Direct contrast-enhanced 3D MR venography

Non-enhanced two-dimensional (2D) time-of-flight (TOF) MRA is well established for imaging of the deep venous system. However, based on the acquisition of multiple axial images, it can be time-consuming and often fails to delineate small superficial and perforating veins. The presented low-dose, direct-contrast-injection 3D MR venography technique allows rapid acquisition of high-quality MR venograms and can be employed for the display of the deep and superficial venous system of upper and lower extremity including pelvic and central thoracic veins. This article describes the employed technique and provides a comprehensive image-based overview of the various indications for direct-infusion 3D MR venography such as post-/thrombotic changes, varicosities, and assessment of the greater saphenous vein prior to bypass surgery. Received: 17 March 2000 Revised: 16 June 2000 Accepted: 19 June 2000     

磁共振脑静脉系血管成像技术及其临床应用

目的探讨磁共振脑静脉系血管成像的技术方法和最佳扫描方案，评价磁共振静脉系血管成像技术(MR venography，MRV)对静脉系疾病的诊断价值及临床意义。方法采用二维时间飞跃法MR血管造影(2D-TOF-MRA)、二维相位对比血管造影(2D-PCA)和三维对比增强MR血管造影(3D-CE-MRA)3种血管成像技术分别对20例健康志愿者和20例临床或MRI疑有静脉系疾病的患者行MRV成像，并采用最大强度投影(MIP)、多平面或曲面重建(MPR)及数字减影MRA(DSMRA)技术对图像进行后处理，观察脑静脉系在MRV中的显示情况及脑静脉系疾病在MRV中表现形式，制定脑静脉系成像的最佳方案。结果本组经3D-CE-MRA静脉系成像诊断为13例颅内静脉窦血栓形成(CVST)及7例颅内肿瘤累及静脉系的阳性显示率为100％，均经临床治疗复诊及手术证实。2D-PCA及2D-TOF-MRA对细小引流静脉显示欠佳，且2D-TOF-MRA对复杂区域内静脉血管亦显示欠佳。结论3D-CE-MRA结合2D-PCA及2D-TOF-MRA静脉成像技术形成全脑静脉系成像，为脑静脉系的最佳成像方案，对临床术前评估和指导治疗有极其重要的意义。     

Time-resolved contrast-enhanced 3D MR angiography

An MR angiographic technique, referred to as 3D TRICKS (3D time-resolved imaging of contrast kinetics) has been developed. This technique combines and extends to 3D imaging several previously published elements. These elements include an increased sampling rate for lower spatial frequencies, temporal interpolation of k-space views, and zero-filling in the slice-encoding dimension. When appropriately combined, these elements permit reconstruction of a series of 3D image sets having an effective temporal frame rate of one volume every 2-6 s. Acquiring a temporal series of images offers advantages over the current contrast-enhanced 3D MRA techniques in that it i) increases the likelihood that an arterial-only 3D image set will be obtained, ii) permits the passage of the contrast agent to be observed, and iii) allows temporal-processing techniques to be applied to yield additional information, or improve image quality.     

Separating arterial and venous components from 3D dynamic contrast-enhanced MRI studies using factor analysis.

Dynamic contrast-enhanced MRI has been used extensively for angiography but in order to generate separate arterial and venous images some form of postprocessing is required. This typically involves the subtraction of one image in a dynamic sequence from another in order to suppress unwanted signal; however, this also has the effect of decreasing the signal-to-noise ratio (SNR) of the image. In this study, factor analysis, a technique related to eigenimage filtering, is used to separate arterial and venous components from dynamic contrast-enhanced images of the legs acquired with a temporal resolution of 30 sec. The SNR of the venous and arterial images extracted from a series of 20 patients using conventional single subtraction, a double subtraction method, and factor analysis were compared. Results show that the use of factor analysis improved the SNR in the venous images by a factor of 2.3 compared with the use of simple subtraction. A subjective comparison of the maximum intensity projection images generated from the venous images was also carried out and showed a significant preference for those generated using factor analysis over those generated using other subtraction methods.     

3D contrast-enhanced MR angiography

Safe, fast, accurate contrast arteriography can be obtained utilizing gadolinium (Gd) and 3D MR data acquisition for diagnosing vascular diseases. Optimizing contrast enhanced MRA (CE MRA), however, requires understanding the complex interplay between Gd injection timing, the Fourier mapping of 3D MR data acquisition and a multitude of parameters determining resolution, anatomic coverage, and sensitivity to motion artifacts. It is critical to time the bolus peak to coincide with central k-space data acquisition, which dominates image contrast. Oversampling the center of k-space allows reconstruction of multiple 3D acquisitions in rapid succession to time-resolve the passage of the contrast bolus. Parallel imaging increases resolution, shortens scan time and compresses the center of k-space into a shorter period of time, thereby minimizing motion and timing artifacts. Absence of ionizing radiation allows MRA to be repeated and combined with additional sequences to more fully characterize anatomy, flow, and physiology. Utilizing stepping table technology and thigh compression, whole body MRA is possible with a single contrast injection. As MR technology continues to advance, CE MRA becomes better and simpler to perform, increasing its efficacy in the diagnosis and management of vascular diseases.     

Imaging of the intracranial venous system with a contrast-enhanced volumetric interpolated examination

A contrast-enhanced interpolated, three-dimensional (3D) gradient-echo MR sequence with asymmetric k-space sampling, which we refer to as volumetric interpolated brain examination (VIBE), was evaluated for its depiction of the normal intracranial venous system and compared with two-dimensional (2D) time-of-flight (TOF) MR venography (MRV). Fifteen subjects underwent contrast-enhanced VIBE imaging (TR/TE 8 ms/4.4 ms, flip angle 18°, acquisition time, 2 min 20 s, voxel size approximately 1.5 mm³) and standard 2D TOF MRV (TR/TE 27 ms/9 ms, flip angle 35°). The presence of 19 venous structures per subject was assessed on maximum intensity projections (MIP) of the whole data set (whole-brain MIP) and on MIP images reconstructed spontaneously from source images (interactive MIP/source images). Results from a consensus reading where all imaging techniques and display modalities were available were taken as the standard of reference for the presence of venous structures. In addition, 10 subjects underwent both unenhanced and enhanced VIBE imaging. The value of subtracted data sets (unenhanced VIBE subtracted from enhanced VIBE) was then evaluated. Overall, VIBE provided a superior visualization of the cerebral veins than 2D TOF MRV (VIBE, sensitivity (reader 1/reader 2): 98%/99%, negative predictive value 64%/71%; TOF sensitivity: 85%/84%, negative predictive value 15%/15%; Wilcoxon signed-rank test VIBE vs TOF, p<0.001 for both readers). The VIBE interactive MIP/source images were superior to whole-brain MIP reconstructions. Image subtraction was not necessary for delineation of venous structures but improved small vein conspicuity. Contrast-enhanced VIBE acquisitions are faster and enable a visualization of the normal intracranial venous system superior to that of 2D TOF MRV. Electronic Publication     

3D MR angiography with ramp-shaped flip-angle distribution

This study addressed the use of 3D MR angiography with flip angles (FAs) linearly varying across the excitation volume in order to diminish spin saturation. The shape of the ramp profile was varied to optimize the method for different regions and pathological alterations. Radio frequency pulses with ramp-shaped excitation profiles were generated flow-compensated 3D-FISP sequence. With the use of ramp-shaped excitation profiles good results were obtained for intracranial arteries as well as for neck arteries (i.e. carotid and vertebral arteries) which were demonstrated in 6 healthy volunteers and in 5 patients with various stenoses and anomalies of the carotid and vertebral arteries. With this technique it was possible to use increased thicknesses of the excitation volume (slab) up to 256 mm. Ramp-shaped excitation pulses with linearly increasing FAs in main flow direction can provide improved contrast of the vessel parts located distally to the entry side of the slab. Although this method has no advantage concerning complex flow or other dephasing effects; its particular effectiveness lies in the reduction of spin saturation. Correspondence to: T. Nägele     

Time-resolved contrast-enhanced MR angiography of intracranial lesions

PURPOSE: To determine if contrast-enhanced (CE) MRI of intracranial lesions benefits from time-resolved MR angiography (MRA) during contrast agent injection. MATERIALS AND METHODS: For 126 patients with suspected intracranial lesions undergoing routine CE MRI at 3.0T (N = 88) or 1.5T (N = 38), time-resolved CE MRA (three-dimensional [3D] time-resolved imaging of contrast kinetics [TRICKS]) was performed during injection of the routine gadolinium (Gd) dose of 0.1 mmol/kg. Time to peak (TTP) enhancement of lesions as well as time to internal carotid artery (ICA), middle cerebral artery (MCA), superior sagittal sinus (SSS), and jugular vein enhancement were measured. Source and maximum intensity projection (MIP) images were reviewed to delineate the spatial relationship of lesions and the vasculature. RESULTS: In 61 patients (48%), additional important findings were detected on time-resolved MRA that were not seen on the routine CE protocol, including aneurysms (N = 6), arteriovenous malformations (N = 7), ICA stenoses (N = 2), vascular anomalies (N = 18), and relationships between lesions and vessels (N = 28). In addition, tumor TTP correlated with glioma grade (r = 0.87) and discriminated epithelial from nonepithelial meningiomas (P = 2.6 x 10(-5)). MRA added eight minutes to the total exam time. CONCLUSION: Time-resolved MRA performed during contrast agent injection adds information to the routine brain CE MRI examination of intracranial lesions with only a small time penalty and no additional risk to the patient.     

3T high-spatial-resolution contrast-enhanced MR angiography of the intracranial venous system with parallel imaging

The diagnostic image quality of contrast-enhanced (CE) 3D MR venography (MRV) was prospectively compared with that of 2D time-of-flight (TOF) MRV and contrast-enhanced 3D magnetization-prepared rapid acquisition of gradient echo (MPRAGE) sequences for the visualization of the intracranial venous system at 3T in 22 patients. CE MRV provides high-quality images and was shown to be superior to TOF MRV and MPRAGE sequences in visualizing the normal intracranial venous system.     

Improved venous suppression and spatial resolution with SENSE in elliptical centric 3D contrast-enhanced MR angiography.

The elliptical centric (EC) view order samples a 3DFT acquisition from the center of k-space outward, and when applied to contrast-enhanced MR angiography (CE-MRA) provides intrinsic venous suppression. This is because the veins enhance several seconds after the scan is initiated, and are thus encoded solely by noncentral k-space frequencies. A separate method, sensitivity encoding (SENSE), accelerates the k-space sampling rate by reducing the phase FOV or, equivalently, by increasing the k-space sampling interval, and has been used to increase spatiotemporal resolution. We hypothesized that by combining SENSE with EC, sampling of central k-space would be accelerated and the k-space radius at which the veins first showed contrast enhancement would be increased over a reference scan, thus providing improved venous suppression and spatial resolution without additional scan time. This hypothesis was studied with the use of phantom and carotid CE-MRA experiments, and the results demonstrated an approximate 25% reduction in venous signal when SENSE was used.     

Recessed elliptical-centric view-ordering for contrast-enhanced 3D MR angiography of the carotid arteries.

Fast arterial-venous transit in the carotid arteries requires accurate, reliable timing of the acquisition to the bolus transit to maximize arterial signal and minimize venous artifacts. The rising edge of the bolus is not utilized in conventional elliptical-centric view-ordering because the critical k-space center must be acquired with full arterial enhancement. In this study, a recessed elliptical-centric view-ordering scheme is introduced in which the k-space center is acquired a few seconds following scan initiation. The recessed view-ordering is shown to be more robust to timing errors than the conventional scheme in a study of 37 patients.     

Dynamic 3D MR angiography of the pulmonary arteries in under four seconds

Although 3D MRA has been shown to provide excellent depiction of the pulmonary arterial tree, its clinical use has been limited due to lengthy breath-holding requirements. Employing the newest gradient generation (1.5 T MR system, amplitude of 40 mT/m and a slew rate of 200 mT/m/msec), we evaluated a technique permitting the dynamic acquisition of 3D data sets of the entire pulmonary tree in under 4 seconds. Coronal image sets were collected using a repetition time of 1.64 msec and an echo time of 0.6 msec, resulting in an acquisition time of 3.74 seconds. Three volunteers and eight dyspneic patients with known or suspected pulmonary embolism underwent MRI of the pulmonary arteries. The pulmonary arterial tree was visible to a subsegmental level in all examined subjects. Regarding the presence of pulmonary emboli in four patients, there was complete concordance between MR angiographic findings and those of corroborative studies. We conclude that diagnostic MRA of the pulmonary vasculature can be obtained even in patients with severe respiratory distress.     

重症硬脑膜静脉窦血栓的局部溶栓治疗

目的 研究重症硬脑膜静脉窦血栓的局部溶栓治疗的方法及疗效。方法 总结我院自2000年以来6例重症硬脑膜静脉窦血栓的局部溶栓治疗经验，男4例，女2例，其中4例采用一侧股动脉及对侧股静脉Seldinger穿刺，2例采用股动脉Seldinger穿刺及上矢状窦前1／3穿刺。导管置入一侧颈内动脉及静脉窦血栓处后，于颈内动脉及静脉窦血栓处先后各用尿激酶50万U，以每分钟1万U泵入，再于静脉窦血栓处泵入尿激酶持续溶栓，维持外周血中纤维蛋白原含量1．0～1．5g／L，同时予全身肝素化，维持外周血活化部分凝血活酶时间正常值的2～3倍。结果 本组6例，5例痊愈，颅内压转正常，头痛消失，无神经功能障碍，其中4例数字减影血管造影(DSA)见浅表静脉扩张消失，静脉窦显影正常，1例浅表静脉扩张明显改善，静脉窦显影较前好转；1例好转，颅内压较前降低，头痛好转，DSA见浅表静脉扩张消失，静脉窦显影正常，抗凝治疗1个月后颅内压正常，头痛消失，神经功能恢复正常。结论 重症硬脑膜静脉窦血栓采用动静脉系统联合应用尿激酶局部溶栓治疗是快速、安全、有效的方法，经股静脉途径不易到达静脉窦血栓处者，可以行上矢状窦入路。     

MR angiography of the intracranial venous system

PURPOSE: To compare the effectiveness of different imaging planes at time-of-flight (TOF) magnetic resonance (MR) angiography and phase-contrast MR angiography in the visualization of the normal intracranial venous system. MATERIALS AND METHODS: In 12 healthy volunteers, two-dimensional (2D) TOF MR angiography and three-dimensional (3D) phase-contrast MR angiography were performed in transverse, sagittal, and coronal planes. All data were displayed as maximum intensity projection (MIP) images. Four neuroradiologists assessed the visibility of 28 intracranial venous structures on the MIP images. Statistical analysis was performed by using the Friedman two-way analysis of variance and the Cochran Q test. RESULTS: Visualization of the normal intracranial venous system was better with 3D phase-contrast and coronal 2D TOF MR angiography than with transverse or sagittal 2D TOF MR angiography (P < .05, Friedman test) for each observer and the group of observers. Differences were found between each of the 2D TOF and 3D phase-contrast MR angiographic sequences in the visualization of individual venous structures (Cochran Q test). The kappa values ranged from 0.36 to 0.71, which indicated a moderate to good agreement between observers. CONCLUSION: The normal intracranial venous system is adequately visualized with 3D phase-contrast and coronal 2D TOF MR angiography.     

脑内静脉窦血栓形成MRI表现的再探讨和MR静脉成像的选择

目的：明确脑内静脉血栓形成的脑内MRI表现和MR血管造影的诊断及检查方法。材料和方法：共9例病人，男性2例，女性7例。年龄30－56岁，平均38．2岁。使用Siemens-vision-plus超导高场MRI系统，场强1．5T。采用常规SE序列，tuberSE，TOF血管成像（用于动脉血管显示），PC法20静脉血管成像和增强3D静脉血管成像（用于矢状窦显示）。结果：MR的动脉血管成像显示阳性率为0％，2D和3D静脉血管成像阳性率为100％，3D增强静脉血管造影可更好地显示阻塞的静脉。脑实质内均有阳性表现，表现为矢状窦旁白质区对称或非对称性异常改变，呈斑片状和片状，T1W为低信号，T2W为高信号。增强后脑膜强化2例。合并脑内出血5例。结论：MRI结合MR静脉血管造影，尤其增强3D静脉血管造影是诊断脑内静脉血栓形成的有效手段。     

Dependence of venous enhancement on the field of view in 3D contrast-enhanced MRA using the elliptical centric view order.

The dependence of venous suppression on the acquisition field of view (FOV) in elliptical centric 3D contrast-enhanced magnetic resonance angiography (CE-MRA) is studied theoretically and experimentally. It is hypothesized that a reduced FOV in an arterial phase acquisition results in improved venous suppression. An expression is derived linking the k-space representation of a vein to venous return time and acquisition parameters. For a y x z FOV reduction from 24 cm x 7.2 cm to 18 cm x 3.6 cm, equivalent voxel size, and venous return times ranging from 0-7 s, the mean improvement in venous suppression ranged from 7.0% for the 19-mm-diameter vein to 32.1% in the 6-mm-diameter vein, assuming a step function-shaped venous enhancement profile. Decreased venous enhancement with reduced FOV is also observed for scans with equivalent acquisition times, although the degree of suppression is dependent on the shape of the venous enhancement curve.     

透视触发三维快速梯度回波技术在颅内静脉成像的应用

目的探讨透视触发血管成像技术在脑静脉系统疾病诊断中的价值。方法使用三维快速梯度回波技术（Flash 3D）序列透视触发血管成像,通过调节扫描参数、薄层、高像素,并减少造影剂量等方法,对50例临床怀疑脑内静脉系统病变的患者进行对比增强静脉成像,并评价所获影像中血管主干及分支解剖显示情况。结果50例临床怀疑脑内静脉系统病变患者均成功完成了透视触发Flash 3D序列扫描血管成像,均能满意地显示血管影像,12例未见异常,脑静脉血栓4例,静脉型血管瘤19例,动脉静脉畸形6例,血液病浸润2例,肿瘤压迫及侵犯7例。结论Flash 3D对比增强血管成像能清楚地显示脑部静脉系统及其与病变的关系,为临床对疾病的诊断和治疗提供依据。     

高分辨CE-MRV对颅内静脉系统的显示

目的:评价高分辨CE-MRV对正常颅内静脉不同解剖部位的显示能力。方法:对30例无颅脑疾病受检者进行高分辨CE-MRV检查,利用MIP和VR等图像后处理方法对颅内预设的15个解剖部位静脉血管进行分级评价。结果:30例高分辨率CE-MRV检查均获得成功,对预设的各解剖部位静脉血管均能良好且完整地显示。结论:高分辨CE-MRV能较好地显示颅内静脉系统的结构。     

脑静脉窦闭塞的MR表现及与颅内压关系初探

目的：分析脑静脉窦闭塞的ＭＲ表现及其病理生理学改变，区分脑静脉窦闭塞与脑动脉缺血ＭＲ表现的不同点。材料与方法：回顾性总结３０例脑静脉窦闭塞ＭＲ平扫和增强扫描资料，其中男１２例，女１８例，年龄６～６９岁。观察有无占位效应，Ｔ２加权像异常信号，脑室大小改变以及造影后异常强化等ＭＲ表现。结果：１００％（３０／３０）病例于Ｔ１加权像见脑肿胀，３７％（１１／３０）病例于Ｔ２加权像出现异常信号，１６％（５／３０）病例脑室扩大，６％（２／３０）病例脑出血或脑水肿形成，８０％（２４／３０）病例出现静脉异常强化。结论：脑静脉窦闭塞ＭＲ表现与动脉性闭塞ＭＲ表现明显不同，它具有特殊的病理生理学变化，其发病机理与颅内压变化有关。仔细观察Ｔ１加权像对诊断静脉窦闭塞具有重要意义。     

HYPR TOF: time-resolved contrast-enhanced intracranial MR angiography using time-of-flight as the spatial constraint

Purpose

To investigate the feasibility of using time‐of‐flight (TOF) images as a constraint in the reconstruction of a series of highly undersampled time‐resolved contrast‐enhanced MR images (HYPR TOF), to allow simultaneously high temporal and spatial resolution and increased SNR.

Materials and Methods

Ten healthy volunteers and three patients with aneurysms underwent a HYPR TOF study, which includes a clinical routine TOF scan followed by a first pass time‐resolved contrast‐enhanced exam using an undersampled three‐dimensional (3D) projection trajectory (VIPR). Image quality, waveform fidelity and signal to background variation ratio measurements were compared between HYPR TOF images and VIPR images without HYPR reconstruction.

Results

Volunteer results demonstrated the feasibility of using the clinical routine TOF as the spatial constraint to reconstruct the first pass time‐resolved contrast‐enhanced MRA acquired using highly undersampled 3D projection trajectory (VIPR). All the HYPR TOF images are superior to the corresponding VIPR images with the same temporal reconstruction window on both spatial resolution and SNR.

Conclusion

HYPR TOF improves the spatial resolution and SNR of the rapidly acquired dynamic images without losing the temporal information. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.