The development of specific MRI criteria to monitor the implantation process may provide valuable information of individual tissue response. Using MRI and histological methods, the biointegration of carbon-carbon (C-C) composites into the subcutaneous tissues of BDF1 mice and their biocompatibility were investigated. The study focused on autopsy specimens containing C-C composite implants, both uncoated and coated with synthetic hydroxyapatite (Ca-P) via electrodeposition or detonation techniques, assessed at 6 and 12 weeks post-implantation. The results revealed that the radiological characteristics of the connective tissue capsule surrounding the implants allowed for the differentiation between loose and dense connective tissues. Fat-suppressed T1-weighted MRI scans showed that the volume of both loose and dense connective tissue in the capsule increased proportionally at 6 and 12 weeks, with distinct ratios observed between the coated and uncoated specimens. The proposed MRI criteria provided a strategy for evaluating the density and homogeneity of the connective tissue capsule. This approach could be valuable for further non-invasive in vivo studies on implant biointegration.