Latest Advances in Clinical and Pre-Clinical Cardiovascular MRI

Heart failure is the potential result of a large number of heterogeneous diseases leaving the heart unable to provide an adequate blood supply for the body. The optimal diagnosis and management of this diverse syndrome requires the accurate synthesis of a large amount of clinical information but often the underlying diagnosis is elusive. The use of Cardiac Magnetic Resonance (CMR) is growing rapidly and it has established itself as a powerful, non-invasive, non-ionising radiation based tool. CMR is able to interrogate not only ventricular function and morphology but also characterise the tissue itself on a scale validated with histology, investigate cellular function as well as myocardial mechanics and energetics. Within this chapter we will summarise for the reader the current use of CMR in heart failure, the emerging pulse sequences and the state of the art application of CMR in specific settings within heart failure. CMR is already proven to make significant clinical impact but challenges remain in harnessing the wealth of information it can provide, proving the incremental value of each technique and in widening the availability of CMR in order to maximise its benefit. This chapter will provide an in-depth introduction to the topic, act as an update for the more advanced practitioner and provide a platform for further interest and research.

Ischemic heart disease is the most frequent cause of cardiovascular morbidity and mortality. Early detection and accurate evaluation are essential to guide optimal patient treatment and assess the individual’s prognosis. Cardiovascular Magnetic Resonance (CMR) has proven accuracy and is an established technique for the assessment of myocardial function both at rest and during stress. CMR is widely used for structural heart disease and its use in ischemic cardiomyopathy evaluation is growing. It allows stress perfusion analysis with high spatial and temporal resolution and applies to differentiate tissue, such as distinguishing between reversibly and irreversibly injured myocardium. Evaluation of ischemic heart disease with CMR includes imaging of coronary arteries, assessment of ventricular morphology and function, myocardial perfusion and viability. Late Gadolinium Enhancement (LGE) CMR techniques can clearly differentiate necrotic to viable areas of the myocardium leading to proper patients’ revascularization management. CMR is considered to be a safe imaging modality with limited restrictions mainly to patients with implantable defibrillators and pacemakers. It is noninvasive and radiation-free and the burden of the high cost appears to diminish as it becomes more popular. CMR is considered to be a safe imaging modality with limited restrictions mainly to patients with implantable defibrillators and pacemakers. It is noninvasive and radiation-free and the burden of the high cost appears to diminish as it becomes more popular. CMR is an established imaging modality for both functional and structural ischemic heart disease.

Displacement-encoded MRI is a class of imaging sequences and protocols that are based on the idea of displacement-encoding with stimulated echo (DENSE). Due to its ability to encode the displacement information over an extended period of time into the phase value of individual pixels in the image, it is a suitable method for track tissue motion at high resolution, which is valuable imaging tool in the assessment of cardiovascular diseases. This chapter describes the application of displacementencoded MRI in the assessment of ischemic heart disease through strain mapping, and in the assessment of carotid artery lesions through wall strain measurements in compliance to arterial pressure fluctuations.

Flow quantification with magnetic resonance (MR) imaging is an established method for assessing patients with a variety of cardiovascular diseases, particularly valvular heart disease and congenital heart disease. This chapter reviews basic MR physics and clinical applications for flow quantification, from one-directional flowsensitive MR to time-resolved, three-directional flow-sensitive MR.

Non-proton spectroscopy is a powerful tool that allows the assessment of specific and significant metabolites in cardiac tissue, such as key intermediates in energy metabolism. The technique uses spectroscopy, or less often imaging, of nuclei such as ³¹P, ¹⁹F and ²³Na. Due to the non-invasive nature of MRS, the technique is also applicable in the clinic, where it is used to assess changes in cardiac metabolism, such as due to a heart infarct. This chapter reviews the main developments in non-proton cardiac MRS and MRI, both clinical and preclinical. Major issues and challenges are also summarized. Finally, the promise of exciting new developments, particularly hyper-polarization, is discussed.

Cardiac magnetic resonance (CMR) is an imaging modality that allows for a non-invasive assessment of anatomy, function, structure, viability and metabolism in hearts of patients and of small animal models (e.g., mice and rats) with cardiovascular disease. Dedicated techniques to accelerate the inherently slow MR imaging process have resulted in a shift of paradigm in clinical CMR. The application of fast imaging techniques in preclinical CMR research lags far behind the clinical standard. The aim of this chapter is to review the challenges and advances in fast preclinical CMR. More specifically, parallel imaging, and reconstruction based techniques, including k-t- BLAST, k-t-PCA and Compressed Sensing will be discussed and examples for each application will be provided. We conclude that there is indeed a need for accelerating preclinical CMR, to increase the amount of information obtainable from each animal, to reduce the number animals used in preclinical research and to make an inherently expensive imaging modality more cost-efficient.

This chapter summarizes regional cardiac functional studies using MRI that span the past 25 years. In addition to the comparison of the three major MRI techniques that achieve detailed studies of myocardial mechanics, an extensive reference to DENSE-MRI and its imaging and image-processing features is presented. The mouse paradigm, as a direct manifestation of international efforts for image-based phenotyping in health, disease and post-transgenetic modification, is also introduced. The appropriateness of extrapolations of inferences drawn from mouse studies to man are well-justified from presented evidence on isometric and allometric scaling of global and regional cardiac functional indices, however, noted mismatches of the fiber structure, force-frequency and energetic/metabolic reserves exist between the two species. While such arguments limit the range of possible pathological models that can associate human and murine disease, the mouse still remains a potentially attractive animal model for cardiovascular research today.

Understanding of the structural-functional relationships of the heart, in both normal and diseased states, is not complete without incorporating precise knowledge of the underlying tissue microstructure, in terms of myocyte organization and orientation. By probing the effects on the diffusion of water molecules exerted by their microscopic environment, magnetic resonance diffusion tensor imaging (MR-DTI, or DTI for short) has emerged as a promising alternative to conventional histology for mapping fiber organization in ordered tissues such as the myocardium. In this chapter, the basic principles and recent advances in mapping myocardial structure using DTI are reviewed. Instances when DTI has advanced the understanding of the functionalstructural relationship in the heart are also highlighted.