Advanced cardiac MRI techniques for evaluation of left-sided valvular heart disease

Fully Automated Valve Segmentation for Blood Flow Assessment From 4D Flow MRI Including Automated Cardiac Valve Tracking and Transvalvular Velocity Mapping

BACKGROUND

Automated 4D flow MRI valvular flow quantification without time-consuming manual segmentation might improve workflow.

PURPOSE

Compare automated valve segmentation (AS) to manual (MS), and manually corrected automated segmentation (AMS), in corrected atrioventricular septum defect (c-AVSD) patients and healthy volunteers, for assessing net forward volume (NFV) and regurgitation fraction (RF).

STUDY TYPE

Retrospective.

POPULATION

27 c-AVSD patients (median, 23 years; interquartile range, 16-31 years) and 24 healthy volunteers (25 years; 12.5-36.5 years).

FIELD STRENGTH/SEQUENCE

Whole-heart 4D flow MRI and cine steady-state free precession at 3T.

ASSESSMENT

After automatic valve tracking, valve annuli were segmented on time-resolved reformatted trans-valvular velocity images by AS, MS, and AMS. NFV was calculated for all valves, and RF for right and left atrioventricular valves (RAVV and LAVV). NFV variation (standard deviation divided by mean NFV) and NFV differences (NFV difference of a valve vs. mean NFV of other valves) expressed internal NFV consistency.

STATISTICAL TESTS

Comparisons between methods were assessed by Wilcoxon signed-rank tests, and intra/interobserver variability by intraclass correlation coefficients (ICCs). P < 0.05 was considered statistically significant, with multiple testing correction.

RESULTS

AMS mean analysis time was significantly shorter compared with MS (5.3 ± 1.6 minutes vs. 9.1 ± 2.5 minutes). MS NFV variation (6.0%) was significantly smaller compared with AMS (6.3%), and AS (8.2%). Median NFV difference of RAVV, LAVV, PV, and AoV between segmentation methods ranged from -0.7-1.0 mL, -0.5-2.8 mL, -1.1-3.6 mL, and - 3.1--2.1 mL, respectively. Median RAVV and LAVV RF, between 7.1%-7.5% and 3.8%-4.3%, respectively, were not significantly different between methods. Intraobserver/interobserver agreement for AMS and MS was strong-to-excellent for NFV and RF (ICC ≥0.88).

DATA CONCLUSION

MS demonstrates strongest internal consistency, followed closely by AMS, and AS. Automated segmentation, with or without manual correction, can be considered for 4D flow MRI valvular flow quantification.

LEVEL OF EVIDENCE

3 TECHNICAL EFFICACY: Stage 3.

Clinical Applications of Four-Dimensional Flow MRI

Four-dimensional flow MRI is a powerful phase contrast technique used for assessing three-dimensional (3D) blood flow dynamics. By acquiring a time-resolved velocity field, it enables flexible retrospective analysis of blood flow that can include qualitative 3D visualization of complex flow patterns, comprehensive assessment of multiple vessels, reliable placement of analysis planes, and calculation of advanced hemodynamic parameters. This technique provides several advantages over routine two-dimensional flow imaging techniques, allowing it to become part of clinical practice at major academic medical centers. In this review, we present the current state-of-the-art cardiovascular, neurovascular, and abdominal applications.

Personalized biomechanical insights in atrial fibrillation: opportunities & challenges

INTRODUCTION

Atrial fibrillation (AF) is an increasingly prevalent and significant worldwide health problem. Manifested as an irregular atrial electrophysiological activation, it is associated with many serious health complications. AF affects the biomechanical function of the heart as contraction follows the electrical activation, subsequently leading to reduced blood flow. The underlying mechanisms behind AF are not fully understood, but it is known that AF is highly correlated with the presence of atrial fibrosis, and with a manifold increase in risk of stroke.

AREAS COVERED

In this review, we focus on biomechanical aspects in atrial fibrillation, current and emerging use of clinical images, and personalized computational models. We also discuss how these can be used to provide patient-specific care.

EXPERT OPINION

Understanding the connection betweenatrial fibrillation and atrial remodeling might lead to valuable understanding of stroke and heart failure pathophysiology. Established and emerging imaging modalities can bring us closer to this understanding, especially with continued advancements in processing accuracy, reproducibility, and clinical relevance of the associated technologies. Computational models of cardiac electromechanics can be used to glean additional insights on the roles of AF and remodeling in heart function.

Four-Dimensional Flow MRI for the Evaluation of Aortic Endovascular Graft: A Pilot Study

We aimed to explore the feasibility of 4D flow magnetic resonance imaging (MRI) for patients undergoing thoracic aorta endovascular repair (TEVAR). We retrospectively evaluated ten patients (two female), with a mean (±standard deviation) age of 61 ± 20 years, undergoing MRI for a follow-up after TEVAR. All 4D flow examinations were performed using a 1.5-T system (MAGNETOM Aera, Siemens Healthcare, Erlangen, Germany). In addition to the standard examination protocol, a 4D flow-sensitive 3D spatial-encoding, time-resolved, phase-contrast prototype sequence was acquired. Among our cases, flow evaluation was feasible in all patients, although we observed some artifacts in 3 out of 10 patients. Three individuals displayed a reduced signal within the vessel lumen where the endograft was placed, while others presented with turbulent or increased flow. An aortic endograft did not necessarily hinder the visualization of blood flow through 4D flow sequences, although the graft could generate flow artifacts in some cases. A 4D Flow MRI may represent the ideal tool to follow up on both healthy subjects deemed to be at an increased risk based on their anatomical characteristics or patients submitted to TEVAR for whom a surveillance protocol with computed tomography angiography would be cumbersome and unjustified.

Recent technologies in cardiac imaging

Cardiac imaging allows physicians to view the structure and function of the heart to detect various heart abnormalities, ranging from inefficiencies in contraction, regulation of volumetric input and output of blood, deficits in valve function and structure, accumulation of plaque in arteries, and more. Commonly used cardiovascular imaging techniques include x-ray, computed tomography (CT), magnetic resonance imaging (MRI), echocardiogram, and positron emission tomography (PET)/single-photon emission computed tomography (SPECT). More recently, even more tools are at our disposal for investigating the heart's physiology, performance, structure, and function due to technological advancements. This review study summarizes cardiac imaging techniques with a particular interest in MRI and CT, noting each tool's origin, benefits, downfalls, clinical application, and advancement of cardiac imaging in the near future.

Intra-cardiac pressure drop and flow distribution of bicuspid aortic valve disease in preserved ejection fraction

Background

Bicuspid aortic valve (BAV) is more than a congenital defect since it is accompanied by several secondary complications that intensify induced impairments. Hence, BAV patients need lifelong evaluations to prevent severe clinical sequelae. We applied 4D-flow magnetic resonance imaging (MRI) for in detail visualization and quantification of in vivo blood flow to verify the reliability of the left ventricular (LV) flow components and pressure drops in the silent BAV subjects with mild regurgitation and preserved ejection fraction (pEF).

Materials and methods

A total of 51 BAV patients with mild regurgitation and 24 healthy controls were recruited to undergo routine cardiac MRI followed by 4D-flow MRI using 3T MRI scanners. A dedicated 4D-flow module was utilized to pre-process and then analyze the LV flow components (direct flow, retained inflow, delayed ejection, and residual volume) and left-sided [left atrium (LA) and LV] local pressure drop. To elucidate significant diastolic dysfunction in our population, transmitral early and late diastolic 4D flow peak velocity (E-wave and A-wave, respectively), as well as E/A ratio variable, were acquired.

Results

The significant means differences of each LV flow component (global measurement) were not observed between the two groups (p > 0.05). In terms of pressure analysis (local measurement), maximum and mean as well as pressure at E-wave and A-wave timepoints at the mitral valve (MV) plane were significantly different between BAV and control groups (p: 0.005, p: 0.02, and p: 0.04 and p: <0.001; respectively). Furthermore, maximum pressure and pressure difference at the A-wave timepoint at left ventricle mid and left ventricle apex planes were significant. Although we could not find any correlation between LV diastolic function and flow components, Low but statistically significant correlations were observed with local pressure at LA mid, MV and LV apex planes at E-wave timepoint (R: −0.324, p: 0.005, R: −0.327, p: 0.004, and R: −0.306, p: 0.008, respectively).

Conclusion

In BAV patients with pEF, flow components analysis is not sensitive to differentiate BAV patients with mild regurgitation and healthy control because flow components and EF are global parameters. Inversely, pressure (local measurement) can be a more reliable biomarker to reveal the early stage of diastolic dysfunction.

Rationale and clinical applications of 4D flow cardiovascular magnetic resonance in assessment of valvular heart disease: a comprehensive review

BACKGROUND

Accurate evaluation of valvular pathology is crucial in the timing of surgical intervention. Whilst transthoracic echocardiography is widely available and routinely used in the assessment of valvular heart disease, it is bound by several limitations. Although cardiovascular magnetic resonance (CMR) imaging can overcome many of the challenges encountered by echocardiography, it also has a number of limitations.

MAIN TEXT

4D Flow CMR is a novel technique, which allows time-resolved, 3-dimensional imaging. It enables visualisation and direct quantification of flow and peak velocities of all valves simultaneously in one simple acquisition, without any geometric assumptions. It also has the unique ability to measure advanced haemodynamic parameters such as turbulent kinetic energy, viscous energy loss rate and wall shear stress, which may add further diagnostic and prognostic information. Although 4D Flow CMR acquisition can take 5-10 min, emerging acceleration techniques can significantly reduce scan times, making 4D Flow CMR applicable in contemporary clinical practice.

CONCLUSION

4D Flow CMR is an emerging CMR technique, which has the potential to become the new reference-standard method for the evaluation of valvular lesions. In this review, we describe the clinical applications, advantages and disadvantages of 4D Flow CMR in the assessment of valvular heart disease.

ACR Appropriateness Criteria® Dyspnea-Suspected Cardiac Origin (Ischemia Already Excluded): 2021 Update

Dyspnea is the symptom of perceived breathing discomfort and is commonly encountered in a variety of clinical settings. Cardiac etiologies of dyspnea are an important consideration; among these, valvular heart disease (Variant 1), arrhythmia (Variant 2), and pericardial disease (Variant 3) are reviewed in this document. Imaging plays an important role in the clinical assessment of these suspected abnormalities, with usually appropriate procedures including resting transthoracic echocardiography in all three variants, radiography for Variants 1 and 3, MRI heart function and morphology in Variants 2 and 3, and CT heart function and morphology with intravenous contrast for Variant 3. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Risk of Stroke With Mitral Stenosis: The Underlying Mechanism, Treatment, and Prevention

Mitral stenosis (MS), a valvular heart disease, is defined by the narrowing of the mitral valve orifice. The common risk factors for stroke include mitral annular calcification (MAC), diabetes mellitus (DM), male gender, hypertension (HTN), hyperlipidemia, and obesity. Endothelial damage, hypercoagulability, and blood stasis in the left atrium promote the development of the thrombus. Among all the risk factors described, MAC is the independent predictor of stroke. The complicated mechanisms responsible for thromboembolism, predisposing factors for thromboembolism, the risk of cerebrovascular accident (CVA) in MS patients, advanced standardized assessment models for identifying those at risk for stroke, and the possible advantages and disadvantages of available therapies have all been discussed in this review article. We have also discussed newer oral anticoagulants (NOACs) like dabigatran, edoxaban, apixaban, and rivaroxaban. Non-pharmacological therapies are also highlighted such as left atrial appendage ligation and occlusion devices. We also conducted a thorough review of the literature on the efficacy and safety of various NOACs in reducing the risk of stroke.

Multi-modality imaging assessment of native valvular regurgitation: an EACVI and ESC council of valvular heart disease position paper

Valvular regurgitation represents an important cause of cardiovascular morbidity and mortality. Imaging is pivotal in the evaluation of native valve regurgitation and echocardiography is the primary imaging modality for this purpose. The imaging assessment of valvular regurgitation should integrate quantification of the regurgitation, assessment of the valve anatomy and function, and the consequences of valvular disease on cardiac chambers. In clinical practice, the management of patients with valvular regurgitation largely relies on the results of imaging. It is crucial to provide standards that aim at establishing a baseline list of measurements to be performed when assessing native valve regurgitation. The present document aims to present clinical guidance for the multi-modality imaging assessment of native valvular regurgitation.

Multiparametric MRI identifies subtle adaptations for demarcation of disease transition in murine aortic valve stenosis

Aortic valve stenosis (AS) is the most frequent valve disease with relevant prognostic impact. Experimental model systems for AS are scarce and comprehensive imaging techniques to simultaneously quantify function and morphology in disease progression are lacking. Therefore, we refined an acute murine AS model to closely mimic human disease characteristics and developed a high-resolution magnetic resonance imaging (MRI) approach for simultaneous in-depth analysis of valvular, myocardial as well as aortic morphology/pathophysiology to identify early changes in tissue texture and critical transition points in the adaptive process to AS. AS was induced by wire injury of the aortic valve. Four weeks after surgery, cine loops, velocity, and relaxometry maps were acquired at 9.4 T to monitor structural/functional alterations in valve, aorta, and left ventricle (LV). In vivo MRI data were subsequently validated by histology and compared to echocardiography. AS mice exhibited impaired valve opening accompanied by significant valve thickening due to fibrotic remodelling. While control mice showed bell-shaped flow profiles, AS resulted not only in higher peak flow velocities, but also in fragmented turbulent flow patterns associated with enhanced circumferential strain and an increase in wall thickness of the aortic root. AS mice presented with a mild hypertrophy but unaffected global LV function. Cardiac MR relaxometry revealed reduced values for both T1 and T2 in AS reflecting subtle myocardial tissue remodelling with early alterations in mitochondrial function in response to the enhanced afterload. Concomitantly, incipient impairments of coronary flow reserve and myocardial tissue integrity get apparent accompanied by early troponin release. With this, we identified a premature transition point with still compensated cardiac function but beginning textural changes. This will allow interventional studies to explore early disease pathophysiology and novel therapeutic targets.

Estimating the Haemodynamic Streamline Vena Contracta as the Effective Orifice Area Measured from Reconstructed Multislice Phase-contrast MR Images for Patients with Moderately Accelerated Aortic Stenosis

PURPOSE

In aortic stenosis (AS), the discrepancy between moderately accelerated flow and effective orifice area (EOA) continues to pose a challenge. We developed a method of measuring the vena contracta area as hemodynamic EOA using cardiac MRI focusing on AS patients with a moderately accelerated flow to solve the problem that AS severity can currently be determined only by echocardiography.

METHODS

We investigated 40 patients with a peak transvalvular velocity > 3.0 m/s on transthoracic echocardiography (TTE). The patients were divided into highly accelerated and moderately accelerated AS groups according to whether or not the peak transvalvular velocity was ≥ 4.0 m/s. From the multislice 2D cine phase-contrast MRI data, the cross-sectional area of the vena contracta of the reconstructed streamline in the Valsalva sinus was defined as MRI-EOAs. Patient symptoms and echocardiography data, including EOA (defined as TTE-EOA), were derived from the continuity equation using TTE.

RESULTS

All participants in the highly accelerated AS group (n = 19) showed a peak velocity ≥ 4.0 m/s in MRI. Eleven patients in the moderately accelerated AS group (n = 21) had a TTE-EOA < 1.00 cm². In the moderately accelerated AS group, MRI-EOAs demonstrated a strong correlation with TTE-EOAs (r = 0.76, P < 0.01). Meanwhile, in the highly accelerated AS group, MRI-EOAs demonstrated positivity but a moderate correlation with TTE-EOAs (r = 0.63, P = 0.004). MRI-EOAs were overestimated compared to TTE-EOAs. In terms of the moderately accelerated AS group, the best cut-off value for MRI-EOAs was < 1.23 cm², compatible with TTE-EOAs < 1.00 cm², with an excellent prediction of the New York Heart Association classification ≥ III (sensitivity 87.5%, specificity 76.9%).

CONCLUSION

MRI-EOAs may be an alternative to conventional echocardiography for patients with moderately accelerated AS, especially those with discordant echocardiographic parameters.

Four-Dimensional Flow MRI of Abdominal Veins: A Systematic Review

The aim of this systematic review is to provide an overview of the use of Four-Dimensional Magnetic Resonance Imaging of vector blood flow (4D Flow MRI) in the abdominal veins. This study was composed according to the PRISMA guidelines 2009. The literature search was conducted in MEDLINE, Cochrane Library, EMBASE, and Web of Science. Quality assessment of the included studies was performed using the QUADAS-2 tool. The initial search yielded 781 studies and 21 studies were included. All studies successfully applied 4D Flow MRI in abdominal veins. Four-Dimensional Flow MRI was capable of discerning between healthy subjects and patients with cirrhosis and/or portal hypertension. The visual quality and inter-observer agreement of 4D Flow MRI were rated as excellent and good to excellent, respectively, and the studies utilized several different MRI data sampling strategies. By applying spiral sampling with compressed sensing to 4D Flow MRI, the blood flow of several abdominal veins could be imaged simultaneously in 18-25 s, without a significant loss of visual quality. Four-Dimensional Flow MRI might be a useful alternative to Doppler sonography for the diagnosis of cirrhosis and portal hypertension. Further clinical studies need to establish consensus regarding MRI sampling strategies in patients and healthy subjects.

Left ventricular reverse remodeling and function by strain analysis in aortic stenosis: A CMR analysis of the EPICHEART study

INTRODUCTION AND OBJECTIVES

In severe aortic stenosis (AS), the impact of aortic valve replacement (AVR) on left ventricular (LV) systolic function assessed by strain and measured by echocardiography or cardiac magnetic resonance (CMR) has been controversial. We aimed to investigate LV systolic myocardial function changes six months after AVR using global longitudinal (GLS), circumferential (GCS) and radial (GRS) strain derived from CMR imaging.

METHODS

We included 39 severe AS patients (69.3±7.8 years; 61.5% male) with preserved LV ejection fraction (LVEF) who were recruited as part of the EPICHEART study and underwent successful AVR (aortic valvular area: 0.8 cm² (IQR: 0.2) pre- to 1.8 cm² (IQR:0.5) post-AVR). Structural and functional parameters were assessed at baseline and six months after AVR, including LV GRS, GCS and GLS analysis by CMR, using cine short-axial and two-, three-, and four-chamber long-axial view. Comparison between baseline and postoperative LV remodeling was performed using Student t-test and Wilcoxon test.

RESULTS

At six-month follow-up, LV mass, end-diastolic and end-systolic volumes, stroke volume, cardiac output, lateral E/e', tricuspid annular plane systolic excursion, right ventricular (RV) S wave velocity, GLS [-15.6% (IQR: 4.39) to -13.7% (IQR: 4.62)] and GCS [-17.8±3.58% to -16.1±2.94%] reduced significantly, while LVEF and GRS remained unchanged and lateral e' velocity increased.

CONCLUSIONS

Despite favorable reverse LV structural and diastolic functional remodeling six months following AVR, GLS and GCS assessed by CMR reduced compared to baseline, LVEF remained unchanged. The clinical utility and timing of assessment of postoperative strain changes as a marker of systolic function progression needs further research.

A review of the pivotal role of cardiac MRI in mitral valve regurgitation

Cardiac imaging is the cornerstone of defining the etiology, quantification, and management of mitral regurgitation (MR). This continues to be even more so the case with emerging transcatheter techniques to manage MR. Transthoracic echocardiography remains the first-line imaging modality to assess MR but has limitations. Cardiac MRI(CMR) provides the advantages of quantitative nonvisual estimation, 3D volumetric data, late gadolinium, T1, and extracellular volume measurements to comprehensively assess mitral valvular pathology, cardiac remodeling, and the prognostic impact of therapies. This review describes the superiority, technical aspects and growing evidence behind CMR, and lays the roadmap for the future of CMR in MR.

[Assessment of intracardiac flows by Magnetic Resonance Imaging: The 4D Flow imaging]

2D flow cardiac MRI is a well-established technique but has some current limitations in routine practice. New 4D flow MRI may overcome these limitations, providing dramatic dynamic imaging, easily understandable, allowing robust quantification of flows. 4D flow imaging should become soon the reference technic for valvular regurgitations and congenital heart disease.

Cardiac Magnetic Resonance Feature Tracking in Aortic Stenosis: Exploration of Strain Parameters and Prognostic Value in Asymptomatic Patients with Preserved Ejection Fraction

Objective

To determine the most valuable cardiac magnetic resonance feature tracking (CMR-FT) parameters for evaluating aortic stenosis (AS) and determine whether they can predict the prognosis in asymptomatic AS patients with preserved ejection fraction (pEF).

Materials and Methods

A prospective cohort of 123 moderate to severe AS patients (60 males, 68.6 ± 9.2 years) and 32 control subjects (14 males, 67.9 ± 4.4 years) underwent echocardiography and 3T CMR imaging from 2011–2015. CMR cine images were analyzed using CMR-FT to assess the left ventricular radial, circumferential, and longitudinal peak strain (PS) in 2- and 3-dimensions. The primary endpoints were clinical cardiac events (CCEs), including cardiac death, heart failure, and AS-associated symptom development. For statistical analysis, logistic regression and log-rank tests were used.

Results

Global PSs differed between AS patients and controls and between severe and moderate AS patients (p < 0.05). Two-dimensional (2D) global radial and longitudinal PSs changed gradually with the severity of AS groups (p < 0.001). Twenty-two of 67 asymptomatic AS patients with pEF experienced CCEs during the follow-up (median: 31.1 months). 2D global longitudinal PS (GLPS) was the single risk factor for CCE (p = 0.017). The relative risk for CCE was 3.9 (p = 0.016, 95% confidence interval: 1.2–11.9) based on 2D GLPS with a cutoff of −17.9% according to receiver operating characteristic curve analysis. Survival analysis demonstrated that asymptomatic AS patients with pEF having impaired 2D GLPS experienced worse event-free survival than the others (p = 0.041).

Conclusion

2D global longitudinal and radial PSs may reflect cardiac dysfunction according to the degree of AS. 2D GLPS might be a prognostic predictor of CCEs in asymptomatic AS patients with pEF.

4D flow imaging of the thoracic aorta: is there an added clinical value?

Four-dimensional (4D) flow MRI has emerged as a powerful non-invasive technique in cardiovascular imaging, enabling to analyse in vivo complex flow dynamics models by quantifying flow parameters and derived features. Deep knowledge of aortic flow dynamics is fundamental to better understand how abnormal flow patterns may promote or worsen vascular diseases. In the perspective of an increasingly personalized and preventive medicine, growing interest is focused on identifying those quantitative functional features which are early predictive markers of pathological evolution. The thoracic aorta and its spectrum of diseases, as the first area of application and development of 4D flow MRI and supported by an extensive experimental validation, represents the ideal model to introduce this technique into daily clinical practice. The purpose of this review is to describe the impact of 4D flow MRI in the assessment of the thoracic aorta and its most common affecting diseases, providing an overview of the actual clinical applications and describing the potential role of derived advanced hemodynamic measures in tailoring follow-up and treatment.

Evaluation of aortic stenosis using cardiovascular magnetic resonance: a systematic review & meta-analysis

BACKGROUND

As the average age of patients with severe aortic stenosis (AS) who receive procedural intervention continue to age, the need for non-invasive modalities that provide accurate diagnosis and operative planning is increasingly important. Advances in cardiovascular magnetic resonance (CMR) over the past two decades mean it is able to provide haemodynamic data at the aortic valve, along with high fidelity anatomical imaging.

METHODS

Electronic databases were searched for studies comparing CMR to transthoracic echocardiography (TTE) and transoesophageal echocardiography (TEE) in the diagnosis of AS. Studies were included only if direct comparison was made on matched patients, and if diagnosis was primarily through measurement of aortic valve area (AVA).

RESULTS

Twenty-three relevant, prospective articles were included in the meta-analysis, totalling 1040 individual patients. There was no significant difference in AVA measured as by CMR compared to TEE. CMR measurements of AVA size were larger compared to TTE by an average of 10.7% (absolute difference: + 0.14cm2, 95% CI 0.07-0.21, p < 0.001). Reliability was high for both inter- and intra-observer measurements (0.03cm2 +/- 0.04 and 0.02cm2 +/- 0.01, respectively).

CONCLUSIONS

Our analysis demonstrates the equivalence of AVA measurements using CMR compared to those obtained using TEE. CMR demonstrated a small but significantly larger AVA than TTE. However, this can be attributed to known errors in derivation of left ventricular outflow tract size as measured by TTE. By offering additional anatomical assessment, CMR is warranted as a primary tool in the assessment and workup of patients with severe AS who are candidates for surgical or transcatheter intervention.

Usefulness of Cardiac Magnetic Resonance Imaging in Aortic Stenosis

The objective of this review is to provide an overview of the role of cardiac magnetic resonance (CMR) in aortic stenosis (AS). Although CMR is undeniably the gold standard for assessing left ventricular volume, mass, and function, the assessment of the left ventricular repercussions of AS by CMR is not routinely performed in clinical practice, and its role in evaluating and quantifying AS is not yet well established. CMR is an imaging modality integrating myocardial function and disease, which could be particularly useful in a pathology like AS that should be considered as a global myocardial disease rather than an isolated valve disease. In this review, we discuss the emerging potential of CMR for the diagnosis and prognosis of AS. We detail its utility for studying all aspects of AS, including valve anatomy, flow quantification, left ventricular volumes, mass, remodeling, and function, tissue mapping, and 4-dimensional flow magnetic resonance imaging. We also discuss different clinical situations where CMR could be useful in AS, for example, in low-flow low-gradient AS to confirm the low-flow state and to understand the reason for the left ventricular dysfunction or when there is a suspicion of associated cardiac amyloidosis.

Pseudo-spiral sampling and compressed sensing reconstruction provides flexibility of temporal resolution in accelerated aortic 4D flow MRI: A comparison with k-t principal component analysis

INTRODUCTION

Time-resolved three-dimensional phase contrast MRI (4D flow) of aortic blood flow requires acceleration to reduce scan time. Two established techniques for highly accelerated 4D flow MRI are k-t principal component analysis (k-t PCA) and compressed sensing (CS), which employ either regular or random k-space undersampling. The goal of this study was to gain insights into the quantitative differences between k-t PCA- and CS-derived aortic blood flow, especially for high temporal resolution CS 4D flow MRI.

METHODS

The scan protocol consisted of both k-t PCA and CS accelerated 4D flow MRI, as well as a 2D flow reference scan through the ascending aorta acquired in 15 subjects. 4D flow scans were accelerated with factor R = 8. For CS accelerated scans, we used a pseudo-spiral Cartesian sampling scheme, which could additionally be reconstructed at higher temporal resolution, resulting in R = 13. 4D flow data were compared with the 2D flow scan in terms of flow, peak flow and stroke volume. A 3D peak systolic voxel-wise velocity and wall shear stress (WSS) comparison between k-t PCA and CS 4D flow was also performed.

RESULTS

The mean difference in flow/peak flow/stroke volume between the 2D flow scan and the 4D flow CS with R = 8 and R = 13 was 4.2%/9.1%/3.0% and 5.3%/7.1%/1.9%, respectively, whereas for k-t PCA with R = 8 the difference was 9.7%/25.8%/10.4%. In the voxel-by-voxel 4D flow comparison we found 13.6% and 3.5% lower velocity and WSS values of k-t PCA compared with CS with R = 8, and 15.9% and 5.5% lower velocity and WSS values of k-t PCA compared with CS with R = 13.

CONCLUSION

Pseudo-spiral accelerated 4D flow acquisitions in combination with CS reconstruction provides a flexible choice of temporal resolution. We showed that our proposed strategy achieves better agreement in flow values with 2D reference scans compared with using k-t PCA accelerated acquisitions.

[Evaluation of mitral regurgitation : How much quantification do we need?]

Severe mitral regurgitation (MR) is associated with increased morbidity and mortality. Thus, the correct evaluation of the underlying etiology, pathomechanism and severity is crucial for optimal treatment. Echocardiography is the predominant diagnostic modality in the clinical routine as it enables grading of mitral regurgitation, which can frequently be achieved by readily available qualitative parameters. Additionally, echocardiography provides several methods to quantify the hemodynamic significance of MR. The effective regurgitation orifice area (EROA) is the quantitative parameter best correlated with clinical events. American and European imaging guidelines both recommend the use of quantitative parameters even though they disagree on the cut-off values for secondary MR. The evaluation of MR should always include an assessment of the adjacent heart chambers in order to be able to assess the impact of volume overload on size and function of the left ventricle and left atrium. The final interpretation of the quantitative parameters requires knowledge of left ventricular volume and ejection fraction. Newer 3D-echocardiographic approaches to quantify MR are less dependent on mathematical assumptions and have shown convincing results in several studies but still lack sufficient clinical validation. As an alternative to echocardiography, for specific indications cardiac magnetic resonance imaging (MRI) has proven to be a systematic and observer-independent method for quantification of MR.

"Where is the Heart?" When Cardiac Magnetic Resonance Imaging Helps if Echocardiography is Inconclusive

Cardiovascular magnetic resonance (CMR) is the gold standard technique to comprehensively assess cardiac structure and function. A 64-year-old male, planned for surgical coronary revascularization, underwent transthoracic and transesophageal echocardiography for a mitral regurgitation, with an eccentric jet of unclear mechanism; these examinations were inconclusive because of the lack of adequate visualization of the cardiac structures. A CMR was then performed to quantify mitral regurgitation and, additionally, it documented a giant hiatus hernia with gastric sliding into the thorax. In this case, CMR helped to better define the severity of a valvular disease and provided ancillary information from the extracardiac findings.