The aim of this thesis was to investigate the role of imaging in the management of PTLD, with focus on [18F]FDG PET/CT. Additionally, we set out to explore new diagnostic methods with potential for clinical translation. In Part I (chapters 2-7), we reviewed the published literature on the role of different imaging modalities in PTLD and evaluated the diagnostic performance of [18F]FDG PET/CT for PTLD lesion detection in adults and children. Furthermore, we explored the role of [18F]FDG PET/CT semiquantification in PTLD for lesion classification and prognostication. In Part II (chapters 8-10) we proceeded to explore new avenues of research including: radiomics, identification of radiotracers adjunct to [18F]FDG and cfDNA analysis.