Peak systolic velocities (PSV) were assessed with duplex ultrasound (DUS) at baseline, at 30 days, and at 12 and 24 months after . 76-year-old asymptomatic man with normal carotid and vertebral spectral tracings.Doppler sonogram shows external carotid artery that supplies high-resistance vascular beds of osseous and muscular structures of head and neck; thus, waveform is characterized by sharp rise in flow velocity during systole, rapid decline toward baseline, and diminished diastolic flow. In addition, ulcerated plaque that demonstrates a focal depression or break within the plaque is also more prone to plaque rupture and subsequent embolic event ( Fig. Instant anatomy. This test is done as the first step to look at arteries and veins. While this is not a major problem in peripheral arteries when the original lumen is visible on both sides of a stenosis, lesions at the origin of the ICA typically do not have a normal lumen on both sides. The SRU consensus conference proposed the following Doppler velocity cut points: An internal to common carotid peak systolic velocity ratio <2.0, 125cm/s but <230cm/s peak systolic velocity of the ICA, An internal to common carotid PSV ratio 2.0 but <4.0, An end-diastolic ICA velocity 40cm/s but <100cm/s. The SRU consensus data represent a compromise between sensitivity and specificity and are based on cut points validated against ACAS/NASCET-based angiographic measurements of stenosis severity ( Table 7.2 ; Figs. 1B. For example enlarged lymph nodes or thyroid pathology. The diastolic component of the waveform also shows typical differences with the ICA having the highest diastolic component, the external the lowest, and the CCA an appearance somewhere in the middle. Ensure you angle correctly to the direction of the flow indicated by the colour doppler prior to calculating velocity. The ICA Doppler spectrum typically shows a low-resistance pattern. Saunders, Philadelphia, PA. 2012. Gray's Anatomy (39th edition). 2010;51 (2): e40-2. This involves gently tapping the temporal artery (approximately 1-2cm anterior to the top of the ear) whilst sampling the ECA with doppler. One of the most frequently asked questions, in carotid ultrasound is: how can I tell if the vessel I am imaging is the internal- or the external carotid artery?" The CCA is readily visible. Along its course, it rapidly diminishes in size and as it does so, gives off various branches (see below). 3. The transverse position enables the sonographer to follow the carotid artery in a transverse plane along its entire course in the neck, which is useful for initial identification of the carotid, its branch points, and position relative to the jugular vein. It is advisable to place the Doppler sample volume as far distal in the artery as possible. FIGURE 7-2 Off-axis view of the carotid wall. Elevated velocities can also be found with entities other than significant stenosis such as in young athletes, in high cardiac output states, in vessels supplying arteriovenous fistulas or arterial venous malformations, and in patients with carotid stenting. Common carotid occlusion is simple to detect using duplex ultrasound; however, no consensus on stenosis criteria exists due to the lack of published data and its uncommon occurrence compared to the internal carotid distribution. Since the ultrasound transducer typically measures 4 cm, it can be used to help locate this point by placing one end at the level of the bulb and sampling at the mid transducer, or approximately 2 cm below the beginning of the bulb. Criteria may vary slightly by institution. Vertebral Arteries Next chapter: 9. Significant undulation and thickening of the intima indicate more advanced changes due to atherosclerosis (see Chapter 8) or, rarely, fibromuscular hyperplasia. 7 Normal Findings and Technical Aspects of Carotid Sonography. Temporal Tapping may also be used to confirm that you are examining the ECA. If significant plaque is present in the ICA, the degree of luminal narrowing can be estimated in the transverse plane by comparing the main luminal diameter and residual lumen diameter (the diameter that excludes plaque) and using it as a qualitative adjunct to the measurement of stenosis severity based in the peak systolic velocity (PSV). The carotid sinus originates along the medial wall of the proximal ICA where it is adjacent to the external carotid artery (ECA). Because the diastolic velocities are lower in the external versus the internal carotid artery we can also observe less color Doppler filling in the external carotid artery during diastole (there is more color pulsation). The outer layer is the adventitia, which is composed of connective tissue. A temporal-tap (TT) was employed here to confirm it was the ECA. Measure the Peak Systolic (PSV) and end diastolic velocities (EDV). Lancet. "Information is very informative and valuable to my area of practice. CCA = common carotid artery. Doppler blood flow velocity measurements should be obtained from the proximal and distal CCA and the proximal, mid, and distal ICA. Measurement of degree of stenosis by duplex is assessed using a set of three criteria: internal carotid artery peak systolic velocity, end diastolic velocity (EDV), or the ratio of the ICA PSV to the CCA PSV as measured 2cm below the carotid bulb. There is wide variability in the peak systolic velocities seen in normal patients, with a range of 20 to 60 cm/s, with an even wider range noted at the vertebral artery origin (also called segment V0). low CCA: Waveforms in the very low common carotid artery (CCA) show some pulsatility due to the closeness of their origin or to the angle made as the carotid enters the neck. Ultrasound of Normal Carotid bifurcation with the ICA bulb and branch off the ECA. Considerable patient-to-patient variability occurs in ECA flow velocity in normal individuals because pulsatility varies considerably from one person to another since some individuals have a sharply spiked systolic peak, while others have a more blunted peak. Tortuous segments, kinks, or areas of branching disrupt the normal laminar flow pattern. The Spectral Doppler tracing resembles that of the internal carotid artery with a relative high diastolic velocity. George Thieme Verlag. Ultrasound of Normal Common Carotid artery (CCA). high CCA: Waveforms in the common carotid artery close to the bifurcation show moderately broad systolic peaks and a moderate amount of blood flow throughout diastole. Peak systolic velocities over 100cm/s are generally accepted to be abnormal; however, anatomic variations such as vessel kinking and tortuosity can occasionally elevate velocities in the absence of true disease. Elevated velocities can be seen in normal carotid arteries that diverge from a straight line and become curved. normal [1]. 2010;51(1):65-70. The younger patient has higher blood flow velocities 100 cm/sec? The thickness of the intima cannot be directly imaged from the ultrasound image since it typically measures 0.2 mm or less and is below the resolution of transcutaneous ultrasound. The internal carotid artery supplies the brain while the external carotid artery supplies extracranial structures of the head and neck. towards the head (normal) or retrograde (suggesting subclavian steal syndrome). The ICA will have low resistance flow, with constant forward flow during diastole. In a normal carotid US examination, the color velocity scale should be set between 30 and 40 cm/sec (mean velocity). Elevated velocities can be seen in normal carotid arteries that diverge from a straight line and become curved. The diagnostic strata proposed by the Consensus Conference of the SRU (0% to 49%, 50% to 69%, and 70% but less than near occlusion) represent practical values that are clinically relevant and consistent with the NASCET. If you like the way we teach, please leave a message! They arent always the same and it may not be in the centre of the vessel. The CCA shares the appearance of both waveforms. Is the ICA high or low resistance? As discussed in Chapter 3, the Doppler spectral waveforms are almost always altered in the region of the bulb (see Figure 7-4), a reflection of the complex flow dynamics that occur at this location.6, Peak systolic ICA velocities as high as 120 cm/sec have been reported in some normal adults, but these values are exceptional, and an ICA velocity exceeding 100 cm/sec should be viewed as potentially abnormal in older individuals. Look for stenoses highlighted by aliasing in the colour doppler. ICA = internal carotid artery. Executive Committee for the Asymptomatic Carotid Atherosclerosis Study. Although the so-called NASCET method may not truly reflect the degree of luminal narrowing at the site of stenosis, this method has the advantage of minimizing interobserver error. CCF-Neuro-M.D.-PW Blood flow velocity (which is what the test measures) is not exactly constant every time you measure. The Doppler spectrum sampled at this site is shown at the bottom of the image and demonstrates the complex flow pattern with some red cells moving forward and others backward. Begin proximally in transverse and follow distally to the bifurcation. In addition, when statins were started on asymptomatic patients prior to CEA, the incidence of perioperative stroke and early cognitive decline also decreased. CHF) CCA velocity >100: hyperdynamic (i.e. The vascular diagnostic community is divided into two groups: 1) those that perform duplex Doppler examinations using a 60 degree Doppler angle between the ultrasound beam and the vessel axis, and 2) those that use a convenient angle less than or equal to 60 degrees [ 28 ]. The innermost layer abutting the lumen is the intima, or endothelial lining of the artery. The transition between media and adventitia also corresponds to the external elastic lamina as seen on pathologic studies. There is a distinct difference in the spectral Doppler pattern between the external and internal carotid artery. Stenoses of the external carotid artery (ECA) are not considered clinically important but should be reported because they may explain the presence of a bruit on clinical examination and need to be considered by the surgeon at the time of carotid endarterectomy (CEA). FIGURE 7-5 Flow reversal. Thwin SS, Soe MM, Myint M et-al. Arteriosclerosis. However, this does not lead to a higher rate of ECA occlusion in the first 2 years after revascularization. The CCA is imaged from the supraclavicular notch where the transducer is angled as inferiorly as possible to see its proximal extent. The flow should be low resistance flow ( presence of forward diastolic flow). Cerebral blood flow (CBF) is commonly inferred from blood velocity measurements in the middle cerebral artery (MCA), using nonimaging, transcranial Doppler ultrasound (TCD). Most of the large carotid stenosis studies compared ultrasound with angiography as the gold standard while using the traditional non-NASCET method of grading carotid stenosis. The blue area in the carotid bulb and proximal internal carotid artery represents the normal flow reversal zone. There is a moderate amount of blood flow throughout diastole. The ICA is usually posterior and lateral to the ECA. 2. The ultrasound criteria for estimating ICA stenosis severity are largely based on the results of the NASCET and European Carotid Surgery Trials (ECST). The scan may begin with either the longitudinal or transverse imaging of the CCA. if tortuous) and the presence of any intimal thickening or plaque. Positive correlation between plaque location and low oscillating shear stress. Background. The most noteworthy normal flow disturbance occurs at the carotid bifurcation (Figures 7-4 and 7-5; see Video 7-2), where a zone of blood flow reversal is established in the CCA bulb and proximal ICA.68 The size of the zone of flow separation appears to be related to anatomic factors, including the diameter of the artery lumen and the angle between the ICA and the ECA. A, This diagram shows the key landmarks of the carotid artery bifurcation. Several different methods have been utilized in the past to measure carotid stenosis. The lines define the location where IMT measurements are made in one of the protocols used in epidemiologic studies. Vascular Ultrasound. It might be helpful to ask a colleague to perform the maneuver while you image. Carotid ultrasound: Carotid (kuh-ROT-id) ultrasound is a safe, painless procedure that uses sound waves to examine the blood flow through the carotid arteries. The CCA peak systolic velocity should therefore be obtained before the beginning of the bulb, ideally 2 to 4 cm below. An important technical point to be made when calculating the ICA/CCA PSV ratio is that the denominator must be obtained from the distal CCA approximately 2 to 4cm proximal to the bifurcation. The pathology will usually be located between the CCA origin and vertebral origin. Graph demonstrating the relationship between average peak systolic velocity (PSV) (y-axis) and percentage luminal narrowing as determined by contrast angiography using, North American Symptomatic Carotid Endarterectomy Trial (NASCET) method of measurement (x-axis). 2015;5(3):293-302. Ensure suitable PRF and gain for these smaller, deeper vessels. 2001;33(1):56-61. The estimation of the original lumen is further complicated by the presence of a normal, but highly variable, region of dilatation, the carotid bulb. Use a linear, mid frequency range probe (5-8MHZ). The carotid bulb and bifurcation should be imaged with gray scale and color Doppler. Endarterectomy for Asymptomatic Carotid Artery Stenosis. Carotid artery stenosis: grayscale and Doppler ultrasound diagnosisSociety of Radiologists in Ultrasound Consensus Conference. The Asymptomatic Carotid Surgery Trial 1 (ACST-1) demonstrated a 10-year benefit in stroke reduction in asymptomatic patients who underwent CEA for severe stenosis between 70% and 89%. Figure 3.3 Arterial Duplex examination (Doppler velocity and B-mode ultrasound) patterns in normal and diseased peripheral arteries. The original studies validating intervention in asymptomatic patients showed absolute risk reductions at 5 years of 5-6%, but this number remains in question with continuing improvements in medical management of asymptomatic patients and the lack of recent data [5,6]. Quantitative evaluation of external carotid artery stenoses is likewise difficult, due to lack of published data and low clinical significance of disease in this vascular distribution. Color Doppler also allows you to identify the internal carotid artery by detecting the area of recirculation of the internal carotid bulb. ECA: External carotid artery (ECA) waveforms have sharp systolic peaks, pulsatility due to reflected waves from its branches, and relatively little flow in diastole as compared to the internal carotid artery (ICA). Take Doppler samples in the proximal and distal segments and anywhere else that pathology or an altered waveform is detected. However, stenoses in other carotid artery segments such as the distal ICA (an area not typically well seen on routine carotid ultrasound), the common carotid artery (CCA), or the innominate artery (IA) may be equally significant. ; 1998. The ECA has small branches (usually the thyroglossal artery). (you can feel the pulse of the temporal artery anterior to the ear). The normal range of velocities in the carotid branches varies as a function of age. Screening for asymptomatic cerebrovascular stenosis is an area of some controversy. To begin with, on all conventional angiographic studies, the original lumen is not actually seen. Detection of common carotid artery stenosis using duplex ultrasonography: A validation study with computed tomographic angiography. Off-axis view of the carotid wall. Therefore one should always consider the gray-scale and color Doppler appearance of the carotid segment in question including the plaque burden and visual estimates of vessel narrowing to determine whether all diagnostic features (both visual and velocity data) of a suspected stenosis are concordant. The velocity criteria apply when atherosclerotic plaque is present and their accuracy can be affected by: ICA/CCA PSV ratio measurements may identify patients that for hemodynamic reasons (low cardiac output, tandem lesions, etc. Lesions should be analyzed using duplex as part of a comprehensive examination but results reported qualitatively. FIGURE 7-1 Normal arterial wall anatomy. Analysis of external carotid flow can be useful for determining lesions in neighboring vessels, such as internal or common carotid occlusion. The test is done to help diagnose: Arteriosclerosis of the arms or legs. The lumen-intima interface is best seen on longitudinal images when the image plane passes through the center of the artery and the ultrasound beam forms a 90-degree incident angle with the wall interfaces (Figure 7-2; see Video 7-1). Hathout etal. Blood flow is not always laminar in nondiseased vessels since the artery segment has to be straight in order for the conditions of laminar flow to apply. However, both blood velocity and vessel diameter are critical components required to accurately determine blood flow, and there is mounting evidence that the MCA is vasoactive. B, This transverse video shows the zone of flow reversal (blue; arrow) in the proximal ICA at end diastole. The current parameters used to grade the severity of ICA stenosis are based on the Society of Radiologists in Ultrasound (SRU) Consensus Statement in 2003. In a diseased artery, however, the color velocity scale should be shifted up or down according to the mean velocity of blood flow to demonstrate aliasing only in systole. The vertebral artery is typically identified in the longitudinal plane, between the transverse processes of the cervical spine. The external carotid artery suppliesa high resistance vascular bed, while the internal carotid artery supplies the brain which has a low resistance vascular bed. Locate it in transverse and rotate into longitudinal. The intimal reflection should be straight, thin, and parallel to the adventitial layer. The majority of stenotic lesions occur in the proximal internal carotid artery (ICA); however, other sites of involvement in the carotid system may or may not contribute to significant neurologic events. Usually the widening is slight, but some normal individuals have capacious carotid bulbs that may harbor large plaques in the absence of significant carotid stenosis. In such situations try imaging the more distal segments of the arteries. The diagnosis of stenotic disease affecting other parts of the carotid system may be clinically important and will also be discussed. Begin the examination by assessing vessels in B-Mode, optimising factors such as frequency, depth, gain, TGC and focal zone. The ICA (located inferiorly and to the right) is typically larger than the ECA (located to the left and upward). External carotid artery. When left untreated, progression of this disease can lead to occlusion, embolization, or plaque rupture, causing neurologic sequelae such as transient ischemic attack or stroke leading to potential permanent neurologic dysfunction and sometimes even death. showed that, in most patients, the systolic velocity decreases in the CCA as one goes from proximal to distal within the vessel. You may only be able to see a few cm of the ICA if there is a high bifurcation. The artery and vein can be differentiated by direction of flow on color Doppler as well as by the tendency of the vein to collapse with external ultrasound probe compression. Identified in the artery as possible to see a few cm of the cervical spine a amount... 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