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Vascular ultrasound for the assessment of carotid atherosclerosis
Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Background: Atherosclerotic cardiovascular disease (CVD) is a common cause for mortality globally, and is expected to remain the single leading cause of death as the global population ages and as life expectancy increases.

Cardiovascular screening models have been developed, and continue to be developed, to identify individuals at high-risk of CVD.  This is necessary to establish prevention strategies to decrease the occurrence of an acute event or debilitating syndrome. These strategies largely take the form of lifestyle modification and pharmacological intervention. The Framingham risk score, NCEP/ATP II guidelines and SCORE risk assessment protocol are widely used screening models. Ultrasound based methods are non-invasive, affordable and have been suggested to improve assessment and definition of individual patients potential risk of CVD. Increased carotid artery intima-media thickness (cIMT) is a known and established sign of early atherosclerosis. The presence of plaque and the overall burden of atherosclerosis seems to have even greater value in predicting cerebrovascular and cardiovascular events. Ultrasound based texture characteristics of plaques such as entropy, grey scale median, discrete white area, coarseness and juxtaluminal hypoechoic black area have been proposed as useful possible predictors of plaque vulnerability. Moreover, ultrasound contrast agents have been developed to improve visualization and subsequent quantification of an atherosclerotic plaque. Considering the current available data and research, the importance of developing tools and techniques for detection and characterization of atherosclerotic changes, to indicate risk for CVD and the subsequent early intervention and prevention, appears clearly as an effort to improve public health. In this present collection of studies (4 papers) we aim to contribute to the development of clinically useful ultrasound methods and tools for the accurate assessment, understanding and management of atherosclerosis.

Methods: To validate ultrasound-based methods for assessment of early signs of atherosclerosis, measured as cIMT, a total of 144 subjects underwent bilateral carotid ultrasound. In study I, the performance of an ultrasonography software capable of fully automated on-screen cIMT measurements was tested and compared with the traditional manual measurement approach. The coefficient of variation and the intraclass correlation coefficient for both methods were compared to verify the reliability and reproducibility of results generated by the new ultrasound software. To test the accessibility and possible clinical applications of this new technology tested in study I, the new software was used by novice’s scanners in study II, and the intraobserver variability of the cIMT measurements were assessed and compared with that of an expert operator. In study III, ultrasound texture characteristics of 327 plaques including entropy, grey scale median, discrete white area, coarseness and juxtaluminal hypoechoic black area were assessed as possible predictors of future cerebrovascular events in a cohort of 133 patients with symptomatic carotid stenosis waiting for carotid surgery. The reproducibility of measuring plaque area (expressed as intraclass correlation coefficient) using conventional ultrasound and contrast enhanced ultrasound was tested in study IV in an attempt to find a simple and reproducible parameter for monitoring changes in atherosclerotic burden.

Results: The technology tested in study I was found to have good inter- and intra-system reproducibility compared with conventional methods. Moreover, it was found to produce reproducible results when used by expert and novice operators after a short period of training (study II), confirming the possibility for the employment of this technology in a large screening public health programs. Although such technology may have immediate practical application, other and more sophisticated ultrasound based plaque characteristics (such as grey scale median, entropy, coarseness, juxtaluminal hypoechoic black area) were not shown to be beneficial in predicting plaque vulnerability (study III). Contrast enhanced ultrasound technic tested in study IV did not improve quantification of atherosclerotic plaque burden. 

Conclusion: Medical ultrasound technology by using a automatically measure of carotid intima media thickness can be used with high reproducibility and also possible to be transferred to primary care by a well designed training program.  Plaque characteristic using carotid ultrasound was not found to be useful in risk stratifying symptomatic patients with severe carotid stenosis. Furthermore, contrast enhanced ultrasound technique was found to have high reproducibility in plaque area assessment but not better than conventional b-mode based method in quantifying the atherosclerotic burden. Therefore, more sophisticated ultrasound based methods for assessment plaque characteristics was not found to be beneficial in predicting plaque vulnerability.

Place, publisher, year, edition, pages
Umeå: Umeå University , 2017. , 50 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1912
Keyword [en]
Ultrasound, Plaque, IMT, Atherosclerosis, CEUS, Carotid vessels
National Category
Public Health, Global Health, Social Medicine and Epidemiology
Research subject
Medicine, cardiovascular disease
Identifiers
URN: urn:nbn:se:umu:diva-139538ISBN: 978-91-7601-748-7 (print)OAI: oai:DiVA.org:umu-139538DiVA: diva2:1141822
Public defence
2017-10-13, Sal D, 9 tr, Norrlands Universitetssjukhus, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2017-09-22 Created: 2017-09-16 Last updated: 2017-09-21Bibliographically approved
List of papers
1. Fully automated on-screen carotid intima-media thickness measurement: A screening tool for subclinical atherosclerosis
Open this publication in new window or tab >>Fully automated on-screen carotid intima-media thickness measurement: A screening tool for subclinical atherosclerosis
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2013 (English)In: Journal of Clinical Ultrasound, ISSN 0091-2751, E-ISSN 1097-0096, Vol. 41, no 6, 333-339 p.Article in journal (Refereed) Published
Abstract [en]

Purpose Carotid intima-media thickness (CIMT) is generally considered an appropriate direct vascular method for cardiovascular risk assessment. The objective of this study was to evaluate the feasibility and reproducibility of a newly developed automated on-screen carotid ultrasound with respect to manual measurement with a conventional system. Methods We assessed CIMT in 50 consecutive patients (age 62 +/- 5 years, range 21-79 years, 36 men) twice, using a newly developed automated ultrasound (CardioHealth Station) and a conventional system with manual measurement (Acuson, Sequoia). For each patient, three frozen frames of the distal 10 mm of the right and left common carotid arteries were acquired on the two systems, by operators blinded to each other. The average of the mean value of three readings of each system was calculated. Results The intraclass correlation coefficient of the interoperator variability was 0.95 and 0.94 for the automated and manual measurements, respectively. The comparative coefficient of variation of the interoperator variability was 8.2 and 8.7% for the automated and manual measurements, respectively. There was no clinically relevant difference between measurements obtained by the two systems (intraclass correlation coefficient=0.98). The acquisition time of the automated system was significantly shorter than the conventional system (p<0.01). Conclusions Fully automated on-screen measurements of CIMT are feasible, faster, and as reproducible as conventional manual measurements and may be suitable and cost-effective for screening application in community medicine.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2013
Keyword
ultrasound, carotid artery, intima-media thickness, atherosclerosis, screening
National Category
Cardiac and Cardiovascular Systems
Identifiers
urn:nbn:se:umu:diva-78429 (URN)10.1002/jcu.22041 (DOI)000320440100001 ()
Available from: 2013-07-23 Created: 2013-07-22 Last updated: 2017-09-21Bibliographically approved
2. Successful novice's training in obtaining accurate assessment of carotid IMT using an automated ultrasound system
Open this publication in new window or tab >>Successful novice's training in obtaining accurate assessment of carotid IMT using an automated ultrasound system
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2014 (English)In: European Heart Journal Cardiovascular Imaging, ISSN 2047-2404, E-ISSN 2047-2412, Vol. 15, no 6, 637-642 p.Article in journal (Refereed) Published
Abstract [en]

Aims The aim of this study was to assess the feasibility and learning curve of training novice operators in using automated ultrasound to achieve satisfactory carotid intima-media thickness (CIMT) measurements. Methods and results Four novices underwent 4 weeks carotid ultrasound training using a newly developed automated ultrasonograph. A longitudinal B-mode image of the distal right common carotid artery (CCA) was acquired in 96 patients. The interoperator CIMT reproducibility was analysed by the coefficient of variation (CV) and intraclass correlation coefficient (ICC) for every week and compared with that from an expert operator. The weekly mean CV of the measurements on the 24 patients made by all novices was consistently reduced: 0.06, 0.05, 0.03, and 0.02, respectively. For the expert, the mean CV was 0.02, 0.02, 0.03, and 0.02, respectively. The novices' standard deviation (SD) of CVs also reduced weekly from 0.04 in the first week to 0.01 in the last week (P < 0.05). The corresponding weekly variation in the SD for the expert was 0.02 for the first week to 0.01 in the last week (P = 0.27). The agreement between measurements made by the novices was expressed by the ICC being 0.97 (P < 0.001) in the first week and increased to 0.99 (P < 0.001) in the fourth week. Conclusion CIMT assessment by novices using an automated ultrasound could be reliably achievable after a short training period. These results may have encouraging implications when designing screening programmes for primary prevention in community health service.

Keyword
Carotid artery, Intima-media thickness, Health screening, Vascular ultrasound
National Category
Cardiac and Cardiovascular Systems
Identifiers
urn:nbn:se:umu:diva-91057 (URN)10.1093/ehjci/jet254 (DOI)000336994300009 ()
Available from: 2014-07-11 Created: 2014-07-10 Last updated: 2017-09-21Bibliographically approved
3. Ultrasound-based plaque texture characteristics are not useful in risk stratification in patients with symptomatic carotid stenosis waiting for carotid surgery
Open this publication in new window or tab >>Ultrasound-based plaque texture characteristics are not useful in risk stratification in patients with symptomatic carotid stenosis waiting for carotid surgery
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(English)Manuscript (preprint) (Other academic)
National Category
Public Health, Global Health, Social Medicine and Epidemiology
Identifiers
urn:nbn:se:umu:diva-139765 (URN)
Available from: 2017-09-21 Created: 2017-09-21 Last updated: 2017-09-21
4. Quantification of atherosclerotic plaque area by vascular ultrasound: reproducibility and comparison between conventional B-mode imaging and contrast-enhanced ultrasound
Open this publication in new window or tab >>Quantification of atherosclerotic plaque area by vascular ultrasound: reproducibility and comparison between conventional B-mode imaging and contrast-enhanced ultrasound
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(English)Manuscript (preprint) (Other academic)
National Category
Public Health, Global Health, Social Medicine and Epidemiology
Identifiers
urn:nbn:se:umu:diva-139766 (URN)
Available from: 2017-09-21 Created: 2017-09-21 Last updated: 2017-09-21

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