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: 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

What is the Carotid Sinus; What does it do? Anatomy effected by Carotid Sinus Massage. Why would Carotid Sinus Massage be performed? (Indications) What would be the reason that a Carotid Sinus Massage be done? (Contraindications)

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

Anatomy effected by Carotid Sinus Massage 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