INVESTIGATION

1. INVESTIGATION Non-invasive Vascular Assessment (NIVA) The Carotid Duplex Ultrasonography

2. What is Non-invasive Vascular Assessment? • NIVA uses advanced imaging techniques to painlessly evaluate the circulatory system without the use of needles, dye or radiation • NIVA includes ultrasound, which uses sound waves far above the range of human hearing to look inside the veins and arteries or listen to the sound of blood flow • Complementary information can be obtained for diagnosis of cerebrovascular disease in patients with acute, subacute, chronic, or asymptomatic conditions. These techniques are also used for monitoring purposes, followup studies, clinical trials evaluating the benefit of medical and surgical procedures and for treatment and prevention of stroke

3. Carotid duplex ultrasonography • It combines high-resolution gray scale imaging and pulsed Doppler spectral analysis to yield excellent anatomic and physiologic data • In addition, color-flow imaging helps the examiner and interpreter confirm vessel orientation, anatomic variants and various pathologies • Carotid duplex ultrasound can reliably detect stenotic disease that may be the source of an embolus in a stroke patient • Also, ultrasonography can be used to confirm occlusion of the internal carotid artery, which may also produce a stroke.

4. What will happen during a Carotid NIVA Exam? • GEL - neck area • TRANSDUCER - converts electrical energy into sound waves - placed over each side of the neck - Sound waves bounce off the organs and tissue in the body and the blood moving in the arteries AND creates echoes that are reflected back to the transducer • TELEVISION MONITOR - shows images as the transducer converts the echoes to electronic signals • These IMAGES may beviewed immediatelyorphotographed for further study This exam takes 45 to 60 minutes

5. The ultrasound demonstrates grey scale imaging in the upper portion with spectral Doppler graphed on the bottom.  The velocity measured at 3 meters/second is elevated and signifies an area of stenosis.  Also the waveform is broadened consistent with flow disturbance which is seen in regions of stenosis.

6. The procedure is done in the CCA, internal carotid artery (ICA), and external carotid artery (ECA); at least 2 or 3 spectral analyses of each vessel should be obtained • Color imaging and Power Doppler may be used but may not necessarily provide additional information. • After assessment of the anterior circulation, the vertebral circulation is assessed. Usually, the C4-C6 segment is accessible

7. Power Doppler • · Color imaging that is independent of direction or velocity of flow • · Gives “angiographic-like” picture of artery • Power Doppler: Observation of flow is independent of velocity or direction.

8. Plaque Characteristics • The primary purpose of carotid scanning is the detection and assessment of carotid stenosis • Ultrasound has been used to image and characterize plaque within the carotids. It is characterized as low, medium, or high in echogenicity and as homogenous or heterogenous. • Low echo plaque contains a large amount of lipid material and is difficult to image. Moderate echo plaque is fibrous plaque made up of collagen and lipids. Strong echo plaque has strong reflections caused by vessel calcification. • Calcified plaque can also be termed as heterogenous. Homogenous plaque is more uniform in texture.

9. When disease is detected in the carotid arteries, it is important to measure prestenotic, stenosic, and post stenotic velocities. It is very important that velocities are taken at the highest velocity.

10. Degree of Stenosis • The most commonly used methods of acoustic estimation of the degree of stenosis include the following: • ·Measurement of peak systolic velocities (PSV) and peak diastolic velocities (PDV) • ·Measurement of peak systolic frequencies (PSF) and peak diastolic frequencies (PDF) • ·Measurement of ratios (eg, ICA systolic frequency/CCA systolic frequency)

11. General rules of thumb • PSVs over 200 cm/s or PSFs over 5 kHz correspond to stenosis greater than 50% • As stenosis approaches 80-99%, PSVs and PSFs tend to rise (as high as 400 cm/sec and 10 kHz, respectively), and the PDVs and PDFs tend to rise as well (often over 150 cm/s and 2.5 kHz, respectively) • With stenosis over 90% (near occlusion), velocities and frequencies may actually drop as mechanisms to maintain flow fail • Ratios may be particularly helpful in situations in which cardiovascular factors (eg, poor ejection fraction) limit the increase in velocity and frequency. In such cases, ICA/CCA ratios above 3 may signify significant stenosis

12. Vessel Identification • Common carotid artery (CCA) • ·Pulsatile walls • ·Smaller caliber than jugular vein • ·Systolic peak and diastolic endpoints in between that of external and internal carotid arteries on spectral analysis

13. Distinguishing internal and external carotid arteries • Differentiating between the ICA and ECA is probably the most difficult part of a carotid exam • Anatomically, the ICA usually runs more posterior and lateral, while the ECA runs more anterior and medial. The ICA is normally larger than the ECA and slowly tapers as it travels toward the head. The extracranial ICA has no branches • The ECA has many branches to feed the neck and face • Vessel identity can be aided by spectral and color Doppler. Differences in pulsatility between the ICA and ECA are also visible with color flow Doppler

14. Internal Carotid artery as seen on spectral analysis • Note that flow is continuous through diastole. • The ICA has a low resistance waveform with a blunted systolic upstroke and more diastolic flow • Blood flow continues throughout the entire cardiac cycle in the ICA resulting in continuous color fill

15. External Carotid Artery as seen on Spectral analysis • Note the absence of flow in diastole and the sharp upstroke in systole • The ECA waveform is more high resistance with a steeper systolic upstroke, and little to no diastolic flow • In the ECA, color flickers or flashes because flow is diminished or absent in diastole .

16. ICA ECA

17. Advantages • Carotid duplex ultrasonography (CUS) is a useful diagnostic tool for assessing cervical carotid artery disease and examine the extracranial cerebrovascular system. • Duplex scanning can localize arterial disease in the extracranial carotid arteries • It can differentiate between a tight stenosis and occlusion • This exam provides information about the surface character of plaque and can also evaluate pulsatile masses in the carotid. • It is noninvasive, safe and relatively inexpensive.  • It does not involve use of radiation or contrast dye

18. Limitations • Patients may have dressings, skin staples, or sutures that interfere with the exam • The size and contour of the neck can also make the exam difficult • Acoustic shadowing from calcified vessels may impair visualization • Disease can be over estimated when an artifact is mistaken for plaque • Disease may also be underestimated by failing to appreciate the low level echoes of soft plaque • Using the wrong Doppler angle can either over or under estimate the severity and extent of the disease.