Cardiac MRI Methods Research Articles

Applications and implementation of generative artificial intelligence in cardiovascular imaging with a focus on ethical and legal considerations: what cardiovascular imagers need to know!

Abstract Machine learning (ML) and deep learning (DL) have potential applications in medicine. This overview explores the applications of AI in cardiovascular imaging, focusing on echocardiography, cardiac MRI (CMR), coronary CT angiography (CCTA), and CT morphology and function. AI, particularly DL approaches like convolutional neural networks, enhances standardization in echocardiography. In CMR, undersampling techniques and DL-based reconstruction methods, such as variational neural networks, improve efficiency and accuracy. ML in CCTA aids in diagnosing coronary artery disease, assessing stenosis severity, and analyzing plaque characteristics. Automatic segmentation of cardiac structures and vessels using AI is discussed, along with its potential in congenital heart disease diagnosis and 3D printing applications. Overall, AI integration in cardiovascular imaging shows promise for enhancing diagnostic accuracy and efficiency across modalities. The growing use of Generative Adversarial Networks in cardiovascular imaging brings substantial advancements but raises ethical concerns. The “black box” problem in DL models poses challenges for interpretability crucial in clinical practice. Evaluation metrics like ROC curves, image quality, clinical relevance, diversity, and quantitative performance assess GAI models. Automation bias highlights the risk of unquestioned reliance on AI outputs, demanding careful implementation and ethical frameworks. Ethical considerations involve transparency, respect for persons, beneficence, and justice, necessitating standardized evaluation protocols. Health disparities emerge if AI training lacks diversity, impacting diagnostic accuracy. AI language models, like GPT-4, face hallucination issues, posing ethical and legal challenges in healthcare. Regulatory frameworks and ethical governance are crucial for fair and accountable AI. Ongoing research and development are vital to evolving AI ethics.

Abstract 12714: Superior Longitudinal Aortic Strain and Ventriculoarterial Coupling in Older Women is Independent of Body Size, Blood Pressure, and Moderately Correlated With Framingham 10-year Risk

Background: Traditional risk factors are less helpful in predicting cardiovascular (CV) risk in women (1, 2). We used a novel cardiac MRI (CMR) method to determine sex differences in aortic global longitudinal strain (AoGLS), pulse wave velocity (AAPWV), and ventriculoarterial coupling (VAC) and correlated to Framingham Risk Scores (FRS). Methods: Community adults without CV disease underwent CMR. AoGLS was the maximal absolute Lagrangian strain tracking the phasic distance between brachiocephalic artery origin and aortic annulus. VAC was calculated as AAPWV divided by LVGLS. Sex-specific simplified FRS 10-year risk (TYR) and Heart/Vascular Age (HVA) were derived from pooled cohort equations (3). Results: These n=202 subjects (46% female) were similar in age (69.7 vs. 70.7, p=0.433). Women had better AAPWV (8.4m/s vs. 9.1m/s, p=0.020), AoGLS (6.2% vs. 5.2%, p=0.030), LVGLS (-21.9% vs. -20.1%, p=0.021), RVGLS (-32.8% vs. -29.9%, p=0.020), VAC (-0.39m/s·% vs. -0.47m/s·%, p=0.006), and smaller cardiac volumes (Table A). Female sex was associated with better AoGLS (β=0.838, p=0.030; R 2 =0.103) and VAC (β=-0.93, p=0.006; R 2 =0.113) independent of smoking, DBP, and BSA. Age only weakly correlated with AoGLS (β=-0.128 p<0.001; R 2 =0.277). AoGLS correlated moderately with FRS in women (TYR r=-0.400 p=<0.001; HVA r=-0.621 p<0.001) and weakly in men (TYR r=-0.354 p=<0.001; HVA r=-0.365 p=<0.001). VAC was associated with adverse TYR (β=-6.915, p=0.017; R 2 =0.145) and HVA (β=-14.948, p=0.001; R 2 =0.084); VAC correlated moderately with FRS in women (TYR r=-0.233 p=0.024; HVA r=-0.364 p<0.001) but not in men (TYR r=-0.175 p=0.068; HVA r=-0.183 p=0.056). Conclusion: Novel CMR-derived aortic strain identified sex differences in aortic age correlating with 10-year CV risk. Women had better aorto-ventricular strain and coupling independent of DBP and BSA. Chronological age was not useful in estimating aortic age. Advanced aortic imaging may augment CV risk assessment in women.

Free-breathing 2D radial cine MRI with respiratory auto-calibrated motion correction (RAMCO).

To develop a free-breathing (FB) 2D radial balanced steady-state free precession cine cardiac MRI method with 100% respiratory gating efficiency using respiratory auto-calibrated motion correction (RAMCO) based on a motion-sensing camera. The signal from a respiratory motion-sensing camera was recorded during a FB retrospectively electrocardiogram triggered 2D radial balanced steady-state free precession acquisition using pseudo-tiny-golden-angle ordering. With RAMCO, for each acquisition the respiratory signal was retrospectively auto-calibrated by applying different linear translations, using the resulting in-plane image sharpness as a criterium. The auto-calibration determines the optimal magnitude of the linear translations for each of the in-plane directions to minimize motion blurring caused by bulk respiratory motion. Additionally, motion-weighted density compensation was applied during radial gridding to minimize through-plane and non-bulk motion blurring. Left ventricular functional parameters and sharpness scores of FB radial cine were compared with and without RAMCO, and additionally with conventional breath-hold Cartesian cine on 9 volunteers. FB radial cine with RAMCO had similar sharpness scores as conventional breath-hold Cartesian cine and the left ventricular functional parameters agreed. For FB radial cine, RAMCO reduced respiratory motion artifacts with a statistically significant difference in sharpness scores (P < 0.05) compared to reconstructions without motion correction. 2D radial cine imaging with RAMCO allows evaluation of left ventricular functional parameters in FB with 100% respiratory efficiency. It eliminates the need for breath-holds, which is especially valuable for patients with no or impaired breath-holding capacity. Validation of the proposed method on patients is warranted.

Impact of advanced imaging techniques on cardiac surgery-New insights provided by cardiac magnetic resonance.

This dialog between a cardiac surgeon (C.L.) and cardiac imager (J.W.W.) provides an overview of cardiac MRI (CMR) methods relevant to cardiac surgery. Major areas of focus include logistics of performing a CMR exam, as well as established and emerging methods for assessment of cardiac structure, function, valvular performance, and tissue characterization. Regarding tissue characterization, a major area of focus concerns CMR assessment of viability, for which this modality has been shown to provide incremental utility to conventional techniques for detection of presence and transmural extent of infarction, as well as powerful predictive utility of recovery of left ventricular systolic function as well as long term clinical prognosis in patients with an array of clinical conditions, including coronary artery disease and valvular heart disease both before and following cardiac surgery.

Compact pediatric cardiac magnetic resonance imaging protocols.

Cardiac MRI is in many respects an ideal modality for pediatric cardiovascular imaging, enabling a complete noninvasive assessment of anatomy, morphology, function and flow in one radiation-free and potentially non-contrast exam. Nonetheless, traditionally lengthy and complex imaging acquisition strategies have often limited its broader use beyond specialized centers. In this review, the author presents practical cardiac MRI imaging protocols to facilitate the performance of succinct yet successful exams that provide the most salient clinical data for the majority of congenital and acquired pediatric cardiac disease. In addition, the author reviews newer and evolving techniques that permit more rapid but similarly diagnostic MRI, including compressed sensing and artificial intelligence/machine learning reconstruction, four-dimensional flow acquisition and blood pool contrast agents. With the modern armamentarium of cardiac MRI methods, the goal of compact yet comprehensive exams in children can now be realized.

Myocardial First-Pass Perfusion With Increased Anatomic Coverage at 3T Using Autocalibrated Multiband Imaging.

Myocardial first-pass perfusion (FPP) imaging is a useful cardiac MRI method for the diagnosis of coronary artery disease. However, conventional 2D multislice FPP acquisitions usually have gaps between myocardium slices, which limits the overall assessment of myocardial ischemia. To increase the anatomic coverage of myocardial FPP imaging at 3 T by implementing both autocalibrated multiband (MB) acquisition and k-t space acceleration with compress sensing (CS) reconstruction, without the need for additional reference scans. Phantom and prospective human studies. A T1MES (T1 Mapping and ECV Standardization in cardiovascular magnetic resonance) phantom and 20 subjects (12 healthy subjects and 8 patients, 10 males, age 42 ± 16 years). A 3 T/saturation recovery prepared gradient echo sequence with contrast administration. Phantom experiments were performed to compare the performance of autocalibrated MB-FPP with k-t acceleration using slice-GRAPPA and CS reconstructions. In vivo experiments were performed to compare the performance of conventional FPP (2.5× acceleration) with autocalibrated MB + CS-FPP (6× acceleration). In phantom experiments, the error maps were calculated. In in vivo experiments, the contrast ratio (CR) and blurring were quantitatively measured, while image quality, perceived signal-to-noise ratio (SNR), and artifact level were qualitatively graded by three cardiologists on a 4-point scale. Wilcoxon signed-rank test, paired t-test. A P value <0.05 was considered statistically significant. In phantom experiments, residual artifact was reduced using the MB + CS-FPP reconstruction method compared with using the MB + slice-GRAPPA reconstruction method. In in vivo experiments, the proposed autocalibrated MB + CS-FPP method demonstrated significantly higher CR (3.52 ± 0.78 vs 2.91 ± 0.81) and had significantly better perceived SNR (2.69 ± 0.29 vs 2.48 ± 0.31) compared to the conventional sequence. Compared with conventional FPP, MB + CS-FPP doubled the spatial coverage (MB + CS-FPP vs conventional FPP) without compromising the image quality (2.69 ± 0.26 vs 2.60 ± 0.30) or increasing the artifact level (2.60 ± 0.26 vs 2.52 ± 0.31). Autocalibrated MB + CS-FPP improved the myocardial coverage and achieved comparable image quality with the same spatial resolution and scan time as conventional FPP and is a promising technique for clinical myocardial perfusion imaging. 2 TECHNICAL EFFICACY: Stage 3.

Comparison of cine and real-time cardiac MRI in rhesus macaques

Cardiac MRI in rhesus macaques, a species of major relevance for preclinical studies on biological therapies, requires artificial ventilation to realize breath holding. To overcome this limitation of standard cine MRI, the feasibility of Real-Time (RT) cardiac MRI has been tested in a cohort of ten adult rhesus macaques using a clinical MR-system. In spite of lower tissue contrast and sharpness of RT-MRI, cardiac functions were similarly well assessed by RT-MRI compared to cine MRI (similar intra-subject repeatability). However, systematic underestimation of the end-diastolic volume (31 ± 9%), end-systolic volume (20 ± 11%), stroke volume (40 ± 12%) and ejection fraction (13 ± 9%) hamper the comparability of RT-MRI results with those of other cardiac MRI methods. Yet, the underestimations were very consistent (< 5% variability) for repetitive measurements, making RT-MRI an appropriate alternative to cine MRI for longitudinal studies. In addition, RT-MRI enabled the analysis of cardio-respiratory coupling. All functional parameters showed lower values during expiration compared to inspiration, most likely due to the pressure-controlled artificial ventilation. In conclusion, despite systematic underestimation of the functional parameters, RT-MRI allowed the assessment of left ventricular function in macaques with significantly less experimental effort, measurement time, risk and burden for the animals compared to cine MRI.

Evidence of occult right ventricular dysfunction in morbidly obese patients

Abstract Background Abnormalities of right ventricular (RV) strain have been shown to occur prior to impairment of global right ventricular function, measured by global RV ejection fraction (RVEF) in patients with increased RV afterload, such as pulmonary hypertension. Obesity is a form of increased afterload involving both the right and left cardiac circulations, raising suspicion that impaired RV strain may be an early indicator of myocardial dysfunction. Purpose This study was designed to assess impairment of RV strain in obese patients with normal right ventricular ejection fraction (RVEF) using cardiac MRI Fast SENC (strain encoded) pulse sequences. Methods An institutional cardiac imaging database was queried for all patients with body mass index (BMI) greater than 35 kg/m2 who underwent measurement of RV global longitudinal strain (GLS), RV global circumferential strain (GCS) and 37 segmental strain measurements using cardiac MRI Fast-SENC pulse sequences. Global RVEF was computed for all patients using a standard cardiac MRI method using non-automated hand drawn RV endocardial borders. Global and regional strain measurements were compared to a cohort of healthy volunteers who also underwent CMR Fast-SENC imaging. Abnormal myocardial strain was defined as a value greater than −17%. Results Of the 356 patients in the database, 48 had a BMI greater than 35 kg/m2. Mean RV GLS and GCS for the study cohort were −16.6 and −15.8 respectively. For healthy volunteers RV GLS and GCS were −20.8 and −19.0 respectively. Comparison of mean RV GLS and GCS of both groups were statistically significant ANOVA p&amp;lt;0.001. The number of normal RV segmental strain values was significantly decreased in obese patients when compared to the normal cohort, ANOVA p&amp;lt;0.001 (Figure 1). Furthermore, the prevalence of abnormal RV GCS in morbidly obese patients with normal RVEF greater than or equal to 40% was 84% (21 of 25 patients). Conclusions These findings suggest that morbidly many obese patients have occult RV dysfunction despite a normal RVEF. This occult RV dysfunction not only affects RV global GLS and GCS, but also the percentage of normal segmental strain values. Detection of occult RV dysfunction is of clinical significance in that it may provide an opportunity for treatment before development of symptomatic right heart failure. Figure 1 Funding Acknowledgement Type of funding source: None

Cardiac MRI Evaluation of Myocarditis.

Cardiac MRI (CMR) is the non-invasive test of choice for the assessment of myocarditis. In 2009, the Lake Louise Criteria for the diagnosis of myocarditis using CMR were first released. The decade since that time has vastly improved our understanding of CMR's strengths and limitations. Traditional CMR methods including T2-weighted imaging and late gadolinium enhancement have proven their diagnostic value, but diagnostic performance is dependent on patient presentation. Newer parametric mapping techniques have begun to be more comprehensively studied and may improve diagnostic accuracy of CMR in an expanded set of clinical scenarios. Additionally, the prognostic value of CMR has begun to solidify. These advances culminated in an update to the Lake Louise Criteria at the end of 2018. In this review, we discuss the evolution of the diagnostic criteria for CMR in the assessment of myocarditis. We also discuss the pathophysiologic premises behind the use of specific MRI sequences and an up-to-date summary of their individual utility.

MRI in cardio-oncology: A review of cardiac complications in oncologic care.

From detailed characterization of cardiac abnormalities to the assessment of cancer treatment-related cardiac dysfunction, cardiac MRI is playing a growing role in the evaluation of cardiac pathology in oncology patients. Current guidelines are now incorporating the use of MRI for the comprehensive multidisciplinary approach to cancer management, and innovative applications of MRI in research are expanding its potential to provide a powerful noninvasive tool in the arsenal against cancer. This review focuses on the application of cardiac MRI to diagnose and manage cardiovascular complications related to cancer and its treatment. Following an introduction to current cardiac MRI methods and principles, this review is divided into two sections: functional cardiovascular analysis and anatomical or tissue characterization related to cancer and cancer therapeutics. Level of Evidence: 5 Technical Efficacy Stage: 1 J. Magn. Reson. Imaging 2019;50:1349-1366.

Feasibility study of highly accelerated phase-sensitive inversion recovery myocardial viability imaging using simultaneous multislice and parallel imaging techniques.

Phase-sensitive inversion recovery (PSIR) is a powerful cardiac MRI method to assess myocardial viability, which can eliminate the background phase and preserve the sign of the desired magnetization during inversion recovery. To shorten the acquisition time of myocardial viability imaging by introducing both simultaneous multislice (SMS) and parallel imaging (PI) into PSIR without additional acquisitions for calibration data. Prospective study. A high-resolution phantom and three vials with doped solutions matching typical postcontrast T1 and T2 values of scar, healthy myocardium, and blood; 18 patients (six with known myocardial infarction) were included in this study. 3T/segmented fast spoiled gradient echo pulse sequence. Phantom and in vivo experiments were performed to compare the performance of conventional PSIR, SMS accelerated PSIR (SMS-PSIR, 2× acceleration), and SMS as well as PI accelerated PSIR (SMS + PI-PSIR, 4× acceleration). In phantom experiments, the error maps, local signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were calculated. In in vivo experiments, the image quality and artifact level of each study were qualitatively graded (by three radiologists). G-factor maps were calculated. The infarct size presented as a percentage of the left ventricle was measured (full-width half-maximum). Acquisition time of each study was recorded. One-way analysis of variance, Kruskal-Wallis test. In phantom experiments, SNR and CNR were well preserved for SMS-PSIR, while they dropped for SMS + PI-PSIR, as expected. In 15 subjects, the overall image quality scores were not significantly different among conventional PSIR (3.70 ± 1.06), SMS-PSIR (3.78 ± 0.99), and SMS + PI-PSIR (3.47 ± 0.94; P = 0.20). The artifact level scores were also comparable among conventional PSIR (3.67 ± 1.04), SMS-PSIR (3.77 ± 1.03), and SMS + PI-PSIR (3.45 ± 1.00; P = 0.22). SMS-PSIR achieved negligible g-factor noise amplification (1.04 ± 0.03) and SMS + PI-PSIR showed higher g-factors (2.83 ± 0.48). The infarct size was consistent among conventional PSIR (22.51 ± 25.05%) and SMS-PSIR (22.98 ± 26.19%), as well as SMS + PI-PSIR (22.93 ± 25.68%; P = 0.98). The acquisition time of two short-axis slices for SMS-PSIR (17.6 ± 1.7 sec, 16 heartbeats) and SMS + PI-PSIR (9.8 ± 1.9 sec, 8 heartbeats) was 30% and 17% of that for conventional PSIR (56.2 ± 8.5 sec, 32 heartbeats), respectively. SMS can be implemented in PSIR without additional reference scan. The image quality is comparable with conventional PSIR, while the acquisition time is much shorter. The proposed method is also compatible with PI to further reduce the scan time. 2 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2019;50:1964-1972.

P232 - The cardiac echo and MRI methods in diagnostics of the cardiotoxic risk factors

P232 - The cardiac echo and MRI methods in diagnostics of the cardiotoxic risk factors

Highly-accelerated self-gated free-breathing 3D cardiac cine MRI: validation in assessment of left ventricular function.

This work presents a highly-accelerated, self-gated, free-breathing 3D cardiac cine MRI method for cardiac function assessment. A golden-ratio profile based variable-density, pseudo-random, Cartesian undersampling scheme was implemented for continuous 3D data acquisition. Respiratory self-gating was achieved by deriving motion signal from the acquired MRI data. A multi-coil compressed sensing technique was employed to reconstruct 4D images (3D+time). 3D cardiac cine imaging with self-gating was compared to bellows gating and the clinical standard breath-held 2D cine imaging for evaluation of self-gating accuracy, image quality, and cardiac function in eight volunteers. Reproducibility of 3D imaging was assessed. Self-gated 3D imaging provided an image quality score of 3.4±0.7 vs 4.0±0 with the 2D method (p=0.06). It determined left ventricular end-systolic volume as 42.4±11.5mL, end-diastolic volume as 111.1±24.7mL, and ejection fraction as 62.0±3.1%, which were comparable to the 2D method, with bias±1.96×SD of -0.8±7.5mL (p=0.90), 2.6±3.3mL (p=0.84) and 1.4±6.4% (p=0.45), respectively. The proposed 3D cardiac cine imaging method enables reliable respiratory self-gating performance with good reproducibility, and provides comparable image quality and functional measurements to 2D imaging, suggesting that self-gated, free-breathing 3D cardiac cine MRI framework is promising for improved patient comfort and cardiac MRI scan efficiency.

Imaging cardiac morphology in hypertrophic cardiomyopathy: recent advances.

To describe new cardiac MRI (CMR) findings on cardiac structure and myocardial composition in hypertrophic cardiomyopathy (HCM). Quantitative CMR assessment of replacement fibrosis and interstitial fibrosis can risk stratify HCM patients for adverse outcomes. Patients with global LVH (increased LV mass index) have more adverse outcomes. The HCM phenotype with a spiral distribution of hypertrophy entails a good prognosis. Myocardial noncompaction can be associated with HCM, as are papillary muscle and mitral apparatus abnormalities. Genotype positive, phenotype negative relatives of HCM probands may be detected by myocardial motion abnormalities. Emerging CMR methods for myocardial fiber disarray and altered myocardial stiffness may shed more light on cardiac structure, function and outcomes in HCM in coming years. CMR structural features of HCM, including severity and distribution of hypertrophy and fibrosis, can augment clinical evaluation of HCM. New CMR phenotypes, associated papillary muscle, mitral leaflet and myocardial noncompaction abnormalities, role of left atrial enlargement, findings in genotype positive phenotype negative HCM, and emerging methods for the detection of myocardial fiber disarray and altered myocardial stiffness may shed light in coming years.

Abstract 94: Comparison of Ultrasound and Compact MRI for the Assessment of Cardiac Function in Mice

Introduction: Ultrasound (US) is a standard for the assessment of cardiovascular function. Pre-clinically, this is due the modality’s translational potential, its high temporal resolution and the absence of infrastructure. Recent advancements in novel high-performance compact MRI has made cardiac MRI a more accessible technique for assessing a variety of pathologies in murine models of CVD while reducing the complexity and costs traditionally associated with superconducting MRI systems. These developments may allow compact MRI to overcome some of the limitations of US meanwhile producing viable solutions for quantification along with new capabilities for cardiovascular biomarker assessment. Hypothesis: This study explores the relative capabilities of novel compact high-performance MRI compared to HFU for phenotypic analysis of mouse models of CVD. Methods: Four normal and one induced myocardial infarct C57BL/6 mice were imaged using both US and MRI. MI mice were prepared by ligation of the left anterior descending artery. In order to assess the ability of each modality to qualitatively and quantitatively characterize cardiac function, CINE loops of long axis and short axis slices were acquired with both systems and analyzed offline. In addition to traditional measures of cardiac function, strain analysis was performed using the HARP method for compact MRI and using speckle tracking for US. Finally, a cardiac MRI method for mapping and measuring infarct extent using gadolinium (Gd) contrast agents is described. Results and Conclusions: Although compact MRI has lower temporal resolution, when compared with US, it still provides many advantages in pre-clinical CVD imaging. In particular, because MRI signal is not attenuated by dense tissue or air, compact MRI can successfully generate artefact-free imaging of pathologies difficult or impossible to image with US, such as clearly visualizing and quantifying endo and epicardial borders. It also provides a whole body image and a “whole heart” image, making pre-clinical CV imaging easier for biologists and helping to reduce inter-operator variability. Finally, high sensitivity to Gd-based contrast agent with compact MRI enable new applications such as infarct quantification.

Echocardiographic Measurement of Left Atrial Strain as a Tool for Assessing Left Atrial Function and Geometric Change

Refer to the page 311-318 The left atrium (LA) serves as a reservoir of blood draining from the pulmonary veins during ventricular systole, a conduit of blood during ventricular diastole, and a booster pump of blood flow during atrial contraction.1) Normal LA function is important in maintaining adequate cardiac performance, and it becomes abnormal in various cardiac or extra-cardiac conditions. The abnormality of LA function can induce geometric changes, which results in the increase of the size and volume of the LA, and it has been non-invasively assessed by measuring the LA size or volume by echocardiography. The previous studies have shown that the LA size or volume is a powerful predictor of cardiovascular outcomes in various cardiac diseases, and thus, can be used as an imaging biomarker of cardiovascular disease or outcomes.2),3) Strain is a measure of deformation, and strain rate is a rate of such deformation. Strain echocardiography has been the most widely used tool to evaluate the ventricular myocardial mechanics in the field of echocardiography, during the last decade.4) Since the normal longitudinal LA strain values were first described in 2006, recent studies have suggested that LA strain or strain rate can be measured either by a tissue Doppler image or 2 dimensional (2D) speckle tracking image based echocardiography, and these measurements are useful tools to evaluate the global or regional LA function.5),6) The measurement of LA deformation is known to be associated with left ventricular filling pressure7) and the severity of chronic mitral regurgitation,8) a predictor of successful outcomes or LA reverse remodeling after catheter ablation of atrial fibrillation.9) In this issue of the journal, Her et al.10) released an interesting and valuable data regarding the usefulness of 2D-speckle tracking based LA strain measurement for the prediction of LA fibrosis in patients with mitral valve disease. According to their data, LA global strain was significantly correlated with the degree of LA fibrosis, regardless of age, underlying rhythm, and the presence or type of rheumatic valvular disease, and the degree of LA fibrosis on histopathologic analysis of the LA was a significant predictor of early and late LA reverse remodeling after mitral valve surgery. Kuppahally et al.11) also demonstrated that LA strain and strain rate is significantly associated with LA wall fibrosis, as measured by the degree of delayed enhancement on cardiac MRI (CMR). These two studies might have complementary clinical significance. CMR is a better tool than that of LA biopsy in that CMR can evaluate the fibrosis of the entire LA wall, but this benefit of CMR is counterbalanced by its limitation of the delayed enhancement on CMR, which is an indirect measure of LA fibrosis, and it cannot accurately reflect or quantify the true LA wall fibrosis. In this point of view, the study of Her et al.10) has its unique clinical significance in that their study adopted a better method, LA biopsy, than the CMR method to evaluate the degree of fibrosis. However, the study of Her et al.10) also has important limitation in that LA biopsy was done in small portion of the LA wall, and thus, it could not reflect the degree of fibrosis of the whole LA wall. Despite its limitations of both studies, it seems reasonable to conclude that LA strain or strain rate would be a useful non-invasive tool to evaluate LA function, including the degree of wall fibrosis by the combination of the results of these studies. The study of Her et al.10) also demonstrated that the degree of LA wall fibrosis was more severe, and the strain values were more severely decreased in patients with mitral stenosis (MS) than in mitral regurgitation (MR). These findings were quite similar to the previous observations of Shin et al.12) in that the patients with MS have greater pathologic physiology of the LA than in patients with MR. It is clear that the evaluation of LA function is clinically important, not only in the risk stratification, but also in the prediction of clinical outcomes in various cardiovascular diseases. With the technical advances of echocardiography and cardiac imaging, our ability or understanding to characterize and quantify the LA function is rapidly improving. The measurement of LA deformation by strain echocardiography seems to be a promising tool to evaluate LA function and hemodynamics, but the current status of the LA strain measurement is still a research tool before accumulating sufficient evidences.

Quantitative assessment of global and regional strain in relation to infarct size in patients with myocardial infarction

Assessment of regional and global left ventricular (LV) function and strain are important in the setting of prior myocardial infarction (MI). Feature tracking (FT-MRI) is a novel cardiac MRI method for assessment of myocardial strain, similar to speckle tracking in 2-D echocardiography, which provides multi-planar strain data without the need for tagged images.

Three‐dimensional T1 mapping of the mouse heart using variable flip angle steady‐state MR imaging

Cardiac MR T(1) mapping is a promising quantitative imaging tool for the diagnosis and evaluation of cardiomyopathy. Here, we present a new preclinical cardiac MRI method enabling three-dimensional T(1) mapping of the mouse heart. The method is based on a variable flip angle analysis of steady-state MR imaging data. A retrospectively triggered three-dimensional FLASH (fast low-angle shot) sequence (3D IntraGate) enables a constant repetition time and maintains steady-state conditions. 3D T(1) mapping of the complete mouse heart could be achieved in 20 min. High-quality, bright-blood T(1) maps were obtained with homogeneous T(1) values (1764 ± 172 ms) throughout the myocardium. The repeatability coefficient of R(1) (1/T(1) ) in a specific region of the mouse heart was between 0.14 and 0.20 s(-1) , depending on the number of flip angles. The feasibility for detecting regional differences in ΔR(1) was shown with pre- and post-contrast T(1) mapping in mice with surgically induced myocardial infarction, for which ΔR(1) values up to 0.83 s(-1) were found in the infarct zone. The sequence was also investigated in black-blood mode, which, interestingly, showed a strong decrease in the apparent mean T(1) of healthy myocardium (905 ± 110 ms). This study shows that 3D T(1) mapping in the mouse heart is feasible and can be used to monitor regional changes in myocardial T(1), particularly in relation to pathology and in contrast-enhanced experiments to estimate local concentrations of (targeted) contrast agent.

Quantification of Regional Myocardial Oxygenation by Magnetic Resonance Imaging

Background— A comprehensive evaluation of myocardial ischemia requires measures of both oxygen supply and demand. Positron emission tomography (PET) is currently the gold standard for such evaluations, but its use is limited because of its ionizing radiation, limited availability, and high cost. A cardiac MRI method was developed for assessing myocardial oxygenation. The purpose of this study was to evaluate and validate this technique compared with PET during pharmacological stress in a canine model of coronary artery stenosis. Methods and Results— Twenty-one beagles and small mongrel dogs without coronary artery stenosis (controls) or with moderate to severe acute coronary artery stenosis underwent MRI and PET imaging at rest and during dipyridamole vasodilation or dobutamine stress to induce a wide range of changes in cardiac perfusion and oxygenation. MRI first-pass perfusion imaging was performed to quantify myocardial blood flow and volume. The MRI blood oxygen level-dependent technique was used to determine the myocardial oxygen extraction fraction during pharmacological hyperemia. Myocardial oxygen consumption was determined by the Fick law. In the same dogs, 15 O-water and 11 C-acetate were used to measure myocardial blood flow and myocardial oxygen consumption, respectively, by PET. Regional assessments were performed for both MR and PET. MRI data correlated nicely with PET values for myocardial blood flow ( R 2 =0.79, P &lt;0.001), myocardial oxygen consumption ( R 2 =0.74, P &lt;0.001), and oxygen extraction fraction ( R 2 =0.66, P &lt;0.01). Conclusions— Cardiac MRI methods may provide an alternative to radionuclide imaging in settings of myocardial ischemia. Our newly developed quantitative MRI oxygenation imaging technique may be a valuable noninvasive tool to directly evaluate myocardial energetics and efficiency.

Abstract 697: Dyssynchrony in Duchenne Muscular Dystrophy Demonstrated by Tagged MRI Analysis is Independent of Ejection Fraction

Patients with Duchenne Muscular Dystrophy (DMD), a dystrophinopathy, universally develop dilated cardiomyopathy, which is associated with abnormal myocardial strain, as well as heterogeneous development of fibrosis as demonstrated by pathology and more recently by cardiac MRI methods. We sought to determine the presence of systolic dyssynchrony in this population using cardiac MRI tagging methods. We analyzed tagged MRI images for the presence of dyssynchrony in 61 males (age 12.5 ± 4.4 y) with a dystrophin mutation undergoing clinical cardiac MRI. Tagged MRI images were analyzed using HARP® analysis of regional strain and strain-time curves. The mid-myocardial slice was specifically analyzed, by dividing it into 6 coronary perfusion regions. Dyssynchrony was defined by the presence of either of 2 previously published indexes modified for use with MRI data: 1) time difference of 1 st to last regional peak strain &gt; 100 ms; 2) standard deviation of time differences to peak strain for each of the six regions &gt; 33 ms. Additional indexes evaluated included heart rate, LV ejection fraction, mid-myocardial composite circumferential strain, and presence of delayed myocardial hyperenhancement (MDE). Among the 61 subjects analyzed, 28 (46%) exhibited dyssynchrony indexes 1 and 2, while 8 additional subjects met dyssynchrony index 2 but not index 1. Only 4 subjects, all of whom met both dyssynchrony criteria, had positive MDE and abnormal EF &lt;55%. The regions of slowest activation were highly dispersed and not clustered to the areas of positive MDE. One additional subject with dyssynchrony by either of the critieria also had abnormal EF but did not have MDE. There was no statistically significant difference between mean EF (61 vs 62%), age (12.58 vs 12.63 yrs), heart rate (105 vs 108 bpm) or mid-myocardial composite circumferential strain (−13.3 vs −12.9%) between those subjects with dyssynchrony (by either criteria) and those without. DMD patients frequently exhibit systolic dyssynchrony even in the presence of normal EF. However, the dispersed nature of the dyssynchrony suggests that resynchronization therapy once EF becomes abnormal is unlikely to be of benefit in DMD cardiomyopathy.