The focus of this thesis is on new detection technologies that can be used in advancing nuclear medicine modalities, particularly positron emission tomography (PET). Several detection technologies are covered in this thesis. First, new Ce3+ doped rare earth trihalide scintillators that can be used in advancing PET imaging are discussed. Here, the particular attention is paid to high light output and high proportionality to achieve high-energy resolution (for good scatter rejection) and fast response for high timing resolution along with possibility of providing time-of-flight data collection (to reduce randoms and to reduce noise in the reconstructed image). In addition to discussion of new scintillators for use in PET, two classes of new scintillators (Ce3+ doped elpasolites and Eu2+ doped alkaline earth halides) that provide high proportionality as well as energy resolution over a broad range of energies for use in single photon emission computed tomography (or SPECT) are also covered. In addition to new scintillators, two solid state photodetector technolgies are also covered in this thesis. This includes silicon avalanche photodiodes (APDs) and silicon based solid state photomultipliers (SSPMs). Standard as well as position sensitive versions of these photodetectors are covered with particular attention paid to the use of these new devices in small volume PET imaging. PET module designs with an ability to provide depth of interaction (in the scintillator element) in order to overcome parallax error in image reconstruction are discussed.