Development of a high temporal resolution spiral 3D phase velocity mapping technique for analysis of regional myocardial mechanics

Abstract

MRI is a powerful tool for imaging the heart, allowing the collection of anatomical and functional information non-invasively. Heart function is routinely assessed by global performance via ventricular masses and ejection fraction. Regional dysfunction, often a precursor of disease, can be hidden by apparently healthy global ventricular function and so there is a clear need for accurate and reproducible methods for measuring regional myocardial mechanics.

Tissue phase velocity mapping is the only MR technique which is capable of measuring motion over the entire cardiac cycle. Unfortunately current sequences are inefficient and do not fully exploit its full potential. This thesis presents the development of a new high temporal resolution sequence which uses spiral k-space trajectories to speed up the acquisitions, and implements retrospective cardiac gating to extend the technique over the entire heartbeat. Two sequence variations are developed and assessed.

The first uses a modified respiratory navigator algorithm to acquire high resolution data in ten healthy volunteers on two occasions, demonstrating very good reproducibility. Measurements in atrial systole have been made for the first time, providing information that previously was only seen from echocardiography. The second sequence variation uses a non-Cartesian SENSE reconstruction to allow the acquisition of similar resolution images within a short breath-hold. This sequence performs as well as the navigator gated sequence despite being acquired in just thirteen heartbeats. Analysis tools have also been developed and colour plots have been used for the first time to present a large amount of data in an easily interpretable way.

By speeding up the acquisition of tissue phase velocity mapping data and by extending it over the entire cardiac cycle, the work presented in this thesis provides the potential to routinely acquire information about regional myocardial mechanics in clinical practice.