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Videodensitometric analysis of advanced carotid plaque: correlation with MMP-9 and TIMP-1 expression
© Baroncini et al; licensee BioMed Central Ltd. 2011
Received: 9 August 2011
Accepted: 18 September 2011
Published: 18 September 2011
Matrix metalloproteinase-9 (MMP-9) and tissue inhibitor of MMP (TIMP) promote derangement of the extracellular matrix, which is ultimately reflected in plaque images seen on ultrasound. Videodensitometry can identify structural disturbances in plaques.
To establish the correlations between values determined using videodensitometry in B-mode ultrasound images of advanced carotid plaques and the total expression of MMP-9 and TIMP-1 in these removed plaques.
Thirty patients underwent ultrasonic tissue characterization of carotid plaques before surgery, using mean gray level (MGL), energy, entropy and homogeneity. Each patient was assigned preoperatively to one of 2 groups: group I, symptomatic patients (n = 16; 12 males; mean age 66.7 ± 6.8 years), and group II, asymptomatic patients (n = 14; 8 males; mean age 67.6 ± 6.81 years). Tissue specimens were analyzed for MMP-9 and TIMP-1 expression. Nine carotid arteries were used as normal tissue controls.
MMP-9 expression levels were elevated in group II and in normal tissues compared to group I (p < 0.001). TIMP-1 levels were higher in group II than in group I, and significantly higher in normal tissues than in group I (p = 0.039). The MGL was higher in group II compared to group I (p = 0.038). Energy had greater values in group II compared to group I (p = 0.02). There were no differences between patient groups in homogeneity and entropy. Energy positively correlated with MMP-9 and TIMP-1 expression (p = 0.012 and p = 0.031 respectively). Homogeneity positively correlated with MMP-9 and TIMP-1 expression (p = 0.034 and p = 0.047 respectively). There were no correlations between protein expression and MGL or entropy.
Videodensitometric computer analysis of ultrasound scanning images can be used to identify stable carotid plaques, which have higher total expression levels of MMP-9 and TIMP-1 than unstable plaques.
Keywordscarotid arteries atherosclerosis ultrasound tissue characterization
Advanced carotid plaques are complex structures, and their classification remains a challenging problem. It is not currently possible to predict whether a carotid plaque will produce symptoms or when symptoms will occur . The American Heart Association classification of human atherosclerotic lesions considers the presence or absence of different tissue components in plaques, but does not account for the proportion of each component or its location in the plaques . Because plaques are dynamic structures, changing through processes of stabilization and destabilization, the locations and the proportions of different plaque components are constantly being modified. Matrix metalloproteinase 9 (MMP-9) and tissue inhibitor of MMP (TIMP-1), which are secreted by infiltrating macrophages and smooth muscle cells, are present in all stages of atherosclerotic plaque progression, from normal tissue to advanced lesions, and are factors involved in plaque remodeling. These proteins promote the derangement of extracellular matrix, which is ultimately reflected in plaque images seen on Doppler ultrasound [3, 4]. Carotid plaques evaluated by ultrasound are usually described in terms of echogenicity, homogeneity, board regularity, ulceration, localization, extension, and the degree of stenosis. The final decision for surgical intervention is primarily based on the degree of plaque stenosis and on the patient symptoms. Previous studies have attempted to correlate the histological composition of surgically removed carotid plaques and their ultrasonic characteristics as determined by presurgical bidimensional imaging [5–8]. In a previous study from our laboratory, we were able to use videodensitometry to correlate the echogenicity of carotid images with the fibrous tissue and lipid components of removed specimens . We established that the first order parameter mean gray level determined from videodensitometric computer analysis of scan images may be used to identify vulnerable and potentially unstable lipid-rich carotid plaques, which are less echogenic in density than stable or asymptomatic, more densely fibrotic plaques. In that same study, we were able to differentiate stable from vulnerable plaques based on second-order parameter energy, although there were no correlation with the amounts of fibrous tissue or lipid components. We believe that videodensitometric second order parameters may be useful in identifying structural derangements in plaques, including inflammatory processes and disrupted extracellular matrix, that are modulated by matrix metalloproteinases and their inhibitors. We choose MMP-9 and TIMP-1 as markers of structural derangement in order to evaluate matrix remodeling in surgically removed carotid plaques. These proteins have been well studied and their role in plaque destabilization has been established. The objectives of the present study were to correlate the results of statistical analysis of videodensitometric parameters with MMP-9 and TIMP-1 expression levels in advanced carotid plaques.
Baseline patient characteristics
(n = 16)
(n = 14)
66.7 ± 6.8
67.6 ± 6.8
B. Tissue specimens and immunoblotting
Carotid plaques were obtained immediately after endarterectomy. All surgeries were performed using standard surgical techniques and with minimal manipulation of the specimen. All plaques were removed en bloc, without fragmentation or significant distortion. Sections used for MMP-9 and TIMP-1 quantification were snap-frozen in liquid nitrogen and stored at -70°C until processing. The protein expression levels of MMP-9 and TIMP-1 in tissue extracts were analyzed by immunoblotting following sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Specific regions of each plaque were not preselected for this analysis. The section was analyzed entirely, as described previously . Briefly, carotid samples (n = 30) were minced and homogenized in lysis buffer containing PBS (pH 7.2), 0.5% Triton X-100, 0.1% SDS, 0.5% sodium deoxycholate, and a protease inhibitor cocktail (Roche) at 4°C. The extracts were centrifuged (5000 rpm, 15 min, 4°C), and supernatants were collected and stored at -20°C until analysis. Total protein concentrations in the lysates were determined using the Bradford protein assay. Proteins (10 μg) were separated through a 10% acrylamide/bisacrylamide SDS gel and transferred to a nitrocellulose membrane. After incubation in nonfat milk, membranes were probed with anti-MMP (1:1000), or anti-TIMP-1 (1: 50) antibodies (Santa Cruz Biotechnology), followed by incubation in secondary antibodies conjugated to horseradish peroxidase (HRP). Reactions were developed using SuperSignal WestPico Chemiluminescent Substrate (Thermo Fisher Scientific Inc., Rockford, IL, USA). For endogenous controls, membranes were also probed with anti-β actin (1:5000; Sigma-Aldrich, St. Louis, MO, USA) and anti-mouse IgG conjugated to HRP (KLP 1:2000; Kirkegaard and Perry Laboratories, Gaithersburg, MD, USA). Densitometry analysis was performed using ImageJ software. Nine carotid arteries were removed from human adult cadavers that had not been preselected for carotid artery disease. These specimens did not have any macroscopic signs of atherosclerotic plaques and were used as normal tissue controls.
D. Ultrasonographic Image Acquisition and Preprocessing
Ultrasound assessment was performed 1 to 2 days before carotid endarterectomy. Conventional echo images were acquired with a commercially available 2D ultrasonic imaging system (Hewlett-Packard Sonos 5500; Andover, MA, USA). The system characterized arterial tissue at the bedside using a 5- to 12- MHz multifrequency linear transducer for all studies. This software enables the acquisition, storage, and retrieval of a sequence of continuous 2D conventional images, forming a continuous-loop digital recording of 2 s (60 frames per 2 s). Anterior, lateral, and posterior projections were used to image the plaque longitudinally. The position of the probe was adjusted so that the ultrasonic beam was vertical to the artery wall. Offline analysis of the 2D images was performed after retrieving the stored data from the built-in optical disc drive in the system. For videodensitometric analysis, the images from the magnetic optical disk were loaded into a computer installed with a specific software program (CaPAS - Carotid Plaque Analysis Software; University of Sao Paulo, Sao Paulo, Brazil). Subjective selection was performed to optimize the contours/borders, area, and contrast of each plaque. Selected static frames considered appropriate for analysis fulfilled the following criteria: 1) blood in the vicinity of the plaques was dark and echoically uniform, and 2) the atherosclerotic plaque was well delineated, horizontal, and of maximum thickness.
E. Quantitative texture analysis
Categorical variables were expressed as percentages, and continuous variables were expressed as means ± SD and medians. The Shapiro-Wilk test was used to evaluate sample normality. For quantitative parameters, the Mann-Whitney nonparametric test was used to compare groups. The Spearman coefficient was used to identify correlations between quantitative variables. Statistical significance was indicated by a value of p < 0.05. Analyses were performed using Statistica v. 8.0. Intra- and inter-examiner variabilities in ultrasonographic measurements were tested for all carotid images as proposed by Lin .
A. Expression of MMP-9 and TIMP-1
MMP-9 and TIMP-1 expression (in arbitrary units of band densitometry, normalized by β-actin expression), in the study groups
B. Videodensitometric Analysis
Comparisons of videodensitometric parameters between groups I and II
C. Correlation Between Immunoblotting and Videodensitometric Analysis
Correlations between protein expressions levels and videodensitometric parameters
The ultrasound imaging description of a plaque requires more than reporting the degree of stenosis. In evaluating the echogenicity of a carotid plaque, the ultrasonographer visualizes the plaque as a unique structure, and s/he can only subjectively determine its characteristics in general terms (i.e., hypoechoic or hyperechoic, heterogeneous or homogeneous). These characteristics are too subjective for daily clinical practice and are affected by the training and experience of the ultrasonographer. Despite advances in duplex ultrasound scanning technology, the process of acquiring, analyzing, and interpreting B-mode images has remained observer-dependent. Because various classifications have relied on the human observer rather than objective measurements, there has been great variability in the incidence of cerebrovascular events in relation to plaque morphology. A previous investigation  based on the appearance of radiofrequency signal determined that the echo coming from the transition between the intima-media arterial wall was of relatively low amplitude in normal and fatty samples compared to others pathologic subsets. This pioneering study from Picano et al. has been a great contribution to the field of ultrasound image analysis and image correlation with different tissues. Therefore, correlating plaque proteins expression with ultrasonic textural characteristics of carotid plaques based on videodensitometry, may be a noninvasive quantitative method for the identification of vulnerable carotid plaques. The videodensitometric method analyzes the echogenic and ultrasonic characteristics of the entire image selected. It reports the parameters obtained from the analyses of the entire selected image and can assess the extent of structural disorder represented by the image. In the present study, we correlated parameters from videodensitometric analyses with protein expression in plaques. In our previous study , we determined that expression levels of MMP-9 and TIMP-1 were higher in surgical specimens from asymptomatic patients, which corresponded to more stable chronic plaques. In that study, the entire section of plaque was analyzed and the total expression of each protein was determined. Another study  has corroborated these findings, and the authors speculated that a certain baseline level of metalloproteinase activity is necessary for the maintenance of a stable carotid plaque. Therefore, in the present study, we assessed the videodensitometric parameters acquired from the total imaging depicted and correlated them with the results from the entire section of plaque that was analyzed. We found positive correlations for MGL, homogeneity, and energy with expressions levels of MMP-9 and TIMP-1. Among first-order parameters, MGL assess overall contrast and the echodensity of an image and correlate well with stable or fibrotic and calcified carotid plaques [8, 13–24]. First-order statistical parameters are mathematical descriptors of the shape of the frequency distribution of a gray-level histogram, and are used to describe the overall brightness of the ROI. Classically, they correlate with structural tissue components based on attenuation of the ultrasound beam, and represent the intensity of image brightness without determining regional variations in the plaque. The second-order parameters are associated with patterns of texture, and depend less on the intensity of brightness and more on heterogeneity of the image. They are mathematical descriptors of the spatial distribution and dependence of gray levels within the ROI. They are based on a co-occurrence matrix that estimates the probability that a pair of pixels, each with its own gray level and separated by a displacement vector, occurs in the considered ROI. The second-order parameters do not indicate the amount of a specific tissue component, but how it is arranged and organised spatially. Therefore, in the present study, we attempted to correlate images derangements to protein expression levels. In that sense, the metalloproteinases are involved in the remodelling processes of the plaque [25–31]. According to our findings, MMP-9 and TIMP-1 were expressed at higher levels in normal tissues and in surgical specimens from asymptomatic patients than in specimens from symptomatic patients. Secreted by macrophages and smooth muscle cells in attempts to stabilize the plaque, MMP-9 and TIMP-1 derange the extracellular matrix and cause imbalances. Finally, attempting to correlate videodensitometric parameters with specific regions inside the plaques, such as regions with increased concentrations of inflammatory cells or highly vulnerable regions like the shoulder of a plaque, does not seem to be feasible. At the present time, it is not possible to use bidimensional imaging to select a specific region in the image and correlate that with immunohistochemical parameters. Bidimensional ultrasound produces an image of gray tone variations and it is impossible for the human eye to distinguish specific or small regions inside the plaque. While magnetic resonance (MRI) can be used to discriminate between the different stages of thrombus and hemorrhage formation, the videodensitometric approach with bidimensional images can not distinguish intra-plaque hemorrhage or classify plaque subtypes [32, 33]. Therefore, we assessed the image of an entire plaque and attempted to correlate with the entire section of the surgically removed plaque. Based on our results, plaques identified in bidimensional images as having higher energy values and greater homogeneity should be more stable and less prone to rupture. Such knowledge would change the clinical approach taken to treat to the patient. Using an inexpensive method, a physician could determine whether an asymptomatic patient with a high-degree of carotid stenosis needed immediate surgical treatment. In addition, since plaques can be easily assessed using this method, they can be frequently evaluated for changes in their structure. However, the videodensitometric approach, like radiofrequency analysis, is still limited to research applications and requires time and analysis away from the echo machine. We believe that this is the first study to use this approach and that future studies are needed with more patients to corroborate our findings.
Videodensitometric computer analysis of ultrasound scanning images may be used to identify more stable carotid plaques, which have higher expression levels of MMP-9 and TIMP-1 than unstable plaques.
- Hermus L, Lefrandt JD, Tio RA, Breek JC, Zeebregts CJ: Carotid plaque formation and serum biomarkers. Atherosclerosis. 2010, 213: 21-29. 10.1016/j.atherosclerosis.2010.05.013View ArticlePubMedGoogle Scholar
- Baroncini LAV, Nakao LS, Ramos SG, Pazin Filho A, Murta LO, Ingberman M, Tefé-Silva C, Précoma DB: Assessment of MMP-9, TIMP-1, and COX-2 in normal tissue and in advanced symptomatic and asymptomatic carotid plaques. Thrombosis Journal. 2011, 9: 6- 10.1186/1477-9560-9-6View ArticleGoogle Scholar
- Cipollone F, Prontera C, Pini B, Marini M, Fazia M, De Cesare D, Iezzi A, Ucchino S, Boccoli G, Saba V, Chiarelli F, Cuccurullo F, Mezzetti A: Overexpression of functionally coupled cyclooxygenase-2 and prostaglandin E synthase in symptomatic atherosclerotic plaques as a basis of prostaglandin E2-dependent plaque instability. Circulation. 2001, 104: 921-927. 10.1161/hc3401.093152View ArticlePubMedGoogle Scholar
- Turu MM, Krupinski J, Catena E, Rosell A, Montaner J, Rubio F, Alvarez-Sabin J, Cairols M, Badimon L: Intraplaque MMP-8 level are increased in asymptomatic patients with carotid plaque progression on ultrasound. Atherosclerosis. 2005, 187: 161-169.View ArticlePubMedGoogle Scholar
- Geroulakos G, Ramaswami G, Nicolaides A, James K, Labropoulos N, Belcaro G, Holloway M: Characterization of symptomatic and asymptomatic carotid plaques using high-resolution real-time ultrasonography. Br J Surg. 1993, 80: 1274-1277. 10.1002/bjs.1800801016View ArticlePubMedGoogle Scholar
- Tegos TJ, Sohail M, Sabetai MM, Robless P, Akbar N, Pare G, Stansby G, Nicolaides AN: Echomorphologic and histopathologic characteristics of unstable carotid plaques. Am J Neuroradiol. 2000, 21: 1937-1944.PubMedGoogle Scholar
- Sabetai MM, Tegos TJ, Nicolaides AN, Dhanjil S, Pare GJ, Stevens JM: Reproducibility of computer - quantified carotid plaque echogenicity. Can we overcome the subjectivity?. Stroke. 2000, 31: 2189-2196. 10.1161/01.STR.31.9.2189View ArticlePubMedGoogle Scholar
- Mazzone AM, Urbani MP, Picano E, Paterni M, Borgatti E, De Fabritiis A, Landini L: In vivo ultrasonic parametric imaging of carotid atherosclerotic plaque by videodensitometric technique. Angiology. 1995, 46: 663-672. 10.1177/000331979504600804View ArticlePubMedGoogle Scholar
- Baroncini LAV, Pazin Filho A, Murta LO, Martins AR, Ramos SG, Cherri J, Piccinato CE: Ultrasonic tissue characterization of vulnerable carotid plaque: correlation between videodensitometric method and histological examination. Cardiovascular Ultrasound. 2006, 4: 32- 10.1186/1476-7120-4-32View ArticlePubMedPubMed CentralGoogle Scholar
- Lin LI: A concordance correlation coefficient to evaluate reproducibility. Biometrics. 1989, 45: 255-268. 10.2307/2532051View ArticlePubMedGoogle Scholar
- Picano E, Landini L, Lattanzi F, Salvadori M, Benassi A, L'Abbate A: Time domain echo pattern evaluations from normal and atherosclerotic arterial walls: a study in vitro. Circulation. 1988, 77: 654-659. 10.1161/01.CIR.77.3.654View ArticlePubMedGoogle Scholar
- Hower CD, Dassow MS, Kajdacsy-Balla A, Seabrook GR, Jean-Claude J, Towne JB, Cambria RA: Metalloproteinase levels are decreased in symptomatic carotid plaques. J Surgical Research. 2000, 88: 155-159. 10.1006/jsre.1999.5794.View ArticleGoogle Scholar
- Beletsky VY, Kelley RE, Fowler M, Phifer T: Ultrasound densitometric analysis of carotid plaque composition. Stroke. 1996, 27: 2173-2177. 10.1161/01.STR.27.12.2173View ArticlePubMedGoogle Scholar
- Aly S, Bishop CC: An objective characterization of atherosclerotic lesion. An alternative method to identify unstable plaque. Stroke. 2000, 31: 1921-1924. 10.1161/01.STR.31.8.1921View ArticlePubMedGoogle Scholar
- Lal BK, Hobson RW, Pappas PJ, Kubicka R, Hameed M, Chakhtura EY, Jamil Z, Padberg FT, Haser PB, Duran WN: Pixel distribution analysis of B - mode ultrasound scan images predicts histologic features of atherosclerotic carotid plaques. J Vasc Surg. 2002, 35: 1210-1217. 10.1067/mva.2002.122888View ArticlePubMedGoogle Scholar
- Sztajel R, Momjian S, Momjian-Mayor I, Murith N, Djebaili K, Boissar G, Comelli M, Pizolato G: Stratified gray-scale median analysis and color mapping of the carotid plaque. Correlation with endarterectomy specimen histology of 28 patients. Stroke. 2005, 36: 742-745.Google Scholar
- Wilhjelm JE, Grønholdt MLM, Wiebe B, Jespersen SK, Hansen LK, Sillesen H: Quantitative analysis of ultrasound B-mode images of carotid atherosclerotic plaque: correlation with visual classification and histological examination. IEEE Trans Med Imag. 1998, 17: 910-922. 10.1109/42.746624.View ArticleGoogle Scholar
- Biasi GM, Froio A, Diethrich EB, Deleo G, Galimberti S, Mingazzini P, Nicolaides NA, Griffin M, Raithel D, Reid DB, Valsecchi MG: Carotid plaque echolucency increases the risk of stroke in carotid stenting. The imaging in carotid angioplasty and risk of stroke (ICAROS) study. Circulation. 2004, 110: 756-762. 10.1161/01.CIR.0000138103.91187.E3View ArticlePubMedGoogle Scholar
- Gray-Weale AC, Graham JC, Burnett JR, Byrne K, Lusby RJ: Carotid artery atheroma: comparison of preoperative B-mode ultrasound appearance with carotid endarterectomy specimen pathology. J Cardiovasc Surg. 1988, 29: 676-681.Google Scholar
- Mathiesen EB, Bonaa KH, Joakimsen O: Echolucent plaques are associated with high risk of ischemic cerebrovascular events in carotid stenosis: the tromso study. Circulation. 2001, 103: 2171-2175.View ArticlePubMedGoogle Scholar
- Gronholdt MLM, Nordestgaard BG, Schroeder TV, Vorstrup S, Sillesen H: Ultrasonic echolucent carotid plaques predict future strokes. Circulation. 2001, 104: 68-73. 10.1161/hc2601.091704View ArticlePubMedGoogle Scholar
- Tegos TJ, Stavropoulos P, Sabetai MM, Khodabakhsh P, Sassano A, Nicolaides AN: Determinants of carotid plaque instability: echoicity versus heterogeneity. Eur J Vasc Endovasc Surg. 2001, 22: 22-30. 10.1053/ejvs.2001.1412View ArticlePubMedGoogle Scholar
- Sabetai MM, Tegos TJ, Nicolaides AN, El-Atrozy TS, Dhanjil S, Griffin M, Belcaro G, Geroulakos G: Hemispheric symptoms and carotid plaque echomorphology. J Vasc Surg. 2000, 31: 39-49. 10.1016/S0741-5214(00)70066-8View ArticlePubMedGoogle Scholar
- Pedro LM, Pedro MM, Gonçalves I, Carneiro TF, Balsinha C, Fernandes e Fernandes R, Fernandes e Fernandes J: Computer -assisted carotid plaque analysis: characteristics of plaques associated with cerebrovascular symptoms and cerebral infarction. Eur J Vasc Endovasc Surg. 2000, 19: 118-123. 10.1053/ejvs.1999.0952View ArticlePubMedGoogle Scholar
- Higashikata T, Yamagishi M, Higashi T, Nagata I, Iihara K, Miyamoto S, Ishibashi-Ueda H, Nagaya N, Iwase T, Tomoike H, Sakamoto A: Altered expression balance of matrix metalloproteinases and their inhibitors in human carotid plaque disruption: Results of quantitative tissue analysis using real-time RT-PCR method. Atherosclerosis. 2006, 185: 165-172. 10.1016/j.atherosclerosis.2005.05.039View ArticlePubMedGoogle Scholar
- Fiotti N, Moretti ME, Bussani R, Altamura N, Zamolo F, Gerloni R, Ukovich L, Ober E, Silvestri F, Grassi G, Adovasio R, Giansante C: Features of vulnerable plaques and clinical outcome of UA/NSTEMI: relationship with matrix metalloproteinase functional polymorphisms. Atherosclerosis. 2011, 215: 153-159. 10.1016/j.atherosclerosis.2010.12.010View ArticlePubMedGoogle Scholar
- Ducharme A, Frantz S, Aikawa M, Rabkin E, Lindsey M, Rhode LE, Schoen FJ, Kelly RA, Werb Z, Libby P, Lee RT: Targeted deletion of matrix-metalloproteinase-9 attenuates legt ventricular enlargement and collagen accumulation after experimental myocardial infarction. J Clin Invest. 2000, 106: 55-62. 10.1172/JCI8768View ArticlePubMedPubMed CentralGoogle Scholar
- Kunte H, Kunte G, Busch MA, Weichert W, Ruckert RI, Harms L: Differences in carotid plaque content of macrophages, T cells and MMP-9 between patients with embolic and hemodynamic cerebral ischemia due to symptomatic carotid stenosis. Atherosclerosis. 2010, 211: 456-460. 10.1016/j.atherosclerosis.2010.03.005View ArticlePubMedGoogle Scholar
- Johnson C, Galis ZS: Matrix metalloproteinase-2 and -9 differentially regulate smooth muscle cell migration and cell-mediated collagen organization. Arterioscler Thromb Vasc Biol. 2004, 24: 54-60. 10.1161/01.ATV.0000100402.69997.C3View ArticlePubMedGoogle Scholar
- Galis ZS, Khatri JJ: Matrix metalloproteinases in vascular remodeling and atherogenesis: the good, the bad and the ugly. Circ Res. 2002, 90: 251-262.PubMedGoogle Scholar
- Fiotti N, Xiong W, Giansante C: MMP-2 genetic variant and plaque features of instability. Atherosclerosis. 2010, 210: 43-44. 10.1016/j.atherosclerosis.2010.02.019View ArticlePubMedGoogle Scholar
- Moody AR, Murphy RE, Morgan PS, Martel Al, Delay GS, Allder S, MacSweeney ST, Tennant WG, Gladman J, Lowe J, Hunt BJ: Characterization of complicated carotid plaque with magnetic resonance direct thrombus imaging in patients with cerebral ischemia. Circulation. 2003, 107: 3047-3052. 10.1161/01.CIR.0000074222.61572.44View ArticlePubMedGoogle Scholar
- Esposito L, Saam T, Heider P, Bockelbrink A, Pelisek J, Sepp D, Feurer R, Winkler C, Liebig T, Holzer K, Pauly O, Sadikovic S, Hemmer B, Poppert H: MRI plaque imaging reveals high-risk carotid plaques especially in diabetic patients irrespective of the degree of stenosis. BMC Medical Imaging. 2010, 10: 27- 10.1186/1471-2342-10-27View ArticlePubMedPubMed CentralGoogle Scholar
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