Comparative Assessment of Motion Averaged Free-Breathing or Breath-Held Cardiac Magnetic Resonance Imaging Protocols in a Porcine Myocardial Infarction Model

Abstract

Breath-held (BH) cardiac magnetic resonance imaging (CMR) is the gold standard for volumetric quantification. However, large animals for pre-clinical research are unable to voluntarily breath-hold, necessitating general anaesthesia and mechanical ventilation, increasing research costs and affecting cardiovascular physiology. Conducting CMR in lightly sedated, free-breathing (FB) animal subjects is an alternative strategy which can overcome these constraints, however, may result in poorer image quality due to breathing motion artefact. We sought to assess the reproducibility of CMR metrics between FB and BH CMR in a porcine model of ischaemic cardiomyopathy. FB or BH CMR was performed in 38 porcine subjects following percutaneous induction of myocardial infarction. Analysis was performed by two independent, blinded observers according to standard reporting guidelines. Subjective and objective image quality was significantly improved in the BH cohort (image quality score: 3.9/5 vs 2.4/5; p < 0.0001 and myocardium:blood pool intensity ratio: 2.6-3.3 vs 1.9-2.3; p < 0.001), along with scan acquisition time (4 min 06 sec±1 min 55 sec vs 8 min 53 sec±2 min 39 sec; p < 0.000). Intra- and inter-observer reproducibility of volumetric analysis was substantially improved in BH scans (correlation coefficients: 0.94-0.99 vs 0.76-0.91; coefficients of variation: <5% in BH and >5% in FB; Bland-Altman limits of agreement: <10 in BH and >10 in FB). Interstudy variation between approaches was used to calculate sample sizes, with BH CMR resulting in greater than 85% reduction in animal numbers required to show clinically significant treatment effects. In summary, BH porcine CMR produces superior image quality, shorter scan acquisition, greater reproducibility, and requires smaller sample sizes for pre-clinical trials as compared to FB acquisition.