[Optimization of conditions for detecting density variations in focal activity in SPECT using the rotating gamma camera. Model calculations, phantom measurements and clinical applications].

The signal to noise ratio (quotient of contrast and mean noise) is a quality parameter for identifying activity gaps during single photon emission computed tomography (SPECT). Contrast and mean noise level are site-dependent on the reconstruction plane which is influenced in a complex manner by absorption conditions (strong or weak absorption), modes of rotation (full angle or partial angle imaging), interdependencies of opposing partial projections (arithmetic or geometric mean), magnitude of defect (relative to the resolution of the imaging system), geometry of the object to be measured, and scatter. In the present study the authors performed analysis and graphical representation of the SPECT imaging properties on the basis of model calculations illustrated by phantom measurements. The optimal conditions of examination or evaluation and the diagnostic criteria in SPECT of the heart, liver, brain and pelvis are discussed by comparative calculation of signal to noise ratios in defect identification.