I am required to show CT Scan images and Xray images via my Tablet app on Android. An app similar to my requirements has already been developed in IOS (www.accelarad.com) .Please let me know which 3rd Party Apis are available on Android to make Medical Imaging possible on Android. Open Source are first preference but I might also prefer licensed libraries for better performance.
Despite not being specifically developed for Android, but developed for touch-based devices , a study titled as "Towards Touch-Based Medical Image Diagnosis Annotation" can be a start for you. In this study, the authors explore the radiologist's receptivity to the current touch device solution. From here, the authors developed several touch prototypes over the BreastScreening project, a project that joins contributions from both MIMBCD-UI and MIDA projects. The BreastScreening project aims to develop several AI-Assisted techniques  to improve the medical diagnostic workflow by automatizing several parts of it. The goal is to develop an Assistant promoting a higher Radiology Room (RR) performance and bringing higher health care results for the patient. The new paradigms of MI in the Health Informatics (HI) field are many and just started. Hope to help you with this answer.
 Francisco M. Calisto, Alfredo Ferreira, Jacinto C. Nascimento, and Daniel Gonçalves. 2017. Towards Touch-Based Medical Image Diagnosis Annotation. In Proceedings of the 2017 ACM International Conference on Interactive Surfaces and Spaces (ISS '17). ACM, New York, NY, USA, 390-395. DOI: https://doi.org/10.1145/3132272.3134111
 Maicas, Gabriel, Gustavo Carneiro, Andrew P. Bradley, Jacinto C. Nascimento, and Ian Reid. "Deep reinforcement learning for active breast lesion detection from dce-mri." In International Conference on Medical Image Computing and Computer-Assisted Intervention, pp. 665-673. Springer, Cham, 2017.