Material-enhanced Magnetic Resonance Angiography Research Articles

Dynamic Contrast-enhanced MR Lymphangiography: Feasibility Study in Swine

To demonstrate the feasibility of dynamic four-dimensional ( 4D four-dimensional ) intranodal contrast material-enhanced magnetic resonance (MR) lymphangiography with inguinal lymph node injection of gadopentetate dimeglumine. All procedures were performed in accordance with the guidelines on the use of animals in research and were approved by the animal care and use committee. Five swine underwent nonenhanced MR lymphangiography with a heavily T2-weighted MR sequence, bilateral inguinal lymph node injection of 2 mL of undiluted gadopentetate at a rate of 1 mL/min, and 60 minutes of MR imaging with T1-weighted high-spatial- and high-temporal-resolution MR angiography. Images were reviewed by a radiologist with expertise in lymphatic imaging and a pediatric cardiac MR imaging specialist for visualization of the thoracic duct ( TD thoracic duct ). Categorical variables were compared by using the exact conditional McNemar test. A difference with a P value less than .05 was considered significant. The TD thoracic duct was visualized in three of the five animals (60%) on T2-weighted images. In contrast, the TD thoracic duct was visualized in all five of the animals (100%) after contrast agent injection (P = .25). The median time for flow of the contrast agent through the lymphatic system to the TD thoracic duct outlet was 244 seconds (range, 201-387 seconds). Enhancement was seen in the TD thoracic duct up to 1 hour after injection. All animals survived without any complications. Dynamic 4D four-dimensional contrast-enhanced MR lymphangiography with intranodal injection of gadopentetate dimeglumine is feasible, produces good images of the central lymphatic system, and demonstrates the time course of flow of contrast agent up the central lymphatic ducts. On the basis of the results of this initial animal experiment, it appears that dynamic 4D four-dimensional contrast-enhanced MR lymphangiography is potentially feasible and safe with commercially available contrast agents.

Time-of-Arrival Mapping at Three-dimensional Time-resolved Contrast-enhanced MR Angiography

This study was HIPAA compliant and institutional review board approved, and informed consent was obtained from all volunteers. The authors describe a method for generating a time-of-arrival (TOA) map of intravenously administered contrast material, as observed in a time series of three-dimensional (3D) contrast material-enhanced magnetic resonance (MR) angiograms. The method may enable visualization and interpretation, on one 3D image, of the temporal enhancement patterns that occur in the vasculature. Colorization of TOA values may further aid interpretation. The quality of the results depends not only on the adequacy of the frame rate, spatial resolution, and signal-to-noise ratio of the MR image acquisition method but also on the accuracy and clarity with which the leading edge of the contrast material bolus is depicted. The criteria for optimizing these parameters are described. The TOA mapping technique is demonstrated by using vascular studies of the hands, brain, and lower leg regions.

Ultrafast Whole-Body MR Angiography with Two-dimensional Parallel Imaging at 3.0 T: Feasibility Study

The study was approved by the local ethics committee, and informed consent was provided by all participants prior to the examination. The aim of the study was to assess the feasibility of whole-body three-dimensional (3D) contrast material-enhanced magnetic resonance (MR) angiography with parallel imaging in the phase- and section-encoding directions (ie, integrated parallel acquisition technique [iPAT(2); Siemens, Erlangen, Germany]) for all anatomic imaging stations in combination with a single injection of contrast material. Whole-body contrast-enhanced MR angiography was performed in 23 patients at 3.0 T. Images were evaluated by two independent observers for quality on a four-point scale (where a score of 1 indicated poor image quality and a score of 4, excellent image quality); signal-to-noise ratios (SNRs) and contrast-to-noise ratios (CNRs) were calculated for representative vessel regions in each station. Mean image quality scores were 3.13 +/- 1.15 (standard deviation) and 3.17 +/- 1.14 for observers 1 and 2, respectively (kappa = 0.81). Signal intensity measurements revealed mean SNR values between 36.2 +/- 8.0 and 56.2 +/- 17.7 and mean CNR values between 29.0 +/- 7.4 and 48.2 +/- 15.7. The data suggest that contrast-enhanced MR angiography with iPAT(2) is feasible for whole-body applications and allows acquisition of 3D data sets with adequate spatial resolution within short measurement times, facilitating a single injection of contrast material.

Will Inversion Recovery with On-Resonant Water Suppression Be Another Way to Routinely Exploit Off-Resonance Effects with MR Imaging?

In this issue of Radiology, Korosoglou et al evaluated the utility of inversion recovery with on-resonant water suppression (IRON) in combination with injection of the long-circulating monocrystalline iron oxide nanoparticle-47 for contrast material-enhanced magnetic resonance (MR) angiography. They found that IRON MR angiography in conjunction with superparamagnetic nanoparticle administration provided high intravascular contrast over a long time and without the need for image subtraction.

Isotropic High-Spatial-Resolution Contrast-enhanced 3.0-T MR Angiography in Patients Suspected of Having Renal Artery Stenosis

The purpose of this study was to prospectively evaluate the diagnostic performance of contrast material-enhanced magnetic resonance (MR) angiography performed at 3 T for assessment of renal artery stenosis (RAS) by using parallel acquisition techniques with high acceleration factors and with digital subtraction angiography (DSA) as the reference standard. The study was institutional review board approved, and written informed consent was obtained from all patients. Twenty-nine patients (18 men, 11 women; mean age, 57.1 years +/- 14.3 [standard deviation]) suspected of having RAS underwent MR angiography. Images were evaluated qualitatively and quantitatively. The interobserver variability, sensitivity, specificity, and positive and negative predictive values of 3-T MR angiography, as compared with DSA (performed in 15 patients), were calculated. All examinations yielded good or excellent image quality. The sensitivity and specificity of MR angiography in grading significant (>75%) stenosis were 94% and 96%, respectively. Owing to its high sensitivity, contrast-enhanced 3-T MR angiography can be used reliably to exclude RAS and can serve as a useful screening method in the diagnostic work-up of patients with arterial hypertension.

Cerebral Arteriovenous Malformation: Spetzler-Martin Classification at Subsecond-Temporal-Resolution Four-dimensional MR Angiography Compared with That at DSA

To prospectively test the hypothesis that subsecond-temporal-resolution four-dimensional (4D) contrast material-enhanced magnetic resonance (MR) angiography at 3.0 T enables the same Spetzler-Martin classification (nidus size, venous drainage, eloquence) of cerebral arteriovenous malformation (AVM) as that at digital subtraction angiography (DSA). Institutional ethics committee approval and written informed consent were obtained. In a prospective intraindividual comparative study, 18 consecutive patients with cerebral AVM (nine men, nine women; mean age, 41.9 years +/- 14.0 [standard deviation]; range, 23-69 years) were examined with 4D contrast-enhanced MR angiography and DSA. Four-dimensional contrast-enhanced MR angiography combined randomly segmented central k-space ordering, keyhole imaging, sensitivity encoding, and half-Fourier imaging, which yielded a total acceleration factor of 60. Fifty dynamic scans were obtained every 608 msec at an acquired spatial resolution of 1.1 x 1.4 x 1.1 mm. Four-dimensional contrast-enhanced MR angiograms were independently reviewed by one neuroradiologist and one neurosurgeon according to Spetzler-Martin classification, overall diagnostic quality, and level of confidence. Kendall W coefficients of concordance (K) were computed to compare reader assessment of image quality, level of confidence, and Spetzler-Martin classification by using 4D contrast-enhanced MR angiography and to compare Spetzler-Martin classification as determined with DSA with that at 4D contrast-enhanced MR angiography. Spetzler-Martin classification of cerebral AVM at 4D contrast-enhanced MR angiography and at DSA matched in 18 of 18 patients for both readers, which yielded 100% interobserver agreement (K = 1). Image quality of 4D contrast-enhanced MR angiography was judged to be at least adequate for diagnosis in all patients by both readers. In three of 18 patients, DSA depicted additional arterial feeders of cerebral AVM. Subsecond-temporal-resolution 4D contrast-enhanced MR angiography at 3.0 T had 100% agreement with DSA with regard to Spetzler-Martin classification of cerebral AVM. radiology.rsnajnls.org/cgi/content/full/2453061684/DC1.

Supraaortic Arteries: Contrast-enhanced MR Angiography at 3.0 T—Highly Accelerated Parallel Acquisition for Improved Spatial Resolution over an Extended Field of View

To prospectively use 3.0-T breath-hold high-spatial-resolution contrast material-enhanced magnetic resonance (MR) angiography with highly accelerated parallel acquisition to image the supraaortic arteries of patients suspected of having arterial occlusive disease. Institutional review board approval and written informed consent were obtained for this HIPAA-compliant study. Eighty patients (44 men, 36 women; age range, 44-90 years) underwent contrast-enhanced MR angiography of the head and neck at 3.0 T with an eight-channel neurovascular array coil. By applying a generalized autocalibrating partially parallel acquisition algorithm with an acceleration factor of four, high-spatial-resolution (0.7 x 0.7 x 0.9 mm = 0.44-mm(3) voxels) three-dimensional contrast-enhanced MR angiography was performed during a 20-second breath hold. Two neuroradiologists evaluated vascular image quality and arterial stenoses. Interobserver variability was tested with the kappa coefficient. Quantitation of stenosis at MR angiography was compared with that at digital subtraction angiography (DSA) (n = 13) and computed tomographic (CT) angiography (n = 12) with Spearman rank correlation coefficient (R(s)). Arterial stenoses were detected with contrast-enhanced MR angiography in 208 (reader 1) and 218 (reader 2) segments, with excellent interobserver agreement (kappa = 0.80). There was a significant correlation between contrast-enhanced MR angiography and CT angiography (R(s) = 0.95, reader 1; R(s) = 0.87, reader 2) and between contrast-enhanced MR angiography and DSA (R(s) = 0.94, reader 1; R(s) = 0.92, reader 2) for the degree of stenosis. Sensitivity and specificity of contrast-enhanced MR angiography for detection of arterial stenoses greater than 50% were 94% and 98% for reader 1 and 100% and 98% for reader 2, with DSA as the standard of reference. Vascular image quality was sufficient for diagnosis or excellent for 97% of arterial segments evaluated. By using highly accelerated parallel acquisition, the described 3.0-T contrast-enhanced MR angiographic protocol enabled visualization and characterization of the majority of supraaortic arteries, with diagnostic or excellent image quality (97% of arterial segments) and diagnostic values comparable with those obtained by using CT angiography and DSA for detection of arterial stenoses.

Fibromuscular Dysplasia of the Main Renal Arteries: Comparison of Contrast-enhanced MR Angiography with Digital Subtraction Angiography

To retrospectively evaluate the sensitivity and specificity of contrast material-enhanced magnetic resonance (MR) angiography by using digital subtraction angiography as the reference standard in patients with hypertension and renal artery fibromuscular dysplasia (FMD). Institutional review board approval was obtained, with waiver of informed consent. The results of renal contrast-enhanced MR angiography were retrospectively analyzed in 25 patients with hypertension (24 women, one man; mean age, 48 years +/- 19 [standard deviation]; age range, 18-72 years) who had FMD diagnosed on the basis of clinical and angiographic features. All examinations were performed at 1.5 T. Results were analyzed by two readers, and a third reader established a consensus in case of discrepancy. Sensitivity, specificity, and 95% confidence intervals (CIs) were calculated for FMD and for each possible type of FMD lesion ("string of pearls" appearance, stenosis, and aneurysm). A linear-weighted kappa statistic was calculated to determine agreement between digital subtraction angiography and contrast-enhanced MR angiography for the diagnosis of FMD and to determine inter- and intraobserver agreement regarding FMD diagnosis. Fifty main renal arteries were analyzed, 35 of which demonstrated abnormal arteriographic features of FMD (stenosis, 22 arteries; string of pearls, 21 arteries; and aneurysm, four arteries). The sensitivity and specificity of contrast-enhanced MR angiography for the diagnosis of FMD were 97% (95% CI: 83%, 100%) and 93% (95% CI: 66%, 100%), respectively. Sensitivity was 68% (95% CI: 83%, 100%), 95% (95% CI: 74%, 100%), and 100% (95% CI: 40%, 100%) for the diagnosis of stenosis, string of pearls, and aneurysm, respectively. Linear-weighted kappa statistics for inter- and intraobserver agreement regarding FMD diagnosis were 0.63 and 0.92, respectively. In patients with renal FMD, contrast-enhanced MR angiography can reliably facilitate diagnosis by demonstrating characteristic lesions.

Uterine Fibroids: Contrast-enhanced MR Angiography to Predict Ovarian Artery Supply—Initial Experience

To prospectively evaluate the diagnostic performance of contrast material-enhanced magnetic resonance (MR) angiography in helping predict ovarian artery supply of uterine fibroids by using postembolization conventional aortography as the reference standard. The protocol for the study was approved by the institutional review board, and each patient gave informed consent. Ninety consecutive women (mean age, 42.5 years; range, 33-63 years) underwent MR angiography before uterine artery embolization (UAE). The number and origin of the ovarian arteries were determined. Ovarian artery supply of fibroids was graded as very unlikely, possible, or very likely by using a scoring system based on a combination of MR angiographic findings. MR angiographic results were compared with those of conventional aortography performed after UAE in all patients and followed by selective angiography in case of a suspected ovarian artery supply of fibroids. Analysis of the association between MR angiographic grading and conventional angiography as the standard of reference was performed with a chi(2) trend test. Sensitivity and specificity, including exact 95% confidence intervals (CIs), of MR angiography were determined. MR angiography depicted 18 ovarian arteries (four bilateral, 10 unilateral), one with an atypical origin. Five ovarian arteries were classified as very likely; three, as possible; and 10, as very unlikely sources of arterial fibroid supply. Seven (39%) of 18 ovarian arteries detected at MR angiography were visible at conventional aortography. Fibroid supply was verified at selective angiography in five ovarian arteries in five (6%) of 90 patients. There was a strong association between MR angiographic grading and the results of conventional angiography (P = .002). Sensitivity of MR angiography in depicting ovarian artery supply (grade, possible or very likely) was 100% (five of five, 95% CI: 48%; 100%) and specificity was 77% (10 of 13, 95% CI: 46%; 95%). Contrast-enhanced MR angiography can help predict ovarian artery supply of uterine fibroids.

Pulmonary Circulation: Contrast-enhanced 3.0-T MR Angiography—Initial Results

To prospectively evaluate the technical feasibility of both high-spatial-resolution and time-resolved contrast material-enhanced magnetic resonance (MR) angiography of the pulmonary circulation at 3.0 T. All examinations were HIPAA compliant. After institutional review board approval and written informed consent, time-resolved and high-spatial-resolution three-dimensional contrast-enhanced MR angiography of the pulmonary circulation was performed with a 3.0-T MR system in 31 adults (13 men, 18 women; age range, 29-87 years old): 22 volunteers and nine patients (two with mediastinal masses, seven with pulmonary arterial hypertension [PAH]). The image quality of pulmonary arterial branches and parenchymal enhancement conspicuity were evaluated independently by two radiologists. The signal-to-noise ratio and quantitative analysis of perfusion parameters was performed. Statistical analysis of data was performed by using Wilcoxon rank sum test and two-sample Student t test, and interobserver variability was tested with kappa coefficient. Visualization up to fourth-order pulmonary arterial branches was observed on time-resolved MR angiograms and that up to fifth-order branches was observed on high-spatial-resolution MR angiograms, with diagnostic-quality blood vessel definition and good interobserver agreement. Evaluation of parenchymal enhancement and semiquantitative analysis of perfusion parameters yielded dynamic information in all subjects. Comparative analysis of definition scores for fourth- and fifth-order pulmonary arterial branches, parenchymal enhancement, the time lag between the pulmonary arterial and parenchymal enhancement, and all of the calculated perfusion indices in patients with PAH showed statistically significant differences from volunteers (P < .05). Three-dimensional contrast-enhanced MR angiography of the pulmonary circulation was feasible at 3.0 T and provided high vascular morphologic detail and dynamic functional information. Clearly detectable abnormalities were present in patients with PAH.

Contrast-enhanced MR Angiography of the Peripheral Vasculature with a Continuously Moving Table and Modified Elliptical Centric Acquisition

This study was approved by the institutional review board and was HIPAA compliant. All subjects provided written informed consent, and subject confidentiality was protected. The purpose of this study was to prospectively evaluate the feasibility of integrating a modified elliptical centric (EC) acquisition with a continuously moving table technique to acquire high-spatial-resolution contrast material-enhanced magnetic resonance (MR) angiograms of the peripheral vasculature. Incorporation of two-dimensional homodyne reconstruction modified the EC view order, allowing improved spatial resolution per unit time while retaining the advantage of venous suppression intrinsic to the EC technique. Spatial resolution was dynamically improved when the table reached the distal-most station. The modified view order provided improved spatial resolution in phantom examinations compared with that in standard examinations. Peripheral MR angiograms were generated in a group of 13 volunteers (eight women; five men; age range, 51-72 years; mean age, 58.5 years +/- 7.9 [standard deviation]) at 1.5 T. Four arterial regions were evaluated on a five-point scale (scores ranged from 0 to 4; a score of 4 was considered excellent); venous suppression was also evaluated. The mean arterial scores exceeded 3.0 for all regions. There was no venous signal or only superficial venous signal in 10 of the 13 cases.

Imaging Peripheral Arterial Disease: A Randomized Controlled Trial Comparing Contrast-enhanced MR Angiography and Multi–Detector Row CT Angiography

To prospectively evaluate clinical utility, patient outcomes, and costs of contrast material-enhanced magnetic resonance (MR) angiography compared with multi-detector row computed tomographic (CT) angiography for initial imaging in the diagnostic work-up of patients with peripheral arterial disease. Institutional review board approval and informed consent were obtained. Patients referred for diagnostic imaging work-up to evaluate the feasibility of a revascularization procedure were randomly assigned to undergo either MR angiography or CT angiography. Clinical utility was assessed with therapeutic confidence (scale of 0-10) at initial imaging and with the need for additional imaging. Patient outcomes included ankle-brachial index, maximum walking distance, change in clinical status, and health-related quality of life. Actual diagnostic and therapeutic costs were calculated from the hospital perspective. Differences between group means were calculated with unpaired t tests and 95% confidence intervals. A total of 157 consecutive patients with peripheral arterial disease were prospectively randomized to undergo MR angiography (51 men, 27 women; mean age, 63 years) or CT angiography (50 men, 29 women; mean age, 64 years). For one of the 78 patients in the MR group, no data were available. Mean confidence for MR angiography (7.7) was slightly lower than that for CT angiography (8.0, P = .8). During 6 months of follow-up, 13 patients in the MR group compared with 10 patients in the CT group underwent additional vascular imaging (P = .5). Although not statistically significant, there was a consistent trend of less improvement in the MR group across all patient outcomes. The average cost for diagnostic imaging was 359 ($438) higher in the MR group than in the CT group (95% confidence interval: 209, 511 [$255, $623]; P < .001). Therapeutic costs were higher in the MR group, but the difference was not significant. The results suggest that CT angiography has some advantages over MR angiography in the initial evaluation of peripheral arterial disease.

Contrast-enhanced MR Angiography for Evaluation of Vascular Complications of the Pancreatic Transplant

Vascular complications are a common cause of postoperative dysfunction in a pancreatic transplant. Coronal three-dimensional (3D) contrast material-enhanced magnetic resonance (MR) angiography performed with high spatial and temporal resolution is a safe and effective method of assessing these vascular complications. A study was performed of selected patients who had undergone MR imaging and MR angiography during the past 6 years for evaluation of graft dysfunction following pancreatic transplantation. Thrombosis within peripheral stump vessels involving either the arterial or venous segments was a commonly observed vascular complication. Isolated distal arterial stump thrombi are incidental findings that may not require treatment, whereas venous stump thrombi may become clinically significant in patients in whom clot propagates proximally to occlude draining pancreatic veins and are typically treated with anticoagulants or thrombectomy. Because it is difficult to predict which patients will experience clot propagation, patients with venous stump thrombi may be followed up with serial imaging regardless of treatment initiated at presentation. Although susceptibility artifacts can mimic anastomotic stenoses at MR imaging, careful attention to the multiple sequences used allows recognition of this potential pitfall. Contrast-enhanced 3D MR angiography is an accurate method of evaluating the vascular anatomy of pancreatic transplants and can help guide clinical management.

In Vivo Evaluation of the Carotid Wallstent on Three-dimensional Contrast Material–enhanced MR Angiography: Influence of Artifacts on the Visibility of Stent Lumina

Contrast material-enhanced magnetic resonance (MR) angiography is increasingly used in postinterventional imaging after implantation of endovascular stents. The main limitations are stent-related artifacts compromising the visibility of the stent lumen. The aim of this in vivo study is the evaluation of contrast-enhanced MR angiography imaging characteristics of the carotid Wallstent. The carotid arteries of 29 patients were examined with contrast-enhanced MR angiography 3-6 days and/or 7-23 months after implantation of a carotid Wallstent into the internal carotid artery. Images were evaluated with regard to the diameter and signal intensity (SI) of the visible stent lumen. Digital subtraction angiography (DSA) was used as the standard of reference. Stent-related artifacts on contrast-enhanced MR angiography caused an artificial lumen narrowing and a reduction of the SI within the stent. Artifacts were pronounced on imaging 3-6 days after stent implantation, but 68% of stents imaged 7-23 months after stent implantation presented with a significantly decreased artificial signal reduction and an improved visibility of the stent lumen. The results of this study indicate that a reliable evaluation of the stent lumen is limited as a result of an artificial decrease of the SI inside the stent. However, in follow-up examinations 7-23 months after stent implantation, visibility of the stent lumen was improved and diagnostic reliability of contrast-enhanced MR angiography was markedly increased. A probable explanation for this phenomenon might be the formation of a neointimal layer covering the stent struts and thereby reducing stent-related artifacts.

Subclavian Steal Syndrome: Diagnosis with Perfusion Metrics from Contrast-enhanced MR Angiographic Bolus-timing Examination—Initial Experience

To retrospectively determine whether differential temporal changes in signal intensity of the vertebral arteries, measured at a bolus-timing examination with a test dose of a gadolinium-based contrast agent, are present in patients with subclavian steal syndrome. Institutional review board exemption was obtained, and informed consent was not required for this retrospective study. The study complied with the Health Insurance Portability and Accountability Act. Twenty-five patients with known or clinically suspected atherosclerotic disease of the aortic arch and branch vessels underwent breath-hold contrast material-enhanced magnetic resonance (MR) angiography with circulation time derived from a timing examination by using a test bolus of a gadolinium-based contrast agent. Eight patients (three men and five women aged 54-80 years; mean, 70 years) had subclavian stenosis or occlusion with retrograde vertebral artery flow confirmed with time-of-flight MR angiography, nine patients (eight men and one woman aged 31-91 years; mean, 70 years) had mild to severe ostial stenosis of a single vertebral artery, and eight patients (including four men and four women aged 53-86 years; mean, 73 years) had normal vertebral arteries. The difference in time to peak signal intensity between the right and left vertebral arteries was compared among the three groups by using Fisher exact and Cochran-Mantel-Haenszel tests. The delay in peak enhancement in the ipsilateral vertebral artery ranged from 2 to 4 seconds (mean, 2.5 seconds) in all eight patients with subclavian steal syndrome. In eight of nine patients with ostial vertebral artery stenosis and eight controls, both vertebral arteries filled simultaneously. The presence of unilateral delayed vertebral artery enhancement was significantly associated with retrograde flow in patients with subclavian steal syndrome, compared with patients with normal flow (P < .01) and those with ostial vertebral artery stenosis (P < .01). A bolus-timing examination performed with a test bolus of the gadolinium-based contrast agent via the neck vessels that demonstrates at least a 2-second delay in peak contrast enhancement in the right or left vertebral arteries may, in the appropriate clinical setting, indicate subclavian steal syndrome.

Contrast-enhanced MR Angiography of Peripheral Arteries including Pedal Vessels at 1.0 T: Feasibility Study with Dedicated Peripheral Angiography Coil

To prospectively determine feasibility of contrast material-enhanced magnetic resonance (MR) angiography of the peripheral arteries from distal aorta to pedal arteries with a 1.0-T system and a dedicated phased-array coil. Twenty-seven patients with peripheral arteriosclerotic occlusive disease underwent contrast-enhanced MR angiography with an automatic moving-table technique. In addition, lower-leg and pedal arteries were examined without table movement (hybrid technique). Two radiologists independently reviewed MR angiograms to assess image quality and grade stenosis in 13 segments per leg. Each was blinded to patients' clinical data. Twenty-five of the patients also underwent conventional angiography. Stenosis grade at conventional angiography was assessed by two radiologists in consensus. Interobserver variability for stenosis grade at MR angiography was calculated with Cohen kappa test. Specificity and sensitivity of MR angiography in detection of stenosis of more than 50% and occlusion were calculated for both observers. The study was approved by the local ethics committee. In 14 of the 27 patients, hybrid technique was superior to moving-table technique because there was less venous overlap (11 patients), fewer motion artifacts (one patient), or both (two patients). In nine patients, there was no difference between techniques; in four patients, moving-table technique was superior. Stenosis grade was analyzed in 698 segments with MR angiography and in 638 segments with both conventional and MR angiography. Kappa analysis of interobserver agreement with MR angiography yielded a score of 0.84. For the 638 segments evaluated with both conventional and MR angiography, observers 1 and 2 assigned same grade of stenosis with both modalities in 558 and 555 segments, respectively. Sensitivity for stenoses greater than 50% and occlusion was 94.4% and 91.1% for observers 1 and 2, respectively, and specificity was 90.6% and 91.3%. More distal runoff vessels were shown with MR angiography in seven cases and with conventional angiography in two cases. Contrast-enhanced MR angiography of the peripheral vessels with a 1.0-T system and dedicated peripheral angiography coil is feasible, and in some cases, it provides additional information compared with conventional angiography.

Stenosis Detection with MR Angiography and Digital Subtraction Angiography in Dysfunctional Hemodialysis Access Fistulas and Grafts

To prospectively assess three-dimensional contrast material-enhanced magnetic resonance (MR) angiography for stenosis depiction in malfunctioning hemodialysis arteriovenous fistulas (AVFs) and grafts (AVGs), as compared with digital subtraction angiography (DSA). Ethical review board approval and written informed consent were obtained. MR angiography and DSA were performed in 51 dysfunctional hemodialysis fistulas and grafts in 48 consecutive patients. Vascular tree of accesses was divided into between three and eight segments depending on access type (AVF or AVG) and length of venous outflow. Images obtained with MR and DSA were interpreted by two MR radiologists and two interventional radiologists, respectively, who were blinded to information from each other and other studies. DSA was reference standard for stenosis detection. Sensitivity, specificity, and predictive values with 95% confidence intervals (CIs) of contrast-enhanced MR in detection of vascular segments containing hemodynamically significant (> or =50%) stenosis were calculated. Linear-weighted kappa statistic was calculated for contrast-enhanced MR and DSA to determine interobserver agreement regarding stenosis detection. A total of 282 vascular segments were evaluated. Contrast-enhanced MR depicted three false-positive stenoses and all but two of 70 significant stenoses depicted with DSA. Sensitivity, specificity, and positive and negative predictive values of MR in detection of vessel segments with significant stenoses were 97% (95% CI: 90%, 99%), 99% (95% CI: 96%, 100%), 96% (95% CI: 88%, 99%), and 99% (95% CI: 97%, 100%), respectively. MR demonstrated significant stenosis in four of five nondiagnostic DSA segments, whereas DSA showed no significant stenosis in four nondiagnostic MR segments. Linear-weighted kappa statistic for interobserver agreement regarding stenosis detection was 0.92 (95% CI: 0.89, 0.95) for MR and 0.95 (95% CI: 0.92, 0.97) for DSA. MR angiography depicts stenoses in dysfunctional hemodialysis accesses but has limited clinical value as result of current inability to perform MR-guided access interventions after stenosis detection. MR of dysfunctional access should be considered only if nondiagnostic vascular segment is present at DSA.

Contrast-enhanced MR Angiography of the Renal Arteries: Blinded Multicenter Crossover Comparison of Gadobenate Dimeglumine and Gadopentetate Dimeglumine

To prospectively and intraindividually compare 0.1 mmol/kg gadobenate dimeglumine with 0.2 mmol/kg gadopentetate dimeglumine for contrast material-enhanced magnetic resonance (MR) angiography of the renal arteries. Institutional review board approval was granted by each of three participating centers. The study accorded with international standards for good clinical practice and Declaration of Helsinki and subsequent amendments. Patients gave written informed consent before enrollment. Patients (n = 34) underwent two MR angiographic examinations more than 48 hours but less than 12 days apart. Gadobenate dimeglumine followed by gadopentetate dimeglumine was administered in 18 patients; the order of administration was reversed in 16 patients. A 1.5-T MR imager was used with a phase-encoded three-dimensional spoiled breath-hold pulse sequence. Two blinded independent readers qualitatively assessed randomized subtracted maximum intensity projection images. A three-point scale for diagnostic quality (0, poor; 1a or 1p, moderate; and 2a or 2p, adequate [a and p refer, respectively, to absence and presence of vascular lesions]) was used to score each of nine segments of the abdominal aorta and both renal arteries (possible overall score, 18). Quantitative assessment (vessel signal-to-noise ratio [SNR], vessel-muscle contrast-to-noise ratio [CNR]) of source images was performed for regions of interest in supra-, juxta-, and infrarenal aorta segments and psoas muscle. Data were tested with analysis of variance for two-period crossover design. Interreader agreement was evaluated with Cohen kappa statistics. No difference in mean image quality between the two contrast agents was observed; scores for gadobenate dimeglumine and gadopentetate dimeglumine were 15.15 and 15.23 for reader 1 and 16.77 and 17.01 for reader 2. The order of contrast material administration likewise produced no quality differences: readers 1 and 2 reported scores of 14.4 +/- 4.2 (standard deviation) and 16.7 +/- 2.3, respectively, when gadobenate dimeglumine was given first, and 15.2 +/- 1.8 and 16.6 +/- 1.6, respectively, when gadopentetate dimeglumine was given first. Results of quantitative evaluation showed increasing SNR and CNR with gadobenate dimeglumine in segments at progressively lower levels of the aorta, but increases in SNR and CNR at the infrarenal aorta (48.3 vs 40.6 and 44.2 vs 36.4, respectively) were not significant (P = .05 for both). Gadobenate dimeglumine at a dose of 0.1 mmol/kg is comparable to gadopentetate dimeglumine at 0.2 mmol/kg for contrast-enhanced renal MR angiography.

Preoperative Evaluation of the Entire Hepatic Vasculature in Living Liver Donors with Use of Contrast-enhanced MR Angiography and True Fast Imaging with Steady-state Precession

To preoperatively assess the entire hepatic vasculature in living related liver donors with use of a combination of contrast material-enhanced magnetic resonance (MR) angiography and true fast imaging with steady-state precession (FISP). Twenty-five living potential liver donors were examined preoperatively on a 1.5T Siemens Sonata system. Twenty-four underwent surgery and two had catheter angiography performed to delineate complex anatomy. Contiguous 5-mm-thick, sub-second true FISP images of the liver were initially obtained during breath-holding in axial and coronal planes (repetition time [TR]/echo time [TE], 3.2/1.6; flip angle, 70 degrees ). MR angiography was performed with use of a three-dimensional (3D) gradient-echo fast low-angle shot (FLASH) pulse sequence (TR/TE, 3.0/1.2; flip angle, 25 degrees ), with 40 mL of Gadolinium DTPA injected at a rate of 2 mL/sec. One precontrast and two postcontrast coronal 3D volumes were acquired, each in a 20-second breath-hold, and two subtracted 3D sets were calculated. Arterial anatomy was assessed with use of maximum-intensity projection, volume rendering, and multiplanar reformatting algorithms. Hepatic and portal venous anatomy was evaluated with use of the true FISP images and the venous phase of the MR angiogram. Visualization of hepatic arterial branches was noted. Visualization of portal vein branches was scored on a scale of 0-5. The presence of anatomic variants was noted. Vascular anatomy was confirmed at the time of surgery and at catheter angiography. Segmental branch vessels were visualized on MR angiography in the majority of cases. The segment four branch was identified in 96% patients. Variant arterial anatomy was seen in 50% of patients. MR angiography detected 10 of 11 arterial variants found at surgery and angiography. Visualization of portal vein branches was generally higher with true FISP compared to MR angiography. Twenty-four percent of patients had variant portal venous anatomy. Caudal hepatic veins were identified in 60% of patients, of which eight were significant (>5 mm). Hepatic and portal venous anatomy was accurately predicted by true FISP and MR angiography in all patients who went on to undergo surgery. Preoperative imaging with use of a combination of contrast-enhanced MR angiography and true FISP provides a comprehensive assessment of the entire hepatic vasculature in living liver donors.

Failing hemodialysis access grafts: evaluation of complete vascular tree with 3D contrast-enhanced MR angiography with high spatial resolution: initial results in 10 patients.

Ten patients with failing hemodialysis access underwent contrast material-enhanced magnetic resonance (MR) angiography within 7 days before digital subtraction angiography (DSA). MR angiography was performed at 1.5 T by using a multistation multiinjection three-dimensional technique, and contrast material was injected via intravenous cannula. In all patients, MR angiographic images displayed the complete arterial inflow tract from the subclavian artery and access proper. The complete venous outflow tract up to the superior caval vein could be evaluated in all but one patient. DSA showed hemodynamically significant stenoses in 13 segments. MR angiography depicted all 13 stenoses and two false-positive findings, resulting in sensitivity of 100% and specificity of 94%.