Comparison of various methods for quantitative evaluation of myocardial infarct volume from magnetic resonance delayed enhancement data

Desynchronization Strain Patterns and Contractility in Left Bundle Branch Block through Computer Model Simulation

Left bundle branch block (LBBB) is associated with specific septal-to-lateral wall activation patterns which are strongly influenced by the intrinsic left ventricular (LV) contractility and myocardial scar localization. The objective of this study was to propose a computational-model-based interpretation of the different patterns of LV contraction observed in the case of LBBB and preserved contractility or myocardial scarring. Two-dimensional transthoracic echocardiography was used to obtain LV volumes and deformation patterns in three patients with LBBB: (1) a patient with non-ischemic dilated cardiomyopathy, (2) a patient with antero-septal myocardial scar, and (3) a patient with lateral myocardial scar. Scar was confirmed by the distribution of late gadolinium enhancement with cardiac magnetic resonance imaging (cMRI). Model parameters were evaluated manually to reproduce patient-derived data such as strain curves obtained from echocardiographic apical views. The model was able to reproduce the specific strain patterns observed in patients. A typical septal flash with pre-ejection shortening, rebound stretch, and delayed lateral wall activation was observed in the case of non-ischemic cardiomyopathy. In the case of lateral scar, the contractility of the lateral wall was significantly impaired and septal flash was absent. In the case of septal scar, septal flash and rebound stretch were also present as previously described in the literature. Interestingly, the model was also able to simulate the specific contractile properties of the myocardium, providing an excellent localization of LV scar in ischemic patients. The model was able to simulate the electromechanical delay and specific contractility patterns observed in patients with LBBB of ischemic and non-ischemic etiology. With further improvement and validation, this technique might be a useful tool for the diagnosis and treatment planning of heart failure patients needing CRT.

Self-configuring nnU-net pipeline enables fully automatic infarct segmentation in late enhancement MRI after myocardial infarction

PURPOSE

To fully automatically derive quantitative parameters from late gadolinium enhancement (LGE) cardiac MR (CMR) in patients with myocardial infarction and to investigate if phase sensitive or magnitude reconstructions or a combination of both results in best segmentation accuracy.

METHODS

In this retrospective single center study, a convolutional neural network with a U-Net architecture with a self-configuring framework ("nnU-net") was trained for segmentation of left ventricular myocardium and infarct zone in LGE-CMR. A database of 170 examinations from 78 patients with history of myocardial infarction was assembled. Separate fitting of the model was performed, using phase sensitive inversion recovery, the magnitude reconstruction or both contrasts as input channels. Manual labelling served as ground truth. In a subset of 10 patients, the performance of the trained models was evaluated and quantitatively compared by determination of the Sørensen-Dice similarity coefficient (DSC) and volumes of the infarct zone compared with the manual ground truth using Pearson's r correlation and Bland-Altman analysis.

RESULTS

The model achieved high similarity coefficients for myocardium and scar tissue. No significant difference was observed between using PSIR, magnitude reconstruction or both contrasts as input (PSIR and MAG; mean DSC: 0.83 ± 0.03 for myocardium and 0.72 ± 0.08 for scars). A strong correlation for volumes of infarct zone was observed between manual and model-based approach (r = 0.96), with a significant underestimation of the volumes obtained from the neural network.

CONCLUSION

The self-configuring nnU-net achieves predictions with strong agreement compared to manual segmentation, proving the potential as a promising tool to provide fully automatic quantitative evaluation of LGE-CMR.

Effect of ischemic postconditioning during primary percutaneous coronary intervention for patients with ST-segment elevation myocardial infarction: A single-center cross-sectional study

Background and Objective

Reperfusion therapy for acute myocardial infarction has been shown to reduce mortality, yet it may also have deleterious effects, including myocardial necrosis and no-reflow. Postconditioning is known measure for cardioprotection from reperfusion injury in animal model. Postconditioning is known measure for cardioprotection from reperfusion injury in animal model and human studies have shown inconsistent results.

Materials and Methods

From February 2013 through October 2014, at Institute of Postgraduate Medical Education and Research, Kolkata Cardiology department, we randomized 43 patients with acute ST-segment elevation myocardial infarction (STEMI) who were undergoing conventional primary percutaneous coronary intervention (PCI) (22 patients) and PCI with postconditioning by repeated transient balloon occlusion after establishment of flow (21 patients). Total creatine kinase-muscle/brain (CPK-MB) released within 72 h was compared as a surrogate marker of infarct size. Myocardial blush grade between two groups was also compared.

Results

The area under curve of serum creatine kinase (CK) release during the 1^st 72 h of reperfusion was significantly reduced (P = 0.0347) in the postconditioned group compared with the control group, averaging 9632 IU in postconditioned compared with 13493 IU in control group which represented 29% of reduction of infarct size. The peak of CPK-MB release was markedly lower in the postconditioned (290 ± 16.24 IU/L) than in the control (414.2 ± 51.34 IU/L) group (P ≤ 0.0001). Blush grading was also significantly improved in postconditioned group (P = 0.005). Mean ST-segment deviation at 48 h between cases and control groups was 0.87 ± 0.68 and 1.4 ± 0.94, respectively (P = 0.08).

Conclusion

In patients with STEMI, postconditioning significantly improves blush grading and enzymatic infarct size reduction with a trend toward significant reduction of mean ST-segment deviation.

Biomechanics of infarcted left Ventricle-A review of experiments

Myocardial infarction (MI) is one of leading diseases to contribute to annual death rate of 5% in the world. In the past decades, significant work has been devoted to this subject. Biomechanics of infarcted left ventricle (LV) is associated with MI diagnosis, understanding of remodelling, MI micro-structure and biomechanical property characterizations as well as MI therapy design and optimization, but the subject has not been reviewed presently. In the article, biomechanics of infarcted LV was reviewed in terms of experiments achieved in the subject so far. The concerned content includes experimental remodelling, kinematics and kinetics of infarcted LVs. A few important issues were discussed and several essential topics that need to be investigated further were summarized. Microstructure of MI tissue should be observed even carefully and compared between different methods for producing MI scar in the same animal model, and eventually correlated to passive biomechanical property by establishing innovative constitutive laws. More uniaxial or biaxial tensile tests are desirable on MI, border and remote tissues, and viscoelastic property identification should be performed in various time scales. Active contraction experiments on LV wall with MI should be conducted to clarify impaired LV pumping function and supply necessary data to the function modelling. Pressure-volume curves of LV with MI during diastole and systole for the human are also desirable to propose and validate constitutive laws for LV walls with MI.

Quantification of intramyocardial hemorrhage volume using magnetic resonance imaging with three-dimensional T1-weighted sequence in patients with ischemia-reperfusion injury: a semi-automated image processing technique

Although intramyocardial hemorrhage (IMH) is a poor prognostic factor caused by ischemia reperfusion injury, little evidence is available regarding the association between IMH volume and biomarkers. In the present study, we measured IMH volume using three-dimensional (3D) T1-weighted magnetic resonance imaging (T1-MRI) and investigated its association with biomarkers. Moreover, the accuracy of semi-automatic measurement of IMH volume was validated. We retrospectively enrolled 33 consecutive patients (mean age 67 ± 11 years) who underwent cardiac MRI after reperfusion therapy for acute myocardial infarction. IMH was observed in 4 patients (12.1%). Receiver operating characteristics (ROC) analysis of creatine kinase (CK) and CK-muscle/brain (CK-MB) tests for detecting IMH were performed. IMH volume measured using semi-automatic methods by a 2 standard deviation (SD) threshold was compared to manual measurements using the Spearman's correlation coefficient (ρ) and Bland-Altman analyses. ROC analysis revealed optimal cutoff values of CK: 2460 IU/l and CK-MB: 231 IU/l (area under the curve: 0.95 and 0.91; sensitivity: 86% and 79%; specificity: 100% for both). IMH volume with the 2SD threshold correlated with that of the manual measurement [5.84 g (3.30 to 9.00) g vs. 8.07 g (5.37 to 9.33); ρ: 0.85, p < 0.01; bias (limit of agreement): - 0.01 g (- 0.51 to 0.49); intraclass correlation coefficients 0.84 (0.75 to 0.90)]. Our findings could help identify the risk of IMH after reperfusion therapy with biomarkers. 3D T1-MRI can semi-automatically provide accurate IMH volume without being time-consuming.

Deep Learning for Diagnosis of Chronic Myocardial Infarction on Nonenhanced Cardiac Cine MRI

Background Renal impairment is common in patients with coronary artery disease and, if severe, late gadolinium enhancement (LGE) imaging for myocardial infarction (MI) evaluation cannot be performed. Purpose To develop a fully automatic framework for chronic MI delineation via deep learning on non-contrast material-enhanced cardiac cine MRI. Materials and Methods In this retrospective single-center study, a deep learning model was developed to extract motion features from the left ventricle and delineate MI regions on nonenhanced cardiac cine MRI collected between October 2015 and March 2017. Patients with chronic MI, as well as healthy control patients, had both nonenhanced cardiac cine (25 phases per cardiac cycle) and LGE MRI examinations. Eighty percent of MRI examinations were used for the training data set and 20% for the independent testing data set. Chronic MI regions on LGE MRI were defined as ground truth. Diagnostic performance was assessed by analysis of the area under the receiver operating characteristic curve (AUC). MI area and MI area percentage from nonenhanced cardiac cine and LGE MRI were compared by using the Pearson correlation, paired t test, and Bland-Altman analysis. Results Study participants included 212 patients with chronic MI (men, 171; age, 57.2 years ± 12.5) and 87 healthy control patients (men, 42; age, 43.3 years ± 15.5). Using the full cardiac cine MRI, the per-segment sensitivity and specificity for detecting chronic MI in the independent test set was 89.8% and 99.1%, respectively, with an AUC of 0.94. There were no differences between nonenhanced cardiac cine and LGE MRI analyses in number of MI segments (114 vs 127, respectively; P = .38), per-patient MI area (6.2 cm² ± 2.8 vs 5.5 cm² ± 2.3, respectively; P = .27; correlation coefficient, r = 0.88), and MI area percentage (21.5% ± 17.3 vs 18.5% ± 15.4; P = .17; correlation coefficient, r = 0.89). Conclusion The proposed deep learning framework on nonenhanced cardiac cine MRI enables the confirmation (presence), detection (position), and delineation (transmurality and size) of chronic myocardial infarction. However, future larger-scale multicenter studies are required for a full validation. Published under a CC BY 4.0 license. Online supplemental material is available for this article. See also the editorial by Leiner in this issue.

Myocardial infarct sizing by late gadolinium-enhanced MRI: Comparison of manual, full-width at half-maximum, and n-standard deviation methods

PURPOSE

To compare three widely used methods for myocardial infarct (MI) sizing on late gadolinium-enhanced (LGE) magnetic resonance (MR) images: manual delineation and two semiautomated techniques (full-width at half-maximum [FWHM] and n-standard deviation [SD]).

MATERIALS AND METHODS

3T phase-sensitive inversion-recovery (PSIR) LGE images of 114 patients after an acute MI (2-4 days and 6 months) were analyzed by two independent observers to determine both total and core infarct sizes (TIS/CIS). Manual delineation served as the reference for determination of optimal thresholds for semiautomated methods after thresholding at multiple values. Reproducibility and accuracy were expressed as overall bias ± 95% limits of agreement.

RESULTS

Mean infarct sizes by manual methods were 39.0%/24.4% for the acute MI group (TIS/CIS) and 29.7%/17.3% for the chronic MI group. The optimal thresholds (ie, providing the closest mean value to the manual method) were FWHM30% and 3SD for the TIS measurement and FWHM45% and 6SD for the CIS measurement (paired t-test; all P > 0.05). The best reproducibility was obtained using FWHM. For TIS measurement in the acute MI group, intra-/interobserver agreements, from Bland-Altman analysis, with FWHM30%, 3SD, and manual were -0.02 ± 7.74%/-0.74 ± 5.52%, 0.31 ± 9.78%/2.96 ± 16.62% and -2.12 ± 8.86%/0.18 ± 16.12, respectively; in the chronic MI group, the corresponding values were 0.23 ± 3.5%/-2.28 ± 15.06, -0.29 ± 10.46%/3.12 ± 13.06% and 1.68 ± 6.52%/-2.88 ± 9.62%, respectively. A similar trend for reproducibility was obtained for CIS measurement. However, semiautomated methods produced inconsistent results (variabilities of 24-46%) compared to manual delineation.

CONCLUSION

The FWHM technique was the most reproducible method for infarct sizing both in acute and chronic MI. However, both FWHM and n-SD methods showed limited accuracy compared to manual delineation. J. Magn. Reson. Imaging 2016;44:1206-1217.

Functional and morphological myocardial changes in hepatitis C virus patients with end-stage liver disease

BACKGROUND AND OBJECTIVES

Cardiovascular complications are common in liver transplant recipient. This study aims to evaluate functional and morphological myocardial changes in hepatitis C virus (HCV) patients with end-stage liver disease (ESLD) by cardiac magnetic resonance (CMR).

METHODS

This cross-sectional study included 84 patients with HCV-related ESLD. They were subjected to 2D-echocardiography and CMR. The presence, distribution, and percentage of delayed myocardial enhancement (DME) were estimated.

RESULTS

The mean Model for End-Stage Liver Disease score was 21.5 ± 6.3. In CMR, all patients showed good global left ventricular (LV) systolic function (mean ejection fraction = 66.5 ± 8.6%; range: 55-80) with normal wall thickness and motion. Left ventricle was mildly dilated in 25 patients (30%). Grade I and grade II diastolic dysfunction was detected in 81 patients (96.4%) with dilated left atrium in 25 patients (30%). Variable degrees of DME were detected in 70 patients (83.3%) with mean percentage of DME (%DME) being 19.5 ± 16% (range: 4-52). A significant negative correlation was found between %DME and LV ejection fraction (r = -0.7; p < 0.001), cardiac output (r = -0.5; p = 0.013), cardiac index (r = -0.5; p = 0.02), and serum albumin level (r = -0.5; p = 0.01). The %DME ≥19% was associated with 85.7% sensitivity and 85.7% specificity for detection of LV ejection fraction <60% as assessed by echocardiography (area under curve = 0.89; p = 0.001).

CONCLUSION

DME with CMR is a common finding among patients with HCV-related ESLD. The extent of DME is significantly associated with global LV systolic function.

Quantitative assessment of myocardial fibrosis in an age-related rat model by ex vivo late gadolinium enhancement magnetic resonance imaging with histopathological correlation

Late gadolinium enhanced (LGE) cardiac magnetic resonance (CMR) imaging can detect the presence of myocardial infarction from ischemic cardiomyopathies (ICM). However, it is more challenging to detect diffuse myocardial fibrosis from non-ischemic cardiomyopathy (NICM) with this technique due to more subtle and heterogeneous enhancement of the myocardium. This study investigates whether high-resolution LGE CMR can detect age-related myocardial fibrosis using quantitative texture analysis with histological validation. LGE CMR of twenty-four rat hearts (twelve 6-week-old and twelve 2-year-old) was performed using a 7T MRI scanner. Picrosirius red was used as the histopathology reference for collagen staining. Fibrosis in the myocardium was quantified with standard deviation (SD) threshold methods from the LGE CMR images and 3D contrast texture maps that were computed from gray level co-occurrence matrix of the CMR images. There was a significant increase of collagen fibers in the aged compared to the young rat histology slices (2.60±0.27 %LV vs. 1.24±0.29 %LV, p<0.01). Both LGE CMR and texture images showed a significant increase of myocardial fibrosis in the elderly compared to the young rats. Fibrosis in the LGE CMR images correlated strongly with histology with the 3 SD threshold (r=0.84, y=0.99x+0.00). Similarly, fibrosis in the contrast texture maps correlated with the histology using the 4 SD threshold (r=0.89, y=1.01x+0.00). High resolution ex-vivo LGE CMR can detect the presence of diffuse fibrosis that naturally developed in elderly rat hearts. Our results suggest that texture analysis may improve the assessment of myocardial fibrosis in LGE CMR images.

Magnetic resonance hypointensive signal primarily originates from extracellular iron particles in the long-term tracking of mesenchymal stem cells transplanted in the infarcted myocardium

PURPOSE

The long-lasting hypointensities in cardiac magnetic resonance (CMR) were believed to originate from superparamagnetic iron oxide (SPIO)-engulfed macrophages during long-term stem cell tracking. However, the iron clearance capacity of the ischemic heart was limited. Therefore, we speculated that the extracellular SPIO particles may also be involved in the generation of false-positive signals.

METHODS AND RESULTS

Male swine mesenchymal stem cells (MSCs) were incubated with SPIO for 24 hours, and SPIO labeling had no significant effects on either cell viability or differentiation. In vitro studies showed that magnetic resonance failed to distinguish SPIO from living SPIO-MSCs or dead SPIO-MSCs. Two hours after the establishment of the female swine acute myocardial infarction model, 2×10(7) male SPIO-labeled MSCs (n=5) or unlabeled MSCs (n=5) were transextracardially injected into the infarcted myocardium at ten distinct sites. In vivo CMR with T2 star weighted imaging-flash-2D sequence revealed a signal void corresponding to the initial SPIO-MSC injection sites. At 6 months after transplantation, CMR identified 32 (64%) of the 50 injection sites, where massive Prussian blue-positive iron deposits were detected by pathological examination. However, iron particles were predominantly distributed in the extracellular space, and a minority was distributed within CD68-positive macrophages and other CD68-negative cells. No sex-determining region Y DNA of donor MSCs was detected.

CONCLUSION

CMR hypointensive signal is primarily caused by extracellular iron particles in the long-term tracking of transplanted MSCs after myocardial infarction. Consideration should be given to both the false-positive signal and the potential cardiac toxicity of long-standing iron deposits in the heart.

[Cardiac MRI: technology, clinical applications, and future directions]

The field of cardiovascular MRI has evolved rapidly over the past decade, feeding new applications across a broad spectrum of clinical and research areas. Advances in magnet hardware technology, and key developments such as segmented k-space acquisitions, advanced motion encoding techniques, ultra-rapid perfusion imaging and delayed myocardial enhancement imaging have all contributed to a revolution in how patients with ischemic and non-ischemic heart disease are diagnosed and treated. Actually, cardiac MRI is a widely accepted method as the "gold standard" for detection and characterization of many forms of cardiac diseases. The aim of this review is to present an overview of cardiac MRI technology, advances in clinical applications, and future directions.