Thomas T. de Weert

In Vivo Characterization and Quantification of Atherosclerotic Carotid Plaque Components With Multidetector Computed Tomography and Histopathological Correlation

Objective—In a previous in vitro study we have demonstrated that atherosclerotic plaque components can be characterized with multidetector computed tomography (MDCT) based on differences in Hounsfield values (HV). Now we evaluated the use of MDCT in vivo to characterize and quantify atherosclerotic carotid plaque components compared with histology as reference standard. Methods and Results—Fifteen symptomatic patients with carotid stenosis (>70%) underwent MDCT angiography before carotid endarterectomy (CEA). From each CEA specimen 3 histological sections and corresponding MDCT images were selected. The HV of the major plaque components were assessed. The measured HV were: 657±416HU, 88±18HU, and 25±19HU for calcifications, fibrous tissue, and lipid core, respectively. The cut-off value to differentiate lipid core from fibrous tissue and fibrous tissue from calcifications was based on these measurements and set at 60 HU and 130 HU, respectively. Regression plots showed good correlations (R2>0.73) between MDCT and histology except for lipid core areas, which had a good correlation (R2=0.77) only in mildly calcified (0% to 10%) plaques. Conclusions—MDCT is able to quantify total plaque area, calcifications, and fibrous tissue in atherosclerotic carotid plaques in good correlation with histology. Lipid core can only be adequately quantified in mildly calcified plaques.

Atherosclerotic Plaque Surface Morphology in the Carotid Bifurcation Assessed With Multidetector Computed Tomography Angiography

Background and Purpose— Complicated (irregular or ulcerated) carotid plaques have proven to be independent predictors of stroke. We analyzed the frequency and location of plaque irregularities in a large cohort of patients with ischemic cerebrovascular disease and the relation with severity of stenosis, cardiovascular risk factors, and symptomatology. Methods— Multidetector CT angiography images from 406 patients were evaluated. Plaque surface morphology was classified as smooth, irregular, or ulcerated. The location of the ulceration was defined as proximal or distal to the point of maximum stenosis. Results— Atherosclerotic plaques with an open lumen were present in 448 carotid arteries; these plaques were classified as: smooth, 276 (62%); irregular, 99 (22%); and ulcerated, 73 (16%). Sixty-two (69%) of the ulcerations were located proximal to the point of maximum luminal stenosis. Complicated plaques were significantly (P<0.001) more common in carotid arteries with stenosis >30% than in those with stenosis <30%. There is an association between complicated plaques and hypercholesterolemia (OR, 3.0) and a trend toward an association with smoking (OR, 1.9). Complicated plaques are more often present in the symptomatic carotid artery than in the contralateral asymptomatic carotid artery; however, this is fully attributed to a significantly higher degree of stenosis in the symptomatic arteries. Conclusions— Multidetector CT angiography allows the classification of atherosclerotic carotid plaque surface. Complicated plaques are frequent in atherosclerotic carotid disease, especially with higher stenosis degree. Ulcerations are mostly located in the proximal part of the atherosclerotic plaque. Hypercholesterolemia and smoking are related with the presence of complicated plaques.

Optimization of CT Angiography of the Carotid Artery with a 16-MDCT Scanner: Craniocaudal Scan Direction Reduces Contrast Material-Related Perivenous Artifacts

OBJECTIVE The objective of our study was to compare the effect of a caudocranial scan direction versus a craniocaudal scan direction on arterial enhancement and perivenous artifacts in 16-MDCT angiography of the supraaortic arteries. SUBJECTS AND METHODS Eighty consecutive patients (51 men; mean age, 62 years; age range, 28-89 years) underwent scanning in the caudocranial direction (group 1; n = 40) or the craniocaudal direction (group 2; n = 40). All patients received 80 mL of contrast material followed by a 40-mL saline chaser bolus, both administered IV at 4 mL/sec. Bolus tracking was used. Attenuation inside the arterial lumen was measured at intervals of 1 sec throughout the data set. Attenuation in the superior vena cava (SVC) was measured. Contrast material-related perivenous artifacts were graded on a scale of 0-3 (none to extensive). RESULTS Attenuation in the ascending aorta, carotid bifurcation, and intracranial arteries was slightly lower in group 2 versus group 1 (231 +/- 64 H, 348 +/- 52 H, and 258 +/- 48 H vs 282 +/- 43 H, 381 +/- 73 H, and 291 +/- 77 H, respectively; p < 0.05). Maximum and mean arterial attenuations were slightly lower in group 2 versus group 1 (369 +/- 58 H and 303 +/- 48 H vs 401 +/- 71 H and 334 +/- 58 H; p < 0.05). Attenuation in the SVC was much lower in group 2 versus group 1 (169 +/- 39 H vs 783 +/- 330 H; p < 0.001). Mean streak artifact score was much lower in group 2 versus group 1 (1.3 +/- 0.9 vs 2.5 +/- 0.6; p < 0.001). CONCLUSION Use of a craniocaudal scan direction results in slightly lower attenuation of the carotid artery and much lower attenuation of the SVC. Streak artifacts are significantly reduced. This technique allows better evaluation of the ascending aorta and supraaortic arteries.

Atherosclerotic Plaque Ulceration in the Symptomatic Internal Carotid Artery Is Associated With Nonlacunar Ischemic Stroke

Background and Purpose— Atherosclerotic carotid plaque ulceration is considered a marker of previous plaque rupture and subsequent thromboembolism. It can be accurately detected with multidetector CTA. We hypothesized that atherosclerotic plaque ulceration is associated with nonlacunar ischemic stroke rather than lacunar stroke. Methods— Prospectively, 750 consecutive patients with transient ischemic attack or ischemic stroke symptoms in the anterior cerebral circulation were evaluated for the presence of atherosclerotic plaque ulceration in the symptomatic carotid artery with multidetector CTA. Patients with stroke attributable to cardiac embolism or other specific etiologies and patients with amaurosis fugax were excluded. Ischemic strokes in the remaining 534 patients were classified as nonlacunar (n=236) or lacunar (n=298) based on clinical symptoms and multidetector CT of the brain. Ulceration was defined as extension of contrast material beyond the vascular lumen into the surrounding plaque. Results— Plaque ulceration in the symptomatic carotid artery was more common in nonlacunar strokes (n=47; 20%) as compared to lacunar strokes (n=20; 7%; P<0.001). After adjustment for age, gender, cardiovascular risk factors, and degree of stenosis, ulcerations were independently associated with nonlacunar stroke compared to lacunar stroke (odds ratio, 2.70; 95% confidence interval, 1.43–5.09). Conclusions— Atherosclerotic carotid plaque ulceration is associated with nonlacunar ischemic stroke, independent of the degree of carotid stenosis. These results suggest that nonlacunar stroke and lacunar stroke are caused by different pathophysiological mechanisms.

Carotid artery segmentation and plaque quantification in CTA

A novel, slice-based, semi-automatic method for plaque segmentation and quantification in CTA of carotid arteries is introduced. The method starts with semi-automatic, levelset based, lumen segmentation initialized with three points. Pixel based GentleBoost classification is used to segment the inner and outer vessel wall region using distance from the lumen, intensity and Gaussian derivatives as features. 3D calcified regions located within the vessel wall are segmented using a similar set of features and the same classification method. Subsequently, an ellipse-shaped deformable model is fitted using the inner-outer vessel wall and calcium classification, and plaque components within the wall are characterized using HU ranges. The method is quantitatively evaluated on 5 carotid arteries. Vessel and plaque segmentation are compared to the interobserver variability. Furthermore, correlation of slice-based plaque component quantification with the ground truth values is determined. The accuracy of our method is comparable to the interobserver variability.

Quadrature coil design for high-resolution carotid artery imaging scores better than a dual phased-array coil design with the same volume coverage

To evaluate the ability of a custom‐built coil design to provide improved signal‐to‐noise ratio (SNR) and less signal drop with increasing depth at the carotid artery.

Evaluation of an improved technique for lumen path definition and lumen segmentation of atherosclerotic vessels in CT angiography

Vessel image analysis is crucial when considering therapeutical options for (cardio-) vascular diseases. Our method, VAMPIRE (Vascular Analysis using Multiscale Paths Inferred from Ridges and Edges), involves two parts: a user defines a start- and endpoint upon which a lumen path is automatically defined, and which is used for initialization; the automatic segmentation of the vessel lumen on computed tomographic angiography (CTA) images. Both parts are based on the detection of vessel-like structures by analyzing intensity, edge, and ridge information. A multi-observer evaluation study was performed to compare VAMPIRE with a conventional method on the CTA data of 15 patients with carotid artery stenosis. In addition to the start- and endpoint, the two radiologists required on average 2.5 (SD: 1.9) additional points to define a lumen path when using the conventional method, and 0.1 (SD: 0.3) when using VAMPIRE. The segmentation results were quantitatively evaluated using Similarity Indices, which were slightly lower between VAMPIRE and the two radiologists (respectively 0.90 and 0.88) compared with the Similarity Index between the radiologists (0.92). The evaluation shows that the improved definition of a lumen path requires minimal user interaction, and that using this path as initialization leads to good automatic lumen segmentation results.

Plaque Ulceration Is Associated With High Stear Stress in Stenotic Carotid Bifurcations

Cerebrovascular events are related to atherosclerotic disease in the carotid arteries and they are often caused by rupture of an atherosclerotic plaque. Rupture-prone, or vulnerable, plaques are characterized by their specific morphology and composition: a large lipid pool covered by a thin fibrous cap infiltrated by macrophages and expansive remodeling. The strength of the cap of a vulnerable plaque is determined by the material properties of the cap and its thickness. Plaque ruptures are often observed at the upstream region of the plaque [1], were the wall shear stress (WSS) is considered to be highest. High WSS is known for its influence on many processes affecting, among others, tissue regression [2]. Therefore, high shear stress induced cap regression might contribute to cap thinning, thus enhancing plaque vulnerability, and eventually leading to cap rupture [3,4]. Here we present the first results of a new approach to study the relationship between WSS and the location of ulcerations in severely stenotic carotid bifurcations by using computational fluid dynamics and computed tomography.Copyright