Effects of a digital filter on detectability of a phantom lesion in a scintigram of the equine tarsus

The aim of this study was to examine the effects of a digital filter on the detectability of a phantom lesion in a scintigram of the equine tarsus, La teral images containing 50, 100, 150, 500, or 1000 kcounts were acquired. A created phantom lesion of 0 (normal), 10, 15, 20, or 30% increased intensi ty relative to local background was placed in the centrodistal tarsal joint area in the images of different count levels. Duplicate images were filter ed with a Metz filter. The complete set of filtered and unfiltered images t otaling 180 images was projected as slides to a group of 9 observers. The s ensitivity in 50 and 100 kcount images was improved by applying the filter, Digital filtering increased the false positive fraction at all count level s but this effect was most pronounced in 500 and 1000 kcount images. Based on receiver operating characteristic analysis, filtering of a 50 kcount ima ge improved image quality to that of a 150 kcount image.