Highly accelerated cardiovascular magnetic resonance myocardial perfusion imaging: studies in spatial resolution, spatial coverage and cardiac phase

Background: Myocardial perfusion imaging with cardiovascular magnetic resonance (CMR) is bound by spatio-temporal constraints. Standard perfusion CMR techniques permit the acquisition of 3-4 myocardial slices with a spatial resolution of 2-3mm. However, acceleration techniques can be applied to achieve higher spatial resolution (<2mm) or 3-dimensional (3D) acquisitions with increased spatial coverage (12-16 slices). Acceleration can also be used to simultaneously acquire perfusion data at different time-points in the cardiac cycle. Accordingly, this thesis includes studies that modify the standard approach to perfusion CMR in order to investigate the impact of spatial resolution, spatial coverage and cardiac phase of acquisition.

Methods and Results: Study 1 and 2 compared high-resolution and standard-resolution perfusion CMR in patients with suspected coronary artery disease (CAD). Study 1 found high-resolution acquisition had greater diagnostic accuracy compared to standard-resolution for detecting CAD (area under curve [AUC]: 0.93 vs. 0.83; p<0.001); and study 2 found it also had greater diagnostic accuracy for specifically identifying 3-vessel CAD (AUC: 0.90 vs. 0.69; p<0.0001). Study 3 compared high-resolution and 3D perfusion CMR in patients with CAD and found limited agreement between myocardial ischaemic burden estimates (95% limits of agreement: -8.68%, 9.82%). Study 4 and 5 compared systolic and diastolic acquisitions using standard perfusion CMR (limited to 1 slice) and 3D perfusion CMR respectively. Both studies found higher estimates of myocardial blood flow (MBF) in diastole compared to systole at stress (p<0.05). Study 6 utilised accelerated perfusion CMR to compare MBF estimates at 5 different time-points in the cardiac cycle in healthy volunteers. Estimates of stress MBF peaked at end-diastole and fell steadily to end-systole (p<0.0001).

Conclusion: By altering the spatial resolution, spatial coverage and cardiac phase of acquisition of perfusion CMR, we have gained valuable insights into the relative impact of these parameters on both qualitative and quantitative assessment of ischaemia.