Combined imaging modalities: PET/CT and SPECT/CT

The recent development of new radiopharmaceuticals now permits molecular imaging of biologic processes at the cellular level to improve both the diagnosis and treatment of disease. Fused PET/CT and SPECT/CT imaging systems now provide metabolic and functional information from PET or SPECT combined with the high spatial resolution and anatomic information of CT. Because the two sets of images are fused, areas of normal and abnormal metabolic activity can be mapped to recognizable anatomic structures. This fusion of function and anatomy has quickly demonstrated its clinical value, especially in the field of oncology. There are also growing clinical indications in the areas of cardiology, neurology, and imaging of infection. F-18 fluorodeoxyglucose (FDG) is the PET imaging agent currently in most common use. While FDG uptake is nonspecific, it has demonstrated important applications, especially for patients with cancer. Continued progress in fused anatomic and molecular imaging can be anticipated, both in the development of more advanced instrumentation (integrated CT or MRI with PET and SPECT camera technology) and with new radiopharmaceuticals that image more specific physiologic aspects of organ and cell biology.