ADVANTAGES OF THE COMPUTER-AIDED IMAGE ANALYSIS SYSTEM FOR ESTIMATING TW SKELETAL MATURITY: INCREASED RELIABILITY AND A CONTINUOUS SCALE

The two major problems besetting the Tanner-Whitehouse estimation of skeletal maturity (as also the Greulich-Pyle) are (1) low inter-observer reliability and (2) a discontinuous scale, so that a change of rating results in a jump in bone age. To solve these problems, we designed an image analysis system producing bone-age estimates automatically. The radiograph is placed under an imaging camera and an operator brings each bone to overlay a template displayed on the screen. The bone is digitized and a degree 64 two-dimensional Fourier transformation is obtained, giving a coefficient matrix characterizing that bone. This matrix is compared with the average matrix for each stage of the bones of the “Golden Series”, the radiographs rated by the originators of the TW method. Distances between these matrices comprise a quantitative scale of measurement so stage scores are generated which run continuously from 0.0 to 9.0. Longitudinal analysis of radiographs of the Harpenden Growth Study shows the smooth increase of score in the computer-aided system compared with the stepped increase obtained manually. Between operator reliability much exceeds that of the manual system; in 300 comparisons whole-stage differences occurred twice compared to the 30 times expected of human operators. The average inter-observer difference was one-third of a stage. Validity is high; the average difference from the Golden Series standards was 0.3 stage. We conclude that the computer-aided method renders manual methods of assigning bone age obsolete. We thank Ares-Serono for support.