Ryan Fries, Saki Kadotani, Carl Toborowsky, Emily A. Javery
Objective: To establish species-specific reference values for myocardial native T1, native T2, and extracellular volume fraction (ECV) in clinically normal dogs and cats using a 3-Tesla (3-T) cardiac MRI (CMRI) and to provide a description of image acquisition and analysis suitable for veterinary clinical and research applications. Methods: Cardiac examinations were performed between 2015 and 2024 using a 3-T system with ECG gating under general anesthesia on clinically normal client-owned dogs and cats. Native T1 and T2 maps were acquired at the midventricular short-axis level using validated mapping sequences adapted from human CMRI protocols. Calculated ECV values were obtained from native and postcontrast T1 measurements in conjunction with Hct values. Reference intervals were determined using parametric methods and expressed as 95% prediction intervals with 90% CIs around the lower and upper reference limits. Results: In dogs (n = 54), native T1, native T2, and ECV reference intervals (95% prediction intervals) were 1,057 to 1,152 ms, 42.0 to 60.9 ms, and 19.3% to 25.7%, respectively. In cats (n = 60), corresponding reference intervals were 1,066 to 1,172 ms, 34.2 to 61.6 ms, and 21.8% to 30.3%. Age was not a significant predictor of myocardial ECV in either species. Conclusions: This study establishes clinically applicable reference values for myocardial T1, T2, and ECV in dogs and cats at 3 T and provides imaging methodology to facilitate reproducibility. Clinical Relevance: Species-specific reference intervals established in this study enable objective quantification of myocardial composition and support clinical implementation of CMRI tissue characterization in dogs and cats.