The buildup factor: effect of scatter on absolute volume determination

We have developed a new method for generating attenuation-corrected images for use in absolute volume and activity measurements. The technique relies on the use of a set of measured buildup factors to correct for the effects of scatter inherent in the broad-beam conditions of clinical nuclear medicine and requires anterior and posterior count-rate measurements. The scatter correction requires that the well-known attenuation factor e-mud be replaced by 1-(1-e-mud)B(infinity), where B(infinity) is the buildup factor at infinite depth. The buildup factors for four different scintillation camera window settings and three different source sizes are reported. The method was validated by calculating phantom volumes and comparing the results to a previously reported technique which does not account for the scatter contribution by assuming mu = 0.15 cm-1. The results showed that the buildup factor method provides less than 7.3% error for volume determinations at all investigated depths, window settings, and source sizes, whereas errors of 3.3-26.7% were found with the other technique.