## 4 Non-Ischemic Heart Diseases  
### Myocarditis  
Myocarditis, or inflammation of the myocardium, is primarily associated with various viral infections [26]. For the diagnosis of acute myocarditis, according to the Lake Louis criteria, LGE with a non-ischemic distribution pattern is often required. The most frequent LGE distribution consists of patchy, non-contiguous lesions localized in the subepicardial or intramural layers of the lateral or septal walls [27]. The use of CCT is generally restricted in the assessment of suspected myocarditis, primarily serving to identify alternative etiologies of acute chest pain, such as coronary artery disease and acute pericarditis [28; 29; 30]. However, CCT was helpful in diagnosing myocardial inflammation [31] and in the assessment of global and regional wall motion abnormalities throughout the cardiac cycle [32]. In fact, LIE-CT has demonstrated high sensitivity and specificity in diagnosing acute myocarditis compared to LGE-CMR [32]. Specifically, dual-source CT has demonstrated encouraging outcomes utilizing the spectral mode, which facilitates the differentiation of tissue components according to their distinct attenuation curves [31; 33]. [PERSON] et al. aimed to compare LIE on spectral CT with the reference LGE-CMR in acute myocarditis, finding the overall accuracy of spectral CT to be 95% [34]. [PERSON] et. al. reported that spectral imaging could reveal LIE in the subepicardial layer of the myocardial wall, indicating edema, hyperemia, and capillary leaks consistent with myopericarditis. The accumulation of iodine-based contrast medium in inflamed tissue reflects increased uptake associated with cellular membrane permeability, suggesting tissue injury in active myocarditis [35]. Furthermore, [PERSON] et al. reported a case of myocarditis associated with immune checkpoint inhibitor therapy diagnosed using spectral CT technology, reaffirming the utility of DECT in identifying myocardial inflammation, particularly in cases where CMR may not be feasible due to patient instability or contraindications [36]. The concept of quadruple-rule-out CT angiography has been recently introduced, combining the triple-rule-out CT angiography approach (based on the simultaneous evaluation of the coronary arteries, aorta, and pulmonary arteries with a single CT acquisition) with DECT in cases of acute chest pain. Studies have shown that quadruple-rule-out CT angiography offers promising results for myocarditis evaluation, with sensitivity, specificity, and positive and negative predictive values of 69%, 100%, 100%, and 94%, respectively. This performance suggests its potential to effectively assess myocardial perfusion deficits. Consequently, quadruple-rule-out CT angiography expands the diagnostic capabilities of the standard triple-rule-out method for myocarditis assessment [37]. In a recent study by [PERSON] et al., the diagnostic value of a comprehensive CT protocol combining angiographic and LIE-CT scans was investigated in troponin-positive acute chest pain patients. Among the 84 participants, triple-rule-out CT and LIE-CT were performed. Among 42 participants without obstructive coronary disease, LIE-CT identified myocarditis in 52%, takotsubo cardiomyopathy in 10%, and other specific diagnoses in 19% of cases. LIE-CT demonstrated the mild underestimation of the scar extension compared to LGE-CMR. However, it showed a good correlation (rho = 0.902) with extracellular volume fraction measured by CMR [38]. These findings highlight the potential of a comprehensive CT protocol, including LIE scans, to accurately diagnose myocarditis and other cardiac conditions in troponin-positive acute chest pain patients, demonstrating promising results in providing valuable information for clinical management.