Projection Magnetic Resonance Angiography Research Articles

Comparison of Rates of Growth between Unruptured and Ruptured Aneurysms Using Magnetic Resonance Angiography

Growth is a key risk factor for rupture of unruptured cerebral aneurysms. There are few reports of investigations into the actual growth of ruptured intracranial aneurysms. The aim of the present study was to ascertain the risk of rupture of aneurysms based on the growth of unruptured and ruptured aneurysms. Changes in size on magnetic resonance angiography (MRA) were examined in 50 patients with ruptured cerebral aneurysms. Images obtained before and after subarachnoid hemorrhage were used. Moreover, changes in aneurysm size were retrospectively examined in 73 patients with 100 unruptured cerebral aneurysms that were followed serially with MRA that was performed using a 1.5-T or 3-T system. The size of the aneurysm was determined by measuring the maximum diameter on maximum intensity projection MRA images. Based on these data, the annual growth rates (mm growth/year) of unruptured and ruptured aneurysms were calculated and compared. The median annual growth rate of ruptured aneurysms was significantly greater than that of unruptured aneurysms (.69 versus .077 mm/year, P < .01). The annual growth rates of ruptured aneurysms showed a negative correlation between the duration from initial MRA to the time of rupture. A high annual growth rate is a key risk factor for aneurysm rupture. This finding provides strong evidence for the treatment of unruptured cerebral aneurysms.

Noninvasive Evaluation of Collateral Blood Flow through Circle of Willis in Cervical Carotid Stenosis Using Selective Magnetic Resonance Angiography

Preoperative assessment of intracranial collateral circulation is helpful in predicting cerebral ischemia during surgical procedures for cervical internal carotid artery (ICA) stenosis. However, magnetic resonance angiography (MRA) and other less-invasive techniques cannot evaluate collateral blood flow because these techniques are nonselective. Hence, by using a newly developed selective MRA technique, we attempted to visualize collaterals via the circle of Willis in patients with ICA stenosis. Twelve patients who underwent carotid endarterectomy were prospectively examined with a 1.5-T MR scanner. Both selective and nonselective MRA were obtained using a 3-dimensional time-of-flight technique, with or without a cylindrical saturation pulse that suppresses the flow signal from the region of the target ICA. Maximum intensity projection MRA images were generated and compared with digital subtraction angiography (DSA) images. In all patients, the distal flow signal of the ipsilateral ICA was completely suppressed on selective MRA compared with nonselective MRA. In addition, collateral blood flow through the anterior and posterior communicating arteries was visualized in 5 and 2 patients, respectively. These findings corresponded well with the DSA imaging. Selective MRA techniques can readily suppress signals from the distal blood flow of the target artery and visualize the presence of collateral flows through the circle of Willis in patients with cervical ICA stenosis.

2121 spin-labeled projection MR angiography of the carotid arteries

2121 spin-labeled projection MR angiography of the carotid arteries

Double‐subtraction maximum intensity projection MR angiography for detecting the artery of Adamkiewicz and differentiating it from the drainage vein

To evaluate the efficacy of double-subtraction magnetic resonance angiography (MRA) (subtraction of the subtracted venous phase image from the subtracted arterial dominant phase image) for depicting the artery of Adamkiewicz and differentiating it from the drainage vein. A total of 170 patients (123 men, 47 women; aged 17-84 years, mean = 67 years), with a thoracoabdominal vascular lesion underwent MRA for detection of the artery of Adamkiewicz. MRA was performed as a five-phase dynamic-enhanced three-dimensional (3D) fast spoiled gradient recalled acquisition in steady state (GRASS) sequence on a 1.5-T system, with double-dose bolus contrast and saline injection. The levels at which the artery of Adamkiewicz and drainage vein originated were determined. Signal intensities of the two vessels were measured with source images to assess the signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and necessity of the double-subtraction technique. The artery of Adamkiewicz was detected in 140 patients (82.4%). Branching occurred at levels T8-T12 on the left and T8-T11 on the right. An additional anterior radiculomedullary artery was detected in 18 patients. The drainage vein was detected in 133 patients (78.2%). It merged at the T9-L2 level on both sides. In six of the 133 patients (4.5%), the drainage vein branched upwardly. Neither SNR nor CNR differed significantly between the artery of Adamkiewicz and the drainage vein in the arterial phase; but on the subtraction image, signal intensity of the artery was higher than that of the drainage vein (P < 0.05). Double-subtraction MRA is useful for detecting the artery of Adamkiewicz when it is necessary to differentiate it from the drainage vein.

Diagnostic Accuracy of Time-Resolved 2D Projection MR Angiography for Symptomatic Infrapopliteal Arterial Occlusive Disease

Our objective was to evaluate the diagnostic accuracy of time-resolved 2D projection MR angiography in detecting calf and pedal artery occlusive disease. Time-resolved MR angiography of calf and pedal arteries was performed on 59 symptomatic legs of 52 patients using the head coil and bolus injections of 6 mL of gadolinium contrast medium. Selective X-ray digital subtraction angiography was performed within 30 days after MR angiography. Calf and pedal arteries were divided into 10 segments. X-ray digital subtraction angiography and MR angiography images were retrospectively interpreted by three expert observers, who graded segments as having no significant stenosis, significant stenosis (> 50%), or occlusion. The accuracy of MR angiography interpretations was compared with the accuracy of consensus X-ray digital subtraction angiography interpretations as the standard of reference. Arterial segments with discrepant grading on X-ray digital subtraction angiography and MR angiography were reviewed again to determine the reasons for disagreement. Arterial phase MR angiography images free of venous contamination were obtained in every case. The agreement between MR angiography and X-ray digital subtraction angiography in depicting infrapopliteal arterial disease was fair to good (kappa = 0.44-0.92). Overall sensitivity and specificity were 83% and 87%, respectively, for detecting significant stenosis of calf and pedal arteries and 86% and 93%, respectively, for detecting occlusions. Accuracy was higher in the larger vessels-for example, calf (84%) compared with foot (71%). In 21% (22/105) of the segments graded differently on MR angiography than on X-ray digital subtraction angiography, it was believed that MR angiography was more likely to be correct than X-ray digital subtraction angiography because of visualization of late-filling arteries on MR angiography that did not opacify on X-ray digital subtraction angiography. Time-resolved 2D projection MR angiography accurately evaluates calf and pedal arteries without degradation from venous contamination.

Soft tissue enhancement on time-resolved peripheral magnetic resonance angiography.

To evaluate the incidence and locations of soft tissue enhancement on time-resolved two-dimensional projection magnetic resonance angiography (MRA) of the calf and foot. Time-resolved two-dimensional projection MRA of the knee, calf, and foot, performed at 1.5 Tesla using the head coil, was retrospectively reviewed in 326 patients. Soft tissue enhancement of the foot was identified and graded by blinded review. Subsequently, patient medical records were reviewed to determine the presence or absence of diabetes, cellulitis, gangrene, and ulceration of the foot and presence of neuropathic joints. Enhancing spots were identified in 228 patients. For those feet without clinical abnormalities, diabetic patients had an average of 1.2 enhancing spots per foot, while nondiabetics had only 0.6 (P < 0.001). Higher-grade lesions were more prevalent in diabetics and in heavier patients. Of 64 patients with follow-up, 8 (13%) developed cellulitis (N = 4) or ulceration (N = 4) at the location of an enhancing spot, including 5 diabetic and 3 nondiabetic patients. Pedal soft tissue enhancement frequently occurs on time-resolved gadolinium (Gd):MRA of the feet. The etiology is uncertain, but the high frequency in diabetic patients and observation of progression to cellulitis/ulceration suggest this soft tissue enhancement may identify sites of subclinical pedal soft tissue injury.

Renal embolization: feasibility of magnetic resonance-guidance using active catheter tracking and intraarterial magnetic resonance angiography.

Magnetic resonance (MR)-guidance of endovascular interventions offers various advantages, including the absence of ionizing radiation, excellent soft tissue contrast, and multiplanar and functional imaging capabilities. The objective of this study was to assess the feasibility of MR-guided renal embolization using active catheter tracking with automatic slice positioning and intraarterial contrast-enhanced MR angiography (MRA). MR-guided embolization of 16 kidneys was attempted in 15 pigs using real-time tracking of active 5-Fr. catheters. Embolization was monitored by selective intraarterial projection MRA. Intraarterial three-dimensional (3D) MRA was used for the assessment of embolization results. Additional pathologic correlation was available in 2 animals. The image quality of intraarterial 3D contrast-enhanced-MRA was rated by an independent radiologist who was not involved in the animal experiments. Active catheter tracking with automatic slice positioning allowed reliable catheter guidance and catheterization of the renal artery in all animals. Embolization was successful in all kidneys (11 left, 5 right), as verified by intraarterial 3D contrast-enhanced MRA (ce-MRA) and/or pathology. The image quality of intraarterial 3D ce-MRA was rated excellent in 10 animals, moderate in 4 animals, and poor in 1 animal. Renal embolization using active catheter tracking and intraarterial ce-MRA is feasible. Selective intraarterial ce-MRA allows the assessment of blood supply and organ perfusion before, during, and after therapeutic interventions, thereby complementing MR-guided endovascular interventions.

Coronary MR imaging using free-breathing 3D steady-state free precession with radial k-space sampling.

To investigate the potential of free-breathing 3D steady-state free precession (SSFP) imaging with radial k-space sampling for coronary MR-angiography (MRA), coronary projection MR-angiography and coronary vessel wall imaging. A navigator-gated free-breathing T2-prepared 3D SSFP sequence (TR = 6.1 ms, TE = 3.0 ms, flip angle = 120 degrees, field-of-view = 360 mm(2)) with radial k-space sampling (384 radials) was implemented for coronary MRA. For projection coronary MRA, this sequence was combined with a 2D selective aortic spin tagging pulse. Coronary vessel wall imaging was performed using a high-resolution inversion-recovery black-blood 3D radial SSFP sequence (384 radials, TR = 5.3 ms, TE = 2.7 ms, flip angle = 55 degrees, reconstructed resolution 0.35 x 0.35 x 1.2 mm(3)) and a local re-inversion pulse. Six healthy volunteers (two for each sequence) were investigated. Motion artifact level was assessed by two radiologists. In coronary MRA, the coronary lumen was displayed with a high signal and high contrast to the surrounding lumen. Projection coronary MRA demonstrated selective visualization of the coronary lumen while surrounding tissue was almost completely suppressed. In coronary vessel wall imaging, the vessel wall was displayed with a high signal when compared to the blood pool and the surrounding tissue. No visible motion artifacts were seen. 3D radial SSFP imaging enables coronary MRA, coronary projection MRA and coronary vessel wall imaging with a low motion artifact level.

Head and neck vascular malformations: time-resolved MR projection angiography.

Extracranial vascular anomalies can be divided into haemangiomas and vascular malformations. The latter can be subdivided on the basis of the predominant type of vascular channels. Separation of high- and low-flow vascular malformations is of clinical importance. We report preliminary observations on time-resolved magnetic resonance projection angiography (MRPA) of vascular malformations of the head and neck. We examined eight patients with vascular anomalies of the head and neck. On MRPA the time between the early arterial phase and enhancement of the malformation could be used to distinguish high- and low-flow lesions. High-flow arteriovenous malformations showed early, intense enhancement. Venous malformations were either not visible on MRPA or showed late enhancement of veins. One patient was examined after embolisation of an arteriovenous fistula of the mandible. Normal MRPA was taken to indicate absence of a residual lesion.

Metallic renal artery MR imaging stent: artifact-free lumen visualization with projection and standard renal MR angiography.

A cardiac-triggered free-breathing three-dimensional (3D) balanced fast field-echo projection renal magnetic resonance (MR) angiographic sequence was investigated for in-stent lumen visualization of a dedicated metallic renal artery stent. Fourteen prototype stents were deployed in the renal arteries of six pigs (in two pigs, three stents were deployed). Projection renal MR angiography was compared with standard contrast material-enhanced 3D breath-hold MR angiography. Artifact-free in-stent lumen visualization was achieved with both projection MR angiography and contrast-enhanced MR angiography. These promising results warrant further studies for visualization of in-stent restenosis.

Dynamic contrast enhancement of paragangliomas of the head and neck: evaluation with time-resolved 2D MR projection angiography.

Our objective was to evaluate tumor hemodynamics of paragangliomas of the head and neck. A 2D magnetic resonance projection angiography (MRPA) protocol was developed. Six patients with histologically proven paragangliomas were included in the study. The sequence protocol and data post-processing procedure were optimized in view of a high temporal resolution and maximum contrast-to-noise ratio. Image-time series of two freely orientated slabs could be obtained. Correlation analysis was performed to generate selective arterial and venous weighted angiographic images. Glomus tumors showed a rapid and intense homogeneous enhancement following the intravenous administration of contrast material. The smallest tumors investigated measured 10 mm and could be visualized clearly. Time-resolved analysis of the tumor enhancement revealed an early bolus arrival within the vascular bed of the tumor and prolonged incomplete washout indicating blood pooling. The dynamic contrast enhancement of glomus tumors can be evaluated non-invasively with MRPA providing a high temporal resolution and high image quality. The characteristic contrast enhancement of glomus tumors can be helpful in the diagnostic workup of lesions that may mimic glomus tumors.

Renal arteries: navigator-gated balanced fast field-echo projection MR angiography with aortic spin labeling: initial experience.

A cardiac-triggered free-breathing three-dimensional balanced fast field-echo projection magnetic resonance (MR) angiographic sequence with a two-dimensional pencil-beam aortic labeling pulse was developed for the renal arteries. For data acquisition during free breathing in eight healthy adults and seven consecutive patients with renal artery disease, real-time navigator technology was implemented. This technique allows high-spatial-resolution and high-contrast renal MR angiography and visualization of renal artery stenosis without exogenous contrast agent or breath hold. Initial promising results warrant larger clinical studies.

Navigator-gated free-breathing 3D balanced FFE projection renal MRA: Comparison with contrast-enhanced breath-hold 3D MRA in a swine model.

A cardiac-triggered, free-breathing, 3D balanced FFE projection renal MR angiography (MRA) technique with a 2D pencil beam aortic labeling pulse for selective aortic spin tagging was developed. For respiratory motion artifact suppression during free breathing, a prospective real-time navigator was implemented for renal MRA. Images obtained with the new approach were compared with standard contrast-enhanced (CE) 3D breath-hold MRA in seven swine. Signal properties and vessel visualization were analyzed. With the presented technique, high-resolution, high-contrast renal projection MRA with superior vessel length visualization (including a greater visible number of distal branches of the renal arteries) compared to standard breath-hold CE-MRA was obtained. The present results warrant clinical studies in patients with renal artery disease.

Real-time projection MR angiography: feasibility study.

Intraarterial injections of small doses of gadopentetate dimeglumine were combined with a fast spoiled-gradient-echo magnetic resonance (MR) sequence to obtain real-time projection angiographic images of the rabbit aorta and canine coronary arteries. Arterial filling and washout, as well as venous and perfusion phases, were clearly displayed, demonstrating that arterial fluoroscopy in which an MR technique is used is feasible.

Display of MR angiograms: maximum intensity projection versus three-dimensional rendering

Objective: The purpose of this study is to clarify the most useful technique of MR imaging in demonstrating the collateral venous pathways due to portal hypertension. Subjects: Twenty-eight cirrhotic patients with collateral venous pathways due to portal hypertension and three patients without them were studied. We evaluated the detectability of collateral vessels of flow-enhanced transverse MR images by time of flight effect, projection MR angiography using the maximum intensity projection technique and three-dimensional (3D) computer graphic images, by using the arterial portography as the standard. Results: Flow-enhanced transverse MR images showed 98% of the collateral vessels detected by angiography, however, the connection of each vessel was obscure. Fully 81% of the collateral vessels were seen by projection MR angiography, and 98% of them by the 3D computer graphic images. Conclusion: The detectability of collateral vessels of 3D computer graphic imaging was better than that of the projection MR angiography and was as accurate as that of transverse MR imaging. 3D Computer graphic images provided complex anatomical information in a more easily understood fashion than either transverse MR images or projection MR angiography.

Human coronary arteries: projection angiograms reconstructed from breath-hold two-dimensional MR images.

The authors sought to render projection magnetic resonance (MR) angiograms depicting a substantial length of human coronary arteries from sequential breath-hold two-dimensional MR images. Tomographic images of the right and left anterior descending coronary arteries were collected with use of a segmented gradient-recalled sequence that incorporated fat suppression and prone positioning of the patient over a surface coil. After editing the images to eliminate overlapping chamber signals and after realigning the images, a maximum-intensity-projection algorithm was applied to create projection angiograms. For the 10 coronary arteries without severe narrowing, visualized length with projection MR angiography was 109 mm +/- 29 (mean +/- standard error of estimate) versus 121 mm +/- 29 with conventional coronary angiography (ranges, 62-147 mm and 70-180 mm, respectively). At conventional angiography linear regression indicated vessel length to be 1.03 times the length depicted at MR angiography with good correlation (r = .8). Results indicate good correlation between measurements of vessel length with both conventional and MR angiography.

5070876 Flow-independent magnetic resonance projection angiography

5070876 Flow-independent magnetic resonance projection angiography

Flow‐independent magnetic resonance projection angiography

The performance of current, flow-based sequences for imaging vasculature using MR is severely restricted in regions with inherently slow flow. We address this problem with a flow-independent imaging method. Specifically, we generate projection images of blood in the limbs while suppressing signal from all other tissues (primarily skeletal muscle, bone marrow, and subcutaneous fat) using a flow-compensated, water-selective, short TI inversion recovery sequence with a long echo time. We experimentally evaluate the effectiveness of this sequence and present in vivo results clearly demonstrating the method's potential.