Instrumentation for PET and SPECT studies

Quantitative emission tomography has been the final goal of much research effort for a number of years in nuclear medicine instrumentation. Multi-headed gamma camera rotating systems have made remarkable progress in quantitative single photon emission computed tomography (SPECT). The detection sensitivity is increased by the use of converging collimators with a fan beam, cone beam or more sophisticated geometry. A triangular SPECT system having three camera heads is particularly useful because it can be used for brain imaging with converging collimators and torso imaging with parallel hole collimators with reasonable geometry. Transmission measurement for attenuation correction is feasible with rod sources placed at the focal lines of the fan beam collimators. Attention is being paid to the SPECT imaging of 18F-deoxyglucose (18FDG) by rotating camera systems. The development of multi-ring positron emission tomography (PET) scanners has also made much progress, with continuing improvement of imaging devices and advances in data processing technology. The spatial resolution has increased from 10-15 mm to 3-4 mm full width at half-maximum in the last two decades. The recent development of 3-D PET has had a significant impact on the design and operation of PET scanners. The true detection sensitivity drastically increases in the 3-D mode by a factor of 5-6, but the scatter fraction also increases by a factor of 3-4. 3-D PET scanners with retractable slice septa have been commercialized, and can be used in the 2-D or 3-D mode depending on the activity level. Intensive research on quantitation in the 3-D mode is now going on to reach the goal of septa-less fully 3-D PET. The need for dedicated animal SPECT and PET scanners is increasing. (author). 26 refs, 5 figs