The main findings of this study include (1) the significant correlation between the p-CS values of conventional and CS cine CMR images, (2) high diagnostic performance of p-CS for identifying MI segments on conventional and CS cine CMR images, and (3) evidence that p-CS on CS cine CMR imaging may help classify myocardial characterization on LGE-CMR into remote, adjacent, subendocardial infarcted, and transmural infarcted segments.
Myocardial strain analysis on CMR images is a quantitative method of cardiac function assessment. It is conventionally performed using tagging CMR scans or displacement- or strain-encoded imaging [11, 13, 14]. However, additional data must be acquired for strain analysis using these methods. FT-strain analysis can be performed after processing cine CMR images, providing additional diagnostic value to the visual assessment of cardiac function . Recently, the CS technique has been used with cine CMR images, enabling quick data acquisition while maintaining the robustness of cardiac function assessment . In the present study, the p-CS values of CS cine CMR images were correlated with those of conventional cine CMR images. Furthermore, there was no significant difference in p-CS values between conventional and CS cine CMR images, which was previously reported . The present findings indicate that data acquisition of the full cardiac cycle is important for accurate FT-strain analysis using CS cine CMR images, as a prospective real-time cine CMR scan may lack complete end-diastolic phase data, resulting in the underestimation of peak strain values relative to those obtained from retrospective conventional cine CMR scans . Consequently, in the present study, we acquired the data of over 1.5 cardiac cycles on CS real-time cine CMR scanning to increase estimate accuracy.
There was no significant difference in the AUC values for detecting MI obtained using conventional and CS cine CMR images. In previous studies, p-CS values obtained using conventional CMR strain analysis for detecting MI had a sensitivity estimate of 71–81% and specificity estimate of 74–75%. These estimates are consistent with the estimated from this study [10, 13]. In the present study, the diagnostic performance of p-CS of CS cine CMR imaging for detecting MI was not inferior to that of conventional cine CMR scanning. Moreover, p-CS values on CS cine CMR images were correlated with the severity and location of MI, as reflected in the categories of remote, adjacent, subendocardial infarcted, and transmural infarcted segments. A previous study has shown that p-CS values obtained from conventional CMR images varied depending on the severity and location of MI on an LGE-CMR image . The use of p-CS on CS cine CMR imaging may help differentiate subendocardial from transmural MI as assessed on LGE-CMR scanning, which is clinically relevant to prognosis and viability after revascularization [17, 18]. Buss et al. have shown that, as with the values obtained from LGE-CMR images, p-CS values from FT-strain analysis may be an independent predictor of cardiac function improvement after revascularization .
FT-strain analysis of CS cine CMR images is a quantitative technique of cardiac function assessment that is quicker than conventional CMR strain analysis. CS cine CMR imaging is becoming increasingly available, and FT-strain analysis of CS cine CMR scans may be applied to various cardiovascular diseases, as is presently used on conventional cine CMR scans [20–22]. This technique, which does not require a contrast medium, may benefit patients who cannot tolerate lengthy examination times and multiple breath-holdings and to those with advanced renal dysfunction and high risk of nephrogenic systemic fibrosis or renal failure.
There are some limitations of the present study. First, this study was conducted at a single center and with a small sample. Second, the present study only used p-CS values, because they are better for detecting MI than other strain parameters (e.g., longitudinal strain) [13, 23]. Further studies using other myocardial strain parameters with CS cine CMR images are required. Third, the reconstruction time for the CS cine CMR image was approximately 3 min. Ongoing technological developments will reduce reconstruction times, thus helping to overcome this limitation.
Fourth, the effects of different types of CMR-FT analysis software on obtained estimates were not assessed. As different software types use different algorithms, they may result in different values; these inherent differences should be considered when comparing findings obtained using different software types . Fifth, the present study did not account for differences in temporal and spatial resolution and regularization during FT strain analysis, the impact of which has been reported . Finally, low temporal resolution or high regularization may result in underestimation of strain values .
In conclusion, FT-strain analysis of CS cine CMR images may help identify and classify MI segments; it may be used alongside or instead of that of conventional cine CMR images.