? |
The vertebral arteries (or VA's) that pass through the foramen magnum and enter the subarachnoid space, which is the V4 segment, and course beneath the brain stem. |
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Where do the major branches, the posterior inferior cerebellar arteries (or PICA's) usually arise from? |
The distal part of the vertebral (V4) and supply the brain stem and cerebellum. |
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The VA's may have a (blank) course and often are of (blank) size. |
The VA's may have a tortuous course and often are of unequal size. |
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How is the Basilar artery (or BA) created? |
By the joining together of the two VA's and ends by terminating into the right and left posterior cerebral arteries (or PCA's). |
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What gives rise to two paried sets of branches, the anterior inferior cerebellar (AICA) and superior cerebellar (SCA) arteries along with numberous small penetrating branches? |
The basilar artery (or BA) |
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What is the initial short segment of the PCA arising from the BA and prior to the PCOA called? |
The P1 or precommunicating segment. |
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Beyond the short segment of the P1, it becomes the P2, or the postcommunicating segment, which goes where? |
It winds around the cerebral peduncle |
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What does the PCOA anatomically connect? |
The anterior and posterior circulations but may be hypoplastic. |
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The PCA normally arises from the BA but can have a "fetal origin" in 18% of the population. What does this mean? |
It is dependent on the ICA for flow, either exclusively or in combination with the BA. |
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What is the best way to prepare the patient for the exam? |
By using simple language explain to explain the test. Instruct the patient to be quiet, and , unless necessary, not to speak during the exam. |
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When performing an exam in the ICU what should you check with the nurse for before doing? |
Changing the level of the head. |
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What should you take and record with this exam? |
Blood pressure |
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How is the patient positioned during this examination? |
Supine with the head slightly elevated durng examination of the anterior circulation when using the transtemporal, transorbital, and submandibular approaches. |
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What is it advisable to use a rolled hand towel or a very small pillow ? |
to allow maximum access to the head and neck |
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What is a factor that is important to obtaining a good study? |
Stillness of the patient |
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What should be done to minimize variations in the spectral waveforms caused by fluctuating physiological variables? |
Allow time for the heart, respiratory rate, and blood pressure to reach a steady state before beginning the study. |
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Where do the VA's and BA require insonation from? |
Through the foramen magnum |
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What is the patient positioning for the exam? |
1) Place the patient in the lateral decubitus position supporting the face and head with a small pillow or towel with the neck aligned centrally.
2) Plapate at midline about 1.25 inches down from the skull base and flex the neck slightly. |
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How should the exam be performed if the patient cannot be turned on his or her side? |
The examination can be performed with the patient supine with the head rotated to the opposite side of insonation and the transducer placed just to the left or right side of the foramen magnum. |
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What is a feasible alternative position for ambulatory patients? |
The upright sitting position with the neck flexed slightly and the head supported by the patient's arms and hands for stabilization. |
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What position can be done for patients in ICU or other hospital inpatients that cannot be turned or optimally positioned? |
The head can be propped up using a rolled towel and turned away from the side of insonation |
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The position of the sonographer may vary according to (blank) |
the setting. |
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How can a sonologist avoid tendonitis and other injuries of the hands? |
Grip the transducer with minimal pressure, rest when the hands become tired, and seek out preventative exercises from an ergonomics specialist. |
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What type of equipment is utilized for TCD and TCDI examinations? |
A dedicated nonimaging TCD instrument that uses a 1 to 2 MHz pulsed wave transducer, spectral analysis, and additionally, may have M-mode capabilities. |
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What does the software in the equipment allow for? |
The computation of peak systolic velocity, end-diastolic velocity, time averaged peak velocity, and Goslings pulsatility index at a minimum. Additional software will function for specific applications such as monitoring for emboli, trending velocities, and displaying temporal changes in velocity. |
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What are the cursors and spectral outline tracers available for? |
To compute values when automatic computations are erroneous. |
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What does the addition of power M-mode do? |
Uses simultaneous signal acquistion from 32 gates to create a display that demonstrates flow intensity and direction in bands of color. |
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What is the display range and correspondence? |
The display ranges from 25 to 85 mm and corresponds to the course and depth of the arteries. |
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What does the information in the power M-mode display help the user find? |
Signals by creating a kind of visual road map much in the way color flow facilitates duplex imaging. |
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Standard duplex ultrasound technology allows for TCDI exams through... |
The use of a broadband phased-arry transducer with a Doppler frequency range usually of 2 to 3 MHz and imaging frequencies in the range of 4 MHz software provides computational packages similar to those found on dedicated TCD systems |
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Why is TCDI not routinely used for monitoring applications? |
Because the transducer size is too large to attach to the head and most companies have not developed instruments, hardware, or software for these applications |
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In general, what is documentation for both TCD and TCDI based on? |
Spectral waveforms |
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What does the B-mode and color Doppler information yielded in TCDI studies primarily facilitate? |
Acquisition of spectral Doppler signals by providing a kind of color road map. |
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What are the exceptions to the B-mode and color Doppler information yielded in TCDI studies? |
Color or power Doppler signals supporting identification of anomalous vessels and B-mode providing evidence of brain midline shifts and the visualization of masses. |
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What does M-mode capture? |
High intensity transient signals representing emboli. |
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Documentation will vary according to... |
The type of study being performed, specifics of the study, why it was ordered, and which arteries are of interest. |
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What are the intracranial arteries a continuation of? |
The cervical internal and vertebral arteries. |
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What order of examination for the intracranial arteries will help facilitate interpretation? |
Examining them in a proximal to distal order |
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What constitutes a complete study? |
Spectral Doppler waveforms from each of the listed arterial segments from the right and left cerebral hemispheres and posterior circulation. |
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What may be required when pathology is present? |
Additional waveforms to demonstrate abnormal flow characteristics. |
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What are some reasons for a limited TCD? |
Repeat exams of affected vessels only, acute stroke when using a fast protocol to determine single vessel patency, when monitoring for microemboli, or when monitoring during an intervention. |
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What is the minimum documentation in normal exams? |
one spectral waveform from each artery or arterial segment studied |
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Multiple waveforms may be required to demonstrate... |
the pathologies that are required for an adequate interpretation to be made. |
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What is essential since interpretation depends almost entirely on these signals? |
Acquisition of a good spectral Doppler waveform from each required segment |
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The sample volume size in TCD studies is... |
relatively large in comparison to the size of the arteries. |
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What is the average size of the arteries? |
On average, only 2 to 4 mm in diameter |
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Why do normal waveforms have the appearance of spectral broadening? |
Because of the sample volume size in relation to the size of the arteries. |
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What is the biggest difference between TCD and extracranial velocity calculations? |
The common use of the TAP-V obtained from the entire cardiac cysle. |
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What is the TAP-V used for? |
Interpretation rather than the single point PSV and EDV used in extracranial carotid studies. |
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The value of TAP-V is often referred to as |
the mean velocity |
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What is used along with quantitative values of mean velocity and PI? |
Waveform morphology and specific signatures seen int he amplitude of the waveform to make the formal interpretation in adults. |
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What are very high velocities and turbulent flow simultaneously displayed in? |
Signals detected in severe stenosis, vasospasm, collateral, and hyperdynamic flow creating complex waveforms. |
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What do instruments generally use that allows for real-time calculations of appropriate values? |
An envelope trace |
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When do envelope tracers frequently fail to follow the true waveform outline and manual calculations become necessary? |
When the velocities become too complicated |
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Different calculation methods are employed depending on what? |
equipment |
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One style of equipment requires setting two cursors at the (blank) and (blank) and the second allows the user to (blank) the waveform contour with a cursor. |
One style of equipment requires setting two cursors at the PSV and EDV and the second allows the user to trace the waveform contour with a cursor. |
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All of the arteries examined during a TCD exam supply the brain with relatively high flow during diastole, except for... |
The OA |
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What are the reasons for the wide range of normal values? |
Age, gender, cardiac effects, and other intrinsic and extrinsic physiologic variables. |
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What are waveforms evaluated for? |
Both quantitative and qualitative characteristics with knowledge of physiological variables that can significantly influence flow findings |
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Doppler signals are (blank) as well as (blank) in the spectral waveform. |
Doppler signals are audible as well as visible in the spectral waveform. |
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What has the trend been towards with the increased sophistication of ultrasound instrumentation? |
Diminishing the importance of hearing Doppler sounds. |
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What is the advantage of hearing a waveform? |
The human ear and brain are exquisitely designed to perceive subtle audio nuances and, when used for vascular studies, provide a feedback loop that informs the hand how to move to acquire a stronger signal and to increase gain to visualize the low amplitude, high velocity (pitch) signals that are otherwise drowned out by the high amplitude, low velocity turbulent signals. |
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What drives the acquisition of good signals during non-imaging TCD but should not be minimized during TCDI examinations? |
Good listening skills |
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What uses the same regions of the cranium to gain access into the basal cerebral arteries? |
Both TCD and TCDI |
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What are the four approaches or acoustic windows used for? |
To gain access into the cerebral vasculature |
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What are the four acoustic windows used to gain access into the cerebral vasculature? |
Transtemporal, transorbital, suboccipital and submandibular |
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What does the fifth approach involve? |
Obtaining the vertebral artery signals at the atlas loop and is used to facilitate calculation of a ration specific to basilar artery vasospasm. |
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Where is the transtemporal approach located? |
Over the temporal bone, superior to the zygomatic arch, and anterior and slightly superior to the tragus of the ear conch. |
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There is significant attenuation of the ultrasound at this interface depsite what? |
The relative thinness of the temporal bone. |
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What did early experiments measuring ultrasound energy transmission through the temporal bone show? |
A large range of energy losses occurred between different skull samples and depended on the thickness of the bone. |
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There are (blank) variations in location of the temporal window. |
There are individual variation in the location of the temporal window. |
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How is the temporal window subdivided? |
Posterior, middle, anterior, and frontal locations. |
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What should be done to find the site of optimal ultrasound penetration? |
All areas should be thoroughly explored. |
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What determines the orientation of the transducer to the initial target of the MCA? |
Window location |
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What will each area require in order to be on axis with the arterial flow? |
A somewhat different transducer angulation |
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how is the beam angled from the posterior window? |
Slightly anterior and from an anterior or frontal window, it is aimed more posterior |
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What does the middle window general require? |
A direct, neutral orientation |
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What does the orbital approach reliy on? |
The transmission of the ultrasound beam through the thin orbital plate of the frontal bone, optic canal, and superior orbital fissure |
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What is lower in the orbital approach than for the temporal bone? |
Signal attenuation |
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Why is the power intensity reduced? |
To limit direct exposure to the eye |
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What is the power intensity guided by? |
Manufacturer's rcommendations and the ALARA principle. |
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What the approach for the foramen magnum? |
The natural opening in the skull through which the spinal cord passes. |
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Where is the transducer placed for the foramen magnum approach? |
Approximately 1.25 inches below the base of the skull and sound beam is aimed toward the nasion. |
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The amount of (blank) in the area of the foramen approach varies considerably between individuals and will influence the (blank) at which the vertebral and basilar arteries are identified. |
The amount of soft tissue in the area of the foramen approach varies considerably between individuals and will influence the depths at which the vertebral and basilar arteries are identified. |
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Why is the submandibular approach notably different than the standard technique used to study the carotid arteries with a linear probe at a 60 degree angle? |
The power can be quite low because the sound is not penetrating bone. |
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How is the retromandibular ICA signal obtained? |
By using the TCD transducer and a zero degree angle of insonation. |
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Where is the transducer placed with the submandibular approach? |
At the angle of the jaw with the beam-directed cephalad. |
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What are the signals obtained usually used for? |
To calculate a lindegaard ratio in patients with vasospasm secondary to SAH or for documenting distal ICA stenosis arising from firbromuscular dysplasia and dissections |
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Which approach was originally described by von Reutern to study the extracranial VA using continuous wave Doppler? |
Atlas loop approach |
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Describe the atlas loop approach |
Used to study the extracranial VA using continuous wave Doppler, obtaining VA signals at this location is used to calculate the BA/VA ratio, which, similar to the Lindegaard ratio, is useful to categorize a vasospasm or to confirm disease in routine examinations. |
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Where is the transducer placed in the atlas loop approach? |
Approximately 1.25 inches below the mastoid process and behind the sternocleidomastoid muscle. |
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Why can the power be lowered in the atlas loop approach? |
It is an extracranial signal and does not require penetration of bone |
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What is a diagnostic tool used in the clinical management of patients with a variety of intracranial vascular abnormalities? |
TCD studies |
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What might the results provide rational for? |
The treatment of brain ischemia and stroke |
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What does a complete standard TCD exam consist of? |
Pulsed wave Doppler insonation of the basal cerebral arteries including the bilateral cavernous and terminal segments of the ICA's, OA's, MCA's, ACA's, PCA's, VA's, and the BA. |
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Why, in some populations, will the extracranial retromandibular ICA's and VA's at the atlas loop be examined? |
To calculate vasospasm ratios |
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In what fashion are Doppler spectral waveforms acquired? |
In a blind fashion without the aid of B-mode or color Doppler |
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What is required in order to acquire Dopple spectral waveforms? |
A good understanding of the anatomy and physiology of the intracranial vessels and a precise, systematic approach to the exam performance. |
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What is the abbreviation for the ophthalmic artery? |
OA |
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What is the number of waveforms for the ophthalmic artery? |
1 |
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What is the abbreviation for the carotid siphon? |
CS |
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What is the number of waveforms for the carotid siphon? |
3 |
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What are the three waveforms for the carotid siphon? |
C2 (supraclinoid), C3 (genu), C4 (parasellar if accessible) |
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What is the abbreviation for the terminal internal carotid artery? |
TICA |
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What is the number of waveforms for the terminal internal carotid artery? |
1 |
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What is the one waveform for the terminal internal carotid artery? |
C1 |
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What is the abbreviation for middle cerebral artery? |
MCA and MCA2 |
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What is the number of waveforms for the middle cerebral artery? |
3 |
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What are the waveforms for the middle cerebral artery? |
proximal, mid, and distal, including MCA2 branches |
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What is the abbreviations for the anterior cerebral artery, precommunicating segment? |
ACA |
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How many waveforms does the anterior cerebral artery have? |
1 |
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What is the abbreviation for the anterior cerebral, post-communicating segment? |
ACA2 |
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How many waveforms does the anterior cerebral, post-communcating segment have? |
1, but this only applies to TCDI |
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What is the abbreviation for the Anterior communicating artery? |
ACOA |
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How many waveforms does the anterior communicating artery have? |
1, when functioning as collateral |
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What is the abbreviation for the posterior cerebral artery, precommunicating segment? |
PCA1 |
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How many waveforms does the posterior cerebral artery, precommunicating segment, have? |
1 |
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What is the abbreviation for the posterior cerebral, post-communicating segment? |
PCA2 |
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How many waveforms does the posterior cerebral, post communicating segment have? |
1 |
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What is the abbreviation for the posterior communicating artery? |
PCOA |
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How many waveforms does the posterior communicating artery have? |
1 when functioning as collateral |
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What is the abbreviation for the submandibular internal carotid artery? |
SM-ICA |
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How many waveforms does the submandibular internal carotid artery have? |
1 when calculating Lindegaard index or documenting distal narrowing |
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What is the abbreviation for the vertebral artery? |
VA4 |
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How many waveforms does the vertebral artery have? |
3 |
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What are the 3 waveforms of the vertebral artery? |
proximal, mid, and distal |
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What is the abbreviation for vertebral at the atlas loop (V3)? |
VA3 |
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How many waveforms does the vertebral at the atlas loop have? |
0 when calculating Sviri ratio for vasospasm |
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What is the abbreviation for the basilar artery? |
BA |
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How many waveforms does the basilar artery have? |
3 |
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What are the waveforms of the basilar artery? |
proximal, mid, and distal |
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What are the five primary criteria used to identify each vessel segment? |
1) Approach: each cranial window provides access to specific arteries only.
2) Sample Volume Depth: Each artery has a specific range of depths over which it courses.
3) Direction of blood flow relative to the ultrasound transducer.
4) The spatial relationship of one artery to another. For the anterior circulation, the reference vessel used to identify other arteries is the birfurcation of the terminal ICA.
5) Flow velocity: In general, the MCA>ACA>PCA=BA=VA. These relationships assist vessel identification and, when reversed, can be helpful in identifying pathological flow states. |
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What are the arteries identified through the orbital window? |
The OA and cavernous carotid, also known as the cavernous siphon. |
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Why is the patient asked to close his or her eyes gently and keep them shut until the end of the orbital exam? |
To avoid getting ultrasound gel into the eye. |
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What is the transducer placement for an orbital approach? |
The transducer is placed gently over the center of the closed eyelid and aimed 15 degrees to 20 degrees, toward the midline, and without applying any pressure to the eye. |
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At what sample volume depths can the OA be identified isolated away from the carotid siphon? |
40 to 60 mm |
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How does the unique waveform of the OA look? |
It has low velocities and, due to the higher resistance bed of the eye compared with the brain, typically have low diastolic flow. |
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Why is the OA studied? |
To determine if flow is antegrade or retrograde. |
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What is a retrograde indicative of? |
An external carotid artery (ECA) to ICA collateral flow. |
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What can be detected by increasing the sample volume to 60to 70 mm? |
Flow in the carotid siphon |
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What is the reasoning behind the name of carotid siphon? |
Because of its tortuous course at this location resulting in flow directionality that may be toward, away, or bidirectional depending on the orientation of the vessel segment to the transducer (although normally, the physiological direction of flow is antegrade). |
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What are the arteries identified through the transtemporal approach? |
The MCA (M1 and proximal M2 segments), the ACA (A1 segment), the terminal ICA (TICA), and the PCA (P1 and proximal P2 segments). |
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When are the ACOA and the PCOA usually only identified? |
When they are carrying an increased volume flow because they function as collaterals. |
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Finding the exact location on the temporal bones that allows the best ultrasound penetration can be ... |
Challenging |
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How will finding the exact location on the temporal bones that allows the best ultrasound penetration be facilitated? |
By being systematic in the exploration of this area and using small hand movements. Power is set at maximum and the sample volume is placed at a depth of 50 mm with the intention of finding the MCA |
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How is the exam of a temporal approach performed? |
By placing the transducer int he posterior window, aiming the beam slightly anterior and superior, and using a circular motion scanning for an audible Doppler signal and visual spectral display. |
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What is done if M-Mode is used? |
Employ the same manual technique while also observing the M-mode display for a red color band at depths ranging from 30 to 65 mm. |
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If weak or no signals are obtained, what is done? |
The transducer is systematically moved to the middle and anterior or frontal locations and scanning is repeated until signal acquisition is accomplished. |
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Once a suitable acoustic window is identified in the temporal approach, where does emphasis change to? |
Identifying each arterial segment. |
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Where do initial signals directed toward the transducer at a depth of 50 mm most often arise from? |
the MCA |
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When can the short segment of the ACA be especially challenging to identify with color flow? |
When the vessel is not oriented axially to the MCA |
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What transducer adjustments are helpful if the ACA is not seen in tandem with the MCA? |
1) twist the front end of the probe upward 2) slide the probe upward 3) tilt the probe upward |
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Does the ACA lie in proximity to bone? |
No |
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Will the surround B-mode image of the ACA display the bright boney reflections seen surrounding the TICA? |
No |
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What is the length of the precommunicating segment of the ACA? |
Short and ends at midline |
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Where can the proximal postcommunicating segment often be seen? |
Coursing toward the left of the screen (anterior) |
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What color is the ACA on color Doppler? |
Blue, but can change direction when acting as collateral. |
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What size increments should the spectral Doppler waveforms be taken in? |
5-mm increments |
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If the color box does not fill, what should you try? |
Using the spectral Doppler at the anticipated location for the ACA |
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What does the ACA have a high incidence of? |
Anatomical variation and may be hypoplastic or atretic, and most often exhibits asymmetries in the caliber between the right and left sides. |
