PET and SPECT: opportunities and challenges for psychiatry.

Positron emission tomography (PET) and single photon emission computed tomography (SPECT) are the most advanced technologies available for the functional imaging of the brain, surpassing magnetic resonance imaging (MRI) and computed tomography (CT) scanners in potential clinical and research applications in neuropsychiatry. PET deals with a small number of radionuclides with short physical half-lives and an exclusive energy of 511 keV; SPECT utilizes an ensemble of radionuclides that exhibit moderate physical half-lives, each with its own characteristic spectrum of energy. PET imaging instrumentation requires substantial refinements to enable utilization with high-energy photons, larger data sets, and a high magnitude of information flow per unit of time. The instrumentation enables greater sensitivity and resolution, as compared with SPECT, but requires a more extensive data acquisition and processing infrastructure, resulting in a significantly higher system cost. SPECT has a number of price/performance alternatives in configuring a system, and has further cost advantages in that it utilizes widely available chemical tracers.