Anatomical segmentation for temporal subtraction images in successive whole-body bone scans

We have developed a computerized scheme for a temporal subtraction (TS) image in successive whole-body bone scans and demonstrated the clinical utility of this scheme in the prospective clinical study. Recently, bone scan index (BSI) has been used for the quantitative analysis of bone metastases. The calculation of BSI requires anatomical segmentations for applying the weight fraction. In this study, in order to evaluate a change of BSIs in successive whole-body bone scans, an anatomical segmentation scheme was incorporated into the temporal subtraction image. Total of 300 cases of successive bone scans in which each case includes a pair of two images for anterior and posterior whole body views, were corrected retrospectively with the following inclusion criteria; 1) at least one abnormal finding in either view, and 2) a maximum number of 20 interval changes. We used 100 cases for training computerized scheme and the remains for the independent test. For the computerized scheme of an anatomical segmentation, one normal case (the standard case) was initially selected to create a standardized image in each view. Each of the standardized images for anterior and posterior views was produced by averaging all training images in which the size, orientation, and location of a skeletal region in a bone scan image were adjusted to those of the standard case by using a linear interpolation. Templates of seven anatomical regions, such as skull, ribs, thoracic vertebrae, lumber vertebrae, pelvis, upper arms, and femurs, were determined manually on the standardized image. A number of parameters for adjusting a current image to the standard image were applied to the templates of anatomical regions to fit those regions into the previous, current and TS image. Preliminary result obtained from 143 test cases (286 TS images) indicated that 99.3% (284/286) of temporal subtraction images were correctly segmented anatomically by use of this proposed method‥