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.

Segmentation of the outer vessel wall of the common carotid artery in CTA.

A novel method is presented for carotid artery vessel wall segmentation in computed tomography angiography (CTA) data. First the carotid lumen is semi-automatically segmented using a level set approach initialized with three seed points. Subsequently, calcium regions located within the vessel wall are automatically detected and classified using multiple features in a GentleBoost framework. Calcium regions segmentation is used to improve localization of the outer vessel wall because it is an easier task than direct outer vessel wall segmentation. In a third step, pixels outside the lumen area are classified as vessel wall or background, using the same GentleBoost framework with a different set of image features. Finally, a 2-D ellipse shape deformable model is fitted to a cost image derived from both the calcium and vessel wall classifications. The method has been validated on a dataset of 60 CTA images. The experimental results show that the accuracy of the method is comparable to the interobserver variability.

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.

Assessment of atherosclerotic carotid plaque volume with multidetector computed tomography angiography.

PURPOSE: The amount of atherosclerotic plaque and its components (calcifications, fibrous tissue, and lipid core) could be better predictors of acute events than the now currently used degree of stenosis. Therefore, we evaluated a dedicated software tool for volume measurements of atherosclerotic carotid plaque and its components in multidetector computed tomography angiography (MDCTA) images. MATERIALS AND METHODS: Data acquisition was approved by the Institutional Review Board and all patients gave written informed consent. MDCTA images of 56 carotid arteries were analyzed by three observers. Plaque volumes were assessed by manual drawing of the outer vessel contour. The luminal boundary was determined based on a Hounsfield-Unit (HU) threshold. The contribution of different components was measured by the number of voxels within defined ranges of HU-values (calcification >130 HU, fibrous tissue 60-130 HU, lipid core <60 HU). Interobserver variability (IOV) was assessed. RESULTS: Plaque volume was 1,259 +/- 621 mm3. The calcified, fibrous and lipid volumes were 238 +/- 252 mm3, 647 +/- 277 mm3 and 376 +/- 283 mm3, respectively. IOV was moderate with interclass correlation coefficients (ICC) ranging from 0.76 to 0.99 and coefficients of variation (COV) ranging from 3% to 47%. CONCLUSION: Atherosclerotic carotid plaque volume and plaque component volumes can be assessed with MDCTA with a reasonable observer variability.

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

PURPOSE: 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. MATERIALS AND METHODS: Phased-array surface coils can provide a high SNR to image the carotid vessel wall. However, given the required field-of-view (FOV) and penetration depth, these coils show either a fast signal drop with increasing depth or a moderate SNR at increased coil size. A quadrature surface coil (a butterfly coil in conjunction with a linear single-loop coil) was compared with a phased-array coil in phantom and human studies. RESULTS: The phantom studies showed that the quadrature coil has better SNR over the required FOV than a standard phased-array coil (26% at 3 cm depth). CONCLUSION: The quadrature coil enables better image quality to be achieved.

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.

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.

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.

Sixteen-detector row CT angiography of carotid arteries: comparison of different volumes of contrast material with and without a bolus chaser.

PURPOSE: To prospectively compare different volumes of intravenously administered contrast material with and without a bolus chaser at 16-detector row computed tomographic (CT) angiography of the carotid arteries. MATERIALS AND METHODS: Institutional Review Board approval and informed consent were obtained. Seventy-five consecutive patients (44 men, 31 women; mean age, 63 years; range, 22-85 years) were allocated to one of three protocols: group 1, 80 mL of contrast material; group 2, 80 mL of contrast material followed by 40 mL of saline; and group 3, 60 mL of contrast material followed by 40 mL of saline. Bolus tracking was used to synchronize contrast material injection with CT scanning. The attenuation in Hounsfield units was measured from the ascending aorta to the intracranial arteries at 1-second intervals. Differences were tested with the Student t test. RESULTS: The maximum attenuation was reached in the proximal internal carotid artery in all groups. The addition of a bolus chaser to 80-mL contrast material resulted in a higher mean attenuation (323 HU +/- 39 vs 351 HU +/- 60, P = .06), higher maximum attenuation (393 HU +/- 53 vs 425 HU +/- 76, P = .09), and higher minimum attenuation (240 HU +/- 34 vs 264 HU +/- 48, P < .05). Group 3 had lower mean, maximum, and minimum attenuation than did groups 1 and 2 (P < .001). CONCLUSION: The addition of a bolus chaser to 80 mL of contrast material results in a slightly higher attenuation. Decreasing the volume of contrast material from 80 to 60 mL results in a significantly lower attenuation.

Carotid plaque composition and cerebral infarction: MR imaging study.

BACKGROUND AND PURPOSE: Besides the severity of carotid artery stenosis, atherosclerotic plaque composition is an important determinant of cerebral symptoms. We analyzed the relationship between the composition of the atherosclerotic plaque at the carotid artery bifurcation and ipsilateral ischemic cerebral lesions on MR imaging. METHODS: Forty-one patients with symptomatic carotid artery stenosis (>70%) underwent black-blood, fast spin-echo imaging of the carotid artery and turbo fluid-attenuated inversion recovery (t-FLAIR) imaging of the brain. Plaque regions with a relative decrease in signal intensity in the plaque from proton density-weighted (TE = 14 ms) to T2-weighted (TE = 50 ms) imaging were considered to be lipid cores. We assessed the number and location of infarcts in the ipsilateral cortex, basal ganglia, and centrum semiovale, and hyperintense white matter lesions on t-FLAIR images. RESULTS: Lipid in the atherosclerotic plaque at the carotid bifurcation was seen in 25 patients. Ipsilateral infarctions were seen in 22 (54%); most often, it involved the centrum semiovale. Patients with a lipid core had an ipsilateral infarct more often than patients without a lipid core (68% vs. 31%; P = .03). Centrum semiovale infarcts were more frequent (56% vs. 25%, P = .06) and the median number of centrum semiovale infarcts was higher P = .04) in patients with a lipid core than in patients without a lipid core. CONCLUSION: Ischemic cerebral lesions were common in patients with symptomatic carotid artery disease. Plaque composition, as assessed with MR imaging, is related to the presence and extent of ischemic cerebral lesions.

In vitro characterization of atherosclerotic carotid plaque with multidetector computed tomography and histopathological correlation.

This in vitro study evaluated the performance of 16-slice multidetector computed tomography (MDCT) in the assessment of carotid plaque components, with histology as the gold standard. Twenty-one specimens (n=21) were scanned and reconstructed after optimization of the protocol. Three corresponding MDCT images and histologic sections were selected from each specimen. The Hounsfield values (HV) of the major plaque components (calcifications, fibrous tissue and lipid) were assessed. Plaque areas (mm2) assessed with MDCT were compared with the results from histologic analysis. A value of 140 kVp and an intermediate reconstruction algorithm was the optimal protocol. In 15 out of 21 specimens it was possible to match MDCT images with histology. The HV of calcifications, fibrous tissue and lipid were 45+/-21, 79+/-20 and 960+/-491 HU (P<0.001), respectively. Plaque areas were compared in 27 matched levels. The calcified and lipid areas on MDCT and histology correlate well (R2=0.83 and R2=0.68, respectively). The mean difference in lipid area was 0.1 mm2 (95% CI=-2.1-2.3 mm2). This in vitro study showed that MDCT is capable of characterizing and quantifying the lipid rich portion of the atherosclerotic plaque.