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Diagnostic Medical Sonography Program
• Chapter 19: Carotid Duplex Scanning and
Color Flow Imaging
• PART B
• Holdorf
Aliasing
• Misrepresentation of Doppler signal due to
limitations of the equipment used, i.e., a low PRF
• Maximum frequency is ½ PRF: flow information
greater than ½ PRF cannot be displayed (Nyquist
limit)
• Wave form has flat, crew-cut appearance
• Methods of increasing the PRF/Nyquist limit
include:
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Decrease the baseline: increase Doppler Scale
Change transducer frequency
Alter angle of insonation
Decrease depth
Use continuous-wave Doppler
Aliasing
Mirror Imaging
• Doppler shifts above and below baseline
• Display duplicate spectrum or color-flow
Doppler
• Artifact from strong reflectors (e.g., pleural
lining) or too much gain.
Helical Flow
• Occurs when flow moves into a wider portion
of the vessel (e.g., carotid bulb)
• Doppler shifts above / below baseline
• Spectral waveforms are different
• Doppler angle constantly changing
• Flow is not laminar; spectral broadening
present
Helical Flow
Intraoperative Monitoring
Capabilities
• Identification of defects secondary to surgery
and or areas of platelet aggregation
• Evaluates hemodynamic significance of wall
irregularity
Intraoperative Monitoring
Technique
• Use highest frequency transducer (e.g., >
12MHz)
• Sterile sleeve/plastic bag containing acoustic
gel
• Wound filled with sterile saline
• Areas of flow disturbance identified with
color-flow Doppler
• Gray scale imaging critical in detecting subtle
wall defects
Intraoperative Monitoring
• Capabilities:
– Identification of defects secondary to surgery and
or areas of platelet aggregation
– Evaluates hemodynamic significance of wall
irregularity
• Technique:
– Use highest frequency transducer (e.g., > 12MHz)
– Sterile sleeve / plastic
Common Carotid Massage of
The Carotid Sinus
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What is the Carotid Sinus; What does it do?
•
Why would Carotid Sinus Massage be
performed? (Indications)
•
What would be the reason that a Carotid
Sinus Massage be done?
(Contraindications)
Anatomy effected by Carotid Sinus
Massage.
The dilated area at the
base of the ICA (internal
carotid artery), directly
superior to the
bifurcation.
• Has baroreceptors
present that detect
blood pressure as
blood moves
through the artery.
• Baroreceptors are
mechanical
receptors that help
in the regulation of
blood pressure.
Anatomy effected by Carotid Sinus Massage
•
•
•
•
Carotid sinus
Internal carotid artery
External carotid artery
Vagus,
Glossopharyngeal,
and carotid sinus
nerves
• Cardiac plexus
• Heart (slowing heart
rate and lowering
blood pressure)
Anatomy effected by Carotid Sinus Massage
Indications for Carotid Sinus
Massage.
•Used to evaluate function of permanent
pacemakers
•Used in cases of unexplained dizziness,
falls, or faints.
Indications for Carotid Sinus
Massage
•Can be used to slow down the heart and stop arrhythmia.
•Used to diagnose tachyarrhythmia.
Overall Contraindications to a
Carotid Sinus Massage
If the patient has any history of:
•Heart Attack
•TIA
•Carotid Artery Occlusion
•Previous Adverse affect to Carotid Sinus Massage
Carotid Sinus Massaging can be
Unknowingly Dangerous
• The most common danger
is when patient has an
unknown plaque build up:
• Plaque could
potentially dislodge
causing:
• Transient Ischemic
Attack (TIA)
• Stroke
Additional Notes
Lecture 19:
Carotid Duplex/Color flow imaging
• Compensatory flow coming from Contralateral
occlusion
• Ipsilateral vs. Contralateral (know the
difference)
Physical Principles
CW Doppler
• No depth perception
• Cannot obtain a small sample volume (It is a fixed
sample size)
Normal spectral analysis
• ICA with CW will have a filled spectral window
• ICA with Pulsed Doppler – look for the Window in
pulsed Doppler
• Color Doppler displays an average of the
frequencies
Normal Doppler signals
• Dicrotic notch clearly seen; oscillations in waveform
seen with tapping of the superior temporal artery
• (Temporal TAP) Do this in front of the ear
Abnormal Doppler signals
• C. Consider disease at carotid siphon when high
resistant flow patterns evident in ICA
• Think Distal problem
• E. Diminished velocities unilaterally suggest proximal
disease, e. g. innominate or common carotid artery.
– Think PROXIMAL disease
– If bilateral disease, think HEART problem
Regarding the chart: % stenosis, PSV, EDV
Draw a line between Less than 50% and 50-79%
Including and above Less than 50% is considered
NOT hemodynamically significant disease
< 125 cm/sec is the number you need to remember
Not including and below Less than 50% is
considered hemodynamically significant disease
> 125 cm/sec is the number you need to remember
ALSO, the number < 140 cm/sec is significant, in
that it signifies that stenosis is 50-79% (borderline
significant disease). Over 140cm/sec is significant
Pre-occlusive Doppler Thumping means that
there is DISTAL disease.
Mirror imaging
Can be seen in the subclavian artery
• Can be caused by TOO MUCH GAIN.
• Displays are not supposed to look like this;
wave forms immediately below one another.
• Helical Flow occurs at the carotid bulb and is
not a mirror image artifact (waveforms are not
demonstrated one above the other.
Homework
• Textbook: Chapter 20: Carotid Duplex
Scanning and Color Flow Imaging
– Pages: 221 – 238
• SDMS Assignments