| In my thesis research, the primary objective was to investigate myofiber orientation in both healthy and diseased hearts using diffusion tensor magnetic resonance imaging (DTMRI). Specifically, changes in myofiber orientation were investigated in a high rate pacing model of dilated cardiomyopathy in swine, and also in excised healthy and diseased human hearts. In addition, the mechanical activation due to cardiac pacing from the right ventricular apex was uniquely characterized in a case study of an isolated human heart using MRI, as cardiac pacing from the right ventricular apex is known to chronically result in deleterious changes in fiber orientation and cardiac function.;My thesis was divided into several chapters, in the first it was considered paramount to gain a thorough understanding of cardiac MRI. As such, a review of cardiovascular MRI is provided in Chapter 1. The goal of this chapter was to familiarize the reader with cardiac MR and nomenclature, review current techniques to quantify cardiac function with MRI, and to introduce the reader to cardiac diffusion tensor magnetic resonance imaging (DTMRI), which is used in the present work to quantify fiber orientation in the heart.;In Chapter 2, a literature review of cardiac fiber orientation and relevant changes resulting from disease is presented, and the measurement of fiber orientation using DTMRI is further discussed. The intent of this chapter is to familiarize the reader with diffusion imaging and the associated parameters used to characterize fiber orientation and tissue integrity. In addition, the methodologies and computational tools developed to measure fiber orientation using a 3 tesla Siemens MRI clinical scanner are described.;Chapters 3-5 describe novel investigations in the assessment of fiber orientation using DTMRI. In chapter 3, the effects of decomposition on the diffusion properties of the myocardium were studied in freshly excised human hearts recovered at varying post mortem intervals. From this study, the time frame for the recovery of a human heart was determined to be 3 days, such that the tissue still remains viable for the measurement of fiber orientation using DTMRI. In Chapter 4, a swine model of dilated cardiomyaphy was used to assess in vivo functional and anatomical changes resulting from severe dilation of both the right and left ventricle. Following in vivo functional imaging, ex vivo DTMRI was used to investigate the resultant fiber orientation. Chapter 5 provides a preliminary comparison of fiber orientation in healthy and diseased human hearts, collected within a post-mortem interval of 3 days.;Furthermore, in Chapter 6, the mechanical activation during pacing from the right ventricular apex was studied in an isolated human heart. Since pacing from the right ventricular apex is known to cause deleterious changes in fiber orientation, it was of great interest to characterize myocardial strain and motion during RVA pacing as part of my thesis work.;In general, this research project has advanced our overall knowledge as to our understanding of ex vivo DTMRI, and the remodeling of the myocardial architecture in heart failure. This described work is not an exhaustive list of the changes in fiber orientation that occur in every type of cardiomyopathy, but provides novel insights into fiber reorganization which occurs in swine due congestive heart failure, and in human hearts excised from patients with a history of heart failure. Additionally, with the development of methodologies and computational tools presented here, and the study of post mortem intervals on the diffusion properties of the myocardium, the framework has been laid for the future analysis of fiber orientation in other cardiomyopathies presented in human cadaveric hearts. (Abstract shortened by UMI.). |
