## 4 Discussion  
Our results suggest that the selection of ROI\({}_{\text{ref}}\) contributes most to the LGE extent variability when using both the 3\(\sigma\) and FWHM quantification methods, but we cannot conclusively confirm this because of low statistical significance. We furthermore compared the results provided by each of these two methods and found that FWHM yielded lower LGE extent values, which we also confirmed based on lower average LGE extent variability; however, again due to low statistical significance it is difficult to conclusively confirm the observation. Specifically, our results demonstrate that the selection of ROI\({}_{\text{ref}}\) presents a significantly greater source of variability than the selection of ROI\({}_{\text{myco3}}\) (Figure 4). This finding may be explained by the fact that the ROI\({}_{\text{ref}}\) regions are selected based on the observer's interpretation, with the only formal requirement being that they be located somewhere within the normal myocardium, which appears dark in the image. The ROI\({}_{\text{myco}}\), on the other hand, is defined by the anatomy and thus is less influenced by the observer's interpretation. Therefore, clinical experts should be especially careful when selecting a reference region when using the 3\(\sigma\) method. The clinical interpretation of the influence of variability magnitude on diagnostics and treatment is not straightforward. The results of studies examining the relationship between the quantitative value of the LGE extent and adverse events are unclear [2]. However, a study conducted by [PERSON] et al. [22] reported that a 10% increase in FWHM-evaluated LGE extent corresponds to a 79% increased risk of MACE. In this context, our findings show that the variability of both methods is within a clinically acceptable range. The general expectation in radiology is that variability should not exceed the 10% limit, and ideally, it should be lower than 5%. Considering this interpretation, our results show that the mean value of the 3\(\sigma\) method's variability exceeds the 5% limit, whereas the mean value of the FWHM method's variability falls within the predicted limit. Our observation of the lower LGE extent generated by the FWHM method is consistent with previously published studies conducted on myocarditis patients [6], as well as those conducted on patients with cardiomyopathy (CMP) [10] and myocardial infarction (MI) [10; 12]. In addition, one study [6] showed that the lower LGE extent calculated with the FWHM method offers a better prognostic association with lower MACE in myocarditis  
Figure 6: Intraobserver variability (calculated as a 1-intraclass correlation coefficient (ICC)), with corresponding 95% confidence intervals, for the 3\(\sigma\) (blue) and FWHM (red) quantification methods. Statistically significant differences are marked with an asterisk. Abbreviations as in Figures 1 and 2.  
its patients, suggesting that FWHM values may correlate better with realistic myocardial damage, which is crucial for making informed decisions on patient treatment plans and interventions. Furthermore, our finding that the FWHM method in myocarditis patients yields lower inter- and intraobserver variability is again consistent with the results published in a previous study [6]. However, in our case, the 95% CIs of the 1-ICC value for the 3\(\sigma\) and FWHM methods mostly overlapped. As a result, the statistical significance of the differences observed remains to be elucidated. We used the reference LGE extent method to determine LGE extent variability, which is an alternative to finding the graphical average of each of the ROIs delineated. A problem arose with the graphical average approach when we tried to determine the graphical average of ROI\({}_{\text{ref}}\) and ROI\({}_{\text{excl}}\). Because these two ROIs can be delineated anywhere within the LV boundaries, their interpretation is highly dependent on the observer. As a result, we found the determination of their graphical average to be a complicated, if not impossible, task.