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USPIO-enhanced MR angiography of arteriovenous fistulas in patients with renal failure.

ABSTRACT: To determine the feasibility of using ferumoxytol-enhanced magnetic resonance (MR) angiography to depict the vasculature of hemodialysis fistulas and improve image quality compared with nonenhanced time-of-flight (TOF) MR angiography.The study was institutional review board approved and was in compliance with HIPAA regulations. All participants provided written informed consent. TOF and first-pass ferumoxytol-enhanced MR angiography were performed in 10 patients with upper extremity autogenous fistulas. Ferumoxytol was administered as a bolus solution containing 430 μmol of elemental iron. A qualitative comparison was performed on maximum intensity projection images. Lumen depiction was evaluated by using a five-point scale. The uniformity of intraluminal signal intensity was measured as the ratio between the mean signal intensity of the entirety of the imaged fistula and its standard deviation. The contrast-to-noise ratio (CNR) between intraluminal signal and adjacent tissue was evaluated as a function of image acquisition time. Lumen depiction scores, luminal signal heterogeneity, and CNR efficiency were compared between TOF and ferumoxytol-enhanced MR angiography by using a Wilcoxon-Mann-Whitney test.Flow artifacts were greatly reduced by the use of ferumoxytol-enhanced MR angiography. Ferumoxytol-enhanced MR angiography had significantly better performance than TOF MR angiography as measured with the following: lumen depiction scores in all segments (mean, 4.7±0.1 [standard error of the mean]; vs 3.0±0.3 for arterial inflow, 4.1±0.3 vs 1.9±0.3 for arterial outflow, 3.7±0.3 vs 1.8±0.2 for anastomosis, and 4.5±0.2 vs 2.1±0.2 for venous outflow; P<.001), intraluminal signal homogeneity (0.3±0.02 vs 0.4±0.06, P=.005), and CNR efficiency in the venous outflow (5.1±0.6 vs 2.5±0.4, P=.01).This study demonstrates the feasibility of using ferumoxytol-enhanced MR angiography in imaging hemodialysis fistulas with consistently superior image quality compared with nonenhanced TOF MR angiography.

SUBMITTER: Sigovan M

PROVIDER: S-EPMC3480811 | biostudies-other | 2012 Nov

REPOSITORIES: biostudies-other

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Project description:ContextThe arteriovenous fistula is the preferred type of vascular access for hemodialysis because of lower thrombosis and infection rates and lower health care expenditures compared with synthetic grafts or central venous catheters. Early failure of fistulas due to thrombosis or inadequate maturation is a barrier to increasing the prevalence of fistulas among patients treated with hemodialysis. Small, inconclusive trials have suggested that antiplatelet agents may reduce thrombosis of new fistulas.ObjectiveTo determine whether clopidogrel reduces early failure of hemodialysis fistulas.Design, setting, and participantsRandomized, double-blind, placebo-controlled trial conducted at 9 US centers composed of academic and community nephrology practices in 2003-2007. Eight hundred seventy-seven participants with end-stage renal disease or advanced chronic kidney disease were followed up until 150 to 180 days after fistula creation or 30 days after initiation of dialysis, whichever occurred later.InterventionParticipants were randomly assigned to receive clopidogrel (300-mg loading dose followed by daily dose of 75 mg; n = 441) or placebo (n = 436) for 6 weeks starting within 1 day after fistula creation.Main outcome measuresThe primary outcome was fistula thrombosis, determined by physical examination at 6 weeks. The secondary outcome was failure of the fistula to become suitable for dialysis. Suitability was defined as use of the fistula at a dialysis machine blood pump rate of 300 mL/min or more during 8 of 12 dialysis sessions.ResultsEnrollment was stopped after 877 participants were randomized based on a stopping rule for intervention efficacy. Fistula thrombosis occurred in 53 (12.2%) participants assigned to clopidogrel compared with 84 (19.5%) participants assigned to placebo (relative risk, 0.63; 95% confidence interval, 0.46-0.97; P = .018). Failure to attain suitability for dialysis did not differ between the clopidogrel and placebo groups (61.8% vs 59.5%, respectively; relative risk, 1.05; 95% confidence interval, 0.94-1.17; P = .40).ConclusionClopidogrel reduces the frequency of early thrombosis of new arteriovenous fistulas but does not increase the proportion of fistulas that become suitable for dialysis. Trial Registration clinicaltrials.gov Identifier: NCT00067119.

Project description:Background and purposeThe diagnosis of spinal vascular malformations may be challenging on conventional MR imaging because neither the location of the signal abnormality in the spinal cord nor the level of the abnormal flow voids correlates with the level of the fistula. We conducted a retrospective evaluation of the utility of using a time-resolved imaging of contrast kinetics sequence in the diagnosis, characterization, and localization of spinal vascular malformations, comparing it with the criterion standard of spinal DSA.Materials and methodsFifty-five consecutive patients with a suspected diagnosis of spinal vascular malformation underwent time-resolved imaging of contrast kinetics followed by spinal DSA. All scans were performed on a 1.5T scanner by using a standard 8-channel spine coil and were reported by a neuroradiologist before the DSA was performed.ResultsForty-seven lesions were confirmed on time-resolved imaging of contrast kinetics and classified as spinal dural arteriovenous fistulas (n = 33, with 1 patient having a type Ib fistula), perimedullary spinal cord arteriovenous fistulas (n = 10), and intramedullary arteriovenous malformations (n = 3). One patient had an extradural spinal vascular malformation. Time-resolved imaging of contrast kinetics identified the location of the arterial feeder to within 1 vertebral level in 27/33 patients (81.8%) with spinal dural arteriovenous fistulas and correctly predicted the side in 22/33 (66.6%) patients. Perimedullary spinal cord arteriovenous fistulas were erroneously considered to represent spinal dural arteriovenous fistulas before spinal DSA. The anatomy of the arterial supply to intramedullary arteriovenous malformations was also poorly characterized on time-resolved contrast-enhanced MR angiography.ConclusionsIt has been our experience that time-resolved imaging of contrast kinetics is a useful confirmatory tool when a spinal vascular malformation is suspected on the basis of clinical and conventional MR imaging findings. As experience with the technique grows and sequences are refined, it may be possible to rely on time-resolved imaging of contrast kinetics as a screening tool for the diagnosis of spinal vascular malformations.

Project description:ObjectivesTo evaluate whether the signal intensity ratio (rSI) of the draining vein on silent MR angiography is correlated with arteriovenous (A-V) transit time on digital subtraction angiography (DSA), thereby identifying high-flow A-V shunt in brain arteriovenous malformation (BAVM), and to analyze whether the rSI and the characteristic of draining veins on silent MRA are associated with hemorrhage presentation.MethodsEighty-one draining veins of 46 participants with BAVM (mean age 33.2 ± 16.9 years) who underwent silent MRA and DSA were evaluated retrospectively. The correlation between the rSI of the draining vein on silent MRA and A-V transit time on DSA was examined. The AUC-ROC was obtained to evaluate the performance of the rSI in determining the presence of high-flow A-V shunt. The characteristics of draining veins with the maximum rSI (rSImax) were further compared between the hemorrhagic and non-hemorrhagic untreated BAVM.ResultsThe rSI of each draining vein on silent MRA was significantly correlated with A-V transit time from DSA (r = -0.81, p < .001). The AUC-ROC was 0.89 for using the rSI to determine the presence of high-flow A-V shunt. A cut-off rSI value of 1.09 yielded a sensitivity of 82.4% and a specificity of 82.8%. The draining vein with rSImax and no ectasia was significantly more observed in the hemorrhagic group (p = 0.045).ConclusionsThe rSI of the draining vein on silent MRA is significantly correlated with A-V transit time on DSA, and it can be used as an indicator of high-flow A-V shunt in BAVM.Key points• The signal intensity ratio (rSI) of the draining vein on silent MRA significantly correlated with arteriovenous (A-V) transit time of brain arteriovenous malformation (BAVM) on digital subtraction angiography (DSA). • The area under the receiver operating characteristic curve (AUC) was 0.89 for using the rSI of draining veins to determine high-flow A-V shunt. • Draining veins with maximum rSI and no ectasia were significantly more observed in the hemorrhagic group of BAVM (p = 0.045).

Project description:Purpose To assess the technical feasibility of the use of ferumoxytol-enhanced (FE) magnetic resonance (MR) angiography for vascular mapping before transcatheter aortic valve replacement in patients with renal impairment. Materials and Methods This was an institutional review board-approved and HIPAA-compliant study. FE MR angiography was performed at 3.0 T or 1.5 T. Unenhanced computed tomographic (CT) images were used to overlay vascular calcification on FE MR angiographic images as composite fused three-dimensional data. Image quality of the subclavian and aortoiliofemoral arterial tree and confidence in the assessment of calcification were evaluated by using a four-point scale (4 = excellent vascular definition or strong confidence). Signal intensity nonuniformity as reflected by the heterogeneity index (ratio between the mean standard deviation of luminal signal intensity and the mean luminal signal intensity), signal-to-noise ratio, and consistency of luminal diameter measurements were quantified. Findings at FE MR angiography were compared with pelvic angiograms. Results Twenty-six patients underwent FE MR angiography without adverse events. A total of 286 named vascular segments were scored. The image quality score was 4 for 99% (283 of 286) of the segments (κ = 0.9). There was moderate to strong confidence in the ability to assess vascular calcific morphology in all studies with complementary unenhanced CT. The steady-state luminal heterogeneity index was low, and signal-to-noise ratio was high. Interobserver luminal measurements were reliable (intraclass correlation coefficient, 0.98; 95% confidence interval: 0.98, 0.99). FE MR angiographic findings were consistent with correlative pelvic angiograms in all 16 patients for whom the latter were available. Conclusion In patients with renal impairment undergoing transcatheter aortic valve replacement, FE MR angiography is technically feasible and offers reliable vascular mapping without exposure to iodine- or gadolinium-based contrast agents. Thus, the total cumulative dose of iodine-based contrast material is minimized and the risk of acute nephropathy is reduced. © RSNA, 2017 Online supplemental material is available for this article.

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USPIO-enhanced MR angiography of arteriovenous fistulas in patients with renal failure.

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