Background: Myocardial fibrosis presence is a known pro-arrhythmic substrate, though growing evidence points towards infiltrated myocardial adipose tissue as also playing an important arrhythmogenic role. On CMR imaging, however, distinguishing between the two can be challenging. Aims: The primary aim of this study is to develop CT-based metrics to characterize the left-ventricle (LV) heterogeneity by identifying regions of adipose and thinning myocardium. A secondary aim is to compute the extracellular volume (ECVCT) to validate the CT-derived thresholds. Methods: A late iodine enhancement CT protocol was carried out pre-procedurally for 10 VT ablations. A diastolic phase CT scan was used to automatically segment the heart anatomy and to define adipose based on the CT attenuation values of –180 to –5 HU. Personalized 3D models were constructed to include the layers of fat, and the LV wall thickness (WT) was calculated as the distance between the endocardium and the subepicardial fat. The distribution of the WT was modeled by three Gaussian mixture models that informed the cut-offs between thinning and healthy tissue. Pre-, post-contrast, and angiography CT scans were used to compute the ECVCT based on the difference in attenuation values. Results: Analysis of the WT returned a 5.89±0.85 mm cut-off value between thinned and healthy myocardium. The median ECV in regions defined as healthy (29.82% [28.03-32.033]) was significantly different than the ECV in thinned (33.69% [32.17-35.29]) or adipose (23.37% [18.29-26.70]) myocardium. The high ECV values present in the thinning myocardial wall define the fibrotic tissue. Conclusion: CT provides a comprehensive modality to computationally characterize the LV tissue and identify potential arrhythmogenic substrate in ICM patients.