PRINCIPLES OF SPECT (SINGLE PHOTON-EMISSION COMPUTED-TOMOGRAPHY) AND THE TECHNICAL REALIZATION

In contrast to Positron Emission Tomography (PET) a SPECT System can be built only using lead collimators. Therefore, spatial resolution depends on the source-collimator distance. In addition, there is a strong relationship between collimator resolution and efficiency, i.e. improving resolution degrades efficiency. As a consequence, existing SPECT systems may be improved only by increasing efficiency without degradation of resolution and vice versa. Therefore, the design of new tomographs tends to arrange as much detector material as possible around the patient, e.g. by using several detector heads or a ring shaped detector. In addition the detectors including their collimators are moved as close as possible towards the patient in order to improve spatial resolution. The principles of SPECT are discussed and examples of modern tomographs are given.