3T Magnetic Resonance Angiography Research Articles

A non-invasive technique for visualization of microvessels in asymptomatic patients with middle cerebral artery steno-occlusion

We determined whether 7T magnetic resonance angiography (MRA) could be used for clearly observing microvessels in a clinically asymptomatic patient with steno-occlusion of the middle cerebral artery (MCA). We utilized 3T magnetic resonance imaging to obtain the brain images of a clinically asymptomatic patient and noted MCA steno-occlusion. In comparison with 3T MRA, 7T MRA could clearly delineate the microvessels, including lenticulostriate arteries and presumed collaterals, and our observation was comparable to that with conventional digital subtraction angiography. We report an interesting case of a clinically asymptomatic patient with MCA steno-occlusion.

Effect of Selected Manual Therapy Interventions for Mechanical Neck Pain on Vertebral and Internal Carotid Arterial Blood Flow and Cerebral Inflow

Manual therapy of the cervical spine has occasionally been associated with serious adverse events involving compromise of the craniocervical arteries. Ultrasound studies have shown certain neck positions can alter craniocervical arterial blood flow velocities; however, findings are conflicting. Knowledge about the effects of neck position on blood flow may assist clinicians in avoiding potentially hazardous practices. The purpose of this study was to examine the effects of selected manual therapeutic interventions on blood flow in the craniocervical arteries and blood supply to the brain using magnetic resonance angiography (MRA). This was an experimental, observational magnetic resonance imaging study. Twenty adult participants who were healthy and had a mean age of 33 years were imaged using MRA in the following neck positions: neutral, rotation, rotation/distraction (similar to a Cyriax manipulation), C1-C2 rotation (similar to a Maitland or osteopathic manipulation), and distraction. The participants were imaged using 3T MRA. All participants had normal vascular anatomy. Average inflow to the brain in neutral was 6.98 mL/s and was not significantly changed by any of the test positions. There was no significant difference in flow in any of the 4 arteries in any position from neutral, despite large individual variations. Only individuals who were asymptomatic were investigated, and a short section of the arteries only were imaged. Blood flow to the brain does not appear to be compromised by positions commonly used in manual therapy. Positions using end-range neck rotation and distraction do not appear to be more hazardous to cerebral circulation than more segmentally localized techniques.

Arterial Head Vascularization Cartographies of Normal Metencephalic Dogs Using Magnetic Resonance Angiography

The aim of our study was to establish head arterial cartographies-useful for the diagnosis of brain diseases leading to cerebral vascular modifications-by means of magnetic resonance angiography (MRA). Casts of the arterial vascular brain system were used to corroborate the MRA results as they can be easily rotated in nonvirtual three-dimensions and give an accurate view of the arteries calibre and origin. Two types of 3T MRA images were used: three-dimensional fast low-angle shot (3D-FLASH) acquisition sequenced every 20 s, paired with injection of a paramagnetic contrast medium, and three-dimensional time-of-flight (3D-TOF) acquisition sequenced every 300 s. 3D-FLASH acquisition gives very accurate images of the cerebral arteries and veins, but must be used with care in debilitated animals. 3D-TOF acquisition is less accurate and gives only images of the main cerebral arteries without showing the venous system. It is, however, a viable diagnostic method for monitoring vascular lesions (e.g., cerebral hemorrhages).

Low-dose contrast-enhanced time-resolved MR angiography at 3 T: Diagnostic accuracy for treatment planning and follow-up of vascular malformations

To assess the accuracy of low-dose contrast-enhanced time-resolved 3T magnetic resonance angiography (MRA) for the morphological and functional assessment of vascular malformations (VM), and to evaluate its diagnostic potential for the depiction of treatment-induced changes. Twenty-five patients with known VM underwent MRA to evaluate the location and extent of lesions and their haemodynamic characteristics. Three-dimensional (3D) T1-weighted time-resolved sequences were acquired following the administration of 0.05mmol/kg of gadobenate dimeglumine. VM were classified according to their morphology and haemodynamic characteristics. All patients thereafter underwent conventional angiography to confirm the diagnosis and to treat the lesions (embolization or sclerotherapy). Follow-up MRA was performed 30 days after treatment to assess morphological and functional changes. A visual analogue scale (VAS) was used to clinically assess the severity of symptoms before and after therapy. Based on haemodynamic characteristics, VM were classified as predominantly arterial [4 (16%)], artero-venous [19 (76%)] or venous [2 (8%)]. Twenty-three (92%) lesions were classified as high-flow VM and two (8%) as low-flow VM. Intralesional thrombosis was present in 17 (68%) lesions before therapy and in 10 lesions (40%) after therapy. The median VAS scores were 5±1 before treatment and 4±2 after treatment. Very good correlation (Spearman's correlation coefficient: rho=0.87; p=0.000) was noted between the reduction of lesion size on follow-up MRA and pain relief as assessed by VAS. Low-dose contrast-enhanced time-resolved 3T MRA can be used to define morphological and functional aspects of VM accurately during treatment planning and follow-up, and can identify post-therapy changes that positively correlate with treatment outcome.

A comparison between magnetic resonance angiography at 3 teslas (time-of-flight and contrast-enhanced) and flat-panel digital subtraction angiography in the assessment of embolized brain aneurysms

PURPOSE:To compare the time-of-flight and contrast-enhanced- magnetic resonance angiography techniques in a 3 Tesla magnetic resonance unit with digital subtraction angiography with the latest flat-panel technology and 3D reconstruction in the evaluation of embolized cerebral aneurysms.INTRODUCTION:Many embolized aneurysms are subject to a recurrence of intra-aneurismal filling. Traditionally, imaging surveillance of coiled aneurysms has consisted of repeated digital subtraction angiography. However, this method has a small but significant risk of neurological complications, and many authors have advocated the use of noninvasive imaging methods for the surveillance of embolized aneurysms.METHODS:Forty-three aneurysms in 30 patients were studied consecutively between November 2009 and May 2010. Two interventional neuroradiologists rated the time-of-flight-magnetic resonance angiography, the contrast-enhanced-magnetic resonance angiography, and finally the digital subtraction angiography, first independently and then in consensus. The status of aneurysm occlusion was assessed according to the Raymond scale, which indicates the level of recanalization according to degrees: Class 1: excluded aneurysm; Class 2: persistence of a residual neck; Class 3: persistence of a residual aneurysm. The agreement among the analyses was assessed by applying the Kappa statistic.RESULTS:Inter-observer agreement was excellent for both methods (K = 0.93; 95 % CI: 0.84-1). Inter-technical agreement was almost perfect between time-of-flight-magnetic resonance angiography and digital subtraction angiography (K = 0.98; 95 % CI: 0.93-1) and between time-of-flight-magnetic resonance angiography and contrast-enhanced-magnetic resonance angiography (K = 0.98; 95% CI: 0.93-1). Disagreement occurred in only one case (2.3%), which was classified as Class I by time-of-flight-magnetic resonance angiography and Class II by digital subtraction angiography. The agreement between contrast-enhanced-magnetic resonance angiography and digital subtraction angiography was perfect (K = 1; 95% CI: 1-1). In three patients, in-stent stenosis was identified by magnetic resonance angiography but not confirmed by digital subtraction angiography.CONCLUSION:Digital subtraction angiography and both 3T magnetic resonance angiography techniques have excellent reproducibility for the assessment of aneurysms embolized exclusively with coils. In those cases also treated with stent remodeling, digital subtraction angiography may still be necessary to confirm eventual parent artery stenosis, as identified by magnetic resonance angiography.

Surgically Implantable Magnetic Resonance Angiography Coils Improve Resolution to Allow Visualization of Blood Flow Dynamics

Magnetic resonance angiography (MRA) is clinically useful but of limited applicability to small animal models due to poor signal resolution, with typical voxel sizes of 1 mm(3) that are insufficient to analyze vessels of diameter <1 mm. We determined whether surgically implantable, extravascular MRA coils increase signal resolution adequately to examine blood flow dynamics A custom MRA coil was surgically implanted near the carotid artery of a New Zealand White rabbit. A stenosis was created in the carotid artery to induce complicated, non-laminar flow. Phase contrast images were obtained on multiple axial planes with 3T MRA and through-plane velocity profiles were calculated under laminar and complicated flow conditions. These velocity profiles were fit to a laminar flow model using ordinary least squares in order to quantify the degree of flow complication (Matlab). Flow was also measured with a Doppler flow probe; vessel diameters and flow velocities were compared with duplex ultrasound Carotid artery blood flow was 24.7 +/- 2.6 ml/min prior to stenosis creation and reduced to 12.0 +/- 1.7 ml/min following injury (n=3). An MRA voxel size of 0.1 x 0.1 x 5 mm was achieved. The control carotid artery diameter was 1.9 +/- 0.1 mm, and cross-sectional images containing 318 +/- 22 voxels were acquired (n=26). Velocity profiles resembled laminar flow proximal to the stenosis, and then became more complicated just proximal and distal to the stenosis. Laminar flow conditions returned downstream of the stenosis Implantable, extra-vascular coils enable small MRA voxel sizes to reproducibly calculate complex velocity profiles under both laminar and complicated flow in a small animal model. This technique may be applied to study blood flow dynamics of vessel remodeling and atherogenesis.

Hypertension Correlates With Lenticulostriate Arteries Visualized by 7T Magnetic Resonance Angiography

Hypertension, a major risk factor for stroke, is associated with altered arterial anatomy and function; however, the limited resolution of current imaging techniques has restricted the in vivo study of microvascular changes in the brain. In this report, we quantitatively examined the lenticulostriate arteries in hypertensive patients using ultrahigh-field 7T MRI. We compared the number of stems and branches, curvature, and tortuosity of the lenticulostriate arteries by 3D time-of-flight magnetic resonance angiography among 20 hypertensive patients (mean age: 46.6+/-9.1 years) and 20 age-matched healthy subjects (mean age: 47.7+/-8.1 years). The average numbers of stems and branches in hypertensive patients were significantly less than those of healthy subjects (P<0.002). However, this difference was abolished in older volunteers (>45 years old), whereas the difference between young hypertensive patients (< or = 45 years old) and age-matched healthy controls was augmented by 55% for stems and 91% for branches (P=0.001). In comparison, there were no differences in the average curvature and tortuosity of the lenticulostriate arteries and no significant difference when corrected for smoking (P=0.064). In conclusion, our results showed that there was a substantial difference in the lenticulostriate arteries of hypertensive patients compared with healthy individuals when observed in vivo by ultrahigh-resolution 7T magnetic resonance angiography, and the difference was considerable in young subjects.

Migraine headache is not associated with cerebral or meningeal vasodilatation—a 3T magnetic resonance angiography study

Migraine headache is not associated with cerebral or meningeal vasodilatation—a 3T magnetic resonance angiography study

The Middle Meningial Artery during a Migraine Attack: 3T Magnetic Resonance Angiography Study

We performed 3T magnetic resonance angiography (MRA) during a spontaneous migraine attack. The patient was a 42-year-old woman migraineur diagnosed by the IHS criteria. The change of the middle meningial artery (MMA) was measured on the axial brain images using MATLAB for three phases (attack-free period, during an attack, a period after medication). There were no dramatic changes of vasodilation in the MMA during the attack (2.0 mm), attack-free period (diameter 1.9 mm), or period after medication (1.7 mm), resembling extrapolations of observations in experimental animal models. This finding suggests that the dramatic vasomotion might not be associated with migraine pathophysiology.

A 3D Model of Human Cerebrovasculature Derived from 3T Magnetic Resonance Angiography

The human cerebrovasculature is extremely complicated and its three dimensional (3D) highly parcellated models, though necessary, are unavailable. We constructed a digital cerebrovascular model from a high resolution, 3T 3D time-of-flight magnetic resonance angiography scan. This model contains the arterial and venous systems and is 3D, geometric, highly parcellated, fully segmented, and completely labeled with name, diameter, and variants. Our approach replaces the tedious and time consuming process of checking and correcting automatic segmentation results done at 2D image level with an aggregate and faster process at 3D model level. The creation of the vascular model required vessel pre-segmentation, centerline extraction, vascular segments connection, centerline smoothing, vessel surface construction, vessel grouping, tracking, editing, labeling, setting diameter, and checking correctness and completeness. For comparison, the same scan was segmented automatically with 59.8% sensitivity and only 16.5% of vessels smaller than 1 pixel size were extracted. To check and correct this automatic segmentation requires 8 weeks. Conversely, the speedup of our approach (the number of 2D segmented areas/the number of 3D vascular segments) is 34. This cerebrovascular model can serve as a reference framework in clinical, research, and educational applications. The wealth of information aggregated with its quantification capabilities can augment or replace numerous textbook chapters. Five applications of the vascular model were described. The model is easily extendable in content, parcellation, and labeling, and the proposed approach is applicable for building a whole body vascular system.

Reply to: Migraine headache is not associated with cerebral or meningeal vasodilatation--a 3T magnetic resonance angiography study

Reply to: Migraine headache is not associated with cerebral or meningeal vasodilatation--a 3T magnetic resonance angiography study

Surgically implantable magnetic resonance angiography coils improve resolution to allow visualization of blood flow dynamics

Fitzgerald, Tamara N. MD, PhD; Muto, Akihito MD, PhD; Fancher, Tiffany T. MD; Brown, Peter B.; Martin, Karen A. RT(R); Muhs, Bart E. MD, PhD; Rothman, Douglas L. PhD; Constable, Todd R. PhD; Sampath, Smita PhD; Dardik, Alan MD, PhD, FACS Author Information

Follow-up of intracranial aneurysms treated with detachable coils: comparison of 3D inflow MRA at 3T and 1.5T and contrast-enhanced MRA at 3T with DSA

The purpose of this prospective study was to compare 3T and 1.5T magnetic resonance angiography (MRA) with digital subtraction angiography (DSA) for the follow-up of endovascular treated intracranial aneurysms to assess the grade of occlusion. Thirty-seven patients with 41 aneurysms who had undergone endovascular treatment with detachable coils were included. MRA was performed on the same day using an eight-channel sensitivity encoding head-coil with 3D axial inflow technique. At 3T, a contrast-enhanced transverse 3D fast gradient echo acquisition was also performed. Most patients underwent DSA the following day. MRA scans and DSA were classified first independently by two neuroradiologists and an interventional neuroradiologist. Secondly, a consensus was done. Source images, maximum intensity projection, multiplanar reconstruction and volume rendering reconstructions were used for MRA evaluations. A modification of the Raymond classification, previously used for DSA evaluation of recanalization, was used. Statistical comparison of the consensus showed that 3T MRA with 3D axial inflow technique had better agreement with DSA (kappa = 0.43) than 1.5T MRA(kappa = 0.21) and contrast-enhanced MRA (CE-MRA) at 3T (kappa = 0.17). The susceptibility artefacts from the coil mesh were significally smaller at 3T (p = 0.002-0.007) than at 1.5T. 3T MRA, using a sensitivity encoding head-coil, showed better agreement with DSA than 1.5T and CE-MRA at 3T for evaluation of aneurysms treated with endovascular coiling.

MRA of intracranial aneurysms embolized with platinum coils: A vascular phantom study at 1.5T and 3T

To analyze the influence of matrix and echo time (TE) of three-dimensional time-of-flight (3D TOF) magnetic resonance angiography (MRA) on the depiction of residual flow in aneurysms embolized with platinum coils at 1.5T and 3T. A simulated intracranial aneurysm of the vascular phantom was loosely packed to maintain the patency of some residual aneurysmal lumen with platinum coils and connected to an electromagnetic flow pump with pulsatile flow. MRAs were obtained altering the matrix and TE of 3D TOF sequences at 1.5T and 3T. The increased spatial resolution and the shorter TE offered better image quality at 3T. For the depiction of an aneurysm remnant, the high-spatial-resolution 3T MRA (matrix size of 384 x 224 and 512 x 256) with a short TE of < or =3.3 msec were superior to the 1.5T MRA obtained with any sequences. 3T MRA is superior to 1.5T MRA for the assessment of aneurysms embolized with platinum coils; the combination of the 512 x 256 matrix and short TE (3.3 msec or less) seems feasible at 3T.

High-resolution intracranial MRA at 7T using autocalibrating parallel imaging: initial experience in vascular disease patients

Greater spatial resolution in intracranial three-dimensional time-of-flight (TOF) magnetic resonance angiography (MRA) is possible at higher field strengths, due to the increased contrast-to-noise ratio (CNR) from the higher signal-to-noise ratio and the improved background suppression. However, at very high fields, spatial resolution is limited in practice by the acquisition time required for sequential phase encoding. In this study, we applied parallel imaging to 7T TOF MRA studies of normal volunteers and patients with vascular disease, in order to obtain very high resolution (0.12 mm(3)) images within a reasonable scan time. Custom parallel imaging acquisition and reconstruction methods were developed for 7T MRA, based on generalized autocalibrating partially parallel acquisition (GRAPPA). The techniques were compared and applied to studies of seven normal volunteers and three patients with cerebrovascular disease. The technique produced high resolution studies free from discernible reconstruction artifacts in all subjects and provided excellent depiction of vascular pathology in patients. 7T TOF MRA with parallel imaging is a valuable noninvasive angiographic technique that can attain very high spatial resolution.

Migraine headache is not associated with cerebral or meningeal vasodilatation—a 3T magnetic resonance angiography study

Migraine headache is widely believed to be associated with cerebral or meningeal vasodilatation. Human evidence for this hypothesis is lacking. 3 Tesla magnetic resonance angiography (3T MRA) allows for repetitive, non-invasive, sensitive assessment of intracranial vasodilatation and blood flow. Nitroglycerine (NTG) can faithfully induce migraine attacks facilitating pathophysiological studies in migraine. Migraineurs (n = 32) randomly received NTG (IV 0.5 microg/kg/min for 20 min; n = 27) or placebo (n = 5; for blinding reasons). Using 3T MRA, we measured: (i) blood flow in the basilar (BA) and internal carotid arteries (ICA) and (ii) diameters of the middle meningeal, external carotid, ICA, middle cerebral, BA and posterior cerebral arteries at three timepoints: (a) at baseline, outside an attack; (b) during infusion of NTG or placebo and (c) during a provoked attack or, if no attack had occurred, at 6 h after infusion. Migraine headache was provoked in 20/27 (74%) migraineurs who received NTG, but in none of the five patients who received placebo. The headache occurred between 1.5 h and 5.5 h after infusion and was unilateral in 18/20 (90%) responders. During NTG (but not placebo) infusion, there was a transient 6.7-30.3% vasodilatation (P < 0.01) of all blood vessels. During migraine, blood vessel diameters were no different from baseline, nor between headache and non-headache sides. There were no changes in BA and ICA blood flow during either NTG infusion or migraine. In contrast to widespread belief, migraine attacks are not associated with vasodilatation of cerebral or meningeal blood vessels. Future anti-migraine drugs may not require vasoconstrictor action.

Computer-assisted measurement of vessel shape from 3T magnetic resonance angiography of mouse brain

Blood vessel morphology (vessel radius, branching pattern, and tortuosity) is altered by a multitude of diseases. Although murine models of human pathology are important to the investigation of many diseases, there are few publications that address quantitative measurements of murine vascular morphology. This report outlines methods of imaging mice in vivo using magnetic resonance angiograms obtained on a clinical 3T unit, of defining mouse vasculature from these images, and of quantifying measures of vessel shape. We provide examples of both healthy and diseased vasculature and illustrate how the approach can be used to assess pathology both visually and quantitatively. The method is amenable to the assessment of many diseases in both human beings and mice.

Intracranial Aneurysm Detection with 3T Magnetic Resonance Angiography

The new 3 Tesla (T) magnetic resonance (MR) scanners yield improved signal-to-noise ratio and spatial resolution with superior background suppression compared to lower field strength systems. This is advantageous for MR angiograms. The purpose of our study was to compare unenhanced three-dimensional time-of-flight magnetic resonance angiography (3D TOF MRA) at 3T with catheter digital subtraction angiography (DSA) in detecting unruptured intracranial aneurysms. Out of 1375 consecutive patients who underwent unenhanced 3D TOF MRA at 3T, 15 patients with unruptured intracranial aneurysms were retrospectively identified. Nine of these 15 patients had DSA as the reference standard for comparison. Aneurysm size, location and morphology were independently assessed on both MRA and DSA by 2 radiologists. Seventeen aneurysms ranging in size from 1 mm to 24 mm were identified in 15 patients on MRA. DSA confirmed the aneurysms in 9 patients with good anatomical correlation compared with the MRA findings. 3D TOF MRA at 3T has good correlation with DSA and aneurysms as small as 1 mm in size can be detected. This can be a promising, non-invasive method for aneurysm surveillance.

Computer-assisted measurement of vessel shape from 3T magnetic resonance angiography of mouse brain

Computer-assisted measurement of vessel shape from 3T magnetic resonance angiography of mouse brain