Rapid Fire Abstracts
Moritz C. Halfmann, MD
Resident physician
University Medical Center Mainz, Germany
Lara van der Meulen, BA
PhD student
Maastricht University, Netherlands
Martijn Smulders, MD
Maastricht University Medical Center, Netherlands
Hedwig M.J.M. Nies, BA
PhD student
Maastricht University, Netherlands
Fritz W. Prizen, PhD
Professor
Maastricht University, Netherlands
Casper Mihl, MD, PhD
Assistant Professor
Maaastricht University, Netherlands
Akos Varga-Szemes, MD, PhD
Associate Professor of Radiology
Medical University of South Carolina
Robert J. Holtackers, MSc, PhD
MR Physicist
Maastricht University Medical Centre, Netherlands
Tilman Emrich, MD
Junior Consultant
University Medical Center Mainz, Germany
Cardiac MRI derived myocardial extracellular volume fraction (ECV) is a reproducible imaging biomarker for myocardial fibrosis assessment even in the light of different scanner types and field strengths. However, well-controlled evidence on the influence of the timing of the scan in relation to the contrast injection is scarce. Therefore, this study aimed to compare ECV measurements at different time points after contrast injection in a large animal infarct model.
Methods:
Animal handling complied with the Dutch Law on Animal Experimentation and the European Directive on the Protection of Animals used for Scientific Purposes (2010/63/EU). This study was approved by the Experimental Animal Committee of Maastricht University (DEC2016-002). Cardiac MRI was performed on a 1.5T scanner (Ingenia, Philips Healthcare, Best, the Netherlands) while the animals were ventilated and under general anesthesia. Hematocrit levels were drawn directly prior to the scan. Using a commercially available 5(3)3 MOLLI sequence, quantitative short-axis T1 maps of basal, midventricular and apical levels of the left ventricle were acquired. 7 and 30 minutes following an intravenous administration of 0.2 mg/kg gadobutrol (Gadovist, Bayer Pharmaceuticals, Berlin, Germany), a 4(1)3(1)2 MOLLI sequence was used to obtain post-contrast T1 maps at identical slice locations. Subsequently, ECV was calculated for both global myocardium and separately for the infarcted and remote myocardium. Results were compared using Pearson’s correlation, Bland-Altman plots and paired sample Student’s t-tests.
Results:
A total of 13 Yorkshire pigs with balloon catheter-induced myocardial infarction were included in this prospective study. However, 7 animals died before the MRI scan due to severe arrhythmias and 2 animals did not undergo the scan due to instability. Thus, MRI was successful in four pigs. The median time between induction of the myocardial infarction and cardiac MRI was 8 days [IQR 8–8]. While there was a strong correlation between measurements at both time points (Pearson’s r=0.94), mean global myocardial ECV was significantly higher at 30 minutes post-contrast compared to 7 minutes post-contrast (32.2 ± 5.0% vs. 27.8 ± 4.2%, P=.015, Figure 1). These findings were confirmed when assessing infarcted (56.9 ± 11.4% vs. 43.7 ± 9.1%, P</em>=.018) and remote myocardium (28.4 ± 2.8% vs. 25.5 ± 3.2%, P=.010) separately. Additionally, Bland-Altmann plots revealed significant bias for global (2.9, P=.003), infarcted (13.2, P=.018), and remote (2.96, P=.025) myocardium, respectively.
Conclusion:
Myocardial ECV values by cardiac MRI significantly increase with increasing time after contrast injection in a large animal infarct model. A similar effect was observed in regions with only remote myocardium and regions with only infarcted myocardium. These findings may be considered when using extracellular volume fractions as a quantitative measure in research studies or clinical care.
