Bright and black blood imaging of the carotid bifurcation at 3.0T

Diagnostic potential of routine brain MRI and high-resolution, multi-contrast vessel wall imaging in the detection of internal carotid artery dissection

Objective

Cervical artery dissection (CAD) is one of the major causes of stroke and most commonly occurs at the site of the extracranial internal carotid artery (ICA). This study aimed to assess the value of routine brain MRI, clinical information, and high-resolution, multi-contrast vessel wall MR imaging (hrVWI) for the timely detection of ICA dissection.

Methods

A total of 105 patients with CAD and 105 without CAD were recruited for this study. The lesion type in the patients was determined based on images from different modalities, including brain MRI, magnetic resonance angiography (MRA), computed tomography angiography (CTA), digital subtraction angiography (DSA), ultrasonography, and hrVWI and clinical information. Each lesion was reviewed to determine the type following a stepwise procedure by referring to (1) brain MRI only; (2) brain MRI and clinical information; (3) hrVWI only; and (4) hrVWI, CTA, DSA, and clinical information.

Results

Typical clinical presentations of patients with potential CAD include headache, neck pain, and/or Horner's syndrome. Representative imaging signs in the brain MRI included a crescentic or circular iso- or hyperintensity around the lumen, a curvilinear and isointense line crossing the lumen, or aneurysmal vessel dilation. Based on brain MRI alone, 54.3% (57/105) of the patients with CAD were correctly classified, and the accuracy increased to 73.3% (77/105) when clinical information was combined (P < 0.001) with high specificity and low sensitivity. Further analysis showed that hrVWI had the superior capability in detecting CAD, with a sensitivity and a specificity of 95.1% and 97.0%, respectively.

Conclusion

The combination of brain MRI and clinical information could be used for the diagnosis of CAD; however, hrVWI should be sought for uncertain cases.

Usefulness of rapid MR angiography using two-point Dixon for evaluating carotid and aortic plaques

PURPOSE

Recently, various magnetic resonance imaging (MRI) modalities have been developed to easily detect carotid and aortic plaques, but these techniques are time-consuming and vulnerable to motion artifacts. We investigated the utility of a gradient echo MRI technique known as liver acquisition with volume acceleration flexible (LAVA-Flex) to detect carotid and aortic atherosclerotic plaques.

METHODS

Ten patients who underwent carotid endarterectomy (CEA) were assessed regarding the correspondence between LAVA-Flex findings and the histopathology of excised carotid plaques. In addition, 47 patients with cryptogenic ischemic stroke underwent LAVA-Flex and transesophageal echocardiography (TEE) for detection of embolic sources in the thoracic aorta. We analyzed the relationship between the thickness of the aortic plaque measured by TEE and the presence of high-intensity lesions on LAVA-Flex.

RESULTS

Nine of 10 patients (90.0%) who underwent CEA showed a high-intensity carotid lesion on LAVA-Flex, which corresponded pathologically to plaques containing large lipid cores and hemorrhage. Twenty-four (51.1%) of 47 cryptogenic stroke patients showed a high-intensity lesion in the thoracic aorta on LAVA-Flex; of these, 21 (87.5%) also demonstrated a large plaque (thickness ≥4 mm) on TEE. Twenty-two (95.7%) of 23 patients without a high-intensity lesion on LAVA-Flex demonstrated no large plaque on TEE. LAVA-Flex had a sensitivity of 95.5% and a specificity of 88.0% in patients with large plaques.

CONCLUSION

This study showed that LAVA-Flex successfully detected carotid and aortic plaques. This imaging technique may be useful to rapidly diagnose and evaluate carotid and aortic plaques, which are critical risk factors for aortogenic stroke.

Advantage in Bright-blood and Black-blood Magnetic Resonance Imaging with High-resolution for Analysis of Carotid Atherosclerotic Plaques

BACKGROUND

About 50% of the cerebral ischemia events are induced by intracranial and extracranial atherosclerosis. This study aimed to evaluate the feasibility and accuracy for displaying atherosclerotic plaques in carotid arteries and analyzing their ingredients by using high-resolution new magnetic resonance imaging (MRI) techniques.

METHODS

Totally, 49 patients suspected of extracranial carotid artery stenosis were subjected to cranial MRI scan and magnetic resonance angiography (MRA) examination on carotid arteries, and high-resolution bright-blood and black-blood MRI analysis was carried out within 1 week. Digital subtraction angiography (DSA) examination was carried out for 16 patients within 1 month.

RESULTS

Totally, 103 plaques were detected in the 49 patients, which were characterized by localized or diffusive thickening of the vessel wall, with the intrusion of crescent-shaped abnormal signal into lumens. Fibrous cap was displayed as isointensity in T1-weighted image (T1WI) and hyperintensities in proton density weighted image (PDWI) and T2-weighted image (T2WI), lipid core was displayed as isointensity or slight hyperintensities in T1WI, isointensity, hyperintensities or hypointensity in PDWI, and hypointensity in T2WI. Calcification in plaques was detected in 11 patients. Eight patients were detected with irregular plaque surface or ulcerative plaques, which were characterized by irregular intravascular space surface in the black-blood sequences, black hypointensity band was not detected in three-dimensional time-of-flight, or the hypointensity band was not continuous, and intrusion of hyperintensities into plaques can be detected. Bright-blood and black-blood techniques were highly correlated with the diagnosis of contrast-enhanced MRA in angiostenosis degree, Rs = 0.97, P < 0.001. In comparison to DSA, the sensitivity, specificity, and accuracy of MRI diagnosis of stenosis for ≥50% were 88.9%, 100%, and 97.9%, respectively.

CONCLUSIONS

High-resolution bright-blood and black-blood sequential MRI analysis can accurately analyze ingredients in atherosclerotic plaques. Determined by DSA, MRI diagnosis of stenosis can correctly evaluate the serious degree of arteriostenosis.

Increased microvascularization and vessel permeability associate with active inflammation in human atheromata

BACKGROUND

Studies have shown the feasibility of imaging plaques with 2-deoxy-2-[(18)F]fluoroglucose (FDG) positron emission tomography and dynamic contrast-enhanced magnetic resonance imaging with inconsistent results. We sought to investigate the relationship between markers of inflammatory activation, plaque microvascularization, and vessel wall permeability in subjects with carotid plaques using a multimodality approach combining FDG positron emission tomography, dynamic contrast-enhanced magnetic resonance imaging, and histopathology.

METHODS AND RESULTS

Thirty-two subjects with carotid stenoses underwent noninvasive imaging with FDG positron emission tomography and dynamic contrast-enhanced magnetic resonance imaging, 46.9% (n=15) before carotid endarterectomy. We measured FDG uptake (target:background ratio [TBR]) by positron emission tomography and K(trans) (reflecting microvascular permeability and perfusion) by magnetic resonance imaging and correlated imaging with immunohistochemical markers of macrophage content (CD68), activated inflammatory cells (major histocompatibility complex class II), and microvessels (CD31) in plaque and control regions. TBR and K(trans) correlated significantly with tertiles of CD68(+) (P=0.009 and P=0.008, respectively), major histocompatibility complex class II(+) (P=0.003 and P<0.001, respectively), and CD31(+) (P=0.004 and P=0.008, respectively). Regions of plaques were associated with increased CD68(+) (P=0.002), major histocompatibility complex class II(+) (P=0.002), CD31(+) (P=0.02), TBR (P<0.0001), and K(trans) (P<0.0001), as compared with those without plaques. Microvascularization correlated with macrophage content (rs=0.52; P=0.007) and inflammatory activity (rs=0.68; P=0.0001) and TBR correlated with K(trans) (rs=0.53; P<0.0001). In multivariable mixed linear regression modeling, TBR remained independently associated with K(trans) (β[SE], 2.68[0.47]; P<0.0001).

CONCLUSIONS

Plaque regions with active inflammation, as determined by macrophage content and major histocompatibility complex class II expression, showed increased FDG uptake, which correlated with increased K(trans) and microvascularization. The correlation between K(trans) and TBR was moderate, direct, highly significant, and independent of clinical symptoms and plaque luminal severity.

Reduction of motion artifacts in carotid MRI using free-induction decay navigators

PURPOSE

To develop a framework for prospective free-induction decay (FID)-based navigator gating for suppression of motion artifacts in carotid magnetic resonance imaging (MRI) and to assess its capability in vivo.

MATERIALS AND METHODS

An FID-navigator, comprising a spatially selective low flip-angle sinc-pulse followed by an analog-to-digital converter (ADC) readout, was added to a conventional turbo spin-echo (TSE) sequence. Real-time navigator processing delivered accept/reject-and-reacquire decisions to the sequence. In this Institutional Review Board (IRB)-approved study, seven volunteers were scanned with a 2D T2-weighted TSE sequence. A reference scan with volunteers instructed to minimize motion as well as nongated and gated scans with volunteers instructed to perform different motion tasks were performed in each subject. Multiple image quality measures were employed to quantify the effect of gating.

RESULTS

There was no significant difference in lumen-to-wall sharpness (2.3 ± 0.3 vs. 2.3 ± 0.4), contrast-to-noise ratio (CNR) (9.0 ± 2.0 vs. 8.5 ± 2.0), or image quality score (3.1 ± 0.9 vs. 2.6 ± 1.2) between the reference and gated images. For images acquired during motion, all image quality measures were higher (P < 0.05) in the gated compared to nongated images (sharpness: 2.3 ± 0.4 vs. 1.8 ± 0.5, CNR: 8.5 ± 2.0 vs. 7.2 ± 2.0, score: 2.6 ± 1.2 vs. 1.8 ± 1.0).

CONCLUSION

Artifacts caused by the employed motion tasks deteriorated image quality in the nongated scans. These artifacts were alleviated with the proposed FID-navigator.

Association of carotid atherosclerotic plaque features with acute ischemic stroke: a magnetic resonance imaging study

BACKGROUND AND PURPOSE

It remains unclear whether direct vessel wall imaging can identify carotid high-risk lesions in symptomatic subjects and whether carotid plaque characteristics are more effective indicators for cerebral infarct severity than stenosis. This study sought to determine the associations of carotid plaque characteristics by MR imaging with stenosis and acute cerebral infarct (ACI) sizes on diffusion weighted imaging (DWI).

MATERIALS AND METHODS

One hundred and fourteen symptomatic patients underwent carotid and brain MRI. ACI volume was determined from symptomatic internal carotid artery territory on DWI images. Ipsilateral carotid plaque morphological and compositional characteristics, and stenosis were also determined. The relationships between carotid plaque characteristics, stenosis and ACIs size were then evaluated.

RESULTS

In carotid arteries with 30-49% stenosis, 86.7% and 26.7% were found to have lipid-rich necrotic core (LRNC) and intraplaque hemorrhage, respectively. Furthermore, 45.8% of carotid arteries with 0-29% stenosis developed LRNCs. Carotid morphological measurements, such as % wall volume, and the LRNC size were significantly associated with ipsilateral ACIs volume before and after adjustment for significant demographic factors (age and LDL) or stenosis in patients with carotid plaque (all p<0.05).

CONCLUSIONS

A substantial number of high-risk plaques characterized by vessel wall imaging exist in carotid arteries with lower grade stenosis. In addition, carotid plaque characteristics, particularly the % wall volume and LRNC size, are independently associated with cerebral infarction as measured by DWI lesions. Our findings indicate that characterizing atherosclerotic plaque by MR vessel wall imaging might be useful for stratification of plaque risk and infarction severity.

A comparative analysis of double inversion recovery TFE and TSE sequences on carotid artery wall imaging

OBJECTIVE

To analyze the characteristics of double inversion recovery (DIR) turbo field echo (TFE) and turbo spin echo (TSE) sequences and explore the value of double inversion recovery TFE sequence on carotid artery wall imaging.

PATIENTS AND METHODS

56 patients (32 males and 24 females, aged 31-76 years with a mean age of 53 years) were performed with DIR TFE and DIR TSE T1 weighted imaging (T1WI) sequences on carotid artery bifurcations. Image quality acquired by different techniques were evaluated and scored by two physicians. Whether there is significant difference is determined by SPSS 11.0 software. Paired-samples t test was used for statistics.

RESULTS

There was no significant difference in the image quality scores between two sequences (t = 0.880, P = 0.383 > 0.05).

CONCLUSIONS

DIR TFE sequence has short scanning time and high spatial resolution. DIR TFE sequence can be used as the preferred sequence for screening carotid atherosclerotic plaque compared with DIR TSE sequence.

T1-weighted-SPACE dark blood whole body magnetic resonance angiography (DB-WBMRA): initial experience

PURPOSE

To evaluate the feasibility of the dark blood fast spin echo (FSE) T1-weighted-Sampling Perfection with Application of optimized Contrasts using different flip angle Evolution (T1w-SPACE) sequence in assessing whole body arterial wall information from the extracranial carotids to the popliteal artery.

MATERIALS AND METHODS

Twenty-eight subjects were subjected to noncontrast, dark blood whole body magnetic resonance angiography (DB-WBMRA) using a T1w-SPACE sequence optimized for each of the individual stations: carotid artery, thoracic aorta, abdominal aorta, and thigh/superficial femoral artery (SFA). Image quality/vessel wall visualization and the time required to image the four stations were evaluated. Two observers checked the reproducibility of vessel wall depiction by performing quantitative measurements in registered initial and repeat studies (six subjects) of vessel wall and lumen area at 17 locations along the arterial tree.

RESULTS

In 25 of the 28 scanned subjects, dark blood arterial images acquired in approximately 1 hour total imaging time allowed whole body arterial vessel wall visualization. Quantitative measurements showed high correlation between the initial and repeat studies for each of the observers as well as high interobserver reproducibility (r > 0.95; P < 0.01).

CONCLUSION

DB-WBMRA using T1w-SPACE is feasible and can be performed with a high degree of reliability.

Variations in atherosclerosis and remodeling patterns in aorta and carotids

BACKGROUND

Atherosclerosis is a progressive disease that causes vascular remodeling that can be positive or negative. The evolution of arterial wall thickening and changes in lumen size under current "standard of care" in different arterial beds is unclear. The purpose of this study was to examine arterial remodeling and progression/regression of atherosclerosis in aorta and carotid arteries of individuals at risk for atherosclerosis normalized over a 1-year period.

METHODS

In this study, 28 patients underwent at least 2 black-blood in vivo cardiovascular magnetic resonance (CMR) scans of aorta and carotids over a one-year period (Mean 17.8 +/- 7.5 months). Clinical risk profiles for atherosclerosis and medications were documented and patients were followed by their referring physicians under current "standard of care" guidelines. Carotid and aortic wall lumen areas were matched across the time-points from cross-sectional images.

RESULTS

The wall area increased by 8.67%, 10.64%, and 13.24% per year (carotid artery, thoracic aorta and abdominal aorta respectively, p < 0.001). The lumen area of the abdominal aorta increased by 4.97% per year (p = 0.002), but the carotid artery and thoracic aorta lumen areas did not change significantly. The use of statin therapy did not change the rate of increase of wall area of carotid artery, thoracic and abdominal aorta, but decreased the rate of change of lumen area of carotid artery (-3.08 +/- 11.34 vs. 0.19 +/- 12.91 p < 0.05).

CONCLUSIONS

Results of this study of multiple vascular beds indicated that different vascular locations exhibited varying progression of atherosclerosis and remodeling as monitored by CMR.

High-resolution MR imaging of the cervical arterial wall: what the radiologist needs to know

The emergence of high-resolution rapid imaging methods has enabled magnetic resonance (MR) imagers to noninvasively image the fine internal structure of cervical arterial walls. In this article, a comprehensive guide to performing high-resolution MR imaging of cervical arteries is provided, including the choice of coils, sequences, and imaging parameters, as well as tips for optimal image quality. Explanations and illustrations are given of using high-resolution MR imaging to quantify plaque volume, determine atherosclerotic plaque burden, depict plaque composition, and ultimately identify unstable plaque before it leads to a clinical event. Finally, the role of high-resolution MR imaging in the diagnosis of cervical dissection and inflammatory disease of the arterial wall is emphasized.

Evaluation of carotid artery atherosclerotic plaque distribution by using long-axis high-resolution black-blood magnetic resonance imaging

Object

The goal of this study was to evaluate the usefulness of long-axis black-blood MR (BB–MR) imaging for assessing plaque morphology and distribution in patients with atherosclerotic carotid artery (CA) stenosis.

Methods

Sixty-eight carotid arteries in 67 patients who were scheduled to undergo CA endarterectomy or CA stent placement due to atherosclerotic stenosis were included in this study. The patients had undergone CA BB–MR imaging and digital subtraction (DS) angiography within 3 weeks of revascularization. The DS angiography studies were performed using the transfemoral artery approach with selective common CA catheterization. The BB–MR images were acquired using a 1.5-T whole-body MR imaging unit, and T1-weighted images parallel to the long axis of the artery at 1-mm intervals were obtained. Plaque distribution was evaluated by measuring the distance between the CA bifurcation and the point that appeared to be the distal extent of the plaque on BB–MR imaging (D–MR imaging) and DS angiography images (D–DS angiography).

Results

Plaque distribution was clearly shown in 88.2% of the cases using long-axis BB–MR images, except for 8 arteries with poor image quality. In 4 arteries, D–DS angiography could not be obtained because the distal plaque end could not be confirmed. In 56 vessels, both the D–DS angiography and D–MR imaging could be measured; the mean D–MR imaging (19.75 ± 6.85 mm [standard deviation]) was significantly longer than the average D–DS angiography (16.32 ± 7.07 mm).

Conclusions

Long-axis BB–MR imaging can provide a noninvasive and accurate way to show CA plaque distribution; it is of great use not only for stroke risk assessment in patients with CA atherosclerosis but also for preoperative evaluation in patients requiring CA endarterectomy or CA stent placement.

Does black blood MRA have a role in the assessment of intracerebral aneurysms?

The aim of this study was to assess whether the addition of a black blood (BB) sequence to standard three-dimensional time-of-flight (3D-TOF) imaging yields improved quantitative assessment of intracranial aneurysms. Thirty seven patients with 42 proven intracranial aneurysms underwent intra-arterial digital subtraction angiography, 3D-TOF and BB MRI imaging. This multimodality imaging was used to create a composite reference aneurysm description. The 3D-TOF and BB imaging were graded on a subjective seven-point scale to determine what improvement if any the addition of BB imaging yielded. Comparison of measurements from all imaging modalities demonstrated no significant difference (p < 0.01) in aneurysm length/width or parent vessel width. Aneurysm neck measurements were underestimated on 3D-TOF images although there was still a significant correlation (R(2) = 0.72, p < 0.05). Comparison of TOF and BB examinations to the composite reference using the Wilcoxon signed-rank test showed significant improvement in the demonstration of the aneurysm to parent/branch vessels and the morphology/size of the aneurysm neck, particularly in the setting of local haematoma or slow flow (p < 0.001). We propose the addition of the BB sequence as a useful adjunct to 3D-TOF imaging particularly when detailed aneurysm morphology is required or there is thrombus in subarachnoid space.

Cardiovascular MRI at 3 T

Cardiovascular magnetic resonance (CMR) imaging at 3 T has started to demonstrate real clinical advantages compared to cardiac imaging at 1.5 T. This article provides an overview of 3 T CMR imaging and its clinical use in the diagnosis of cardiovascular diseases. In addition, an outlook is given on new and improved applications to fully utilize the advantages connected to the higher field strength.

3.0 T plaque imaging

OBJECTIVES

The aim of this article is to evaluate 3.0 T magnetic resonance imaging for characterization of vessel morphology and plaque composition. Emphasis is placed on early and moderate stages of carotid atherosclerosis, where increases in signal-to-noise (SNR) and contrast-to-noise (CNR) ratios compared with 1.5 T are sought. Comparison of in vivo 3.0 T imaging to histopathology is performed for validation. Parallel acceleration methods applied with an 8-channel carotid array are investigated as well as higher field ex vivo imaging to explore even further gains. The overall endeavor is to improve prospective assessment of atherosclerosis stage and stability for reduction of atherothrombotic event risk.

METHODS

A total of 10 male and female subjects ranging in age from 22 to 72 years (5 healthy and 5 with cardiovascular disease) participated. Custom-built array coils were used with endogenous and exogenous multicontrast bright and black-blood protocols for 3.0 T carotid imaging. Comparisons were performed to 1.5 T, and ex vivo plaque was stained with hematoxylin and eosin for histology. Imaging (9.4 T) was also performed on intact specimens.

RESULTS

The factor of 2 gain in signal-to-noise SNR is realized compared with 1.5 T along with improved wall-lumen and plaque component CNR. Post-contrast black-blood imaging within 5-10 minutes of gadolinium injection is optimal for detection of the necrotic lipid component. In a preliminary 18-month follow-up study, this method provided measurement of a 50% reduction in lipid content with minimal change in plaque size in a subject receiving aggressive statin therapy. Parallel imaging applied with signal averaging further improves 3.0 T black-blood vessel wall imaging.

CONCLUSIONS

The use of 3.0 T for carotid plaque imaging has demonstrated increases in SNR and CNR compared with 1.5 T. Quantitative prospective studies of moderate and early plaques are feasible at 3.0 T. Continued improvements in coil arrays, 3-dimensional pulse sequences, and the use of novel molecular imaging agents implemented at high field will further improve magnetic resonance plaque characterization.