Cardiovascular magnetic resonance feature tracking in small animals - a preliminary study on reproducibility and sample size calculation.

Background: Cardiovascular magnetic resonance feature tracking (CMR-FT) is a novel tissue tracking technique developed for noninvasive assessment of myocardial motion and deformation. This preliminary study aimed to evaluate the observer's reproducibility of CMR-FT in a small animal (mouse) model and define sample size calculation for future trials.
Methods: Six C57BL/6 J mice were selected from the ongoing experimental mouse model onsite and underwent CMR with a 3 Tesla small animal MRI scanner. Myocardial deformation was analyzed using dedicated software (TomTec, Germany) by two observers. Left ventricular (LV) longitudinal, circumferential and radial strain (Ell _LAX , Ecc _SAX and Err _SAX ) were calculated. To assess intra-observer agreement data analysis was repeated after 4 weeks. The sample size required to detect a relative change in strain was calculated.
Results: In general, Ecc _SAX and Ell _LAX demonstrated highest inter-observer reproducibility (ICC 0.79 (0.46-0.91) and 0.73 (0.56-0.83) Ecc _SAX and Ell _LAX respectively). In contrast, at the intra-observer level Ell _LAX was more reproducible than Ecc _SAX (ICC 0.83 (0.73-0.90) and 0.74 (0.49-0.87) Ell _LAX and Ecc _SAX respectively). The reproducibility of Err _SAX was weak at both observer levels. Preliminary sample size calculation showed that a small study sample (e.g. ten animals to detect a relative 10% change in Ecc _SAX ) could be sufficient to detect changes if parameter variability is low.
Conclusions: This pilot study demonstrates good to excellent inter- and intra-observer reproducibility of CMR-FT technique in small animal model. The most reproducible measures are global circumferential and global longitudinal strain, whereas reproducibility of radial strain is weak. Furthermore, sample size calculation demonstrates that a small number of animals could be sufficient for future trials.