Dynamic CE-MRA for Endoleak Classification after Endovascular Aneurysm Repair

Dynamic Radial MR Imaging for Endoleak Surveillance after Endovascular Repair of Abdominal Aortic Aneurysms with Inconclusive CT Angiography: A Prospective Study

Background/Objectives: To assess free-breathing, dynamic radial magnetic resonance angiography (MRA) for detecting endoleaks post-endovascular aortic repair (EVAR) in cases with inconclusive computed tomography angiography (CTA). Methods: This prospective single-center study included 17 participants (mean age, 70 ± 9 years; 13 males) who underwent dynamic radial MRI (Golden-angle RAdial Sparse Parallel-Volumetric Interpolated BrEath-hold, GRASP-VIBE) after inconclusive multiphasic CT for the presence of endoleaks during the follow-up of EVAR-treated abdominal aortic aneurysms. CT and MRI datasets were independently assessed by two radiologists for image quality, diagnostic confidence, and the presence/type of endoleak. Statistical analyses included interrater and intermethod agreement, and diagnostic performance (sensitivity, specificity, area under the curve (AUC)). Results: Subjective image analysis demonstrated good image quality and interrater agreement (k ≥ 0.6) for both modalities, while diagnostic confidence was significantly higher in MRA (p = 0.03). There was significantly improved accuracy for detecting type II endoleaks on MRA (AUC 0.97 [95% CI: 0.87, 1.0]) compared to CTA (AUC 0.66 [95% CI: 0.41, 0.91]; p = 0.03). Although MRA demonstrated higher values for sensitivity, specificity, AUC, and interrater agreement, none of the other types nor the overall detection rate for endoleaks showed differences in the diagnostic performance over CT (p ≥ 0.12). CTA and MRA revealed slight to moderate intermethod concordance in endoleak detection (k = 0.3-0.64). Conclusions: The GRASP-VIBE MRA characterized by high spatial and temporal resolution demonstrates clinical feasibility with good image quality and superior diagnostic confidence. It notably enhances diagnostic performance in detecting and classifying endoleaks, particularly type II, compared to traditional multiphase CTA with inconclusive findings.

Improved Detection of Endoleaks in Virtual Monoenergetic Images in Dual-Energy CT Angiography Following EVAR

OBJECTIVES

The objective of this prospective study was to evaluate the virtual monoenergetic images (VMI) and virtual noncontrast (VNC) phase in the detection of endoleaks after endovascular abdominal aortic repair (EVAR). The potential dose reduction of abbreviated examination protocols was calculated.

MATERIALS AND METHODS

Ninety-seven patients after the EVAR procedure were enrolled in this study. An initial single-source noncontrast acquisition was followed by two dual-energy acquisitions (arterial and 60 s delayed). Fast-kVp switching scanner was used. VNC images were reconstructed from the delayed phase. First examination session (reference) included a full triphasic study protocol consisting of true noncontrast (TNC) images and two postcontrast phases, the latter ones presented as classical polyenergetic reconstructions. Reading sessions II and III were performed by two independent and blinded readers evaluating VMIs in abbreviated protocols-biphasic (VNC + arterial, delayed phase), monophasic (VNC + delayed phase). The diagnostic accuracy of sessions II and III was calculated.

RESULTS

The calculated sensitivity of the biphasic protocol with the use of VMIs in endoleak detection was 100%, with a statistically significant increase in the number of endoleaks detected in comparison with the reference study. The monophasic protocol showed 83.33% sensitivity. The use of abbreviated examination protocols led to a decrease in the mean effective dose (ED) of 23.28% (biphasic protocol) and 61.37% (monophasic protocol).

CONCLUSION

The use of VMIs increases the number of endoleaks diagnosed with a possible radiation reduction by up to ¼ (biphasic protocol). Further reduction to a monophasic protocol leads to over 60% dose reduction but with a decrease in diagnostic accuracy.

Dynamic Imaging of Aortic Pathologies: Review of Clinical Applications and Imaging Protocols

The past decade has seen significant advances in dynamic imaging of the aorta. Today's vascular surgeons have the opportunity to choose from a wide array of imaging modalities to evaluate different aortic pathologies. While vascular ultrasound and aortography are considered to be the bread and butter imaging modalities, newer dynamic imaging techniques provide time-resolved information in various aortic pathologies. However, despite growing evidence of their advantages in the literature, they have not been routinely adopted. In order to understand the role of these emerging modalities, one must understand their principles, advantages, and limitations in the context of various clinical scenarios. In this review, we provide an overview of dynamic imaging techniques for aortic pathologies and describe various dynamic computed tomography and magnetic resonance imaging protocols, clinical applications, and potential future directions.

Contemporary imaging methods for the follow-up after endovascular abdominal aneurysm repair: a review

Abdominal aortic aneurysm (AAA) is defined as a localized enlargement of the aortic cross-section where the diameter is greater than 3 cm or more than 50% larger than the diameter in a normal segment. The most important complication of AAA is rupture, which, if untreated, results in mortality rates of up to 90%. Conventional open surgical repair is associated with significant 30-day mortality. Endovascular aneurysm repair (EVAR) is a significantly less invasive procedure; it is related to a lower early mortality rate and a lower number of perioperative complications. Although EVAR is a minimally invasive technique, lifelong follow-up imaging is necessary due to possible late complications including endoleak, recurrent aneurysm formation, graft infection, migration, kinking and thrombosis. The total rate of complications after EVAR is estimated at approximately 30%, and the rate of complications that require intervention is 2–3%. Early detection and progression analysis of such situations is crucial for proper intervention.

Current status of the treatment of infrarenal abdominal aortic aneurysms

Aortic aneurysms are the 13^th leading cause of death in the United States. While aneurysms can occur along the entire length of the aorta, the infrarenal location is the most common. Targeted ultrasound screening has been found to be an effective and economical means of preventing aortic aneurysm rupture. The indication for repair includes either symptomatic aneurysms or aneurysms with a diameter greater than 5.4 cm. Treatment options for the repair of infrarenal aortic aneurysms are open surgical repair (OSR) and endovascular aneurysm repair (EVAR). Currently, EVAR is the primary treatment method for the repair of infrarenal aortic aneurysms due to improved short-term morbidity and mortality outcomes. This article is intended to review the current status of the management of infrarenal abdominal aortic aneurysms (AAA).

Hemodynamic changes lead to alterations in aortic diameters and may challenge further stent graft sizing in acute aortic syndrome

Background

Precise stent graft sizing in Thoracic endovascular aortic repair (TEVAR) is crucial to receive optimal long-term results. Computed tomography (CT), as the current standard in assessing aortic diameters (ADs), is often performed at initial diagnosis. Since several acute aortic diseases are associated with blood loss and/or volume re-distribution, assessed AD might be influenced by impaired hemodynamic conditions. Intravascular ultrasound (IVUS) offers real-time assessment, especially after hemodynamic restoration, and might help for stent graft choice.

Methods

We investigated the correlation between CT and later IVUS measurements in elective (n=83) and emergency patients (n=32) at the level distal to the left subclavian artery (LSA), a frequent proximal landing zone in TEVAR. Patients were grouped depending on their shock index (heart rate/systolic blood pressure): emergency patients with diagnosis of acute aortic syndrome, urgently required treatment after admission and had a shock index >1, otherwise were grouped as elective. Basic hemodynamics were assessed for both groups at admission and at definite IVUS-procedure.

Results

At time of admission the emergency group showed lower blood pressure (99±19.8 vs. 141±24 mmHg; P=0.001) and higher heart rate (98±13 vs. 70±12 bpm; P=0.001) compared to elective patients. By hemodynamic stabilization comparable blood pressure and heart rate were achieved in both groups at time of IVUS. In the emergency group, we found a significantly increase in AD after hemodynamic stabilization, whereas the diameters did not change in the elective group (IVUS_meanvs. CT_mean: 5.1±1.0 vs. 0.4±2.2 mm; P=0.001 and IVUS_minvs. CT_mean: 3.9±1.3 vs. -0.3±2.2 mm; P=0.011).

Conclusions

IVUS for stent graft sizing is a valuable approach during TEVAR, especially in the light of emergency treatment by offering real-time assistance. Impaired hemodynamic conditions might lead to relevant changes in AD and may strongly influence stent graft choice. In these cases, careful stent graft selection might contribute to avoidance of stent graft related complication.

Imaging for surveillance and operative management for endovascular aortic aneurysm repairs

Endovascular aortic aneurysm repairs rely heavily on radiologic imaging modalities for preoperative surveillance, intraoperative management, and postoperative follow-up. Ultrasonography, computed tomography (CT), magnetic resonance imaging (MRI) and angiography all have utility at different stages of management. Often one imaging modality compliments another by providing supplementary information. Data from the imaging exams must be synthesized into one coherent plan for managing patients with aortic aneurysms.

A Systematic Review of Ultrasound or Magnetic Resonance Imaging Compared With Computed Tomography for Endoleak Detection and Aneurysm Diameter Measurement After Endovascular Aneurysm Repair

PURPOSE

To analyze the literature comparing ultrasound [duplex (DUS) or contrast-enhanced (CEUS)] or magnetic resonance imaging (MRI) with computed tomography angiography (CTA) for endoleak detection and aneurysm diameter measurement after endovascular aneurysm repair (EVAR).

METHODS

A systematic review identified 31 studies that included 3853 EVAR patients who had paired scans (DUS or CEUS vs CTA or MRI vs CTA) within a 1-month interval for identification of endoleaks during EVAR surveillance. The primary outcome was the number of patients with an endoleak detected by one test but undetected by another test. Results are presented for all endoleaks and for types I and III endoleaks only. Aneurysm diameter measurements between CTA and ultrasound were examined using meta-analysis.

RESULTS

Endoleaks were seen in 25.6% (985/3853) of patients after EVAR. Fifteen studies compared DUS with CTA for the detection of all endoleak types. CTA had a significantly higher proportion of additional endoleaks detected (214/2346 vs 77/2346 for DUS). Of 19 studies comparing CEUS with CTA for the detection of all endoleak types, CEUS was more sensitive (138/1694) vs CTA (51/1694). MRI detected 42 additional endoleaks that were undetected by CTA during the paired scans, whereas CTA detected 2 additional endoleaks that MRI did not show. CTA had a similar proportion of additional types I and III endoleaks undetected by CEUS or MRI. Of 9 studies comparing ultrasound vs CTA for post-EVAR aneurysm diameter measurement, the aneurysm diameter measured by CTA was greater than ultrasound (mean difference -1.70 mm, 95% confidence interval -2.45 to -0.96, p<0.001).

CONCLUSION

This study demonstrated that CEUS and MRI are more accurate than CTA for the detection of post-EVAR endoleaks, but they are no better than CTA for detecting types I and III endoleaks specifically. Aneurysm diameter differences between CTA and ultrasound should be considered when evaluating the change in aneurysm diameter postoperatively.

Detecting Aortic Graft Complications: A Spectrum of Computed Tomography Findings

Endovascular aneurysm repair (EVAR) is a successful technique as well as an excellent alternative to the surgical management of abdominal aortic aneurysms. EVAR has improved the mortality and morbidity of many patients who would have otherwise suffered greatly from the consequences of abdominal aortic aneurysms. However, EVAR is not without complications. Some complications require lifelong surveillance, whereas others may necessitate immediate surgical intervention. We discuss the various modalities available for the surveillance as well as the common complications that can be seen on computed tomography.

Importance of dynamic aortic evaluation in planning TEVAR

Dynamic aortic evaluation in planning thoracic endovascular aortic repair (TEVAR) is important to provide optimal stent graft sizing. Static imaging protocols do not consider normal aortic dynamics and may lead to stent graft to aorta mismatch, causing stent graft related complications, such as type I endoleak and stent graft migration. Dynamic imaging can assist in accurate stent graft selection and sizing preoperatively, and evaluate stent graft performance during follow-up. To create new imaging technologies, integration of knowledge between diverse scientific fields is essential (i.e., engineering, informatics and medicine). Different dynamic imaging modalities, such as electrocardiographic-gated computed tomography angiography (ECG-gated CTA) and four-dimensional phase-contrast MRI (4D PC-MRI), are progressively investigated and implemented into clinical practice as important instruments in preoperative planning for TEVAR. In time, further application of dynamic imaging tools for preoperative screening and follow-up after TEVAR might lead to better outcomes for patients. The advances in dynamic imaging for evaluation of the thoracic aorta using new imaging modalities and their future perspectives are addressed in this manuscript.

Contrast-enhanced magnetic resonance angiography of the peripheral arteries: technique, tips, pitfalls and problems

Contrast-enhanced magnetic resonance angiography is a reliable way to assess peripheral vascular disease. This article reviews the basic physics behind this technique and discusses our institution's experience with regard to the clinical role, recent advances in image acquisition and use of contrast agents. Problems that can affect image quality and interpretation are also highlighted.

Magnetic resonance imaging is more sensitive than computed tomography angiography for the detection of endoleaks after endovascular abdominal aortic aneurysm repair: a systematic review

OBJECTIVES

The purpose of this systematic review was to examine whether magnetic resonance imaging (MRI) or computed tomography angiography (CTA) is more sensitive for the detection of endoleaks in patients with abdominal aortic aneurysm (AAA) after EVAR.

DESIGN

Systematic review.

MATERIALS AND METHODS

A systematic electronic search was performed. Articles were included when post-EVAR patients were evaluated by both MRI as index test and CTA as comparison. Methodological quality was assessed with the Quality Assessment of Diagnostic Accuracy Studies (QUADAS) tool. Primary outcome was the proportion of patients in whom MRI detected additional endoleaks, which were not seen with CTA.

RESULTS

Eleven articles were included. The overall methodological quality of the articles was good. In total, 369 patients with 562 MRI and 562 CTA examinations were included. A total of 146 endoleaks were detected by CTA; MRI detected all but two of these endoleaks. With MRI 132 additional endoleaks were found.

CONCLUSIONS

MRI is more sensitive compared to CTA for the detection of post-EVAR endoleaks, especially for the detection of type II endoleaks. MRI should be considered in patients with continued AAA growth and negative or uncertain findings at CTA.

A multidetector tomography protocol for follow-up of endovascular aortic aneurysm repair

OBJECTIVE

The purpose of this study was to improve the use of 64-channel multidetector computed tomography using lower doses of ionizing radiation during follow-up procedures in a series of patients with endovascular aortic aneurysm repair.

METHODS

Thirty patients receiving 5 to 29 months of follow-up after endovascular aortic aneurysm repair were analyzed using a 64-channel multidetector computed tomography device by an exam that included pre-and postcontrast with both arterial and venous phases. Leak presence and type were classified based on the exam phase.

RESULTS

Endoleaks were identified in 8/30 of cases; the endoleaks in 3/8 of these cases were not visible in the arterial phases of the exams.

CONCLUSION

The authors conclude that multidetector computed tomography with pre-contrast and venous phases should be a part of the ongoing follow-up of patients undergoing endovascular aortic aneurysm repair. The arterial phase can be excluded when the aneurism is stable or regresses. These findings permit a lower radiation dose without jeopardizing the correct diagnosis of an endoleak.

Endoleak detection and classification after endovascular treatment of abdominal aortic aneurysm: value of CEUS over CTA

This paper focuses on the diagnostic value of CEUS in the detection and characterization of endoleaks in comparison with other imaging modalities, primary CDUS and CTA in the follow-up of endovascular abdominal aortic aneurysm repair. CEUS is an interesting alternative technique because of its limited costs and lack of exposure to ionizing radiation. However, CTA cannot currently be substituted because it enables a more precise evaluation of aneurysm morphologic changes, aneurysm sac diameter, graft anchorage and integrity. CEUS could be used along with CTA when the latter reveals the presence of endoleak, to provide a better characterization of it taking advantage of the angiodynamic behavior of the contrast agent that permits an easier visualization of the agent flow into the sac. It could also be indicated when aneurysm diameter increases and CTA did not show sac reperfusion or to monitor type II endoleaks reducing the use of CTA with consequent reduction of costs and exposure to radiation.

Imaging Techniques for Detection and Management of Endoleaks after Endovascular Aortic Aneurysm Repair1

Endovascular aortic aneurysm repair (EVAR) is evolving into a viable alternative to open surgical repair for many patients with abdominal and thoracic aortic aneurysms. Endoleak development is a complication of EVAR and represents one of the limitations of this procedure. Endoleaks represent blood flow outside the stent-graft lumen but within the aneurysm sac. Lifelong imaging surveillance of patients after EVAR is critical to detect endoleaks for the patient's benefit and to determine the long-term performance of the stent-graft. Although computed tomographic angiography is the most commonly used examination for imaging surveillance, magnetic resonance angiography, ultrasonography, and digital subtraction angiography all have a role in endoleak detection and management. This review will focus on imaging techniques used for endoleak detection and the role imaging surveillance plays in the overall care of the post-EVAR patient.

MR angiography for patient surveillance after endovascular repair of abdominal aortic aneurysms

OBJECTIVE

The objective of this article is to demonstrate how new imaging sequences and techniques allow characterization of postoperative complications after endovascular surgery and offer the physician more information for planning treatment than ever before.

CONCLUSION

MR angiography is an excellent technique for the surveillance of patients after endovascular repair of abdominal aortic aneurysms because it is highly sensitive for the detection of postoperative complications. A thorough knowledge of the physical properties of the endovascular components is essential to choose the appropriate patients for this form of surveillance.

The effect of endograft relining on sac expansion after endovascular aneurysm repair with the original-permeability Gore Excluder abdominal aortic aneurysm endoprosthesis

OBJECTIVE

Endovascular abdominal aortic aneurysm repair (EVAR) with the original-permeability Excluder (W.L. Gore & Associates, Flagstaff, Ariz) has been associated with postoperative sac expansion in the absence of endoleak. In these cases, we have performed an endovascular revision, relining the original endograft with another Excluder, in an effort to arrest sac expansion by reducing permeability. We have studied these cases to determine the effect of relining on aneurysm expansion.

METHODS

Patients who demonstrated sac expansion (>or=5 mm diameter, >or=5% three-dimensional volume) after EVAR with the original Excluder were evaluated. Between 1999 and 2004, the original-permeability endoprosthesis was used in 97 patients who underwent EVAR for asymptomatic abdominal aortic aneurysm (AAA). Sac expansion occurred in 24 patients, of which multiple imaging modalities showed 12 had expansion without demonstrable endoleak. Nine of the 12 have had endovascular relining, and five of these nine have >6 months follow-up to form the primary basis for this report.

RESULTS

AAA size was stable or smaller in the first 6 months after the original EVAR for all patients. Once expansion began (typically in the time frame of 6 to 12 months), multimodality imaging showed no aneurysm spontaneously decreased in size without intervention, despite the absence of endoleak (n = 12). Expansion exceeded clinically significant thresholds at 30 months (mean) by diameter criteria and 22 months (mean) by three-dimensional volume criteria for the five patients with >6 months follow-up after relining. Endovascular relining was performed at a mean of 36 months, with a mean hospital stay of 1 day, and no morbidity or mortality. Over the entire duration of expansion (mean, 26 months), aneurysms expanded by 6.0 +/- 1 mm/year diameter and by 12% +/- 2%/year by three-dimensional volume. At a mean of 16 months follow-up after relining with another Excluder, the mean diameter decrease was 2.0 mm/year (P < .03) and the mean volume decrease was 2.6%/year (P < .01). After relining, all AAAs were smaller by diameter or volume, or both, exceeding thresholds defining shrinkage in two of the five with >6 months follow-up after relining. There was no rupture, migration, endoleak, conversion to open repair, or aneurysm-related death in any patient.

CONCLUSIONS

It appears from the initial follow-up that AAA expansion owing to permeability issues after EVAR with the original Excluder can be arrested by endovascular relining with a low-permeability Excluder endoprosthesis.

Future of Endograft Surveillance

Frequent and sustained surveillance continues to be mandated for all patients who undergo endovascular repair of the aneurysmal aorta in order to minimize the small but attendant risk of aneurysm rupture. The primary motivation for surveillance includes evaluation of residual aneurysm sac size and presence of endoleak, as well as potential adverse device specific events, such as endograft migration, module disconnection, or component fatigue and failure. The current standard of care and future surveillance modalities after endovascular repair of both abdominal aortic and thoracic aortic aneurysms will be reviewed.

Magnetic resonance imaging-guided vascular interventions

Magnetic resonance imaging (MRI), which provides superior soft-tissue imaging and no known harmful effects, has the potential as an alternative modality to guide various medical interventions. This review will focus on MR-guided endovascular interventions and present its current state and future outlook. In the first technical part, enabling technologies such as developments in fast imaging, catheter devices, and visualization techniques are examined. This is followed by a clinical survey that includes proof-of-concept procedures in animals and initial experience in human subjects. In preclinical experiments, MRI has already proven to be valuable. For example, MRI has been used to guide and track targeted cell delivery into or around myocardial infarctions, to guide atrial septal puncture, and to guide the connection of portal and systemic venous circulations. Several investigational MR-guided procedures have already been reported in patients, such as MR-guided cardiac catheterization, invasive imaging of peripheral artery atheromata, selective intraarterial MR angiography, and preliminary angioplasty and stent placement. In addition, MR-assisted transjugular intrahepatic portosystemic shunt procedures in patients have been shown in a novel hybrid double-doughnut x-ray/MRI system. Numerous additional investigational human MR-guided endovascular procedures are now underway in several medical centers around the world. There are also significant hurdles: availability of clinical-grade devices, device-related safety issues, challenges to patient monitoring, and acoustic noise during imaging. The potential of endovascular interventional MRI is great because as a single modality, it combines 3-dimensional anatomic imaging, device localization, hemodynamics, tissue composition, and function.