Cardiac Magnetic Resonance Elastography: Why Multiplex Approaches Hold the Key to Clinical Translation

Magnetic resonance elastography (MRE) presents a fascinating clinical opportunity: despite being developed nearly three decades ago at Mayo Clinic in 1995 and emerging as a powerful, noninvasive diagnostic tool for quantifying tissue mechanics, it has yet to achieve widespread clinical adoption in cardiac applications [1]. MRE has successfully transitioned to routine clinical practice for liver fibrosis assessment, receiving FDA clearance in 2009 and deployment on over 2000 MRI systems worldwide. In contrast, cardiac MRE remains largely confined to research settings, despite the unique and highly clinically relevant capability of MRE to characterize mechanical abnormalities of the myocardium. The disparity between clinical adoption of MRE for hepatic and cardiac indications underscores the need to address technical barriers unique to cardiac imaging. Among emerging solutions, multiplex MRE (MMRE) is well positioned as the catalyst for bridging this translational gap. The path from research to clinical routine has proven notably more challenging for cardiac MRE compared to its hepatic counterpart. Liver MRE has benefitted from standardized protocols, uniform single-frequency and single-transducer hardware, and validated stiffness thresholds across vendors [2]. In contrast, cardiac MRE must contend with the heart's rhythmic motion, anisotropic architecture, and proximity to lung interfaces—factors that exacerbate wave attenuation and, thus, limit reproducibility in single-frequency setups. Despite demonstrating feasibility in healthy volunteers and preliminary utility in hypertrophic cardiomyopathy and cardiac amyloidosis, early single-frequency studies struggled to move beyond proof-of-concept [3-5]. These limitations stem from inadequate spatial resolution, suboptimal wave penetration, and synchronization challenges with cardiac motion, confining most investigations to small cohorts rather than diverse patient populations. MMRE surmounts these hurdles through multifrequency excitation and multi-driver systems, which optimize shear-wave propagation across myocardial regions prone to signal loss, such as the lateral wall. By integrating frequencies spanning 80–100 Hz, MMRE achieves comprehensive left ventricular stiffness mapping in under 1 min with a high reproducibility in healthy volunteers and patients with aortic stenosis [6]. Reported intraclass correlation coefficients exceeding 0.90 support its robustness. This technical leap addresses critical clinical needs: rapid acquisition times, diagnostic accuracy, and patient tolerance—a prerequisite for clinical adoption. A key strength of MMRE lies in its ability to capture frequency-dependent viscoelastic behavior of the myocardium, an inherently property of myocardial tissue [7]. At higher frequencies, MMRE predominantly captures elastic responses—primarily influenced by the extracellular matrix. In contrast, lower frequencies are more sensitive to viscous damping properties, which may relate to early cellular dysfunction such as impaired relaxation and cytoskeletal abnormalities. By integrating data across multiple frequencies, MMRE can derive dispersion metrics and viscoelastic models that reflect both collagen-based stiffness and myocyte-level dynamics, offering a more complete picture of myocardial health. These technical advances unlock a range of clinical applications, particularly in conditions marked by subtle mechanical abnormalities such as heart failure with preserved ejection fraction (HFpEF), where subtle mechanical abnormalities often elude detection by conventional imaging [8]. The enhanced granularity from frequency-dependent analysis could unmask regional or early mechanical dysfunction, potentially guiding targeted therapeutic strategies and improving diagnostic sensitivity in diseases with spatially heterogeneous pathology. Furthermore, MMRE may hold value in monitoring therapeutic response such as reverse remodeling following TAVI or progression of myocardial fibrosis. Despite its promise, MMRE's clinical adoption hinges on overcoming hardware limitations. Current setups rely on external pneumatic drivers connected via long tubing—a configuration prone to workflow disruption and inter-institutional variability. MRI-compatible actuator designs and embedded vibrational elements represent critical areas for development. Emulating liver MRE's success requires vendor-agnostic systems with integrated vibration hardware, and real-time frequency modulation. Such advancements would align MMRE with the plug-and-play usability of contemporary CMR sequences, such as T1/T2 mapping and 4D flow. Moreover, cardiac MMRE must be contextualized within the broader ecosystem of advanced cardiovascular imaging. Techniques such as T1 mapping, extracellular volume (ECV) quantification, and diffusion tensor imaging (DTI) have redefined tissue characterization in cardiomyopathies. For instance, while late gadolinium enhancement (LGE) identifies focal fibrosis and T1 mapping quantifies diffuse interstitial changes, MMRE adds a functional dimension by mapping mechanical stiffness—a parameter directly linked to diastolic impairment and ventricular-arterial coupling. Incorporating DTI with MMRE enables high-resolution mapping of fiber orientations and their corresponding mechanical properties, overcoming one of the main limitations of MMRE [9]. Moreover, implementing prospective gating throughout the entire cardiac cycle could enable quantification of both systolic and diastolic ventricular stiffness, providing a comprehensive assessment of myocardial mechanics across all phases of cardiac function [10]. Such temporal profiling could support personalized therapy in heart failure syndromes, particularly in early-stage detection. Cardiac MMRE stands at a pivotal juncture, poised to transition from technical curiosity to clinical necessity. Its ability to quantify myocardial viscoelasticity fills a critical gap in the non-invasive assessment of diastolic function, fibrosis, and microstructural remodeling. MMRE-derived stiffness maps, integrated with other CMR biomarkers, could enhance multiparametric diagnostic pipelines and even feed machine learning algorithms for patient stratification. By aligning with precision medicine paradigms and demonstrating concordance with established biomarkers, MMRE could revolutionize the management of complex cardiomyopathies. The path forward demands collaboration among researchers, clinicians, and industry partners to standardize protocols, validate clinical utility, and integrate MMRE into the advanced imaging armamentarium. Only then will this decades-old technology realize its potential in routine patient care.