MR imaging of middle cerebral artery stenosis and occlusion: value of MR angiography.

PURPOSETo investigate the effectiveness of MR angiography in conjunction with spin-echo imaging for evaluating vascular patency in patients with middle cerebral artery (MCA) stenosis or occlusion.METHODSSeven patients with MCA stenosis or occlusion, verified with contrast angiography in five and correlated with transcranial Doppler sonography in two, were examined using two-dimensional and/or three-dimensional time-of-flight MR angiographic techniques as well as conventional spin-echo imaging.RESULTSOf the seven patients, six demonstrated basal ganglionic and/or cortical infarct in the MCA territory. Except one case with minimal stenosis immediately distal to the MCA origin, all six cases with either severe stenosis or occlusion of the main trunk of the MCA showed the absence of normal flow voids using spin-echo imaging in the sylvian fissure on the affected side. However, it was not possible to discriminate between stenosis and occlusion. Although different mechanisms (ie, flow-induced spin dephasing for the 2-D technique and progressive spin saturation for the 3-D technique) were predominantly responsible for the loss of signal through the area of stenosis, both the 2-D and 3-D MR angiograms clearly depicted the compromised flow of the MCA: a focal discontinuity with decreased vessel caliber corresponded to stenosis, and nonvisualization of distal MCA branches represented occlusion.CONCLUSIONEither 2-D or 3-D time-of-flight MR angiography is a useful adjunct to conventional parenchymal spin-echo imaging for evaluating vascular patency in patients with MCA stenosis or occlusion, although it is important to recognize that each technique has a different basis for the loss of signal through the area of stenosis.     

MR imaging of middle cerebral artery occlusion without cerebral infarction

Magnetic resonance (MR) images of 12 patients with angiographically proven middle cerebral artery (MCA) occlusion were analyzed, retrospectively. In three of the 12 patients, cerebral infarctions related to the MCA occlusions were not evident. Two of the three patients were cases of atherosclerotic occlusion and the remaining patient had an acute thromboembolism. In all of the occluded M1 portions of the MCA the flow void was absent and there were isointense linear structures, with or without a hyperintense component in the Sylvian vallecula, on T1-weighted images. For nine of the 12 patients, the absence of flow void in the ipsilateral Sylvian fissure was evident on the T2-weighted images. Therefore, even in cases with no evidence of a cerebral infarction, the presence of flow void in the Sylvian vallecula and Sylvian fissure must be searched for in routine reviews of MR images. If MR imaging can be obtained on an emergency basis, appropriate interventional therapy may be immediately initiated.     

Intracranial vascular stenosis and occlusion: evaluation with three-dimensional time-of-flight MR angiography.

To assess the usefulness of magnetic resonance (MR) angiography in the characterization of intracranial arterial stenosis and occlusion, a three-dimensional time-of-flight method was compared with conventional angiography in 214 vessels in 29 patients. Studies were independently interpreted by two neuroradiologists who scored each vessel as normal, narrowed, or occluded. Overall, 97% of normal vessels and 100% of occlusions were correctly graded. Sixty-one percent of stenoses were graded correctly; the remainder were graded as normal. The portions of the intracranial vessels near the skull base and especially the paracavernous and supraclinoid segments of the internal carotid arteries were areas of frequent over- and underestimation of stenosis due to the presence of dephasing artifacts. In patients with stenosis or occlusion, MR angiography also provided information regarding the presence of collateral flow in the circle of Willis. When used in conjunction with MR imaging of the brain and MR angiography of the extracranial carotid arteries, intracranial MR angiography allows a more complete evaluation of the patient with symptoms of cerebral ischemia or infarction.     

Fenestration of the middle cerebral artery detected by MR angiography.

Unlike fenestration of the posterior cerebral arterial circulation, fenestration of the anterior cerebral arterial circulation has not been well described. We investigated the location and configuration of fenestration of the middle cerebral artery (MCA) detected by magnetic resonance (MR) angiography. We found 6 fenestrations of the MCA among cranial MR angiography images obtained from about 2,000 patients during the past 9 years at our institution using either of two 1.5T imagers. All images were obtained by the three-dimensional time-of-flight technique. Maximum-intensity projection images in the horizontal rotation view were displayed stereoscopically. All 6 fenestrations had small slit-like configurations, five located at the proximal M1 segment, the other, at the middle M1 segment. No associated aneurysm was found. Although MCA fenestration is extremely rare and cerebral artery fenestration usually has no clinical significance, an aneurysm can arise at the proximal end of the fenestration. Thus, recognizing MCA fenestration is important when interpreting cranial MR angiograms.     

Fast three-dimensional time-of-flight MR angiography of the intracranial vasculature

Magnetic resonance angiography is most commonly performed with the three-dimensional (3D) time-of-flight (TOP) technique. As currently practiced, this requires long image acquisition times (5–10 minutes). The authors show that the acquisition time of 3D TOP images can be reduced to less than 1 minute by using a very short TR (<10msec). Under normal flow conditions, the major vessels of the circle of Willis were consistently well demonstrated on these fast 3D TOP images. Signal saturation was observed in studies of patients with abnormal blood flow. In those cases, it was demonstrated that serial acquisition of fast 3D TOP data during and after contrast agent administration could be used to overcome the saturation effects. Time-resolved fast 3D TOP imaging during and after contrast agent administration can also provide qualitative assessment of flow and may depict other features that cannot be observed in TOP studies with long imaging times.     

Three-dimensional time-of-flight MR angiography in the evaluation of cerebral aneurysms

We review our preliminary experience with the use of three-dimensional (3D) time-of-flight (TOF) magnetic resonance (MR) angiography (MRA) in the assessment of intra- and extracranial aneurysms. Six patients were examined: Five had intracranial aneurysms and one had a cervical carotid pseudoaneurysm. A 3D rephased gradient recalled echo pulse sequence and maximum intensity projection (MIP) reconstruction algorithm were used. Magnetic resonance angiography, spin echo MR, and conventional angiography were retrospectively reviewed with specific regard to individual vessel visualization, aneurysm depiction, and presence of artifact related to acquisition techniques or MIP reconstruction. All aneurysms were detected on MRA, and anatomical correlation with conventional angiography was excellent. Significant problems included loss of visualization of small vessels, intraluminal signal loss in large vessels, subacute thrombus simulating flow on MIP reconstructions, and limited projections obtainable with MIP techniques. Adequate MRA assessment of aneurysms can be obtained using a combination of T1-weighted spin echo images and 3D TOF MRA. Review of all components of the MRA is required. MRA may be useful in screening asymptomatic patients for intracranial aneurysms as well as in the follow-up of patients treated with balloon occlusion.     

The three-dimensional shape analysis of the M1 segment of the middle cerebral artery using MRA at 3T

Introduction

The M1 segment of the middle cerebral artery (MCA) is of great importance to neurosurgery and interventional radiology. The purpose of this study was to describe the M1 segment in three dimensions based on shape projection using magnetic resonance angiography (MRA).

Methods

A three-view method was established and used in the retrospective analysis of 717 M1 segments derived from 3D-TOF MRA images. In this method, the M1 segment was first projected on three orthogonal planes (axial, coronary, and sagittal plane); the courses of the projected vessels were classified as line-shape, C-shape, or S-shape on each orthogonal plane; and then the actual parameters, including internal diameter and so on, were measured on the projected images. The shape classifications and the measured parameters were efficient methods of describing the M1 segment. Twelve geometric models of the vessels were reconstructed and were compared with those from an actual validation method.

Results

The 3D shape of the M1 segment in the 3D orthogonal views was not uniform. Only 17.3 % M1 segments were straight, 43.5 % followed plane curves, and nearly 40 % were tortuous in 3D space. The probability distributions of shape classifications changed with age. The proportion of the tortuous vessels increased with age. We also showed that the three-view method is effective with a volume relative error of less than 13 %.

Conclusion

The three-view method is convenient for describing the 3D morphology, including the shape information, of the M1 segment. It is a potential method for planning and predicting risk in neurosurgery/neurointervention.     

MR angiography and imaging for the evaluation of middle cerebral artery atherosclerotic disease

Intracranial atherosclerotic disease may constitute the most common cause of ischemic stroke worldwide; yet, in the developed world, imaging research has largely focused on extracranial atherosclerosis. Many studies in populations of Asian, African, and Hispanic descent demonstrate the preponderance of intracranial stenosis compared with carotid stenosis. This review examines the clinical presentations of MCA atherosclerosis and stenosis and the use of noninvasive MR imaging in the assessment of intracranial vasculature. MRA is a well-validated technique that offers great advantage over traditional angiography. Advances in high-resolution MR imaging of MCA stenosis have the potential to yield excellent visualization of plaque. Future developments in high-resolution MR imaging to depict intracranial atherosclerosis are explored in this review; these advances will guide endovascular therapy and the comparison of novel interventions.     

Autocorrection of three-dimensional time-of-flight MR angiography of the Circle of Willis

OBJECTIVE. The purpose of this study was to investigate the efficacy of a retrospective adaptive motion correction technique known as autocorrection for reducing motion-induced artifacts in high-resolution three-dimensional time-of-flight MR angiography of the circle of Willis. MATERIALS AND METHODS. Ten consecutive volunteers were imaged with an unenhanced gradient-recalled echo three-dimensional time-of-flight MR angiography sequence of the circle of Willis. Each volunteer was asked to rotate approximately 2 degrees after completion of one third and one half of the acquisition in the axial, sagittal, and oblique planes (45 degrees to the axial and sagittal planes). A single static data set was also acquired for each volunteer. Unprocessed and autocorrected maximum-intensity-projection images were reviewed as blinded image pairs by six radiologists and were compared on a five-point image quality scale. RESULTS. Mean improvement in image quality after autocorrection was 1.4 (p < 0.0001), 1.1 (p < 0.0001), and 0.2 (p = 0.003) observer points (maximum value, 2.0), respectively, for examinations corrupted by motion in the axial, oblique, and sagittal planes. All three axes had statistically significant improvement in image quality compared with the uncorrected images. Changes in image quality after the application of the autocorrection algorithm to static angiogram data were not statistically significant (mean change in score = -0.13 points; p = 0.29). CONCLUSION. Autocorrection can reduce artifacts in motion-corrupted MR angiography of the circle of Willis without distorting motion-free examinations.     

Acetazolamide challenge for three-dimensional time-of-flight MR angiography of the brain.

PURPOSEWe compared three-dimensional time-of-flight MR angiograms obtained before and after acetazolamide administration to evaluate whether use of this drug could improve visualization of small peripheral intracranial arteries and atherosclerotic stenosis.METHODSFor evaluation of small peripheral arteries, 10 patients with clinical diagnosis of ischemic cerebrovascular disease and 10 healthy volunteers were investigated, and for evaluation of stenosis, another 6 patients were investigated. Vascular images were obtained by three-dimensional time-of-flight MR angiography. After a baseline scan, 17 mg/kg acetazolamide was injected intravenously and the second scan was performed 20 minutes later.RESULTSSeveral small peripheral arteries that had not been seen on the baseline images were visible on the acetazolamide images without any augmentation of the background signals. Stenotic lesions in the main trunks of the major cerebral arteries were detected more clearly on acetazolamide images.CONCLUSIONSAcetazolamide improves visualization of small peripheral intracranial arteries and sensitivity in detecting atherosclerotic stenosis in the main trunk of major cerebral artery by three-dimensional time-of-flight MR angiography without changing MR apparatus and software.     

MRI of middle cerebral artery occlusion

Magnetic resonance imagings (MRIs) of ten patients with angiographically proved middle cerebral artery (MCA) occlusion were retrospectively reviewed. Eight of the ten patients had cerebral infarcts, one had an intraventricular hemorrhage, and the remaining one had no significant abnormalities. All patients were examined by the 1.5 Tesla SIGNA (GE), using spin-echo pulse sequences. In all patients, occluded MCA could be detected by MRI. All occluded arteries showed absence of flow void and were demonstrated as iso- or hyperintense structures relative to gray matter on T1-weighted images, iso- or hypointense on T2-weighted images. In eight of the ten patients, absence of flow void in the sylvian fissure was observed on T2-weighted images. Thus, MRI was proved to be a pertinent diagnostic modality for evaluating MCA occlusions.     

利用CTA的侧支循环评分预测大脑中动脉M1段闭塞后脑梗死体积及分布情况

目的:探讨大脑中动脉M1段闭塞患者CTA的侧支循环评分与各脑血管危险因素、脑梗死体积及分布的相关性.方法:回顾性分析60例大脑中动脉M1段闭塞的患者,利用CTA评估侧支循环,根据侧支代偿优劣分为2组,按多田公式测量48h后的最终梗死体积,利用二元逻辑回归分析,判定侧支循环评分与各脑血管危险因素及最终脑梗死体积的关系.根据MRI(DWI)记录各患者梗死部位及数目,2组间以单多发、有无PAI、有无PI及有无BZ进行比较.结果:60例患者中,侧支循环不良组21例,侧支循环良好组39例.2组间患者症状及DWI梗死体积评分比较,差异有统计学意义(Z=18.266,t=-5.682,均为P=0.000).2组患者年龄、性别、发病侧、高血压、糖尿病、高脂血症、吸烟史及既往脑卒中史比较,差异无统计学意义(P＞0.05).二元逻辑回归分析显示DWI梗死体积在2组间差异有统计学意义(P=0.01,＜0.05),而症状在2组间差异无统计学意义.2组患者脑梗死多发较单发者多见,组间以单多发、有无PAI及有无PI比较差异无统计学意义(P＞0.05),以有无BZ比较差异有统计学意义(x2=12.493,P=0.000,P＜0.05).结论:大脑中动脉M1段闭塞后可运用CTA侧支循环评分对最终梗死体积进行简单量化评估,并对了解梗死分布有一定帮助,对临床治疗及预后有参考价值.     

Retrograde flow in the dural sinuses detected by three-dimensional time-of-flight MR angiography

Introduction Retrograde flow in the left dural sinuses is sometimes detected by three-dimensional time-of-flight (3D-TOF) magnetic resonance (MR) angiography. The purpose of this study was to evaluate the incidence of this phenomenon and its characteristic features on 3D-TOF MR angiograms. Methods We retrospectively reviewed cranial MR angiography images of 1,078 patients examined at our institution. All images were obtained by the 3D-TOF technique with one of two 1.5-T scanners. Maximum intensity projection (MIP) images in the horizontal rotation view were displayed stereoscopically. We reviewed the source images, inferosuperior MIP images, and horizontal MIP images and identified retrograde flow in the dural sinuses. Results We found retrograde flow in the dural sinuses of 67 patients on the source images from 3D-TOF MR angiography; the incidence was 6.2%. In 47 of the 67 patients, retrograde flow was identified in the left inferior petrosal sinus, in 13, it was seen in the left sigmoid sinus, and in 6, it was seen in the left inferior petrosal and left sigmoid sinuses. The remaining patient had retrograde flow in the left inferior petrosal and left and right sigmoid sinuses. The mean age of the patients with retrograde flow was slightly greater than that of the patients without this phenomenon (70 years vs 63 years). Conclusion Retrograde flow in the dural sinuses frequently occurs on the left side in middle-aged and elderly patients during 3D-TOF MR angiography performed with the patient in the supine position. This phenomenon should not be misdiagnosed as a dural arteriovenous fistula. This article was presented as an electronic poster paper at the 31st Congress of the ESNR held in Geneva in September 2006.     

Follow-up of coiled cerebral aneurysms at 3T: comparison of 3D time-of-flight MR angiography and contrast-enhanced MR angiography

BACKGROUND AND PURPOSE: Our aim was to compare contrast-enhanced MR angiography (CE-MRA) and 3D time-of-flight (TOF) MRA at 3T for follow-up of coiled cerebral aneurysms.MATERIALS AND METHODS: Fifty-two patients treated with Guglielmi detachable coils for 54 cerebral aneurysms were evaluated at 3T MRA. 3D TOF MRA (TR/TE = 23/3.5; SENSE factor = 2.5) and CE-MRA by using a 3D ultrafast gradient-echo sequence (TR/TE = 5.9/1.8; SENSE factor = 3) enhanced with 0.1-mmol/kg gadobenate dimeglumine were performed in the same session. Source images, 3D maximum intensity projection, 3D shaded surface display, and/or 3D volume-rendered reconstructions were evaluated in terms of aneurysm occlusion/patency and artifact presence.RESULTS: In terms of clinical classification, the 2 MRA sequences were equivalent for 53 of the 54 treated aneurysms: 21 were considered fully occluded, whereas 16 were considered to have a residual neck and 16 were considered residually patent at follow-up MRA. The remaining aneurysm appeared fully occluded at TOF MRA but had a residual patent neck at CE-MRA. Visualization of residual aneurysm patency was significantly (P = .001) better with CE-MRA compared with TOF MRA for 10 (31.3%) of the 32 treated aneurysms considered residually patent with both sequences. Coil artifacts were present in 5 cases at TOF MRA but in none at CE-MRA. No relationship was apparent between the visualization of patency and either the size of the aneurysm or the interval between embolization and follow-up.CONCLUSION: At follow-up MRA at 3T, unenhanced TOF and CE-MRA sequences are similarly effective at classifying coiled aneurysms as occluded or residually patent. However, CE-MRA is superior to TOF MRA for visualization of residual patency and is associated with fewer artifacts.

Regular imaging follow-up of patients with intracranial aneurysms treated with Guglielmi detachable coils (GDCs) is necessary because of the risk of aneurysm reconfiguration (ie, coil compaction and/or growth of a residual aneurysm neck or body remnant) with time.^1–4 Of the techniques available for monitoring the results of embolization therapy, MR angiography (MRA) has emerged as the technique of choice at most institutions. Advantages over conventional digital subtraction angiography (DSA) include minimal invasiveness with no associated risk of neurologic complications, reduced patient discomfort and inconvenience, greater cost savings, and no exposure to ionizing radiation or potentially nephrotoxic iodinated contrast media. An alternative minimally invasive procedure is CT angiography (CTA). However, whereas this technique has proved useful for aneurysm detection,^5–9 limitations to its use for follow-up of coiled aneurysms include streak and other coil-related artifacts.^10–12 Moreover, CTA also requires exposure to ionizing radiation and iodinated contrast media, which may be undesirable if repeat follow-up examinations are required.Studies performed to date have shown that nonenhanced 3D time-of-flight (TOF) MRA sequences on 1.5T scanners are frequently satisfactory for the follow-up of coiled aneurysms^1–20 but that 3D TOF MRA on 3T scanners offers improved depiction of both treated²¹ and untreated²² aneurysms due to the greater spatial and contrast resolution achievable at a higher magnetic field strength. Concerning the use of gadolinium contrast material, some studies have suggested that contrast-enhanced MRA (CE-MRA) provides no additional benefit compared with nonenhanced 3D TOF MRA at either 1.5T^15,20 or 3T,²¹ whereas other studies have shown that CE-MRA permits better visualization of coiled aneurysms and of branch arteries and residual neck, particularly in large or giant aneurysms.^14,22–26 Recently, Nael et al²⁷ demonstrated that CE-MRA with highly accelerated (×4) parallel acquisition at 3T provides comparable information to accelerated (×2) 3D TOF MRA at 3T for the characterization of untreated intracranial aneurysms without the known drawbacks of TOF MRA techniques (ie, prolonged acquisition time, spin saturation, and flow-related artifacts). On the other hand, Gibbs et al²⁸ showed that with elliptic-centric imaging, 3D TOF MRA at 3T is superior to CE-MRA at 3T in terms of both image quality and detection of untreated intracranial aneurysms. Our study was performed to evaluate CE-MRA with accelerated (×3) parallel acquisition at 3T compared with accelerated (×2.5) 3D TOF MRA at 3T for the follow-up of GDC-treated intracranial aneurysms. To the authors’ knowledge, this is the first study to compare MRA sequences at 3T for follow-up of coiled aneurysms.