Time-of-flight Magnetic Resonance Angiography Research Articles

Abstract WMP31: Integration of MRA and CTA for Brain Aneurysm Follow up

Introduction: Because MR does not involve ionizing radiation and may be used without contrast, recently there has been a trend towards monitoring aneurysms primarily with MRA and then use CTA as needed. Our goal is to establish a machine learning technique for aneurysm evaluation that can generate images with comparable image quality to CTA based on time of flight (TOF) MRA. Methods: TOF MRA and CTA images acquired less than 2 weeks apart were used. A set of clinical TOF MRA and CTA were used for training and five additional sets were used for testing. TOF was obtained with gradient recalled echo (TR = 33ms, TE=3.2ms) on 1.5T scanners. CTA scans were acquired using 64 slice scanner (pitch=1.0, reconstruction kernel H30f). During the training stage, cross modality registration was performed to maximize mutual information between TOF and the corresponding CTA. To generate machine learning angiography (MLA) images, the input TOF were divided into sliding patches and their coefficient was estimated and used as an input to the neural network to infer voxelwise CTA values. Figure: images used for learning (aneurysm, right ICA; greyscale, CTA; red, TOF MRA). Results: The MLA images enhanced visibility of artery structures from the original TOF. High geometric agreement was achieved between MLA images and CTA. In comparison to CTA, MLA images had sub-mm Hausdorff distance and pairwise distance of 0.24±0.12mm for all aneurysm localities for all tested image sets. With an aneurysm growth threshold defined as size change more than 0.6 mm in CTA, MLA provides sufficient resolution for cross modality follow up comparisons. Conclusions: This pilot study has demonstrated promise to enhance artery visibility and interpretation from MRA using machine learning techniques to yield CTA-like images. The performance of the current method is affected by the dependence of flow enhancement with respect to imaging planes in TOF and requires consistent imaging protocols for training and testing subjects.

Abstract WP124: Signal Intensity Ratio Does Not Predict Recurrent Stroke in Patients with Symptomatic Intracranial Atherosclerotic Disease

Background: Symptomatic intracranial atherosclerotic disease (ICAD) is associated with high risk for recurrent stroke. Identification of patients remains a challenge using clinical and radiographic markers. Recent research has identified signal intensity ratio (SIR) across stenotic lesions on time-of-flight magnetic resonance angiography (TOF-MRA) as a novel noninvasive marker of recurrent stroke risk. We sought to externally validate this approach in a single center analysis. Methods: From a prospective observational stroke registry since August 2012, we identified patients with ischemic stroke due to ICAD causing moderate-severe stenosis of the basilar, intracranial vertebral, intracranial internal carotid, or middle cerebral arteries. Using the method described previously, we calculated SIR values across the stenotic lesions corrected for background signal intensity from TOF-MRA performed within 7 days of index stroke admission. Outcomes were prospectively captured by phone interview at 1 and 3 months after stroke. Recurrent stroke was defined by new infarct in the territory of the stenotic artery or absent imaging confirmation, territory-specific clinical symptoms lasting > 24 hours. We evaluated whether baseline SIR values were different between patients with and without recurrent stroke overall and in subgroups by ICAD location. P-value < 0.05 was considered significant. Results: Among 99 consecutive patients with ICAD, 79 (80%) had interpretable MRAs at baseline (mean age 68.4 +11.2 years, 53.2% male, 53.2% black, median NIHSS score 3; 27.7% posterior circulation stenosis). Recurrent stroke occurred in 21.5% and 25.3% of patients at 1 and 3 months, respectively. Median SIR at baseline was 0.86 (interquartile range 0.56-1.04) and was not different those with vs. without recurrent stroke (1-month: 0.79 vs. 0.86, p=0.93; 3-month: 0.79 vs. 0.86, p=0.68). Results were not different by ICAD location. Discussion: In this single center prospective registry, we were unable to validate SIR on time-of-flight MRA as a marker of early recurrent stroke risk in patients with symptomatic ICAD. Further research is needed to identify novel predictors of recurrence in this high-risk cohort.

Abstract TMP33: High Intensity Signal in the Plaque on 3DTOF MRA is Associated With Ischemic Stroke in the Patients With Low Grade Carotid Artery Stenosis

Background: Carotid artery stenosis is one of the major causes of ischemic strokes. However, degree of stenosis is not always correlated with frequency of ischemic strokes. Recently, it was reported that carotid intraplaque hemorrhage (IPH) was associated with accelerated plaque growth, luminal narrowing and development of symptomatic events. Maximum intensity projection (MIP) images are easily reformatted within from 5 minute, routine time-of-flight (TOF) sequences. The aim of this study was to evaluate the relationships between high intensity signal (HIS) in the carotid plaques on MIP images detected by routine three-dimensional TOF magnetic resonance angiography (3D-TOF MRA) and ischemic strokes. Materials and Methods: One hundred fifty two patients with low-grade carotid artery stenosis (North American Symptomatic Carotid Endarterectomy Trial criteria: 30% - 49%) were included. IPH was defined as the presence of HIS in the carotid plaques on MIP images of 3D-TOF MRA using the previously reported criteria. We analyzed the relationship between the presence of HIS in the plaques and prior ischemic strokes defined as ischemic lesions on diffusion weighed images of the brain. Results: HIS in the carotid plaque was present in 56 (37%) of 152 carotid arteries. Prior ipsilateral ischemic strokes were observed more frequently in HIS-positive group (12 of 56, 21.4%) than HIS-negative group (1 of 34: 2.9%) [p<0.001]. In multivariate logistic regression analysis, HIS (Odds ratio: 77.7, 95%CI: 6.4 - 944.0, p<0.001) and diabetes mellitus type 2 (odds ratio: 10.45, 95%CI: 1.6 - 67.9, p=0.014) were independent determinants of prior ischemic strokes after adjustment for age. Conclusions: HIS in the carotid plaques on MIP images of 3D-TOF MRA was an independent determinant of prior ischemic stroke in patients with low-grade carotid artery stenosis, and this finding may provide a reliable risk stratification of future stroke in patients with low-grade carotid artery stenosis.

Circulating bacterial lipopolysaccharide-induced inflammation reduces flow in brain-irrigating arteries independently from cerebrovascular prostaglandin production

Brain dysfunction is a frequent complication of the systemic inflammatory response to bacterial infection or sepsis. In the present work, the effects of intravenous bacterial lipopolysaccharide (LPS) administration on cerebral arterial blood flow were assessed with time-of-flight (TOF)-based magnetic resonance angiography (MRA) in mice. Cerebral expression of the transcription factors nuclear factor-kappaB (NF-κB) and c-Fos and that of enzymes synthesizing vasoactive mediators, such as prostaglandins and nitric oxide, known to be increased under inflammatory conditions, were studied in the same animals. Time-resolved TOF MRA revealed no differences in blood flow in the internal carotids upstream of the circle of Willis, but indicated lower flow in its lateral parts as well as in the middle and anterior cerebral arteries after intravenous LPS injection as compared to saline administration. Although LPS did not increase c-Fos expression in ventral forebrain structures of these animals, it did induce NF-κB in meningeal blood vessels. LPS also increased cerebral expression of cyclooxygenase-2 and prostaglandin E synthase mRNAs, but de novo expression occurred in veins rather than in arteries. In conclusion, our work indicates that LPS-induced systemic inflammation does not necessarily affect filling of the circle of the Willis from the periphery, but that circulating LPS alters outflow from the circle of Willis to the middle and anterior cerebral arteries. These modifications in arterial flow were not related to increased cerebral synthesis of prostaglandins, but may instead be the consequence of the action of circulating prostaglandins and other vasoactive mediators on brain-irrigating arteries during systemic inflammation.

Vulnerable carotid plaque imaging and histopathology without a dedicated MRI receiver coil.

Stroke is associated with vulnerable carotid artery plaques showing specific histopathologic features, namely a lipid-rich necrotic core, intraplaque hemorrhage, ulceration, and thin fibrous cap. While ultrasound and computed tomography (CT) can identify carotid plaques and determine the extent of stenosis, magnetic resonance imaging (MRI) provides further information regarding plaque composition and morphology. In this feasibility study, three patients with symptomatic, moderately stenosed plaques were imaged with CT angiography (CTA) and MRI (3T and 1.5T) without a dedicated receiver coil. The patients subsequently underwent carotid endarterectomy with en-bloc excision of the plaque. The CT and MR images were analyzed independently by three neuroradiologists to identify vulnerable plaque features. The images were correlated with the histopathology to confirm the findings. All three patients had one or more vulnerable plaque features on histopathology. MRI allowed for better characterization of these features when compared to CTA. The pre- and post-contrast T1-weighted (T1W) images were most helpful for identifying the lipid-rich necrotic core and thin fibrous cap, while the time of flight-magnetic resonance angiography (TOF-MRA) and contrast-enhanced (CE)-MRA were excellent for detecting plaque hemorrhage and ulceration, respectively. The 3T images showed superior spatial and contrast resolution compared to the 1.5T images for all sequences. By providing direct correlation between imaging and histopathology, this study demonstrates that 3T MRI without a dedicated surface coil is an excellent tool for assessing plaque vulnerability. In smaller hospitals or those with limited resources, it is reasonable to consider conventional MRI for patient risk stratification. Further studies are needed to determine how MRI and plaque vulnerability can be incorporated into routine clinical practice.

Direct Assessment of Wall Shear Stress by Signal Intensity Gradient from Time-of-Flight Magnetic Resonance Angiography.

The aim of the study was to calculate the arterial wall signal intensity gradient (SIG) from time-of-flight MR angiography (TOF-MRA) and represent arterial wall shear stress. We developed a new algorithm that uses signal intensity (SI) of a TOF-MRA to directly calculate the signal intensity gradient (SIG). The results from our phantom study showed that the TOF-MRA SIG could be used to distinguish the magnitude of blood flow rate as high (mean SIG ± SD, 2.2 ± 0.4 SI/mm for 12.5 ± 2.3 L/min) and low (0.9 ± 0.3 SI/mm for 8.5 ± 2.6 L/min) in vessels (p < 0.001). Additionally, we found that the TOF-MRA SIG values were highly correlated with various flow rates (β = 0.96, p < 0.001). Remarkably, the correlation coefficient between the WSS obtained from the computational fluid dynamics (CFD) analysis and the TOF-MRA SIG was greater than 0.8 in each section at the carotid artery (p < 0.001 for all β values). This new technique using TOF-MRA could enable the rapid calculation of the TOF-MRA SIG and thereby the WSS. Thus, the TOF-MRA SIG can provide clinicians with an accurate and efficient screening method for making rapid decisions on the risk of vascular disease for a patient in clinical practice.

Probabilistic Modeling of Blood Vessels for Segmenting Magnetic Resonance Angiography Images

A new adaptive probabilistic model of blood vessels on magnetic resonance angiography (MRA) images is proposed. The model accounts for both laminar (for normal subjects) and turbulent blood flows (in abnormal cases like anemia or stenosis) and results in a fast algorithm for extracting a 3D cerebrovascular system from MRA data. To accurately separate blood vessels from other regions-of-interest, the marginal distribution is precisely approximated with an adaptive linear combination of the derived model and a number of dominant and subordinate discrete Gaussians, rather than with a mixture of only three pre-selected Gaussian and uniform or Rician components. To validate the accuracy of the proposed algorithm, a special 3D geometrical phantom motivated by statistical analysis of the time-of-flight MRA (TOF-MRA) data is designed. Experiments with synthetic and 50 real data sets confirm the high accuracy and reduced computational cost of the proposed approach.Keywords: MRA, PC-MRA, TOF-MRA, Vascular Signals

3D-TOF MRA序列筛查脑微出血在脑梗死出血性转化中的预警价值

目的：探讨三维时间飞跃法磁共振血管成像(Three dimensional time-of-flight magnetic resonance angiography, 3D-TOF MRA)原始图像评估脑梗死患者脑微出血(Cerebral microbleeds, CMBs)病灶的可行性，进一步探讨3D-TOF序列在预测脑梗死出血性转化中的应用价值。方法：选取192例脑梗死患者为研究对象，分别进行磁敏感加权成像(Susceptibility weighted imaging, SWI)和3D-TOF序列扫描，评估SWI及3D-TOF MRA原始轴位图像显示CMBs的优劣。观察脑梗死出血性转化在CT、T1WI、DWI、SWI及3D-TOF MRA序列原始图像中的影像学表现及CMBs的分布和信号特点，明确基于3D-TOF序列CMBs病灶数量分级与出血性转化的关系，探讨3D-TOF序列在预测脑梗死出血性转化中的应用价值。结果: 因影像学资料显示不清排除12例，实际纳入180例脑梗死患者，SWI共发现微出血病灶264个，CMBs数目分级：28例为轻度，8例为中度，4例为重度。3D-TOF MRA序列原始图像发现微出血病灶188个，其中24例为轻度，4例为中度，4例为重度。两种序列对微出血病灶的检出率比较差异有统计学意义(皮质和皮质下、丘脑、小脑，p < 0.05)；两者对基底节和脑干的微出血病灶检出率差异无统计学意义(p < 0.05)。180例患者中，24例发生出血性转化(13.3%)，T1WI、DWI、SWI及3D-TOF MRA序列检测出血性转化的敏感度分别为25.0%、62.5%、100%及83.3%。CMBs病灶数量与出血性转化的发生率呈正相关。结论：在缺乏SWI序列的情况下，3D-TOF MRA原始图像可有效显示CMBs病灶，可作为预测脑梗死发生出血性转化的有效手段之一。 Objective: To investigate the feasibility of the original image of the three-dimensional time of flight MR angiography (Three dimensional time-of-flight magnetic resonance angiography, 3D- TOF MRA) assessing cerebral microbleeds (CMBs) in the patients with cerebral infarction, and further investigate the application value of 3D-TOF sequence in predicting hemorrhagic transformation from cerebral infarction. Methods: 192 cases of patients with cerebral infarction were enrolled into this study, and susceptibility weighted imaging (SWI) and 3D-TOF sequence scanning were performed to assess the ability of SWI and original axial images of 3D-TOF MRA showing CMBs. We investigated the imaging signal distribution of hemorrhagic transformation with cerebral infarction in the original image of CT, T1WI, DWI, SWI and 3D-TOF MRA sequences and the characteristics of CMBs to clarify the relationship between the number grade of lesions and hemorrhagic transformation a clear sequence of CMBs based on 3D-TOF sequence, and explored the application value of 3D-TOF predicting hemorrhagic transformation with cerebral infarction. Results: 12 cases were excluded for the unclear imaging data. SWI found 264 lesions of CMBs among 180 cases with cerebral infarction. Classification of CMBs: 28 cases of mild, 8 cases of moderate, and 4 cases of severe. The original sequences of 3D-TOF MRA found 188 lesions of CMBs including 24 cases of mild, four cases of moderate, and four cases of severe. There was statistically significant difference in the CMBs lesions detection rate between these two sequences (cortical vs. subcortical, thalamus, cerebellum, p < 0.05). There was no significant difference in CMBs lesions detection rate in the basal ganglia and brainstem between them (p < 0.05). Among 180 patients, there were a total of 24 cases of hemorrhagic transformation (13.3%). The detection sensitivities of hemorrhagic transformation of T1WI, DWI, SWI and 3D-TOF MRA sequence were 25.0%, 62.5%, 100% and 83.3%. CMBs lesions number was positively correlated with the incidence of hemorrhagic transformation. Conclusion: In the absence of SWI sequence, the original image of 3D-TOF MRA sequence can effectively display CMBs lesions, which can be used as an effective means of predicting hemorrhagic transformation of cerebral infarction.

Reduction of Scan Time and Echo Time in 3D Time-of-Flight (TOF) MR Angiography, Using Reverse Elliptical Centric Dual-Echo Acquisition

In the conventional single-echo three dimension (3D) time-of-flight (TOF) magnetic resonance angiography (MRA), it always takes long scan time to obtain the good images. In addition, high-resolution MRA with flow compensation requires long echo time (TE). Here, a reverse elliptical centric dual-echo 3D TOF MRA pulse sequence was developed to reduce the scan time and minimize the effective TE. Dual-echo and reverse elliptical centric acquisition in the phase encoding and slice phase encoding direction were used to reduce the scan time by 61%. Furthermore, the effective echo time (TE) was also minimized from 4.8ms to 4.1ms. The developed pulse sequence was tested on clinical MRI systems and the contrast to noise ratio (CNR) was measured to evaluate the results. The results show that the CNR only decrease by 2.5% with the scan time reduced to 39% when compared with the conventional single-echo 3D TOF. Compared with the conventional dual-echo 3D TOF acquisition, the developed pulse sequence brings advantages in three aspects: (1) reduce scan time by 22%; (2) increase CNR by 10%; (3) reduce the artifacts induced by dual-echo effects. In addition, while keeping the similar scan time as the conventional single-echo 3D TOF acquisition, the results show that reverse elliptical centric dual-echo 3D TOF acquisition increase CNR by 54.3%.

The Role of Whole-Body Magnetic Resonance Imaging (WB-MRI) in Patients with Paroxysmal Nocturnal Hemoglobinuria (PNH)

▪INTRODUCTION: Paroxysmal nocturnal hemoglobinuria (PNH) is a rare clonal blood disorder of the hematopoietic stem cells characterized by chronic, uncontrolled complement-mediated intravascular hemolysis resulting in thrombophilia with thromboembolic events (TEs) and cytopenia due to bone marrow failure. PNH is the most vicious acquired thrombophilic state and TEs represent the leading cause of morbidity and mortality in PNH. PNH clone size correlates with the possibility to acquire a thrombosis but thromboses are also present in patients (pts) with small clones. Early detection of TEs is critically to improve the outcome in PNH with the availability of the terminal complement inhibitor eculizumab.METHODS: Between Dec 2013 and Jan 2016 whole-body magnetic resonance imaging (WB-MRI) scans at 1.5 Tesla (T) (Siemens MAGNETOM® Avanto) were performed in 37 pts (51% (19/37) females; median age 44 years (range 24-73 years), median D-dimer 0.23 mg/l (range 0.2-5.1 mg/l) with either PNH (n=23) or AA/PNH-syndrome (n=14). The protocol included a cranial time-of-flight magnetic resonance angiography (TOF-MRA), an arterial and venous contrast-enhanced MRA (CE-MRA), and a T1-weighted contrast-enhanced fat-suppressed gradient-echo sequence (radial volumetric interpolated breath-hold examination (VIBE)). Median clone size of GPI-deficient granulocytes (FLAER) was 88% (range 2.6-100%) and all pts were treated according to the German PNH guidelines, including the use of the terminal complement inhibitor eculizumab (70% (26/37)), with eculizumab being initiated in 23 pts prior to MRI. In the remaining pts eculizumab was initiated post MRI for reasons other than TEs. In 64% (24/37) of the pts no TEs were documented prior to the MRI scans. Two pts had a possible clinical history of TEs, including pulmonary embolism (PE) or deep venous thrombosis (DVT). The remaining pts (29% (11/37)) had a history of venous thromboses (e.g. DVT (5/11), portal venous thromboses (4/11), or vena caval thromboses (2/11)). One pt even had a myocardial infarction and two had a cerebral venous sinus thrombosis or a thalamic infarction. Six pts (16%) had more than just one documented TE in their medical history.RESULTS: In pts with the history of TEs we did not observe a progression of the existing TEs. There was no evidence of PE throughout observation time. In pts under chronic eculizumab therapy and prior TEs, additional bone infarcts involving the lower extremities were seen in one pt. In a second pt the diagnosis of a bilateral renal infarction was made. In two pts with no history of TEs bone infarcts of the lower extremities were seen (clone size >50%). In another pt a previously undiagnosed left renal infarction was observed. Moreover, a clinical non-critical occlusion of the right posterior tibial artery was identified in one pt.CONCLUSIONS: In contrast to previous studies there was no evidence for silent major TEs (e.g. PE) at the time of analysis. We were able to identify previously undiagnosed renal and bone infarctions (overall unknown prevalence) in our cohort of PNH pts. This is the first description of bone infarctions as possible thromboembolic complications in PNH. WB-MRI scans seem to be a novel and feasible method for the assessment of the whole vascular status of a PNH pt and allow the detection of previously unidentified vascular complications. This might directly affect treatment as eculizumab is indicated in PNH pts with TEs. Furthermore, in pts with existing TEs WB-MRI scans might be implicated to document their impact prior to treatment, especially in pts with major TEs or in pts with high disease acitivity and suspicion for TEs (e.g. recurrent abdominal pain or persisting dyspnea). DisclosuresDührsen:Amgen: Honoraria, Research Funding; Roche: Honoraria, Research Funding; Alexion Pharmaceuticals: Honoraria, Research Funding. Röth:Alexion Pharmaceuticals: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Novartis: Honoraria.

Clinical vascular imaging in the brain at 7 T

Stroke and related cerebrovascular diseases are a major cause of mortality and disability. Even at standard-field-strengths (1.5T), MRI is by far the most sensitive imaging technique to detect acute brain infarctions and to characterize incidental cerebrovascular lesions, such as white matter hyperintensities, lacunes and microbleeds. Arterial time-of-flight (TOF) MR angiography (MRA) can depict luminal narrowing or occlusion of the major brain feeding arteries, and this without the need for contrast administration. Compared to 1.5T MRA, the use of high-field strength (3T) and even more so ultra-high-field strengths (7T), enables the visualization of the lumen of much smaller intracranial vessels, while adding a contrast agent to TOF MRA at 7T may enable the visualization of even more distal arteries in addition to veins and venules. Moreover, with 3T and 7T, the arterial vessel walls beyond the circle of Willis become visible with high-resolution vessel wall imaging. In addition, with 7T MRI, the brain parenchyma can now be visualized on a submillimeter scale. As a result, high-resolution imaging studies of the brain and its blood supply at 7T have generated new concepts of different cerebrovascular diseases. In the current article, we will discuss emerging clinical applications and future directions of vascular imaging in the brain at 7T MRI.

The application of Silenz MR angiography in the follow-up assessment of intracranial aneurysms embolization

Objectives To explore the value of Silenz MRA in the follow-up assessment of intracranial aneurysms embolization. Methods Fifteen patients underwent coiled embolization were prospectively collected. Silenz and time of flight MRA (TOF MRA) were performed on the same day as DSA examination. Two neuro-radiologists scored the structures of peripheral vascular with a 4-score grading system and evaluate embolism status (two-grade montreal scale). The scores of vascular structures were compared using Wilcoxon signed rank tests. Weighted Kappa statistics was used to assess the inter-observer agreement on each MRA scoring, the inter-modality agreement between MRA and DSA, the inter-modality agreement between the MRA methods. Results There were 11 cases with complete occlusion, 4 cases with residual aneurysm revealed by DSA. For depiction, Silenz MRA was significantly better than TOF MRA [(3.50±0.62) vs. (3.00±0.63), Z=-3.12, P=0.002]. Inter-modality agreement of Silenz MRA and DSA was excellent (Kappa=0.82), while the agreement of TOF MRA and DSA was moderate(Kappa=0.60). Inter-modality agreement between Silenz MRA and TOF MRA was good (Kappa=0.76). Conclusions Silenz MRA is superior to TOF MRA for depiction of vascular structures and evaluation of embolism status, which is highly related with DSA. It has the value in the postoperative follow-up evaluation. Key words: Magnetic resonance angiography; Intracranial aneurysm; Embolization, therapeutic; Comparative study

Visual Quantification of the Circle of Willis: An Automated Identification and Standardized Representation

AbstractThis paper presents a method for the visual quantification of cerebral arteries, known as the Circle of Willis (CoW). It is an arterial structure with the responsibility of supplying the brain with blood, however, dysfunctions can lead to strokes. The diagnosis of such a time‐critical/urgent event depends on the expertise of radiologists and the applied software tools. They use basic display methods of the volumetric data without any support of advanced image processing and visualization techniques. The goal of this paper is to present an automated method for the standardized description of cerebral arteries in stroke patients in order to provide an overview of the CoW's configuration. This novel representation provides visual indications of problematic areas as well as straightforward comparisons between multiple patients. Additionally, we offer a pipeline for extracting the CoW from Time‐of‐Flight Magnetic Resonance Angiography (TOF‐MRA) data sets together with an enumeration technique for labelling the arterial segments by detecting the main supplying arteries of the CoW. We evaluated the feasibility of our visual quantification approach in a study of 63 TOF‐MRA data sets and compared our findings to those of three radiologists. The obtained results demonstrate that our proposed techniques are effective in detecting the arteries and visually capturing the overall configuration of the CoW.

Carotid artery stenosis with a high-intensity signal plaque on time-of-flight magnetic resonance angiography and association with evidence of intraplaque hypoxia.

OBJECTIVE Hypoxia induces angiogenesis and plays a major role in the progression of carotid plaques. During carotid intervention, plaques with high-intensity signals on time-of-flight (TOF) magnetic resonance angiography (MRA) often cause ischemic stroke and embolic complications. However, the role of intraplaque hypoxia before carotid endarterectomy (CEA) and carotid artery stenting is not presently understood. In this study the authors aimed to investigate the relationship between intraplaque hypoxia and MRA findings. METHODS Nineteen consecutive patients with 20 carotid artery stenoses who underwent CEA at Saga University Hospital between August 2008 and December 2014 were enrolled in the study. The expressions of hypoxia-inducible transcription factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) were analyzed by immunohistochemical analysis. In addition, the relationship between the findings on TOF MRA and pathology for the carotid plaques was analyzed. RESULTS High-intensity plaques on TOF MRA showed higher expression levels of HIF-1α (p = 0.015) and VEGF (p = 0.007) compared with isointensity plaques. The rate of intraplaque hemorrhage (IPH) on TOF MRA was also significantly higher in the high-intensity plaques than in the isointensity plaques (p = 0.024). Finally, the mean number of neovessels was significantly higher in those without plaque hemorrhage than in those with plaque hemorrhage (p = 0.010). CONCLUSIONS Plaques with high-intensity signals on TOF MRA were associated with IPH and evidence of intraplaque hypoxia. This fact may represent an opportunity to establish novel therapeutic agents targeting intraplaque hypoxia.

Diabetes mellitus and carotid artery plaques exhibiting high-intensity signals on MR angiography are related to increased platelet reactivity after carotid artery stenting

BackgroundIncreased platelet reactivity after carotid artery stenting (CAS) may cause thromboembolic complications.ObjectiveThis study aimed to investigate the incidence of increased platelet reactivity after CAS and to determine the factors related...

Comparison of conventional magnetic resonance imaging and nonenhanced three dimensional time-of-flight magnetic resonance angiography findings between dogs with meningioma and dogs with intracranial histiocytic sarcoma: 19 cases (2010-2014).

OBJECTIVE To compare conventional MRI and nonenhanced 3-D time-of-flight (TOF) magnetic resonance angiography (MRA) findings between dogs with meningioma and dogs with intracranial histiocytic sarcoma (IHS). DESIGN Retrospective case series. ANIMALS 14 dogs with meningioma and 5 dogs with IHS. PROCEDURES Medical records of dogs with meningioma or IHS that were examined at a tertiary veterinary hospital from 2010 through 2014 and underwent 3-D TOF MRA in conjunction with conventional MRI were reviewed. Findings for conventional MRI and 3-D TOF MRA were compared between the 2 groups of dogs to evaluate whether there were any characteristics that could be used to differentiate meningioma from IHS. RESULTS Tumor type was significantly associated with signal intensity on conventional T2-weighted and fluid-attenuated inversion recovery MRI images; most meningiomas were hyperintense, and most IHSs were isointense or hypointense on those images. Tumor type was not associated with signal uniformity, tumor location, tumor origin, or the presence of edema, midline shift, or brain herniation. On MRA, blood vessels adjacent to the tumor were identified and characterized for 9 of 14 dogs with meningioma and all 5 dogs with IHS. Vessels adjacent to meningiomas were displaced in 8 of 9 dogs, whereas vessels adjacent to IHSs were not displaced. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated nonenhanced 3-D TOF MRA findings provided additional information that can be assessed in conjunction with conventional MRI findings to help differentiate meningiomas from IHSs in dogs.

Diminished Signal Intensities Distal to Intracranial Arterial Stenosis on Time-of-Flight MR Angiography Might Indicate Delayed Cerebral Perfusion

Background: Intracranial arterial stenosis (ICAS) is a predominant cause of ischemic stroke in Asia. Changes in the signal intensities (SIs) across ICAS lesions on time-of-flight magnetic resonance angiography (TOF-MRA) have been indicated to partially reflect the hemodynamic significance of the lesions, which we aimed to verify by correlating it with cerebral perfusion features provided by CT perfusion (CTP) imaging. Methods: Ischemic stroke or transient ischemic attack patients with unilateral symptomatic stenosis (≥50%) of intracranial internal carotid artery or middle cerebral artery (MCA) were included in this study. Change of SIs across an ICAS lesion on TOF-MRA was calculated by the distal and proximal SI ratio (SIR). Cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) within the MCA territory of ipsilateral and contralateral hemispheres were evaluated on the CTP images at the basal ganglia level. Relative CBV, CBF and MTT were defined as ratios of the values obtained from ipsilateral and contralateral hemispheres. The relationships between SIR and CTP parameters were analyzed. Results: Fifty subjects (74% male, mean age 62) were recruited. Overall, the mean SIR was 0.77 ± 0.17. SIR of ICAS was significantly, linearly and negatively correlated with ipsilateral CBV (r = -0.335, p = 0.017), ipsilateral MTT (r = -0.301, p = 0.034), and ipsilateral/contralateral MTT ratio (r = -0.443, p = 0.001). Conclusions: Diminished SIs distal to ICAS on TOF-MRA might be associated with delayed ipsilateral cerebral perfusion. Changes of the SIs across ICAS lesions on TOF-MRA may be a simple marker to reflect cerebral perfusion changes in patients with symptomatic ICAS.

Unenhanced Time-of-Flight MR Angiography versus Gadolinium-Enhanced Time-of-Flight MR Angiography in the Follow-Up of Coil-Embolized Aneurysms.

Background and Purpose Coil embolization of ruptured and unruptured aneurysms has emerged as a widely accepted alternative to clipping. Unfortunately, coil-embolized aneurysms need a long-term imaging follow-up to confirm the stability of the occlusion status. We investigated whether contrast-enhanced time-of-flight (ToF) magnetic resonance angiography (MRA) (gadolinium [Gd]-ToF) provides any diagnostic benefit over conventional ToF MRA (nonenhanced [NE]-ToF) in this context. Material and Methods From October 2013 to January 2015, all patients who were regularly scheduled for their follow-up after coil embolization were examined with Gd-ToF and NE-ToF angiography. The general visibility of the occlusion result was compared between the two MRAs as well as with the last digital subtraction angiography (DSA) available. Subgroups of interest (follow-up after stent-assisted coil embolization, cases with already known aneurysm remnants) were also analyzed. Results A total of 70 patients (44 female) harboring 74 treated aneurysms were examined. The reproducibility of the DSA result in terms of therapeutic relevance was 100%. In 10 of 74 cases (14%), the aneurysm status was more difficult to judge in the NE-ToF images (p = 0.02), and the visualization of small vessels was significantly better in the Gd-ToF (p = 0.003). NE-ToF did not fail to show any aneurysm remnants but were more difficult to depict in 35% of the cases (p = 0.09). Regarding the aneurysms that were coiled with stent assistance, there was no significant difference in terms of the visualization (p = 0.1). Conclusion Gd-ToF angiography is in general not superior to NE- ToF for the follow-up of coil-embolized aneurysms.

A Parallel Markov Cerebrovascular Segmentation Algorithm Based on Statistical Model

For segmenting cerebral blood vessels from the time-of-flight magnetic resonance angiography (TOF-MRA) images accurately, we propose a parallel segmentation algorithm based on statistical model with Markov random field (MRF). Firstly, we improve traditional non-local means filter with patch-based Fourier transformation to preprocess the TOF-MRA images. In this step, we mainly utilize the sparseness and self-similarity of the MRA brain images sequence. Secondly, we add the MRF information to the finite mixture mode (FMM) to fit the intensity distribution of medical images. We make use of the MRF in image sequence to estimate the proportion of cerebral tissues. Finally, we choose the particle swarm optimization (PSO) algorithm to parallelize the parameter estimation of FMM. A large number of experiments verify the high accuracy and robustness of our approach especially for narrow vessels. The work will offer significant assistance for physicians on the prevention and diagnosis of cerebrovascular diseases.

Abstract WP62: Regional Leptomeningeal Score on TOF-MRA Predicts Collateral Flow Grade and Clinical Outcome in Patients with Acute Ischemic Stroke

Background: Collateral status at baseline is an important predictor of clinical outcome in patients with acute ischemic stroke (AIS). Non-contrast time-of-flight MR angiography (TOF-MRA) might provide information of blood flow features non-invasively. TOF-MRA could become a marker of collateral status and clinical outcome in patients with AIS. Methods: We retrospectively reviewed patients with AIS who had internal carotid artery or middle cerebral artery occlusion in three comprehensive stroke centers from August 2011 to July 2015. Those who underwent TOF-MRA sequence before endovascular therapy were investigated. Collateral status on TOF-MRA was graded by the previously-published regional leptomeningeal collateral (rLMC) score on CT angiography (0-20); collateral grade on angiography was assessed with the American Society of Interventional and Therapeutic Neuroradiology Collateral Grading System (0-4). We analyzed the relationship between rLMC score on TOF-MRA and patient characteristics, collateral flow grade, and good clinical outcome (modified Rankin Scale [mRS] of 0-2 at 90 days). Results: A total of 38 patients (aged 71.7 ± 10.3 years; men, 71%; NIHSS score, 20 ± 6; median DWI-ASPECTS, 8) were included. Collateral grade on angiography was 0 to 1 in 10 (26%) patients, 2 in 6 (15%), 3 in 19 (50%), and 4 in 3 (7%), which was correlated to rLMC score on TOF-MRA (p &lt; 0.001). Higher rLMC score on TOF-MRA was not related to baseline DWI-ASPECTS and reperfusion (Thrombolysis in Cerebral Infraction [TICI] 2b/3) after endovascular treatment, but was related to mRS 0-2 at 90 days (p = 0.021). All patients with high rLMC score (15-20) demonstrated mRS 0-2 at 90 days, whereas 69% of those with medium rLMC score (8-14) and 31% of those with low rLMC score did. In multivariate analysis, both rLMC score on TOF-MRA (OR, 1.5 per 1 point; p = 0.009) and reperfusion (TICI 2b/3 reperfusion; OR, 49.9; p &lt; 0.001) were independent predictors of mRS 0-2 at 90 days. Conclusions: rLMC score on TOF-MRA is a noninvasive and feasible parameter of collateral flow status and related to clinical outcome in patients with AIS. TOF-MRA might be a useful non-invasive imaging method to select candidates for endovascular therapy.