经颈静脉肝内门体静脉分流术术前MRA评价

目的探讨磁共振血管成像（MRA）在经颈静脉肝内门体静脉分流术（TIPS）术前检查中的应用。方法对59例拟行TIPS治疗的患者行术前MRA检查,观察引起门静脉高压的病因、肝静脉及门静脉形态、走行,测量穿刺点处血管管径,并与正常对照组（50例）比较。结果门静脉高压组中单纯肝硬化49例,肝硬化合并肝癌4例,单纯门静脉血栓3例,脾静脉狭窄1例,布-加综合征2例。门静脉高压组与正常对照组肝静脉分型（3支型∶2支型∶1支型）分别为14∶39∶12、12∶34∶14 肝右静脉、肝中静脉、肝左静脉穿刺点管径符合数为52∶40∶28、46∶34∶23。门静脉右支和左支安全穿刺点分别位于（16.2±3.1）mm、（14.2±3.8）mm以远。结论MRA是一种有价值无损伤的检查方法,对TIPS术前疾病诊断及血管定位有着重要的意义。     

MR angiography of the forearm--visualization of the internal dialysis shunt

Phase contrast MR angiography (MRA) of the forearm was performed in 10 healthy volunteers and 3 patients with chronic renal failure. In all volunteers, MRA demonstrated two arteries (radial artery and ulnar artery) and several cutaneous veins. In patients with chronic renal failure, internal dialysis shunts were clearly visualized and the stenoses of the shunts which were confirmed by later DSA were also well defined. It is concluded that MRA may be a valuable technic in the evaluation of internal dialysis shunts.     

MR angiography by selective inversion recovery

A modified inversion-recovery sequence is introduced which performs subtraction angiography by varying time-of-flight effects of blood flowing into an imaged slab. The selective 180 degrees excitation inverts different regions between measurements to isolate arterial and/or venous blood. On normal human subjects, high-resolution carotid artery angiograms have been obtained.     

Time-of-flight MR angiography

Time-of-flight effects depend on the displacement of blood with respect to a region of excitation. When combined with static material suppression and projection imaging, time-of-flight effects provide a flexible means of flow sensitization for magnetic resonance (MR) angiography. Bolus tracking, flow enhancement by spin replacement, and selective tagging are three classes of methods being pursued for MR angiography.     

Contrast-enhanced MR angiography

Contrast-enhanced magnetic resonance angiography (CE-MRA) is challenging conventional angiography as the primary diagnostic tool for vascular visualization. This article describes CE-MRA techniques, equipment and many of the applications currently in use, as well as applications under development. The advantages of CE-MRA also are discussed.     

Peripheral MR angiography

Atherosclerotic disease of the lower extremities is a common disorder in western society. Its debilitating nature calls for accurate diagnosis and treatment. The gold standard for diagnosing this disease by depiction of vessel morphology is X-ray angiography (either conventional or digital subtraction angiography). However, the invasive nature of this technique and the possible harmful effects of iodinated contrast agents have led to the idea that non-invasive MR angiography might be a good alternative for acquiring information about vessel morphology. Most extensively studied was time-of-flight MR angiography. Although first results with this technique were encouraging, it is now apparent that time-of-flight MR angiography is hampered by the virtue of which it exists, since blood flow not only generates vessel-to-background contrast, but is also the cause of disturbing artifacts. However, with the introduction of minimally invasive contrast-enhanced MR angiography, using gadolinium chelates to reduce the T1 of blood, image quality has improved dramatically. Moreover, using contrast-enhanced MR angiography, high-resolution three-dimensional data about the entire peripheral vascular tree can be obtained within several minutes, which might make MR angiography a true competitor of X-ray angiography as a diagnostic tool in the clinical work-up of a patient with complaints of peripheral atherosclerosis. The purpose of this article is to explain working mechanisms and usefulness of both time-of-flight and contrast-enhanced MR angiography. Received: 28 August 1998; Revised: 7 December 1998; Accepted: 9 February 1999     

Gadolinium-enhanced MR angiography

Experience in three patients (one each with meningioma, pineal tumor, and prominent jugular bulb) illustrates that magnetic resonance (MR) angiography can benefit from the administration of gadolinium diethylenetriaminepentaacetic acid. Data were acquired with a three-dimensional velocity-compensated (fast imaging with steady-state precession) sequence. MR angiograms were obtained with a ray projection algorithm by using maximum intensity values. Portions of the vascular anatomy--particularly venous structures and smaller arteries--were better portrayed on the postcontrast than on the precontrast angiograms. Enhancing lesions were also seen on the projection images. Enhancement of dura and extracranial tissues (sinus and nasal mucosa) can obscure vascular detail.     

Nonenhanced MR angiography

While nonenhanced magnetic resonance (MR) angiographic methods have been available since the earliest days of MR imaging, prolonged acquisition times and image artifacts have generally limited their use in favor of gadolinium-enhanced MR angiographic techniques. However, the combination of recent technical advances and new concerns about the safety of gadolinium-based contrast agents has spurred a resurgence of interest in methods that do not require exogenous contrast material. After a review of basic considerations in vascular imaging, the established methods for nonenhanced MR angiographic techniques, such as time of flight and phase contrast, are considered and their advantages and disadvantages are discussed. This article then focuses on new techniques that are becoming commercially available, such as electrocardiographically gated partial-Fourier fast spin-echo methods and balanced steady-state free precession imaging both with and without arterial spin labeling. Challenges facing these methods and possible solutions are considered. Since different imaging techniques rely on different mechanisms of image contrast, recommendations are offered for which strategies may work best for specific angiographic applications. Developments on the horizon include techniques that provide time-resolved imaging for assessment of flow dynamics by using nonenhanced approaches.     

Contrast-enhanced MR angiography

Summary Despite many optimizations, the current limitations of plain MR angiography include: saturation that impairs the visualization of veins and arteries with slow flow and spin-dephasing signal voids in locations with turbulent flow. Recently, the use of contrast agents has been proposed to cope with these remaining problems. Because of induced shortening of the T1 of the blood, saturation in the blood vessels is overcome. As a result, arteries and veins are visualized with the same signal intensity, which makes the technique less flow-dependent. In combination with short T1-weighted acquisitions, today CE MRA can be obtained while the patient is holding his breath. This last approach is most promising for abdominal applications since the respiratory motion can be frozen. As these acquisitions also use very short echo times, spin dephasing can be reduced. In conclusion, the use of contrast agents has greatly increased the clinical usefulness of MR angiography.      

Vasovist-enhanced MR angiography

Vasovist (MS-325) is the first intravascular contrast agent approved for use with magnetic resonance angiography in the European Union. Vasovist reversibly binds to albumin, providing extended intravascular enhancement compared to existing extracellular magnetic resonance contrast agents. Prior to approval, Vasovist underwent extensive testing to evaluate the safety and efficacy of the drug; the clinical trials program included blinded, placebo-controlled dose ranging, efficacy in a variety of vascular beds (AIOD, renal, pedal), examination of potential drug interaction with warfarin and comparison with XRA. The clinical trials show that Vasovist-enhanced MR angiography is safe and well-tolerated in patients with vascular disease, effective for the detection of vascular stenosis and aneurysms, significantly more accurate (both more sensitive and specific) than non-contrast MR angiography for the diagnosis of vascular stenoses, and similar to conventional angiography for the overall characterization of vascular disease, without the need for catheterization.     

Basilar artery fenestrations detected by MR angiography

Basilar artery (BA) fenestrations are the most frequently observed fenestrations of the cerebral arteries. Our goal was to examine the magnetic resonance (MR) angiographic incidence, location, and characteristic configuration of BA fenestration. Between April 1996 and March 2000, 600 cranial MR angiographies were performed at our institution. The majority of the patients examined had or were suspected to have cerebrovascular disease. We retrospectively reviewed these 600 MR angiograms. A 1.5 Tesla scanner was used in all studies, and maximum intensity projection (MIP) images obtained using the three-dimensional time-of-flight (3D-TOF) technique were displayed stereoscopically. Ten BA fenestrations (1.7%) were detected on MR angiograms. In 87 cases from the early period, the vertebrobasilar (VB) junction was unfortunately not included in the imaging slices. Eight of the 10 fenestrations were located at the proximal BA: six of them were small with a slit-like shape, and two were relatively large with a convex-lens-like shape. A small fenestration was located at the distal BA, and the remaining one was a total duplication of the BA. We stress that knowledge and recognition of BA fenestration are useful and important in the interpretation of cranial MR angiography. Since saccular aneurysms are reported to arise frequently at BA fenestration, the VB junction should be included in the imaging slices of routine cranial MR angiography.     

Coronary MR angiography

MR angiography of the coronary arteries became possible in 1991 with the development of a new group of fast MR imaging sequences. Although the role of coronary MR angiography in screening for coronary artery lesions has not yet been established, coronary MR angiography already has been very successful in the detection of coronary artery variants and the imaging of coronary stents and bypass grafts. Variants of these new MR imaging techniques also can quantitate velocity in native coronary arteries. Several generations of coronary MR angiographic techniques exist; all techniques use EKG-triggering. The use of MR contrast agents appears to further improve all techniques. Technical progress and changes in this subfield of cardiac MR imaging have been so fast that large-scale preclinical trials have not been conducted with the majority of the first and second generation coronary MR angiographic pulse sequences as known today. This article reviews the development of these new cardiac MR imaging techniques and the initial successes with clinical application using commercial MR scanners.     

Intracranial aneurysms: evaluation by MR angiography

The purpose of this study was to compare the accuracy of a volume gradient-echo MR angiography (MRA) technique with that of intraarterial digital subtraction angiography (IA DSA) in the identification of intracranial aneurysms. The intracranial vasculature was examined in 47 patients by MRA and compared with IA DSA findings in 19 of these patients who had saccular or giant intracranial aneurysms. The remaining 28 patients, in whom no aneurysm was found, served as a control group. MRA was performed with the use of a velocity-compensated gradient-echo sequence (TR = 40-50/TE = 7-15) with a 15 degrees flip angle. The sensitivity and specificity were calculated for the evaluation of the cine 3D reconstructions (cine MRA) only, cine MRA + inspection of the individual partitions, and cine MRA + individual partitions + spin-echo studies. Of 21 aneurysms, of which three were missed in two patients, the sensitivity varied from 67% for cine MRA only to 86% for the cine MRA + partitions + spin-echo studies; of the 19 patients, among whom it was assumed that the diagnosis of any one aneurysm in a patient would lead to angiography and detection of additional aneurysms, the sensitivity varied from 73% for the cine MRA only to 95% for the cine MRA + partitions + spin-echo studies. The results of this study suggest that MRA can define the circle of Willis sufficiently to allow detection of intracranial aneurysms as small as 3-4 mm. MRA holds promise as a truly noninvasive screening examination of intracranial vasculature in patients at risk for aneurysms.     

Intracranial aneurysms: evaluation by MR angiography

The purpose of this study was to compare the accuracy of a volume gradient-echo MR angiography (MRA) technique with that of intraarterial digital subtraction angiography (IA DSA) in the identification of intracranial aneurysms. The intracranial vasculature was examined in 47 patients by MRA and compared with IA DSA findings in 19 of these patients who had saccular or giant intracranial aneurysms. The remaining 28 patients, in whom no aneurysm was found, served as a control group. MRA was performed with the use of a velocity-compensated gradient-echo sequence (TR = 40-50/TE = 7-15) with a 15 degree flip angle. The sensitivity and specificity were calculated for the evaluation of the cine 3D reconstructions (cine MRA) only, cine MRA + inspection of the individual partitions, and cine MRA + individual partitions + spin-echo studies. Of 21 aneurysms, of which three were missed in two patients, the sensitivity varied from 67% for cine MRA only to 86% for the cine MRA + partitions + spin-echo studies; of the 19 patients, among whom it was assumed that the diagnosis of any one aneurysm in a patient would lead to angiography and detection of additional aneurysms, the sensitivity varied from 73% for the cine MRA only to 95% for the cine MRA + partitions + spin-echo studies. The results of this study suggest that MRA can define the circle of Willis sufficiently to allow detection of intracranial aneurysms as small as 3-4 mm. MRA holds promise as a truly noninvasive screening examination of intracranial vasculature in patients at risk for aneurysms.     

MR angiography enhanced by sodium acetazolamide]

We tried to use sodium acetazolamide to enhance MR angiography (MRA). Sodium acetazolamide, one of carbonic anhydrase inhibitors, has an effect to increase regional cerebral blood flow. We made a direct comparison between pre and post enhanced MRA (both 3D-TOF and 3D-PC techniques). MRA after administration of sodium acetazolamide could depict more details of cortical branches without enhancement of back-ground. So we recommend this simple method to be used widely in any examination of MR angiography.     

Demonstration of subclavian steal by MR angiography.

We present three cases of subclavian steal syndrome demonstrated by MR angiography. By using a presaturation pulse located at the bottom or at the top of the acquisition volume we demonstrated the flow direction of vertebral arteries. We used a new investigational two-dimensional time-of-flight sequence.     

有孔型椎基底动脉的MR血管成像诊断

目的 描述有孔型椎基底动脉的MR血管成像(MRA)表现，以提高对该血管异常的认识。方法 回顾分析178例头颈部增强磁共振血管造影(CEMRA)中10例诊断为有孔型椎基底动脉病例，其中7例行颅脑CEMRA，3例行颈部CEMRA，钆喷替酸葡甲胺(Gd-DTPA)0．2mmol／kg高压注射，小剂量团注测试延迟时间，增强前后行连续动态扫描。原始和减影图像经SGI02工作站后处理，经容积重建(实时三维，R13D)、最大信号强度投影(MLP)、薄层最大信号强度投影多平面或曲面重建血管图像(TS MIP)，比较各组图像对血管异常的显示情况。5例患者同时行三维时间飞跃法(3D TOF)MRA，3例经DSA证实。结果 有孔型基底动脉7例(检出率3．9％，7／178)全部位于基底动脉下1／2段，4例位于基底动脉干，3例位于椎基底动脉吻合部；3例有孔型椎动脉(检出率1．7％，3／178)中2例位于左侧V4段，1例位于右V3段。4例有孔型异常2支血管间形成小圆孔状充盈缺损，6例呈部分重复形。4例有孔型血管异常合并其他血管异常，2例有孔型基底动脉合并脑动静脉畸形；2例有孔型椎动脉合并对侧永存三叉动脉，其中1例还合并同侧远端椎动脉瘤，另1例有孔型椎动脉同时伴有颈、基底动脉粥样硬化。RT3D能显示血管立体空间和毗邻关系，兴趣区MIP和TS MIP可清楚显示异常血管细节。结论 CEMRA结合图像工作站后处理能清楚显示和诊断有孔型椎基底动脉这一少见的血管异常。