General Leung

Moderate Carotid Artery Stenosis: MR Imaging–depicted Intraplaque Hemorrhage Predicts Risk of Cerebrovascular Ischemic Events in Asymptomatic Men

PURPOSE To investigate the association between magnetic resonance (MR) imaging-depicted intraplaque hemorrhage (IPH) in the carotid artery wall and the risk of future ipsilateral cerebrovascular events in men with asymptomatic moderate carotid stenosis by using a rapid three-dimensional T1-weighted fat-suppressed spoiled gradient-echo sequence. MATERIALS AND METHODS The institutional ethics review board approved this retrospective chart review and waived the requirement for written informed consent. All patients gave informed verbal consent at follow-up telephone interviews. Ninety-one men (mean age, 74.8 years; range, 47-88 years) who attended a vascular clinic between 2003 and 2006, who had asymptomatic carotid stenosis (50%-70% at Doppler ultrasonography), and who had undergone MR imaging for IPH detection were retrospectively identified. Seventy-five men with 98 eligible carotid arteries were included in the study. Patients were followed for a minimum of 1 year (mean follow-up, 24.92 months; range, 12-43 months). Kaplan-Meier survival and univariate Cox regression analyses were conducted to compare future ipsilateral cerebrovascular event rates between carotid arteries with and those without MR-depicted IPH. RESULTS Of the 98 carotid arteries included, 36 (36.7%) had MR-depicted IPH. Six cerebrovascular events (two strokes and four transient ischemic attacks) occurred in the carotid arteries with IPH, as compared with no clinical events in the carotid arteries without IPH. Univariate Cox regression analysis confirmed that MR-depicted IPH was associated with an increased risk of cerebrovascular events (hazard ratio, 3.59; 95% confidence interval: 2.48, 4.71; P < .001). MR-depicted IPH negatively predicted outcomes (negative predictive value = 100%). CONCLUSION In this cohort with asymptomatic moderate carotid stenosis, MR-depicted IPH was associated with future ipsilateral cerebrovascular events. Conversely, patients without MR-depicted IPH remained asymptomatic during follow-up. The absence of IPH at MR imaging, therefore, may be a reassuring marker of plaque stability and of a lower risk of thromboembolism.

In Vivo 3D High-Spatial-Resolution MR Imaging of Intraplaque Hemorrhage

PURPOSE To apply magnetic resonance (MR) imaging of intraplaque hemorrhage (IPH), as compared with histologic analysis as the reference standard, to detect T1 hyperintense intraplaque signal and to test the hypothesis that T1 hyperintense material represents blood products (methemoglobin). MATERIALS AND METHODS Institutional review board approval and patient informed consent were obtained. Eleven patients undergoing carotid endarterectomy were examined with MR imaging of IPH, and MR images were assessed for T1 hyperintense intraplaque signal. A total of 160 images per patient were available for coregistration with corresponding histologic slices. Because of endarterectomy specimen size and degradation and processing artifacts, only 97 images were coregistered to corresponding histologic slices. A grid that consisted of 16 segments was overlaid on images for correlation of MR images and histologic slices. Only one of 16 segments was chosen randomly per slide and used in the analysis. Agreement between MR images and histologic slices was measured with the Cohen kappa statistic. RESULTS Strong agreement was seen between MR images and histologic slices, with T1-weighted high signal intensity corresponding to hemorrhagic material (kappa = 0.7-0.8). There was a low 2% false-negative rate for the detection of hemorrhage on the basis of T1-weighted hyperintensity (two of 97 measured segments). The results of diagnostic tests for T1 hyperintense detection of hemorrhage were as follows: sensitivity of 100%, specificity of 80%, positive predictive value of 70%, and negative predictive value of 100% for reader 1 and sensitivity of 94%, specificity of 88%, positive predictive value of 78%, and negative predictive value of 97% for reader 2. CONCLUSION With its high spatial resolution, MR imaging of IPH permits detection of plaque hemorrhage location, resulting in strong agreement between imaging and histologic findings.

Late Stage Complicated Atheroma in Low-Grade Stenotic Carotid Disease: MR Imaging Depiction—Prevalence and Risk Factors

PURPOSE To determine if complicated plaque can be found by using magnetic resonance (MR) imaging-depicted intraplaque hemorrhage (IPH), even among symptomatic patients with low-grade (≤50%) carotid stenosis. MATERIALS AND METHODS The institutional ethics review board approved this retrospective study and waived requirements for written informed consent. Symptomatic patients with bilateral 0%-50% carotid stenosis referred for carotid MR imaging were considered. Risk factors (age, sex, hypertension, diabetes, hyperlipidemia, myocardial infarction, atrial fibrillation, smoking, coronary artery disease, and cerebrovascular disease), medications (antihypertensive drugs, diabetes drugs, statins, and aspirin), and the brain side causing symptoms were recorded. MR-depicted IPH prevalence in the carotid arteries ipsilateral and contralateral to the symptomatic side was compared by using the Fisher exact test. Multivariable regression was used to compare the MR-depicted IPH prevalence, while adjusting for risk factors and medications. RESULTS A total of 217 patients (434 carotid arteries) were included. MR-depicted IPH was found in 13% (31 of 233) of carotid arteries ipsilateral and 7% (14 of 201) of arteries contralateral to symptoms (P < .05). Male sex (P < .05) and increasing age (P < .05) were associated with MR-depicted IPH after controlling for risk factors and medications. CONCLUSION Complicated carotid atheroma can be found among symptomatic patients with low-grade (≤50%) stenosis, and this is associated with male sex and increasing age. MR-depicted IPH may be useful to stratify risk for patients with low-grade carotid stenosis.

Innovations in imaging for chronic total occlusions: a glimpse into the future of angiography’s blind-spot

Chronic total occlusions (CTOs) are a subset of lesions that present a considerable burden to cardiovascular patients. There exists a strong clinical desire to improve non-surgical options for CTO revascularization. While several techniques, devices, and guide wires have been developed and refined for use in CTOs, the inability of angiography to adequately visualize occluded arterial segments makes interventions in this setting technically challenging. This review describes the current status of several invasive and non-invasive imaging techniques that may facilitate improved image guidance during CTO revascularization, with the goals of improving procedure safety and efficacy while reducing the time required to complete these interventions. Cardiac imaging also has important potential roles in selecting patients most likely to benefit from revascularization as well as pre-procedural planning, post-procedural assessment of revascularized segments and long-term outcomes studies. Modalities discussed include non-invasive techniques, such as CT(computed tomography) angiography and cardiac magnetic resonance imaging (MRI), as well as invasive techniques, such as intravascular ultrasound, optical coherence tomography, intravascular MRI, and conventional angiography. While some of these techniques have some evidence to support their use at present, others are at earlier stages of development. Strategies that combine imaging techniques with the use of interventional therapies may provide significant opportunities to improve results in CTO interventions and represent an active area of investigation.

Forward-looking intravascular orthogonal-solenoid coil for imaging and guidance in occlusive arterial disease.

Recent intravascular imaging coil configurations have focused on side‐viewing catheters capable of imaging the vessel wall of a patent vessel. These designs suffer from the presence of signal nulls and the inability to image in front of a device when it is oriented along the main static field. This is of particular importance when a device is being navigated through an occlusive lesion. To address these limitations we propose a new intravascular coil design consisting of two independent orthogonal solenoids located at the catheter tip. The two coils are oriented in such a way that signal nulls are eliminated and imaging is possible in planes located directly in front of the catheter. Complete characterization of the spatial signal‐to‐noise ratio (SNR) distribution of the design is presented. The coil configuration was fabricated on a 6F guide catheter, and its use is demonstrated in phantoms and in vivo. Magn Reson Med 60:489–495, 2008.

In Vivo Identification of Complicated Upper Thoracic Aorta and Arch Vessel Plaque by MR Direct Thrombus Imaging in Patients Investigated for Cerebrovascular Disease

OBJECTIVE The objective of this article was to assess the feasibility of MR direct thrombus imaging (MRDTI) to evaluate the prevalence and location of complicated upper thoracic aortic and arch vessel plaque in patients referred for evaluation of cerebrovascular disease. SUBJECTS AND METHODS Patients referred for investigation of cerebrovascular disease by MRI were enrolled. Reasons for referral included transient ischemic attack/amaurosis fugax, acute infarct, remote infarct, or asymptomatic carotid disease. Of the 348 patients initially scanned, 17 were excluded from the analysis. The final patient population included 331 patients (199 men, 132 women; mean age, 67.7 years). Patients were scanned using MRDTI, a 3D, T1-weighted, fat-suppressed spoiled gradient echo that exploits the T1 shortening effects of methemoglobin, directly visualizing hemorrhage/thrombus in the vessel wall, thus identifying complicated plaque. Complicated plaque was defined as a high signal within the atherosclerotic plaque at least twice the signal intensity of muscle. RESULTS Forty-three of 331 patients (13%) had complicated upper thoracic aortic atherosclerotic disease, arch vessel atherosclerotic disease, or both. The upper thoracic aorta was involved in 36 of 43 patients (83.7%), and the left subclavian artery was involved in 14 of 43 patients (32.6%). Both the right subclavian artery and the brachiocephalic artery were involved in one of 43 patients (2.3%). Complicated carotid plaque was seen in 25 of 43 patients (58.1%). CONCLUSION MRDTI can be applied in the detection of complicated plaque in the upper thoracic aorta and arch vessels. Complicated plaque was identified in 13% of the patient population. The upper thoracic aorta was the most common site involved. This technique could be useful for the screening of asymptomatic at-risk patients.

MR imaging depicts oxidative stress induced by methemoglobin.

PURPOSE To correlate the effect of red blood cell hemoglobin on signal generation during magnetic resonance (MR) imaging and local oxidation of low-density lipoprotein (LDL). MATERIALS AND METHODS Informed consent was obtained from all volunteers participating in this study, which was approved by the research ethics board. T1 relaxometry of blood samples from six volunteers was performed. Lipid peroxidation was assayed by using thiobarbituric acid reactive species (TBARS) and fluorescence quenching of cis-parinaric acid. Two-tailed Student t tests were used to detect differences between means. A Pearson correlation coefficient was calculated to determine the linearity of the data. RESULTS Lipid oxidation was significantly enhanced after addition of blood, according to results of the TBARS assay; greater oxidation occurred with ferric than with ferrous blood. The cis-parinaric acid assay demonstrated increased oxidative stress caused by extracellular as compared with intracellular ferric hemoglobin. MR imaging measures showed a T1 relaxivity that was 10 times higher for ferric than for ferrous forms of hemoglobin. CONCLUSION Extracellular ferric hemoglobin is significantly more pro-oxidant and has higher T1 relaxivity than its ferrous counterparts. These results support the hypothesis that ferric methemoglobin-generated T1 high signal intensity reflects a pro-oxidant environment that, in the setting of vessel wall disease, might be proatherogenic.

Brain Structure and Function Associated with a History of Sport Concussion: A Multi-Modal Magnetic Resonance Imaging Study.

There is growing concern about the potential long-term consequences of sport concussion for young, currently active athletes. However, there remains limited information about brain abnormalities associated with a history of concussion and how they relate to clinical factors. In this study, advanced MRI was used to comprehensively describe abnormalities in brain structure and function associated with a history of sport concussion. Forty-three athletes (21 male, 22 female) were recruited from interuniversity teams at the beginning of the season, including 21 with a history of concussion and 22 without prior concussion; both groups also contained a balanced sample of contact and noncontact sports. Multi-modal MRI was used to evaluate abnormalities in brain structure and function. Athletes with a history of concussion showed frontal decreases in brain volume and blood flow. However, they also demonstrated increased posterior cortical volume and elevated markers of white matter microstructure. A greater number of prior concussions was associated with more extensive decreases in cerebral blood flow and insular volume, whereas recovery time from most recent concussion was correlated with reduced frontotemporal volume. White matter showed limited correlations with clinical factors, predominantly in the anterior corona radiata. This study provides the first evidence of the long-term effects of concussion on gray matter volume, blood flow, and white matter microstructure within a single athlete cohort. This was examined for a mixture of male and female athletes in both contact and noncontact sports, demonstrating the relevance of these findings for the overall sporting community.

Neuroimaging of sport concussion: persistent alterations in brain structure and function at medical clearance

The medical decision of return to play (RTP) after a sport concussion is largely based on symptom status following a graded exercise protocol. However, it is currently unknown how objective markers of brain structure and function relate to clinical recovery. The goal of this study was to determine whether differences in brain structure and function at acute injury remain present at RTP. In this longitudinal study, 54 active varsity athletes were scanned using magnetic resonance imaging (MRI), including 27 with recent concussion, imaged at both acute injury and medical clearance, along with 27 matched controls. Diffusion tensor imaging was used to measure fractional anisotropy (FA) and mean diffusivity (MD) of white matter and resting-state functional MRI was used to measure global functional connectivity (Gconn). At acute injury, concussed athletes had reduced FA and increased MD, along with elevated Gconn; these effects remained present at RTP. Athletes who took longer to reach RTP also showed elevated Gconn in dorsal brain regions, but no significant white matter effects. This study presents the first evidence of altered brain structure and function at the time of medical clearance to RTP, with greater changes in brain function for athletes with a longer recovery time.

Comparison of Sagittal FSE T2, STIR, and T1-Weighted Phase-Sensitive Inversion Recovery in the Detection of Spinal Cord Lesions in MS at 3T

BACKGROUND AND PURPOSE: Determining the diagnostic accuracy of different MR sequences is essential to design MR imaging protocols. The purpose of the study was to compare 3T sagittal FSE T2, STIR, and T1-weighted phase-sensitive inversion recovery in the detection of spinal cord lesions in patients with suspected or definite MS. MATERIALS AND METHODS: We performed a retrospective analysis of 38 patients with suspected or definite MS. Involvement of the cervical and thoracic cord segments was recorded on sagittal FSE T2, STIR, and T1-weighted phase-sensitive inversion recovery sequences independently by 2 readers. A consensus criterion standard read was performed with all sequences available. Sensitivity, specificity, and interobserver agreement were calculated for each sequence. RESULTS: In the cervical cord, the sensitivity of T1-weighted phase-sensitive inversion recovery (96.2%) and STIR (89.6%) was significantly higher (P < .05) than that of FSE T2 (50.9%), but no significant difference was found between T1-weighted phase-sensitive inversion recovery and STIR. In the thoracic cord, sensitivity values were 93.8% for STIR, 71.9% for FSE T2, and 50.8% for T1-weighted phase-sensitive inversion recovery. Significant differences were found for all comparisons (P < .05). No differences were detected in specificity. Poor image quality and lower sensitivity of thoracic T1-weighted phase-sensitive inversion recovery compared with the other 2 sequences were associated with a thicker back fat pad. CONCLUSIONS: The use of an additional sagittal sequence other than FSE T2 significantly increases the detection of cervical and thoracic spinal cord lesions in patients with MS at 3T. In the cervical segment, both STIR and T1-weighted phase-sensitive inversion recovery offer high sensitivity and specificity, whereas in the thoracic spine, STIR performs better than T1-weighted phase-sensitive inversion recovery, particularly in patients with a thick dorsal fat pad.