Dead-time Effects in Nuclear Medicine Imaging Studies

Dead-time effects cause loss of counts that can degrade the quantitative capability of nuclear medicine images. Corrections for this image-degrading effect is becoming more relevant as the quantitative analysis of medical images gains importance – both in the diagnosis and treatment planning of disease. This chapter begins with a description of the sources of dead time, followed by an explanation of existing models used to characterize this effect. We then present a brief description of nuclear medicine procedures in which dead-time corrections must be applied. The rest of the chapter focuses on explaining different methods by which dead time can be measured and corrected for both single photon computed tomography (SPECT) and positron emission tomography (PET). For SPECT, we highlight analytic methods and the marker source method, although we provide references for readers who might want to understand this effect in more detail. We show how very high count rates result in pile-up effects that may significantly alter the shape of the detected spectra and may cause further losses of counts within a particular energy window. For PET, we highlight the new challenges that arise by the measurement of coincidences and provide a historical review of the methods that have been used to correct for dead time in this modality.