MRI in CFD for chronic type B aortic dissection: Ready for prime time?

https://doi.org/10.1016/j.compbiomed.2022.106138Get rights and content

Highlights

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    A systematic review of integrating magnetic resonance imaging (MRI) and computational fluid dynamics (CFD) in Type B aortic dissection (TBAD).

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    MRI plays roles in providing flow data for CFD boundary conditions, validating simulation results, and giving wall motion information.

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    Proposal of incorporating multiple MRI modalities to provide patient-specific data and improve the computational modelling of TBAD.

Abstract

Objectives

Better tools are needed for risk assessment of Type B aortic dissection (TBAD) to determine optimal treatment for patients with uncomplicated disease. Magnetic resonance imaging (MRI) has the potential to inform computational fluid dynamics (CFD) simulations for TBAD by providing individualised quantification of haemodynamic parameters, for assessment of complication risks. This systematic review aims to present an overview of MRI applications for CFD studies of TBAD.

Methods

Following PRISMA guidelines, a search in Medline, Embase, and the Scopus Library identified 136 potentially relevant articles. Studies were included if they used MRI to inform CFD simulation in TBAD.

Results

There were 20 articles meeting the inclusion criteria. 19 studies used phase contrast MRI (PC-MRI) to provide data for CFD flow boundary conditions. In 12 studies, CFD haemodynamic parameter results were validated against PC-MRI. In eight studies, geometric models were developed from MR angiography. In three studies, aortic wall or intimal flap motion data were derived from PC/cine MRI.

Conclusions

MRI provides complementary patient-specific information in CFD haemodynamic studies for TBAD that can be used for personalised care. MRI provides structural, dynamic and flow data to inform CFD for pre-treatment planning, potentially advancing its integration into clinical decision-making. The use of MRI to inform CFD in TBAD surgical planning is promising, however further validation and larger cohort studies are required.

Introduction

Type B aortic dissection (TBAD) is a cardiovascular catastrophe with a prevalence of 2.9–4.0 per 100 000 person-years [1]. At present, optimal treatment for TBAD has yet to be determined [2], and improving understanding of its haemodynamics may provide insight. There is strong evidence that complicated TBAD requires emergent intervention [3] to prevent death through end-organ ischemia or aortic rupture [4], where thoracic endovascular aortic repair (TEVAR) has become the optimal option [[3], [4], [5]]. For uncomplicated TBAD, however, the evidence guiding management is relatively weak, owing to limited clinical trials data comparing medical treatment, open repair and TEVAR [3]. Acutely, medical management is standard practice, aiming to limit aortic dilation over time and thereby prevent potential complications, using imaging for surveillance [5]. In chronic TBAD, either recurrent symptoms (e.g. uncontrollable back pain) or aortic dilation are the conventional factors that determine when to intervene [3]. However, this paradigm may not be optimal, with Booher et al. [6] reporting endovascular treatment is associated with the highest cumulative survival within 60 days (Fig. 1), superior to medical management.

Computational fluid dynamics (CFD), which analyses fluid flow with the use of computer-based simulation, has an important potential role in identifying potential haemodynamic risk factors for TBAD complications [7]. CFD simulates blood flow non-invasively and with high-resolution in arteries, by typically making assumptions about flow or pressure information within the boundaries of blood vessels, known as setting boundary conditions. This has traditionally relied upon a series of assumptions [8] including rigid vessel walls and simplified boundary conditions. More recently, CT angiography (CTA) has been used for patient-specific vessel geometry [9]. Magnetic resonance imaging (MRI) offers further promise to inform CFD boundary conditions with patient-specific haemodynamic data in addition to morphologic information, or to validate results of CFD simulations. Besides, MRI does not impart ionising radiation, an important factor for younger patients undergoing long-term follow-up [10].

A prior mini review of the literature on the potential role of MRI and CFD in TBAD covered studies published before 2012 [11]. However, limited studies were reviewed non-systematically and body of literature has significantly grown since then. With advances in MR technology in recent years, especially volumetric phase contrast MRI (PC-MRI) for quantifying flow, known as 4D Flow MRI [12], MRI has increasingly been used to supplement or validate CFD studies of TBAD. In this systematic review, we examine the role of MRI in CFD applications of chronic TBAD. It begins with a brief overview of current triggers for intervention and haemodynamics of TBAD. We then review how it can be assessed with MRI and CFD, with reference to the existing literature and examples from our own experience. Finally, we discuss steps required for clinical application in the future.

Section snippets

Review criteria

Original articles published before 15th August 2022 were eligible for this review. Inclusion criteria were studies of the human aorta, and: a) studies which used MRI to inform CFD simulations of type B aortic dissection (de novo or residual following Type A proximal repair), including MRI-derived geometry, haemodynamics derived from phase contrast techniques or vessel movement, and; b) studies using MRI to validate CFD.

Non-English language studies, scientific abstracts without an available full

Search results

136 records were identified, with 73 articles remaining after elimination of duplicates. After screening the remaining articles for appropriateness, 37 articles proceeded to full-text assessment. Of these, 20 studies met the inclusion criteria [[14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33]] (Fig. 2). Results and key features for each study are summarised in Table 1.

All included studies reported hemodynamic parameters in

TBAD management: when to intervene?

Patients with uncomplicated TBAD typically receive medical therapy for pain and blood pressure control with close surveillance [35], although favourable results of TEVAR challenge the traditional approach [36,37].

Clinical factors and morphology currently dictate when invasive management is required. In addition to recurrent symptoms and signs such as uncontrolled hypertension, morphologic findings predicting adverse outcomes include initial aortic diameter ≥40 mm with a patent false lumen [38],

Conclusion

MRI is a non-invasive and versatile imaging modality that can be used to obtain patient geometric, blood flow and motion data. It is an invaluable complementary tool in computational simulations of TBAD, providing information about boundary conditions, distension of the vessel wall and flap motion. It can also provide in-vivo validation of haemodynamic metrics, with good agreement between CFD simulations and MRI measurements, particularly for the TL. Studies performed to date demonstrate the

Funding

The authors gratefully acknowledge funding support from the Royal Australian and New Zealand College of Radiologists (number: 2017/RANZCR/002).

Data availability statement

The raw data supporting this article can be made available from the corresponding author upon reasonable request, subject to institutional ethics approval.

Declaration of competing interest

None Declared.

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