A non-invasive assessment of cardiopulmonary hemodynamics with MRI in pulmonary hypertension

Time-Resolved 3D cardiopulmonary MRI reconstruction using spatial transformer network

The accurate visualization and assessment of the complex cardiac and pulmonary structures in 3D is critical for the diagnosis and treatment of cardiovascular and respiratory disorders. Conventional 3D cardiac magnetic resonance imaging (MRI) techniques suffer from long acquisition times, motion artifacts, and limited spatiotemporal resolution. This study proposes a novel time-resolved 3D cardiopulmonary MRI reconstruction method based on spatial transformer networks (STNs) to reconstruct the 3D cardiopulmonary MRI acquired using 3D center-out radial ultra-short echo time (UTE) sequences. The proposed reconstruction method employed an STN-based deep learning framework, which used a combination of data-processing, grid generator, and sampler. The reconstructed 3D images were compared against the start-of-the-art time-resolved reconstruction method. The results showed that the proposed time-resolved 3D cardiopulmonary MRI reconstruction using STNs offers a robust and efficient approach to obtain high-quality images. This method effectively overcomes the limitations of conventional 3D cardiac MRI techniques and has the potential to improve the diagnosis and treatment planning of cardiopulmonary disorders.

Parametric analysis of an efficient boundary condition to control outlet flow rates in large arterial networks

Substantial effort is being invested in the creation of a virtual human-a model which will improve our understanding of human physiology and diseases and assist clinicians in the design of personalised medical treatments. A central challenge of achieving blood flow simulations at full-human scale is the development of an efficient and accurate approach to imposing boundary conditions on many outlets. A previous study proposed an efficient method for implementing the two-element Windkessel model to control the flow rate ratios at outlets. Here we clarify the general role of the resistance and capacitance in this approach and conduct a parametric sweep to examine how to choose their values for complex geometries. We show that the error of the flow rate ratios decreases exponentially as the resistance increases. The errors fall below 4% in a simple five-outlets model and 7% in a human artery model comprising ten outlets. Moreover, the flow rate ratios converge faster and suffer from weaker fluctuations as the capacitance decreases. Our findings also establish constraints on the parameters controlling the numerical stability of the simulations. The findings from this work are directly applicable to larger and more complex vascular domains encountered at full-human scale.

Left atrial acceleration factor as a magnetic resonance 4D flow measure of mean pulmonary artery wedge pressure in pulmonary hypertension

Background

Mean pulmonary artery wedge pressure (PAWP) represents a right heart catheter (RHC) surrogate measure for mean left atrial (LA) pressure and is crucial for the clinical classification of pulmonary hypertension (PH). Hypothesizing that PAWP is related to acceleration of blood throughout the LA, we investigated whether an adequately introduced LA acceleration factor derived from magnetic resonance (MR) four-dimensional (4D) flow imaging could provide an estimate of PAWP in patients with known or suspected PH.

Methods

LA 4D flow data of 62 patients with known or suspected PH who underwent RHC and near-term 1.5 T cardiac MR (ClinicalTrials.gov identifier: NCT00575692) were retrospectively analyzed. Early diastolic LA peak outflow velocity (v_E) as well as systolic (v_S) and early diastolic (v_D) LA peak inflow velocities were determined with prototype software to calculate the LA acceleration factor (α) defined as α = v_E/[(v_S + v_D)/2]. Correlation, regression and Bland-Altman analysis were employed to investigate the relationship between α and PAWP, α-based diagnosis of elevated PAWP (>15 mmHg) was analyzed by receiver operating characteristic curve analysis.

Results

α correlated very strongly with PAWP (r = 0.94). Standard deviation of differences between RHC-derived PAWP and PAWP estimated from linear regression model (α = 0.61 + 0.10·PAWP) was 2.0 mmHg. Employing the linear-regression-derived cut-off α = 2.10, the α-based diagnosis of elevated PAWP revealed the area under the curve 0.97 with sensitivity/specificity 93%/92%.

Conclusions

The very close relationship between the LA acceleration factor α and RHC-derived PAWP suggests α as potential non-invasive parameter for the estimation of PAWP and the distinction between pre- and post-capillary PH.

Cardiac Magnetic Resonance Imaging in Pulmonary Arterial Hypertension: Ready for Clinical Practice and Guidelines?

Purpose of Review

Pulmonary arterial hypertension (PAH) is a progressive disease with high mortality. A greater understanding of the physiology and function of the cardiovascular system in PAH will help improve survival. This review covers the latest advances within cardiovascular magnetic resonance imaging (CMR) regarding diagnosis, evaluation of treatment, and prognostication of patients with PAH.

Recent Findings

New CMR measures that have been proven relevant in PAH include measures of ventricular and atrial volumes and function, tissue characterization, pulmonary artery velocities, and arterio-ventricular coupling.

Summary

CMR markers carry prognostic information relevant for clinical care such as treatment response and thereby can affect survival. Future research should investigate if CMR, as a non-invasive method, can improve existing measures or even provide new and better measures in the diagnosis, evaluation of treatment, and determination of prognosis of PAH.

Advanced Imaging in Pulmonary Vascular Disease

Although the diagnosis of pulmonary hypertension requires invasive testing, imaging serves an important role in the screening, classification, and monitoring of patients with pulmonary vascular disease (PVD). The development of advanced imaging techniques has led to improvements in the understanding of disease pathophysiology, noninvasive assessment of hemodynamics, and stratification of patient risk. This article discusses the current role of advanced imaging and the emerging novel techniques for visualizing the lung parenchyma, mediastinum, and heart in PVD.

The feasibility in estimating pulmonary vascular resistance by cardiovascular magnetic resonance in pulmonary hypertension: A systematic review and meta-analysis

PURPOSE

Cardiac magnetic resonance (CMR) is a substitute technique for noninvasively assessing pulmonary hemodynamics. Some preliminary studies have shown that CMR has the potential to quantify pulmonary vascular resistance (PVR). However, the evaluative value has not been well established. The purpose of the systematic review is to assess the feasibility of CMR in the measurement of PVR in patients with pulmonary hypertension (PH).

METHODS

Studies were retrieved from multiple databases. Methodological evaluation of CMR and right heart catheterization (RHC) in estimating PVR were obtained from included studies. The Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) tool was used to assess the quality of studies. The results of comparisons of continuous variables are reported as weighted mean difference (WMD), together with the corresponding 95% confidence intervals (CIs). Summary correlation coefficient (r) values were extracted from each study, and 95% CIs were calculated after Fisher's z transformation. Sensitivity analysis was conducted to investigate potential heterogeneity.

RESULTS

A total of 15 studies were included in the systematic review, and 6 of these studies were included in the meta-analysis. The pooled WMD with fixed-effects analysis revealed no statistical significance between PVR-CMR and PVR-RHC in patients with PH (WMD = 0.278 WU; 95% CI: -0.415 to 0.972; p = 0.431). The pooled r value for all studies was 0.85 (95% CI: 0.81, 0.89), and notable heterogeneity was evident. The pooled r value after the exclusion of one heterogeneous article was 0.81 (95% CI: 0.74, 0.87) and was not significantly heterogeneous.

CONCLUSIONS

CMR and RHC have good consistency in the testing of PVR in the meta-analysis. The systematic review shows that completely noninvasive evaluation of PVR with CMR in patients with pH is feasible.

Multiparametric Magnetic Resonance Imaging in the Assessment of Pulmonary Hypertension: Initial Experience of a One-Stop Study

INTRODUCTION

Our goal was to assess the diagnostic performance of magnetic resonance imaging (MRI) as a single method to diagnose pulmonary hypertension (PH) compared to right heart catheterization (RHC), computed tomography (CT), and ventilation/perfusion (V/Q) scintigraphy.

METHODS

We identified 35 patients diagnosed with PH by RHC in our institution who have also undergone a CT, a scintigraphy, and an MRI within a month. All cases were discussed in multidisciplinary meetings. We performed correlations between the MRI-derived hemodynamic parameters and those from RHC. The sensitivity and specificity of MRI were determined to identify its diagnostic performance to identify chronic thromboembolic pulmonary hypertension (CTEPH) and interstitial lung disease PH. The gold standard reference for the diagnosis of CTEPH and ILD was based on a review of multimodality imaging (V/Q scintigraphy and CT scan) and clinical findings.

RESULTS

Our results showed a good correlation between the hemodynamic parameters of cardiac MRI and RHC. Pulmonary vascular resistance had the best correlation between both methods (r = 0.923). The sensitivity and specificity of MRI to diagnose CTEPH was 100 and 96.8%, respectively. For the ILD-related PH, the MRI yielded a sensitivity of 60.0% and a specificity of 100%. Additionally, cardiac MRI was able to confirm all cases of PAH due to congenital heart disease initially detected by echocardiography.

CONCLUSIONS

MRI represents a promising imaging modality as an initial, single-shot study, for patients with suspected PH with the advantages of being non-invasive and having no radiation exposure.

Evaluation of the hemodynamics and right ventricular function in pulmonary hypertension by echocardiography compared with right-sided heart catheterization

The present study aimed to evaluate hemodynamics and right ventricular function in patients with pulmonary hypertension (PH) using transthoracic echocardiography and to compare these results with measurements obtained using right-sided heart catheterization (RHC). A total of 75 patients with PH were examined using echocardiography and RHC. Patients were divided into the following two groups according to their difference between SPAP_echo and SPAP_RHC measurement: The overestimated group and underestimated group. The overestimated group included the subgroups group_over-A (difference <20 mmHg) and group_over-B (difference ≥20 mmHg), and the underestimated group included group_under-A (absolute value of the difference <20 mmHg) and group_under-B (absolute value of the difference ≥20 mmHg). SPAP_echo measurements were revealed to be significantly positively correlated with SPAP_RHC measurements (r=0.794; P<0.01). Among all echocardiographic measurements, only tricuspid annular plane systolic excursion (TAPSE) was significantly different between groups; it was increased in group_over-A and group_under-A compared with group_over-B (P<0.01). Although SPAP measurements obtained using echocardiography were significantly positively correlated with those obtained using RHC, a high proportion of overestimation or underestimation of SPAP by echocardiography remained.

MR phase-contrast imaging in pulmonary hypertension

Pulmonary hypertension (PH) is a life-threatening, multifactorial pathophysiological haemodynamic condition, diagnosed when the mean pulmonary arterial pressure equals or exceeds 25 mmHg at rest during right heart catheterization. Cardiac MRI, in general, and MR phase-contrast (PC) imaging, in particular, have emerged as potential techniques for the standardized assessment of cardiovascular function, morphology and haemodynamics in PH. Allowing the quantification and characterization of macroscopic cardiovascular blood flow, MR PC imaging offers non-invasive evaluation of haemodynamic alterations associated with PH. Techniques used to study the PH include both the routine two-dimensional (2D) approach measuring predominant velocities through an acquisition plane and the rapidly evolving four-dimensional (4D) PC imaging, which enables the assessment of the complete time-resolved, three-directional blood-flow velocity field in a volume. Numerous parameters such as pulmonary arterial mean velocity, vessel distensibility, flow acceleration time and volume and tricuspid regurgitation peak velocity, as well as the duration and onset of vortical blood flow in the main pulmonary artery, have been explored to either diagnose PH or find non-invasive correlates to right heart catheter parameters. Furthermore, PC imaging-based analysis of pulmonary arterial pulse-wave velocities, wall shear stress and kinetic energy losses grants novel insights into cardiopulmonary remodelling in PH. This review aimed to outline the current applications of 2D and 4D PC imaging in PH and show why this technique has the potential to contribute significantly to early diagnosis and characterization of PH.

Advanced flow MRI: emerging techniques and applications

Magnetic resonance imaging (MRI) techniques provide non-invasive and non-ionising methods for the highly accurate anatomical depiction of the heart and vessels throughout the cardiac cycle. In addition, the intrinsic sensitivity of MRI to motion offers the unique ability to acquire spatially registered blood flow simultaneously with the morphological data, within a single measurement. In clinical routine, flow MRI is typically accomplished using methods that resolve two spatial dimensions in individual planes and encode the time-resolved velocity in one principal direction, typically oriented perpendicular to the two-dimensional (2D) section. This review describes recently developed advanced MRI flow techniques, which allow for more comprehensive evaluation of blood flow characteristics, such as real-time flow imaging, 2D multiple-venc phase contrast MRI, four-dimensional (4D) flow MRI, quantification of complex haemodynamic properties, and highly accelerated flow imaging. Emerging techniques and novel applications are explored. In addition, applications of these new techniques for the improved evaluation of cardiovascular (aorta, pulmonary arteries, congenital heart disease, atrial fibrillation, coronary arteries) as well as cerebrovascular disease (intra-cranial arteries and veins) are presented.