Stenosis detection with MR angiography and digital subtraction angiography in dysfunctional hemodialysis access fistulas and grafts

Applications of Vascular Imaging and Interventional Radiology Modalities in the Upper Extremity: A Review

Hand and upper extremity (HUE) vascular disorders are encountered frequently by hand surgeons in clinical practice. A wide array of imaging and vascular interventional radiology modalities exists for the diagnosis and treatment of HUE vascular disorders, some of which may not be familiar to the HUE surgeons. In this review article, we summarize the vascular imaging and vascular interventional radiology modalities and their relative advantages, disadvantages, and indications with respect to HUE pathology. We aim to familiarize HUE surgeons with the available types of diagnostic and therapeutic options for HUE vascular pathologies and aid interdisciplinary communication with vascular interventional radiology specialists during the clinical decision-making process.

The diagnostic value of multi-detector CT angiography for catheter-related central venous stenosis in hemodialysis patients

The objective is to compare Multi-detector CT angiography (MDCTA) and digital subtraction angiography (DSA) in diagnosing hemodialysis catheter related-central venous stenosis (CVS). During a period of 6 years, hemodialysis patients with suspected catheter related-CVS who received both MDCTA and DSA were retrospectively enrolled. We analyzed the sensitivity, specificity, accuracy, Cohen's kappa coefficient (κ) and other diagnostic parameters for MDCTA compared to DSA. A total of 1533 vascular segments in 219 patients were analyzed. Among the 280 lesions identified by DSA, 156 were correctly identified by MDCTA. There were 124 false negative and 41 false positive diagnoses. MDCTA had a high specificity (96.73%) but a low sensitivity (55.71%), with a moderate inter-test agreement (κ = 0.5930). In stratified analyses of vascular segments, the specificities of MDCTA were 89.93% (superior vena cava), 98.95% (left brachiocephalic vein), 95.33% (right brachiocephalic vein), 99.53% (left subclavian vein), 97.61% (right subclavian vein), 97.13% (left internal jugular vein), and 95.86% (right internal jugular vein), while the sensitivities were 90.00%, 65.52%, 66.67%, 87.50%, 40.00%, 20.00% and 8.11%, respectively. Good to excellent inter-test agreement was observed for the superior vena cava (κ = 0.7870), left brachiocephalic vein (κ = 0.7300), right brachiocephalic vein (κ = 0.6610), and left subclavian vein (κ = 0.8700) compared with poor to low agreement for the right subclavian vein (κ = 0.3950), left internal jugular vein (κ = 0.1890), and right internal jugular vein (κ = 0.0500). MDCTA had a high specificity in diagnosing hemodialysis catheter related-CVS. Its sensitivity varied by central venous segments, with better performance in superior vena cava and brachiocephalic veins.

CT and MR imaging of the upper extremity vasculature: pearls, pitfalls, and challenges

Imaging is needed for diagnosis, treatment planning, and follow-up of patients with pathologies affecting upper extremity vasculature. With growth and evolution of imaging modalities [especially CT angiography (CTA) and MR angiography (MRA)], there is need to recognize the advantages and disadvantages of various modalities and obtain the best possible imaging diagnostic test. Understanding various limitations and pitfalls as well as the best practices to minimize and manage these pitfalls is very important for the diagnosis. This article reviews the upper extremity arterial vascular anatomy, discusses the CTA and MRA imaging, various pitfalls, and challenges and discuss imaging manifestations of upper extremity arterial pathologies.

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.

Online measurement of hemodialysis adequacy using effective ionic dialysance of sodium-a review of its principles, applications, benefits, and risks

Dialysis dose is an important determinant of clinical outcomes in patients with end stage renal disease on maintenance dialysis. In clinical practice dialysis dose is monitored at least monthly by urea clearance based on Urea Kinetic Modeling. Online clearance monitoring using effective ionic dialysance (EID) of sodium (Na⁺ ) is available on some hemodialysis machines. This paper reviews the background, methodology, additional applications, and potential risks associated with EID. Effective ionic dialysance provides a reliable, real-time, noninvasive, and inexpensive measurement of dialysis dose during an ongoing hemodialysis (HD) session to allow interventions and assess the impact of these changes on clearance. Surveillance of vascular access flow rates can be used to screen for access dysfunction and refer for interventions. There is a concern that EID measurements may cause Na⁺ loading because of high dialysate Na⁺ used during these measurements, however, mathematical models, in vitro experiments, and clinical studies in patients on maintenance HD do not show any evidence of Na⁺ loading during EID measurements. We cannot rule out the possibility of nonosmotic Na⁺ accumulation in the skin because no published literature exists on this topic as it pertains to clearance measurements based on EID of Na⁺ .

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.

Imaging of haemodialysis: renal and extrarenal findings

Electrolyte alterations and extra-renal disorders are quite frequent in patients undergoing haemodialysis or peritoneal dialysis. The native kidneys may be the site of important pathologies in patients undergoing dialysis, especially in the form of acquired renal cystic disease with frequent malignant transformation. Renal neoplasms represents an important complication of haemodialysis-associated acquired cystic kidney disease and imaging surveillance is suggested. Extra-renal complications include renal osteodistrophy, brown tumours, and thoracic and cardiovascular complications. Other important fields in which imaging techniques may provide important informations are arteriovenous fistula and graft complications.

Teaching points

• Renal neoplasms represent a dreaded complication of haemodialysis.

• In renal osteodystrophy bone resorption typically manifests along the middle phalanges.

• Brown tumours are well-defined lytic lesions radiographically, possibly causing bone expansion.

• Vascular calcifications are very common in patients undergoing haemodialysis.

• Principal complications of the AV fistula consist of thrombosis, aneurysms and pseudoaneurysms.

MR Venography for the Assessment of Deep Vein Thrombosis in Lower Extremities with Varicose Veins

OBJECTIVE

To assess the performance of magnetic resonance venography (MRV) for pelvis and deep vein thrombosis in the lower extremities before surgical interventions for varicose veins.

MATERIALS AND METHODS

We enrolled 72 patients who underwent MRV and ultrasonography before stripping for varicose veins of lower extremities. All images of the deep venous systems were evaluated by time-of-flight MRV.

RESULTS

Forty-six patients (63.9%) of all were female. Mean age was 65.2 ± 10.2 years (37-81 years). There were forty patients (55.6%) with varicose veins in both legs. Two deep vein thrombosis (2.8%) and three iliac vein thrombosis (4.2%) were diagnosed. All patients without deep vein thrombosis underwent the stripping of saphenous veins, and post-thrombotic change was avoided in all cases.

CONCLUSION

MRV, without contrast medium, is considered clinically useful for the lower extremity venous system.

Radiological Assessment of Vascular access in Haemodialysis Patients

Clinical examination is still the most important diagnostic tool and duplex ultrasonography is the imaging method of first choice. Radiological assessment of vascular access for haemodialysis includes preoperative analysis of vessel anatomy and postoperative surveillance for access maturation as well as diagnosis in vascular access insufficiency. Compared to ultrasonography digital subtraction angiography is superior for the evaluation of the central veins and allows diagnosis and treatment in one session. Computed tomography should only be used in patients with inconclusive ultrasonography results, for example, for the assessment of the central veins and visualization of the vascular tree. Gadolinium-enhanced magnetic resonance imaging is no longer recommended in dialysis patients, because it may trigger nephrogenic systemic fibrosis. In patients with a history of previous central venous catheters additional preoperative imaging of the central veins should be performed. In this article we review the different radiological imaging methods for preoperative assessment and suspected vascular access dysfunction.

Diagnostic accuracy of computer tomography angiography and magnetic resonance angiography in the stenosis detection of autologuous hemodialysis access: a meta-analysis

Purpose

To compare the diagnostic performances of computer tomography angiography (CTA) and magnetic resonance angiography (MRA) for detection and assessment of stenosis in patients with autologuous hemodialysis access.

Materials and Methods

Search of PubMed, MEDLINE, EMBASE and Cochrane Library database from January 1984 to May 2013 for studies comparing CTA or MRA with DSA or surgery for autologuous hemodialysis access. Eligible studies were in English language, aimed to detect more than 50% stenosis or occlusion of autologuous vascular access in hemodialysis patients with CTA and MRA technology and provided sufficient data about diagnosis performance. Methodological quality was assessed by the Quality Assessment of Diagnostic Studies (QUADAS) instrument. Sensitivities (SEN), specificities (SPE), positive likelihood ratio (PLR), negative likelihood values (NLR), diagnostic odds ratio (DOR) and areas under the receiver operator characteristic curve (AUC) were pooled statistically. Potential threshold effect, heterogeneity and publication bias was evaluated. The clinical utility of CTA and MRA in detection of stenosis was also investigated.

Result

Sixteen eligible studies were included, with a total of 500 patients. Both CTA and MRA were accurate modality (sensitivity, 96.2% and 95.4%, respectively; specificity, 97.1 and 96.1%, respectively; DOR [diagnostic odds ratio], 393.69 and 211.47, respectively) for hemodialysis vascular access. No significant difference was detected between the diagnostic performance of CTA (AUC, 0.988) and MRA (AUC, 0.982). Meta-regression analyses and subgroup analyses revealed no statistical difference. The Deek’s funnel plots suggested a publication bias.

Conclusion

Diagnostic performance of CTA and MRA for detecting stenosis of hemodialysis vascular access had no statistical difference. Both techniques may function as an alternative or an important complement to conventional digital subtraction angiography (DSA) and may be able to help guide medical management.

Evaluation of immature hemodialysis arteriovenous fistulas based on 3-French retrograde micropuncture of brachial artery

OBJECTIVE

The objective of our study was to assess outcomes after evaluation of immature hemodialysis arteriovenous fistulas (AVFs) via 3-French brachial artery access and to identify the incidence of arterial and venous puncture site spasm.

MATERIALS AND METHODS

One hundred twenty-three outpatients (82 men, 41 women; mean age, 58 years; age range, 20-90 years) with immature AVF were identified retrospectively in whom diagnostic fistulography was performed via 3-French retrograde brachial artery puncture. Percutaneous transluminal angioplasty was performed via a separate venous puncture during the same visit in 95 patients. Patient age and sex, fistula age and type, and technical success and complications were recorded. Images were reviewed for lesion location, potentially competing vessels, and arterial and venous puncture-related spasms.

RESULTS

The mean fistula age was 99 days (range, 21-639 days). There were 49 AVFs in the left forearm; 30 in the left upper arm; 26 in the right forearm; and 18 in the right upper arm. Twenty-eight AVFs were transposed. Angioplasty was technically successful in 81 of 95 patients (85%; mean diameter, 7 mm; range, 4-10 mm). Brachial artery puncture caused no major complication. Arterial spasm occurred in 19 patients (15%) and was severe in one patient. There were two hematomas (1.6%). Venous spasm, ranging from mild (four patients) to occlusive (8 patients), occurred in 38 patients (40%) at the site of venipuncture for intervention. Nitroglycerin (mean, 325 mcg; range, 100-600 mcg) was used in 26 procedures (21%). Venous spasm was more common with forearm (50%) than upper arm (24%) fistulas (p = 0.02) and with decreasing vein diameter (p = 0.02).

CONCLUSION

Evaluation of immature AVFs based on 3-French micropuncture of the brachial artery can be safely performed on an outpatient basis. Spasm is more common in forearm AVFs and in smaller veins.

Three-dimensional gadolinium-enhanced MR venography to evaluate central venous steno-occlusive disease in hemodialysis patients

AIM

To determine the agreement and diagnostic accuracy of three-dimensional gadolinium-enhanced magnetic resonance venography (3D-Gd-MRV) in central venous steno-occlusive disease (CVSD) in haemodialysis patients.

MATERIALS AND METHODS

Fourteen consecutive haemodialysis patients underwent interventional procedures to evaluate or treat CVSD. 3D-Gd-MRV was performed before the procedures and the results were compared with digital subtraction angiography (DSA).

RESULTS

DSA showed >50% stenosis in all 14 patients, 13 of whom were diagnosed correctly using 3D-Gd-MRV. Moderate stenosis was missed at 3D-Gd-MRV in one case whereby the indwelling dialysis central venous catheter may have caused an artefact on the images and hindered the accuracy of the result. The sensitivity of 3D-Gd-MRV in revealing stenosis was 93% (13/14). No complications caused by contrast agent toxicity occurred in any patient.

CONCLUSION

3D-Gd-MRV employing a non-breath-hold technique is highly sensitive in the diagnosis of CVSD and may be an alternative technique to DSA for the visualization of central veins.

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.

64-slice MDCT angiography of upper extremity in assessment of native hemodialysis access

OBJECTIVE

To compare multidetector row computed tomographic (MDCT) angiography with conventional digital subtraction angiography (DSA) in the evaluation of vascular access stenoses in hemodialysis patients.

MATERIALS AND METHODS

Twenty-one consecutive patients were imaged with MDCT angiography and subsequent DSA. The superficial vein of leg was used as the route for intravenous administration. The vascular stenosis was assessed in not significant (<50% stenosis), moderate stenosis (50%-74% stenosis), severe stenosis (75%-99%), and total occlusion (100%). The accuracy, sensitivity, specificity, positive, and negative predictive values were calculated for significant vascular stenosis using DSA as the standard reference.

RESULTS

The sensitivity and specificity of MDCT angiography for the detection of significant hemodialysis vascular access were 100% (95% CI, 89.3%-100%) and 94.8% (95% CI, 89.1%-97.6%), respectively. The positive and negative predictive values were 84.2% (95% CI, 68.1%-93.4%) and 100% (95% CI, 95.8%-100%), respectively. The accuracy of MDCT angiography for detection of significant stenoses was 95.9% (95% CI, 91.4%-97.0%).

CONCLUSIONS

MDCT angiography provides excellent correlation in vascular stenosis as compared with DSA in hemodialysis access. Complete assessment of entire vascular segments could be performing with MDCT angiography in planning before endovascular intervention or surgical correction.

Assessment of vascular disorders of the upper extremity with contrast-enhanced magnetic resonance angiography: pictorial review

We reviewed the role of contrast magnetic resonance angiography (MRA) in patients with vascular disorders of the upper extremity. MRA accurately defines stenoocclusive lesions in patients with atherosclerosis and embolus. It helps to diagnose thoracic outlet syndrome, vascular malformations, and vasculitis. It demonstrates vascular injuries after blunt or occupational trauma, corkscrew collaterals in Burger's disease, and pathological vessels in malignant tumors. Also, it detects the cause of hemodialysis fistula dysfunction. We concluded that contrast MRA is a noninvasive imaging modality that can be used for planning the treatment of vascular disorders of the upper extremity.

Numerical and experimental study of blood flow through a patient-specific arteriovenous fistula used for hemodialysis

Arteriovenous fistula (AVF) pathologies related to blood flow necessitate valid calculation tools for local velocity and wall shear stress determination to overcome the clinical diagnostic limits. To illustrate this issue, a reconstructed patient-specific AVF was investigated, using computational fluid dynamics (CFDs) and particle image velocimetry (PIV). The aim of this study was to validate the methodology from medical images to numerical simulations of an AVF by comparing numerical and experimental data. Two numerical grids were presented with a refinement difference of a factor of four. A mold of the same volume was created and mounted on an experimental bench with similar boundary conditions. The patient's acquired echo D006Fppler flow waveform was injected at the arterial inlet. Experimental and numerical velocity vector cartography qualitatively produced similar flow fields. Quantification with a point-to-point approach thoroughly investigated the velocity profiles using the mean difference between both results. The finest mesh generated CFD results with a mean percentage of the difference in velocity magnitude, taking the PIV as reference, did not exceed 10%. At specific zones, the coarse mesh required adaptive meshing to improve fitting with experimental data. Meshing refinement was necessary to improve velocity accuracy at wide diameters and wall shear stress at narrow diameters. Provided that these criteria were properly respected, we show through this difficult example the validity of using CFD to properly describe flow patterns in image-based reconstructed blood vessels.

Imaging arteriovenous fistulas

OBJECTIVE

Arteriovenous fistulas (AVFs) are abnormal communications with shunting of blood from an artery to a vein. AVFs mainly involve the peripheral vascular system but can affect virtually any organ or system in the body. They may be congenital, created surgically for hemodialysis, or caused by pathologic processes. This review describes the diverse origins of AVFs and illustrates the spectrum of imaging findings at radiography, ultrasound, CT, MRI, and digital angiography for AVFs in different locations: the CNS, thorax, abdomen, musculoskeletal system, and peripheral vascular system. We also discuss syndromes associated with AVFs and describe recent interventional techniques for treating AVFs.

CONCLUSION

Familiarity with the spectrum of imaging findings in AVFs is essential for the accurate interpretation of images and facilitates diagnosis and therapeutic management. Radiologists can play a critical role in the diagnosis and treatment of AVFs. Digital angiography is helpful in elaborating a vascular map for endovascular treatment.

[Contrast enhanced MR angiography: evolving towards whole-body real time acquisitions]

MRA includes all techniques used to depict vessels with MR. Gadolinium contrast injection combined with gradient echo sequences is the technique of choice for vascular imaging. Technical advances now allow faster acquisitions. The purpose of this article is to present two main advances with MRA: whole-body MRA and dynamic 3D MRA. Technical considerations, acquisition techniques, advantages and pitfalls based on our experience with a 1.5T MR unit will be discussed in order to promote their use in routine clinical practice.

Longitudinal assessment of hyperplasia using magnetic resonance imaging without contrast in a porcine arteriovenous graft model

RATIONALE AND OBJECTIVES

Chronic hemodialysis requires a vascular access that provides high blood-flow rates for the extracorporeal recirculation of blood. Synthetic arteriovenous (AV) grafts often fail because of clotting caused by underlying hyperplasia formation. The authors report the use of magnetic resonance (MR) imaging (MRI) without contrast agent to monitor tissue hyperplasia formation as well as luminal area in a porcine model of AV graft stenosis.

MATERIALS AND METHODS

Expanded reinforced polytetrafluoroethylene grafts were surgically placed between the common carotid artery and the external jugular vein, bilaterally, in pigs. Animals underwent MRI in a 3-T scanner at 3, 4, or 6 weeks after graft placement, followed by euthanasia and the collection of grafts and adjacent tissues for histologic analysis. Two animals underwent sequential scanning at 1, 2, 3, 5, and 7 weeks after graft placement, followed by histologic analysis.

RESULTS

Measurements of hyperplasia obtained from the MR images were compared with, and correlated well with, measurements obtained from the histologic cross-sections (r = 0.932, P = .02). The MR images provided a more complete view of the venous hyperplasia throughout the graft compared with histology. The MR images could be examined from multiple angles and were unaffected by histologic preparation artifacts.

CONCLUSION

Unlike histology, MRI provided longitudinal 3-dimensional views of hyperplasia within the AV grafts. This ability of MRI to more completely identify the geometry of hyperplasia and to quantify the tissue volume in vivo could provide benefits over histologic analysis in assessing the pathology of AV graft failure and the efficacy of antihyperplasia interventions.

Central veins of the chest: evaluation with time-resolved MR angiography

PURPOSE

To retrospectively assess the diagnostic performance of time-resolved magnetic resonance (MR) angiography in the detection of stenoses and occlusions in the central veins of the chest, with angiographic and surgical findings and consensus readings serving as the reference standard.

MATERIALS AND METHODS

Institutional review board approval was obtained, and the informed consent requirement was waived for this HIPAA-compliant study. Retrospective analysis was performed with 27 consecutive patients (12 male, 15 female; age range, 16-67 years) who underwent MR venography of the central veins. Six radiologists with varying levels of experience interpreted the studies. For each study, the readers were presented with time-resolved maximum intensity projection (MIP) images only, high-spatial-resolution images only, or both. Sensitivity and specificity were calculated for detection of stenoses and occlusions, as well as for confidence levels, study interpretation time, and determination of the side of the body on which upper extremity contrast material injection was performed.

RESULTS

The addition of time-resolved angiographic images to the high-spatial-resolution images resulted in improved specificity in the detection of venous occlusions (0.99 vs 0.96, P = .03), in reader confidence (P < .001), and in the ability to infer the side of injection (83% correct compared with 32% correct, P < .001), without increasing the average time required for study interpretation. Use of time-resolved angiographic data sets as a stand-alone technique had high sensitivity (0.95) but only moderate specificity (0.56) in the detection of venous stenoses or occlusions.

CONCLUSION

Time-resolved angiographic images are a useful adjunct to high-spatial-resolution images in the evaluation of central venous stenoses and occlusions.

Comparison of hemodialysis blood access flow rates using online measurement of conductivity dialysance and ultrasound dilution

BACKGROUND

Routine access flow (AF) surveillance is recommended by the Kidney Disease Outcomes Quality Initiative as one of several components for an arteriovenous vascular access maintenance program. A reliable, but affordable, measurement tool is needed for outpatient hemodialysis facilities.

STUDY DESIGN

Diagnostic test study.

SETTING & PARTICIPANTS

50 adult patients with 27 grafts and 23 fistulas from a single center who consented to sequential AF measurements, all performed within the first 90 minutes of the hemodialysis treatment.

INDEX TEST

AF measured by using online conductivity dialysance (OLC-AF).

REFERENCE TEST

AF measured by using ultrasound dilution (UD-AF).

RESULTS

Mean UD-AF was 1,086 +/- 629 mL/min, and mean OLC-AF was 951 +/- 575 mL/min, with a mean difference of 135 +/- 229 mL/min. OLC-AF correlated significantly with UD-AF (0.93; P < 0.0001), becoming tighter for flows less than 1,000 mL/min (0.95; P < 0.0001). The coefficient of variation for sequential measurement by using UD was 6.4%, and for OLC, 11.5%, with the difference becoming insignificant (7.6% versus 8.8%; P = 0.5) for flows less than 1,000 mL/min. The average of 2 sequential UD-AF measurements correlated tightly with that of OLC-AF (0.99; P < 0.0001).

LIMITATIONS

Tests were performed by 2 highly trained coordinators in a single clinic with a small sample size, and clinical outcomes were not evaluated.

CONCLUSION

The OLC method is a reasonable alternative to UD for flow surveillance of arteriovenous hemodialysis accesses and provides an option for widespread implementation of a vascular access surveillance program. Additional studies are needed to determine whether routine use impacts on clinical outcomes.

Contrast-enhanced magnetic resonance angiography (CE-MRA) of intra- and extra-cranial vessels in dogs

Until recently intra- and extra-cranial vessels in dogs have been imaged using conventional X-ray or digital subtraction angiography. As both of these methods are surgically demanding and involve the use of complex equipment with potential risks for the animal, they are now mainly used in experimental work. In this study, a method for delineating the intra- and extra-cranial vessels of dogs using contrast-enhanced magnetic resonance angiography (CE-MRA) has been examined. The MR images were acquired on a 1.5-T scanner after a bolus injection of gadolinium contrast medium. CE-MRA showed most of the major intra- and extra-cranial arteries and veins as well as most venous sinuses and plexuses of the brain. Difficulties may arise in differentiating between minor arterial and venous vessels as well as in the measurement of vessel diameter. More frequent use of this diagnostic method in clinical cases will indicate whether MRA of the head and brain is of as much use in veterinary medicine as it has become in human medicine. There is certainly potential value in detecting rare conditions in animals such as aneurysms and vascular malformations, as well as in examining vessels feeding intracranial masses and the investigation of cerebrovascular accidents.

Time-resolved, high-resolution contrast-enhanced MR angiography of dialysis shunts using the CENTRA keyhole technique with parallel imaging

PURPOSE

To evaluate the use of a dynamic keyhole magnetic resonance angiography (MRA) sequence combined with sensitivity encoding (SENSE) for hemodialysis shunts, because surveillance with conventional contrast-enhanced MRA (CE-MRA) is limited by its low temporal resolution, resulting in arteriovenous overlay.

MATERIALS AND METHODS

A total of 12 patients with Brescia-Cimino shunts were investigated prospectively using the new technique. During the contrast passage (gadoterate, Gd-DOTA) a series of five to nine dynamic central k-space measurements (10% for upper-arm shunt, 25% for lower-arm shunt) followed by a full reference data set were acquired. The outer k-space data of the single reference scan were used to complete the dynamic data sets.

RESULTS

All studies were diagnostic (17 stenoses, three aneurysms) without complications. The acquisition times for a single dynamic scan of the upper- and lower-arm shunts were 2.2 and 3.2 seconds, respectively, while the reference scan needed 13 and 22.4 seconds, respectively. The dynamic angiograms allowed the differentiation of arterial and venous filling despite a mean peak delay time of only 4.2 seconds in the shoulder region. Image quality qualified in consensus by two experienced readers was rated "good" in 19 cases and "intermediate" in five cases with high mean values for signal-to-noise ratios (SNRs) and contrast-to-noise-ratios (CNRs).

CONCLUSION

We have successfully implemented a fast, dynamic, CE-MRA technique with CE timing robust angiography (CENTRA) keyhole and SENSE in clinical routine. High spatial and temporal resolution improve the diagnostics of dialysis shunts and allow the assessment of detailed, dynamic, four-dimensional (4D) information.

Time-resolved MR angiography with generalized autocalibrating partially parallel acquisition and time-resolved echo-sharing angiographic technique for hemodialysis arteriovenous fistulas and grafts

PURPOSE

To evaluate the imaging of hemodialysis arteriovenous (AV) fistulas and grafts with use of magnetic resonance (MR) angiography with generalized autocalibrating partially parallel acquisition (GRAPPA) and time-resolved echo-sharing angiographic technique (TREAT) and compare the findings with those of digital subtraction angiography (DSA).

MATERIALS AND METHODS

The vascular tree directly related to AV fistulas and grafts was divided into nine segments. Images of each segment obtained on GRAPPA MR angiography were evaluated for the presence of stenosis, occlusion, and any other disease (eg, pseudoaneurysm) by two independent observers and compared with a consensus reading of the same segments on DSA imaging. Sensitivity and specificity were calculated with use of DSA as the gold standard modality, and each image on MR angiography and DSA was rated for quality. Linear-weighted kappa scores were calculated as a measure of interobserver variability in the detection of pathologic processes.

RESULTS

A total of 80 segments were evaluated by each observer. For both observers, sensitivity rates for the detection of stenosis, occlusion, and any disease were 100% (95% CI, 52%-100%), 100% (95% CI, 20%-100%), and 100% (95% CI, 60%-100%), respectively. For observer 1, specificity rates for the detection of stenosis, occlusion, and any disease were 96% (95% CI, 88%-99%), 100% (95% CI, 94%-100%), and 96% (95% CI, 88%-99%), respectively. For observer 2, the specificity rates for the detection of stenosis, occlusion, and any disease were 93% (95% CI, 84%-98%), 100% (95% CI, 94%-100%), and 93% (95% CI, 84%-97%), respectively. Linear-weighted kappa values for MR angiography and DSA were 0.78+/-0.084 and 0.62+/-0.152, respectively.

CONCLUSION

Time-resolved MR angiography with GRAPPA and TREAT offers excellent image quality and provides an accurate and reliable modality for the detection of pathologic processes in hemodialysis AV fistulas and grafts.

Inflow stenoses in dysfunctional hemodialysis access fistulae and grafts

BACKGROUND

The aim of the study is to prospectively determine the incidence of inflow stenoses in dysfunctional hemodialysis access arteriovenous fistulae (AVFs) and grafts (AVGs).

METHODS

Contrast-enhanced magnetic resonance angiography (CE-MRA) was performed of 66 dysfunctional AVFs and 35 AVGs in 56 men and 45 women (mean age, 62 years; age range, 31 to 86 years). Complete inflow (from the subclavian artery), shunt region, and complete outflow (including subclavian vein) were shown at CE-MRA. In addition to standard digital subtraction angiography (DSA) of the shunt region and outflow, DSA of the complete inflow was obtained through access catheterization of all cases in which CE-MRA showed an inflow stenosis. Vascular stenosis is defined as greater than 50% decrease in luminal diameter compared with an uninvolved vascular segment located adjacent to the stenosis. Endovascular intervention of stenoses was performed in connection with DSA.

RESULTS

CE-MRA showed 19 arterial stenoses in 14 patients (14%). DSA confirmed 18 of these lesions in 13 patients and showed no additional inflow lesions. Of the 13 patients, 7 patients had arterial stenoses only and 6 patients had accompanying stenoses in the shunt region and/or outflow. Referral criteria for the 13 patients to undergo access evaluation had been decreased flow rates (9 patients), steal symptoms (2 patients), and insufficient access maturation (2 patients). Access flow of the 9 patients with a low-flow access improved from 477 +/- 74 mL/min to 825 +/- 199 mL/min after angioplasty. One patient with steal symptoms became symptom free after angioplasty. Endovascular intervention in 3 patients proved to be unsuccessful.

CONCLUSION

Inflow stenoses are not uncommon in dysfunctional hemodialysis access shunts. We suggest that radiological evaluation comprise assessment of the complete arterial inflow.

Time-Resolved 3D MR Angiography with Parallel Imaging for Evaluation of Hemodialysis Fistulas and Grafts: Initial Experience

OBJECTIVE

We optimized a time-resolved 3D contrast-enhanced MR angiography sequence with integrated parallel imaging technique that can provide a large field of view with high temporal and spatial resolution, by which the hemodialysis access and the entire course of the inflow and outflow vessels can be imaged at a single anatomic station. Our objective was to evaluate the feasibility and usefulness of this method in the evaluation of patients referred for possible abnormalities in hemodialysis access.

CONCLUSION

Time-resolved contrast-enhanced 3D MR angiography with parallel imaging has the potential to provide a rapid and comprehensive evaluation for the surveillance and diagnosis of hemodialysis access malfunctions. This technique may function as an important complement to conventional digital subtraction angiography and may be able to help guide medical management. The MR angiography protocol we present is a noninvasive, versatile, and time-efficient technique, without the need of direct graft puncture or flow interruption, and can be performed using a single injection of contrast material at a single station.

Access Monitoring Is Worthwhile and Valuable

During the past several years, a limited number of small clinical trials have questioned the role of surveillance in the management of vascular accesses, since the prolongation of access longevity until replacement was not altered. Although prolongation of access life span is an important endpoint, it is not the only one. Reduction in thrombotic events reduces the risks to the patient resulting from loss of access patency. The body of evidence suggests that the detection of stenosis and prevention of thrombosis are valuable. When a test indicates the likely presence of a stenosis, venography or fistulography should be used to definitely establish the presence and the degree of the stenosis. In most cases, angioplasty should be performed if the stenosis is greater than 50% by diameter. The value of routine use of any surveillance technique for detecting anatomic stenosis alone without concomitant functional assessment by measurement of access flow, venous pressure, recirculation, or other physiologic parameter has not been established. Stenotic lesions should not be repaired merely because they are present. If such correction is performed, then intra-procedural studies of access flow or intra-access pressure prior to and following percutaneous transluminal angioplasty should be conducted to demonstrate a functional improvement with a 'successful' percutaneous transluminal angioplasty.

Stenosis detection in failing hemodialysis access fistulas and grafts: comparison of color Doppler ultrasonography, contrast-enhanced magnetic resonance angiography, and digital subtraction angiography

OBJECTIVE

Several imaging modalities are available for the evaluation of dysfunctional hemodialysis shunts. Color Doppler ultrasonography (CDUS) and digital subtraction angiography (DSA) are most widely used for the detection of access stenoses, and contrast-enhanced magnetic resonance angiography (CE-MRA) of shunts has recently been introduced. To date, no study has compared the value of these three modalities for stenosis detection in dysfunctional shunts. We prospectively compared CDUS and CE-MRA with DSA for the detection of significant (> or = 50%) stenoses in failing dialysis accesses, and we determined whether the interventionalist would benefit from CDUS performed before DSA and endovascular intervention.

METHODS

CDUS, CE-MRA, and DSA were performed of 49 dysfunctional hemodialysis arteriovenous fistulas and 32 grafts. The vascular tree of the accesses was divided into three to eight segments depending on the access type (arteriovenous fistula or arteriovenous graft) and the length of venous outflow. CDUS was performed and assessed by a vascular technician, whereas CE-MRA and DSA were interpreted by two magnetic resonance radiologists and two interventional radiologists, respectively. All readers were blinded to information from each other and from other studies. DSA was used as reference standard for stenosis detection.

RESULTS

DSA detected 111 significant (> or = 50%) stenoses in 433 vascular segments. Sensitivity and specificity of CDUS for the detection of significant stenosed vessel segments were 91% (95% CI, 84%-95%) and 97% (95% CI, 94%-98%), respectively. We found a positive predictive value of 91% (95% CI, 84%-95%) and a negative predictive value of 97% (95% CI, 94%-98%). The sensitivity, specificity, positive predictive value, and negative predictive value of MRA were 96% (95% CI, 90%-98%), 98% (95% CI, 96%-99%), 94% (95% CI, 88%-97%), and 98% (95% CI, 96%-99%), respectively. CDUS and CE-MRA depicted respectively three and four significant stenoses in six nondiagnostic DSA segments. The interventionalist would have chosen an alternative cannulation site in 38% of patients if the CDUS results had been available.

CONCLUSIONS

We suggest that CDUS be used as initial imaging modality of dysfunctional shunts, but complete access should be depicted at DSA and angioplasty to detect all significant stenoses eligible for intervention. CE-MRA should be considered only if DSA is inconclusive.