Practical scatter-independent gamma camera dead-time correction for iodine-131

Dead-time estimation is an important stage in the overall quantification of therapeutic gamma camera images. Up to 3 GBq of ¹³¹I was imaged under four different scatter conditions. Some distortion of the image was found, leading to limited “warping” of the image between sources, as expected for a camera with a paralysable dead-time component. Dead-time correction factors could be calculated for each of the energy windows used in the scatter correction, and this would enable the rapid increase in the triple energy window (TEW) scatter fraction (SF) as the count rate increases to be corrected. However, the most suitable solution was found to be the application of a single dead-time factor to TEW-corrected photopeak window counts. A global correction factor is probably sufficient, as the correction (as implemented here) appears to be independent of the scatter fraction. Contrary to most dead-time implementations, the dead-time factor was applied after performing scatter correction. The factor itself was derived from TEW-corrected photopeak window counts, and not based on uncorrected main window or total recorded count data, as is usually used. If the raw photopeak window dead-time factor is used, the correction can be underestimated by more than 20%