Value and limitations of contrast-enhanced MR angiography in spinal arteriovenous malformations and dural arteriovenous fistulas

BACKGROUND AND PURPOSE: The purpose of this work was to study the validity of MR angiography (MRA) for identification of spinal arteriovenous (AV) abnormalities. MATERIALS AND METHODS: Thirty-four consecutive patients with suspicion of spinal vascular abnormalities underwent digital subtraction angiography (DSA) after MRA. The level and side of the suspected spinal dural arteriovenous fistula (SDAVF) and the feeding arteries in spinal arteriovenous malformations (SAVMs) were determined from the MRA and compared with DSA. RESULTS: DSA revealed SDAVF in 20 abnormalities of which 19 were spinal and 1 was tentorial with spinal drainage, as well as SAVM in 11 patients. In 3 patients, MRA and DSA were both normal. For detection of spinal arteriovenous abnormalities, neither false-positive nor false-negative MRA results were obtained. The MRA-derived level of the feeding artery in SDAVF agreed with DSA in 14 of 19 cases. In 5 cases, a mismatch of 1 vertebral level (not side) was noted for the feeding artery. For the tentorial AVF, only the spinal drainage was depicted; the feeding artery was outside the MRA field of view. In intradural SAVM, the main feeding artery was identified by MRA in 10 of 11 patients. MRA could differentiate between glomerular and fistulous SAVM in 4 of 6 cases and between sacral SDAVF and filum terminale SAVM in 2 of 5 cases. CONCLUSIONS: MRA reliably detects or excludes various types of spinal AV abnormalities and localizes the (predominant) arterial feeder of most spinal AV shunts. Although classification of the subtype of SAVMs remains difficult, with MRA it greatly helps to focus subsequent DSA.     

Intracranial dural arteriovenous fistulas: evaluation with combined 3D time-of-flight MR angiography and MR digital subtraction angiography

OBJECTIVE: The purpose of this study was to compare the diagnostic utility of 3D time-of-flight (TOF) MR angiography and MR digital subtraction angiography in patients with angiographically proven moderate- to high-flow intracranial dural arteriovenous fistula. MATERIALS AND METHODS: Two neuroradiologists, unaware of patients' histories and angiographic findings, retrospectively reviewed 17 MR angiograms with 3D TOF MR angiography and MR digital subtraction angiography in 15 patients with dural arteriovenous fistula and also reviewed 35 MR angiograms in control patients without findings of dural arteriovenous fistula on angiography. Disagreements were resolved by consensus. RESULTS: In patients with dural arteriovenous fistula, source images of 3D TOF MR angiography showed two abnormal findings: multiple high-intensity curvilinear or nodular structures adjacent to the sinus wall and high-intensity areas in the venous sinus. Findings of multiple high-intensity structures adjacent to the sinus wall were observed in all cases of dural arteriovenous fistula. Findings of high-intensity areas in the venous sinus were observed in 13 of 17 cases of dural arteriovenous fistula. Findings of multiple high-intensity structures adjacent to the sinus wall were not observed in any control subjects. Findings of high-intensity areas within the venous sinus were observed in five of 35 control subjects. Findings of MR digital subtraction angiography showed early filling of the venous sinus, suggestive of dural arteriovenous fistula, in 13 of 15 patients with dural arteriovenous fistula. Sensitivity and specificity of multiple high-intensity structures adjacent to the sinus wall, high-intensity areas in the venous sinus, and early filling of the venous sinus were 100% and 100%, 76% and 86%, and 87% and 100%, respectively. Although 3D TOF MR angiography failed to show the findings of retrograde cortical venous drainage and venous sinus occlusion, MR digital subtraction angiography clearly showed both findings in all five subjects. CONCLUSION: A protocol including both 3D TOF MR angiography (source images) and MR digital subtraction angiography allowed the diagnosis of moderate- to high-flow dural arteriovenous fistula. In addition, cortical venous drainage was reliably noted in a small subset of patients.     

Assessment of dural arteriovenous fistulas of the cavernous sinuses on 3D dynamic MR angiography

BACKGROUND AND PURPOSE: Flow voids within the cavernous sinuses and/or certain venous drainage on spin-echo MR imaging and time-of-flight (TOF) flow enhancement on MR angiography (MRA) have indicated high-velocity shunt flow and have been used for screening patients with dural arteriovenous fistulas (DAVFs) of the cavernous sinuses. In this investigation, the capabilities of 3D dynamic MRA as a flow-independent approach and those of conventional MR imaging techniques were compared with selective angiography for the diagnosis of DAVFs of the cavernous sinuses.MATERIALS AND METHODS: This retrospective study involved 18 patients with angiographically proved DAVFs of the cavernous sinuses and 12 control subjects. Sixteen partially overlapping sequential MR images were acquired on contrast-enhanced 3D dynamic MRA between the petrosal bone and the orbital roof. Two experienced observers blinded to the clinical data and results of angiography independently graded 3D dynamic MRA, fast spin-echo T2-weighted imaging (FSE T2WI), and TOF MRA.RESULTS: The average area under the receiver operating characteristic curve values and interobserver κ scores for the diagnosis of DAVFs on 3D dynamic MRA, FSE T2WI, and TOF MRA were 0.99, 0.89, and 0.95; and 0.92, 0.71, and 0.73, respectively. Those for the diagnosis of anterior, posterior, and retrograde cortical venous drainage on 3D dynamic MRA were 0.72, 0.95, and 0.81; and 0.56, 0.50, and 0.49, respectively.CONCLUSION: In this small series, screening 3D dynamic MRA directly demonstrates DAVFs of the cavernous sinuses and has improved diagnostic capability.

In patients with the classic triad of pulsating exophthalmos, orbital bruit, and conjunctival chemosis, the clinical diagnosis of arteriovenous fistulas (AVFs) of the cavernous sinuses is not difficult, and cerebral angiography is performed for definitive diagnosis. However, dural AVFs (DAVFs) without anterior drainage may not cause typical congestive orbito-ocular features, and thrombosis of the draining veins may lead to spontaneous resolution of the disorder.^1–6 Therefore, it is desirable to perform less invasive diagnostic examinations before conventional angiography. So far, flow voids within the cavernous sinuses and/or inferior petrosal sinuses on spin-echo MR images followed by time of flight (TOF) flow enhancement on source images of MR angiography (MRA) have been indicative of AVF.^7–10 Although these are safe and practical methods, dependence on flow velocity sometimes makes it impossible to distinguish fast normal flow from abnormal shunt flow or slow abnormal shunt flow from normal flow.^9–13The recent advancement of MR imaging technology has allowed first-pass contrast-enhanced dynamic MRA and 2D MR digital subtraction angiography to be applied to cerebral arteriovenous malformations (AVMs) or DAVFs.^14–18 In addition, although the conventional use of 3D dynamic MRA for their diagnosis has been difficult due to the limitation of low temporal resolution, its application has been described in recently published articles.^19,20 However, until now, there has not been a comparative study of dynamic MRA and conventional MR imaging for the diagnosis of DAVFs of the cavernous sinuses.According to a study of dynamic CT of the cavernous sinuses²¹ and physiologic studies on the cerebral circulation time,^22,23 it was hypothesized that imaging temporal resolution under several seconds would demonstrate DAVFs of the cavernous sinuses on dynamic MRA. Therefore, we used the 3D data-acquisition technique, a standard pulse sequence, and postulated that early enhancement of the cavernous sinuses was a main direct feature of the shunts. This methodology will improve the diagnostic capability for screening of DAVFs of the cavernous sinuses.     

Usefulness of source images from three-dimensional time-of-flight MR angiography after treatment of cavernous dural arteriovenous fistulas

PURPOSE: Source images from three-dimensional time-of-flight MR angiography (3D TOF MRA) are useful for the diagnosis of cavernous dural arteriovenous fistulas. The purpose of this study was to assess the accuracy of source images from 3D TOF MRA compared with digital subtraction angiography (DSA) as a follow-up technique for the detection of residual or recurrent fistulas after treatment. We also assessed the effect of embolized materials in the evaluation of MRA. MATERIALS AND METHODS: In 14 patients who were treated with embolization and/or radiation therapy, follow-up MRA and DSA were performed after a mean follow-up duration of 3 months. Two observers independently reviewed the source images from MRA in regard to the presence of hyperintense regions within the cavernous sinus and enlargement of the draining veins. They also assessed whether embolized materials affected the evaluation. RESULTS: Sensitivity, specificity, and positive predictive value of source images from MRA in revealing residual or recurrent fistulas were 100% (9 of 9 true positive findings), 80% (4 of 5 true negative findings), and 90% (9 of 10 positive findings), respectively. In all five patients treated with platinum coils, hypointense areas in the cavernous sinus were observed but did not affect image evaluation. CONCLUSION: Source images from 3D TOF MRA provided accurate diagnosis with no effect of embolized materials in the follow-up of treated cavernous dural arteriovenous fistulas.     

2D Thick-section MR digital subtraction angiography for the assessment of dural arteriovenous fistulas

BACKGROUND AND PURPOSE: Although dynamic contrast-enhanced MR angiography studies for arteriovenous malformations (AVFs) and brain tumors have shown promising results, no formal attempt has yet been made to similarly evaluate dural AVFs. To assess the practical applicability of 2D thick-section contrast enhanced MR digital subtraction angiography (MRDSA) for the diagnosis and management of dural AVFs, MRDSA and intra-arterial digital subtraction angiography (IADSA) were comparatively evaluated. METHODS: We performed 80 consecutive MRDSA studies for 25 dural AVFs, including 11 cavenous sinuses, 9 sigmoid sinuses, 2 tentorial sinuses, one anterior condylar vein, one craniocervical junction, and one spine. MR images were continuously obtained following the initiation of a bolus injection of gadrinium chelates and subtraction images were constructed. We thereafter evaluated the imaging quality and hemodynamic information from all 46 MRDSA images performed in parallel with IADSA in either perioperative or follow-up studies. RESULTS: Most MRDSA images detected early venous filling, sinus occlusion, leptomeningeal venous drainage, and varices. It was difficult, however, to identify the feeding arteries because of both the partial volume effect and a low spatial resolution. Most important, MRDSA accurately detected aggressive lesions with leptomeningeal venous drainage and varices. CONCLUSION: Our MRDSA technique was found to have limited value for depicting all the anatomic details of dural AVFs, though it was able to identify important hemodynamic abnormalities related to the risk of hemorrhaging. MRDSA is therefore useful as a less invasive, dynamic angiographic tool, not only for perioperative studies but also for follow-up studies.     

The accuracy and utility of contrast-enhanced MR angiography for localization of spinal dural arteriovenous fistulas: the Toronto experience

Objectives

The purpose of this study was to determine the accuracy and utility of contrast-enhanced MR angiography (CE-MRA) in spinal dural arteriovenous fistulas (SDAVF).

Methods

A retrospective analysis from 1999–2012 identified 70 patients clinically suspected of harboring a SDAVF. Each patient underwent consecutive conventional MR-imaging, CE-MRA, and digital subtraction angiography (DSA). The presence or absence of serpentine flow voids, T2-weighted hyperintensity, and cord enhancement were evaluated, as well as location of the fistula as predicted by CE-MRA. DSA was used as the reference standard.

Results

Of the 70 cases, 53 were determined to be a SDAVF, 10 cases were shown to be other forms of vascular malformation, and 7 were DSA-negative. On MRI, all reported cases of SDAVF showed serpentine flow voids (100 %). T2-weighted hyperintensity was seen in 48 of 50 cases (96 %), extending to the conus in 41 of 48 cases (85 %). Cord enhancement was seen in 38 of 41 cases (93 %). CE-MRA correctly localized the SDAVF in 43 of the 53 cases (81 %).

Conclusions

CE-MRA is a useful non-invasive examination for the detection and localization of SDAVF. CE-MRA facilitates but does not replace DSA as confirmation of location, fistula type, and arterial detail, which are required before treatment.

Key Points

? CE-MRA correctly localized the site of the SDAVF in over 80 % of cases. ? CE-MRA facilitates diagnostic DSA and expedites the diagnostic process. ? CE-MRA does not replace diagnostic DSA in SDAVF cases as confirmative test. ? CE-MRA provides better understanding of missed or mislocalized SDAVF cases.     

Pulmonary arteriovenous malformation: Characterization with time-resolved ultrafast 3D MR angiography

To avoid potentially deadly consequences from paradoxical emboli, early detection and accurate characterization of pulmonary arteriovenous malformations (AVMs) is highly desirable. We report on a patient with a suspected pulmonary AVM who underwent ultrafast time-resolved 3D MR angiography of the pulmonary arteries. The case documents the suitability of the MRA technique as a noninvasive alternative to computed tomographic angiography and digital subtraction angiography for accurate pre-therapeutic characterization of pulmonary AVMs.     

The role of time-resolved 3D contrast-enhanced MR angiography in the assessment and grading of cerebral arteriovenous malformations

Purpose

To assess the role of three-dimensional (3D) contrast-enhanced, time-resolved MR angiography (CE TR MRA) in patients with intracranial arteriovenous malformations (AVMs).

Methods

We studied 12 patient with intracranial AVMs on a 3.0 T MR imaging system (Magentom TIM Trio, Siemens Medical Solutions, Erlangen, Germany) using 3D CE TR MRA with autocalibrating partially parallel acquisitions and echo sharing schemes, which provided temporal resolution of 0.58 or 1.7 s and near isotropic voxels. We qualitatively assessed image quality of the 3D CE TR MRA and compared the grading of the AVMs based on modified Spetzler-Martin system for 3D CE TR MRA and catheter digital subtraction angiography (DSA).

Results

CE TR MRA provided good quality images in the 3 standard orthogonal planes, and good arterial-venous separation in all cases. All AVMs were correctly graded by CE TR MRA when compared with DSA.3D CE TR MRA provides a non-invasive alternative to DSA for the evaluation of cerebral AVMs.     

Postoperative assessment of extracranial-intracranial bypass by time-resolved 3D contrast-enhanced MR angiography using parallel imaging

PURPOSE: Our goals were to assess image quality of time-resolved contrast-enhanced MR angiography (CE MRA), by using 3D data acquisition along with a parallel imaging technique that can improve temporal resolution and to compare this technique with 3D-time-of-flight (TOF) MRA in the postoperative assessment of extracranial (EC)-intracranial (IC) bypass surgery. METHODS: On a 1.5T imaging system, we performed CE MRA by using a 3D fast field-echo sequence in combination with a parallel imaging technique, to obtain images in the coronal plane centered at the postoperative site. Our patient group comprised 17 patients, including 13 after superficial temporal artery-middle cerebral artery (MCA) anastomosis, 3 after external carotid artery-MCA anastomosis, and one after extracranial vertebral artery-posterior cerebral artery anastomosis. Visualization of the anastomosis and the distal flow on the CE-MRA images was assessed comparatively with that on 3D-TOF MR angiograms obtained at the same time. In 6 patients, we also compared the efficiency of visualization on CE-MRA images with that on conventional angiograms. RESULTS: A temporal resolution of 0.8 s/frame could be achieved with the technique employed. The bypass was better demonstrated postoperatively on CE-MRA images than on 3D-TOF MR angiograms in 13 patients (76%), whereas the 2 methods were equivalent in 4 patients (24%). Good correspondence of results was observed in the 6 patients for whom CE MRA and conventional digital subtraction angiography (DSA) images were compared. CONCLUSION: CE MRA by using the parallel imaging technique can increase image acquisition speed with sufficient image quality. This technique is at least equivalent to 3D-TOF MRA to evaluate the postoperative status of EC-IC bypass.     

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.     

Intracranial time-resolved contrast-enhanced MR angiography at 3T

BACKGROUND AND PURPOSE: A method is presented for high-temporal-resolution MR angiography (MRA) using a combination of undersampling strategies and a high-field (3T) scanner. Currently, the evaluation of cerebrovascular disorders involving arteriovenous shunting or retrograde flow is accomplished with conventional radiographic digital subtraction angiography, because of its high spatial and temporal resolutions. Multiphase MRA could potentially provide the same diagnostic information noninvasively, though this is technically challenging because of the inherent trade-off between signal intensity-to-noise ratio (S/N), spatial resolution, and temporal resolution in MR imaging. METHODS: Numerical simulations addressed the choice of imaging parameters at 3T to maximize S/N and the data acquisition rate while staying within specific absorption rate limits. The increase in S/N at 3T was verified in vivo. An imaging protocol was developed with S/N, spatial resolution, and temporal resolution suitable for intracranial angiography. Partial Fourier imaging, parallel imaging, and the time-resolved echo-shared acquisition technique (TREAT) were all used to achieve sufficient undersampling. RESULTS: In 40 volunteers and 10 patients exhibiting arteriovenous malformations or fistulas, intracranial time-resolved contrast-enhanced MRA with high acceleration at high field produced diagnostic-quality images suitable for assessment of pathologies involving arteriovenous shunting or retrograde flow. The technique provided spatial resolution of 1.1 x 1.1 x 2.5 mm and temporal resolution of 2.5 seconds/frame. The combination of several acceleration methods, each with modest acceleration, can provide a high overall acceleration without the artifacts of any one technique becoming too pronounced. CONCLUSION: By taking advantage of the increased S/N provided by 3T magnets over conventional 1.5T magnets and converting this additional S/N into higher temporal resolution through acceleration strategies, intracranial time-resolved MRA becomes feasible.     

Brain arteriovenous malformation diagnosis: value of time-resolved contrast-enhanced MR angiography at 3.0T compared to DSA

Introduction

This study was conducted in order to evaluate the value of time-resolved contrast-enhanced magnetic resonance angiography (TR-CE-MRA) with a 3.0-T magnetic field compared to digital subtraction angiography (DSA) as the reference standard for the diagnosis of brain arteriovenous malformation (bAVM).

Methods

Nineteen patients with 19 angiographically confirmed untreated bAVM were investigated with both DSA and TR-CE-MRA for the initial diagnosis. Examinations were compared by two independent readers. Interobserver agreement and intermodality agreement with respect to nidus size, arterial feeders, and venous drainage were determined using the K statistic test. Also, the quality of the TR-CE-MRA images was evaluated.

Results

Seventeen of the 19 bAVM (89.5%) detected with DSA were diagnosed with TR-CE-MRA. Interobserver agreement for TR-CE-MRA was good for nidus size, venous drainage, and arterial feeders (K?=?0.75, 95% CI 0.50–1.00; K?=?0.77, 95% CI 0.54–1.00; and K?=?0.80, 95% CI 0.59–1.00 respectively). Intermodality agreement was good for nidus size and venous drainage (K?=?0.75, 95% CI 0.49–1.00 and K?=?0.77, 95% CI 0.54–1.00, respectively) and moderate for arterial feeders (K?=?0.44, 95% CI 0.17–0.70).

Conclusion

TR-CE-MRA at 3.0?T has a good sensitivity for bAVM detection and good agreement with DSA for determining nidus size and the type of venous drainage, suggesting that TR-CE-MRA is potentially a reliable tool for the diagnosis and assessment of bAVMs. However, it still suffers from low spatial resolution and vessel superposition, making differentiation of the arterial feeders of the nidus difficult at times.     

Combining time-resolved and single-phase 3D techniques in contrast-enhanced carotid MR angiography.

We established an easy-to-use technique for performing contrast-enhanced carotid MR angiography (MRA) with a commercial scanner. Twenty-three patients with suspected carotid or vertebral arterial lesions were prospectively studied. Two techniques were applied in the study. After performing sagittal time-resolved acquisitions, we undertook a coronal single-phase 3D acquisition, in which the injection timing was estimated from the preceding images. In each case, we obtained multidirectional images with sufficient venous suppression. The combined use of time-resolved and single-phase 3D MRA is a feasible technique for obtaining selective arterial images without the use of special applications or hardware.     

Breath-hold 3D MR angiography of the renal vasculature using a contrast-enhanced multiecho gradient-echo technique

OBJECTIVE: Significant evolution of contrast-enhanced MR angiography for evaluating vascular diseases in the abdomen has occurred during the past several years. The state-of-the-art gradient-echo imaging technique employs a short echo time (TE) and a short repetition time (TR) for rapid vascular imaging with contrast-enhanced MR angiography. However, because of the short TR (< or = 3-8 msec), the background stationary tissue becomes saturated, with resultant poor contrast resolution of visceral organs. The authors present a new approach to vascular imaging using a multiecho gradient-echo technique with a TR sufficiently long (41 msec) to image the renal vasculature and parenchyma without background tissue suppression. METHODS: Twenty-four partitions (3D slab thickness = 72 mm) with an in-plane resolution of 224 x 256 were obtained in 21 seconds. Three measurements were performed with an interscan delay of 8 seconds. In the pulse sequence, the partition loop is defined as the innermost loop, in which Kz views are acquired centrically for a fixed Ky, followed by Ky views in a conventional linear or sequential order. The partition encodings are segmented to permit multiple encodings in which two TR loops were used to span a total of 24 echoes with 12 along the positive and 12 along the negative direction in k space. A large bandwidth of 650 Hz/pixel was used to keep the echo train length short, with an echo spacing of 1.86 msec. A frequency-selective fat saturation pulse was placed before slab-selective excitation. The other parameters in the pulse sequence were TR/TE/flip = 41/2.2/45; the field of view was 360 to 390 mm. Maximum intensity projections of each 3D contrast-enhanced measurement were performed. The vascular-to-background contrast, bowel-related magnetic susceptibility artifact, and background stationary signals were subjectively graded. The authors examined the utility of this technique in 16 randomly selected patients (3 normal, 13 abnormal) with varied renal vasculature and parenchymal abnormalities. Results were confirmed with conventional x-ray angiography, surgery, or clinical follow-up. RESULTS: Vascular-to-background contrast was graded as very good (grade III/III) in all cases. The bowel-related magnetic susceptibility artifacts were not considered significant. Background visceral organ soft tissue contrast was not suppressed and was graded as good (grade III/III) in all cases. Eight hemodynamically significant (> 50% diameter) stenoses in seven patients were accurately assessed (one with fibromuscular dysplasia). Three patients with renal masses (two with renal cell carcinoma and one with renal lymphoma) were accurately assessed for arterial anatomy and venous extension. Other renal venous abnormalities seen were retroaortic renal vein (n = 1), chronic occlusion (n = 1), and accessories (total of five) (n = 1). CONCLUSIONS: Rapid breath-hold contrast-enhanced MR angiography of the renal vasculature with a multiecho gradient-echo using a long TR depicted the renal vasculature with high vessel-to-background contrast without significant bowel-related susceptibility artifact and without background visceral organ tissue signal suppression, resulting in high background soft tissue contrast resolution.     

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.