Background: Myocardial strain is increasingly recognized as an important assessment for myocardial function. However, there is lack of standardization in strain evaluation by cardiac MRI (CMR). In this study we compared strain value using multiple modalities and multiple vendor products.
Methods: Prospectively recruited patients (N=77) with cardiomyopathy of diverse etiology and normal controls (N=10) underwent cardiac MRI on a 1.5 T scanner. Tagging, displacement encoding with simulated echoes (DENSE) and stead state free precession cine imaging were acquired on all subjects. A single matched mid ventricular short axis plane was used for the comparisons of peak circumferential (Ecc) and radial strain (Err) and a 4-chamber view for longitudinal strain (Ell). Tagging images were analyzed using HARP and DENSE images using a proprietary program. Feature tracking (FT) was evaluated using 3 commercially available software including Tomtec, CIM and Circle. Statistic analyses were performed using paired t-test, intraclass correlation coefficient (ICC) and Bland Altman limits of agreement.
Results: Average left ventricular ejection fraction was 50% ranging from 32% to 62%. Regional wall motion abnormality was common (49%). The average Ecc was -13±4, -13±4, -16±6, -10±3 and -14±4 for tagging, DENSE, Tomtec, CIM and Circle. When tagging was used as a reference standard DENSE and Circle showed the best agreement in Ecc evaluation with ICC 0.778 and 0.763, respectively. The Err was highly varied with poor agreement across the modalities, 32±24, 40±28, 47±26, 64±33 and 23±9 for tagging, DENSE, Tomtec, CIM and Circle, respectively. The average Ell was -14±4, -8±3, -13±5, -11±3 and -12±4 for tagging, DENSE, Tomtec, CIM and Circle, respectively with the best agreement seen in Tomtec and Circle with tagging. Overall, the reproducibility of each modality was excellent in the intra- and inter-observer variability analysis.
Conclusions: To conclude, small but important differences are evident in Ecc and Ell comparisons while large differences are seen in Err assessment. Our findings suggest that CMR strain value is modality and vendor dependent. Hence, it is essential to develop reference standard for clinical use from each modality and analytical product.