Atherosclerosis of the carotid artery: evaluation by magnetic resonance angiography

Intraplaque high-intensity signal on time-of-flight magnetic resonance angiography and restenosis after carotid artery stenting

OBJECTIVE

To test the hypothesis that intraplaque hemorrhage is a predictor of restenosis after carotid artery stenting (CAS), the association between intraplaque high-intensity signal (HIS) on time-of-flight MR angiography (TOF-MRA), as a marker of intraplaque hemorrhage, and restenosis after CAS was assessed in the present observational study.

METHODS

Consecutive patients who underwent initial CAS for atherosclerotic stenosis in the cervical internal carotid artery in the authors' department were enrolled. Of these, patients without preprocedural cervical TOF-MRA were excluded. Outcome measures were ≥ 50% restenosis, defined as a peak systolic velocity of > 1.3 m/sec; or occlusion and ≥ 70% restenosis, defined as a peak systolic velocity of > 2.1 m/sec; or occlusion on carotid duplex ultrasound.

RESULTS

Of 230 consecutive patients who underwent initial CAS, 22 without preprocedural cervical TOF-MRA were excluded. Of the remaining 208 patients (mean age 73 years; 33 women), 46 had intraplaque HIS. Ultrasound follow-up was not performed in 4 patients. The median follow-up duration was 3.2 years (interquartile range 1.7-5.1 years). During the follow-up period, 102 patients had ≥ 50% restenosis and 36 had ≥ 70% restenosis. Intraplaque HIS was significantly associated with increased risk of ≥ 50% restenosis (adjusted hazard ratio 2.18; 95% CI 1.28-3.68) and ≥ 70% restenosis (adjusted hazard ratio 3.12; 95% CI 1.32-7.52).

CONCLUSIONS

Intraplaque HIS on TOF-MRA was associated with increased risk of restenosis after CAS. The present results indicate that intraplaque hemorrhage is a predictor of restenosis after CAS.

Carotid Cavernous Fistula during Thrombectomy for Acute Ischemic Stroke: A Case Report

Objective

We report a rare complication, carotid cavernous fistula (CCF), due to vessel perforation during thrombectomy for acute ischemic stroke (AIS).

Case Presentation

An 88-year-old woman underwent thrombectomy for left C4 occlusion of the internal carotid artery. There was strong resistance at the medial C4 while the microguidewire was guided distally, and a CCF was found after deploying and retrieving the stent. It was thought to have been caused by perforation due to intracranial atherosclerotic stenosis of the internal carotid artery.

Conclusion

During thrombectomy for intracranial large vessel occlusion underlying intracranial atherosclerotic stenosis, the risk of vascular injury should be kept in mind.

Lipid Core Plaque Distribution Using Near-infrared Spectroscopy Is Consistent with Pathological Evaluation in Carotid Artery Plaques

Carotid artery stenting (CAS) is performed as a treatment for carotid artery stenosis. However, lipid-rich plaques cause embolic complications and sequelae. Near-infrared spectroscopy (NIRS) can identify lipid components by applying a near-infrared absorption pattern, and the distribution of lipid components can be evaluated as the maximum lipid core burden index (maxLCBI). Intravascular ultrasound (IVUS) equipped with NIRS has been clinically applied recently, and its diagnostic usefulness and validation have been reported for coronary arteries; however, its consistency with actual pathological diagnosis in carotid artery lesions has not been validated. In this study, we investigated the consistency between the maxLCBI values and histopathological diagnoses. Patients with cervical carotid artery stenosis who underwent carotid endarterectomy (CEA) were examined in this prospective study. Pathological diagnosis was determined after NIRS evaluation, which was performed on the extracted plaques ex vivo. The histological slices of decalcified and paraffin-embedded sections were stained by hematoxylin–eosin (HE) and Elastica van Gieson (EVG), and for low-density lipoprotein (LDL), C-reactive protein (CRP), CD68, and glycophorin A. The correlation between maxLCBI values and histological findings. Seventy lesions assessed by NIRS were pathologically analyzed. There was a positive linear correlation between maxLCBI values and pathological findings as determined by HE (angle), HE (area%), EVG, CRP, and CD68 staining (respectively, r = 0.624, p <0.001; r = 0.578, p <0.001; r = 0.534, p <0.001; r = 0.723, p <0.001; r = 0.653, p <0.001). In conclusion, the maxLCBI values assessed by NIRS showed a significant positive linear correlation with pathological evaluations in carotid lesions. The maxLCBI values in carotid arteries are consistent with pathological evaluations.

Evaluation of carotid atherosclerotic plaque surface characteristics utilizing simultaneous noncontrast angiography and intraplaque hemorrhage (SNAP) technique

PURPOSE

To evaluate the feasibility of the Simultaneous Noncontrast Angiography and intraPlaque hemorrhage (SNAP) technique in identification of carotid plaque surface characteristics compared with the conventional multicontrast vessel wall imaging protocol.

MATERIALS AND METHODS

Thirty symptomatic patients with carotid plaque were recruited and underwent carotid artery magnetic resonance imaging (MRI) (3.0T) using a conventional multicontrast protocol and SNAP sequence. As an intrinsic multicontrast sequence, SNAP could generate a gray blood reference (Ref) image set, a black blood corrected real (CR) image set, and a bright blood MR angiography (MRA) image set. A bright blood SNAP Ref2 image was implemented by combining Ref and MRA images for facilitating plaque surface characteristics evaluation. The presence/absence of calcification (CA), juxtaluminal calcification (JCA), and ulceration was assessed. The agreement between SNAP and multicontrast vessel wall protocol in identifying CA, JCA, and ulceration was analyzed using Cohen's kappa analysis. The interreader and intrareader reproducibility of SNAP imaging in identifying plaque surface characteristics was also assessed.

RESULTS

Good to excellent agreement was found between SNAP and conventional multicontrast protocol in identifying CA (κ = 0.74, 95% confidence interval [CI]: 0.54-0.93), JCA (κ = 0.81, 95% CI: 0.66-0.97), and ulceration (κ = 0.82, 95% CI: 0.65-0.99). In addition, excellent intrareader and interreader reproducibility was found for SNAP imaging in identification of CA, JCA, and ulceration.

CONCLUSION

SNAP imaging showed excellent agreement with multicontrast imaging and high reproducibility in identification of both JCA and ulceration, suggesting that SNAP imaging may be a time-efficient, alternative tool in identification of plaque surface characteristics in carotid arteries.

LEVEL OF EVIDENCE

4 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:634-639.

High-intensity signal on time-of-flight magnetic resonance angiography indicates carotid plaques at high risk for cerebral embolism during stenting

BACKGROUND AND PURPOSE

A major disadvantage of carotid artery stenting (CAS) compared to carotid endarterectomy is the increased risk of cerebral embolism. Thus, establishing a simple method to discriminate fragile plaques on preoperative routine examination is important. The present study examined whether high-intensity signal (HIS) in the plaque on time-of-flight (TOF) MRA, performed for screening, can discriminate plaque at high risk for cerebral embolism during CAS.

METHODS

In the 30 patients treated using carotid endarterectomy, relationships between pathological findings of the plaques and TOF-MRA findings were analyzed. In the 112 patients treated using CAS, postoperative ipsilateral ischemic lesions on diffusion-weighted imaging and periprocedural ischemic symptoms were analyzed.

RESULTS

The percentage area of intraplaque hemorrhage stained by glycophorin A was significantly larger in HIS-positive plaques (51.8%±9.8%) than in HIS-negative plaques (8.6%±9.4%; P<0.001). Postoperative ischemic lesions on diffusion-weighted imaging were more frequent in the HIS-positive plaques (25/38; 65.8%) than in the HIS-negative plaques (26/74; 35.1%; P=0.002). Periprocedural ischemic symptoms were more frequently observed in HIS-positive plaques (7/38; 18.4%) than in HIS-negative plaques (1/74; 1.4%; P=0.003). Multivariate logistic regression analysis identified HIS on TOF-MRA as an independent predictor of periprocedural ischemic symptoms (odds ratio, 15.08; 95% confidence interval, 1.76-129.0).

CONCLUSIONS

HIS in the plaque on TOF-MRA performed for screening could discriminate plaques at high risk for cerebral embolism during CAS.

MR imaging in carotid artery atherosclerosis plaque characterization

AIM

To evaluate the potential role of carotid artery atherosclerosis plaque magnetic resonance (MR) microimaging as magnetic resonance imaging (MRI) marker, ex vivo MR images were acquired at optimized parameters on 9.4T Bruker animal imager for occluded tissue resected by carotid endarterectomy (CEA) and corresponding histopathological analysis was made.

METHODS AND MATERIALS

For imaging, CEA tissues of size 2-6 cm long and 0.5-1.5 cm wide, were transferred to 15 ml co-polymer laboratory culture tubes containing either 10% formalin in phosphate buffered saline (PBS) or in 50% glycerol in PBS. Imaging protocol was set at TE=30 ms, TR=1.5 s, matrix size=265 x 512, NEX=128, slice thickness=1 mm and in-plane resolution=0.1 mm for total sample size 2.5 cm. Soon after imaging done, carotid artery tissues were cut into 5-mm segments and processed for histological section for successive 5-micrometer slices. To compare morphology of 5 mum thin CEA section with that of 1 mm MR slices, registration was obtained between histologic sections and MR slices. Contrast and magnetic resonance relaxation characteristics were analyzed.

RESULTS

Total carotid artery area computed by MR imaging was correlated with areas determined from histologic sections (r(2)=0.989, p=0.0001). For the lumen area, the correlation between MR images and histologic area was (r(2)=0.942, p=0.0001). Relaxation times and T(2) parametric images of different plaque components were determinant for contrast resolution. Scan parameters were optimized for fibrous cap and atheroma. Scan parameters were characteristic for comparison at 1.5T and 9.4T MR imagers.

CONCLUSION

The observed correlation validated MR microimaging to assess morphological features of carotid artery plaques and contrast resolution highlighted the potential of in vivo MR imaging as non-invasive MRI marker to monitor carotid artery plaque morphometry and plaque composition.

A Critical Appraisal of the Performance, Reporting, and Interpretation of Studies Comparing Carotid Plaque Imaging With Histology

Background and Purpose— Carotid plaque instability is an important determinant of stroke risk. There are now a number of different imaging techniques that provide information on carotid plaque morphology. However, it is unclear how they compare with one another or whether they can reliably assess plaque instability. Studies comparing imaging with pathology have shown highly variable results, even for similar imaging techniques. This may be because of variable pathology techniques rather than differences in imaging.

Methods— We performed a systematic review of studies that compared carotid imaging with histology of the excised plaque published between January 1995 and September 2004. We assessed the quality and comparability of these studies. In particular, we determined which histology methods were used and whether observer reproducibility of the histology assessment was reported.

Results— Among 73 eligible studies, histological methods were poorly reported and highly variable; 23% reported reproducibility data for imaging and only 12% reported reproducibility data for histology. Of 29 studies that reported quantitative results of blinded comparisons, there were methodological deficiencies and the results were highly variable. No study considered the extent to which the lack of reproducibility influenced the imaging-pathological correlations reported.

Conclusions— Pathological correlation in studies of carotid plaque imaging cannot be reliably interpreted or compared because of incomparable and poorly reported histology methods. We make recommendations for the performance, reporting, and interpretation of imaging–pathological correlation studies and highlight the need for consensus guidelines.

Cross-sectional magnetic resonance angiography is accurate in predicting degree of carotid stenosis

Carotid stenosis is currently estimated using methods based on flow velocity or two-dimensional projection images. Manipulation of magnetic resonance (MR) images in three dimensions (3-D MR) allows for direct measurement of carotid artery cross-sectional luminal area. The objectives of this study were (1) to assess the accuracy of 3-DMR as a technique for estimating carotid artery stenosis, and (2) to compare 3-D MR results with estimates from duplex ultrasound sonography (DUS) and conventional angiography. Twenty-nine patients underwent rapid, contrast-enhanced MRA within 1 month prior to carotid endarterectomy to obtain 3-D angiographic images of the carotid bifurcation. From these data, post-processing software was used to generate a longitudinal axis through the center of the vessel along which orthogonal cross-sectional images were taken. Luminal area measurements at the location of tightest stenosis and the distal normal internal carotid artery were obtained and used to calculate percent area stenosis. Applying the same procedure, 18 en bloc, ex vivo carotid plaques served as the standard against which we compared in vivo 3-D MR measurements at the location of tightest stenosis. Percent stenosis comparisons between MRA, angiography, and duplex ultrasound were also made. Our results showed that the measurement of luminal area by 3-DMR is accurate in predicting the degree of carotid stenosis. Direct measurement of luminal area may overcome limitations inherent to methods that rely on flow velocities and two-dimensional views of the carotid vasculature. A larger prospective study is necessary to confirm the reliability of this technique.

Comparison of carotid vessel wall area measurements using three different contrast-weighted black blood MR imaging techniques

Measuring carotid artery plaque burden from MRI is a reliable method for monitoring regression and progression of atherosclerosis. However, to measure all available images would be very time consuming, and in practice the image quality (IQ) of these images may be inconsistent, which can directly impact the quality of measurement. It is hypothesized that if IQ is comparable among different contrast weighted images, then carotid artery area measurements obtained from different contrast images of the same location will produce identical results. To test this, T1, proton density and T2 weighted images were acquired from ten patients (51 +/- 7 years old). Carotid lumen and vessel wall area was measured using a custom designed software program. The results showed strong agreement evidenced with only small differences on both lumen (mean: 40.5 mm(2)) and wall (mean: 52.6 mm(2)) area measurement among different weighted images. The maximum absolute mean differences are less than 2.7 mm(2) and 4.4 mm(2), and 90(th) percentile of the absolute differences are 5.6 mm(2) and 8.2 mm(2) respectively. In conclusion, different contrast weighted images with high and comparable IQ will yield similar results in lumen and vessel wall area measurement. At each matched location, it is recommended that the image with the highest IQ be used for area measurement.

Visualization of fibrous cap thickness and rupture in human atherosclerotic carotid plaque in vivo with high-resolution magnetic resonance imaging

BACKGROUND

The results of studies of advanced lesions of atherosclerosis suggest that the thickness of the fibrous cap that overlies the necrotic core distinguishes the stable lesion from one that is at high risk for rupture and thromboembolic events. We have developed a high-resolution MRI technique that can identify the fine structure of the lesion, including the fibrous cap, in vivo. The aim of the present study was to determine the agreement between in vivo MRI and lesion architecture as seen on histology and gross tissue examination to identify fibrous cap thickness and rupture.

METHODS AND RESULTS

Twenty-two subjects who were scheduled for carotid endarterectomy underwent MRI with a 3-dimensional multiple overlapping thin slab angiography protocol. The appearance of the fibrous cap was categorized as (1) an intact, thick, (2) an intact, thin, or (3) a ruptured fibrous cap on MRI, gross, and histological sections. Thirty-six sites were available for comparison between MRI and histology. There was a high level of agreement between MRI and histological findings: 89% agreement, kappa (95% CI)=0.83 (0.67 to 1. 0), weighted kappa=0.87. Spearman's correlation coefficient was 0.88 (significant to the 0.01 level).

CONCLUSIONS

These findings indicate that high-resolution MRI with a 3-dimensional multiple overlapping thin slab angiography protocol is capable of distinguishing intact, thick fibrous caps from intact thin and disrupted caps in atherosclerotic human carotid arteries in vivo. This noninvasive technique has the potential to permit studies that examine the relationship between fibrous cap changes and clinical outcome and to permit trials that evaluate therapy intended to "stabilize" the fibrous cap.

Giant cell (temporal) arteritis involving both external and internal carotid arteries

A 76-year-old woman with giant cell (temporal) arteritis was described; she presented with a one year history of headache and tinnitus. Histopathological findings from a superficial temporal artery showed arteritis with granulomatous changes. Bilateral carotid arteriograms demonstrated the stenoses of both internal carotid arteries as well as the narrowing of the superficial temporal arteries. Although we dermatologists rarely encounter the disease in daily clinical practice, it is of clinical importance to perform cerebral angiography in patients suspected of temporal arteritis.

Multiple region MRI

Traditional Fourier MR imaging (FT MRI) utilizes the Whittaker-Kotel'nikov-Shannon (WKS) sampling theorem. This theorem specifies the spatial frequency components which need to be measured to reconstruct an image with a known field of view (FOV). In this paper, we generalize this result in order to find the optimal k-space sampling for images that vanish except in multiple, possibly non-adjacent regions within the FOV. This provides the basis for "multiple region MRI" (mrMRI), a method of producing such images from a traction of the k-space samples required by the WKS theorem. Image reconstruction does not suffer from noise amplification and can be performed rapidly with fast Fourier transforms, just as in conventional FT MRI. The mrMRI method can also be used to reconstruct images that have low spatial-frequency components throughout the entire FOV and high spatial frequencies (i.e. edges) confined to multiple small regions. The greater efficiency of mrMRI sampling can be parlayed into increased temporal or spatial resolution whenever the imaged objects have signal or "edge" intensity confined to multiple small portions of the FOV. Possible areas of application include MR angiography (MRA), interventional MRI, functional MRI, and spectroscopic MRI. The technique is demonstrated by using it to acquire Gd-enhanced first-pass 3D MRA images of the carotid arteries without the use of bolus-timing techniques.

Mild carotid artery atherosclerosis: assessment by 3-dimensional time-of-flight magnetic resonance angiography, with reference to intravascular ultrasound imaging and contrast angiography

BACKGROUND AND PURPOSE

Our aim was to evaluate the usefulness of 3-dimensional time-of-flight magnetic resonance angiography (3-D TOF MRA) in detection and quantification of mild atherosclerotic changes of carotid arteries with reference to intravascular ultrasound (IVUS) and contrast angiography.

METHODS

TOF MRA at 1.5 T, IVUS, and selective digital subtraction angiography were performed on 31 extracranial carotid arteries of 27 patients (mean age, 52 years; age range, 17 to 75 years) undergoing neuroendovascular interventions. The atherosclerotic lesions were registered, and quantitative measurements of plaque thickness, luminal diameters, and diameter stenosis were independently performed for the imaging modalities.

RESULTS

Among 170 arterial segments analyzed, IVUS revealed a total of 48 atherosclerotic lesions (mean diameter stenosis, 17%; range, 4% to 40%), only 25 of which were depicted on digital subtraction angiography. Analysis of the axial source images of TOF MRA resulted in sensitivity of 77% to 83% and specificity of 71% to 80% in lesion depiction for the 2 readers with reference to IVUS. The values of diameter stenosis measured from MRA and IVUS were closely interrelated (r=0.53 to 0.61, P<0.001).

CONCLUSIONS

Three-dimensional TOF MRA is feasible and moderately accurate for evaluation of mild atherosclerotic changes of carotid arteries.

Lower extremity occlusive disease: diagnostic imaging with a combination of cardiac-gated 2D phase-contrast and cardiac-gated 2D time-of-flight MRA

PURPOSE

The goal of this work was to test the ability of a combination of 2D phase-contrast MR angiography (2D-PC-MRA) and triggered 2D time-of-flight MRA (2D-TOF-MRA) in comparison to intraarterial digital subtraction angiography (DSA) to correctly diagnose the location and shape of occlusive lesions in the iliac and femoral arteries and to determine whether 2D-TOF-MRA is helpful to clarify questionable lesions demonstrated by 2D-PC-MRA.

METHODS

In 50 patients with claudication, 2D-PC-MRA was performed in three consecutive coronal positions from the aortic bifurcation to below the trifurcation. Axial 2D-TOF-MRA was performed additionally at the site of detected lesions of >50% and lesions in doubt to obtain more precise information about the stenosis. Lesions were classified as follows: low grade occlusion, <50%; high grade occlusion, >50%. MRA was performed within 24 h of a DSA examination.

RESULTS

In all patients, the arterial tree from the aortic bifurcation to the trifurcation could be visualized. One hundred twelve lesions were detected by MRA. Sensitivity was 96% and specificity was 92%. Sixty-two lesions were classified as high grade occlusion and reevaluated. In this category, sensitivity was 100% and specificity was 96%.

CONCLUSION

The combination of 2D-PC-MRA with triggered 2D-TOF-MRA detects stenotic lesions in the lower extremity arterial system with high sensitivity and specificity.

Intravascular ultrasound and magnetic resonance imaging in the assessment of atherosclerotic lesions in rabbit aorta. Correlation to histopathologic findings

RATIONALE AND OBJECTIVES

The authors compare the usefulness of intravascular ultrasound (IVUS) and magnetic resonance imaging (MRI) for quantitation of atherosclerosis in hyperlipidemic rabbits, correlated with histopathology.

METHODS

Magnetic resonance imaging with T1- and T2-weighted spin echo sequences and three-dimensional time-of-flight MR angiography of the abdominal aorta was performed on seven rabbits using a 1.5 T MR imager and a standard head coil. X-ray angiography and IVUS examination (3.5 F/30 MHz imaging catheter) was performed via carotid artery access.

RESULTS

Time-of-flight MR angiography source images provided the best resolution and plaque-lumen contrast in visual comparison between the different MRI sequences. Intra- and interobserver reproducibilities of the lesion thickness and area measurements were similar in IVUS and MRI (Pearson correlations 0.52-0.97; P < 0.01). The measurements from IVUS and MRI correlated closely with each other as well as with those made from histopathologic specimens (Pearson correlations 0.50-0.79; P < 0.001). The measurements from IVUS were somewhat more accurate than those made from MRI.

CONCLUSIONS

Both MRI and IVUS with clinically available imaging equipments are feasible and accurate for the quantitation of experimental atherosclerosis of rabbit aorta.