Recent advances in hybrid molecular imaging systems.

Nuclear medicine imaging methods that use radionuclides, such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT), offer highly sensitive and quantitative tools for the detection and localization of the biochemical and functional abnormalities associated with various diseases. The introduction of dual-modality PET/CT and SPECT/CT systems to the clinical environment in the late 1990s is regarded as a revolutionary advance in modern diagnostic imaging, bringing precise anatomical localization to conventional PET and SPECT imaging techniques and enhancing the quantitation capabilities of these modalities. The great success of PET/CT has also revived interest in the combination of PET and MR scanners, leading to commercially available clinical PET/MR systems. In this article, we review the recent improvements made in these hybrid molecular imaging systems, which have been dramatic in terms of both hardware and software over the past decade. We focus primarily on the hybrid imaging systems that are currently used in clinical practice and the technologies applied in those systems, with emphasis on the efforts to improve their diagnostic performances for musculoskeletal diseases.