Magnetic resonance angiography as a technique for the visualization of hemodialysis shunts

Magnetic Resonance Techniques in Hemodialysis access Management

In this review we describe current applications and future perspectives of MR angiography, MR flow quantification, and interventional MRI in hemodialysis access management. Each section starts with a brief overview of the main techniques that are currently available or under development. This is followed by a survey of the pertinent literature. Each section concludes with a discussion of the reported findings and an indication of research opportunities.

Multi-Slice Computed Tomographic Angiography for Stenosis Detection in Forearm Hemodialysis Arteriovenous Fistulas

Purpose

A method of diagnosing the extent and severity of arteriovenous fistula (AVF) stenoses is multi-slice computed tomographic angiography (MS-CTA). The aim of this prospective study was to assess the accuracy of MS-CTA for the detection and grading of stenoses in AVF in comparison to digital subtraction angiography (DSA), which was used as the gold standard of reference.

Methods

Fifteen hemodialysis (HD) patients with dysfunctioning forearm AVF were included. These AVFs were evaluated by both DSA and MS-CTA and were read in a prospective, blinded manner by two radiologists experienced in vascular imaging.

Results

ROC analysis revealed areas under the curve of 0.90 ± 0.07 for observer I and 0.87 ± 0.08 for observer II at a stenosis cut-off level of ≥50% diameter reduction. The combined results for MS-CTA showed sensitivity, specificity and positive and negative predictive values of 82%, 98%, 82% and 98% for stenoses ≥50% and 71%, 99%, 77% and 98% for stenoses ≥75%. Inter-observer agreement for the detection of stenoses ≥50% diameter reduction was 0.70 and 1.0, for MS-CTA and DSA, respectively.

Conclusion

MS-CTA can provide good visualization of forearm HD access AVF and has moderate sensitivity, but high specificity for the detection of flow-limiting stenoses.

Series of Noncontrast Time-of-Flight Magnetic Resonance Angiographies to Identify Problems with Arteriovenous Fistula Maturation

BACKGROUND

Successful maturation of arteriovenous fistulas (AVFs) remains a challenge for those managing patients with end-stage renal disease. Time-of-flight magnetic resonance angiography (TOF-MR) can be used to evaluate AVFs without the risk of radiation exposure, intravenous contrast, or reliance on the operator-dependent modality of color Doppler ultrasonography (CDUS). The objective of our study was to assess the utility of TOF-MR in the evaluation of nonmaturing AVFs and to identify the best clinical situations to use this technology.

METHODS

Consecutive patients with abnormal findings on CDUS or physical examination after AVF creation underwent 3-dimensional (3D) TOF-MR. Imaging was performed at 3 T with a scan acquisition time of approximately 15 min. The technique was similar to head and neck magnetic resonance angiography (MRA), except presaturation bands were not used, thereby allowing simultaneous visualization of both arterial and venous flow. A total of 19 TOF-MR studies were performed.

RESULTS

Nineteen patients underwent imaging and were the focus of this study. Seventeen of 19 TOF-MR studies were of diagnostic quality and yielded findings which enabled the vascular surgeon to take corrective measures. Findings included inflow stenosis, anastomotic narrowing, venous outflow stenosis, and hemodynamically significant venous tributaries. Twelve of 17 patients required conventional digital subtraction angiography (DSA). The congruence rate between TOF-MR and DSA was 83.3%. Four patients (21%) avoided DSA and went directly to definitive surgical treatment including branch ligation (3) or new access (1).

CONCLUSIONS

This is the first report in the literature of successful implementation of 3D TOF-MR to assist in identifying AVF maturation problems. This unique noninvasive imaging modality provides actionable images without contrast or radiation exposure and can obviate the need for invasive diagnostic procedures or provide an anatomic map for planning corrective intervention.

MDCT angiography with 3D image reconstructions in the evaluation of failing arteriovenous fistulas and grafts in hemodialysis patients

BACKGROUND

Arteriovenous fistulas and grafts are the methods of choice for vascular access in renal failure patients in need of hemodialysis. Their major complication, however, is stenosis, which might lead to thrombosis.

PURPOSE

To demonstrate the usefulness of 16-MDCTA with 3D image reconstructions, in long-term hemodialysis patients with dysfunctional arteriovenous fistulas and grafts (AVF and AVG).

MATERIAL AND METHODS

During a 17-month period, 31 patients with dysfunctional AVF and AVG (24 AVF and seven AVG) were examined with MDCTA with 3D image postprocessing. Parameters such as comprehension of the anatomy, quality of contrast enhancement, and pathological vascular changes were measured. DSA was then performed in 24 patients.

RESULTS

MDCTA illustrated the anatomy of the AVF/AVG and the entire vascular tree to the heart, in a detailed and comprehensive manner in 93.5% of the evaluated segments, and depicted pathology of AVF/AVG or pathology of the associated vasculature. MDCTA demonstrated a total of 38 significant stenoses in 25 patients. DSA verified 37 stenoses in 24 patients and demonstrated two additional stenoses. MDCTA had thus a sensitivity of 95%. All 24 patients were treated with percutaneous transluminal angioplasty (PTA) with good technical results.

CONCLUSION

MDCTA with 3D reconstructions of dysfunctioning AVFs and AVGs in hemodialysis patients is an accurate and reliable diagnostic method helping customize future intervention.

MDCT angiography for evaluation of the complete vascular tree of hemodialysis fistulas

OBJECTIVE

The purpose of our study was to assess the clinical feasibility of MDCT angiography for evaluating hemodialysis arteriovenous fistulas (AVFs).

MATERIALS AND METHODS

MDCT angiography of the complete vascular trees of 36 failing AVFs or AVF-related complications (20 native and 16 polytetrafluoroethylene graft AVFs) was reviewed. The numbers and degrees of stenoses at the anastomoses, graft loops, and draining and central veins and the presence of aneurysms or thrombosis were recorded. Wilcoxon's signed rank test was used to compare the findings of MDCT angiography with those of digital subtraction angiography (DSA) (n = 10), surgery (n = 22), or both (n = 4) performed within 2-6 days. Kappa statistics were used to correlate the clinical feasibility of MDCT angiography assessed by two reviewers.

RESULTS

Among the 14 AVFs examined with both MDCT angiography and DSA, no significant difference was seen in the detection and grading (p = 0.317 to > 0.999) of stenoses at various segments of the entire vascular tree. Among the 36 AVFs examined, MDCT angiography also showed no significant difference from DSA or surgery in revealing vascular stenoses, aneurysms, and thromboses from the supplying artery to central veins (p = 0.317 to > 0.999). Overall, the sensitivity, specificity, positive and negative predictive values, and accuracy of MDCT angiography in lesion detection were 98.7%, 97.5%, 98.8%, 97.2%, and 98.3%, respectively. High image quality with superb interobserver correlation (kappa = 0.809 to > 0.999) validated the clinical feasibility of MDCT angiography for assessing AVFs.

CONCLUSION

MDCT angiography is clinically feasible for evaluating the complete vascular tree of failing AVFs and in showing uncommon complications, including brachial aneurysms and central vein lesions.

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%.

Stenosis detection in forearm hemodialysis arteriovenous fistulae by multiphase contrast-enhanced magnetic resonance angiography: preliminary experience

PURPOSE

To assess the feasibility and accuracy of multiphase contrast-enhanced magnetic resonance angiography (CE-MRA) in patients with dysfunctioning hemodialysis arteriovenous fistulae (AVF), using digital subtraction angiography (DSA) as the standard of reference.

MATERIALS AND METHODS

Fifteen patients with dysfunctioning AVF (eight radiocephalic and seven graft AVF) underwent CE-MRA. Dysfunction was defined as a flow decline of more than 25% in 1 month measured by dilutional flow measurements. CE-MRA was performed during injection of 35 mL of gadolinium-DTPA. The CE-MRA sequence consisted of a time-resolved series of 10 scans, each lasting approximately 10 seconds. The technical parameters were TR/TE/FA/voxel = 5.4/1.6/40/3.1 mm(3), and a rectangular surface reception coil was used. All patients were scheduled to undergo DSA at which an intervention was carried out when a stenosis >or=50% was seen. Two observers, unaware of each other's findings and the findings at DSA, quantified the number and degree of stenosis in the failing AVF. Image quality for CE-MRA and DSA was scored on a 3-point scale. The diagnostic performance of CE-MRA was analyzed with receiver-operator characteristic (ROC) analysis.

RESULTS

CE-MRA and DSA examinations were performed without side effects in all 15 patients. Image quality was scored significantly better on CE-MRA (observer 1: CE-MRA, 2.0; DSA, 1.3; P =.001; observer 2: CE-MRA, 2.0; DSA, 1.4; P =.002). Interobserver agreement for detection of >or=50% stenosis was 0.81 (95% confidence interval (CI) = 0.71-0.92) for CE-MRA and 0.69 (95% CI = 0.55-0.84) for DSA. ROC analysis revealed a mean area under the curve of 0.78. On the patient level, at the >or=50% threshold, mean sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 100% (95% CI = 69%-100%), 10% (95% CI = 0%-78%), 70% (95% CI = 38%-92%), and 100% (95% CI = 50%-100%), respectively. At the >or=75% threshold, mean sensitivity, specificity, PPV, and NPV were 75% (95% CI = 20%-99%), 78% (95% CI = 39%-98%), 55% (95% CI = 12%-96%), and 89% (95% CI = 52%-100%), respectively.

CONCLUSION

CE-MRA is a useful diagnostic tool for detecting stenoses in flow-declined hemodialysis AVF prior to interventional DSA.