Carotid IMT and Lumen Narrowing Measurements - USA

This course includes information on disease epidemiology, vessel wall anatomy, measurement of the intima-media thickness (IMT), and determining narrowing of the carotid lumen based on linear, and area, measurements.

Cardiovascular disease (CVD) includes both heart disease and stroke with a global mortality rate estimated at 17 million individuals.1 The economics of CVD become difficult to quantify due to the diverse causes. For example, up to ten percent of health costs treat diabetes while smoking results in a global cost of approximately a quarter of a billion dollars.1  In the United States there is a myocardial infarction (MI) and stroke every 40 seconds.2 This course will help you understand the epidemiology, vascular wall anatomy, and measurement techniques used to determine wall thickness and lumen narrowing in large vessels.  Congratulations! You have completed the Carotid IMT and Lumen Narrowing Measurements course. Listed below are the key points presented in this course. Take time to review the material before you try the final assessment.   Download and print a copy of the detailed Course Review.   In this course you have learned to: Explain risk factors contributing to an increased incidence of cardiovascular disease (CVD). Discuss the layers of the artery. Describe technical factors to increase visualization of vessel layers to perform an intima-media thickness (IMT) measurement. ​List the methods of determining lumen reduction using the grayscale, 2D-mode image. Upon completion of this course, you will be able to: Explain risk factors contributing to an increased incidence of cardiovascular disease (CVD). Discuss the layers of the artery. Describe technical factors to increase visualization of vessel layers to perform an intima-media thickness (IMT) measurement. List the methods of determining lumen reduction using the grayscale, 2D-mode image. View these instructions for information on navigating through the self-evaluation tools we call ‘Your Turns’. These questions help you gauge your understanding of key topics.  Click the icon below to view the self-evaluation instructions. Note: This is not part of the final Assessment. Learn How to Navigate the Your Turns Learn how to navigate the Your Turns. Instructions:Flash File:HTML5 File:/content/generator/Course_90022875/Navigation_Instructions_CM-Meas-Navigation/index.htmlPDF File: Seventy-years-ago a third of men developed cardiovascular disease (CVD) before their sixth decade of life with women not far behind.3 At that time little was known about the cause, whether genetic or lifestyle, which contributed to heart disease and strokes.    In an effort to discover the foundations of these health problems, the Framingham Heart Study, named after the town in the United States where the study population lives, began. The goal was, and still is, to collect data that helps us understand what shared behaviors contribute to CVD using long-term participants. The multi-generational subjects return every two years to continue data collection.4   Risk factors found using the Framingham Heart Study apply to populations regardless of geography.3, 5 Cardiovascular disease is a general term used to describe narrowing of blood vessels regardless of body location. The cause of CVD has a multi-factorial basis, occurring to a mild degree in most individuals. Progression to a more serious condition (i.e., myocardial infarction or stroke) involves the interplay between the many known factors that increase risk of cardiovascular disease.1   Arteriosclerosis is the stiffening or hardening of arterial walls. Atherosclerosis is the narrowing due to the accumulation of fatty deposits. Learn More About CVD Risk Factors Learn more about CVD risk factors.1, 2 Tab TitleTextIncreased in Women These factors increase the risk of CVD in females higher than in males. Using tobacco products High TG (triglyceride) levels Diabetes mellitus (undiagnosed and diagnosed) Depression ​Obesity Similar between Gender These risk factors increase the risk of CVD regardless of gender. Hypertension (aka: HTN or high blood pressure) Total cholesterol above normal Low high-density lipoprotein (HDL) cholesterol Increased low-density lipoprotein (LDL) and triglyceride levels with decreased HDL (aka: combined hyperlipidemia). Nutrition (i.e., salt and sugar intake, levels of fruit, vegetables and grains) Lack of exercise Stress Sleep variations (i.e., insomnia, apnea) Chronic inflammation (i.e., periodontitis, rheumatoid arthritis)6, 7 Women OnlyThis group of risk factors pertain to females only. Polycystic ovarian syndrome Contraceptives taken orally Fertility treatment8 HRT (hormone replacement therapy) Greatest MI risk early in each menstrual cycle Pregnancy induced HTN and gestational diabetes Fixed Characteristics Risk factors beyond our control include: Increasing age – age 12 and older Sex (male versus female) Genetics Our race or ethnicity All vessels have three layers with thickness variations due to composition or disease.  The three layers of the vessel are the: Tunica adventitia (outer layer). Tunica media. Tunica intima (inner layer). The media of the larger arteries (i.e., carotid, aorta, brachiocephalic, subclavian, femoral), contain a larger amount of elastic tissue and fewer smooth muscle cells. The media in a medium to small artery (anterior tibial, dorsalis pedal, etc.) has mainly smooth muscle with very little elastic tissue.10 Learn More About Vessel Layers Learn more about vessel layers.10, 11 Tab TitleTextTunica Intima The single endothelial layer of the vessel, the tunica intima (orange), is in contact with the blood flow.  The intimal epithelium folds to create venous valves and help blood flow to the heart aiding in identification. Tunica Media The smooth muscle fibers of the tunica media (orange) have a hypoechoic appearance on the ultrasound image. This layer has various amounts of elastic and collagenous tissue. This allows for arterial compliance during the heart cycle.  In the larger arteries elastic fibers layers alternate with muscle fibers. Tunica Adventitia The external layer, the tunica adventitia (orange) or externa contains loose connective tissue with scattered smooth muscle cells or a bundle of cells arranged longitudinally.  In all but the smaller arteries, this layer contains some elastic tissue. The structure and relative thickness vary with the size of the artery. Artery versus Vein This transverse image of the posterior tibial vessels demonstrates the differences between the vessel walls. The artery wall (brackets) have thick muscular walls while the vein (arrows) has thinner walls. The three layers of the venous walls are the same as those of the arteries, however; there are differences in the structure. The adventitia and the tunica media are thinner with fewer muscle cells in the veins. Your Turn Your Turn. Instructions:Flash File:HTML5 File:/content/generator/Course_90022875/CA-Meas-YourTurn-01c/index.htmlPDF File: The cause of atherosclerotic formation is a complex interplay of risk factors such as inflammation, damage to the vessel wall, repair, and development of fibrous tissue within the tunica intima.12, 13 As this cycle repeats, one of the first consequences of this process is a thickening of the arterial wall often seen during an examination of the carotid arteries. This increase, called intima-media thickness (IMT), was a direct observation of a link with MI during the Cardiovascular Health Study (CHS).14 As a result, we now know that the increase in the IMT is an indicator of atherosclerotic disease within the heart and the chances of a heart event.    The progression of vascular disease begins to decrease the diameter of the vessel lumen. The consequence of this narrowing is an increase in flow velocity distal to the constriction.15 We are able to quantify this narrowing via 2D-image   In the following sections you will find methods to measure the IMT, and both linear and area reduction methods to estimate vessel narrowing.   The development of atherosclerosis is due to accumulation of fats in the intima of the artery as a response to chronic inflammation and fibroproliferative disease.12 Studies have shown cardiovascular disease increases as the IMT increases regardless of gender or race.16-18 In the examples shown, we use the carotid intima-media thickness (CMIT).   Atherosclerosis in the carotid arteries increases the chances of similar findings in other vessels such as the coronary arteries.13 The earliest sign of atherosclerotic plaque development is an increase in two inner vessel layers, the intima and media. The result is an ultrasound image showing wall extension, due to the plaque, into the lumen of the artery.    Normal IMT measurements increase with age.13 Increasing Axial Resolution of the IMT Image Increasing axial resolution of the IMT image.19, 20 Checklist TitleChecklist TypeChecklist ContentWas the highest frequency transducer used?HTMLSelect the highest frequency transducer available allowing for the highest axial resolution to differentiate the vessel wall layers. A 16L4 MHz transducer easily demonstrates the wall layers in this image of a common carotid artery (CCA). Regardless of location (anterior versus posterior) the intima and adventitia layers display as echogenic lines surrounding a hypoechoic media. To measure the IMT include the intima and media (calipers; posterior wall) of the vessel in multiple locations.13 Does reverberation obscure the vessel wall?HTMLUse minimal transducer pressure to avoid pushing the vessel into the reverberation artifacts which may obscure the vessel walls. In the patient with superficial vessels, use a standoff pad or image the vessel from a lateral approach.      This image of a carotid bulb shows a reverberation artifact (double arrows) in the anterior portion of the vessel.Has the field of view been decreased?HTML Narrowing the field of view, by decreasing the image width and the region of interest (ROI), eliminates unnecessary information. This includes artifacts such as grating lobes or shadowing from bony structures.Is the focal carat adjusted correctly?HTML This image of the CCA shows positioning of the focal carat at the posterior vessel wall. Positioning the focal zone (i.e. focal carat) at or just posterior to the vessel wall places the focal zone in the appropriate location increasing our resolution.  Was write zoom activated?HTML Increasing the size of the image allows for easier identification of the vessel walls. The read zoom (or magnify) function increases the image size, however; the write zoom (HD Z) provides the best detail. Remember, the write zoom increases the size of the image with a region of ROI. As a result, the ultrasound system uses all available information in this one area increasing our image detail.    Write zoom only occurs with the image in a real-time format.  What is the angle of incidence?HTML Ensure the angle of incidence with the vessel wall is at 90-degrees. Most ultrasound systems allow steering of the beam, however, tilting the transducer also changes the angle of incidence.     These images show the increase in wall detail (axial resolution) when changing the transducer angle. A 90-degree (left) angle of incidence shows intact wall layers. Using a transducer angle towards the patient’s head (right) decreases the receive signal, thus decreasing detail (yellow arrow). Manual measurements of the IMT introduces unintended inter-observer error. To reduce variations, automatic IMT measurements perform multiple distance measurements of the intima-media of the carotid or other superficial arteries.21 Using an automated method helps to: Increase the consistency and reliability of IMT measurements. Reduce the effort required to successfully carry out IMT measurements. Minimize the time needed to complete an IMT study.   This image shows the automatic measurement of the posterior wall of a CCA using the syngo® Arterial Health Package (AHP). Your Turn Your Turn. Instructions:Flash File:HTML5 File:/content/generator/Course_90022875/CA-Meas-YourTurn-02/index.htmlPDF File: The North American Symptomatic Endarterectomy Trial (NASCET)22 and the European Carotid Surgery Trialists’ Collaborative Group (ECST)23 helped establish methods to determine the amount of diameter reduction within the internal carotid artery (ICA).  Based on methods used during angiography, these methods show equal accuracy when helping to determine the percentage of concentric vessel diameter reduction.24 Keep in mind that calcified plaque tends to reduce the accuracy of measurements due to the difficulty in determining the diameter reduction boundaries.   Due to the high incidence of asymmetric plaque, spectral Doppler velocity values supersede 2D-mode diameter reduction measurements.24 Use Clarify™ vascular enhancement (VE) technology to increase visualization of the internal lumen of the artery. Learn More about Measuring Diameter Reduction Learn more about measuring diameter reduction. Tab TitleTextNASCET Measurement15, 25The NASCET method uses the normal lumen size, measured intima-to-intima distal to the diameter reduction and the residual lumen.   D = Original lumen – Residual lumen                   Original lumen                     X 100    Left line = 8 mm Right line = 4 mm   D = (8 – 4 / 8) X 100 D = (4 / 8) x 100 D = 0.5 x 100 D = 50 or 50% diameter reduction   ECST Measurement15, 25The ECST method uses the normal lumen size, measured intima-to-intima at the diameter reduction and the residual lumen.   D = Full diameter of the vessel – Residual lumen                   Full diameter of the vessel                     X 100    Residual lumen (left line) = 3 mm Full diameter (right line) = 9 mm   D = (9 – 3 / 9) X 100 D = (6 / 9) x 100 D = 0.66 x 100 D = 67 or 67% diameter reduction Learn More about Clarify VE Technology Learn more about Clarify VE Technology. Tab TitleTextClarify VE technologyClarify VE technology helps image the vessel lumen through using the power Doppler signal. The result is a decrease in artifacts, an increased visualization of vascular structures, and contrast resolution.   For a detailed description of Clarify VE Technology, click here to download the white paper.   This dual image shows a vessel partially filled due to high overall gain on the left. The right dual uses Clarify VE increasing the visualization of the carotid artery lumen In the presence of irregular formation of plaque, it becomes possible to over- or under-estimate disease when measuring on the longitudinal plane.24 This transverse image shows the importance of measurement planes when determining the percent diameter reduction. When imaging from the lateral neck (orange line) minimal to no plaque appears. A higher diameter reduction estimate occurs when using an anterior to posterior scan plane (green line) on the same vessel.13     To minimize error due to eccentrically placed atherosclerosis, an area calculation helps determine the percent diameter reduction.  Learn More about Area Reduction Learn more about area reduction. Tab TitleTextFormula Using a transverse image, measurements the normal lumen and residual lumen provide the data to calculation the diameter reduction.26 This is the same method used to calculate the percent diameter reduction on the longitudinal image; however, the measurements display as a squared value due to the area.    % area reduction = Original lumen2 – Stenotic lumen2   X 100                                            Original lumen2    Original lumen = 0.64 cm2 Stenotic lumen = 0.51 cm2   = (0.64 - 0.51 / 0.64) 100 = (0.13 / 0.64) 100 = 0.20 x 100 = 20 or 20% diameter reduction   For follow-up exams, use the same method of determining diameter reduction.  Image This image shows the method to perform the area reduction measurement. Start with the original lumen (A1) followed by the stenotic lumen (A2).  Explore the links below for the Glossary, References, and Further Reading opportunities. Glossary Glossary. Tab TitleTextA - MAsymmetric – Irregular buildup of plaque in a vessel.   Atherosclerosis - Fatty buildup found in the vessel walls which results in narrowing (diameter reduction).   Apnea – Temporary suspension of breathing usually occurring during sleep.   Axial resolution - Ability to separate or resolve two structures along the parallel axis of the ultrasound beam.   Concentric – Regular (symmetric) buildup of plaque in a vessel.   Diabetes mellitus - High blood sugar usually due to pancreatic malfunction.   Echogenic - Higher echo strength than the surrounding tissue.   Epidemiology - Study of disease patterns.   Hyperlipidemia - High cholesterol.   Hypertension - Blood pressure above normal.   Hypoechoic - echo texture below or less than the surrounding tissue.   Insomnia – Chronic inability to sleep.   Multifactorial – Encompassing many different disease processes, lifestyle, and genetic contributions.   Myocardial infarction (MI) – Alternate term for heart attack.P - SPeriodontitis – Progression of the inflammation (gingivitis) to an infection of gum tissue around the teeth.     Plaque - General term for lipid or calcific material found within the vessel walls.   Polycystic ovarian syndrome (PCOS) – Chronic ovarian dysfunction resulting in irregular to absent menses, acne, obesity and hirsutism (excessive hair growth).   Rheumatoid arthritis – A chronic autoimmune process resulting in joint and organ inflammation.   Stroke – general term describing an acute disruption of flow to the vessels in the brain due to either rupture or obstruction.  References / Further Reading References / Further Reading. Tab TitleText1 - 71. Organization, W.H. (2019). Cardiovascular disease. 2019 [cited 2019     12/09]; Available from:   2. Benjamin, E.J., Muntner, P., Alonso, A., Bittencourt, M.S., Callaway,     C.W., Carson, A.P., . . . Virani, S.S. (2019). Heart disease and stroke     statistics-2019 update: A report from the American Heart Association.     Circulation. 139(10): e56-e528.   3. D'Agostino Sr., R.B., Pencina, M.J., Massaro, J.M., and Coady, S.     (2013). Cardiovascular disease risk assessment: Insights from     Framingham. Global Heart. 8(1): 11-23.   4. Andersson, C., Johnson, A.D., Benjamin, E.J., Levy, D., and Vasan,     R.S. (2019). 70-year legacy of the Framingham Heart Study. Nature     Reviews Cardiology. 16(11): 687-698.   5. Ikram, M.A., Brusselle, G.G.O., Murad, S.D., van Duijn, C.M., Franco,     O.H., Goedegebure, A., . . . Hofman, A. (2017). The Rotterdam study:     2018 update on objectives, design and main results. European    Journal of Epidemiology. 32(9): 807-850.   6. Liao, K.P. (2017). Cardiovascular disease in patients with rheumatoid     arthritis. Trends in Cardiovascular Medicine. 27(2): 136-140. 7. Carrizales-Sepúlveda, E.F., Ordaz-Farías, A., Vera-Pineda, R., and     Flores-Ramírez, R. (2018). Periodontal disease, systemic     inflammation and the risk of cardiovascular disease. Heart, Lung and     Circulation. 27(11): 1327-1334.  8 - 138. Udell, J.A., Lu, H., and Redelmeier, D.A. (2017). Failure of fertility     therapy and subsequent adverse cardiovascular events. CMAJ:     Canadian Medical Association Journal = journal de l'Association     medicale canadienne. 189(10): E391-E397.   9. Saeed, A., Kampangkaew, J., and Nambi, V. (2017). Prevention of     cardiovascular disease in women. Cardiovascular Journal. 13(4):     185-192.   10. Moore, K.L., Dalley, A.F., and Agur, A.M.R. (2015). Introduzione       all'anatomia umana a orientamento clinica. In Moore, K.L., Dalley,       A.F., and Agur, A.M.R., (Eds.), Anatomia umana: a orientamento       clinico (pp. 1-77). Philadelphia: Casa Editrice Ambrosiana.   11. Moore, K.L., Dalley, A.F., and Agur, A.M.R. (2015). Collo. In Moore,       K.L., Dalley, A.F., and Agur, A.M.R., (Eds.), Anatomia umana: a       orientamento clinico (pp. 1041-1113). Philadelphia: Casa Editrice       Ambrosiana.   12. Perrotta, I. (2011). Ultrastructural features of human atherosclerosis.       Ultrastructural pathology. 37.   13. Bluth, E.I. (2012). Ultrasound assessment of carotid plaque. In       Pellerito, J.S. and Polak, J.F., (Eds.), Introduction to vascular       ultrasonography (pp. 147-157). Philadelphia: Elsevier Sanders.14 - 1814. National Heart, L., and Blood Institute. (2019). Cardiovascular        Health Study (CHS). 2019 [cited 2020 12 March]; Available       from:       chs. 15. Grant, E.G. and Melany, M. (2012). Ultrasound assessment of      carotid stenosis. In Pellerito, J.S. and Polak, J.F., (Eds.), Introduction      to vascular ultrasonography (pp. 158-173). Philadelphia: Elsevier      Sanders. 16. Villines, T.C., Hsu, L.L., Blackshear, C., Nelson, C.R., and       Griswold, M. (2017). Relation of carotid intima-media thickness       to cardiovascular events in black americans (From the Jackson       Heart Study). The American Journal of Cardiology. 120(9):       1528-1532.             17. Lorenz, M.W., Gao, L., Ziegelbauer, K., Norata, G.D., Empana, J.P.,       Schmidtmann, I., . . . Thompson, S.G. (2018). Predictive value for       cardiovascular events of common carotid intima media thickness       and its rate of change in individuals at high cardiovascular risk       - Results from the PROG-IMT collaboration. PloS One. 13,       e0191172 DOI: 10.1371/journal.pone.0191172.   18. Alshawabkeh, L.I., Yee, L.M., Gardin, J.M., Gottdiener, J.S.,      Odden, M.C., Bartz, T.M., . . . Wallace, R.B. (2015). Years of      able life in older persons-the role of cardiovascular imaging      and biomarkers: The Cardiovascular Health Study. Journal of      the American Heart Association. 4(4): e001745.    19 - 2419. Hedrick, W. (2013). Technology for diagnostic sonography.       St. Louis, MO: Elsevier.   20. Kremkau, F.W. (2016). Sonography: principles and instruments.       9th ed., St. Louis: Elsevier.   21. Menchón-Lara, R., Bastida-Jumilla, M., Morales-Sánchez, J.,       and Sancho-Gómez, J. (2014). Automatic detection of the       intima-media thickness in ultrasound images of the common       carotid artery using neural networks. Medical & Biological       Engineering & Computing. 52(2): 169-181. 22. Ferguson, G., Eliasziw, M., Barr Hugh, W.K., Clagett, G.P.,       Barnes, R.W., Wallace, M.C., . . . Barnett Henry, J.M. (1999).       The north american symptomatic carotid endarterectomy trial.       Stroke. 30(9): 1751-1758.   23. Rothwell, P.M., Gutnikov, S.A., and Warlow, C.P. (2003). Reanalysis       of the final results of the european carotid surgery trial. Stroke.       34(2): 514-523.   24. von Reutern, G., Goertler, M., Bornstein Natan, M., Sette Massimo,       D., Evans David, H., Goertler, M., . . . Yasaka, M. (2012). Grading       carotid stenosis using ultrasonic methods. Stroke. 43(3): 916-921.25 - 2625. Oates, C.P., Naylor, A.R., Hartshorne, T., Charles, S.M., Fail, T.,       Humphries, K., . . . Khodabakhsh, P. (2009). Joint recommendations       for reporting carotid ultrasound investigations in the United Kingdom.       European Journal of Vascular and Endovascular Surgery. 37(3):       251-261.   26. Carnicelli, A.P., Stone, J.J., Doyle, A., Chowdhry, A.K., Mix, D.,       Ellis, J., . . . Chandra, A. (2013). Cross-sectional area for the       calculation of carotid artery stenosis on computed tomographic       angiography. Journal of Vascular Surgery. 58(3): 659-665. The reproduction, transmission or distribution of this training or its contents is not permitted without express written authority. Offenders will be liable for damages.   All names and data of patients, parameters and configuration dependent designations are fictional and examples only.   All rights, including rights created by patent grant or registration of a utility model or design, are reserved.   Please note that the learning material is for training purposes only!   For the proper use of the software or hardware, please always use the Operator Manual or Instructions for Use (hereinafter collectively “Operator Manual”) issued by Siemens Healthineers. This material is to be used as training material only and shall by no means substitute the Operator Manual. Any material used in this training will not be updated on a regular basis and does not necessarily reflect the latest version of the software and hardware available at the time of the training.   The Operator Manual shall be used as your main reference, in particular for relevant safety information like warnings and cautions. Note: Some functions shown in this material are optional and might not be part of your system. The information in this material contains general technical descriptions of specifications and options as well as standard and optional features that do not always have to be present in individual cases.   Certain products, product related claims or functionalities described in the material (hereinafter collectively “Functionality”) may not (yet) be commercially available in your country. Due to regulatory requirements, the future availability of said Functionalities in any specific country is not guaranteed. Please contact your local Siemens Healthineers sales representative for the most current information.   Clarify VE technology and syngo Arterial Health Package are trademarks of Siemens Medical Solutions USA, Inc.   Copyright © Siemens Healthcare GmbH, 2020

  • Atherosclerosis
  • arteriosclerosis
  • Framingham heart study
  • Cardiovascular disease
  • CVD
  • stroke
  • intima-media thickness
  • intima media thickness
  • IMT
  • heart disease
  • area
  • cerebrovascular
  • ultrasound
  • vascular