DOI: 10.1148/rg.256045013
Sonographic Examination of the Carotid Arteries1
Hamid R. Tahmasebpour, BSc, RDMS,
Anne R. Buckley, MD,
Peter L. Cooperberg, MD and
Cathy H. Fix, RDMS
1 From the Department of Radiology, St Paul’s Hospital, 1081 Burrard St, Vancouver, BC, Canada V6Z 1Y6 (H.R.T., P.L.C., C.H.F.); the Department of Radiology, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada (H.R.T.); and the Department of Radiology, Vancouver General Hospital, Vancouver, BC, Canada (A.R.B.). Recipient of a Certificate of Merit award and an Excellence in Design award for an education exhibit at the 2003 RSNA Annual Meeting. Received February 2, 2004; revision requested March 29; final revision received May 18, 2005; accepted May 20. All authors have no financial relationships to disclose.
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Figure 1. Suggested format for documentation of the results of carotid US. Graphic representation of the plaque is important for follow-up examinations. EDV = end-diastolic velocity, ID = identification, LT = left, N/A = not applicable, PSV = peak systolic velocity, RT = right, VA = vertebral artery.
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Figure 2a. Location and angle of the sample volume in a diseased ICA with soft plaque. LT = left, SV = sample volume. (a) Color Doppler image shows the sample volume angle incorrectly aligned with the wall contour of the ICA. The PSV reading in the ICA is 229 cm/sec, resulting in overestimation of the degree of stenosis as more than 70%. (b) Color Doppler image shows the sample volume angle correctly aligned with the flow vector (the contour of the soft plaque). The resultant PSV reading in the ICA is 161 cm/sec; thus, the degree of stenosis was reclassified as 50%–69%.
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Figure 2b. Location and angle of the sample volume in a diseased ICA with soft plaque. LT = left, SV = sample volume. (a) Color Doppler image shows the sample volume angle incorrectly aligned with the wall contour of the ICA. The PSV reading in the ICA is 229 cm/sec, resulting in overestimation of the degree of stenosis as more than 70%. (b) Color Doppler image shows the sample volume angle correctly aligned with the flow vector (the contour of the soft plaque). The resultant PSV reading in the ICA is 161 cm/sec; thus, the degree of stenosis was reclassified as 50%–69%.
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Figure 3. Location of the sample volume box in a tortuous artery. Color Doppler image shows a tortuous left (LT) ICA. The change in the color depiction of the ICA is not due to a change in blood flow velocity but instead reflects changing direction of the blood flow relative to the Doppler angle of incidence. To sample the velocities at points B and C, the color box and angle of incidence require operator correction of the Doppler angle of incidence by steering the color box or angling the transducer. In this case, the correct position of the sample volume box is at point A.
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Figure 4a. Adjustment of the color Doppler sampling window. (a) Color Doppler image shows that the leftward position of the color Doppler sampling window results in a poor Doppler angle of incidence to the direction of blood flow in the proximal ECA. The result of an angle of incidence of almost 90° is ambiguous color display in this segment of the ECA. (b) Color Doppler image shows that correcting the angle of incidence by changing the position of the color Doppler sampling window or angling the transducer improves depiction of this area and is crucial for accurate velocity measurements.
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Figure 4b. Adjustment of the color Doppler sampling window. (a) Color Doppler image shows that the leftward position of the color Doppler sampling window results in a poor Doppler angle of incidence to the direction of blood flow in the proximal ECA. The result of an angle of incidence of almost 90° is ambiguous color display in this segment of the ECA. (b) Color Doppler image shows that correcting the angle of incidence by changing the position of the color Doppler sampling window or angling the transducer improves depiction of this area and is crucial for accurate velocity measurements.
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Figure 5. Adjustment of the color Doppler sampling window in a tortuous ICA. Color Doppler image shows the color Doppler sampling window steered to the "center" or "straight" position to increase color sensitivity in those segments of the artery that subtend angles of more than 60° to the Doppler beam. Red and blue regions represent blood flow toward and away from the transducer, respectively.
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Figure 6a. Adjustment of the color scale in a carotid artery stenosis. (a) Color Doppler image obtained with the color scale set too low (4 cm/sec) shows aliasing in the entire segment of the ICA. (b) Color Doppler image obtained with the color scale set too high (115 cm/sec) shows no aliasing. (c) Color Doppler image obtained with the optimal color scale setting shows the region of highest velocity, which corresponds to the narrowest segment of the ICA. Velocity sampling should be performed at this site.
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Figure 6b. Adjustment of the color scale in a carotid artery stenosis. (a) Color Doppler image obtained with the color scale set too low (4 cm/sec) shows aliasing in the entire segment of the ICA. (b) Color Doppler image obtained with the color scale set too high (115 cm/sec) shows no aliasing. (c) Color Doppler image obtained with the optimal color scale setting shows the region of highest velocity, which corresponds to the narrowest segment of the ICA. Velocity sampling should be performed at this site.
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Figure 6c. Adjustment of the color scale in a carotid artery stenosis. (a) Color Doppler image obtained with the color scale set too low (4 cm/sec) shows aliasing in the entire segment of the ICA. (b) Color Doppler image obtained with the color scale set too high (115 cm/sec) shows no aliasing. (c) Color Doppler image obtained with the optimal color scale setting shows the region of highest velocity, which corresponds to the narrowest segment of the ICA. Velocity sampling should be performed at this site.
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Figure 7a. Adjustment of the color scale in a near occlusion. (a) Color Doppler image obtained with the color scale set at 46 cm/sec shows a false-positive appearance of absent flow in the left ICA. (b) On a color Doppler image obtained with the color scale setting lowered to 4 cm/sec, trickle flow is evident, thus indicating the correct diagnosis of a near occlusion in the left ICA. Note the color noise in the background (arrowheads), which is a reassuring indicator of the optimal color gain setting for low-velocity flow.
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Figure 7b. Adjustment of the color scale in a near occlusion. (a) Color Doppler image obtained with the color scale set at 46 cm/sec shows a false-positive appearance of absent flow in the left ICA. (b) On a color Doppler image obtained with the color scale setting lowered to 4 cm/sec, trickle flow is evident, thus indicating the correct diagnosis of a near occlusion in the left ICA. Note the color noise in the background (arrowheads), which is a reassuring indicator of the optimal color gain setting for low-velocity flow.
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Figure 8a. Adjustment of the color gain. (a) Color Doppler image obtained with the color gain set at 80% shows marked turbulence in both the ICA and ECA, but no luminal narrowing is evident. (b) On a color Doppler image obtained with the color gain lowered to 66%, the anatomy of the bifurcation is demonstrated more accurately. The improved demonstration of the anatomy aids accurate placement of the sample volume box on the narrowest segment, with subsequent alignment of the Doppler angle parallel to the flow vectors.
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Figure 8b. Adjustment of the color gain. (a) Color Doppler image obtained with the color gain set at 80% shows marked turbulence in both the ICA and ECA, but no luminal narrowing is evident. (b) On a color Doppler image obtained with the color gain lowered to 66%, the anatomy of the bifurcation is demonstrated more accurately. The improved demonstration of the anatomy aids accurate placement of the sample volume box on the narrowest segment, with subsequent alignment of the Doppler angle parallel to the flow vectors.
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Figure 9. Measuring the intima-media thickness in the left CCA. Gray-scale US image shows the cursors placed perpendicular to the long axis of the CCA to include only the intima and media in the thickness measurement. In this case, the distance between the cursors is 2.8 mm.
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Figure 10. Homogeneous plaque. Gray-scale US image shows an echogenic soft homogeneous plaque in the proximal right ICA. Note how smooth the surface of the plaque is (arrowheads). This smoothness may indicate that the plaque is stable.
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Figure 11. Heterogeneous plaque. Gray-scale US image shows a heterogeneous plaque in the proximal right ICA. Note the irregular surface of the plaque, which contains echogenic and echo-poor areas. This type of plaque is considered unstable with the potential for inducing a transient ischemic attack or cerebrovascular accident.
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Figure 12. Intraplaque hemorrhage. Gray-scale US image shows a plaque containing an echo-poor area (arrow), which may be due to hemorrhage or lipids. In contrast to fat deposits, intraplaque hemorrhage is associated with a rapid increase in the size of the plaque, which is more likely to become symptomatic.
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Figure 13a. Comparison of color flow and gray-scale flow imaging of a diseased ICA. (a) Color Doppler image of the right ICA shows a moderate amount of plaque in the proximal ICA with questionable eddy flow at the plaque surface. The questionable eddy flow could be due to bleeding of color or ulceration in the plaque. (b) Gray-scale flow image shows an irregular plaque surface (arrowheads) with several depressions. In addition, the true lumen of the ICA is narrower than it appears on the color Doppler image.
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Figure 13b. Comparison of color flow and gray-scale flow imaging of a diseased ICA. (a) Color Doppler image of the right ICA shows a moderate amount of plaque in the proximal ICA with questionable eddy flow at the plaque surface. The questionable eddy flow could be due to bleeding of color or ulceration in the plaque. (b) Gray-scale flow image shows an irregular plaque surface (arrowheads) with several depressions. In addition, the true lumen of the ICA is narrower than it appears on the color Doppler image.
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Figure 14a. Differentiation of ulcerated plaque and twinkle artifact. (a) Color Doppler image of the right ICA shows a moderate amount of hard plaque in the proximal ICA with some questionable flow at the plaque surface. (b) Color Doppler image obtained in diastole with the color scale setting increased to 86 cm/sec shows that the color flow has disappeared, but the color artifact from the hard plaque continues to twinkle.
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Figure 14b. Differentiation of ulcerated plaque and twinkle artifact. (a) Color Doppler image of the right ICA shows a moderate amount of hard plaque in the proximal ICA with some questionable flow at the plaque surface. (b) Color Doppler image obtained in diastole with the color scale setting increased to 86 cm/sec shows that the color flow has disappeared, but the color artifact from the hard plaque continues to twinkle.
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Figure 15a. Circumferential calcified plaque in the proximal ICA. (a) PW Doppler image of the right ICA obtained immediately distal to a circumferential shadowing plaque shows no sign of turbulence, and the PSV is within normal limits. Therefore, there is unlikely to be a significant stenosis behind the calcified plaque. (b) PW Doppler image of the proximal right ICA shows a tardus-parvus waveform. A severe proximal stenosis behind the shadowing plaque is suspected; therefore, evaluation with another imaging modality is required. (c) PW Doppler image of the right ICA shows spectral broadening (turbulence) with an elevated PSV. These results may be due to a high degree of stenosis immediately proximal to the point of sampling; therefore, further investigation with another imaging modality is required.
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Figure 15b. Circumferential calcified plaque in the proximal ICA. (a) PW Doppler image of the right ICA obtained immediately distal to a circumferential shadowing plaque shows no sign of turbulence, and the PSV is within normal limits. Therefore, there is unlikely to be a significant stenosis behind the calcified plaque. (b) PW Doppler image of the proximal right ICA shows a tardus-parvus waveform. A severe proximal stenosis behind the shadowing plaque is suspected; therefore, evaluation with another imaging modality is required. (c) PW Doppler image of the right ICA shows spectral broadening (turbulence) with an elevated PSV. These results may be due to a high degree of stenosis immediately proximal to the point of sampling; therefore, further investigation with another imaging modality is required.
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Figure 15c. Circumferential calcified plaque in the proximal ICA. (a) PW Doppler image of the right ICA obtained immediately distal to a circumferential shadowing plaque shows no sign of turbulence, and the PSV is within normal limits. Therefore, there is unlikely to be a significant stenosis behind the calcified plaque. (b) PW Doppler image of the proximal right ICA shows a tardus-parvus waveform. A severe proximal stenosis behind the shadowing plaque is suspected; therefore, evaluation with another imaging modality is required. (c) PW Doppler image of the right ICA shows spectral broadening (turbulence) with an elevated PSV. These results may be due to a high degree of stenosis immediately proximal to the point of sampling; therefore, further investigation with another imaging modality is required.
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Figure 16. Severe stenosis (70% to near occlusion) of the ICA. Duplex US image of the left ICA shows a high PSV (366 cm/ sec), a significant amount of visible plaque, the presence of aliasing despite a high color scale setting (114 cm/sec), color flow turbulence immediately distal to the stenotic segment, broadening of the PW Doppler spectrum, and a high end-diastolic velocity (182 cm/sec).
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Figure 17. Severe stenosis of the innominate artery. PW Doppler spectral image of the right CCA shows a tardus-parvus waveform, which is suggestive of a severe stenosis proximal to the point of sampling. A severe stenosis of the innominate artery was subsequently demonstrated at angiography. EDV = end-diastolic velocity.
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Figure 18. Trickle flow in the ICA. Color Doppler image shows a narrow patent channel (the string sign) in the right ICA. This finding is suggestive of near occlusion of the ICA.
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Figure 19. Thud flow. Color Doppler image of the right ICA and carotid bulb shows no flow in the ICA lumen and reversed flow in the bulb at the point of occlusion. The red and blue arrows indicate the direction of the reversed flow at the point of obstruction (thud flow). The PW Doppler spectrum also demonstrates thud flow, which manifests as damped systolic flow and reversed flow in early diastole.
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Figure 20. Internalization of the ECA. Color Doppler image of the left carotid bifurcation shows no flow in the distal CCA. The ICA and ECA are both patent, but flow in the ECA is reversed to supply antegrade flow in the ICA above the level of the occluded CCA. The curved arrows indicate the direction of blood flow from the ECA to the ICA.
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Figure 21. PW Doppler spectrum in internalization of the ECA. PW Doppler spectral image shows a reversed low resistive flow pattern with delayed systolic acceleration (tardus wave) in the ECA. The patient had an occluded CCA. In addition, reflections from the temporal tap maneuver are demonstrated as ripples in the Doppler spectrum.
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Figure 22a. Occult and partial subclavian steal. (a) PW Doppler spectral image of the right vertebral artery shows midsystolic deceleration with antegrade late-systolic velocities (occult steal). (b) PW Doppler spectral image obtained after the patient exercised the right arm (by opening and closing the hand for 2 minutes). The Doppler spectrum shows midsystolic deceleration with retrograde late-systolic velocities. The subclavian artery "steals" blood from the vertebral artery to supply the ischemic arm.
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Figure 22b. Occult and partial subclavian steal. (a) PW Doppler spectral image of the right vertebral artery shows midsystolic deceleration with antegrade late-systolic velocities (occult steal). (b) PW Doppler spectral image obtained after the patient exercised the right arm (by opening and closing the hand for 2 minutes). The Doppler spectrum shows midsystolic deceleration with retrograde late-systolic velocities. The subclavian artery "steals" blood from the vertebral artery to supply the ischemic arm.
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Figure 23. Complete subclavian steal. PW Doppler spectral image of the left vertebral artery shows completely reversed flow.
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Copyright © 2005 by the Radiological Society of North America.
