Keywords: Myocardium, Cardiomyopathy, non-compaction , cardiac diffusion tensor imaging, cDTI

Motivation: Left ventricular non-compaction cardiomyopathy (LVNC) is characterized by the presence of excessive trabeculation in the left ventricle.

Goal(s): To characterize the myocardial microstructure of LVNC patients in comparison to healthy controls using cardiac Diffusion Tensor Imaging (cDTI).

Approach: Second order motion compensated spin echo cardiac DTI was acquired in six LVNC patients and six healthy controls. Myocyte aggregate orientation is characterized by helix angle and relative percentage of right handed helical orientated myocytes.

Results: In the compacted myocardium, LVNC patients exhibited lower endocardial helix angles and a loss of the endocardial right handed helix when compared to controls.

Impact: Our findings indicate that in LVNC patients, a portion of the endocardial helix is dissolved into the non-compacted myocardium, which may impair optimal myocardial contraction in the affected segments as well as apical rotation as observed in LVNC patients.

Keywords: Myocardium, Radiomics

Motivation: DTI data in the heart are currently averaged to yield per-patient values that cannot detect local variations in the microstructural microenvironment.

Goal(s): We aimed to develop a voxel-based phenomapping approach to cluster the voxels in the myocardium into distinct groups based on their microstructural properties.  We then used the  approach to compare subjects with aortic stenosis (AS) to age-matched controls (CTL).

Approach: A population matrix of voxels was created using z-score normalization and evaluated with k-means clustering (k=4).

Results: 4 distinct clusters of voxels were present, each with different microstructural properties. No significant differences were seen between the AS and CTL subjects.

Impact: An approach to perform voxel-based phenomapping of DTI data in the heart was developed and used to classify the voxels in the myocardium into distinct microstructural clusters.  

Keywords: Myocardium, Diffusion Tensor Imaging

Motivation: Segmentation is central to cDTI post-processing, but remains subjective, time-intensive, and observer-dependent. Faster methods are needed.

Goal(s): To develop and validate a U-Net for automating and standardizing left ventricle segmentations for cDTI. Our target was for U-net generated masks to yield cDTI metric maps within 5% of ground-truth and Dice scores comparable to a human reader.

Approach: We developed a U-Net to automatically segment cDTI data then compared generated masks to expert annotations.

Results: Median Dice score was 0.79 with cDTI metrics within 5% of ground truth. A multiple-reader study demonstrated the need for further generalization of datasets at different resolutions.

Impact: An automated U-Net approach to cardiac DTI segmentation of the left ventricle minimizes segmentation variability, reduces processing time, and preserves cDTI metric measurement accuracy.

Keywords: Myocardium, Heart, Diffusion tensor imaging, Cardiac magnetic resonance, Myocardium, Swine model

Motivation: Diffusion tensor cardiac magnetic resonance (DT-CMR) has shown potential for non-invasive characterization of myocardial fiber orientation.

Goal(s): The purpose of this study is to validate the accuracy of high-resolution DT-CMR in evaluating the arrangement of biventricular myocardial fibers in a miniature-swine model, using histological findings as the reference standard.

Approach: High-resolution ex-vivo DT-CMR data of one healthy miniature-swine were acquired by a 3.0 T MRI system. Helix angles (HAs) in each segment from DT-CMR was compared with that from histology.

Results: HAs evaluated by DT-CMR were closely correlated with those derived from histology (r = 0.958, P < 0.001) in 64 myocardial segments.

Impact: Using histological validation in a miniature-swine model, high-resolution DT-CMR demonstrated good performance in non-invasively evaluating the arrangement of biventricular myocardial fibers. It provides histological evidence for DT-CMR to add more diagnostic and prognostic information in human cardiovascular diseases.

Keywords: Myocardium, Cardiomyopathy

Motivation: Cardiac MRI with diffusion-weighted imaging (DWI) non-invasively characterizes myocardial infarction, potentially identifying salvageable 'gray zone' areas without contrast agents.

Goal(s): This study aimed to evaluate the diagnostic value of DWI combined with T1 mapping, ECV, and LGE in assessing viable myocardium in acute MI patients.

Approach: By comparing ADC values across infarcted, peri-infarct, and healthy myocardium, significant ADC discrepancies highlighted the viability of the 'gray zone.'

Results: These findings could influence treatment strategies to recover endangered myocardium, enhancing clinical outcomes in acute myocardial infarction scenarios.

Impact: Investigating the 'gray zone' through CMR DWI sequences and ADC value changes, this study advances our understanding of myocardial viability in acute MI, potentially guiding interventions to salvage myocardium and improve patient outcomes in acute ischemic events.

Keywords: Myocardium, Diffusion Tensor Imaging

Motivation: The non-invasive imaging evaluation of myocyte disarray in hypertrophic cardiomyopathy (HCM) is still challenging.

Goal(s): We aimed to explore the myocardial microstructural characteristics of HCM by in-vivo cardiac diffusion tensor imaging (cDTI).

Approach: We prospectively enrolled thirty-five HCM patients and fifteen healthy controls for cDTI at 3.0T scanner.

Results: Myocardial disarray and abnormal microstructural dynamics of HCM can be characterized by in vivo cDTI. Moreover, cDTI allows early identification of myocardial microstructural changes, even before cardiovascular magnetic resonance (CMR) signs of fibrosis and hypertrophy.

Impact: Our findings shed light on the potential of cDTI for the early detection of myocyte disarray, further improving the value of CMR in the non-invasive myocardial tissue characterization of HCM.

Keywords: Myocardium, Cardiovascular, Fibrosis

Motivation: T1ρ mapping is an emerging non-contrast pulse sequence for measuring cardiac fibrosis, but current techniques suffer from lack of coverage, poor spatial resolution, and long scan time.

Goal(s): We aimed to develop an accelerated, free-breathing 3D cardiac T1ρ mapping pulse sequence using XD-GRASP reconstruction extended to include both respiratory and spin-locking time dimensions.

Approach: Our 3D T1ρ sequence was tested in 12 patients undergoing clinically indicated cardiac MRI to compare T1ρ with extracellular volume fraction (ECV) and late gadolinium enhancement (LGE).

Results: Myocardial T1ρ correlates with ECV of non-ischemic myocardium but not with a mixture of acute and chronic ischemic myocardium.

Impact: 3D T1ρ mapping achieves robust image quality and T1ρ values that agree with literature. 3D  T1ρ could be used for measuring fibrosis in patients where contrast should be avoided, after further research into the nature of T1ρ in focal scar.   

Keywords: Myocardium, Cardiomyopathy, T1rho

Motivation: This study employs T1rho imaging to examine myocardial changes in the LGE grey zone of patients with myocardial infarction, presenting a possible non-invasive approach for patients who cannot undergo contrast-enhanced procedures.

Goal(s): provide a possible non-invasive approach for patients who are unable to undergo contrast-enhanced surgery.

Approach: This study employs T1rho imaging to examine myocardial changes in the LGE gray area in patients with myocardial infarction.

Results: T1rho localization provides a viable diagnostic tool for the detection of diffuse myocardial fibrosis in patients with infarction.

Impact: This study explores the potential of T1rho in evaluating the tissue characteristics of gray myocardium adjacent to infarcted myocardium to provide a new clinical, non-invasive, accurate, and contrast-free method for monitoring diffuse fibrosis in the myocardium. 

Keywords: Myocardium, Cardiovascular

Motivation: Most cardiac T1ρ mapping techniques collect data in 2D, while the few existing 3D methods use a Cartesian sampling trajectory. 

Goal(s): In this study, we report the first use of a 3D radial trajectory for whole-heart T1ρ mapping at 1.5 T. 

Approach: The proposed technique was validated in a phantom, tested in one volunteer, and compared to a 2D reference method. 

Results: Our results show that the T1ρ values obtained from our 3D technique are comparable to the 2D reference values for both phantom and volunteer. However, we observed an underestimation of the T1ρ values using the 3D method in the phantom.  

Impact: 3D radial free-breathing electrocardiogram-triggered cardiac T1ρ mapping at 1.5 T has the potential to serve as a contrast agent-free adjunct to late gadolinium enhancement imaging for the whole-heart motion-robust quantification of tissue properties such as myocardial fibrosis.

Keywords: Myocardium, Quantitative Imaging

Motivation: We aim to develop a new method based on multi-compartment modeling to quantify myocardial tissue composition using MOLLI T1 mapping sequence. 

Goal(s): In this pilot study, we evaluated how the cardiac function, respiration, and age may impact the quantification. 

Approach: Data were acquired at end-systole/diastole, and end-expiration/inspiration. A series of maps were derived, including T1/T2 relaxation times, and fractions of three compartments: macromolecular proton, bound water and free water pools.

Results: The changes found in bound water and free water quantification matched human physiology. The developed method could provide a new non-invasive imaging tool for mapping tissue composition.

Impact: Quantifying myocardial tissue composition is valuable but very challenging. This pioneering work quantifies myocardial bound water and free water in a single breath-hold scan. It reveals the underlying tissue microstructure, which may open a new door for many applications.

Keywords: Myocardium, Cardiovascular, Transplant, Heart Transplant, Ischemia, Ischemic Cardiomyopathy

Motivation: Ischemic dilated cardiomyopathy (DCM) is associated with low-grade chronic inflammation which may persist after heart transplantation (HTx) and impact graft function and tissue characteristics in the post-HTx period.

Goal(s): Our goal was verify whether any difference in graft tissue characteristics or function was evident during long-term follow up by cardiac MRI between patients transplanted for ischemic DCM and those transplanted for non-ischemic indications.

Approach: Longitudinal analysis of graft tissue mapping and 2D FTS was performed on patients transplanted for ischemic DCM (n=13) and non-ischemic indications (n=50).

Results: In the non-ischemic DCM cohort, tissue mapping and FTS parameters, ECV and GCS, worsened over time.

Impact: No effect of pre-HTx low grade inflammation was evident on graft tissue characteristics and function in patients transplanted for ischemic DCM. Cardiac MRI may play an important role in long term monitoring of patients undergoing HTx. 

Keywords: Myocardium, Quantitative Imaging

Motivation: Motivated by the time-consuming process of dictionary matching in quantitative cardiac MRI, this study aims to develop a faster and more accurate method for myocardial multi-parametric quantitative mapping. 

Goal(s): The goal is to overcome the limitations of discretization errors and incomplete inversion pulses, which lead to inaccurate parameter estimation. 

Approach: The proposed approach utilizes Bloch equation simulation-based fitting, enabling rapid reconstruction of T1, T2, and T1ρ maps simultaneously.

Results: Experimental results demonstrate excellent quality of fit and significant acceleration (100x) compared to the traditional method.

Impact: This novel method has the potential to revolutionize myocardial quantitative mapping, offering improved efficiency and precision in clinical applications.

Keywords: Myocardium, Myocardium, T2mapping

Motivation: We focused on the similarity between 3D T₂prep T₂ mapping and whole-heart MRCA and developed a new sequence for simultaneous T₂ mapping and MRCA sequence.

Goal(s): Our goal of this study is to validate the simultaneous acquisition of 3D T₂ mapping with whole heart MRCA.

Approach: We visually assessed the image quality of 3D T₂ mapping and MRCA. T₂ values were compared with 2D T₂ mapping (2D-GRASE).

Results: This method, which enables simultaneous acquisition of 3D T₂ mapping and MRCA, can provide stable image quality and T₂ values.

Impact: Our method, which enables simultaneous acquisition of 3D T₂ mapping and MRCA, can provide stable image quality and T₂ values, and will be of great benefit in future imaging.

Keywords: Data Processing, Contrast Agent

Motivation: Late Gadolinium Enhancement (LGE) imaging is the gold-standard CMR imaging for distinguishing heart tissue viability. However, not all patients can receive gadolinium-based contrast agent. Native T₁ have been proposed in place of LGE.

Goal(s): This study explores pre-contrast cardiac MRF T₁ and T₂ measurements as potential indicators of ischemic myocardial scar.

Approach: Native T₁ and T₂ values were measured using cMRF in eleven ischemic patients using ROIs in both scar and non-scar myocardial tissue identified through LGE imaging.

Results: Native cMRF measurements differ between scar and non-scar areas. Synthetic images from these maps highlight scar tissue, offering a potential LGE imaging alternative.

Impact: Native cMRF T₁ and T₂ maps and synthetic images derived from these maps may enable differentiation of scar tissue from viable myocardium without the need for gadolinium-based contrast agents.

Keywords: Myocardium, Radiomics

Motivation: Diffusion tensor imaging of the heart can be performed with sub-mm resolution. However, established metrics do not fully take advantage of this improved resolution.

Goal(s): We aimed to determine whether local gradients in helix angle (HA) could be calculated and used to characterize the microstructural response of the heart to the load imposed by aortic stenosis.

Approach: Voxel-wise maps of radial, circumferential, minimum and maximum HA gradients were generated.

Results: The radial HA gradient was reduced in aortic stenosis, but microstructural coherence was well preserved in these patients despite a marked increase in the thickness of the myocardium. 

Impact: DTI of the heart with sub-mm in-plane resolution allows maps of local HA gradients to be generated, providing novel insights into the microstructure of the heart.

Keywords: Myocardium, Tissue Characterization, Cardiac Diffusion Tensor Imaging, cDTI, Heart, Data Analysis

Motivation: cDTI is a useful method for evaluating cardiac microstructure with proven clinical utility. To better enable the use of cDTI in the diagnosis of various cardiomyopathies, establishing quantitative baseline values in healthy subjects is needed.

Goal(s): Goal: To quantify healthy baseline cDTI metrics on a regional basis to understand normal regional differences in cDTI metrics.

Approach: Healthy volunteers received a cDTI exam covering the entire LV. Regional and global analyses of cDTI metrics were completed using the AHA 16-segment model.

Results: Statistically significant regional differences were found across all parametric maps, with the majority of them in basal segments.

Impact: Characterizing regional differences in cDTI measures provides data to define healthy baseline values for several cDTI metrics. Defining this baseline regionally provides a normative database for understanding patient-specific changes in these quantitative diffusion metrics.