MR angiography of the intracranial vessels: technical aspects and clinical applications

Evaluation of the intracranial circulation provides valuable information in the diagnosis and prognosis of various intracranial abnormalities and may influence patient management. Technical advances in magnetic resonance angiography (MRA) have improved the accuracy of this technique in various clinical situations, such as aneurysms, arterial and venous steno-occlusive diseases, vascular malformations, inflammatory arterial diseases, preoperative assessment of the patency of dural sinuses, and congenital vascular abnormalities. In many centers, MRA has replaced conventional digital subtraction angiography in screening for intracranial vascular disease, because of its non-invasive and non-ionizing character. Several MRA techniques have been developed for the imaging of the intracranial vascular system, such as time-of-flight MRA (TOF MRA), phase-contrast MRA (PC MRA), and more recently contrast-enhanced MRA (CE MRA). In the evaluation of steno-occlusive disease, the three-dimensional (3D) TOF-MRA technique is recommended for arterial evaluation, and the 2D TOF or 2D PC-MRA technique for venous evaluation. For the evaluation of aneurysms and arteriovenous malformations (AVMs), we recommend the 3D CE-MRA technique, especially dynamic sequences in case of AVM. In this review, the technical aspects, limitations, and optimization of these MRA techniques will be discussed together with their indications in intracranial disease.     

MR diagnosis of vein of Galen aneurysmal malformations using virtual cisternoscopy.

Vein of Galen aneurysmal malformations (VGAMs) are rarely seen intracranial congenital vascular malformations with extremely complex vascular architectures. We present two newborns with an unclear intracranial mass being discovered in routine intrauterine ultrasonography. Magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) identified these lesions as VGAMs. Besides conventional MRA analysis, "virtual cisternoscopy"-a special kind of virtual endoscopy combining perspective volume rendering and motion-was applied to assess the intracranial vasculature. One newborn was treated by means of interventional neuroradiology with coiling of the median prosencephalic vein. The clinical outcome in this case was excellent. The other will undergo interventional therapy shortly.     

MR-based assessment of vascular morphology and function

Initially, time-of-flight angiography found its way into clinical routine for imaging vascular morphology. In conjunction with phase-contrast imaging, functional and morphological assessment of vascular pathology became possible. The flow dependence and associated artifacts inherent to these techniques have restricted the clinical use of these magnetic resonance angiography (MRA) techniques to the extra- and intracranial arterial, as well as the systemic and portal, venous systems. With the advent of high-performance gradient systems a new, promising MRA strategy has been developed: contrast-enhanced 3D MR angiography. It is based on the combination of rapid 3D imaging and the T1-shortening effect of intravenously infused paramagnetic contrast. This review provides a technical overview and critically discusses the clinical application for the different MRA techniques regarding morphological as well as functional assessment of the vascular system. Received: 27 November 1997; Accepted 29 December 1997     

脑血管疾病TOF法磁共振血流成像的初步探讨

笔者搜集了７０例诊断明确的脑血管疾病ＭＲＡ资料进行分析。其中２２例经Ｘ线脑血管造影证实。所有患者均进行了三维ＴＯＦ法ＭＲＡ扫描。结果表明，三维ＴＯＦ法能清楚地显示出脑动脉瘤、血管畸形、大动脉的狭窄和阻塞等血管病变，但由于饱和作用的影响，不能显示小动脉分支和静脉血管，并且在血管狭窄的显示方面存在着夸张作用和假象。与Ｘ线血管造影相比，ＭＲＡ虽具有成像迅速、无创伤等优点，但在小血管病变及血管狭窄的显示方面仍有不足。     

磁共振脑血管造影与数字减影血管造影的比较

通过对５５例脑血管磁共振血管造影（ＭＲＡ）和动脉数字减影血管造影（ＩＡ－ＤＳＡ）的对比分析，探讨了ＭＲＡ在颅内血管病变诊断中的可靠性。结果表明，ＭＲＡ可以对４８例患者做出正确诊断，结合常规ＭＲＩ和ＭＲＡ原始切层图像，其敏感性为９０．９％。对动脉瘤的敏感性为８７．５％，动静脉畸形为７８．６％。３例血管狭窄闭塞性病变和１例脑膜瘤患者的血管改变也与ＤＳＡ完全符合。可以认为，作为一种常规筛选工具，ＭＲＡ用于脑血管病变的检查和诊断，具有安全、可靠和方便的优点。     

Magnetic resonance angiography of intracranial aneurysms: comparison with intra-arterial digital subtraction angiography

Summary Magnetic resonance angiography (MRA) with flow rephased gradient-echo sequences is a new non-invasive method for vascular imaging. We compared MRA and intra-arterial digital subtraction angiography in 18 patients with intracranial aneurysms to test whether MRA presently provides an alternative to cerebral angiography for the diagnosis of these anomalies. MRA showed 19 of the 22 aneurysms detected (86.4%). However, problems, especially with turbulent or slow flow, resulted in 6 studies (27.3%) with limited and 2 with questionable demonstration of an aneurysm, and 1 false negative study. At present, MRA is definitely inferior to angiography for the demonstration of intracranial aneurysms, due to its lower resolution and other limitations.     

脑动脉瘤的MR血管造影与IA—DSA的对照研究

对经手术证实的２０例脑动脉瘤的ＭＲＡ和ＩＡ－ＤＳＡ的影像进行了对照分析研究，经ＭＲＡ检出１９例（９５％）动脉瘤，１０ｍｍ以下的动脉瘤９例，最小的为４ｍｍ，与ＤＳＡ检出率（１９／２０）相仿。ＭＲＡ的定位符合率为８４％，低于ＤＳＡ（９５％）。１３／１９例（６８％）在ＭＲＡ图象上能显示动脉瘤的瘤颈。作者认为ＭＲＡ是一种新的非侵入性的血管影像方法，可作为脑动脉瘤高危病例的筛选检查，随着ＭＲＡ技术的进一步完善，ＭＲＡ有望在神经外科领域替代部分侵入性血管造影检查。     

MR imaging findings of intracranial dural arteriovenous fistulas: relations with venous drainage patterns

BACKGROUND AND PURPOSE: Venous drainage patterns are a major determinant of clinical outcome in intracranial dural arteriovenous fistula (DAVF) patients. In this study, we sought to identify MR imaging finding differences between DAVF types classified on the basis of venous drainage patterns. METHODS: Twenty-seven patients diagnosed as having DAVFs by conventional angiography were included. Medical records (n = 27), and MR imaging (n = 27) and MR angiography (MRA; n = 11) findings were retrospectively reviewed. MR imaging findings included flow void cluster, engorged ophthalmic vein/proptosis, white matter hyperintensity, intracranial hemorrhage, dilated leptomeningeal or medullary vessels, venous pouch, and leptomeningeal or medullary vascular enhancements. MRA findings included identifiable fistula, venous flow-related enhancement, and prominent extracranial vessels. Patients' presentations and MR imaging findings were compared among angiographic type I, II, and III cases (according to Borden's classification), and MRA findings were compared between cases with and without retrograde leptomeningeal venous drainage (RLVD). RESULTS: Patient presentations were aggressive in one (13%) of the type I cases, 5 (50%) of the type II cases, and 8 (100%) of the type III cases (P = .002). Aggressive presentations included hemorrhage, focal neurologic deficits, seizures, intracranial hypertension, and an altered mental status. MR images showed significantly higher frequencies of dilated leptomeningeal or medullary vessels in a higher type [0 in type I, 5 (42%) in type II, and 7 (100%) in type III], and of leptomeningeal or medullary vascular enhancements [0 in type I, 4 (33%) in type II, and 7 (100%) in type III]. By using MRA, fistulas were identified only in cases with RLVD (5 [83%]). Venous flow-related enhancement was present in 10 cases (91%). A sole false-negative case on MRA, as compared with conventional angiography, resulted from nonvisualization of the slow venous flow (8%). No false-positive fistula was found at the other intracranial sites in all cases. Overall, MRA assessment for DAVF was adequate for both fistula and venous flow-related enhancement in 10 cases (91%) and inadequate in a remaining case because of the fistular location out of field. CONCLUSION: MR imaging demonstration of leptomeningeal or medullary vascular dilation and enhancements may be associated with features that are considered predictors of a poor outcome and indicates a need for urgent therapy in intracranial dural AVF patients. MRA is a complementary tool for the identification of dural AVF with venous flow-related enhancement.     

Assessing Blood Flow in an Intracranial Stent: A Feasibility Study of MR Angiography Using a Silent Scan after Stent-Assisted Coil Embolization for Anterior Circulation Aneurysms

BACKGROUND AND PURPOSE:Blood flow in an intracranial stent cannot be visualized with 3D time-of-flight MR angiography owing to magnetic susceptibility and radiofrequency shielding. As a novel follow-up tool after stent-assisted coil embolization, we applied MRA by using a Silent Scan algorithm that contains an ultrashort TE combined with an arterial spin-labeling technique (Silent MRA). The purpose of this study was to determine whether Silent MRA could visualize flow in an intracranial stent placed in the anterior circulation.MATERIALS AND METHODS:Nine patients treated with stent-assisted coil embolization for anterior circulation aneurysms underwent MRAs (Silent MRA and TOF MRA) and x-ray digital subtraction angiography. MRAs were performed in the same session on a 3T unit. Two neuroradiologists independently reviewed the MRA images and subjectively scored flow in a stent as 1 (not visible) to 4 (excellent) by referring to the latest x-ray digital subtraction angiography image as a criterion standard.RESULTS:Both observers gave MRA higher scores than TOF MRA for flow in a stent in all cases. The mean score for Silent MRA was 3.44 ± 0.53, and for TOF MRA, it was 1.44 ± 0.46 (P < .001).CONCLUSIONS:Silent MRA was able to visualize flow in an intracranial stent more effectively than TOF MRA. Silent MRA might be useful for follow-up imaging after stent-assisted coil embolization, though these study results may be only preliminary due to some limitations.

Endovascular therapy for intracranial aneurysms has been widely used since the International Subarachnoid Aneurysm Trial.¹ The number of cases of coil embolization for aneurysms is increasing, and the stent-protection technique has widened the applicability to cases that had been otherwise difficult to treat with conventional coil embolization.² Nevertheless, there is a risk of coil compaction or in-stent restenosis after stent-assisted coil embolization. X-ray digital subtraction angiography is the optimal technique used to examine these adverse events, and it is commonly used as a follow-up tool after using an intracranial stent. However, DSA presents some unavoidable risks related to the catheter procedure, radiation, and contrast media.^3–53D time-of-flight MR angiography is widely used for the assessment of cerebral vascular diseases and has also been examined as a noninvasive substitute for DSA.^6–9 These studies generally reported difficulty in visualizing flow in a stent with TOF MRA because of magnetic susceptibility and radiofrequency shielding, though some beneficial aspects were observed in assessing the residual lumen of aneurysms. As a novel follow-up tool after stent-assisted coil embolization, we applied MRA by using a Silent Scan algorithm (GE Healthcare, Milwaukee, Wisconsin) that contains an ultrashort TE combined with an arterial spin-labeling technique (Silent MRA). In this situation, visualizing flow means visualizing arterial geometry and patency. It does not mean directly visualizing blood flow rate. The purpose of this study was to determine whether Silent MRA can visualize flow in an intracranial stent placed at the anterior circulation.     

Normal variants of the intracranial circulation demonstrated by MR angiography at 3T

Magnetic resonance angiography (MRA) at 3T offers increased signal to noise ratio with better background suppression, leading to exquisite depiction of the intracranial circulation. We present a pictorial review of the normal variations and anomalies of the intracranial circulation detected on MRA performed on a high field 3T clinical scanner using parallel imaging techniques. The salient imaging features of these anomalies and normal variations are discussed with relevance to clinical practice.     

Investigation of cerebrovascular disease with MR angiography: comparison of volume rendering and maximum intensity projection algorithms--initial assessment

We assessed the clinical utility of the volume-rendering (VR) algorithm as a postprocessing technique of intracranial magnetic resonance angiography (MRA) for the evaluation of cerebrovascular disease in comparison with the maximum intensity projection (MIP) algorithm. VR and MIP images were compared with digital subtraction angiography (DSA). Volume-rendered views improved the perceptibility of intracranial vasculature and consequently augmented diagnostic confidence, improved the characterization of underlying vascular pathologies, and facilitated image interpretation. Volume rendering has the potential to expand the role of cerebral MRA in the diagnostic investigation and treatment planning of cerebrovascular disease.     

Intracranial vascular malformations

Many efforts and much research have been dedicated to the field of non-invasive angiographic techniques in the past few years. Thanks first to magnetic resonance angiography (MRA) and subsequently to computed tomographic angiography (CTA), very interesting results have been obtained in the diagnosis of cerebrovascular diseases. Neck vessels are most successfully evaluated by both MRA and CTA, and the need for digital subtraction angiography (DSA) examinations in patients at risk for vascular occlusions has significantly decreased. The role and the diagnostic accuracy of these non-invasive modalities in intracranial vascular pathology is still under investigation, and several studies have been and are being performed. Both techniques have a better spatial resolution and sensitivity in detecting cerebrovascular malformations than DSA. In the diagnosis of cerebral aneurysms, both MRA and CTA – due to their high sensitivity – have become screening techniques in the population at risk for subarachnoid hemorrhage, these techniques may become basic diagnostic modalities in treatment planning. The results are less satisfying in the evaluation of brain arteriovenous malformations and in the different steps of pre- and post-therapeutic evaluation. Received 9 February 1998; Accepted 13 February 1998     

Moderne Schnittbildgebung der Kopf-Hals-Gefäße

Although digital subtraction angiography (DAS) remains the gold standard for neurovascular imaging, the number of diagnoses made on the basis of less invasive cross-sectional imaging techniques (CT and MR angiography) is increasing. The present article provides important technical principles of CT and MR angiography, followed by an analysis of the diagnostic possibilities and limitations of vascular cross-sectional imaging. The particular importance of post-processing of vascular cross-sectional datasets is also discussed. Using the typical clinical diagnostic work-up of extra- and intracranial vascular diseases as a basis, the article explains how a suitable examination technique and protocol is chosen and which limitations need to be borne in mind. After taking at look at the technical advances expected in the future (3-Tesla MRA, dual-energy CTA, post-processing workflow in PACS), the remaining indications for diagnostic DSA will be presented and explained.     

PCA技术在颅内血管成像中的临床应用

目的扩大相位对比血管成像(PCA)技术在颅内血管成像中的临床应用,并与流人(Inflow)技术比较。方法46例颅内血管异常患(男34例,女12例,年龄3～60岁,平均年龄41．3岁)于临床症状出现后均经PCA与Inflow两种方法检查。本研究全部MR成像均采用PHILIPS GYROSCAN NT 1．0磁共振超导扫描机进行。两种成像方法的后处理均采用MIP重建。结果在46例颅内血管异常患中,PCA测出动静脉畸形20例,动脉瘤15例,海绵状血管瘤6例,单纯静脉瘤1例,以及静脉窦栓塞2例,只有2例海绵状血管瘤未测出,而Inflow相应地测出动静脉畸形18例,动脉瘤15例,海绵状血管瘤8例但静脉系血管畸形未测出1例。PCA与Infolw的检出率分别为95．6％(44／46)和86．9％(40／46)。结论虽然Inflow显示颅内血管异常与PCA有些相似,但它未能显示静脉系血管异常。相比之下,PCA能显示各种颅内血管异常,值得临床广泛应用。     

Cerebrovascular pathology. Comparison of magnetic resonance and magnetic resonance angiography]

After making the visualization of the intracranial circulation possible without contrast media, the radiologist is now evaluating the diagnostic role of the different techniques of MRA. Attempts are also being made to characterize the main patterns of intracranial vascular diseases. The authors examined, with 3D TOF MRA, 40 patients presenting with 50 vascular lesions on MRI scans. Twenty of 40 patients were also studied with angiography. Seventeen aneurysms were detected, together with 3 stenoses of the cerebral arteries, 13 arteriovenous malformations, 12 dolichobasilar arteries, 3 postoperative and 2 post-embolization controls. MRI was performed with a superconductive magnet (1.5 T), a dedicated coil and gradient-echo 3D TOF FT sequences. The refocused sequence for flux, FISP 3DFT, required the following parameters: TR = 0.04 s, TE = 10 ms, flip angle = 15 degrees, 256 x 256 matrix, 1 acquisition. The 64-80 mm volume along the axial plane was divided so that an actual 1-mm thickness was excited. In post-processing, the maximum-intensity projection was employed on the axial plane 0 degrees-90 degrees (15 degrees interval). In the various conditions, the results obtained with MRA were correlated and compared with MRI findings. MRA provided useful additional information in 27.4% of cases in the study of aneurysms, arteriovenous malformations, vascular occlusion and dolichobasilar arteries, as well as in the follow-up of these lesions. MRA is currently suggested in the evaluation of cerebral circulation and is considered a complementary technique to MRI. MRA is also to be used preliminary to angiography.     

Cranial MRI and MR angiography in Menkes' syndrome

We report two boys with Menkes' syndrome who underwent cranial MRI and MR angiography (MRA). In both, CT and MRI revealed progressive cerebral atrophy with a subdural haematoma or effusion. Delayed myelination or dysmyelination of the white matter was suggested. Tortuosity of the cervical and intracranial vessels was well demonstrated by MRA, obviating more invasive conventional angiography should it be thought necessary to demonstrate the characteristic systemic vascular changes of this syndrome.     

The non-invasive detection of intracranial aneurysms: are neuroradiologists any better than other observers?

Can non-neuroradiologists detect intracranial aneurysms as well as neuroradiologists, using CT and MR angiography? Sixty patients undergoing intra-arterial digital subtraction angiography (IADSA) to detect aneurysms also underwent computed tomographic angiography (CTA) and time-of-flight magnetic resonance angiography (MRA). Consensus review of IADSA by two neuroradiologists was the reference standard. Two neuroradiologists, a neurosurgeon, a neuroradiographer and a general radiologist blinded to IADSA, plain CT and clinical data, independently reviewed hard-copy base and reconstructed maximum intensity projection images of the CTA and MRA studies. Thirty patients had a total of 63 aneurysms, 71.4% were 相似文献   

脑血管畸形的MRI及MRA诊断

目的：研究脑动静脉畸形与海绵状血管瘤的ＭＲＩ及ＭＲＡ特征，评价不同的成像方法对脑血管畸形的诊断价值。材料与方法：对２１例脑动静脉畸形及６例海绵状血管瘤分别作了常规ＭＲ成像及ＭＲ血管成像，ＭＲＩ采用ＳＥＴ１和Ｔｕｒｂｏ ＳＥ Ｔ２加权序列，ＭＲＡ采用２Ｄ－ＦＬＡＳＨ及３Ｄ－ＦＩＳＰ序列，６例海绵状血管瘤ＭＲＡ仅使用２Ｄ－ＦＬＡＳＨ序列。所有成像以环形激化头线圈在１．０Ｔ ＭＲ仪上完成。结果：Ｔ１及Ｔ     

3D time-of-flight MR angiography of the intracranial vessels: optimization of the technique with water excitation, parallel acquisition, eight-channel phased-array head coil and low-dose contrast administration

The aim of this study is three folds: to compare the eight-channel phased-array and standard circularly polarized (CP) head coils in visualiazation of the intracranial vessels, to compare the three-dimentional (3D) time-of-flight (TOF) MR angiography (MRA) techniques, and to define the effects of parallel imaging in 3D TOF MRA. Fifteen healthy volunteers underwent 3D TOF MRA of the intracranial vessels using eight-channel phased-array and CP standard head coils. The following MRA techniques were obtained on each volunteer: (1) conventional 3D TOF MRA with magnetization transfer; (2) 3D TOF MRA with water excitation for background suppression; and (3) low-dose (0.5 ml) gadolinium-enhanced 3D TOF MRA with water excitation. Results are demonstrating that water excitation is a valuable background suppression technique, especially when applied with an eight-channel phased-array head coil. For central and proximal portions of the intracranial arteries, unenhanced TOF MRA with water excitation was the best technique. Low-dose contrast enhanced TOF MRA using an eight-channel phased-array head coil is superior in the evaluation of distal branches over the standard CP head coil. Parallel imaging with an accelaration factor of two allows an important time gain without a significant decrease in vessel evaluation. Water excitation allows better background suppression, especially around the orbits and at the periphery, when compared to conventional acquisitions.     

蛛网膜下腔出血患者的MRA和DSA的对照研究

目的：研究ＭＲ血管造影（ＭＲＡ）在蛛网膜下腔出血（ＳＡＨ）患者病因诊断中的应用准确性和可靠性。材料和方法：回顾性分析３３例ＳＡＨ患者的ＭＲＡ资料，并与ＤＳＡ作了对比分析，ＭＲＡ采用三维时间流逝（３Ｄ－ＴＯＦ）法。结果：ＭＲＡ上显示了２６例血管病变中的２２例，包括１５个动脉瘤中的１３个，８例动静脉畸形中的６例和３例血管狭窄闭塞性病变。１个完全血栓形成的右颈内动脉瘤ＭＲＡ上未显示。但常规ＭＲＩ和ＭＲＡ原始图像上显示，ＭＲＡ结合ＭＲＩ和ＭＲＡ原始图像可以对９１％的患者做出正确诊断和评价，动脉瘤和周围血管的关系及ＡＶＭ的供血动脉和畸形结节能在ＭＲＡ上被准确评价。结论：作为一种非损伤性的血管成像方法，ＭＲＡ具有安全、可靠和方便的优点，可以做为常规用于ＳＡＨ患者的筛选检查。