A new method for quantification of false lumen thrombosis in aortic dissection using magnetic resonance imaging and a blood pool contrast agent

A Monte Carlo Sensitivity Analysis for a Dimensionally Reduced-Order Model of the Aortic Dissection

PURPOSE

Aortic dissection is associated with a high mortality rate. Although computational approaches have shed light on many aspects of the disease, a sensitivity analysis is required to determine the significance of different factors. Because of its complex geometry and high computational expense, the three-dimensional (3D) fluid-structure interaction (FSI) simulation is not a suitable approach for sensitivity analysis.

METHODS

We performed a Monte Carlo simulation (MCS) to investigate the sensitivity of hemodynamic quantities to the lumped parameters of our zero-dimensional (0D) model with numerically calculated lumped parameters. We performed local and global analyses on the effect of the model parameters on important hemodynamic quantities.

RESULTS

The MCS showed that a larger lumped resistance value for the false lumen and the tears result in a higher retrograde flow rate in the false lumen (the coefficient of variation,c v , i = 0.0183 , the sensitivityS X i σ = 0.54 , Spearman's coefficient,ρ s = 0.464 ). For the intraluminal pressure, our results show a significant role in the resistance and inertance of the true lumen (the coefficient of variation,c v , i = 0.0640 , the sensitivityS X i σ = 0.85 , and Spearman's coefficient,ρ s = 0.855 for the inertance of the true lumen).

CONCLUSION

This study highlights the necessity of comparing the results of the local and global sensitivity analyses to understand the significance of multiple lumped parameters. Because of the efficiency of the method, our approach is potentially useful to investigate and analyze medical planning.

Management of the False Lumen in Post Type A Aortic Dissection Arch Aneurysms Treated With Branched Endografts

INTRODUCTION

The treatment of chronic postdissection aneurysms of the aortic arch is a challenge. This study aims to describe false lumen management after aortic arch endovascular repair of post-type A dissection aneurysms treated with a branched endograft.

METHODS

In this single-center retrospective observational study, all consecutive patients undergoing endovascular treatment of aneurysmal degeneration of chronic type A aortic dissections following open repair were enrolled. The primary endpoint was maximal aortic diameter evolution measured on computed tomography angiography (CTA) performed during follow-up. Secondary endpoints included procedural success, aortic re intervention, and remodeling during follow-up.

RESULTS

Between January 2017 and June 2020, 22 patients underwent endovascular branched arch repair for post type A dissection aneurysms. Technical success was 100%. Thirteen patients (59%) had dissection involvement of at least 1 supra-aortic vessel. Midterm follow-up CTA was performed for 20 patients, 23.1 (±13.3) months after the procedure. Maximal aortic diameter at the level of the repair was decreasing in 13 (65%) patients, increasing in 2 (10%) patients, and no change was observed in 5 (25%) patients. During follow-up, 7 patients (35%) required aortic reintervention. Thoracic candy plugs were implanted for distal false lumen occlusion in 15 patients and associated with a high rate of complete remodeling (6/15 patients, 40%).

CONCLUSION

Arch branch endografting of aneurysmal evolution of a post type A dissection aortic arch is a safe and feasible option in experienced hands. Candy plug use in favorable anatomies seems to be associated with accelerated remodeling of the aorta.

CLINICAL IMPACT

There are currently no recommendations on dissected supra- aortic vessels management and the use of thoracic aorta false lumen occlusion devices during endovascular repair of chronic post dissection aneurysm of the aortic arch with branched endografts. Based on our clinical experience reported in the current manuscript, we propose a treatment algorithm for the management of the false lumen in this setting.

Risk profile analysis of uncomplicated type B aortic dissection patients undergoing thoracic endovascular aortic repair: Laboratory and radiographic predictors

BACKGROUND

There is emerging evidence to support pre-emptive thoracic endovascular aortic repair (TEVAR) intervention for uncomplicated type B aortic dissection (unTBAD). Pre-emptive intervention would be particularly beneficial in patients that have a higher baseline risk of progressing to complicated TBAD (coTBAD). There remain debate on the optimal clinical, laboratory, morphological, and radiological parameters, which would identify the highest-risk patients that would benefit most from pre-emptive TEVAR.

AIM

This review summarizes evidence on the clinical, laboratory, and morphological parameters that increase the risk profiles of unTBAD patients.

METHODS

A comprehensive literature search was carried out on multiple electronic databases including PubMed, EMBASE, Ovid, and Scopus to collate all research evidence on the clinical, laboratory, and morphological parameters that increase the risk profiles of unTBAD patients RESULTS: At present, there are no clear clinical guidelines using risk-stratification to inform the selection of unTBAD patients for TEVAR. However, there are noticeable literature trends that can assist with the identification of the most at-risk unTBAD patients. Patients are at particular risk when they have refractory pain and/or hypertension, elevated C-reactive protein (CRP), larger aortic diameter, and larger entry tears. These risks should be considered alongside factors that increase the procedural risk of TEVAR to create a well-balanced approach. Advances in biomarkers and imaging are likely to identify more pertinent parameters in the future to optimize the development of balanced, risk-stratified treatment protocols.

CONCLUSION

There are a variety of risk profiling parameters that can be used to identify the high-risk unTBAD patient, with novel biomarkers and imaging parameters emerging. Longer-term evidence verifying these parameters would be ideal. Further randomized controlled trials and multicentre registry analyses are also warranted to guide risk-stratified selection protocols.

Mid- and long-term outcomes of thoracic endovascular aortic repair in acute and subacute uncomplicated type B aortic dissection

BACKGROUND

Uncomplicated type B aortic dissection (un-TBAD) has been managed conservatively with medical therapy to control the heart rate and blood pressure to limit disease progression, in addition to radiological follow-up. However, several trials and observational studies have investigated the use of thoracic endovascular aortic repair (TEVAR) in un-TBAD and suggested that TEVAR provides a survival benefit over medical therapy. Outcomes of TEVAR have also been linked with the timing of intervention.

AIMS

The scope of this review is to collate and summarize all the evidence in the literature on the mid- and long-term outcomes of TEVAR in un-TBAD, confirming its superiority. We also aimed to investigate the relationship between the timing of TEVAR intervention and results.

METHODS

We carried out a comprehensive literature search on multiple electronic databases including PubMed, Scopus, and EMBASE to collate and summarize all research evidence on the mid- and long-term outcomes of TEVAR in un-TBAD, as well as its relationship with intervention timing.

RESULTS

TEVAR has proven to be a safe and effective tool in un-TBAD, offering superior mid- and long-term outcomes including all-cause and aorta-related mortality, aortic-specific adverse events, aortic remodeling, and need for reintervention. Additionally, performing TEVAR during the subacute phase of dissection seems to yield optimal results.

CONCLUSION

The evidence demonstrating a survival advantage in favor TEVAR over medical therapy in un-TBAD means that with further research, particular trials and observational studies, TEVAR could become the gold-standard treatment option for un-TBAD patients.

Proximal False Lumen Thrombosis is Associated with Low False Lumen Pressure and Fewer Complications in Type B Aortic Dissection

BACKGROUND

Improved risk stratification is a key priority for type B aortic dissection (TBAD). Partial false lumen thrombus morphology is an emerging predictor of complications however, partial thrombosis is poorly defined and its evaluation in clinical studies is inconsistent.

PURPOSE

This work aims to characterise hemodynamic pressure in TBAD and determine how pressure relates to false lumen thrombus morphology and clinical events.

METHODS

Retrospective admission computed tomography angiography of 69 patients with acute TBAD was used to construct three-dimensional computational models for simulation of cyclical blood flow and calculation of pressure. Patients were categorised based on false lumen thrombus morphology: minimal; proximal; distal; or extensive thrombosis. Linear regression analysis compared the luminal pressure difference between the true and false lumen for each morphology group. The impact of morphology classification on acute complications within 14 days was studied using logistic regression adjusted for clinical parameters. A survival analysis for adverse aortic events at one-year was also performed using Cox regression.

RESULTS

44 patients experienced acute complications and 45 had an adverse aortic event at one-year. Mean (±standard deviation) age was 62.6 (±12.6) years and 75.4% were male. Compared to patients with minimal thrombosis, those with proximal thrombosis had reduced false lumen pressure by 10.1mmHg (95% CI 4.3-15.9mmHg, p=.001). Individuals that did not experience an acute complication had reduced relative false lumen pressure (-6.35mmHg vs -0.62mmHg, p=.03). Proximal thrombosis was associated with fewer acute complications (OR 0.17, 95% CI 0.04-0.60 p=.01) and one-year adverse aortic events (HR 0.36, 95% CI 0.16-0.80, p=.01).

CONCLUSIONS

Proximal false lumen thrombosis is a marker of reduced false lumen pressure. This may explain how proximal false lumen thrombosis appears protective of acute complications (refractory hypertension or pain, aortic rupture, visceral or limb malperfusion and acute expansion) and adverse aortic events within the first year.

Before and after Endovascular Aortic Repair in the Same Patients with Aortic Dissection: A Cohort Study of Four-Dimensional Phase-Contrast Magnetic Resonance Imaging

(1) Background: We used four-dimensional phase-contrast magnetic resonance imaging (4D PC-MRI) to evaluate the impact of an endovascular aortic repair (TEVAR) on aortic dissection. (2) Methods: A total of 10 patients received 4D PC-MRI on a 1.5-T MR both before and after TEVAR. (3) Results: The aortas were repaired with either a GORE TAG Stent (Gore Medical; n = 7) or Zenith Dissection Endovascular Stent (Cook Medical; n = 3). TEVAR increased the forward flow volume of the true lumen (TL) (at the abdominal aorta, p = 0.047). TEVAR also reduced the regurgitant fraction in the TL at the descending aorta but increased it in the false lumen (FL). After TEVAR, the stroke distance increased in the TL (at descending and abdominal aorta, p = 0.018 and 0.015), indicating more effective blood transport per heartbeat. Post-stenting quantitative flow revealed that the reductions in stroke volume, backward flow volume, and absolute stroke volume were greater when covered stents were used than when bare stents were used in the FL of the descending aorta. Bare stents had a higher backward flow volume than covered stents did. (4) Conclusions: TEVAR increased the stroke volume in the TL and increased the regurgitant fraction in the FL in patients with aortic dissection.

Chest CT Angiography for Acute Aortic Pathologic Conditions: Pearls and Pitfalls

Chest CT angiography (CTA) is essential in the diagnosis of acute aortic syndromes. Chest CTA quality can be optimized with attention to technical parameters pertaining to noncontrast imaging, timing of contrast-enhanced imaging, contrast material volume, kilovolt potential, tube-current modulation, and decisions regarding electrocardiographic-gating and ultra-fast imaging, which may affect the accurate diagnosis of acute aortic syndromes. An understanding of methods to apply to address suboptimal image quality is useful, as the accurate identification of acute aortic syndromes is essential for appropriate patient management. Acute aortic syndromes have high morbidity and mortality, particularly when involving the ascending aorta, and include classic aortic dissection, penetrating atherosclerotic ulcer, and acute intramural hematoma. An understanding of the pathogenesis and distinguishing imaging features of acute aortic syndromes and aortic rupture and some less common manifestations is helpful when interpreting imaging examinations. Related entities, such as ulcerated plaque, ulcerlike projections, and intramural blood pools, and mimics, such as vasculitis and aortic thrombus, are important to recognize; knowledge of these is important to avoid interpretive pitfalls. In addition, an awareness of postsurgical aortic changes can be useful when interpreting CTA examinations when patient history is incomplete. The authors review technical considerations when performing CTA, discuss acute aortic syndromes, and highlight diagnostic challenges encountered when interpreting aortic CTA examinations. ^©RSNA, 2021.

Aortic dissection assessment by 4D phase-contrast MRI with hemodynamic parameters: the impact of stent type

Background

To explore the diagnostic performance of 4-dimensional phase-contrast magnetic resonance imaging (4D PC-MRI) in evaluating aortic dissection in different clinical scenarios.

Methods

The study group comprised 32 patients with a known aortic dissection who each underwent computed tomography angiography (CTA), and then 4D PC-MRI with a 1.5-T MR scanner. The 4D PC-MRI images were compared with the CTA images to evaluate the aortic size, branch identification, and iliac and femoral arterial access.

Results

The patients were divided into three groups: (I) patients diagnosed with Type B aortic dissection but did not undergo intervention (n=8); (II) patients with residual aortic dissection after open repair of Type A dissection (n=7); (III) patients who underwent endovascular aortic repair with or without open surgery (n=17). Without radiation or contrast media injection, 4D PC-MRI provided similar aortic images for patients in Group 1 and most of those in Group 2. In Group 3, stainless steel stents affected image quality in three patients. High-quality 4D PC-MRI images were obtained for the remaining 14 patients in Group 3, who had non-stainless steel stents, and provided major aortic information comparable to that provided by CTA with contrast media. The hemodynamic parameters of true and false lumens were evaluated between three patients with Type B aortic dissections and three patients who underwent thoracic endovascular aortic repair for their aortic dissection. The stroke volume was higher in the true lumen of the patients with stent-grafts than in the patients with Type B aortic dissection without intervention. The regurgitant fraction, an indicator of nonlaminar flow, was higher in the false lumens than in the true lumens. All 32 patients in this study tolerated 4D PC-MRI without adverse events.

Conclusions

4D PC-MRI is radiation- and contrast media-free option for imaging aortic dissection. It not only provided images comparable in quality to those obtained with CTA but also provided information on hemodynamic parameters, including endoleak detection after thoracic endovascular aortic repair. 4D PC-MRI was safe and accurate in evaluating chronic Type B aortic dissection and residual aortic dissection after surgery for acute Type A aortic dissection. Therefore, it could be a potential tool in treating pathology in aortic dissection, especially for patients with malperfusion syndrome of visceral vessels and in young patients with renal function impairment. However, certain endograft materials, especially stainless steel, may prevent the further application of 4D PC-MRI and should be avoided.

Clinical and Morphologic Outcomes of Endovascular Repair for Subacute and Chronic Type B Aortic Dissection

BACKGROUND

The objective of the study was to assess long-term remodeling, survival, and reintervention outcomes after thoracic endovascular aortic repair (TEVAR) for subacute and chronic type B aortic dissection (TBAD).

METHODS

All patients who underwent TEVAR for subacute or chronic TBAD at a tertiary referral center between 1999 and 2015 were included in this cohort study. The primary outcome was aortic remodeling, and secondary outcomes included survival, rate of major complications, and reinterventions.

RESULTS

Fifty patients were included, with mean age of 62.4 years, 10 (20%) DeBakey type IIIA and 40 (80%) DeBakey type IIIB dissection; 45 standard TEVAR, 2 branched TEVAR, 3 TEVAR combined with fenestrated or branched EVAR. Indication for TEVAR was intact (n = 40) or ruptured (n = 1) postdissection aneurysm, hypoperfusion (n = 4), treatment-refractory pain (n = 2), or a combination (n = 3). Mean clinical follow-up was 76 months, and median radiological follow-up was 46 months. Thirty-day survival was 96%, stroke 4%, renal failure 0%, paraplegia 0%. Three- and five-year survival was 92% (95% confidence interval (CI) [79; 97]) and 77% (95% CI [61; 87]), respectively. Of 19 late deaths, 6 were confirmed aorta related. Five-year freedom from reintervention was 69% (95% CI [53-80]). Distal stent graft extension due to aortic dilatation composed most reinterventions. Mean maximal aortic diameter was 58.7 mm preoperatively and 51.9 mm on last follow-up (P = 0.003). On thoracic level, true lumen expanded (+10.0 mm, 95% CI [6.4; 13.6]) (P < 0.001) and false lumen decreased (-11.9 mm, 95% CI [-15.2; -8.5]) (P < 0.001) from baseline to the last computed tomography. In the abdominal aorta, true lumen diameter change was +3.1 mm (95% CI [1.4; 4.8]) (P = 0.001); false lumen diameter change was +1.0 mm (95% CI [-1.8; 3.8]) (P = 0.464).

CONCLUSIONS

TEVAR for subacute and chronic TBAD results in favorable remodeling of the thoracic but not the abdominal aorta. Five-year survival is almost 80%, but late aortic deaths still occur. Aortic dilatation distal to the treated segment requiring reintervention is common, emphasizing the importance of follow-up.

Experimental Insight into the Hemodynamics and Perfusion of Radiological Contrast in Patent and Non-patent Aortic Dissection Models

PURPOSE

In a curved vessel such as the aortic arch, the velocity profile closer to the aortic root is normally skewed towards the inner curvature wall, while further downstream along the curve, the velocity profile becomes skewed towards the outer wall. In an aortic dissection (AD) disease, blood velocities in the true lumen (TL) and false lumen (FL) are hypothesized to depend on the proximity of the entry tear to the root of aortic arch. Faster velocity in the FL can lead to higher hemodynamic loading, and pose tearing risk. Furthermore, the luminal velocities control the perfusion rate of radiological contrast media during diagnostic imaging. The objective in this study is to investigate the effect of AD disease morphology and configuration on the blood velocity field in the TL and FL, and on the relative perfusion of radiological enhancement agents through the dissection.

METHODS

Eight in vitro models were studied, including patent and non-patent FL configurations. Particle image velocimetry (PIV) was used to quantify the AD velocity field, while laser-induced fluorescence (LIF) was implemented to visualize dynamical flow phenomena and to quantify the perfusion of injected dye, in mimicry of contrast-enhanced computed tomography (CT).

RESULTS

The location of the proximal entry tear along the aortic arch in a patent FL had a dramatic impact on whether the blood velocity was higher in the TL or FL. The luminal velocities were dependent on the entry/reentry tear size combination, with the smaller tear (whether distal or proximal) setting the upper limit on the maximal flow velocity in the FL. Upon merging near the distal reentry tear, the TL/FL velocity differential gave rise to the roll up and shedding of shear layer vortices that convected downstream in close proximity to the wall of the non-dissected aorta. In a non-patent FL, the flow velocity was practically null with all the blood passing through the TL. LIF imaging showed much slower perfusion of contrast dye in the FL compared to the TL. In a patent FL, however, dye had a comparable perfusion rate appearing around the same time as in the TL.

CONCLUSIONS

Blood velocities in the TL and FL were highly sensitive to the exact dissection configuration. Geometric case A1R, which had its proximal entry tear located further downstream along the aortic arch, and had its entry and reentry tears sufficiently sized, exhibited the highest FL flow velocity among the tested models, and it was also higher than in the TL, which suggest that this configuration had elevated hemodynamic loading and risk for tearing. In contrast-enhanced diagnostic imaging, a time-delayed acquisition protocol is recommended to improve the detection of suspected cases with a non-patent FL.

Proposed Magnetic Resonance Imaging Criteria to Diagnose Intramural Haematoma and to Predict Aortic Healing after Acute Type B Aortic Syndrome

OBJECTIVE

Type B acute aortic syndrome (AAS) encompasses aortic dissection (AD) and intramural haematoma (IMH), the diagnosis, evolution, and treatment of which are subject to controversies. The aim of this pilot investigation was to assess the ability of specific magnetic resonance imaging (MRI) criteria to differentiate AD from IMH and predict optimal aortic remodeling following AAS.

METHODS

In this retrospective study, all patients presenting between 2008 and 2015 with type B AAS, who had diagnostic MRI following admission, were included. Three MRI criteria were proposed to identify IMH: (i) no visualised entry tear; (ii) no contrast uptake in the aortic lesion on the first pass angiographic run; (iii) no contrast uptake in the aortic lesion on the equilibrium phase T1 sequence. On each patient's diagnostic and follow up imaging studies, the volume of (i) false lumen/IMH, (ii) total aorta, and (iii) true lumen were calculated. Using the Wilcoxon signed rank test, the evolution of these volumes according to the presence or absence of the aforementioned criteria were compared.

RESULTS

Of 39 patients, in seven all MRI criteria were positive (group IMH) and 32 had one or more negative criteria (group AD). Patients with IMH and AD were similar with respect to sex, age, and delay between onset of symptoms and diagnostic and follow up imaging studies. Eighteen patients had a follow up imaging study after a mean period of 11.2 months: six in the IMH group and 12 in the AD group. Lesion volume decrease and relative true lumen volume increase were statistically significant in group IMH (p = .046 and p = .046, respectively), whereas there was a statistically significant increase of lesion volume (p = .008) in the AD group.

CONCLUSION

This pilot study proposed three simple MRI criteria to differentiate between AD and IMH. Once prospectively and clinically validated, this could have substantial therapeutic benefits as IMH are likely to heal spontaneously.

Data-driven Modeling of Hemodynamics and its Role on Thrombus Size and Shape in Aortic Dissections

Aortic dissection is a pathology that manifests due to microstructural defects in the aortic wall. Blood enters the damaged wall through an intimal tear, thereby creating a so-called false lumen and exposing the blood to thrombogenic intramural constituents such as collagen. The natural history of this acute vascular injury thus depends, in part, on thrombus formation, maturation, and possible healing within the false lumen. A key question is: Why do some false lumens thrombose completely while others thrombose partially or little at all? An ability to predict the location and extent of thrombus in subjects with dissection could contribute significantly to clinical decision-making, including interventional design. We develop, for the first time, a data-driven particle-continuum model for thrombus formation in a murine model of aortic dissection. In the proposed model, we simulate a final-value problem in lieu of the original initial-value problem with significantly fewer particles that may grow in size upon activation, thus representing the local concentration of blood-borne species. Numerical results confirm that geometry and local hemodynamics play significant roles in the acute progression of thrombus. Despite geometrical differences between murine and human dissections, mouse models can provide considerable insight and have gained popularity owing to their reproducibility. Our results for three classes of geometrically different false lumens show that thrombus forms and extends to a greater extent in regions with lower bulk shear rates. Dense thrombi are less likely to form in high-shear zones and in the presence of strong vortices. The present data-driven study suggests that the proposed model is robust and can be employed to assess thrombus formation in human aortic dissections.

Update on the Therapeutic Strategy of Type B Aortic Dissection

Stanford type B aortic dissection (TBAD) is a life-threatening disease. Current therapeutic guidelines recommend medical therapy with aggressive blood pressure lowering for patients with acute TBAD unless they have fatal complications. Although patients with uncomplicated TBAD have relatively low early mortality, aorta-related adverse events during the chronic phase worsen the long-term clinical outcome. Recent advances in thoracic endovascular aortic repair (TEVAR) can improve clinical outcomes in patients with both complicated and uncomplicated TBAD. According to present guidelines, complicated TBAD patients are recommended for TEVAR. However, the indication in uncomplicated TBAD remains controversial. Recent results of randomized trials, which compared the clinical outcome in patients treated with optimal medical therapy and those treated with TEVAR, suggest that preemptive TEVAR should be considered in uncomplicated TBAD with suitable aortic anatomy. However, these trials failed to show improvement in early mortality in patients treated with TEVAR compared with patients treated with optimal medical therapy, which suggest the importance of patient selection for TEVAR. Several clinical and imaging-related risk factors have been shown to be associated with early disease progression. Preemptive TEVAR might be beneficial and should be considered for high-risk patients with uncomplicated TBAD. However, an interdisciplinary consensus has not been established for the definition of patients at high-risk of TBAD, and it should be confirmed by experts including physicians, radiologists, interventionalists, and vascular surgeons. This review summarizes the current understanding of the therapeutic strategy in patients with TBAD based on evidence and expert consensus.

Contrast opacification on thoracic CT angiography: challenges and solutions

Contrast flow and enhancement patterns seen on thoracic CT angiography (CTA) can often be challenging and may often reveal more than is immediately apparent. A non-diagnostic CTA following the initial contrast injection can be secondary to many causes; these include both extrinsic factors, such as injection technique/equipment failure (iv cannula, power injector), and intrinsic, patient-related factors. Contrast pressure and flow graphs often contain useful information regarding the etiology of a non-diagnostic scan. Understanding these graphs will help the radiologist plan a repeat contrast injection to overcome the deficiencies of the first injection and thus obtain a diagnostic scan. The current review article outlines normal and abnormal intravenous contrast dynamics, discusses how to recognize etiologies of non-diagnostic scans, and ultimately addresses techniques to overcome obstacles towards obtaining normal contrast opacification of the target vessel. In addition, there are some life-threatening findings, which unless sought for, may remain hidden in plain sight.

Key Points

• Using contrast enhancement and flow patterns to identify the cause of a non-diagnostic CTA.

• Recognize life threatening causes of altered contrast dynamics such as cardiac asystole.

• Non-target vessel opacification may hold key to underlying pathophysiology.

X-ray computed tomography imaging of a tumor with high sensitivity using gold nanoparticles conjugated to a cancer-specific antibody via polyethylene glycol chains on their surface

Contrast agents are often used to enhance the contrast of X-ray computed tomography (CT) imaging of tumors to improve diagnostic accuracy. However, because the iodine-based contrast agents currently used in hospitals are of low molecular weight, the agent is rapidly excreted from the kidney or moves to extravascular tissues through the capillary vessels, depending on its concentration gradient. This leads to nonspecific enhancement of contrast images for tissues. Here, we created gold (Au) nanoparticles as a new contrast agent to specifically image tumors with CT using an enhanced permeability and retention (EPR) effect. Au has a higher X-ray absorption coefficient than does iodine. Au nanoparticles were supported with polyethylene glycol (PEG) chains on their surface to increase the blood retention and were conjugated with a cancer-specific antibody via terminal PEG chains. The developed Au nanoparticles were injected into tumor-bearing mice, and the distribution of Au was examined with CT imaging, transmission electron microscopy, and elemental analysis using inductively coupled plasma optical emission spectrometry. The results show that specific localization of the developed Au nanoparticles in the tumor is affected by a slight difference in particle size and enhanced by the conjugation of a specific antibody against the tumor.

Update in the management of type B aortic dissection

Stanford type B aortic dissection (TBAD) is a life-threatening aortic disease. The initial management goal is to prevent aortic rupture, propagation of the dissection, and symptoms by reducing the heart rate and blood pressure. Uncomplicated TBAD patients require prompt medical management to prevent aortic dilatation or rupture during subsequent follow-up. Complicated TBAD patients require immediate invasive management to prevent death or injury caused by rupture or malperfusion. Recent developments in diagnosis and management have reduced mortality related to TBAD considerably. In particular, the introduction of thoracic stent-grafts has shifted the management from surgical to endovascular repair, contributing to a fourfold increase in early survival in complicated TBAD. Furthermore, endovascular repair is now considered in some uncomplicated TBAD patients in addition to optimal medical therapy. For more challenging aortic dissection patients with involvement of the aortic arch, hybrid approaches, combining open and endovascular repair, have had promising results. Regardless of the chosen management strategy, strict antihypertensive control should be administered to all TBAD patients in addition to close imaging surveillance. Future developments in stent-graft design, medical therapy, surgical and hybrid techniques, imaging, and genetic screening may improve the outcomes of TBAD patients even further. We present a comprehensive review of the recommended management strategy based on current evidence in the literature.

Advances in the diagnosis of acute aortic syndromes: Role of imaging techniques

Aortic diseases include a wide range of pathological conditions: aortic aneurysms, pseudoaneurysms, acute aortic syndromes, atherosclerotic and inflammatory conditions, genetic diseases and congenital anomalies. Acute aortic syndromes have acute onset and may be life-threatening. They include aortic dissection, intramural haematoma, penetrating aortic ulcer and traumatic aortic injury. Pain is the common denominator to all acute aortic syndromes. Pain occurs regardless of age, gender and other associated clinical conditions. In this review, we deal with the main findings in the clinical setting and the most recent indications for diagnostic imaging, which are aimed to start an appropriate treatment and improve the short- and long-term prognosis of these patients.

Experience With Fenestrated Endovascular Repair of Juxtarenal Abdominal Aortic Aneurysms at a Single Center

To present the early and mid-term results of fenestrated endovascular aneurysm repair (FEVAR) using the Zenith fenestrated device for juxtarenal abdominal aortic aneurysms (JAAAs) at our center in China.

DESIGN

Retrospective study.The study included 15 male patients with JAAAs, who underwent FEVAR using the Zenith fenestrated device at our center between February 2011 and June 2015.All custom-made Zenith fenestrated devices were designed according to computed tomography angiography (CTA) images obtained preoperatively. The patients with renal insufficiency underwent duplex ultrasonography, while the patients with normal renal function underwent 3 CT data acquisitions including nonenhanced CT, arterial phase, and venous phase. These examinations and blood examinations were completed at 3, 6, and 12 months after discharge, and annually thereafter.The mean age of the patients was 73.13 ± 9.06 years (range, 57-86 years), and the median follow-up period was 30 months (8-52 months). Small fenestrations were used in 27 renal arteries, scallops were used in 7 superior mesenteric arteries (SMAs) and 2 renal arteries, and large fenestrations were used in 2 SMAs. Conversion to an open procedure was not required in any of the patients, and the technical success rate was 100%. The mean length of hospital stay was 11.33 ± 2.02 days (7-15 days). No patient died within the 1st 30 days after the operation. One patient had a type Ia endoleak, which disappeared at 6 months after the operation, 1 patient had a type Ib endoleak, which was detected at 17 months after the operation, and 2 patients had type II endoleaks. One patient died at 17 months and another patient died at 30 months after the operation. Therefore, the all-cause mortality rate was 13.33% (2/15). The target vessel patency rate was 100% without occlusion.The early and mid-term results of FEVAR using the Zenith fenestrated device were good, demonstrating that this procedure is effective for the treatment of JAAAs.

Modern diagnostics for type B aortic dissection

Background

Undifferentiated chest pain is one of the most common complaints in the acute care setting. Type B aortic dissection is an important cause of chest pain and a complex clinical entity, which carries significant morbidity and mortality and requires accurate clinical and radiological evaluation.

Methods

Imaging technologies have become an irreplaceable tool to establish the diagnosis of aortic dissection and to plan treatment strategies. Computed tomography is an important component in this process, replacing catheter-based angiography as the most commonly used preoperative and postoperative imaging modality for the thoracic aorta. The use of functional imaging methods, such as magnetic resonance imaging and echocardiography is evolving. These methods are able to provide the clinically relevant anatomical, hemodynamic and biomechanical information that is necessary for accurate diagnosis, risk stratification and patient selection for treatment.

Conclusion

Advanced image acquisition equipment and expertise are increasingly available in a growing number of institutions and as a consequence, existing strategies for the management of type B dissection are rapidly evolving.

Development and testing of a silicone in vitro model of descending aortic dissection

BACKGROUND

Stanford type B dissection of the descending aorta is a potentially fatal condition that is poorly understood. Limited scientific understanding of the role of current interventional techniques, as well as heterogeneity in the condition, contributes to lack of consensus as to the most effective treatment strategy. This study introduces an anatomically accurate model for investigating aortic dissection in a laboratory setting.

MATERIALS AND METHODS

A silicone model was fabricated and filled with fluid to mimic human blood. Flow was established, and the model was scanned using a four-dimensional flow magnetic resonance imaging protocol. On analysis, luminal flow rates were quantified by multiplying local velocity by included area.

RESULTS

The upstream total flow was compared with the sum of the flow in the true and false lumens. The two values were within the margin of error. Furthermore, flow rates matched with the relative areas of each compartment.

CONCLUSIONS

These results validate our model as a novel and unique system that mimics a type B aortic dissection and will allow for more sophisticated analysis of dissection physiology in future studies.

Management of acute aortic dissection

A new appraisal of the management of acute aortic dissection is timely because of recent developments in diagnostic strategies (including biomarkers and imaging), endograft design, and surgical treatment, which have led to a better understanding of the epidemiology, risk factors, and molecular nature of aortic dissection. Although open surgery is the main treatment for proximal aortic repair, use of endovascular management is now established for complicated distal dissection and distal arch repair, and has recently been discussed as a pre-emptive measure to avoid late complications by inducing aortic remodelling.

Usefulness of new imaging methods for assessment of type B aortic dissection

While the medical management of uncomplicated type B aortic dissection has good outcomes in the short term, the longer term mortality can be in the region of 50% at 5 years. Up to 40% of the survivors can have significant dilatation of the false lumen with the risk of aneurysm formation and death due to rupture. The results of the randomized controlled trials ADSORB and INSTEAD-XL have shown that beneficial aortic remodelling occurs after endoluminal stent graft placement, but these trials were underpowered to show any effect on survival. Static computed tomography (CT) angiography imaging methods have been used to try to identify high risk patients using parameters such as diameter, the position and size of the entry tear, and the amount of false lumen thrombus, but these so far are not able to clinically risk stratify individual patients. In this manuscript, we present our initial experience with new MR imaging methods. These have allowed us to develop a greater understanding of aortic dissection by providing information regarding the underlying hemodynamic and biomechanics of the dissection, as well as more accurate assessment of important clinical imaging endpoints, such as false lumen thrombosis.

Endovascular repair of acute uncomplicated aortic type B dissection promotes aortic remodelling: 1 year results of the ADSORB trial

OBJECTIVES

Uncomplicated acute type B aortic dissection (AD) treated conservatively has a 10% 30-day mortality and up to 25% need intervention within 4 years. In complicated AD, stent grafts have been encouraging. The aim of the present prospective randomised trial was to compare best medical treatment (BMT) with BMT and Gore TAG stent graft in patients with uncomplicated AD. The primary endpoint was a combination of incomplete/no false lumen thrombosis, aortic dilatation, or aortic rupture at 1 year.

METHODS

The AD history had to be less than 14 days, and exclusion criteria were rupture, impending rupture, malperfusion. Of the 61 patients randomised, 80% were DeBakey type IIIB.

RESULTS

Thirty-one patients were randomised to the BMT group and 30 to the BMT+TAG group. Mean age was 63 years for both groups. The left subclavian artery was completely covered in 47% and in part in 17% of the cases. During the first 30 days, no deaths occurred in either group, but there were three crossovers from the BMT to the BMT+TAG group, all due to progression of disease within 1 week. There were two withdrawals from the BMT+TAG group. At the 1-year follow up there had been another two failures in the BMT group: one malperfusion and one aneurysm formation (p = .056 for all). One death occurred in the BMT+TAG group. For the overall endpoint BMT+TAG was significantly different from BMT only (p < .001). Incomplete false lumen thrombosis, was found in 13 (43%) of the TAG+BMT group and 30 (97%) of the BMT group (p < .001). The false lumen reduced in size in the BMT+TAG group (p < .001) whereas in the BMT group it increased. The true lumen increased in the BMT+TAG (p < .001) whereas in the BMT group it remained unchanged. The overall transverse diameter was the same at the beginning and after 1 year in the BMT group (42.1 mm), but in the BMT+TAG it decreased (38.8 mm; p = .062).

CONCLUSIONS

Uncomplicated AD can be safely treated with the Gore TAG device. Remodelling with thrombosis of the false lumen and reduction of its diameter is induced by the stent graft, but long term results are needed.

Gadofosveset trisodium: abdominal and peripheral vascular applications

OBJECTIVE

The purpose of this review is to illustrate various applications of gadofosveset trisodium in evaluating abdominal and peripheral vascular disease. The basic properties, technical considerations, and clinical and potential future applications of gadofosveset are described.

CONCLUSION

Gadofosveset trisodium facilitates comprehensive high-resolution arterial and venous MR angiography. Because of its prolonged intravascular residence time, gadofosveset trisodium is particularly useful for evaluating venous, dynamic, and functional vascular disease with a single low-dose contrast injection.

Extent of preoperative false lumen thrombosis does not influence long-term survival in patients with acute type A aortic dissection

Background

Partial thrombosis of the false lumen has been related to aortic growth, reoperations, and death in the chronic phase of type B and repaired type A aortic dissections. The impact of preoperative false lumen thrombosis has not been studied previously. We used data from a contemporary, multinational database on aortic dissections to evaluate whether different degrees of preoperative false lumen thrombosis influenced long‐term prognosis.

Methods and Results

We examined the records of 522 patients with surgically treated acute type A aortic dissections who survived to discharge between 1996 and 2011. At the preoperative imaging, 414 (79.3%) patients had patent false lumens, 84 (16.1%) had partial thrombosis of the false lumen, and 24 (4.6%) had complete thrombosis of the false lumen. The annual median (interquartile range) aortic growth rates were 0.5 (−0.3 to 2.0) mm in the aortic arch, 2.0 (0.2 to 4.0) mm in the descending thoracic aorta, and similar regardless of the degree of false lumen thrombosis. The overall 5‐year survival rate was 84.7%, and it was not influenced by false lumen thrombosis (P=0.86 by the log‐rank test). Independent predictors of long‐term mortality were age >70 years (hazard ratio [HR], 2.34; 95% confidence interval [CI], 1.20 to 4.56, P=0.012) and postoperative cerebrovascular accident, coma, and/or renal failure (HR, 2.62; 95% CI, 1.40 to 4.92, P=0.003).

Conclusions

Patients with acute type A aortic dissection who survive to discharge have a favorable prognosis. Preoperative false lumen thrombosis does not influence long‐term mortality, reintervention rates, or aortic growth.

Imaging modalities for the early diagnosis of acute aortic syndrome

The term acute aortic syndrome (AAS) incorporates aortic dissection, intramural haematoma, and penetrating atherosclerotic ulcer. The common feature of these entities is disruption of the medial layer of the aortic wall. Owing to the life-threatening nature of these conditions, prompt and accurate diagnosis is of paramount importance--misdiagnosis can be fatal. The noninvasive imaging techniques that have a fundamental role in the diagnosis and management of patients with AAS include CT, MRI, transoesophageal echocardiography (TEE), and transthoracic echocardiography (TTE). CT is the most-commonly used imaging modality owing to its wide availability, accuracy, and large field of view. CT plus TTE is the best combination for diagnosing AAS and its complications, and allows important morphological and dynamic aspects of AAS to be assessed and appropriately managed. Ideally, TEE should be performed immediately before surgery or endovascular treatment, in the operating theatre and under general anaesthesia. In stable patients with an uncertain diagnosis of intramural haematoma despite high clinical suspicion, MRI is the technique of choice to make a definitive diagnosis. Imaging techniques have an important role in the primary diagnosis, treatment strategy, and risk stratification of patients with AAS.

MRI for acute chest pain: current state of the art

This article reviews the magnetic resonance imaging (MRI) and angiography (MRA) techniques, imaging findings, and evidence for evaluating patients with acute chest pain due to acute pulmonary embolus (PE), aortic dissection (AD), and myocardial infarction (MI). When computed tomographic angiography (CTA) is contraindicated, MRI and MRA are important alternative imaging modalities for diagnosis and management of patients with acute PE, AD, and MI. Familiarity with the techniques, imaging findings, and evidence is critical to safely and appropriately managing patients presenting with acute chest pain.

The role of mandatory lifelong annual surveillance after thoracic endovascular repair

Thoracic endovascular aortic repair (TEVAR) has become an attractive and well-accepted option for the management of the various thoracic aortic pathologies that vascular surgeons are confronted with. As in the abdominal aorta, current management trends include the treatment of younger patients with longer life expectancies, raising the issue of postoperative surveillance. There are several relevant differences between these anatomic areas when it comes to surveillance, including the relative inaccessibility of the thoracic aorta to ultrasound interrogation and the increased variability of thoracic aortic pathologies and post-TEVAR complications. In addition, concerns regarding radiation-induced carcinogenesis and contrast-induced nephropathy reduce the enthusiasm of many surgeons for regular computed tomography surveillance. Most agree that surveillance is important after TEVAR, but the method, duration, and frequency of that surveillance is much less clear and is the topic of this debate.

Integration of the computational fluid dynamics technique with MRI in aortic dissections

Short-term and long-term prognosis and their determining factors of Type III/Stanford B aortic dissections (TB-AD), which separate the aorta distal at the origin of the subclavian artery into a true lumen and false lumen, have been elusive: One quarter of patients thought to be treated successfully, either by medical or by surgical means, do not survive 3 years. Unfavorable hemodynamic conditions are believed to lead to false lumen pressure increases and complications. A better characterization of TB-AD hemodynamics may therefore impact therapeutic decision making and improve outcome. The large variations in TB-AD morphology and hemodynamics favor a patient-specific approach. Magnetic resonance imaging with its capability to provide high-resolution structural images of the lumen and aortic wall and also to quantify aortic flow and kinetics of an exogenous tracer is a promising clinical modality for developing a deeper understanding of TB-AD hemodynamics in an individual patient. With the information obtained with magnetic resonance imaging, computational fluid dynamics simulations can be performed to augment the image information. Here, an overview of the interplay of magnetic resonance imaging and computational fluid dynamics techniques is given illustrating the synergy of these two approaches toward a comprehensive morphological and hemodynamic characterization of TB-AD.

Remodeling of intramural thrombus and collagen in an Ang-II infusion ApoE-/- model of dissecting aortic aneurysms

Fibrillar collagen endows the normal aortic wall with significant stiffness and strength and similarly plays important roles in many disease processes. For example, because of the marked loss of elastic fibers and functional smooth cells in aortic aneurysms, collagen plays a particularly important role in controlling the dilatation of these lesions and governing their rupture potential. Recent findings suggest further that collagen remodeling may also be fundamental to the intramural healing of arterial or aneurysmal dissections. To explore this possibility further, we identified and correlated regions of intramural thrombus and newly synthesized fibrillar collagen in a well-established mouse model of dissecting aortic aneurysms. Our findings suggest that intramural thrombus that is isolated from free-flowing blood creates a permissive environment for the synthesis of fibrillar collagen that, albeit initially less dense and organized, could protect that region of the dissected wall from subsequent expansion of the dissection or rupture. Moreover, alpha-smooth muscle actin positive cells appeared to be responsible for the newly produced collagen, which co-localized with significant production of glycosaminoglycans.

Recovery of paraplegia after type B dissection due to spinal collateral recruitment

Acute paraplegia could be a symptom of aortic dissection due to sudden compromise of arterial spinal cord blood supply. Complete spontaneous neurologic recovery is possible and was observed in the present case 3 hours after symptom onset. Spontaneous spinal cord reperfusion after acute type B dissection was probably due to two main mechanisms. Reperfusion of false lumen and collateral vascular network recruitment, recently confirmed by anatomic animal studies, serve as potential explanations. Favorable evolution of acute paraplegia after aortic dissection exists, but prognosis is uncertain, probably due to individual variable anatomic distribution of spinal cord blood supply.

Predictors of outcome after endovascular repair for chronic type B dissection

OBJECTIVES

To assess the durability of endovascular repair (TEVAR) in chronic type B dissection (CD) and identify factors predictive of outcome.

DESIGN

Retrospective analysis of a prospective database.

MATERIALS

Patients undergoing TEVAR for CD at a tertiary referral centre 2000-2010.

METHODS

Analysis of pre-operative characteristics, operative outcome, false lumen thrombosis, aortic diameter and survival.

RESULTS

58 consecutive patients were included (49 elective, 9 urgent, mean age 66 years). Mean aortic diameter was 6.4 cm (Standard deviation SD 1.3 cm). Three patients died perioperatively (5%, 1 urgent, 2 elective). Complications included retrograde type A dissection (n = 3), paraplegia (1), and transient ischaemic attack (1). Estimated survival (Kaplan-Meier) was 89% (1-year) and 64% (3-years). Forty-seven patients had mid-term imaging follow-up at mean 38 months. Reintervention rate was 15% at 1-year and 29% at 3-years. Aortic diameter decreased in 24, was stable in 15 and increased in 8. Mid-term survival was higher in patients with aortic remodelling (reduction of aortic diameter >0.5 cm; 3-year 89%) than without (54%; Log Rank p = 0.005). Remodelling occurred with extensive false lumen thrombosis.

CONCLUSION

Satisfactory mid-term outcome after TEVAR for CD remains a challenge. Survival is associated with aortic remodelling, which is related to persistence of flow in the false lumen.