A paediatric bone index derived by automated radiogrammetry

Abstract

SUMMARY: Hand radiographs are obtained routinely to determine bone age of children. This paper presents a method that determines a Paediatric Bone Index automatically from such radiographs. The Paediatric Bone Index is designed to have minimal relative standard deviation (7.5%), and the precision is determined to be 1.42%. INTRODUCTION: We present a computerised method to determine bone mass of children based on hand radiographs, including a reference database for normal Caucasian children. METHODS: Normal Danish subjects (1,867), of ages 7-17, and 531 normal Dutch subjects of ages 5-19 were included. Historically, three different indices of bone mass have been used in radiogrammetry all based on A = piTW(1 - T/W), where T is the cortical thickness and W the bone width. The indices are the metacarpal index A/W(2), DXR-BMD = A/W, and Exton-Smith's index A/(WL), where L is the length of the bone. These indices are compared with new indices of the form A/(W(a) L(b)), and it is argued that the preferred index has minimal SD relative to the mean value at each bone age and sex. Finally, longitudinal series of X-rays of 20 Japanese children are used to derive the precision of the measurements. RESULTS: The preferred index is A/(W(1.33) L(0.33)), which is named the Paediatric Bone Index, PBI. It has mean relative SD 7.5% and precision 1.42%. CONCLUSIONS: As part of the BoneXpert method for automated bone age determination, our method facilitates retrospective research studies involving validation of the proposed index against fracture incidence and adult bone mineral density.