Magnetic resonance pulse sequences for rapid imaging of myocardial motion and strain.

摘要

Measuring myocardial motion and strain using magnetic resonance imaging (MRI) techniques such as MR tagging provide sensitive diagnostic indicators of heart disease. MR tagging non-invasively introduces features in the myocardial walls at an early time frame. The deformation of these features are then used to determine the myocardial motion at any later time frame. The clinical adoption of MR tagging has partly been limited due to the lengthy image acquisitions involved, multiple long patient breath-holds, and manually intensive post-processing. The recent implementations of the harmonic phase (HARP) MRI methodology provided fast and efficient post-processing tools for tagged images.; In this thesis, we present MR pulse sequences that specifically exploit HARP-MRI concepts to provide rapid imaging of myocardial motion and strain from MR tagged images. A tagged image comprises of multiple spectral peaks, and the HARP-MRI methodology states that the image obtained by isolating an off-centered harmonic peak is sufficient to measure cardiac motion and strain. A significant reduction in imaging time was thus obtained by designing pulse sequences that acquire reduced regions in Fourier space centered on the desired harmonic peak.; We describe the development of the 2-D FastHARP pulse sequence and post-processing software that can provide free-breathing, real-time 2-D motion and strain imaging of the heart. Using this pulse sequence, full visualization of in-plane strains can now be obtained from data acquired in just two heartbeats with updates in strain every heartbeat. We also present the design and implementation of a 3-D FastHARP-SENC MRI pulse sequence. Using this pulse sequence, circumferential, radial, and longitudinal strains on a stack of short axis slices can be obtained in 1--4 breath-holds. A new method, SF-HARP MRI, that can be used to measure true 3-D motion trajectories of material points in a moving object is also described. The development of a pulse sequence used to implement this technique on the MR scanner is presented. A rich body of experimental data that validates the significance of these pulse sequences are also presented in this thesis.